JP3449492B2 - Pretreatment method for wafer etching - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to the removal of dirt and lapping agents generated in a lapping process before etching a wafer such as silicon with a mixed acid (hydrofluoric acid, nitric acid, acetic acid, pure water), and a wafer. The present invention relates to a pretreatment method mainly performed for flattening the surface.

[0002]

2. Description of the Related Art A semiconductor wafer used as a substrate for a semiconductor device is a single crystal ingot such as silicon.
Sliced to its own rod axis, chamfered with respect to those obtained by slicing, lapping, etching, obtained by sequentially performing the processes of polishing and the like.

Of these, the semiconductor wafer is etched for the purpose of removing a damage layer caused by lapping which is a pre-process and a lapping agent (powder) embedded in the surface. Particularly, chemical etching is performed on the wafer by using a mixed acid (fluorine). It is carried out by immersing it in an etching solution such as acid, nitric acid, acetic acid, pure water) for a predetermined time.

However, if the lapping wafer is put into the etching process as it is and chemically treated with a mixed acid, there is a problem that uneven etching occurs on the wafer due to stains attached in the lapping process.

In addition to uneven etching due to dirt or the like, when the damaged layer produced in the lapping process is directly subjected to chemical etching, there is a problem that the surface becomes rough and projections are generated. These protrusions cause dimples during polishing as a post-process, resulting in a significant decrease in wafer yield.

Furthermore, if the lapping-processed wafer is put into the etching process as it is, the lapping agent from the previous process is brought into the etching layer, which causes impurities to adhere to the surface of the wafer even after the chemical etching. There was a problem of doing.

Therefore, prior to chemical etching, precleaning is performed using a cleaning solution in which a trace amount of a surfactant is added to a low-concentration alkaline solution for the purpose of removing contaminants adhering to the wafer in a lapping step, which is a previous step. Pretreatment) was performed.

[0008]

However, the conventional cleaning solution obtained by adding a trace amount of a surfactant to a low-concentration alkaline solution is
Although some effects can be expected to remove the dirt attached in the lapping process, the surfactant remains on the surface of the wafer and is not removed even after the wafer is chemically etched. This has been a cause of lowering the wafer yield.

The present invention has been made in view of the above problems of the prior art. By using hydrogen peroxide solution in place of the surfactant, it is possible to prevent the cleaning liquid itself from remaining and to make it suitable. The purpose is to efficiently remove the stain in the previous step by utilizing the redox reaction.

[0010]

In order to achieve the above-mentioned object, the wafer etching pretreatment method of the present invention comprises an inorganic alkali component of 0.08% to 0.08% before mixed acid etching.
1.0 mol / l , an aqueous solution of hydrogen peroxide of 0.05-0.
45 mol / l , the redox solution having a removal capacity of 10 Å / min or more and the inorganic alkali component is 7 mol / l
It is characterized in that cleaning is continuously performed using a high-concentration inorganic alkaline solution having a removal capacity of 1 or more and a removal capacity of 0.7 to 1.2 μm / min.

[0011]

Before performing chemical etching using a mixed acid composed of hydrofluoric acid, nitric acid, acetic acid, pure water, etc., first, the inorganic alkaline component is 0.08 to 1.0 mol / l and the hydrogen peroxide solution is 0.05 %. The lapping-completed wafer is washed with an oxidation-reduction solution having a removal capacity of 0.45 mol / l and a removal capacity of 10Å / min or more.

Dirt in the lapping process is removed by the redox effect of the hydrogen peroxide solution, and since the hydrogen peroxide solution freely mixes with the water, the wafer surface can be cleaned with pure water after that. It does not remain in.

Next, the inorganic alkali component is 7 mol / l
The wafer is cleaned using the high-concentration inorganic alkali solution described above. With this high-concentration inorganic alkaline solution, the surface of the wafer is adjusted and the surface protrusion density due to the damaged layer can be reduced. In particular, removal capacity (etching rate) is a surface projection density decreases because it is 0.7 [mu] m / min or more (see FIG. 2). Further, if the removal capacity is 1.2 μm / min or more, surface roughness occurs, and this surface roughness is promoted in the subsequent chemical etching, which is not preferable.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a process diagram showing a pretreatment process for wafer etching according to an embodiment of the present invention, and FIG. 2 is a second view of the same embodiment.
FIG. 3 is a graph showing the relationship between the etching rate in the cleaning step and the protrusion density on the wafer surface. FIG. 3 shows the pretreated wafer of the same example being chemically etched with mixed acid.
It is a graph which shows the result of having analyzed the amount of impurities of the obtained wafer by SIMS (the surface trace element analysis method by the secondary electron).

For example, when manufacturing a silicon wafer (polished wafer, mirror-polished wafer), a single crystal ingot of silicon or the like is sliced in the rod axis direction, and the sliced product is chamfered and lapped. 1 is performed sequentially (wrapped wafer). After that, etching 5 is performed for the purpose of removing the damage layer caused by the lapping 1 and the wrapping agent (powder) embedded in the surface.
Particularly in chemical etching, the wafer is immersed in an etching solution such as mixed acid (hydrofluoric acid, nitric acid, acetic acid, pure water) for a predetermined time.

In this embodiment, pretreatment is performed before the etching 5. Specifically, as shown in FIG. 1, wrapping 1
A first cleaning 2 is performed on the silicon wafer (wrapped wafer) that has been subjected to the step 1 in order to remove the dirt attached in the lapping step 1.

The cleaning solution used in the first cleaning step 2 is a mixed solution of an inorganic alkali having a redox reaction ability and hydrogen peroxide. In particular, a redox solution having an inorganic alkaline component of 0.08 to 1.0 mol / l and an aqueous hydrogen peroxide solution of 0.05 to 0.45 mol / l is used.

Further, such a cleaning liquid soil removal capability in order to efficiently exhibit, you the etching rate (removal capability) and 10 Å / min or more.

By adopting a mixed solution of an inorganic alkali and hydrogen peroxide as the cleaning liquid, the dirt in the lapping step 1 is removed by the redox effect of the hydrogen peroxide water, and the hydrogen peroxide water is mixed with the water. Since they are freely mixed, if they are subsequently washed with pure water or the like, they will not remain on the wafer surface.

After performing the first cleaning 2, the second cleaning 3 is continuously performed. The main purpose of the second cleaning 3 is to adjust the surface of the silicon wafer when performing the chemical etching 5 which is a post-process, and reduce the surface protrusion density due to the damaged layer in the lapping process 1.

Specifically, a high-concentration inorganic alkaline solution is used as the cleaning liquid in the second cleaning step 3. At this time, in order to satisfy the surface protrusions density, inorganic alkali components in the high density inorganic alkali solution and 7 mol / l or more.

Further, in order to minimize the surface protrusion density ,
Etching rate (removal capacity) 0.7-1.2 μm /
Set to min. Fig. 2 shows the relationship between the etching rate and the surface protrusion density for the etched wafer surface. The surface protrusion density is obtained by counting a portion higher than the surface level observed at the time of overfocus by observing an optical microscope image (unit area: Per piece). It is understood that the surface protrusion density becomes the minimum when the etching rate is 0.7 to 1.2 μm / min.

Finally, the silicon wafer is washed with pure water to remove the alkaline component of the cleaning liquid used in the first cleaning step 2 and the second cleaning step 3 (pure water cleaning step 4). At this time, the hydrogen peroxide component used in the first cleaning step 2 is also removed and does not remain on the silicon wafer.

FIG. 3 shows the results of analyzing the amount of impurities adhering to the resulting etched wafer by SIMS (secondary electron surface trace element analysis method) after pretreatment and chemical etching with mixed acid. Yes, ◯ is the SIMS relative peak value of the amount of impurities when the conventional pretreatment method and □ are the pretreatment methods of the present invention. Compared with the etched wafer processed by the conventional pretreatment method,
In particular, it is understood that the levels of Al and Ca elements are reduced.

The silicon wafer thus pretreated is sent to the chemical etching step 5 where it is subjected to etching treatment with mixed acid (etched wafer) and then subjected to various steps such as polishing and mirror polishing. It becomes a wafer.

It should be noted that the embodiments described above are described for facilitating the understanding of the present invention, and not for limiting the present invention. Therefore, each element disclosed in the above-described embodiments is intended to include all design changes and equivalents within the technical scope of the present invention.

[0027]

As described above, according to the present invention, as compared with the conventional cleaning solution in which a trace amount of a surfactant is added to a low-concentration alkaline solution, the cleaning solution itself removes the dirt attached in the lapping process. Since it does not remain on the surface of the wafer, it is possible to prevent a decrease in wafer yield due to the adhesion of impurities.

Further, since the surface of the damaged layer produced in the lapping step is properly adjusted, it is possible to suppress dimples produced in the polishing step which is a post step, and also from this point, it is possible to prevent a decrease in wafer yield. .

Further, since it is possible to prevent the lapping agent in the lapping step and the cleaning agent in the pretreatment step from being brought into the etching step, it is possible to reduce the adhesion of impurities to the etched wafer caused by this.

[Brief description of drawings]

FIG. 1 is a process explanatory view showing a pretreatment process of wafer etching according to an embodiment of the present invention.

FIG. 2 is a graph showing the relationship between the etching rate and the protrusion density on the wafer surface in the second cleaning step of the same example.

FIG. 3 is a graph showing the results of chemical etching of the pretreated wafer of the same example with mixed acid and analysis of the amount of impurities in the obtained wafer by SIMS (secondary electron surface trace element analysis method). .

[Explanation of symbols]

1 ... Wrapping 2 ... First cleaning (removal of dirt) 3 ... Second cleaning (projection density control) 4… Pure water cleaning (removal of alkaline components) 5 ... Etching

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Kazunari Takaishi               3-8-16 Iwamotocho, Chiyoda-ku, Tokyo               Mitsubishi Materials Silicon Co., Ltd. (72) Inventor Tadashi Okada               3-8-16 Iwamotocho, Chiyoda-ku, Tokyo               Mitsubishi Materials Silicon Co., Ltd.                (56) References JP-A-60-92621 (JP, A)

Claims (2)

(57) [Claims] 1. Before performing mixed acid etching, the inorganic alkali component is 0.08 to 1.0 mol / l , the hydrogen peroxide solution is 0.05 to 0.45 mol / l , and the removal ability is 1.
Redox solution of 0Å / min or more, inorganic alkali component of 7 mol / l or more, and removal capacity of 0.7 to 1.2μ
A pretreatment method for wafer etching, characterized in that cleaning is continuously performed using a high-concentration inorganic alkali solution of m / min. 2. The surface protrusion density of the wafer is reduced by treating with a high-concentration inorganic alkaline solution having an inorganic alkaline component of 7 mol / l or more and a removal capacity of 0.7 to 1.2 μm / min. 1. The pretreatment method for wafer etching according to 1.