JP2742799B2 - Method of forming semiconductor thin film - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method for forming a semiconductor thin film on a substrate by decomposing a raw material gas by light energy in a normal pressure reaction vessel to form a semiconductor thin film on a substrate. It relates to a forming method.

[Conventional technology]

In general, optical CVD does not cause plasma damage to a substrate unlike plasma CVD, and thus is widely used for forming, for example, an amorphous silicon thin film or a microcrystalline silicon thin film.

Recently, “28p-ZG-11 normal pressure optical CV” on page 329 of the 1st volume of the 35th Symposium on Applied Physics, Spring 1988
Production of a-Si Film by Method D ''
It has been proposed that the optical CVD at normal pressure eliminates the need for an expensive evacuation pump, reduces impurities from the inner surface of the reaction vessel, and improves the film quality.

By the way, in the case of optical CVD including the normal-pressure optical CVD described above, in order to obtain a semiconductor thin film having good film quality, as in ordinary plasma CVD, the substrate is heated to about 100 to 300 ° C. It is necessary to provide thermal energy as energy required for the film radical to move to an optimal position on the substrate surface.

[Problems to be solved by the invention]

As described in the related art, heating the substrate to a high temperature has the following problems.

When different types of thin films are stacked on a substrate, atoms of the lower thin film and impurity atoms such as doped boron are mixed into the upper thin film by thermal diffusion, thereby deteriorating the film quality of the upper thin film.

In an atmosphere containing a large amount of hydrogen radicals, such as a mercury-sensitized CVD using hydrogen gas as a diluent gas, when forming a semiconductor thin film on a transparent conductive film (TCO) to create a photovoltaic device, In addition, TCO is reduced by hydrogen radicals, TCO is damaged, and the transmittance of TCO is reduced. This phenomenon becomes more remarkable as the temperature is higher, and causes a decrease in photoelectric conversion efficiency.

The time required to heat the substrate before the start of the film formation reaction and the time required to cool the substrate after the film formation is required, and the total time required for the film formation is increased.

Equipment for cooling the reaction vessel with cooling water is required, and the apparatus becomes expensive.

In view of the above, the present invention has been made in consideration of the above-mentioned points, and enables a semiconductor thin film to be formed while keeping the substrate temperature at about room temperature. The purpose is to be able to be obtained in a short time.

[Means for solving the problem]

In order to achieve the above object, a translucent window plate is provided in a reaction vessel having an internal pressure maintained at normal pressure, a substrate is provided in the vessel, a source gas is supplied into the vessel, and a light source is used for the window. The container is irradiated with irradiation light through the plate, and the energy of the irradiation light decomposes the source gas to generate film-forming radicals. In a method of forming a semiconductor thin film by atmospheric pressure photo-CVD for forming a semiconductor thin film, in the present invention, while applying vibration to the substrate, the substrate temperature is set to 20 to 50
It is characterized in that it is kept at ° C.

[Action]

With the above configuration, the film forming radical generated by the decomposition of the source gas by the energy of the irradiation light from the light source reacts on the substrate surface, and the film forming radical is located at an optimum position on the substrate surface by the vibration energy. Move, and a semiconductor thin film grows on the substrate.

At this time, the energy required for the film-forming radical to move to the optimal position on the substrate surface is given in the form of vibration energy instead of the conventional thermal energy, and the substrate temperature at the time of film formation is set to about 20 to about room temperature. Since the temperature is kept at 50 ° C, the film quality deteriorates due to thermal diffusion of impurities in the lower layer when different kinds of thin films are stacked, TCO is damaged when a photovoltaic device is created, the time required for film formation is prolonged, and the cost of the device is increased. In addition, all problems caused by heating the substrate at a high temperature of about 100 to 300 ° C. are all solved.

〔Example〕

 Embodiments will be described with reference to the drawings.

Embodiment 1 First, FIGS. 1 to 3 showing Embodiment 1 will be described.

In FIG. 1 showing a forming apparatus, (1) is a reaction vessel,
(2) is a translucent window plate made of quartz provided on the upper surface of the reaction vessel (1), (3) is a substrate holder provided in the reaction vessel (1), and (4) is a holder (3). (5) a source gas supply pipe for feeding a source gas to the substrate (4), the tip of which is introduced into the reaction vessel (1);
(6) is a purge gas supply pipe whose tip is introduced into the reaction vessel (1) and blows out a purge gas such as He, Ar, N ₂ , H _2, etc. to prevent fogging into the window plate (2), (7), (8) Is a valve provided in the middle of both supply pipes (5) and (6),
(9) is a mercury bubbler, and a source gas supply pipe (5)
It is provided to bypass the valve (7) via the valves (10a) and (10b) connected to the inlet side and the outlet side of the side valve (7), and keeps the mercury vapor pressure constant during use. It has a structure capable of controlling the temperature.

(11) is a quartz piezoelectric vibrator mounted on the lower surface of the substrate holder (3) and energized by the high frequency power supply (12) to vibrate the substrate (4) through the substrate holder (3). (13) is a reaction vessel (1). The exhaust port formed in (14) is a vacuum valve (1
An evacuation pump connected to the exhaust port (13) through 5), and (16) is connected to the exhaust port (13) through the exhaust valve (17) to exhaust gas from inside the reaction vessel (1). An exhaust gas treatment device for processing, (18) a lamp house formed above the window plate (2), (19) a low-pressure mercury lamp as a light source, which is housed in the lamp house (18) and (2)
Irradiation light is irradiated into the reaction vessel (1) through the reactor, and the irradiation light energy decomposes the raw material gas supplied into the reaction vessel (1) to generate film-forming radicals. By the reaction on the surface of (4), a semiconductor thin film grows on the substrate (4).

Reference numeral (20) denotes a heater for heating the substrate (4) provided for comparison of characteristics.

Then, using the device shown in FIG. 1, a pin-type photovoltaic device is prepared without performing mercury sensitization. In this photovoltaic device, as shown in FIG. 2, a transparent conductive film (TCO) (22) is formed on a glass substrate (21) with a spatter or the like.
Amorphous silicon carbide (hereinafter a-SiC)
), Amorphous silicon (hereinafter a)
-Si), an i layer (24) and an n layer (25) are sequentially laminated, and a back electrode (26) made of aluminum [Al] or the like is formed on the n layer (25). It is created by the following procedure.

First, the glass substrate (21) on which the TCO (22) is formed is mounted on the holder (3) in the container (1), only the valve (15) is opened, and the inside of the container (1) is temporarily stopped by the vacuum pump (14). Evacuate and then close valve (15), valve (7),
(8) is opened to supply the raw material gas and the purge gas into the container (1), and when the pressure in the container (1) becomes slightly higher than the atmospheric pressure (up to 780 Torr), the valve (17) is opened to exhaust the gas. The gas in the container (1) is discharged by the gas processing device (16).

At this time, in order to discharge the gas in the container (1) without a pump, the pressure in the container (1) needs to be slightly higher than the atmospheric pressure. If the pressure is too high, there is a safety problem.
Set to 0 Torr.

In addition, since mercury sensitization is not performed, valves (10a), (1
0b) is closed.

Next, a high frequency of 1 MHz is applied to the vibrator (11) by the power supply (12) to drive the vibrator (11), and the vibrator (11) applies vibration energy to the substrate (4) through the holder (3). Irradiates irradiation light with a mercury lamp (19), and the TCO (2
2) Form p, i, and n layers (23) to (25) thereon.

As described above, when the irradiation light is irradiated from the mercury lamp (19), the irradiation light energy decomposes the raw material gas to generate film-forming radicals, and the generated film-forming radicals react on the surface of the substrate (4). A-SiC or a-S on the substrate (4)
Although the thin film of i grows, the energy required for the film forming radical to move to the optimal position on the surface of the substrate (4) is not the heat energy as in the past, but the form of the vibration energy by the vibrator (11). Therefore, the substrate temperature at the time of film formation is only about room temperature, and various problems caused by heating the substrate in the conventional photo CVD are solved.

The conditions for forming each of the layers (23) to (25) of p, i, and n are as shown in Table 1. The output of the power supply (12) is 10 W, i, and n at the time of forming the p layer (23). (24) and (25) were set to 20 W at the time of formation, and after the formation of the p-layer (23), the inside of the container (1) was evacuated to prevent impurities from being mixed into the i-layer (24).

The thickness of each of the layers (23) to (25) of p, i, and n is 2
The substrate temperature at the time of forming each layer was approximately room temperature of 40 ° C.

For comparison, when forming the i-layer (24), the substrate (4) was heated to 300 ° C. by the heater (20) instead of the vibration by the vibrator (11). The layers (23) to (25) of p, i, and n were formed under the same conditions, and various characteristics of the obtained photovoltaic device were measured.

When the i-layer (24) is heated, it is necessary to leave the substrate (4) for about 1 hour after the formation of the p-layer (23) and the i-layer (24) for heating and cooling the substrate (4). On the other hand, such a leaving time is not necessary when the vibration is performed by the vibrator. However, in order to match the conditions, when the vibration is performed by the vibrator (11), the p-layer (23) and the i-layer (24) ) Is left for about 1 hour after formation, however, the characteristics are the same as those of the photovoltaic device in which no leaving time is provided.

At this time, when the case where vibration is applied during the formation of the i-layer (24) is the case and the case where the substrate (4) is heated to 300 ° C. is the case, the characteristics of the i-layer itself are not much different from those of the case. Optical band gap Eopt = 1.68 eV, dark conductivity σd ~ ^{10 -10} Ω ^-1 cm ^-1 , photoconductivity σph ~ 10 ^-4 Ω ^-1 cm
⁻¹ , and the characteristics of the photovoltaic device in the case were as shown in Table 2. However, in Table 2,
Voc is the open circuit voltage, Isc is the short-circuit photocurrent density, FF is the film actuator, and η is the photoelectric conversion efficiency.

By the way, as can be seen from Table 2, the case, i.e., i
When the substrate (4) is heated to 300 ° C. during the formation of the layer (24), Voc, Isc, FF, and η are greatly reduced as compared with the case, that is, when vibration is applied during the formation of the i-layer (24). However, the cause is considered to be that boron [B] atoms as dopants in the p-layer (23) were mixed into the i-layer (24) by thermal diffusion. B concentration distribution in the depth direction of the i-layer (24) of the photovoltaic device
When measured by SIMS (secondary ion mass spectrometry),
The result of the case is as shown by the solid line and the broken line in FIG. 3, respectively.
At a depth of about 3000 ° near the interface with the p-layer (23), the B concentration sharply increases, and B is not mixed in the i-layer (24). B in the entire area of (24)
Are diffused and mixed.

Even in the case of the case, as a result of the experiment, good characteristic data was obtained when the temperature of the substrate (4) was 20 to 50 ° C., so that the substrate temperature was set to 20 to 50 ° C. ,
What is necessary is just to adjust the vibration energy given to the board | substrate (4).

Therefore, according to the first embodiment, the energy required for the film-forming radical to move to the optimum position on the surface of the substrate (4) is given in the form of vibration energy instead of the conventional thermal energy. The temperature of the substrate (4) at the time can be kept at about 20-50 ° C., which is about room temperature, the film quality deteriorates due to the thermal diffusion of impurities in the lower layer when different kinds of thin films are laminated, Various problems caused by high-temperature heating of the substrate, such as damage, prolonged time required for film formation and increased cost of equipment, can be solved.
A semiconductor thin film such as a-SiC or a-Si having excellent film quality can be formed in a shorter time than in the past, and a photovoltaic device or the like having excellent characteristics can be obtained.

Second Embodiment Next, FIG. 4 showing a second embodiment will be described.

The device used in Example 2 is the same as that shown in FIG. 1. The following shows the measurement results of various characteristics of the pin-type photovoltaic device produced by mercury sensitization using the device shown in FIG. Will be described.

At this time, the structure of the photovoltaic device produced was the same as the structure shown in FIG. 2 except that the material of the p layer (23) in FIG. 2 was microcrystalline silicon carbide (hereinafter referred to as μC-SiC). As a forming procedure, a p-layer of μC-SiC (2
During formation of 3), in order to perform mercury sensitization, except that the valve (7) is closed, the valves (10a) and (10b) are opened, and mercury vapor from the mercury bubbler (9) is introduced into the container (1). Is the same as in the first embodiment.

 However, the temperature of the mercury bubbler (9) is maintained at 70 ° C.

The conditions for forming the layers (23) to (26) of p, i, and n are as shown in Table 3, and the thickness of each layer (23) to (25) is 300, 2000, and 300 mm, respectively. For the p-layer (2
In the formation of 3), the substrate (4) is heated to 200 ° C. by the heater (20) instead of the vibration by the vibrator (11). Each layer of n (23)
(25) was formed, and various characteristics of the obtained photovoltaic device were measured.

At this time, if the case where vibration is applied during the formation of the p-layer (23) is the case and the case where the substrate (4) is heated to 200 ° C. is the case, the characteristics of the p-layer itself are not much different from those of the case. ^{Eopt = 2.1eV, σd~10 0 Ω -1} cm -1, σph~
Characteristics of 10 ⁰ Ω ^-1 cm ^-1, and the case, a photovoltaic device in the has fallen as shown in Table 4.

And, as can be seen from Table 4, when the substrate (4) is heated to 200 ° C. during the formation of the case, that is, the p-layer (23),
Voc and Isc are remarkably reduced as compared with the case, that is, when vibration is applied during the formation of the p layer (23). The cause is that the p layer (23) is formed on the TCO (22) by the mercury sensitization method. Since hydrogen is used as a diluent gas for mercury vapor when formed, TCO (22) is reduced by hydrogen radicals at high temperatures, which damages TCO (22) and reduces the transmittance of TCO (22). It is conceivable that poor bonding at the interface between the TCO (22) and the p-layer (23) has occurred.

Further, the collection efficiency spectrum of the obtained photovoltaic device was measured in order to confirm the decrease in the transmittance of the TCO (22). The results of the case were shown by a solid line and a broken line in FIG. 4, respectively. As can be seen from the figure, the case has a lower collection efficiency over the entire wavelength range of 300 to 800 nm than the case, confirming the decrease in the transmittance of the TCO (22). The bias at the time of measuring the collection efficiency spectrum was -5V.

Therefore, according to the second embodiment, the same effect as that of the first embodiment can be obtained, and a semiconductor thin film having excellent film quality such as μC-SiC or a-Si can be formed in a shorter time than the conventional one by an inexpensive configuration. Can be formed.

In both of the above embodiments, the high frequency applied to the vibrator (11) by the power supply (12) is set to 1 MHz. However, the present invention is not limited to this, and an audio frequency may be used.

Further, the present invention is not limited to the single-chamber reaction furnace type shown in FIG.

Further, in addition to the photovoltaic device as in the above two embodiments,
Needless to say, the present invention can be applied to the fabrication of devices using materials that are weak to thermal diffusion, such as Al and other materials that use dopants, such as TFTs and semiconductor sensors.

Needless to say, the light source is not limited to the low-pressure mercury lamp described above.

〔The invention's effect〕

Since the present invention is configured as described above,
The following effects are obtained.

The energy required for the film-forming radicals generated by the decomposition of the source gas by the irradiation light energy to move to the optimum position on the substrate surface is not the heat energy as in the past, but the heat energy.
Since the substrate is applied in the form of vibration energy,
There is no need to raise the temperature to about 0 to 300 ° C., and the substrate temperature during film formation can be kept at about 20 to 50 ° C., which is about room temperature, and various problems caused by high-temperature heating of the substrate can be solved. With a low-cost configuration, a semiconductor thin film with an excellent film chamber can be formed in a shorter time than in the past, which is extremely effective in producing a semiconductor device having good characteristics.

[Brief description of the drawings]

The drawings show an embodiment of the method for forming a semiconductor thin film according to the present invention. FIGS. 1 to 3 show an embodiment 1, FIG. 1 is a schematic view of a forming apparatus, and FIG. FIG. 3 is a cross-sectional view of the device, FIG. 3 is a distribution diagram of boron concentration in the i-layer of the photovoltaic device of FIG. 2, and FIG. (1) ... reaction vessel, (2) ... translucent window plate, (4) ...
... substrate, (19) ... low-pressure mercury lamp.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shinya Tsuda 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (72) Inventor Shoichi Nakano 2-18-3 Keihanhondori, Moriguchi-shi, Osaka (56) References JP-A-1-298169 (JP, A)

Claims (1)

(57) [Claims] 1. A translucent window plate is provided in a reaction vessel whose inside is maintained at normal pressure, a substrate is provided in the vessel, a source gas is supplied into the vessel, and a light source passes through the window plate. The container is irradiated with irradiation light, the source gas is decomposed by the energy of the irradiation light to generate film-forming radicals, and the film-forming radicals react on the substrate surface to form a semiconductor thin film on the substrate. In the method of forming a semiconductor thin film by atmospheric pressure photo-CVD to be formed, while applying vibration to the substrate, the substrate temperature is set to 20 to 50 ° C.
A method for forming a semiconductor thin film, comprising: