JP2000340503A - Method for manufacturing semiconductor film, method for manufacturing thin film transistor, active matrix substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacture for a high quality semiconductor film which has a large particle size, high in crystallinity, and low in surface roughness. SOLUTION: Energy light irradiation for obtaining a polycrystalline silicon film is conducted twice, and the first irradiation is made in a vacuum having no oxide film removal processing of a semiconductor film surface, or is made in the atmosphere or in the ambience in which any gas is filled up to the exclusion of vacuum. A surface processing of a semiconductor film is performed prior to the second irradiation, and after the oxide film is eliminated, the irradiation is made in vacuum. Furthermore, intensity of second energy light irradiation is adjusted so as not to exceed the irradiation intensity of the first energy lights.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a semiconductor thin film in which a semiconductor thin film formed on a substrate surface is irradiated with energy light to perform a crystallization treatment or a treatment for improving crystallinity, and to use the method. Thin film transistor (hereinafter, T
It is called FT. ), A TFT manufactured by this method
More specifically, the present invention relates to an active matrix substrate using the same and an annealing apparatus used for a method of manufacturing a semiconductor film.

[0002]

2. Description of the Related Art In an active matrix substrate used for a liquid crystal display device, it is desired to manufacture a TFT by a low-temperature process so that a general-purpose inexpensive glass substrate can be used as the substrate. Here, among the silicon films necessary for forming the channel region and the like of the TFT, an amorphous silicon film can be formed by a low-temperature process, but the amorphous silicon film has a drawback that the mobility of the obtained TFT is low. .

Therefore, a method (laser annealing) of irradiating a laser beam (energy light) to an amorphous silicon film formed on a substrate to melt and crystallize the film is being studied. In such melt crystallization using laser light, the crystal grain size, crystallinity, and surface roughness of the obtained crystalline semiconductor film vary depending on the intensity of the irradiated laser light, the irradiation atmosphere, and the surface state of the amorphous silicon film.
When molecules such as oxygen are present in the process atmosphere or on the surface of the amorphous silicon film, crystal growth occurs with the molecules as nuclei, and the grain size increases, but there are many defects. In addition, large roughness occurs on the surface. On the other hand, when laser annealing is performed in a vacuum after removing the oxide film on the surface of the amorphous silicon film by the surface treatment, the grain size is somewhat small but the crystallinity is high and the surface roughness is small. Among these processing conditions, laser annealing is performed in the air because the relatively high TFT characteristics are easily obtained when the particle size is increased.

[0004]

However, in the conventional method of manufacturing a semiconductor film, if a large grain size is not applied to the channel portion of the TFT, the TFT characteristics are lowered and cause a variation. In addition, since large surface roughness occurs, there is a problem that the withstand voltage of the gate insulating film is reduced.

[0005] In view of these problems, an object of the present invention is to provide:
A method of manufacturing a high-quality semiconductor film that can obtain a large grain size, reduce variation by improving crystallinity, and improve gate breakdown voltage by suppressing surface roughness. And an active matrix substrate using the TFT manufactured by this method.

[0006]

According to the present invention, there is provided a film forming step of forming a semiconductor film on a substrate, and a step of irradiating the semiconductor film with energy light to form a crystalline semiconductor film. A step of irradiating the semiconductor film with a first energy light; a step of performing a surface treatment of the semiconductor film after the step of irradiating the first energy light; A step of irradiating the semiconductor film with second energy light after the step of performing the treatment.

In the present invention, the semiconductor film is irradiated with the first energy light in a vacuum without removing the oxide film on the surface of the semiconductor film, or in the atmosphere or in an atmosphere except a vacuum filled with a predetermined gas. Since the intensity of the energy light does not exceed the threshold of the energy intensity at which microcrystallization occurs in the semiconductor film, the crystal growth occurs due to nuclei of oxygen molecules and the like. Is increased in particle size.

Subsequently, after performing a surface treatment for removing an oxide film on the surface of the semiconductor film, the semiconductor film is irradiated with a second energy light in a vacuum, and the intensity of the energy light is applied to the semiconductor film. Since the irradiation is performed at an intensity not exceeding the threshold of the energy intensity at which microcrystallization occurs and not exceeding the irradiation intensity of the first energy light, the large particle size formed by the first irradiation is maintained. In addition, the crystallinity within the grains is improved and the surface roughness is reduced.

Further, the irradiation of the semiconductor film with the second energy light is performed by rotating the longitudinal direction of the energy light as a line beam by 90 degrees with respect to the longitudinal direction of the line beam at the time of the first energy light irradiation. Therefore, the uniformity of crystallinity is further improved by canceling the irradiation trace of the line beam.

In the present invention, the semiconductor film has a large grain size and high uniform crystallinity by combining the irradiation of energy light for crystallization twice and the timing of surface treatment. Therefore, when a TFT is manufactured using the semiconductor film configured as described above, high electric characteristics without variation can be obtained.

In the method for producing a crystalline semiconductor film according to the present invention, it is preferable to produce a TFT from the crystalline semiconductor film obtained by this method. It is suitable for forming a drive circuit and a pixel switching element on an active matrix substrate for a liquid crystal display device which requires the following.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Before describing each embodiment of the present invention, a basic configuration of an active matrix substrate and a basic process for forming a TFT common to each embodiment will be described.

[Basic Configuration of Active Matrix Substrate]
FIG. 1A is an explanatory diagram schematically illustrating a configuration of an active matrix substrate used for a liquid crystal display device.

In FIG. 1, a data line 3 and a scanning line 4 are formed on an active matrix substrate 2 of a liquid crystal display device 1. Then, the data line 3 and the scanning line 4
Is connected to a pixel electrode through a pixel thin film transistor 10, and a pixel region 5 is formed on a matrix. Further, an image signal is input thereto through a TFT 10 for a pixel, and a liquid crystal capacitor 6 of a liquid crystal cell is formed.

For the data line 3, a shift register 7
1, a data driver unit 7 including a level shifter 72, a video line 73, and an analog switch 74, and a scanning driver unit 8 including a shift register 81 and a level shifter 82 for the scanning line 4.
Note that a storage capacitor 25 may be formed between the pixel region 5 and the preceding scanning line 4.

In the data driver section 7 and the scan driver section 8, as shown in FIG.
A CMOS circuit or the like constituted by N-type TFTs n1 and n2 and P-type TFTs p1 and p2 is formed at high density. However, the TFT 10 of the active matrix section 9
And the TFTs n1 and n2 of the data driver section 7 and the P-type TFTs.
FTp1 and p2 have the same basic structure and are basically manufactured in the same process.

The active matrix substrate 2 includes only the active matrix section 9 on the substrate, the same substrate having the data driver section 7 on the same substrate as the active matrix section 9, and the same substrate as the active matrix section 9. The one on which the scanning driver unit 8 is configured,
In some cases, both the data driver section 7 and the scanning driver section 8 are formed on the same substrate as the active matrix section 9. Further, even if the active matrix substrate 2 has a built-in driver, the shift register 71, the level shifter 72, the video line 7
3. a complete driver built-in type in which all of the analog switches 74 and the like are configured on the active matrix substrate 2,
Although there is a partial driver built-in type in which a part of them is formed on the active matrix substrate 2, the present invention can be applied to any of them.

FIG. 2 is an enlarged plan view showing a part of the active matrix portion where the pixel region 5 is formed in the active matrix substrate 2 of the present embodiment.
FIG. 3A is a cross-sectional view taken along line AA ′ in FIG.
FIG. 3 is a sectional view taken along line BB ′ of FIG. 2. Note that the TFTs of the data driver section 7 and the like have basically the same structure, and are not shown.

In these figures, any pixel region 5
The TFT 10 in FIG.
6, a drain region 12 and a drain region 12 electrically connected to a pixel electrode 19 via a contact hole 18 formed in an interlayer insulating film 16. A source region 11 and a channel region 13, and a gate electrode 15 opposed to the channel region 13 via a gate insulating film 14. This gate electrode 15 is configured as a part of the scanning line 4. Note that a base protective film 21 made of a silicon oxide film is formed on the front surface side of the substrate 20.

[Basic Configuration of Manufacturing Method of Active Matrix Substrate 2] The basic steps of the manufacturing method of the TFT will be described with reference to FIG. FIG. 4 is a process sectional view of the TFT corresponding to a section taken along line AA ′ of FIG.

In this embodiment, the glass substrate is 300 mm
The following steps are performed using a non-alkali glass plate having a corner (underlying protective film forming step). In FIG.
Under the temperature condition of 250 to 400 ° C. by the ECVD method, the thickness of the undercoating protective film 21 on the surface of the glass substrate 20 is 30
A 0 nm silicon oxide film is formed. The silicon oxide film can also be formed by the APCVD method. In this case, the silicon oxide film is formed using monosilane and oxygen as a source gas while the temperature of the substrate 20 is set in a range from 250 ° C. to 450 ° C. .

(Semiconductor Film Deposition Step) Next, the underlying protective film 2
50 n of intrinsic silicon film 30 (semiconductor film)
about m. In this example, the amorphous silicon film 30 is deposited at a deposition temperature of 425 ° C. using a high vacuum LPCVD apparatus while flowing disilane as a source gas at 200 SCCM. In forming the silicon film 30, a PECVD method or a sputtering method may be used, and according to these methods, the film formation temperature can be set in a range from room temperature to 350 ° C.

(Annealing Step by Laser Melt Crystallization) Subsequently, the amorphous silicon film 30 is irradiated with laser light to modify the amorphous silicon film 30 into polycrystalline silicon. In this example, Zenon chloride (XeC
1) Irradiate with an excimer laser (wavelength: 308 nm). By passing this laser beam having an output of 200 W through an optical system, the longitudinal direction is 150 mm, and the cross-sectional beam shape is 0.35 mm at the upper base and 0.45 m at the lower base.
m is formed as a trapezoidal line beam. By irradiating the line beam while overlapping the substrate at a pitch equal to or less than the upper bottom beam width, the amorphous silicon film becomes a polycrystalline silicon film by melt crystallization.

In the present invention, the laser irradiation in this annealing step is performed twice, and a surface treatment for removing an oxide film is performed between successive laser irradiations. I do.

(Silicon film patterning step)
As shown in FIG. 4B, the silicon film 30 polycrystallized in the annealing step is patterned by using a photolithography technique to form an island-shaped silicon film 31.

(Step of Forming Gate Insulating Film) Next, FIG.
(C) As shown in FIG.
A gate oxide film 14 made of a silicon oxide film is formed on the silicon film 31 at a temperature of 00 ° C.

(Gate Electrode Forming Step) Next, a tantalum thin film having a thickness of 600 nm is formed on the surface side of the gate oxide film 14 by sputtering, and then patterned by photolithography to form the gate electrode 15. Form. In this example, when forming a tantalum thin film, the substrate temperature is set to 180 ° C., and an argon gas containing 6.7% of a nitrogen gas is used as a sputtering gas. The tantalum thin film thus formed has an α-structure crystal structure and a low specific resistance.

(Impurity Introducing Step) Next, using a bucket type non-mass separation type ion implantation apparatus (ion doping apparatus), the silicon film 31 is formed using the gate electrode 15 as a mask.
Is implanted with impurity ions. In the case of forming an N-channel TFT, a hydrogen gas having a concentration of 5 is used as a source gas.
% Phosphine or the like is used. As a result, the source region 11 and the drain region 12 are formed in a self-aligned manner with respect to the gate electrode 15. At this time, the portion of the silicon film 31 where the impurity ions have not been implanted becomes the channel region 13. At this time,
A region where a P-channel TFT is to be formed is covered with a resist mask.

Conversely, when a P-channel TFT is formed, diborane or the like diluted with hydrogen gas to a concentration of 5% is used as a source gas.
A region where a channel type TFT is to be formed is covered with a resist mask.

(Step of Forming Interlayer Insulating Film) Next, FIG.
(D) As shown in FIG.
Under a temperature condition of 00 ° C., a silicon oxide film having a thickness of 500 nm as the interlayer insulating film 16 is formed. The source gases at this time are TEOS and oxygen.

(Activation Step) Next, heat treatment is performed at 400 ° C. for 1 hour in an argon gas atmosphere containing 3% of hydrogen to activate the implanted phosphorus ions and to modify the interlayer insulating film 16. .

(Wiring Step) Next, contact holes 17 and 18 are formed in the interlayer insulating film 16. After a while, FIG.
As shown in (A), the source electrode (data line 3) is electrically connected to the source region 11 via the contact holes 17 and 18, and the drain electrode (pixel electrode 19) is electrically connected to the drain region 12. To form a TFT 10.

The above manufacturing method is an example of manufacturing the TFT 10 in a self-aligned structure.
The present invention can also be applied to a case where 10 is manufactured with an LDD structure or an offset gate structure. Although a description of the structure and the manufacturing method in this case is omitted, a low concentration source / drain region is formed in a portion of the source / drain region facing the end of the gate electrode 15 using a resist mask or a sidewall. (LDD region) or an offset region is formed.

[Energy Density and Film Quality During Laser Irradiation] Next, in the annealing step described with reference to FIG. 4A, the energy density (energy intensity) of the laser light applied to the amorphous silicon film 30 is as follows: The relationship with the film quality after laser irradiation will be described with reference to FIGS.

In any of the embodiments of the present invention, an amorphous silicon film is polycrystallized by a laser melting crystallization method as described later. In this laser melting crystallization method, as shown in FIG. As E is increased, the silicon film is melt-solidified and polycrystallized above Ec indicated by “▲” and dashed line L1. Here, as the energy density E increases, the polycrystallization progresses, but when the energy density E exceeds “Ea” indicated by “□” and the dotted line L2, the silicon film is microcrystallized, and the mobility decreases. .

When the thickness of the silicon film is small,
Even if the energy density E does not exceed Ea, if the energy density E exceeds Eb indicated by “「 ”and the two-dot chain line L3, it returns to the amorphous silicon film. If the energy density E exceeds “Δ” and Ed shown by the solid line L4, the silicon film is evaporated and ablated.

FIG. 6 shows the crystallinity and surface roughness of the silicon film when the energy density E of the pulsed laser beam was changed. Here, “○”, solid line L11 in FIG. 6A and L13 in FIG. 6B indicate that after performing a surface treatment for removing an oxide film before laser irradiation, the laser irradiation is performed in a vacuum. The results shown in FIG. 6 (A), solid line L12 in FIG. 6 (A) and L14 in FIG. 6 (B) indicate that laser irradiation was not performed before laser irradiation. This is the result obtained in a vacuum. Further, even when laser irradiation is performed in the atmosphere or in an atmosphere filled with some gas, the same result as the latter is obtained.

The vertical axis in FIG. 6A is the half width of the Raman peak, and the smaller the value, the higher the crystallinity. The vertical axis in FIG. 6B represents the intensity of the Raman peak. Therefore, the smaller the value is, the smaller the scattered light from the semiconductor film surface is, which means that the surface roughness is small.

As can be seen from a comparison of these results, in laser melting crystallization, the crystallinity can be increased by setting the maximum value of the energy density E to a value very close to the upper limit value Ea. Higher crystallinity can be obtained by performing laser irradiation in a vacuum after performing the surface treatment. The peak near the half-width of the Raman peak slightly exceeding the upper limit Ea is a state in which the silicon film is microcrystallized.

On the other hand, the surface roughness is maximized when the energy density E is slightly lower than the upper limit value Ea. In particular, laser irradiation is performed in vacuum without performing surface treatment before laser irradiation, or in air or air. This is more remarkable when laser irradiation is performed in an atmosphere filled with some gas.

As a condition for determining the characteristics of the TFT 10, the higher the crystallinity of the silicon film 30, the better. However, the influence of the size of the crystal grain forming the semiconductor film is greater than that. In general, in order to increase the size of crystal grains, the presence of molecules such as oxygen in the process atmosphere or the surface of the amorphous silicon film facilitates crystal growth using the molecules as nuclei, so that the grain size can be easily increased. For this reason, crystallization is performed without performing laser irradiation in the air or surface treatment of an amorphous film, despite the above-described problems such as crystallinity and surface roughness.

However, according to such a crystallization method, the case where the large crystal grains are located in the channel portion of the TFT 10 and the group of small crystal grains existing so as to fill the space between the large crystal grains A difference occurs in the electrical characteristics of the TFT 10 when compared to the case where the TFT 10 is located in the channel portion, which causes variation. In particular, as described above, since the crystallinity of the small crystal grains obtained in this case is not high, the influence is remarkable. In addition, even when a large surface roughness occurs on the surface of the semiconductor film, there is a problem that the electric breakdown voltage of the gate insulating film covering the surface is reduced.

Therefore, the present invention is characterized in that laser irradiation is performed twice. Before the first irradiation, the laser irradiation is performed in vacuum without performing the surface treatment of the amorphous film, or in the air. Alternatively, the size of crystal grains is increased by performing laser irradiation in an atmosphere filled with some gas. Subsequently, before the second irradiation, a surface treatment is performed on the polycrystalline silicon film obtained by the first irradiation, an oxide film is removed, and then a second irradiation with energy light is performed in a vacuum. The energy light intensity at this time does not exceed the threshold of the energy intensity at which microcrystallization occurs in the semiconductor film, and the intensity does not exceed the irradiation intensity of the first energy light. Without breaking the large grain size formed by the irradiation, the crystallinity in the grain is improved and the surface roughness is reduced, so that a high-quality crystalline semiconductor film can be formed without variation.

Example 1 An amorphous silicon film 30 formed by using an LPCVD apparatus is carried into a laser annealing apparatus without performing a surface treatment. The atmosphere of the first laser irradiation is vacuum, and the irradiation energy density is the upper limit indicated by Ea in FIG. This irradiation increases the size of the crystal grains.

Subsequently, the polycrystalline silicon film taken out is subjected to etching for about several tens of seconds with a dilute hydrofluoric acid solution of about 5% as a surface treatment for removing an oxide film. Immediately after this surface treatment, the wafer is again transported to the laser annealing apparatus, and the second laser irradiation is performed in a vacuum atmosphere. The irradiation energy density is also the upper limit Ea in FIG.
By lowering it by about 10 mJ / cm ² , the crystallinity is improved as compared with the first irradiation with Ea in the atmosphere, and the signal intensity from the polycrystalline silicon film is reduced to half or less.

FIG. 6 shows the results of laser irradiation on the amorphous silicon film. Strictly speaking, the state of the low energy density region is somewhat different from the case where laser irradiation is performed on the polycrystalline silicon film. However, the energy density at which the upper limit Ea appears and the state before and after it can be regarded as the same as the result of laser irradiation on the amorphous silicon film.

As a result, not only the crystallinity within the grains having a large grain size is improved, but also the crystallinity of small crystal grains in the vicinity thereof and the crystallinity of the grain boundaries are improved, so that the TFT characteristics themselves are improved and the substrate characteristics are improved. In this case, the variation in the elements within the device can be reduced.

Further, since a line beam is used as the laser beam for irradiation, the second energy light irradiation rotates the longitudinal direction of the line beam by 90 degrees with respect to the longitudinal direction of the line beam of the first laser irradiation. are doing. This makes it possible to remove non-uniformity such as fine energy distribution generated in the line beam, and is effective in improving the uniformity of crystallinity in the substrate.

FIG. 7 shows the characteristics of the TFT 10 obtained by this method. The solid line shows the results obtained by using the present invention, and the rising characteristics which are considered to be due to the improvement in the crystallinity as compared with the TFT formed from the semiconductor film obtained by only one irradiation shown by the wavy line. Improvement is seen.

[0050]

As described above, in the active matrix substrate according to the present invention, the crystal grains are enlarged by performing the energy light irradiation for obtaining the polycrystalline silicon film twice before and after the surface treatment. In addition, a high-quality crystalline semiconductor film having high crystallinity can be formed, and a TFT with high mobility can be manufactured with high uniformity.

[Brief description of the drawings]

FIG. 1A is an explanatory diagram schematically showing an active matrix substrate of a liquid crystal display device, and FIG. 1B is an explanatory diagram of a CMOS circuit used for a driving circuit thereof.

FIG. 2 is an enlarged plan view showing a pixel region on an active matrix substrate of the liquid crystal display device.

FIG. 3A is a sectional view taken along line AA ′ of FIG. 2;
FIG. 3B is a cross-sectional view taken along line BB ′ of FIG.

FIG. 4 is a diagram illustrating an embodiment of the present invention;
FIG. 4 is a process sectional view of the TFT with respect to a section taken along line A ′.

FIG. 5 is an explanatory diagram showing a relationship between an energy density in laser melting crystallization and a change occurring in a silicon film.

FIG. 6 is a graph showing the relationship between energy density, crystallinity, and surface roughness in laser melting crystallization.

FIG. 7 is a graph showing electric characteristics of a TFT formed using a crystalline semiconductor film according to an example of the present invention.

[Explanation of symbols]

 Reference Signs List 1 liquid crystal display device 2 active matrix substrate 3 data line 4 scanning line 5 pixel region 6 liquid crystal capacitor 9 active matrix section 10 TFT 11 source region 12 drain region 13 channel region 14 gate insulating film 15 gate electrode 16 interlayer insulating film 17, 18 contact Hole 19 Pixel electrode 20 Glass substrate 21 Base protective film 25 Storage capacitor 30 Silicon film (silicon film 30) 31 Island-shaped silicon film (silicon film 30)

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) H01L 21/336 F-term (Reference) 2H092 JA24 JA34 KA05 MA07 MA09 MA29 MA30 NA24 NA27 5C094 AA21 BA03 BA43 CA19 DA09 DA13 DB04 EB02 FB03 FB14 GB10 JA09 5F052 AA02 BA02 BA07 BB07 CA04 CA07 DA02 DB02 EA11 EA15 FA19 HA01 JA01 5F110 AA01 BB02 CC02 DD02 DD13 DD24 EE04 EE44 FF02 FF30 GG02 GG13 GG25 GG47 HJ01 PP23 NN02 PP02 NN

Claims (12)

[Claims] 1. A method for manufacturing a semiconductor film, comprising: forming a semiconductor film on a substrate; and irradiating the semiconductor film with energy light to obtain a crystalline semiconductor film. Irradiating light;
A step of performing a surface treatment on the semiconductor film after the step of irradiating the first energy light; and a step of irradiating the semiconductor film with second energy light after the step of performing the surface treatment. A method for manufacturing a semiconductor film. 2. The method according to claim 1, wherein at least one of the first and second energy beams is a laser beam. 3. The method according to claim 2, wherein the laser beam is a line beam. 4. The method for manufacturing a semiconductor film according to claim 1, wherein the irradiation of the first energy light is performed in a vacuum. 5. The semiconductor film according to claim 1, wherein the irradiation of the first energy light is performed in the air or in an atmosphere other than a vacuum filled with a predetermined gas. Production method. 6. The semiconductor according to claim 1, wherein the intensity of the first energy light does not exceed a threshold of an energy intensity at which microcrystallization occurs in the semiconductor film. Manufacturing method of membrane. 7. The semiconductor film according to claim 1, further comprising a step of removing an oxide film on a surface of the semiconductor film after the step of irradiating the first energy light. Manufacturing method. 8. The method according to claim 1, wherein the irradiation of the second energy light is performed in a vacuum. 9. The semiconductor device according to claim 1, wherein the irradiation of the second energy light is such that the intensity of the energy light exceeds a threshold value of the energy intensity at which microcrystallization occurs in the semiconductor film. A method of manufacturing a semiconductor film, wherein the irradiation intensity of the first energy light is not exceeded. 10. The method according to claim 1, wherein the irradiation of the second energy light is performed by changing a longitudinal direction of the energy light that is a line beam into a longitudinal direction of the line beam when the first energy light is irradiated. Is a method for manufacturing a semiconductor film, which is rotated by 90 degrees. 11. A method for manufacturing a thin film transistor, comprising: forming a thin film transistor from a crystalline semiconductor film obtained by the method for manufacturing a semiconductor film according to claim 1. 12. An active matrix substrate comprising a thin film transistor manufactured by the method for manufacturing a thin film transistor according to claim 11.