【０００１】
【発明の属する技術分野】
この発明は、半導体装置の解析方法に係り、特に解析箇所を集束イオンビーム（ＦＩＢ：Ｆｏｃｕｓｅｄ Ｉｏｎ Ｂｅａｍ）を用いて作製する透過型電子顕微鏡（ＴＥＭ：Ｔｒａｎｓｍｉｓｓｉｏｎ Ｅｌｅｃｔｒｏｎ Ｍｉｃｒｏｓｃｏｐｅ）の観察試料の作製方法に係る透過型電子顕微鏡用試料の解析方法および透過型電子顕微鏡用試料に関するものである。
【０００２】
【従来の技術】
半導体デバイス等の試料の微細構造解析をする方法の一つとしてＴＥＭは良く知られている。数百ｋＶ以上の高電圧によって加速された電子ビームを試料の観察したい部位を有するＴＥＭ観察面に照射し、そのＴＥＭ観察面を透過した通過電子を結像させて観察（ＴＥＭ観察）する。このＴＥＭ観察は極めて高い分解能での原子レベルの観察が可能である。また、ナノメートル領域のＥＤＸ分析やＥＥＬＳ分析が可能である。
【０００３】
近年、集束イオンビーム（ＦＩＢ）を用いて、半導体ウエーハや半導体チップから特定箇所のＴＥＭ観察面を直接分離するＴＥＭ試料作製方法が可能となり、半導体ウエーハやチップを割ることなくＴＥＭ試料を分離でき、非常に近づいた複数個のＴＥＭ試料作製が可能となり、半導体デバイスの不良解析に活用されている。
【０００４】
従来、ＦＩＢによって半導体ウエーハや半導体チップからＴＥＭ試料を分離しＴＥＭ観察する方法には２種類ある。ひとつには、ＦＩＢを用いてＴＥＭ観察可能な薄片試料を作製し、光学顕微鏡を用いたマニピュレーションシステムによって試料を分離する方法がある（特許文献１参照）。また、ＦＩＢ装置で作製した試料片をＦＩＢ装置中に組み込まれたマニピュレーションシステムにより分離する方式がある（特許文献２および３参照）。前者を従来試料作製方法１、後者を従来試料作製方法２とする。
【０００５】
従来試料作製方法１を図７、図８を用いて説明する。図７は、従来の試料作製方法１の一例を示す工程の流れ図である。まず、図７（ａ）に示すように、半導体基板１、例えば、半導体ウエーハや半導体チップから、ＴＥＭ観察する特定箇所２を含み相対する辺をＦＩＢ３により透過型電子顕微鏡で観察が可能な程度まで薄片化（例えば、０．２μｍ以下の厚さ）し、底部と側部を切り離しＴＥＭ試料４を分離する。図７（ｂ）で示すように光学顕微鏡とマニピュレータシステムを用い、マニピュレータ先端５に前記試料を静電吸着させる。次に図７（ｃ）に示すように、この試料を透過型電子顕微鏡用メッシュ６に落下させる。分離したＴＥＭ試料４は薄い薄片であるので、透過型電子顕微鏡用メッシュ６に密着した状態でＴＥＭ観察する。
【０００６】
図８は、従来試料作製方法１により、ＦＩＢ３によって加工されて分離された試料の形状および、透過型電子顕微鏡用メッシュ６に貼り付けた断面構造の形状を示す説明図である。図８（ｂ）に示すように、ＦＩＢ３によって加工されて分離されたＴＥＭ試料４は、透過型電子顕微鏡で観察可能な厚さ（例えば、厚さ０．１μｍ）の平面状の試料である。その試料を透過型電子顕微鏡用メッシュ６に貼り付けた時の断面構造は、図８（ｃ）で示すように、ＴＥＭ試料４と透過型電子顕微鏡用メッシュ６上に貼り付けた支持膜７とが密着している形状である。
【０００７】
従来の試料作製方法２では、ＦＩＢを用いて半導体ウエーハの観察目的部分を局所的に切り出すウエーハ用試料ステージと、切り出した試料を装着して透過型電子顕微鏡により観察可能な厚さまで加工するＴＥＭ試料ステージと、ウエーハ用ステージで切り出した試料をつかみ出し、ＴＥＭ試料ステージに固定するマニピュレータとをＦＩＢ装置中に備えたＦＩＢ試料作製装置を用い（特許文献３参照）、半導体ウエーハや半導体チップからＦＩＢ加工により特定箇所を含む微細な試料片を分離し、ＦＩＢ中で分離した試料上でマニピュレータおよび試料に金属を堆積することで試料をつかみ出し、ＦＩＢ装置中で、ＴＥＭ試料ステージに装着された透過型電子顕微鏡用メッシュに金属を堆積して試料片を固定する。試料を固定した後に更にＴＥＭ観察可能なまで、ＦＩＢにより試料片を薄片化する。ＦＩＢ加工とＴＥＭ観察の繰り返しが可能であるが、ＦＩＢ中にウエーハ用ステージとＴＥＭ試料ステージとマニピュレータを備えた専用の装置が必要である。
【０００８】
【特許文献１】
特開２００１−２７２３１６号公報（図１）
【特許文献２】
特開平０５−５２７２１号公報
【特許文献３】
特開２００２−６２２２６号公報（図１）
【０００９】
【発明が解決しようとする課題】
しかしながら、上記の従来試料作製方法１では、ＴＥＭ観察可能な薄片試料を光学顕微鏡マニピュレーションシステムの絶縁棒により機械的に分離するため、ＴＥＭで格子像を得られるほど試料薄片を薄くしすぎると壊れてしまうという問題があった。また、特定箇所の加工精度をあげるためには、ＦＩＢによる試料薄片化とＴＥＭ観察あるいは、ＳＥＭ観察を繰り返す必要があるが、透過型電子顕微鏡用メッシュに密着させて貼り付けるため、ＴＥＭ観察した後に更にＦＩＢ加工を追加できないという問題があった。また、試料薄片を観察する際に透過型電子顕微鏡用メッシュに固定する役割である支持膜が、ＴＥＭ観察時に格子像等を観察する高分解能観察を妨げるという問題があった。
【００１０】
上記の従来試料作製方法２では、試料の薄片化やＦＩＢの再加工が可能であるが、ウエーハ用ステージとＴＥＭ試料ステージとマニピュレータとを搭載した専用のＦＩＢ装置は非常に高価であるという問題があった。
【００１１】
したがって、この発明の目的は、このような従来の方法にあった課題を解決するもので、半導体ウエーハまたは半導体チップからＦＩＢにより特定箇所を壊すことなく分離し、透過型電子顕微鏡用メッシュに固定した試料をさらにＦＩＢにより薄片化でき、高価な専用のＦＩＢなしで作製できる透過型電子顕微鏡用試料の解析方法および透過型電子顕微鏡用試料を提供することである。
【００１２】
【課題を解決するための手段】
上記目的を達成するためにこの発明の請求項１記載の透過型電子顕微鏡用試料の解析方法は、半導体基板から分離した試料を透過型電子顕微鏡用メッシュに貼り付けて透過型顕微鏡で観察する透過型電子顕微鏡用試料の解析方法であって、前記半導体基板上の特定箇所を集束イオンビームを用いてコの字型に切り出す工程と、前記特定箇所に位置する観察領域を含むように切り出したコの字型試料をマニピュレータシステムを用いて分離する工程と、前記コの字型試料の凹部が前記透過型電子顕微鏡用メッシュ側になるように前記観察領域を前記メッシュから離隔させて固定する工程と、前記メッシュに固定されたコの字型試料を前記透過型顕微鏡で観察する工程とを含む。
【００１３】
このように、半導体基板上の特定箇所を集束イオンビームを用いてコの字型に切り出す工程と、特定箇所に位置する観察領域を含むように切り出したコの字型試料をマニピュレータシステムを用いて分離する工程と、コの字型試料の凹部が透過型電子顕微鏡用メッシュ側になるように観察領域をメッシュから離隔させて固定する工程と、メッシュに固定されたコの字型試料を透過型顕微鏡で観察する工程とを含むので、透過型顕微鏡用メッシュの支持膜と観察したい特定箇所を含む観察領域との間に空間ができることにより、この空間を用いて、観察した後に更に特定箇所の両側からＦＩＢで再加工できることとなる。また、コの字型試料を分離する際、観察領域の厚さがＴＥＭ観察可能となる膜厚になるまで薄片化しなくてもよいので、試料を壊すことなく分離することができる。
【００１４】
請求項２記載の透過型電子顕微鏡用試料の解析方法は、請求項１記載の透過型電子顕微鏡用試料の解析方法において、コの字型試料を観察する工程は、特定箇所が鮮明に観察されない時、前記コの字型試料をさらに集束イオンビーム加工し、観察と集束イオンビーム加工を繰り返し、特定箇所を薄片化した後に観察する。
【００１５】
このように、特定箇所が鮮明に観察されない時、コの字型試料をさらに集束イオンビーム加工し、観察と集束イオンビーム加工を繰り返し、特定箇所を薄片化した後に観察するので、高分解能観察が可能な薄片試料を特定箇所に精度よく加工することができ、半導体の故障解析を精度よく行える。また、最初から特定箇所を極めて薄くする必要がないため、マニピュレータによって分離する際に試料を破損する確率が下がる。また、高価なウエーハ用ステージとＴＥＭ試料ステージとマニピュレータとを搭載した専用のＦＩＢ装置を必要としない。
【００１６】
請求項３記載の透過型電子顕微鏡用試料の解析方法は、請求項１記載の透過型電子顕微鏡用試料の解析方法において、コの字型試料を観察する工程は、集束イオンビームにより特定箇所の下部の前記透過型電子顕微鏡用メッシュの支持膜を部分的にエッチングする。
【００１７】
このように、集束イオンビームにより特定箇所の下部の透過型電子顕微鏡用メッシュの支持膜を部分的にエッチングするので、観察試料にダメージを与えず、支持膜の影響を受けずにＴＥＭで格子像等を高分解能観察できる試料を得ることとなる。また、特定箇所の直下の支持膜がなくなることにより、特定箇所の両側からＳＥＭ観察できるため、観察領域を薄片化する際の加工精度が上がることとなる。
【００１８】
請求項４記載の透過型電子顕微鏡用試料の解析方法は、請求項１記載の透過型電子顕微鏡用試料の解析方法において、コの字型試料を固定する工程は、半円状のメッシュを用い前記メッシュの直線側に近い位置に、前記コの字型試料の半導体基板上面に相当する面が前記直線側になるように固定する。
【００１９】
このように、半円状のメッシュを用いメッシュの直線側に近い位置に、コの字型試料の半導体基板上面に相当する面が直線側になるように固定するので、メッシュに試料を固定した後に、透過型電子顕微鏡用メッシュの支持膜と試料の空間を用いて更にＦＩＢ加工する際にメッシュがＦＩＢ加工の妨げにならず、精度よく再加工することができる。
【００２０】
請求項５記載の透過型電子顕微鏡用試料は、透過型電子顕微鏡用メッシュに貼り付けて透過型顕微鏡で観察される透過型電子顕微鏡用試料であって、半導体基板上の特定箇所をコの字型に加工して形成され、その凹部が前記メッシュ側になるように前記特定箇所に位置する観察領域を前記メッシュから離隔させて固定した。
【００２１】
このように、半導体基板上の特定箇所をコの字型に加工して形成され、その凹部がメッシュ側になるように特定箇所に位置する観察領域をメッシュから離隔させて固定したので、試料が透過型電子顕微鏡用メッシュに固定された後にも、ＦＩＢによる試料の再加工や、メッシュの支持膜のエッチングができ、高分解能観察が可能な薄片試料を特定箇所に精度よく作製できることとなる。
【００２２】
【発明の実施の形態】
この発明の第１の実施の形態を図１および図２に基づいて説明する。図１はこの発明の第１の実施の形態の透過型電子顕微鏡用試料の解析方法を示す説明図で、特にＴＥＭ試料作製工程を示す工程説明図である。同図（ａ）は、ＦＩＢ加工によって試料をコの字型に切り出す工程を示す見取り図、同図（ｂ）は、コの字型試料をマニピュレータ先端によりＦＩＢ加工後のコの字型試料を分離する工程の見取り図、同図（ｃ）は、コの字型試料を透過型電子顕微鏡用メッシュに固定する工程の見取り図、同図（ｄ）は、コの字型試料を透過型電子顕微鏡観用メッシュの支持膜上に固定した試料をＴＥＭ観察する際の真横方向からの見取り図である。
【００２３】
半導体装置を解析する方法の一つとしてＴＥＭ観察する際のこのＴＥＭ試料作製方法は、図１に示すように、半導体基板１上の特定箇所２を集束イオンビーム３を用いてコの字型に切り出す工程と、特定箇所２に位置する観察領域を含むように切り出したコの字型試料１１をマニピュレータシステム１２を用いて分離する工程と、コの字型試料１１の凹部が透過型電子顕微鏡用メッシュ６側になるように観察領域をメッシュ６上の支持膜７に密着させずに離隔させて固定する工程と、メッシュ６に固定されたコの字型試料１１を透過型電子顕微鏡で観察する工程とを含む。
【００２４】
以上のように構成されたＴＥＭ試料作製方法を以下、図１、図２を用いてその工程を詳細に説明する。まず図２はコの字型に試料を切り出す時のＦＩＢ加工の工程を示すものであって、図２（ａ），（ｂ）は、コの字型に試料を切り出す時のＦＩＢ加工範囲を平面から見た模式図、図２（ｃ）は、コの字型試料１１を真横から見た時のＦＩＢ加工範囲を示す模式図である。
【００２５】
図２（ａ）に示すように、半導体基板１上の特定観察箇所２をＦＩＢ３を用いて特定観察箇所２がコの字の凹んでいる辺に含まれるように、ＦＩＢ３を試料表面から走査し、特定箇所前方ＦＩＢ加工領域１３と特定箇所後方ＦＩＢ加工箇所１４の部分を削り、コの字型に加工する。この時、特定箇所２を含むコの字型の凹んでいる一辺がＴＥＭ観察領域１５となる。コの字型のビル（建物）のように加工した後、ビルの下部を切って試料を取り出す。このＴＥＭ観察領域１５の厚さがＴＥＭ観察可能となる膜厚（例えば、０．２μｍ以下）になるまで薄片化する。次に、図２（ｂ），（ｃ）に示すように、ＦＩＢ３を用いて、観察特定箇所２の側面の特定箇所側面ＦＩＢ加工箇所１６と特定箇所底部ＦＩＢ加工領域１７とを削り観察特定箇所を含むコの字型試料１１を半導体基板１から切り離す。
【００２６】
次に、図１（ｂ）に示すように、光学顕微鏡を用いたマニピュレータシステムを用いて、特定箇所２を含むコの字型試料１１を例えばガラス等の絶縁体棒からなるマニピュレータ先端５に静電吸着させ、透過電子顕微鏡用観察メッシュ６に観察特定箇所２を含むコの字型試料１１の凹部が透過型電子顕微鏡用メッシュ６上に張られた支持膜７側になるように観察特定箇所２を含むＴＥＭ観察領域１５が支持膜７と密着しないように固定する。
【００２７】
次に図１（ｄ）示すように、ＦＩＢ３によってコの字型に分離され、マニピュレータ１２によって透過型電子顕微鏡用メッシュ６に貼り付けられた試料１１をＴＥＭ観察領域１５の上部から電子ビーム８を照射し、観察領域１５を透過した電子あるいは、発生した２次電子を観察および分析することにより、半導体装置や半導体装置の製造工程途中の素子の形状や故障を解析する。
【００２８】
以上のように本実施形態によれば、半導体基板１から集束イオンビーム３により観察特定箇所２がコの字の凹んでいる一辺に含まれるように、コの字型試料１１を切り出し、マニピュレータ１２によって、透過電子顕微鏡用メッシュ６に特定箇所２を含むコの字型試料１１の観察領域１５が透過型電子顕微鏡用メッシュ６上の支持膜７側になるように特定箇所２を含むＴＥＭ観察面が支持膜７に密着しないように固定し、観察するため、ＴＥＭ観察および、分析した後に、ＴＥＭ観察領域１５と支持膜７の間の空間を用いて、更にＦＩＢ３によって、特定箇所２の両側あるいは片側を再加工し観察領域を薄片化することができる。従来試料作製方法１では、特定箇所２を含むＴＥＭ試料４が支持膜７と密着しているため、特定箇所２の両側を更にＦＩＢ加工することは不可能である。
【００２９】
なお、第１の実施形態において、コの字型試料を取り出す半導体基板１は、半導体ウエーハであっても、半導体チップであってもよい。
【００３０】
この発明の第２の実施の形態を図３に基づいて説明する。図３は本発明の第２の実施の形態の透過型電子顕微鏡用試料の解析方法を示す説明図で、特にＴＥＭ試料作製工程を示す工程説明図である。同図（ａ）は、ＦＩＢ加工によって試料をコの字型に切り出す工程を示す見取り図、同図（ｂ）は、コの字型試料をマニピュレータ先端によりＦＩＢ加工後のコの字型試料を分離する工程の見取り図、同図（ｃ）は、コの字型試料を透過型電子顕微鏡用メッシュに固定する工程の見取り図、同図（ｄ），（ｅ）は、透過型電子顕微鏡用メッシュに固定されたコの字型試料をＦＩＢによって更に薄片化する際の斜視図および真横からの見取り図、同図（ｆ）はＦＩＢ再加工によって薄片化した試料を観察する工程の見取り図である。
【００３１】
図３において、同図（ａ），（ｂ），（ｃ）の工程は図１の構成と同様なものであり、半導体基板１上の特定箇所２を集束イオンビーム３を用いてコの字型に切り出す工程と、特定箇所２に位置する観察領域を含むように切り出したコの字型試料１１をマニピュレータシステム１２を用いて分離する工程と、コの字型試料１１の凹部が透過型電子顕微鏡用メッシュ６側になるように観察領域をメッシュ６上の支持膜７に密着させずに離隔させて固定する工程とを含む。図１の構成と異なるのは透過型電子顕微鏡用メッシュ６に固定したコの字型試料１１を観察する際に、図３（ｄ），（ｅ）に示すように、コの字型試料１１を透過型電子顕微鏡用メッシュ６上の支持膜７に貼り付け観察した後に、ＦＩＢ装置中で、前記メッシュ６を立て、特定箇所上方ＦＩＢ再加工領域１８或いは、観察領域１５と透過型電子顕微鏡用メッシュ６上の支持膜７との空間を用いて、特定箇所下方ＦＩＢ再加工領域１９をＦＩＢ３によって再加工し、ＴＥＭ観察領域１５を更に薄片化し観察する工程を含む点である。
【００３２】
本実施形態の場合、一度目のＦＩＢ再加工によって、薄片化された試料を観察した際に、まだ、特定箇所２が、鮮明に観察されない場合は、更にＦＩＢ３によって観察領域を薄片化した後に観察する。鮮明に特定箇所２が観察されるまで以上の動作を何度でも繰り返し、最終的にＴＥＭ観察領域１５の上部から電子ビーム８を照射し、観察領域１５を透過した電子あるいは、発生した２次電子を観察および分析することにより、半導体装置や半導体装置の製造工程途中の素子の形状や故障を解析する。
【００３３】
以上のように第２の実施形態は、半導体基板１から集束イオンビーム３により観察特定箇所２がコの字の凹んでいる一辺に含まれるように、コの字型試料１１を切り出し、マニピュレータ１２によって、透過電子顕微鏡用メッシュ６に特定箇所２を含むコの字型試料４の観察領域１５が透過型電子顕微鏡用メッシュ６上の支持膜７側になるように特定箇所２を含むＴＥＭ観察面が支持膜７に密着しないように固定し、観察する工程において、特定箇所２が鮮明に観察されない時には、観察領域１５と透過型電子顕微鏡用メッシュ６上の支持膜７との空間を用いて、更にＦＩＢ加工し、観察とＦＩＢ加工を繰り返し、特定箇所２を薄片化した後に観察する工程を設けることにより、特定箇所２を含むＴＥＭ観察領域１５を精度よくＦＩＢ加工し、鮮明にＴＥＭ観察あるいは分析することができる。また、コの字型試料１１を切り出す際に、非常に薄片化（例えば、１００ｎｍ以下）する必要がないので、マニピュレータ１２で分離する際に試料を破損する確率を低減させることができる。
【００３４】
なお、第２の実施形態において、観察する工程において、特定箇所２が鮮明に観察されない時には、観察領域１５と透過型電子顕微鏡用メッシュ６上の支持膜７との空間を用いて、更にＦＩＢ加工するとしたが、最初のＦＩＢ３によってコの字型試料を切り出す工程で、ＴＥＭ観察可能な厚さ（例えば、０．２μｍ以下）になるまで薄片化する必要はなく、この場合は、透過型電子顕微鏡用メッシュ６に貼り付けたコの字型試料１１は、観察することなしに、ＦＩＢ３によって、観察領域１５をＴＥＭ観察可能となる膜厚（例えば、０．２μｍ以下）になるまで薄片化することとなる。
【００３５】
この発明の第３の実施の形態を図４に基づいて説明する。図４は本発明の第３の実施の形態の透過型電子顕微鏡用試料の解析方法を示す説明図で、特にＴＥＭ試料作製工程を示す工程説明図である。同図（ａ）は、ＦＩＢ加工によって試料をコの字型に切り出す工程を示す見取り図、同図（ｂ）は、コの字型試料をマニピュレータ先端によりＦＩＢ加工後のコの字型試料を分離する工程の見取り図、同図（ｃ）は、コの字型試料を透過型電子顕微鏡用メッシュに固定する工程の見取り図、同図（ｄ），（ｅ）は、透過型電子顕微鏡用メッシュに固定されたコの字型試料の観察箇所直下の支持膜をＦＩＢ加工によってエッチングする工程の斜視図および真横からの見取り図、同図（ｆ）は前記試料を観察する工程の見取り図である。
【００３６】
図３において、同図（ａ），（ｂ），（ｃ）の工程は図１の構成と同様なものであり、半導体基板１上の特定箇所２を集束イオンビーム３を用いてコの字型に切り出す工程と、特定箇所２に位置する観察領域を含むように切り出したコの字型試料１１をマニピュレータシステム１２を用いて分離する工程と、コの字型試料１１の凹部が透過型電子顕微鏡用メッシュ６側になるように観察領域をメッシュ６上の支持膜７に密着させずに離隔させて固定する工程とを含む。図１の構成と異なるのは透過型電子顕微鏡用メッシュ６に固定したコの字型試料１１を観察する際に、図３（ｄ），（ｅ），（ｆ）に示すように、観察箇所を含む観察領域直下の支持膜７をＦＩＢ３によって部分的にエッチングし観察する工程を含む点である。
【００３７】
以下、図３（ｄ），（ｅ），（ｆ）を用いて、支持膜７をエッチングして観察する工程を詳細に説明する。同図（ｄ）に示すように、透過型電子顕微鏡用メッシュ６に固定したコの字型試料１１をＦＩＢ装置中で傾斜し、観察領域１５と透過型電子顕微鏡用メッシュ６上の支持膜７との空間を用いて、観察箇所を含む観察領域直下の支持膜７の支持膜ＦＩＢ加工領域２０を加工する。同図（ｅ）のように真横から見ると、支持膜ＦＩＢ加工領域２０は特定箇所２の直下となる。図３（ｆ）のように、電子線８を上部から照射して、観察領域１５を透過した電子あるいは、発生した２次電子を観察および分析することにより、半導体装置や半導体装置の製造工程途中の素子の形状や故障を解析する。
【００３８】
以上のように第３の実施形態は、半導体基板１から集束イオンビーム３により観察特定箇所２がコの字の凹んでいる一辺に含まれるように、コの字型試料１１を切り出し、マニピュレータ１２によって、透過電子顕微鏡用メッシュ６に特定箇所２を含むコの字型試料１１の観察領域１５が透過型電子顕微鏡用メッシュ６上の支持膜７側になるように特定箇所２を含むＴＥＭ観察面が支持膜６に密着しないように固定し、観察する工程において、観察箇所を含む観察領域直下の支持膜７をＦＩＢ３によって部分的にエッチングし観察する工程を含むので、観察領域１５にダメージを与えず、支持膜７を除去することができる。従来ＴＥＭ試料作製方法におけるＴＥＭ観察において、観察領域がいくら薄片化されていても、電子線８は試料４と支持膜７の両方を透過するため、支持膜７の影響で、格子像等を高分解能で観察することができなかったが、本実施形態によれば、支持膜７の影響を受けずにＴＥＭ観察で格子像等を高分解能観察できる。また、特定箇所２の直下の支持膜７がなくなることにより、特定箇所２の両側からＳＥＭ観察できるため、観察領域を第２の実施形態のように更に薄片化する際の加工精度が上がる。
【００３９】
この発明の第４の実施の形態を図５に基づいて説明する。図５は本発明の第４の実施の形態の透過型電子顕微鏡用試料の解析方法を示す説明図で、特にＴＥＭ試料作製工程を示す工程説明図である。同図（ａ）は、ＦＩＢ加工によって試料をコの字型に切り出す工程を示す見取り図、同図（ｂ）は、コの字型試料をマニピュレータ先端によりＦＩＢ加工後のコの字型試料を分離する工程の見取り図、同図（ｃ）は、コの字型試料を透過型電子顕微鏡用メッシュに固定する工程の見取り図、同図（ｄ）は、透過型電子顕微鏡用メッシュに固定されたコの字型試料の観察箇所をＦＩＢ加工に薄片化する工程の斜視図および真横からの見取り図である。
【００４０】
図５において、同図（ａ），（ｂ）の工程は図２の構成と同様なものであり、半導体基板１上の特定箇所２を集束イオンビーム３を用いてコの字型に切り出す工程と、特定箇所２に位置する観察領域を含むように切り出したコの字型試料１１をマニピュレータシステム１２を用いて分離する工程とを含む。図１の構成と異なるのは、同図（ｃ）のように、分離したコの字型試料１１を透過型電子顕微鏡用メッシュに固定する際に、半円状透過型電子顕微鏡用メッシュ２１を用い、前記メッシュ２１の直線側に近い位置に試料１１の上面（半導体基板上面に相当する面）が直線側になるように固定する工程を含み、同図（ｄ）に示すようにＦＩＢ３によって特定箇所２を更に薄片化する際にＦＩＢ装置中で前記メッシュ２１の直線側が上になるように試料１１を立てＦＩＢ３を上から当てて加工する。次に、電子線８を上部から照射し、観察領域１５を透過した電子あるいは、発生した２次電子を観察および分析することにより、半導体装置や半導体装置の製造工程途中の素子の形状や故障を解析する。
【００４１】
以上のように第４の実施形態は、半導体基板１から集束イオンビーム３により観察特定箇所２がコの字の凹んでいる一辺に含まれるように、コの字型試料１１を切り出し、マニピュレータ１２に分離したコの字型試料１１を透過電子顕微鏡用メッシュに固定する際に、半円状透過電子顕微鏡用メッシュ２１を用い、前記メッシュ２１の直線側に近い位置に試料１１の上面が直線側になるように固定する工程を含むので、支持膜７と試料１１の空間を用いて特定箇所２を更に薄片化する際にＦＩＢ装置中で前記メッシュ２１の直線側が上になるように試料を立てＦＩＢ加工することにより、メッシュ２１がＦＩＢ加工の妨げにならず、精度よく再加工することができる。
【００４２】
この発明の第５の実施の形態を図６に基づいて説明する。図６は本発明の第５の実施の形態の透過型電子顕微鏡用の試料の形状を示す説明図で、同図（ａ）は、コの字型試料を切り出す際のＦＩＢ加工領域の平面図、同図（ｂ）は、コの字型試料を透過型電子顕微鏡用メッシュに貼り付けた際の模式図、同図（ｃ）は、コの字型試料を透過型電子顕微鏡用メッシュに貼り付けた際の断面模式図である。
【００４３】
図６に示すように、透過型電子顕微鏡用試料１１は、半導体基板１上の特定箇所２をコの字型に加工して形成され、その凹部が透過型電子顕微鏡用メッシュ６側になるように特定箇所２に位置する観察領域１５をメッシュ６から離隔させて固定した。
【００４４】
この場合、図６（ａ）に示すように、半導体基板１から集束イオンビーム３により特定箇所２がコの字の凹んでいる一辺に含まれるように、切り出されたコの字型試料１１は、同図（ｂ）のように透過型電子顕微鏡用メッシュ６上の支持膜７に特定箇所２を含む観察領域１５が、前記支持膜７に密着しないように固定された構造である。前記試料の断面構造は、同図（ｃ）のような構造となる。
【００４５】
次に試料の形状を図６を用いて、詳細に説明する。この透過型電子顕微鏡用試料の形状は、例えば、同図（ａ）において特定箇所２を挟んだ横方向の全長が１５〜３０μｍ、観察領域が１０μｍ前後、加工深さは３〜１０μｍとする。同図（ｂ），（ｃ）のように透過型電子顕微鏡用メッシュ６上に固定された時の安定性を考えるとコの字型試料１１の特定箇所下方足部分２２の１個の幅は、３〜５μｍ、特定箇所下方足部分２２の高さは、前記メッシュに固定した後にＦＩＢで更に特定箇所を薄片化する際に、支持膜７からの影響が小さく、安定性がよいと考えられる３μｍが適当である。なお、観察領域１５の厚さは、ＴＥＭ観察可能な厚さ例えば、０．２μｍ以下とすると透過型電子顕微鏡用メッシュ６に固定した後にＴＥＭ観察できるが、ＦＩＢ３で更に薄片化した後ＴＥＭ観察できるため、切り出す際に０．２μｍ以下まで薄片化する必要はない。以上、理解を明瞭にするために試料の形状の詳細を数値をあげて説明したが、ＦＩＢで加工される範囲であって、支持膜に固定された時に安定する範囲であれば、この数値の限りではない。
【００４６】
以上のように第５の実施形態は、半導体基板１から集束イオンビーム３により観察特定箇所２がコの字の凹んでいる一辺に含まれるように、切り出されたコの字型試料１１は、透過型電子顕微鏡用メッシュ６上の支持膜７に特定箇所２を含む観察領域１５が、前記支持膜７に密着しないように固定された構造であることにより、試料１１が観察用メッシュ６に固定された後にも、観察領域１５と支持膜７との間の空間を用いて、ＦＩＢ３による特定箇所２を含む観察領域１５のＦＩＢ３による再加工や、支持膜７のエッチングができ、高分解能観察が可能な薄片試料を特定箇所２に精度よく作製できることとなる。
【００４７】
前述した実施形態は理解を明瞭にするために図解および例示の方法によって詳細に説明されたけれども、特許請求の範囲内で変更してもよい。
【００４８】
【発明の効果】
この発明の請求項１記載の透過型電子顕微鏡用試料の解析方法によれば、半導体基板上の特定箇所を集束イオンビームを用いてコの字型に切り出す工程と、特定箇所に位置する観察領域を含むように切り出したコの字型試料をマニピュレータシステムを用いて分離する工程と、コの字型試料の凹部が透過型電子顕微鏡用メッシュ側になるように観察領域をメッシュから離隔させて固定する工程と、メッシュに固定されたコの字型試料を透過型顕微鏡で観察する工程とを含むので、透過型顕微鏡用メッシュの支持膜と観察したい特定箇所を含む観察領域との間に空間ができることにより、この空間を用いて、観察した後に更に特定箇所の両側からＦＩＢで再加工できることとなる。また、コの字型試料を分離する際、観察領域の厚さがＴＥＭ観察可能となる膜厚になるまで薄片化しなくてもよいので、試料を壊すことなく分離することができる。
【００４９】
請求項２では、特定箇所が鮮明に観察されない時、コの字型試料をさらに集束イオンビーム加工し、観察と集束イオンビーム加工を繰り返し、特定箇所を薄片化した後に観察するので、高分解能観察が可能な薄片試料を特定箇所に精度よく加工することができ、半導体の故障解析を精度よく行える。また、最初から特定箇所を極めて薄くする必要がないため、マニピュレータによって分離する際に試料を破損する確率が下がる。また、高価なウエーハ用ステージとＴＥＭ試料ステージとマニピュレータとを搭載した専用のＦＩＢ装置を必要としない。
【００５０】
請求項３では、集束イオンビームにより特定箇所の下部の透過型電子顕微鏡用メッシュの支持膜を部分的にエッチングするので、観察試料にダメージを与えず、支持膜の影響を受けずにＴＥＭで格子像等を高分解能観察できる試料を得ることとなる。また、特定箇所の直下の支持膜がなくなることにより、特定箇所の両側からＳＥＭ観察できるため、観察領域を薄片化する際の加工精度が上がることとなる。
【００５１】
請求項４では、半円状のメッシュを用いメッシュの直線側に近い位置にコの字型試料の半導体基板上面に相当する面が直線側になるように固定するので、メッシュに試料を固定した後に、透過型電子顕微鏡用メッシュの支持膜と試料の空間を用いて更にＦＩＢ加工する際にメッシュがＦＩＢ加工の妨げにならず、精度よく再加工することができる。
【００５２】
この発明の請求項５記載の透過型電子顕微鏡用試料によれば、半導体基板上の特定箇所をコの字型に加工して形成され、その凹部がメッシュ側になるように特定箇所に位置する観察領域をメッシュから離隔させて固定したので、試料が透過型電子顕微鏡用メッシュに固定された後にも、ＦＩＢによる試料の再加工や、メッシュの支持膜のエッチングができ、高分解能観察が可能な薄片試料を特定箇所に精度よく作製できることとなり、半導体装置や半導体装置の製造工程途中の素子の形状や故障を的確に解析することができる。
【図面の簡単な説明】
【図１】この発明の第１の実施の形態の透過型電子顕微鏡用試料の解析方法の説明図である。
【図２】この発明の第１の実施の形態におけるＦＩＢ加工方法を示す工程説明図である。
【図３】この発明の第２の実施の形態の透過型電子顕微鏡用試料の解析方法の説明図である。
【図４】この発明の第３の実施の形態の透過型電子顕微鏡用試料の解析方法の説明図である。
【図５】この発明の第４の実施の形態の透過型電子顕微鏡用試料の解析方法の説明図である。
【図６】この発明の第５の実施の形態の透過型電子顕微鏡用試料の形状の説明図である。
【図７】従来例における透過型電子顕微鏡用試料の作製方法の説明図である。
【図８】従来例における透過型電子顕微鏡用試料の形状の説明図である。
【符号の説明】
１ 半導体基板
２ 特定箇所
３ 集束イオンビーム
４ ＴＥＭ試料
５ マニピュレータ先端
６ 透過電子顕微鏡用メッシュ
７ 支持膜
８ 電子線
１１ コの字型試料
１２ マニピュレータ
１３ 特定箇所前方ＦＩＢ加工領域
１４ 特定箇所後方ＦＩＢ加工領域
１５ 観察領域
１６ 特定箇所側面ＦＩＢ加工領域
１７ 特定箇所底面ＦＩＢ加工領域
１８ 特定箇所上方ＦＩＢ再加工領域
１９ 特定箇所下方ＦＩＢ再加工領域
２０ 支持膜ＦＩＢ加工領域
２１ 半円状透過型電子顕微鏡用メッシュ
２２ 特定箇所下方足部分[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for analyzing a semiconductor device, and more particularly, to a method for preparing an observation sample of a transmission electron microscope (TEM) in which a portion to be analyzed is manufactured using a focused ion beam (FIB). The present invention relates to a method for analyzing a transmission electron microscope sample and a transmission electron microscope sample.
[0002]
[Prior art]
TEM is well known as one of the methods for analyzing the fine structure of a sample such as a semiconductor device. An electron beam accelerated by a high voltage of several hundreds kV or more is irradiated onto a TEM observation surface having a portion to be observed on the sample, and the passing electrons transmitted through the TEM observation surface are imaged and observed (TEM observation). This TEM observation enables observation at the atomic level with extremely high resolution. In addition, EDX analysis and EELS analysis in the nanometer range are possible.
[0003]
In recent years, using a focused ion beam (FIB), a TEM sample preparation method that directly separates a TEM observation surface at a specific location from a semiconductor wafer or semiconductor chip has become possible, and a TEM sample can be separated without breaking the semiconductor wafer or chip. A plurality of TEM samples that are very close to each other can be produced, and this is used for failure analysis of semiconductor devices.
[0004]
Conventionally, there are two methods for separating a TEM sample from a semiconductor wafer or a semiconductor chip by FIB and performing TEM observation. One is a method in which a thin sample capable of TEM observation is prepared using FIB, and the sample is separated by a manipulation system using an optical microscope (see Patent Document 1). In addition, there is a method of separating a sample piece produced by an FIB apparatus by a manipulation system incorporated in the FIB apparatus (see Patent Documents 2 and 3). The former is a conventional sample preparation method 1 and the latter is a conventional sample preparation method 2.
[0005]
Conventional sample preparation method 1 will be described with reference to FIGS. FIG. 7 is a process flow chart showing an example of a conventional sample preparation method 1. First, as shown in FIG. 7A, from the semiconductor substrate 1, for example, a semiconductor wafer or a semiconductor chip, the opposite sides including the specific portion 2 to be observed by the TEM can be observed by the FIB 3 with a transmission electron microscope. The TEM sample 4 is separated by slicing (for example, a thickness of 0.2 μm or less), separating the bottom and the side. As shown in FIG. 7B, the sample is electrostatically adsorbed on the manipulator tip 5 using an optical microscope and a manipulator system. Next, as shown in FIG. 7C, the sample is dropped onto a transmission electron microscope mesh 6. Since the separated TEM sample 4 is a thin thin piece, TEM observation is performed in a state of being in close contact with the transmission electron microscope mesh 6.
[0006]
FIG. 8 is an explanatory diagram showing the shape of the sample processed and separated by the FIB 3 and the shape of the cross-sectional structure attached to the transmission electron microscope mesh 6 by the conventional sample preparation method 1. As shown in FIG. 8B, the TEM sample 4 processed and separated by the FIB 3 is a planar sample having a thickness (for example, a thickness of 0.1 μm) that can be observed with a transmission electron microscope. As shown in FIG. 8C, the cross-sectional structure when the sample is attached to the transmission electron microscope mesh 6 includes a TEM sample 4 and a support film 7 attached onto the transmission electron microscope mesh 6; Is a shape that is closely attached.
[0007]
In the conventional sample preparation method 2, a wafer sample stage that locally cuts out an observation target portion of a semiconductor wafer using FIB, and a TEM sample that is mounted on the cut sample and processed to a thickness that can be observed with a transmission electron microscope FIB processing is performed from a semiconductor wafer or a semiconductor chip using a FIB sample preparation device that includes a stage and a manipulator for picking up a sample cut out by a wafer stage and fixing the sample to a TEM sample stage (see Patent Document 3). A fine sample piece including a specific part is separated by the above, and the sample is grasped by depositing a metal on the manipulator and the sample on the sample separated in the FIB, and the transmission type mounted on the TEM sample stage in the FIB apparatus A sample is fixed by depositing a metal on an electron microscope mesh. After fixing the sample, the sample piece is thinned by FIB until further TEM observation is possible. Although FIB processing and TEM observation can be repeated, a dedicated apparatus including a wafer stage, a TEM sample stage, and a manipulator is required in the FIB.
[0008]
[Patent Document 1]
JP 2001-272316 A (FIG. 1)
[Patent Document 2]
JP 05-52721 A
[Patent Document 3]
Japanese Patent Laying-Open No. 2002-62226 (FIG. 1)
[0009]
[Problems to be solved by the invention]
However, in the above-described conventional sample preparation method 1, the thin sample that can be observed by TEM is mechanically separated by the insulating rod of the optical microscope manipulation system. Therefore, if the thin sample is thin enough to obtain a lattice image by TEM, the thin sample is broken. There was a problem that. In addition, in order to increase the processing accuracy of a specific location, it is necessary to repeat sample thinning and TEM observation or SEM observation by FIB. However, since it is adhered and adhered to a transmission electron microscope mesh, after TEM observation Furthermore, there has been a problem that FIB processing cannot be added. In addition, there is a problem that the support film, which plays a role of fixing to the transmission electron microscope mesh when observing a sample flake, hinders high-resolution observation for observing a lattice image or the like during TEM observation.
[0010]
In the above-described conventional sample preparation method 2, the sample can be thinned and the FIB can be reprocessed. However, there is a problem that a dedicated FIB apparatus equipped with a wafer stage, a TEM sample stage, and a manipulator is very expensive. there were.
[0011]
Accordingly, an object of the present invention is to solve the problems in the conventional method, and the semiconductor wafer or the semiconductor chip is separated by FIB without breaking a specific portion and fixed to a mesh for a transmission electron microscope. Another object of the present invention is to provide a method for analyzing a transmission electron microscope sample and a transmission electron microscope sample, which can be further thinned by FIB and can be produced without expensive dedicated FIB.
[0012]
[Means for Solving the Problems]
In order to achieve the above object, a method for analyzing a sample for a transmission electron microscope according to claim 1 of the present invention is a transmission method in which a sample separated from a semiconductor substrate is attached to a mesh for a transmission electron microscope and observed with a transmission microscope. A method for analyzing a specimen for a scanning electron microscope, comprising: a step of cutting a specific portion on the semiconductor substrate into a U shape using a focused ion beam; and a core cut out to include an observation region located at the specific portion. Separating the U-shaped sample using a manipulator system, and fixing the observation region separately from the mesh so that the concave portion of the U-shaped sample is on the transmission electron microscope mesh side; and And observing the U-shaped sample fixed to the mesh with the transmission microscope.
[0013]
Thus, using a manipulator system, a step of cutting a specific portion on a semiconductor substrate into a U-shape using a focused ion beam and a U-shaped sample cut out to include an observation region located at the specific location A separation step, a step of fixing the observation region away from the mesh so that the concave portion of the U-shaped sample is on the transmission electron microscope mesh side, and a transmission type of the U-shaped sample fixed to the mesh A step of observing with a microscope, so that a space is formed between the supporting film of the transmission microscope mesh and the observation region including the specific portion to be observed. Therefore, it can be reworked by FIB. Further, when separating the U-shaped sample, it is not necessary to make it thin until the thickness of the observation region becomes a film thickness that enables TEM observation, so that the sample can be separated without breaking.
[0014]
The method for analyzing a sample for a transmission electron microscope according to claim 2 is the method for analyzing a sample for a transmission electron microscope according to claim 1, wherein the step of observing the U-shaped sample does not clearly observe a specific portion. At this time, the U-shaped sample is further subjected to focused ion beam processing, observation and focused ion beam processing are repeated, and the specific portion is observed after being sliced.
[0015]
In this way, when a specific part is not clearly observed, the U-shaped sample is further processed with focused ion beam, and observation and focused ion beam processing are repeated, and the specific part is observed after thinning. Possible thin piece samples can be processed at specific locations with high accuracy, and semiconductor failure analysis can be performed with high accuracy. In addition, since it is not necessary to make the specific portion extremely thin from the beginning, the probability of damaging the sample when separated by the manipulator is lowered. Further, a dedicated FIB apparatus equipped with an expensive wafer stage, a TEM sample stage, and a manipulator is not required.
[0016]
The method for analyzing a sample for a transmission electron microscope according to claim 3 is the method for analyzing a sample for a transmission electron microscope according to claim 1, wherein the step of observing the U-shaped sample is performed using a focused ion beam. The support film of the lower transmission electron microscope mesh is partially etched.
[0017]
In this way, since the support film of the transmission electron microscope mesh below the specific location is partially etched by the focused ion beam, the observation image is not damaged and is not affected by the support film. Thus, a sample that can be observed with high resolution can be obtained. Further, since there is no support film immediately below the specific location, SEM observation can be performed from both sides of the specific location, so that the processing accuracy when thinning the observation region is increased.
[0018]
The method for analyzing a transmission electron microscope sample according to claim 4 is the transmission electron microscope sample analysis method according to claim 1, wherein the step of fixing the U-shaped sample uses a semicircular mesh. The surface corresponding to the upper surface of the semiconductor substrate of the U-shaped sample is fixed at a position close to the straight line side of the mesh so that it is on the straight line side.
[0019]
In this way, a semicircular mesh is used, and the surface corresponding to the upper surface of the semiconductor substrate of the U-shaped sample is fixed to a position close to the straight line side of the mesh, so that the sample is fixed to the mesh. Later, when the FIB processing is further performed using the support film of the mesh for the transmission electron microscope and the space of the sample, the mesh does not interfere with the FIB processing and can be reprocessed with high accuracy.
[0020]
The sample for a transmission electron microscope according to claim 5 is a sample for a transmission electron microscope that is attached to a mesh for a transmission electron microscope and observed with a transmission microscope. The observation area located at the specific location was fixed so as to be separated from the mesh so that the concave portion was formed on the mesh side.
[0021]
In this way, the specific part on the semiconductor substrate is formed into a U-shape, and the observation region located at the specific part is fixed so that the concave part is on the mesh side. Even after being fixed to the transmission electron microscope mesh, the sample can be reprocessed by FIB and the support film of the mesh can be etched, and a thin sample capable of high-resolution observation can be accurately produced at a specific location.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is an explanatory diagram showing a method for analyzing a sample for a transmission electron microscope according to the first embodiment of the present invention. In particular, FIG. 1 is a process explanatory diagram showing a TEM sample preparation step. The figure (a) is a sketch showing the process of cutting the sample into a U-shape by FIB processing, and the figure (b) is the U-shaped sample separated from the U-shaped sample after FIB processing by the tip of the manipulator. (C) is a sketch of the process of fixing the U-shaped sample to the transmission electron microscope mesh, and (d) is a view of the U-shaped sample for the transmission electron microscope. It is a sketch from the lateral direction when TEM observation is performed on a sample fixed on a mesh support film.
[0023]
As shown in FIG. 1, the TEM sample preparation method for TEM observation as one of the methods for analyzing a semiconductor device uses a focused ion beam 3 to convert a specific portion 2 on a semiconductor substrate 1 into a U shape. A step of cutting out, a step of separating the U-shaped sample 11 cut out so as to include the observation region located at the specific location 2 using the manipulator system 12, and a concave portion of the U-shaped sample 11 for the transmission electron microscope A step of fixing the observation region so as to be on the mesh 6 side without being in close contact with the support film 7 on the mesh 6 and a U-shaped sample 11 fixed to the mesh 6 are observed with a transmission electron microscope. Process.
[0024]
The TEM sample manufacturing method configured as described above will be described in detail with reference to FIGS. First, FIG. 2 shows the process of FIB processing when cutting a sample into a U-shape, and FIGS. 2A and 2B show the FIB processing range when cutting a sample into a U-shape. FIG. 2C is a schematic diagram showing the FIB processing range when the U-shaped sample 11 is viewed from the side.
[0025]
As shown in FIG. 2A, the FIB 3 is scanned from the surface of the sample so that the specific observation location 2 on the semiconductor substrate 1 is included in the side where the specific observation location 2 is recessed by using the FIB 3. The specific location front FIB machining area 13 and the specific location rear FIB machining location 14 are cut into a U-shape. At this time, the U-shaped concave side including the specific portion 2 becomes the TEM observation region 15. After processing like a U-shaped building (building), cut the lower part of the building and take out the sample. The TEM observation area 15 is thinned until the thickness becomes a TEM observation thickness (for example, 0.2 μm or less). Next, as shown in FIGS. 2 (b) and 2 (c), using the FIB 3, the specific location side FIB machining location 16 and the specific location bottom FIB machining area 17 on the side surface of the observation specific location 2 are shaved and the observation specific location The U-shaped sample 11 including is separated from the semiconductor substrate 1.
[0026]
Next, as shown in FIG. 1B, using a manipulator system using an optical microscope, a U-shaped sample 11 including a specific portion 2 is placed on a manipulator tip 5 made of an insulator rod such as glass. The specific portion of the observation is such that the concave portion of the U-shaped sample 11 including the observation specific portion 2 on the transmission electron microscope observation mesh 6 is on the side of the support film 7 stretched on the transmission electron microscope mesh 6 The TEM observation region 15 including 2 is fixed so as not to be in close contact with the support film 7.
[0027]
Next, as shown in FIG. 1 (d), the sample 11 separated into a U-shape by the FIB 3 and attached to the transmission electron microscope mesh 6 by the manipulator 12 is applied to the electron beam 8 from above the TEM observation region 15. By irradiating and observing and analyzing the electrons transmitted through the observation region 15 or the generated secondary electrons, the shape and failure of the semiconductor device and the element in the process of manufacturing the semiconductor device are analyzed.
[0028]
As described above, according to the present embodiment, the U-shaped sample 11 is cut out from the semiconductor substrate 1 by the focused ion beam 3 so that the observation specific portion 2 is included in one side where the U-shape is recessed, and the manipulator 12 is cut out. The TEM observation surface including the specific portion 2 so that the observation region 15 of the U-shaped sample 11 including the specific portion 2 on the transmission electron microscope mesh 6 is on the support film 7 side on the transmission electron microscope mesh 6. Is fixed so as not to be in close contact with the support film 7, and after TEM observation and analysis, the space between the TEM observation region 15 and the support film 7 is used, and the FIB 3 is further used on both sides of the specific location 2 or One side can be reworked to thin the observation area. In the conventional sample preparation method 1, since the TEM sample 4 including the specific portion 2 is in close contact with the support film 7, it is impossible to perform further FIB processing on both sides of the specific portion 2.
[0029]
In the first embodiment, the semiconductor substrate 1 from which the U-shaped sample is taken out may be a semiconductor wafer or a semiconductor chip.
[0030]
A second embodiment of the present invention will be described with reference to FIG. FIG. 3 is an explanatory diagram showing a method for analyzing a sample for a transmission electron microscope according to the second embodiment of the present invention, in particular, a process explanatory diagram showing a TEM sample preparation process. The figure (a) is a sketch showing the process of cutting the sample into a U-shape by FIB processing, and the figure (b) is the U-shaped sample separated from the U-shaped sample after FIB processing by the tip of the manipulator. (C) is a sketch of the process of fixing the U-shaped sample to the transmission electron microscope mesh, and (d) and (e) are fixed to the transmission electron microscope mesh. The perspective view and the sketch from the side when the sliced U-shaped sample is further sliced by FIB, and FIG. 5 (f) are the sketches of the process of observing the sliced sample by FIB rework.
[0031]
In FIG. 3, steps (a), (b), and (c) in FIG. 3 are the same as those in FIG. 1, and a specific portion 2 on the semiconductor substrate 1 is placed in a U shape by using a focused ion beam 3. A step of cutting into a mold, a step of separating the U-shaped sample 11 cut out so as to include the observation region located at the specific location 2 using the manipulator system 12, and the concave portion of the U-shaped sample 11 is a transmission electron. And a step of fixing the observation region so as to be on the microscope mesh 6 side without being closely attached to the support film 7 on the mesh 6. 1 is different from the configuration of FIG. 1 in observing the U-shaped sample 11 fixed to the transmission electron microscope mesh 6 as shown in FIGS. 3D and 3E. Is attached to the support film 7 on the transmission electron microscope mesh 6 and observed, and then the mesh 6 is erected in the FIB apparatus, and the FIB reworked region 18 or the observation region 15 and the transmission region 15 for the transmission electron microscope This is a point including a step of re-processing the lower FIB re-processed region 19 at a specific location with the FIB 3 using the space with the support film 7 on the mesh 6 and further thinning and observing the TEM observation region 15.
[0032]
In the case of this embodiment, when observing a thinned sample by FIB reprocessing for the first time, if the specific portion 2 is still not clearly observed, the observation region is further thinned by FIB3 and then observed. To do. The above operation is repeated any number of times until the specific portion 2 is clearly observed. Finally, the electron beam 8 is irradiated from the upper part of the TEM observation region 15 and the electrons transmitted through the observation region 15 or generated secondary electrons. By observing and analyzing the above, the shape and failure of the semiconductor device and the element in the process of manufacturing the semiconductor device are analyzed.
[0033]
As described above, in the second embodiment, the U-shaped sample 11 is cut out from the semiconductor substrate 1 by the focused ion beam 3 so that the observation specific portion 2 is included in one side where the U-shape is recessed, and the manipulator 12 is cut out. The TEM observation surface including the specific portion 2 so that the observation region 15 of the U-shaped sample 4 including the specific portion 2 on the transmission electron microscope mesh 6 is on the support film 7 side on the transmission electron microscope mesh 6. Is fixed so as not to adhere to the support film 7, and when the specific portion 2 is not clearly observed, the space between the observation region 15 and the support film 7 on the transmission electron microscope mesh 6 is used. Further, FIB processing is performed, and observation and FIB processing are repeated, and the step of observing after slicing the specific portion 2 is provided, so that the TEM observation region 15 including the specific portion 2 is FIB processed with high accuracy. It can be clearly TEM observation or analysis. Further, when the U-shaped sample 11 is cut out, it is not necessary to make it very thin (for example, 100 nm or less), so that the probability of damaging the sample when separated by the manipulator 12 can be reduced.
[0034]
In the second embodiment, when the specific portion 2 is not clearly observed in the observing step, the FIB processing is further performed using the space between the observation region 15 and the support film 7 on the transmission electron microscope mesh 6. However, in the process of cutting out the U-shaped sample with the first FIB 3, it is not necessary to make a slice until the thickness becomes TEM observable (for example, 0.2 μm or less). In this case, the transmission electron microscope The U-shaped sample 11 attached to the mesh 6 is sliced without observing until the film thickness of the observation region 15 becomes TEM-observable (for example, 0.2 μm or less) by the FIB 3. It becomes.
[0035]
A third embodiment of the present invention will be described with reference to FIG. FIG. 4 is an explanatory view showing a method for analyzing a sample for a transmission electron microscope according to the third embodiment of the present invention, in particular, a process explanatory view showing a TEM sample preparation process. The figure (a) is a sketch showing the process of cutting the sample into a U-shape by FIB processing, and the figure (b) is the U-shaped sample separated from the U-shaped sample after FIB processing by the tip of the manipulator. (C) is a sketch of the process of fixing the U-shaped sample to the transmission electron microscope mesh, and (d) and (e) are fixed to the transmission electron microscope mesh. The perspective view of the process of etching the support film directly under the observed portion of the U-shaped sample by FIB processing and a sketch from the side, FIG. 5F is a sketch of the process of observing the sample.
[0036]
In FIG. 3, steps (a), (b), and (c) in FIG. 3 are the same as those in FIG. 1, and a specific portion 2 on the semiconductor substrate 1 is placed in a U shape by using a focused ion beam 3. A step of cutting into a mold, a step of separating the U-shaped sample 11 cut out so as to include the observation region located at the specific location 2 using the manipulator system 12, and the concave portion of the U-shaped sample 11 is a transmission electron. And a step of fixing the observation region so as to be on the microscope mesh 6 side without being closely attached to the support film 7 on the mesh 6. 1 is different from the configuration of FIG. 1 in observing the U-shaped sample 11 fixed to the transmission electron microscope mesh 6 as shown in FIGS. 3 (d), 3 (e), and 3 (f). This includes a step of observing the support film 7 directly under the observation region including the portion by etching with the FIB 3.
[0037]
Hereinafter, the step of etching and observing the support film 7 will be described in detail with reference to FIGS. 3 (d), 3 (e), and 3 (f). As shown in FIG. 4D, the U-shaped sample 11 fixed to the transmission electron microscope mesh 6 is tilted in the FIB apparatus, and the observation region 15 and the support film 7 on the transmission electron microscope mesh 6 are supported. Is used to process the support film FIB processing region 20 of the support film 7 immediately below the observation region including the observation part. When viewed from the side as shown in FIG. 5E, the support film FIB processing region 20 is directly below the specific portion 2. As shown in FIG. 3F, by irradiating the electron beam 8 from above and observing and analyzing the electrons transmitted through the observation region 15 or the generated secondary electrons, the semiconductor device and the semiconductor device are being manufactured. Analyze the shape and failure of the element.
[0038]
As described above, in the third embodiment, the U-shaped sample 11 is cut out from the semiconductor substrate 1 by the focused ion beam 3 so that the observation specific portion 2 is included in one side where the U-shape is recessed, and the manipulator 12 is cut out. The TEM observation surface including the specific portion 2 so that the observation region 15 of the U-shaped sample 11 including the specific portion 2 on the transmission electron microscope mesh 6 is on the support film 7 side on the transmission electron microscope mesh 6. In the step of fixing and observing the support film 6 so as not to adhere to the support film 6, the process includes a step of observing the support film 7 directly under the observation area including the observation portion by partially etching with the FIB 3, thereby damaging the observation area 15. Instead, the support film 7 can be removed. In the TEM observation in the conventional TEM sample preparation method, the electron beam 8 passes through both the sample 4 and the support film 7 regardless of how thin the observation region is. Although it could not be observed with a resolution, according to the present embodiment, a lattice image or the like can be observed with a high resolution by TEM observation without being affected by the support film 7. Further, since the support film 7 immediately below the specific location 2 is eliminated, SEM observation can be performed from both sides of the specific location 2, so that the processing accuracy when the observation area is further thinned as in the second embodiment is increased.
[0039]
A fourth embodiment of the present invention will be described with reference to FIG. FIG. 5 is an explanatory diagram showing a method for analyzing a sample for a transmission electron microscope according to the fourth embodiment of the present invention, in particular, a process explanatory diagram showing a TEM sample preparation step. The figure (a) is a sketch showing the process of cutting the sample into a U-shape by FIB processing, and the figure (b) is the U-shaped sample separated from the U-shaped sample after FIB processing by the tip of the manipulator. (C) is a sketch of the process of fixing the U-shaped sample to the transmission electron microscope mesh, and (d) is a schematic of the step of fixing the U-shaped sample to the transmission electron microscope mesh. It is the perspective view of the process of thinning the observation location of a character-shaped sample into FIB processing, and a sketch from the side.
[0040]
5A and 5B, the steps shown in FIGS. 5A and 5B are the same as those shown in FIG. 2, and a specific portion 2 on the semiconductor substrate 1 is cut into a U-shape using the focused ion beam 3. And a step of separating the U-shaped sample 11 cut out so as to include the observation region located at the specific location 2 by using the manipulator system 12. The difference from the configuration of FIG. 1 is that when the separated U-shaped sample 11 is fixed to the transmission electron microscope mesh as shown in FIG. And includes a step of fixing the upper surface of the sample 11 (a surface corresponding to the upper surface of the semiconductor substrate) at a position close to the straight line side of the mesh 21 so as to be on the straight line side. When the portion 2 is further thinned, the sample 11 is set up in the FIB apparatus so that the straight side of the mesh 21 faces upward, and the FIB 3 is applied from above and processed. Next, by irradiating the electron beam 8 from above and observing and analyzing the electrons transmitted through the observation region 15 or the generated secondary electrons, the shape or failure of the semiconductor device or the element during the manufacturing process of the semiconductor device can be observed. To analyze.
[0041]
As described above, in the fourth embodiment, the U-shaped sample 11 is cut out from the semiconductor substrate 1 by the focused ion beam 3 so that the observation specific portion 2 is included in one side where the U-shape is recessed, and the manipulator 12 is cut out. When fixing the U-shaped sample 11 separated into two to the transmission electron microscope mesh, the semicircular transmission electron microscope mesh 21 was used, and the upper surface of the sample 11 was positioned on the straight side at a position close to the straight side of the mesh 21. In order to further thin the specific portion 2 using the space between the support membrane 7 and the sample 11, the sample is set up so that the straight side of the mesh 21 is in the FIB apparatus. By performing the FIB processing, the mesh 21 does not interfere with the FIB processing and can be reprocessed with high accuracy.
[0042]
A fifth embodiment of the present invention will be described with reference to FIG. FIG. 6 is an explanatory view showing the shape of a sample for a transmission electron microscope according to the fifth embodiment of the present invention. FIG. 6 (a) is a plan view of an FIB processing region when a U-shaped sample is cut out. (B) is a schematic diagram when a U-shaped sample is attached to a transmission electron microscope mesh, and (c) is a U-shaped sample attached to a transmission electron microscope mesh. It is a cross-sectional schematic diagram at the time of attaching.
[0043]
As shown in FIG. 6, the transmission electron microscope sample 11 is formed by processing a specific portion 2 on the semiconductor substrate 1 into a U-shape, and the concave portion is on the transmission electron microscope mesh 6 side. The observation region 15 located at the specific location 2 is fixed separately from the mesh 6.
[0044]
In this case, as shown in FIG. 6A, the U-shaped sample 11 cut out from the semiconductor substrate 1 so that the specific portion 2 is included in one side where the U-shaped recess is formed by the focused ion beam 3. As shown in FIG. 4B, the observation region 15 including the specific portion 2 is fixed to the support film 7 on the transmission electron microscope mesh 6 so as not to be in close contact with the support film 7. The cross-sectional structure of the sample is as shown in FIG.
[0045]
Next, the shape of the sample will be described in detail with reference to FIG. The shape of the sample for the transmission electron microscope is, for example, 15 to 30 μm in the lateral length across the specific portion 2 in FIG. 5A, an observation region of about 10 μm, and a processing depth of 3 to 10 μm. Considering the stability when fixed on the transmission electron microscope mesh 6 as shown in FIGS. 5B and 5C, the width of one leg of the lower leg portion 22 at the specific location of the U-shaped sample 11 is as follows. 3 to 5 μm, the height of the lower leg portion 22 at the specific location is considered to have little influence from the support film 7 and have good stability when the specific location is further thinned with FIB after being fixed to the mesh. 3 μm is appropriate. The thickness of the observation region 15 can be measured by TEM observation after fixing to the transmission electron microscope mesh 6 if the thickness is TEM observation or less, for example, 0.2 μm or less, but can be observed by TEM observation after further thinning with the FIB 3. Therefore, it is not necessary to slice into 0.2 μm or less when cutting out. As described above, the details of the shape of the sample have been described with numerical values for the sake of clarity of understanding. However, if the range is a range processed by FIB and stable when fixed to the support membrane, Not as long.
[0046]
As described above, in the fifth embodiment, the U-shaped sample 11 cut out from the semiconductor substrate 1 by the focused ion beam 3 so that the observation specific portion 2 is included in the concave side is Since the observation region 15 including the specific portion 2 is fixed to the support film 7 on the transmission electron microscope mesh 6 so as not to adhere to the support film 7, the sample 11 is fixed to the observation mesh 6. Even after being performed, using the space between the observation region 15 and the support film 7, the FIB 3 can reprocess the observation region 15 including the specific portion 2 using the FIB 3, and the support film 7 can be etched. A possible thin piece sample can be accurately produced at the specific location 2.
[0047]
Although the foregoing embodiments have been described in detail by way of illustration and example for clarity of understanding, changes may be made within the scope of the claims.
[0048]
【The invention's effect】
According to the method for analyzing a sample for a transmission electron microscope according to claim 1 of the present invention, a step of cutting a specific portion on a semiconductor substrate into a U-shape using a focused ion beam, and an observation region located at the specific portion The U-shaped sample cut out so as to include a step is separated using a manipulator system, and the observation region is fixed separately from the mesh so that the concave portion of the U-shaped sample is on the transmission electron microscope mesh side. And a step of observing the U-shaped sample fixed to the mesh with a transmission microscope, so that there is a space between the supporting film of the transmission microscope mesh and the observation region including the specific portion to be observed. As a result, it is possible to re-process with FIB from both sides of the specific portion after observation using this space. Further, when separating the U-shaped sample, it is not necessary to make it thin until the thickness of the observation region becomes a film thickness that enables TEM observation, so that the sample can be separated without breaking.
[0049]
According to the second aspect, when the specific portion is not clearly observed, the U-shaped sample is further subjected to focused ion beam processing, and the observation and the focused ion beam processing are repeated, and the specific portion is observed after being thinned. It is possible to accurately process a thin sample that can be processed at a specific location, and to perform semiconductor failure analysis with high accuracy. In addition, since it is not necessary to make the specific portion extremely thin from the beginning, the probability of damaging the sample when separated by the manipulator is lowered. Further, a dedicated FIB apparatus equipped with an expensive wafer stage, a TEM sample stage, and a manipulator is not required.
[0050]
According to the third aspect of the present invention, since the support film of the transmission electron microscope mesh below the specific portion is partially etched by the focused ion beam, the observation sample is not damaged and is not affected by the support film. A sample capable of observing an image or the like with high resolution will be obtained. Further, since there is no support film immediately below the specific location, SEM observation can be performed from both sides of the specific location, so that the processing accuracy when thinning the observation region is increased.
[0051]
According to the fourth aspect, the semicircular mesh is used and the surface corresponding to the upper surface of the semiconductor substrate of the U-shaped sample is fixed on the straight line side at a position close to the straight line side of the mesh. Later, when the FIB processing is further performed using the support film of the mesh for the transmission electron microscope and the space of the sample, the mesh does not interfere with the FIB processing and can be reprocessed with high accuracy.
[0052]
According to the sample for a transmission electron microscope according to claim 5 of the present invention, the specific portion on the semiconductor substrate is formed into a U-shape, and the concave portion is positioned at the specific portion so as to be on the mesh side. Since the observation area is fixed separately from the mesh, even after the sample is fixed to the transmission electron microscope mesh, the sample can be reprocessed by FIB and the mesh support film can be etched, enabling high-resolution observation. A thin sample can be accurately produced at a specific location, and the shape and failure of the semiconductor device and the element during the manufacturing process of the semiconductor device can be analyzed accurately.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a method for analyzing a sample for a transmission electron microscope according to a first embodiment of the present invention.
FIG. 2 is a process explanatory view showing the FIB processing method in the first embodiment of the invention.
FIG. 3 is an explanatory diagram of a transmission electron microscope sample analysis method according to a second embodiment of the present invention.
FIG. 4 is an explanatory diagram of a method for analyzing a transmission electron microscope sample according to a third embodiment of the present invention.
FIG. 5 is an explanatory diagram of a method for analyzing a transmission electron microscope sample according to a fourth embodiment of the present invention.
FIG. 6 is an explanatory diagram of the shape of a transmission electron microscope sample according to a fifth embodiment of the present invention.
FIG. 7 is an explanatory diagram of a method for producing a transmission electron microscope sample in a conventional example.
FIG. 8 is an explanatory view of the shape of a transmission electron microscope sample in a conventional example.
[Explanation of symbols]
1 Semiconductor substrate
2 specific locations
3 Focused ion beam
4 TEM sample
5 Manipulator tip
6 Mesh for transmission electron microscope
7 Support membrane
8 electron beam
11 U-shaped sample
12 Manipulator
13 Specific area forward FIB machining area
14 Specific location rear FIB machining area
15 Observation area
16 Specific area side FIB machining area
17 Specific area bottom surface FIB machining area
18 FIB rework area above specific location
19 FIB rework area under specific location
20 Support membrane FIB processing area
21 Mesh for semicircular transmission electron microscope
22 Specific part lower leg part