JP4251256B2 - Method for producing microcrystalline film - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
[0002]
The present invention relates to a method for producing a microcrystalline film used for a thin film semiconductor device such as a thin film transistor or a thin film solar cell.
[Prior art]
[0003]
Thin film semiconductor devices using non-single crystal films, especially thin films formed by plasma discharge of alloy films such as amorphous silicon (a-Si) and amorphous silicon germanium (a-SiGe), which are silicon-based non-single crystal thin films Compared to single crystal silicon devices, semiconductor devices can be made in large areas, at low temperatures, and at low cost, and are especially expected for applications in thin film transistors (TFTs) for displays, large area thin film solar cells for power, etc. ing.
[0004]
The thin film formed by the plasma discharge is formed by, for example, the following apparatus. FIG. 7 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, and shows an example of the structure described in Japanese Patent Application Laid-Open No. 8-250431. FIGS. 7A and 7B are schematic cross-sectional views when the film forming chamber is opened and sealed, respectively.
[0005]
As shown in FIG. 7 (a), a box-shaped lower film forming chamber wall 21 and an upper film forming chamber wall 22 are arranged opposite to each other on the upper and lower sides of the flexible substrate 10 that is intermittently conveyed. When the film chamber is sealed, an independent processing space composed of a lower film forming chamber and an upper film forming chamber is formed. In this example, the lower film forming chamber is provided with a high-frequency electrode 31 connected to a power source 40, and the upper film forming chamber is provided with a ground electrode 32 with a built-in heater 33.
[0006]
At the time of film formation, as shown in FIG. 7B, the upper film forming section chamber wall 22 is lowered, and the ground electrode 32 holds the substrate 10 and is attached to the opening side end surface of the lower film forming section chamber wall 21. The member 50 is brought into contact. Thereby, an airtightly sealed film forming space 60 communicating with the exhaust pipe 61 is formed from the lower film forming part chamber wall 21 and the substrate 10. In the film forming chamber as described above, by applying a high frequency voltage to the high frequency electrode 31, plasma is generated in the film forming space 60, and a source gas introduced from an introduction pipe (not shown) is decomposed to form a film on the substrate 10. Can be formed.
[0007]
By the way, a-Si for thin-film solar cells formed by the above-described device has a lower electron mobility than a single crystal. Therefore, when applied to the TFT, the aperture ratio of the display is small and the brightness and contrast are low. There is a problem that makes it worse. In order to solve this problem, the application of microcrystalline silicon (μc-Si) to TFT is being studied. Here, the microcrystal is a thin film made by plasma CVD, photo CVD, thermal CVD, etc., which has 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. By using μc-Si, the electron mobility can be improved by several orders of magnitude compared to a-Si.
[0008]
Furthermore, single crystal germanium is about twice as high in electron mobility and about 2.5 times in hole mobility as compared to single crystal silicon. Similarly, in a microcrystalline film, the use of microcrystalline silicon germanium (μc-SiGe) or microcrystalline germanium (μc-Ge) can be expected to improve the electron mobility compared to μc-Si. Moreover, as a problem different from the above, in solar cells using a-Si or amorphous silicon germanium (a-SiGe), the efficiency is reduced by the so-called Steabler Wronski effect, which reduces the efficiency of the solar cell against long-time light irradiation. There is a problem of lowering than the initial stage.
[0009]
Recently, as a pin-type non-single-crystal solar cell, it has been reported that by applying μc-Si to p, i, and n layer materials, it is possible to create a solar cell free from light degradation ([Report 1] J .Meier, P. Torres, R. Platz, S. Dubail, U. Kroll, AA Anna Selvan, N. Pellaton Vaucher Ch. Hof, D. Fischer, H. Keppner, A. Shah, KD Ufert, P. Giannoules, J. Koehler; "On the way towards high efficiency thin film silicon solar cells by the" micromorph "concept", Mat. Res. Soc. Symp. Proc. Vol. 420, 1996, pp.3).
[Problems to be solved by the invention]
[0010]
However, in order to improve the performance of devices using μc-Si, it is necessary to further improve the crystallinity of μc-Si. One index of crystallinity is the evaluation of the crystal volume fraction using Raman scattering spectroscopy. Specifically, the intensity ratio (I520 / I480) of the peak near 520 cm-1 due to the TO mode of crystalline silicon and the peak near 480 cm-1 due to the TO mode of amorphous silicon is one of the crystal volume fractions. It becomes a standard. In a general 13.56 MHz high-frequency plasma CVD, when SiH4 as a raw material gas is diluted about 20 to 100 times with hydrogen, a typical value of I520 / I480 is about 2 to 5 and shows a low value. In order to improve the performance of the device, it is necessary to further increase I520 / I480.
[0011]
The present invention has been made in view of the above points, and an object of the present invention is to improve the performance of a thin film semiconductor device using a microcrystalline film, that is, a high crystal volume fraction, that is, a high (I520 / I480). The present invention provides a method for producing a microcrystalline film capable of forming a microcrystalline film having a).
[Means for Solving the Problems]
[0012]
In order to achieve the above-described problems, in the present invention, a flat ground electrode disposed on one side of the microcrystalline film forming substrate, a flat high-frequency electrode disposed in parallel with the other side, and a raw material the film forming chamber with a gas inlet, introducing a raw material gas for film formation, method of manufacturing a microcrystalline film forming a microcrystalline film on the substrate main surface by a plasma discharge, fine of the microcrystalline film crystals, microcrystalline silicon, microcrystalline germanium, microcrystalline silicon alloy occurs Izu Rekatoshi ground electrode near to face the light emitting portion and the light emitting portion occurring in the high-frequency electrode vicinity of the microcrystalline germanium alloy A microcrystalline film is formed under a film forming condition adjacent to or overlapping with the light emitting portion (the invention of claim 1).
[0013]
As an embodiment of the invention of claim 1, the inventions of claims 2 to 6 below are suitable. That is, in the method for manufacturing a microcrystalline film according to claim 1, by reducing the electrode interval dimension between the ground electrode and the high-frequency electrode, the film-forming condition is set such that the light emitting portions are adjacent or overlapped. Invention of 2). Further, in the method for manufacturing a microcrystalline film according to claim 1, the film-forming pressure in the film-forming chamber is reduced to form a film-forming condition in which the two light-emitting portions are adjacent to or overlap each other (the invention of claim 3). .
[0014]
Furthermore, in the method for producing a microcrystalline film according to any one of claims 1 to 3, the frequency applied to the electrode is set to 10 MHz to 100 MHz (invention of claim 4). Furthermore, in the method for manufacturing a microcrystalline film according to any one of claims 1 to 4, the high-frequency electrode is formed by removing a ground shield (invention of claim 5).
[0015]
In the method of manufacturing the microcrystalline film of claim 1, wherein the microcrystalline silicon alloy, microcrystalline silicon germanium, microcrystalline silicon carbide, microcrystalline silicon oxide, and any of the microcrystalline silicon nitride ( Invention of Claim 6 ).
[0016]
Each of the above embodiments will be described in detail later along with the experimental results. By reducing the electrode gap size or reducing the film forming pressure, the light emitting portion generated in the vicinity of the high frequency electrode and the light emitting portion are opposed to each other. The reason why the crystallinity of the microcrystalline film is improved is as follows because the light-emitting portion generated in the vicinity of the ground electrode is adjacent to or overlaps with the film-forming condition.
[0017]
For convenience of explanation, FIG. 6 schematically shows a discharge structure of high-frequency plasma CVD related to an example of a conventional method for producing a microcrystalline film. In this example, as a film forming gas, a condition in which SiH4 was diluted 50 times with hydrogen, which is a typical condition for producing a microcrystalline film, was used. As other film forming conditions, the pressure is 67 Pa, the power supply frequency is 100 MHz, the discharge power is 30 W, and the electrode interval d is 30 mm. In the vicinity of either the high-frequency electrode 1 or the ground electrode 3 on which the substrate 2 is placed and the heater 4 is provided, there are dark portions (6, 8) first, followed by light-emitting portions (71, 72). The intermediate part 9 between the light emitting part 71 and the light emitting part 72 is not so bright. From a detailed observation of the discharge structure, the discharge structure is substantially uniform except for the edges with respect to the plane parallel to the electrodes. Further, the thickness of the dark part in the vicinity of both electrodes is almost equal a1≈a2, and the distance from both electrodes to the light emitting part end is also equal b1≈b2. It can be seen that even if the electrode distance d is changed, the distance (b1, b2) from the electrode to the end of the light emitting part and the thickness (a1, a2) of the dark part do not change, but only the thickness c of the intermediate part 9 decreases. It was. Further, when the pressure is decreased, b1 and b2 in the figure increase, and both light emitting parts approach.
[0018]
From the measurement using the probe, it was confirmed that the electron temperature of the light emitting part was higher than that of the intermediate part. That is, it can be said that silane radicals (SiHx (x = 0, 1, 2, 3), etc.) and hydrogen atom radicals (H) contributing to film formation are mainly generated in this light emitting part. On the other hand, since the electron temperature is low in the intermediate portion, the loss of radicals is increased due to the secondary reaction between the radical and the mother gas.
[0019]
The μc-Si film tends to have better crystallinity and increase I520 / I480 when the ratio of hydrogen atom radicals to silane radicals is increased. The threshold value of the hydrogen atom radical generation cross section is higher than the threshold value of the silane radical generation cross section, and the higher the electron temperature, the higher the proportion of hydrogen atom radicals. By superimposing the light emitting portion and the light emitting portion, the central portion between the electrodes becomes a light emitting portion having a high electron temperature, so that the proportion of hydrogen atom radicals is increased and the crystallinity of the microcrystalline film is improved.
[0020]
On the other hand, since hydrogen atom radicals are highly reactive, there are many losses due to secondary reactions with the mother gas. However, by overlapping the light-emitting part and the light-emitting part, there is no intermediate part, and the loss of radicals, particularly the hydrogen atom radicals. It is considered that the loss is suppressed, radicals are effectively supplied to the ground electrode on which the substrate is placed, and the crystallinity of the microcrystalline film is improved.
DETAILED DESCRIPTION OF THE INVENTION
[0021]
Embodiments of the present invention will be described below.
[0022]
FIG. 1 schematically shows a discharge structure of high-frequency plasma CVD according to an embodiment of the present invention. In this embodiment, RF (13.56 MHz) capacitively coupled plasma CVD apparatus is used, and power is supplied to the high-frequency electrode 1 by the high-frequency power source 5. The substrate 2 can be placed on the ground electrode 3 and heated by the heater 4.
[0023]
Plasma is generated between the high-frequency electrode 1 and the ground electrode 3 to decompose the source gas, and a microcrystalline film is formed on the substrate 2. When the electrode interval d is made sufficiently small, the light emitting portions in the vicinity of both electrodes overlap to form one light emitting portion 7. At that time, the thickness of the dark part 6 and the dark part 8 does not change.
[0024]
As film formation conditions for μc-Si, a substrate heater temperature of 200 ° C., a SiH4 flow rate of 5 sccm, a hydrogen flow rate of 250 sccm, a hydrogen dilution rate of 50 times, a pressure of 67 Pa, and a discharge power of 15 to 60 W were used. Here, the electrode interval d is set to 12.5 mm so that the light emitting portions overlap each other. The unit sccm of flow rate indicates standard cc / min (flow rate cm3 / min in standard state conversion).
[0025]
FIG. 2 shows the experimental results of determining the crystal volume fraction (I520 / I480) with respect to the electrode spacing d for μc-Si formed using the apparatus of the embodiment of FIG. As reference data, 100 MHz and 13.6 MHz I520 / I480 with d = 30 mm where the light emitting portions in the vicinity of both electrodes do not overlap are also plotted. When d = 30 mm at 13.6 MHz (B), I520 / I480 = 4-5. When both light emitting parts are overlapped with d = 12.5 mm (D), I520 / I480 = 9-10. In case of 100MHz, when both light emitting parts do not overlap d = 30mm (A) also shows a high value of I520 / I480 = 9-12, but when both light emitting parts are overlapped with d = 12.5mm (C), I520 / I480 further increases and shows a high value of I520 / I480 = 12-16. It is possible to increase I520 / I480 by overlapping both light emitting units, and preferably by raising the power supply frequency.
[0026]
FIG. 3 is a diagram showing an experimental result related to the invention of claim 2, in the case where the pressure is 67 Pa and the electrode interval d = 30 mm is constant, from the ground electrode to the light emitting part end near the ground electrode with respect to the power frequency f. The relationship of distance b2 is shown. As f increases, b2 decreases slightly. The distance b1 from the high-frequency electrode to the light emitting part in the vicinity of the high-frequency electrode also changed with respect to the frequency in the same manner as b2, and b1≈b2. Further, even if the electrode interval is changed, only the thickness of the intermediate portion c is changed.
[0027]
That is, from FIG. 3, by setting the electrode distance d = b2 × 2, it is possible to obtain a condition in which both light emitting portions are adjacent or overlap. From FIG. 3, when d = 30 mm, both light emitting portions do not overlap at d> b2 × 2 at any frequency of 13.6 to 100 MHz. On the other hand, in the case of d = 12.5 mm, it can be seen that both light emitting portions overlap each other at any frequency with d <b2 × 2.
[0028]
FIG. 4 is a diagram showing experimental results relating to the invention of claim 3, and in the case where the electrode interval d = 30 mm is constant, the distance b2 from the ground electrode to the light emitting portion end near the ground electrode with respect to the film forming pressure Pr The relationship is shown. The power frequency is changed as a parameter from 13.6MHz to 100MHz. At any frequency, decreasing Pr increases b2. That is, even in the case where the electrode interval d is constant, both light emitting portions can be overlapped by decreasing Pr. In addition, b1≈b2, and even if the electrode interval is changed, only the thickness of the intermediate portion c is changed. That is, from FIG. 4, by setting the electrode interval d = b2 × 2, it is possible to obtain a condition in which both light emitting units are adjacent or overlap.
[0029]
At an electrode interval of d = 20 mm, at 100 MHz, μc-Si was formed with Pr = 133 Pa where both light emitting portions do not overlap and Pr = 40 Pa where both light emitting portions overlap. In Pr = 133Pa, it was I520 / I480 = 10, but in Pr = 40Pa, it increased to I520 / I480 = 13.5.
[0030]
Next, in relation to the invention of claim 4, it will be described in detail below. The discharge structure in which the dark part and the light emitting part appear symmetrically in the vicinity of the high-frequency electrode and the ground electrode as shown in FIG. 1 or FIG. 6 appears characteristically in the frequency band from RF to VHF. In this frequency band, during the half cycle of the power supply frequency, the electron travel distance is equal to or longer than the electrode spacing, but the ion travel distance is negligibly short with respect to the electrode spacing. That is, electrons move following the power supply frequency, but ions cannot follow the power supply frequency.
[0031]
FIG. 5 shows the relationship between the frequency f and the half-cycle electron travel distance. As shown in FIG. 5, even the lightest hydrogen atom ion (H +) and hydrogen molecular ion (H2 +) at about 1 MHz can move only about 1 mm in a half cycle. Also, when the frequency is increased to about 1 GHz, the electrons can move only about 1 mm this time. In the figure, the traveling distance of electrons when the electron temperature is 5 eV and when the electron temperature is 10 eV is shown.
[0032]
Therefore, at a power supply frequency of 1 MHz to 1 GHz, the traveling distance of electrons is 1 mm or more and the traveling distance of ions is 1 mm or less, and it is considered that the above discharge structure is generated. Typically, such a discharge structure clearly appears at a power supply frequency of 10 MHz to 100 MHz at which the electron travel distance is 10 mm or more and the ion travel distance is 0.1 mm or less.
[0033]
By the way, the high frequency electrode in the Example described so far is a structure without an earth shield. When there is an earth shield, when Pr> 67Pa, discharge occurs between the part where the high-frequency voltage is applied and the earth shield, resulting in non-uniform discharge in the surface direction, producing good μc-Si. I can no longer film. By using a high-frequency electrode without an earth shield, the problem of non-uniform discharge does not occur in the experimental range of Pr of 6.7 to 133 Pa.
[0034]
Note that b2 did not change with respect to the discharge power.
[0035]
The same experiment was performed on microcrystalline germanium, microcrystalline silicon carbide, microcrystalline silicon oxide, microcrystalline silicon nitride, and microcrystalline silicon germanium. When both light emitting portions were overlapped as in μc-Si, I520 / I480 Increased.
【The invention's effect】
[0036]
As described above, according to the present invention, the planar ground electrode disposed on one side of the microcrystalline film forming substrate, the planar high-frequency electrode disposed in parallel with the other side, and the source gas supply port In a method for manufacturing a microcrystalline film, a raw material gas for film formation is introduced into a film forming chamber provided with a plasma discharge to form a microcrystalline film on the main surface of the substrate . One of microcrystalline silicon, microcrystalline germanium, microcrystalline silicon alloy, and microcrystalline germanium alloy, and a light emitting portion generated in the vicinity of the high frequency electrode and a light emitting portion generated in the vicinity of the ground electrode opposite to the light emitting portion, By forming the microcrystalline film under adjacent or overlapping film forming conditions, a favorable microcrystalline film with a high crystal volume fraction can be manufactured.
[0037]
As an embodiment of the above invention, a light-emitting portion of both electrodes can be adjacent to each other or overlapped by reducing the distance between the electrodes or by reducing the pressure, and a microcrystalline film having a high crystal volume fraction is manufactured. be able to.
[0038]
When the microcrystalline film having a high crystal volume fraction prepared as described above is applied to a thin film solar cell, there is an effect in improving the conversion efficiency. In addition, when the microcrystalline film having a high crystal volume fraction prepared as described above is applied to a thin film transistor for a display, it is effective in increasing the aperture ratio of the display and increasing the brightness and contrast.
[Brief description of the drawings]
[0039]
FIG. 1 is a diagram schematically showing a discharge structure according to an embodiment of the present invention. FIG. 2 is a diagram showing an experimental result of a relationship between an electrode interval d and a crystal volume fraction (I520 / I480). FIG. 4 is a diagram showing an experimental result related to the invention of Item 2. FIG. 4 is a diagram showing an experimental result related to the invention of Claim 3. FIG. 5 is a diagram showing a relationship between the frequency f and a half-cycle electron traveling distance. ] Schematic diagram showing a discharge structure related to an example of a conventional method for producing a microcrystalline film. [Fig. 7] Diagram showing an example of a schematic structure of a film forming chamber for a conventional thin film solar cell.
[0040]
1: high frequency electrode, 2: substrate, 3: ground electrode, 4: heater, 5: high frequency power source, 6, 8: dark part, 7: light emitting part.

Claims (6)

A film is formed in a film forming chamber having a flat ground electrode disposed on one side of the substrate for forming a microcrystalline film, a flat high frequency electrode disposed in parallel to the other side, and a source gas supply port. In the method for manufacturing a microcrystalline film, in which a forming source gas is introduced and a microcrystalline film is formed on the main surface of the substrate by plasma discharge, the microcrystalline film includes microcrystalline silicon, microcrystalline germanium, microcrystalline Either a silicon alloy or a microcrystalline germanium alloy, and a microcrystalline film is formed under a film forming condition in which a light emitting portion generated in the vicinity of the high-frequency electrode and a light emitting portion generated in the vicinity of the ground electrode opposite to the light emitting portion are adjacent or overlapped. A process for producing a microcrystalline film characterized by comprising:   2. The method for producing a microcrystalline film according to claim 1, wherein a film forming condition in which the two light emitting portions are adjacent to each other or overlap each other by reducing an electrode interval dimension between the ground electrode and the high frequency electrode. A method for producing a crystal film.   2. The method for producing a microcrystalline film according to claim 1, wherein a film forming condition in which the light emitting units are adjacent to each other or overlap each other by reducing a film forming pressure in the film forming chamber. Production method.   4. The method for producing a microcrystalline film according to claim 1, wherein the frequency applied to the electrode is 10 MHz to 100 MHz.   5. The method for producing a microcrystalline film according to claim 1, wherein the high-frequency electrode is formed by removing an earth shield. 2. The method for producing a microcrystalline film according to claim 1 , wherein the microcrystalline silicon alloy is one of microcrystalline silicon germanium, microcrystalline silicon carbide, microcrystalline silicon oxide, and microcrystalline silicon nitride. A method for producing a microcrystalline film.

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