JP2001332503A - Method of manufacturing fine crystal film by plasma discharge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a fine crystal film of excellent quality at a higher rate by the use of a plasma discharge. SOLUTION: A deposition chamber 1 is equipped with a ground electrode 3 disposed at one side of a fine crystal film forming substrate 5, a high-frequency electrode 2 disposed at the other side of the substrate 5, and a material gas supply inlet 6, film forming material gas is introduced into the deposition chamber 1, and a fine crystal film is formed on the primary surface of the substrate 5 by a plasma discharge through a film manufacturing method, where hydrogenated germanium or halogenated germanium and hydrogen are used as the above material gas, and the inner pressure of the deposition chamber 1 is set at 70 to 700 Pa.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for manufacturing a microcrystalline film in a thin film semiconductor device using the microcrystalline film, such as a thin film transistor or a thin film solar cell.

[0002]

2. Description of the Related Art A thin film semiconductor device using a non-single-crystal film, in particular, an amorphous silicon (a-Si), which is a silicon-based non-single-crystal thin film, and an amorphous silicon germanium (a-SiGe) alloy film are formed by plasma. Thin-film semiconductor devices formed by electric discharge can be made in large areas, at low temperatures, and at low cost compared to single-crystal silicon devices, so they can be used for thin-film transistors (TFTs) for displays and large-area thin-film solar cells for power. It is particularly expected in applications.

[0003] The thin film formed by the plasma discharge is formed by, for example, the following apparatus. FIG.
1 shows an example of a schematic structure of a film forming chamber when an a-Si thin film solar cell is formed by plasma discharge.
An example of the structure described in Japanese Patent No. 50431 is shown. FIG.
(A) and (b) are schematic cross-sectional views when the film forming chamber is opened and sealed, respectively.

As shown in FIG. 8A, a box-shaped lower film-forming section chamber wall 21 and an upper film-forming section chamber wall 22 are arranged opposite to each other above and below a flexible substrate 10 conveyed intermittently. When the film forming chamber is sealed, an independent processing space including the lower film forming section chamber and the upper film forming section chamber is formed. In this example, the lower film forming unit chamber includes a high-frequency electrode 31 connected to a power supply 40, and the upper film forming unit room includes a ground electrode 32 having a built-in heater 33.

At the time of film formation, as shown in FIG. 8B, the upper film formation section chamber wall 22 is lowered, and the ground electrode 32 is connected to the substrate 10.
And is brought into contact with the sealing member 50 attached to the opening-side end face of the lower film-forming-portion-chamber wall 21. As a result, an airtightly sealed film-forming space 60 communicating with the exhaust pipe 61 is formed from the lower film-forming section chamber wall 21 and the substrate 10. In the film forming chamber as described above, a high-frequency voltage is applied to the high-frequency electrode 31 to generate plasma in the film forming space 60, decompose the raw material gas introduced from an introduction pipe (not shown), and form a film on the substrate 10. Can be formed.

By the way, a-Si for a thin film solar cell formed by the above-described apparatus has a smaller electron mobility than a single crystal. Therefore, when applied to the above-mentioned TFT, the aperture ratio of the display is small. There is a problem that the brightness and contrast deteriorate. To solve this, microcrystalline silicon
Application of (μc-Si) to TFT is being studied. Here, microcrystals are thin films made by plasma CVD, optical CVD, thermal CVD, etc., with a crystal volume fraction of several percent to almost 100% and a crystal grain size of several nm to several μm with respect to the amorphous component. Point to. μc-S
By using i, electron mobility can be improved by several orders of magnitude as compared with a-Si.

Further, single crystal germanium is about twice as large in electron mobility and about 2.5 times as large in hole mobility as compared with single crystal silicon. Similarly, by using microcrystalline silicon germanium (μc-SiGe) or microcrystalline germanium (μc-Ge) in a microcrystalline film, an improvement in electron mobility can be expected as compared with μc-Si.

As another problem different from the above, in a solar cell using a-Si or amorphous silicon germanium (a-SiGe), the so-called Steabler Wronski effect, in which the efficiency of the solar cell is reduced due to long-time light irradiation, is obtained. However, there is a problem that the efficiency is lower than the initial one.

Recently, as a pin type non-single-crystal solar cell,
It has been reported that solar cells without photodegradation can be fabricated by applying μc-Si to p, i, and n layer materials ([Report 1] J. Meier, P. Torres, R. Platz, S. Dubail,
U. Kroll, AA Anna Selvan, N. Pellaton Vaucher C
h. Hof, D. Fischer, H. Keppner, A. Shah, KD Ufer
t, P.Giannoules, J.Koehler; "On the way towards hi
gh efficiency thin film silicon solar cells by the
"micromorph" concept ", Mat. Res. Soc. Symp. Pro
c. See Vol.420, 1996, pp.3).

However, μc-Si has a longer wavelength of light sensitivity than a-Si, but has a small absorption coefficient and
It must be about 10 times that of a-Si. Also, when formed by plasma CVD, the film formation rate of μc-Si is 1/2 to 1 compared to a-Si.
There is a slow problem of about / 10. As a result, the film formation time was a-Si
However, there is a problem that it takes a very long time as compared with the above.

Instead of μc-Si, μc-Si for thin film solar cells
A Ge study has recently been reported. μc-
Since SiGe can increase the absorption coefficient, it is expected that the thickness can be reduced as a film for a solar cell. Gangley et al. Use RF (13.56 MHz) capacitively coupled plasma CVD.
We report on μc-SiGe fabricated using a mixed gas of silane (SiH ₄ ), germane (GeH ₄ ), and hydrogen (H ₂ ). ([Report 2] G. Ganguly et al .; "Hydrogenated microcrystall
ine silicon germanium: A bottom cell material for
amorphous silicon-based tandem solar cells ", Appl.
Phys. Lett., 69 (1996) pp.4224; [Report 3] G. Ganguly
et al .; "Microcrystalline silicon germanium: An a
ttractive bottom-cell material for thin-film silic
on-basedtandem-solar-cells ", Mat. Res. Soc. Symp.
Proc. 467 (1997) pp.681.).

In the above report, the pressure range in which the film was formed was 4
~66.5Pa (0.03~0.5torr), hydrogen dilution ratio H ₂ / (SiH ₄ + Ge
H ₄ ) = 50 to 500 times, and the film formation rate is 0.48 to 2.16 nm / min.

Normally, μc-Si is produced at a hydrogen dilution ratio of about 15 to 20 times, but a higher hydrogen dilution ratio is used for the production of μc-SiGe. However, for the composition of Ge,
There is no description as to whether the hydrogen dilution rate is changed. Defect density before light irradiation in low-speed film formation is 10 ¹⁵ cm ^{-3 units.High} -quality a-Si film formation speed is about 2 nm / min.Defect density before light irradiation in high-speed film formation is 10 ¹⁶ cm ^-3. The film forming speed of medium quality a-Si is slower than 10 to 20 nm / min.

Also, Carius et al. Conducted a VHF (95 MHz) capacitively coupled plasma CVD using SiH ₄ or disilane (Si ₂ H ₆ ).
And μc-SiGe fabricated using a mixed gas of GeH ₄ and H ₂ . ([Report 4] R. Carius, et al .; "Micr
osrystalline silicon-germanium alloys for absorpti
on layers in thin film solar cells ", Mat. Res. So
c. Symp. Proc. 507 (1998) pp.813 .; [Report 5] M. Kraus
e, et al .; "Role of bandgap grading for the perfor
mance of microcrystalline silicon germaniumsolar c
ells ", Mat. Res. Soc. Symp. Proc. 557 (1999) pp.59
1.)

Carius et al. Compared μc-SiGe to μc-Si
Reported that as the amount of Ge increased,
ing. SiH_FourΜc-Si using hydrogen is completed at a hydrogen dilution ratio of 20 to 50 times.
To make μc-SiGe, whereas it is all microcrystalline
Report that higher hydrogen dilution rates are needed
You. Specifically, SiH_FourAnd GeH_FourWhen using_Two/ (SiH_Four+ GeH
_Four) Is partially crystallized at 40 times or more and completely fine at 80 times or more.
States that it will be a crystal. Si_TwoH₆And GeH_FourIf you use
Furthermore, it is hard to be microcrystals, and hydrogen dilution rate of 167 times or more
Necessary, where the Ge density in the film is high,_TwoH₆Using μc
-States that SiGe cannot be made. In [Report 5] above,
Very high hydrogen dilution rate of 120 to 320 times
ing. At this time, there is no description about the pressure during film formation.
No. Also uses a very high frequency of 95MHz
Nevertheless, the film formation rate was 3.2 in [Report 4] above.
110.2 nm / min, 2.4 to 7.2 nm / min in [Report 5]
ing.

[0016]

SUMMARY OF THE INVENTION The present inventor has also proposed 13.56M
When μc-SiGe was fabricated using a mixed gas of SiH ₄ , GeH ₄ , and H ₂ by capacitively coupled plasma CVD of Hz, it was confirmed that microcrystals were unlikely to be formed as the Ge density in the film increased. . When the Ge density in the film was 100%, it was particularly difficult to form microcrystals. Therefore, a very high hydrogen dilution rate was required, and as a result, the film forming speed was reduced.

As described above, there is a problem that it is difficult to form a microcrystalline film such as μc-SiGe or μc-Ge with an increase in Ge density in the film. Further, in order to produce μc-SiGe or μc-Ge, an extremely high hydrogen dilution ratio is required, and there is a problem that the film formation speed is reduced.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and an object of the present invention is to provide a method for producing a microcrystalline film by plasma discharge in which a good microcrystalline film is formed and the film forming speed is improved. To provide.

[0019]

In order to achieve the above object, the present invention provides a ground electrode provided on one side of a substrate for forming a microcrystalline film, a high-frequency electrode provided on the other side, and a source gas. In a method for producing a microcrystalline film, in which a source gas for film formation is introduced into a film forming chamber having a supply port and a microcrystalline film is formed on the main surface of the substrate by plasma discharge, at least hydrogen is used as the source gas. Using germanium halide or germanium halide and hydrogen, the pressure of the
To 700 Pa (the invention of claim 1).

A film forming chamber having a ground electrode provided on one side of a substrate for forming a microcrystalline film, a high-frequency electrode provided on the other side, and a material gas supply port is provided with a material for forming a film. In a method for producing a microcrystalline film, wherein a gas is introduced and a microcrystalline film is formed on the main surface of the substrate by plasma discharge, at least germanium hydride or germanium halide and hydrogen are used as the raw material gas, and the film forming chamber is used. Pressure of 70
The pressure is set to Pa or more, and the source gas is supplied so as to be blown out toward the substrate (the invention of claim 2).

Preferred embodiments of the invention according to claim 1 or 2 are as follows. That is, in the method of manufacturing a microcrystalline film according to claim 2, the high-frequency electrode has a plurality of gas flow openings for blowing a raw material gas toward the substrate in a shower shape, and the plurality of gas flow holes are provided. The source gas is supplied from the outlet (the invention of claim 3).

Further, in the method for manufacturing a microcrystalline film according to any one of claims 1 to 3, the microcrystalline film formed on the substrate is a microcrystalline germanium film (the invention of claim 4). Furthermore, in the method for manufacturing a microcrystalline film according to any one of claims 1 to 3, the microcrystalline film formed on the substrate is a microcrystalline silicon germanium film (the invention of claim 5).

Further, in the method for producing a microcrystalline film according to any one of claims 1 to 3, germane (GeH ₄ ) and hydrogen or germane (GeH ₄ ) and silane are used as the source gases. (SiH ₄₎ and will be used and hydrogen (the invention of claim 6).

The operation of the present invention is as follows.
In other words, it is considered that the gas phase reaction in the plasma is greatly changed by setting the pressure at the time of film formation to 70 Pa or more.
It is considered that the germanium-based radical GeHx has a very high reactivity and is liable to cause a polymerization reaction. At a low pressure, the germanium-based radical GeHx tends to be a polymer or a cluster, and as a result, the film tends to be amorphous. By increasing the pressure, GeHx
It is considered that the collision reaction in the gas phase with H ₂ , which is a diluent gas, increases, and the Ge-based cluster is effectively decomposed.

It is considered that, by increasing the pressure, the sheath near the substrate becomes thinner, the energy of ions jumping into the substrate is reduced, and damage to the film due to ion bombardment is suppressed, and microcrystals are likely to be formed. .

However, if the pressure is increased to a predetermined pressure or more, collision between GeHx and GeH ₄ or SiH ₄ cannot be ignored, and powder is generated. For this reason, there is an optimal pressure range in which microcrystals can be produced and no powder is generated.

If the pressure is too high, powder is generated. For gas supply, gas was usually introduced from the wall of the reaction chamber. In this case, powder was generated at 700 Pa or more. In this case, it is considered that gas was supplied to the plasma between the electrodes from the outside by diffusion, and powder was attached to the substrate. Therefore, the optimum range of the pressure is 70 to 700 Pa.

However, by blowing the raw material gas toward the substrate in the form of a shower, the gas flows outward from the plasma between the electrodes, whereby the powder generated in the gas phase can be forced to flow out. it can. As a result, no powder is generated on the substrate even at a pressure of 700 Pa or more, and a favorable microcrystalline film can be manufactured.

[0029]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below.

Example 1 Formation of a Microcrystalline Film with 100% Ge Density FIG. 1 shows the Ge density (Ge / (Ge + Si)) = in a film formed using the apparatus shown in FIG. The result of measuring the Raman scattering spectrum for 100% of the film is shown. The horizontal axis in FIG. 1 shows the Raman shift, and the vertical axis shows the spectrum intensity on an arbitrary scale (au). First, the film forming apparatus and the film forming conditions in FIG. 2 will be described. Figure 2 shows an RF (13.56MHz) capacitively coupled plasma CV
D device. The film forming chamber 1 is, like the apparatus shown in FIG.
A high-frequency electrode 2 and a ground electrode 3 are provided. The substrate 5 can be placed on the ground electrode 3 and heated by the heater 4. The source gas is introduced into the film forming chamber 1 through a gas supply port 6 attached to the wall of the film forming chamber 1. Plasma is generated between the high-frequency electrode 2 and the ground electrode 3 to decompose the raw material gas, and a microcrystalline film is formed on the substrate 5.

The condition of the film, Ge / (Ge + Si) = 100%, can be said to be the condition under which microcrystals are most difficult to be formed. For the production of the film, a mixed gas of GeH ₄ and H ₂ was used as a source gas. Substrate heater temperature is 200
° C, discharge power 50W, GeH ₄ flow rate 5sccm, H ₂ flow rate 500s
ccm, and the hydrogen dilution ratio H ₂ / GeH ₄ was 100 times. Glass was used for the substrate. The unit of flow rate sccm is standard c
c / min (standard condition converted flow rate cm ³ / min).

In the Raman scattering spectrum of FIG.
A sharp peak near 0 cm ^-1 and a broad peak near 280 cm ^-1 are observed. Ge-Ge bonded crystal TO
The peak corresponds to the amorphous TO peak. A crystal peak is observed at a pressure Pr = 67 Pa (0.5 torr) during film formation, and the crystal peak increases as Pr increases. Ge / (Ge + Si) that is the least likely to become microcrystals
Despite the condition of = 100%, it is recognized that μc-Ge can be produced by setting Pr to approximately 70 Pa or more.

FIG. 3 shows the crystal peak (I
c), amorphous peak (Ia) ratio (Ic / Ia) and pressure
(Pr). It can be said that the larger Ic / Ia is, the better the microcrystalline film has a higher crystal volume fraction. As Pr increases, Ic
/ Ia increases. It can be seen that a microcrystalline film is formed at approximately Pr = 70 Pa and Ic / Ia〜1. As Pr increases, Ic / Ia increases monotonically. However, when Pr was larger than 700 Pa, generation of powder was observed, and in particular, adhesion of powder was observed on the substrate near the end of the ground electrode.

Example 2 Regarding the Film-Forming Speed of a Microcrystalline Film with 100% Ge Density FIG. 4 shows the relationship between the film-forming speed (DR) and the pressure (Pr) relating to the film of Example 1 above. . DR increases as Pr increases. That is, by raising Pr to about 70 Pa or more, it is possible to improve the crystallinity and simultaneously increase the film forming speed.

Example 3 Relationship between Ge Density and Pressure FIG. 5 shows the relationship between the Ge density (Ge / (Ge + Si)) in the film and the film formation pressure (Pr) for forming microcrystals. . The determination as to whether or not the material has changed from amorphous to microcrystalline is made by determining the ratio of the crystalline component peak to the amorphous component peak of the Ge-Ge bond peak of Raman scattering (Ic /
Ia) was used. However, when the Ge / (Ge + Si) decreases, the peak wave number of the Ge—Ge bond peak shifts to a lower wave number side almost in proportion to Ge / (Ge + Si). Here, the peak wave numbers of the crystalline component and the amorphous component were identified according to Ge / (Ge + Si), and Ic / Ia was determined. Also in the film containing Si and Ge, Pr becomes Ic / Ia〜1 when the pressure is about 70 Pa or more, indicating that the film is microcrystalline. However, the film with high crystallinity of Ic / Ia> 2 is Ge /
In regions where (Ge + Si) is small, lower Pr can be produced.

FIG. 6 shows an embodiment according to the third aspect of the present invention.
The high-frequency electrode 15 in this embodiment includes an electrode body 15a, a gas supply port 15b, and a perforated metal plate 15c as shown in FIG. Has become. As shown in FIG. 2, the gas supply port and the high-frequency electrode can be separated from each other. However, according to the dual-purpose structure of the high-frequency electrode and the gas supply port shown in FIG. It can be blown out in a shape, which is more preferable.

By blowing the gas in a shower shape, the gas flows outward from between the electrodes, and even if powder is generated in the gas phase, it is swept outward. As a result, a pressure of 7
Even when the pressure was increased to 000 Pa, adhesion of powder on the substrate was no longer observed.

In the above Examples 1-4, GeH ₄ of germanium hydride was used as the Ge source gas.
In addition, higher homologs such as Ge ₂ H ₆ can also be used.
Further, those in which H is substituted with an alkyl group (CH ₃ ) or a silyl group (SiH ₃ ) can also be used.

When germanium tetrafluoride (GeF ₄ ) was used as the germanium halide, a microcrystalline film was obtained by increasing the pressure during film formation to 70 Pa or more. In addition to germanium halide, GeCl ₄ ,
GeBr ₄ , GeI ₄ or the like can also be used. Further, those obtained by substituting H for halogen can also be used.

Hydrogenated silane (SiH ₄ , Si 2 H _6, etc.) is used as a raw material of Si for producing microcrystalline silicon germanium.
And halogenated silanes (SiF ₄ , SiCl _4, etc.) are used.
Further, it is also possible to use a halogenated silane obtained by substituting a part of the halogen with H (SiH ₂ Cl ₂ or the like).

When the hydrogen dilution ratio of the raw material gas is increased at a pressure of 70 Pa or more during film formation, the volume fraction of the microcrystalline film can be further increased.

[0042]

As described above, according to the present invention, the ground electrode provided on one side of the microcrystalline film forming substrate, the high-frequency electrode provided on the other side, and the source gas supply port are provided. In a method for producing a microcrystalline film, in which a source gas for film formation is introduced into a film forming chamber and a microcrystalline film is formed on the main surface of the substrate by plasma discharge, at least germanium hydride or germanium halide is used as the source gas. When hydrogen is used and the pressure in the film formation chamber is set to 70 to 700 Pa, a fine microcrystalline film can be manufactured without generating powder. Further, the film forming speed can be improved.

Further, by blowing the raw material gas toward the substrate in the form of a shower, the pressure in the reaction chamber becomes 700 P.
Even if it is larger than a, generation of powder on the main surface of the substrate can be suppressed.

When the microcrystalline film containing Ge prepared as described above is applied to a thin film solar cell, the film thickness can be reduced by increasing the absorption coefficient, and the production time can be shortened by increasing the film forming speed. .

When the microcrystalline film containing Ge formed as described above is applied to a thin film transistor for a display, the improvement in electron mobility due to the inclusion of Ge is
This is effective in increasing the aperture ratio of the display and improving the brightness and contrast. In addition, an increase in the film forming speed has the effect of shortening the manufacturing time.

[Brief description of the drawings]

FIG. 1 is a diagram showing a Raman scattering spectrum of a microcrystalline film of the present invention.

FIG. 2 is a diagram showing an example of a microcrystalline film forming apparatus of the present invention.

FIG. 3 is a diagram showing a relationship between a peak intensity ratio (Ic / Ia) and a pressure (Pr).

FIG. 4 is a diagram showing a relationship between a film forming speed (DR) and a pressure (Pr).

FIG. 5 is a diagram showing the relationship between the Ge density (Ge / (Ge + Si)) in the film and the film forming pressure (Pr).

FIG. 6 is a diagram showing a film forming apparatus for forming a microcrystalline film according to the present invention.

7 is a diagram showing an example of a schematic configuration of a high-frequency electrode in FIG.

FIG. 8 is a diagram showing an example of a schematic structure of a conventional film forming chamber for a thin film solar cell.

[Explanation of symbols]

1: film forming chamber, 2, 15: high-frequency electrode, 3: ground electrode,
4: heater, 5: substrate, 6, 15b: gas supply port, 15
a: Electrode main body, 15c: Perforated metal plate.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 4K030 AA05 AA17 BA09 BB04 CA06 EA04 FA03 JA09 KA17 LA16 5F045 AA08 AB05 AC01 AD06 AE19 AE21 AF07 CA13 CA15 EF05 EH05 EH12 5F051 AA04 CA07 CA16 CA35 CA36 CA37 GA03

Claims (6)

[Claims] 1. A film forming material provided with a ground electrode provided on one side of a microcrystalline film forming substrate, a high-frequency electrode provided on the other side, and a material gas supply port. Introduce gas,
In the method of manufacturing a microcrystalline film for forming a microcrystalline film on the main surface of the substrate by plasma discharge, as the source gas,
Using at least germanium hydride or germanium halide and hydrogen, the pressure in the film formation chamber is set to 70 to 7
A method for producing a microcrystalline film by plasma discharge, wherein the pressure is set to 00 Pa. 2. A film forming material comprising a ground electrode provided on one side of a microcrystalline film forming substrate, a high-frequency electrode provided on the other side, and a material gas supply port. Introduce gas,
In the method of manufacturing a microcrystalline film for forming a microcrystalline film on the main surface of the substrate by plasma discharge, as the source gas,
Using at least germanium hydride or germanium halide and hydrogen, the pressure in the film formation chamber was set to 70 Pa
As described above, a method for producing a microcrystalline film by plasma discharge, wherein the source gas is supplied so as to be blown out toward a substrate. 3. The method for manufacturing a microcrystalline film according to claim 2, wherein the high-frequency electrode has a plurality of gas flow openings for blowing a source gas toward a substrate in a shower shape. A method for producing a microcrystalline film by plasma discharge, characterized in that a raw material gas is supplied from a gas flow port of (1). 4. The microcrystalline film formed by plasma discharge according to claim 1, wherein the microcrystalline film formed on the substrate is a microcrystalline germanium film. Manufacturing method. 5. The microcrystalline film produced by a plasma discharge according to claim 1, wherein the microcrystalline film formed on the substrate is a microcrystalline silicon germanium film. Manufacturing method of membrane. 6. The method for producing a microcrystalline film according to claim 1, wherein germanium (GeH ₄ ) and hydrogen are used as the source gas, or germane (Ge
A method for producing a microcrystalline film by plasma discharge, characterized by using H ₄ ), silane (SiH ₄ ) and hydrogen.