JPH04342119A - Manufacture of hydrogenated amorphous silicon thin film - Google Patents

Abstract

PURPOSE:To obtain an amorphous silicon film which is dense, whose structural defect is small and whose hydrogen content is small. CONSTITUTION:The following are repeated alternately: a first process wherein a film-forming substrate is heated to and held at 300 to 600 deg.C, a raw-material gas composed of a silane-based gas is pyrolyzed near said film-forming substrate and a hydrogenated amorphous silicon thin film is deposited; and a second process wherein the film-forming substrate is exposed to atomic hydrogen and/or atomic heavy hydrogen which have been produced by using a means different from that to pyrolyze the raw-material gas.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is useful for functional films, particularly for applications in line sensors for image input, imaging devices, solar cells, optical sensors, photoreceptor devices for electrophotography, and semiconductor electronic devices such as thin film transistors. The present invention relates to a method for producing a hydrogenated amorphous silicon thin film.

0002

[Prior Art] Conventionally, amorphous and polycrystalline functional films such as semiconductor films, insulating films, photoconductive films, magnetic films, and metal films have been developed from the viewpoint of desired physical properties and uses. A film formation method suitable for each individual is adopted.

For example, amorphous or polycrystalline non-single-crystal silicon (hereinafter abbreviated as "NON-Si:H") whose unpaired electrons are compensated with a compensating agent such as a hydrogen atom (H) as necessary. , especially when referring to amorphous silicon, "a-S"
i:H", and "poly" to indicate polycrystalline silicon.
-Si:H") film (so-called microcrystalline silicon (μc-Si:H))
H) can be formed using vacuum evaporation, plasma chemical vapor deposition (hereinafter abbreviated as "plasma CVD"), and thermal chemical vapor deposition (hereinafter referred to as "thermal CVD"). (abbreviated), reactive sputtering method, ion plating method, photo-CVD method, etc., and generally, plasma CVD method is widely used and has been commercialized.

0004

[Problem to be solved by the invention] As is well known, a-S
The role of hydrogen (H) in i:H is to bond with the unpaired electrons of silicon atoms (so-called dangling bonds), which are necessary to maintain the irregular network structure that is a characteristic of its crystal structure. The purpose is to compensate for this and reduce the localized level density, which is specific to amorphous semiconductors. Also,
These hydrogens are present in the a-Si:H film at 10 to 20 atomic % (
at. %) and contains silicon atoms and Si-
It is known that they are bonded in the form of H bonds or Si-H2 bonds.

However, in recent years, these hydrogen atoms have caused "fluctuations" in the bond angles and bond distances between adjacent silicon atoms, forming a tail-like level on the valence band side peculiar to a-Si:H. It has been pointed out that In addition, there are medium- and long-range macroscopic phenomena such as micro-voids with hydrogen atoms bonded to their inner surfaces (so-called micro-voids) and microcrystal grain boundaries where many hydrogen atoms exist in the form of Si-H2 bonds at the interface. It is believed that structural defects captured in the structure are deeply involved in the formation of skirt-like levels on the conduction band side and in the electrical properties such as the mobility and lifetime of a-Si:H. Furthermore, a
- Recent research has proposed a model in which the increase in spin density under light irradiation (so-called photodegradation), which is a characteristic characteristic of Si:H, arises from the difference in electronegativity between hydrogen and silicon. . As described above, recent recognition of hydrogen has raised the issue of how to reduce the concentration of hydrogen contained in a-Si:H and form a dense irregular network structure with few microstructural defects. There is.

[0006] Conventionally, in the production of high-purity semiconductors, the CVD process, which decomposes easily purified gaseous raw materials, breaks their chemical bonds, and deposits solids by forming new bonds, has been widely applied. , doping and other device fabrication processes are also considered to be a type of chemical reaction that involves bond cleavage and recombination. Activation energy is required to cause a chemical reaction, but generally the molecular motion is activated by injection of thermal energy, and the reaction is induced by inelastic collisions between molecules in the gas phase or between molecules in the gas phase and the solid surface. It is true. In such molecular design, it is necessary to identify the active species that govern film formation and etching, and to control their amount and movement. SiH2 precursor and H2 are thermally decomposed by a heater made of tungsten, molybdenum, tantalum, etc., which is deposited on a film forming substrate heated to about 200°C to form a structurally good a. -Thermal CVD method (so-called HOMO-CVD method) for forming a-Si:H film produces more gas-phase reaction products than plasma CVD method, which is also used industrially as a method for forming a-Si:H film. The type and distribution of a-S are simple and easy to control, and the ion species generated in the plasma
Since this method does not cause ion damage to the i:H film, it is expected to be a method for forming high-quality a-Si:H films.

However, due to the natural decomposition of the SiH2 precursor, many Si-H polymers are formed in the a-Si:H film, forming a film with many micro defects (micro-voids, microcrystals, etc.). As a result, the amount of hydrogen contained in the film CH
is 11-18 at. %, which is not much different from the amount of hydrogen contained in the a-Si:H film formed by the plasma CVD method.
Bright conductivity σph measured under white light of cm is 10-6 ~
There was a problem in that it was possible to produce a film of about 10-7 Siemens/cm (s/cm), which is about two orders of magnitude inferior to an a-Si:H film formed by plasma CVD.

Therefore, as is generally well known, a
-By heating the Si:H film at a high temperature of 300°C or higher,
The idea was to release and remove the contained hydrogen from the membrane.

[0009] The release form of hydrogen is described by W. Bey.
er) et al. published the magazine “Journal of Non-Crystalline Solids”.
rystalline Solids)” No. 59 & 60
According to data published in Vol. (1983), pages 161 to 168, the emission peaks at a heating temperature of around 370°C and around 600°C, although this varies depending on the substrate temperature during deposition. The release mechanism is different around 370°C and around 600°C. At around 370°C, hydrogen is mainly molecular hydrogen (H
2) is directly desorbed and released from the membrane surface and outermost layer, or Si-H2 bonds in the membrane, Si-H3
It is thought that molecular hydrogen is generated by the cleavage of the (SiH2)n bond (where n is an integer), diffuses along the voids, reaches the surface, and is released. On the other hand, the origin of molecular hydrogen released at around 600° C. is thought to be atomic hydrogen in the film. Atomic hydrogen (a
tm. It is thought that H) is generated, diffuses within the irregular network structure, and when it reaches the surface, combines with other atomic hydrogen to become molecular hydrogen, which is separated and released from the surface. At this time, if a plurality of silicon atoms from which atomic hydrogen has been cut exist adjacently, the Si--Si bond may be restored. However, the hydrogen content is at most 20%
Assuming that there are bond forms other than Si-H bonds, and that Si-H bonds happen to exist adjacent to each other, a dangling bond is created by releasing hydrogen atoms and hydrogen molecules. It is also understandable that the amount increases along with this.

Furthermore, as seen in Japanese Patent Publication No. 2-27824, an a-Si:H film formed by a glow discharge method is
A method has been proposed in which, after heat treatment at a temperature in the range of 00 to 550°C, annealing is performed in hydrogen plasma while applying a voltage so that the a-Si:H film has a negative potential with respect to the hydrogen plasma. , several thousand Å, which is used industrially.
For relatively thick films, since the annealing treatment is performed after film formation, there is a drawback that the distribution of hydrogen content in the film thickness direction cannot be made uniform.

In view of the problems of the prior art as described above, the present invention has been developed to produce a-a-
The purpose is to obtain a Si:H film.

0012

[Means for Solving the Problems] According to the present invention, such an object is to thermally decompose a raw material gas consisting of a silane-based gas in the vicinity of a film-forming substrate to form hydrogenated amorphous silicon on the film-forming substrate. A method for producing a hydrogenated amorphous silicon thin film in which a thin film is deposited includes a first step of depositing a hydrogenated amorphous silicon thin film by heating and holding the film-forming substrate at 300 to 600°C; Hydrogenated amorphous silicon, characterized in that a second step of exposing the film-forming substrate to atomic hydrogen and/or atomic deuterium produced by a means other than thermal decomposition is repeated alternately. This is achieved by a thin film manufacturing method.

In the present invention, the thickness of the deposited layer deposited at one time in the first step is 10 to 60 Å.
It is preferable that Further, in the present invention, a doping gas is mixed with the raw material gas, and the heating and holding temperature of the film-forming substrate in the first step is set to 250 to 550°C, thereby producing hydrogenated amorphous silicon with controlled valence electrons. A thin film can be obtained. Furthermore, in the present invention, the atomic hydrogen and/or atomic deuterium can be generated by glow discharge decomposition of molecular hydrogen gas and/or molecular deuterium gas, and as an alternative method. This can be carried out by thermally decomposing molecular hydrogen gas at a temperature higher than the thermal decomposition temperature of the raw material gas.

[0014]

[Operation] The present invention is applicable to the surface reaction-based thermal CVD method in which an SiH2 precursor produced by thermal decomposition of silane gas is directly deposited on the surface of a film-forming substrate to form an irregular network structure. : By heating the deposition substrate to a high temperature during H film deposition, hydrogen molecules (H
2) In addition to promoting the separation and release of gas, in the process in which a portion of SiH2 in the growth layer spontaneously decomposes into Si-H polymer, the Si-H bonds are thermally dissociated and bonded hydrogen is released outside the film. Furthermore, by injecting and diffusing atomic hydrogen from the surface, the remaining Si-
H-polymer and bonded hydrogen, etc. on the inner surface of micro-voids are cut and diffused to the membrane surface to generate and release hydrogen molecules (i.e., an abstraction reaction of hydrogen in the membrane by hydrogen).
By promoting restoration of Si--Si bonds and compensating for unpaired electrons, an a-Si:H film having a dense irregular network structure with a reduced amount of hydrogen contained in the film is formed. Incidentally, as the silane-based gas, silane (SiH
4) In addition to the gas, higher silane gases such as disilane (Si2 H6) gas and trisilane (Si3 H8) gas can also be used.

On the other hand, when exposed to atomic deuterium (atm.D), the gas molecules desorbed and released from the membrane surface become H2
It acts exactly the same as when exposed to atomic hydrogen, except that it takes the form of HD molecules or D2 molecules.

Here, in order to form a stable irregular network structure in the grown layer, it is necessary to form a thickness of about several atomic layers, that is, about 10 to 60 Å in the first step, although it depends on the film forming conditions. If the thickness is too thick, an inner layer will be formed, and molecular hydrogen will be trapped there and will not be released, making it impossible to fully exhibit the effects of the present invention. In addition, in the second step of exposing to atomic hydrogen, it is necessary for the atomic hydrogen injected from outside the film to diffuse from the growth surface to the inner layer, and the film thickness per cycle of the growth layer is If it is thick, the atomic hydrogen treatment will have a distribution in the film thickness direction, which is not preferable. Moreover, if the atomic hydrogen treatment time is too long, even Si--Si bonds will be cut unnecessarily. Although it depends on the deposition conditions and the amount of atomic hydrogen, within the above film thickness range, about 20 to 50 seconds is preferable. In addition, in the case of atomic deuterium, the injection efficiency is lower than when using atomic hydrogen, and the emission peak shifts to the higher temperature side, so the processing time is lower than when using atomic hydrogen. It is preferable to increase the time. Atomic hydrogen and atomic deuterium can be used regardless of their charge state, but considering that the thermal CVD method is free from ion damage, they are electrically neutral. is preferable. These atomic hydrogen and atomic deuterium can be generated using decomposition means such as glow discharge, but it is preferable to separate the generation from the deposition space.

In addition, when doping is performed, diborane (B2 H6
) gas or phosphine (PH3) gas can be mixed and thermally decomposed to control valence electrons. At this time,
When impurities are mixed in, the activation energy thereof is lowered, so that the peak of hydrogen release is shifted to a lower temperature side by about 50° C., so that the substrate temperature can also be lowered.

[0018]

[Example] Figure 1 shows a thermal CVD method used in an example of the present invention.
FIG. 2 is a sectional view showing the device. Inside the deposition tube 9, there is a constant temperature table 10 that supports the quartz substrate 1 for film formation and keeps its temperature constant. The constant temperature table 10 has a built-in heater 11 for heating and holding the quartz substrate 1. A thermocouple 12 for monitoring the substrate temperature is installed near the quartz substrate 1, and by monitoring this, the heating temperature of the heater 11 can be adjusted to keep the substrate temperature constant. Quartz substrate 1
A tungsten ribbon heater 13 is installed at a position 20 mm directly above the
Can be heated up to 000℃. The surface of the ribbon heater 13 is coated with an alumina ceramic coating material (not shown) to prevent tungsten from being mixed into the a-Si:H film. A source gas introduction pipe 15 and an atomic hydrogen introduction pipe 16 are connected to one end of the deposition tube 9, and an exhaust pipe 17 is connected to the other end of the deposition pipe 9. A high-speed on-off valve 18 is connected to the raw material gas introduction pipe 15, and a T-shaped pipe 20 connected to a high-speed on-off valve 19 and another evacuation device (not shown) is connected to the atomic hydrogen introduction pipe 16. Moreover, the frequency is 2.45GH
An applicator type discharge tube 22 connected to a microwave power source 21 of Z is connected. Further, a vacuum pump 24 is connected to the exhaust pipe 17 via a conductance valve 23.

An embodiment of the present invention carried out using this apparatus will be described with reference to FIG.

First, the quartz substrate 1 is placed on the constant temperature table 10, the door of the deposition tube 9 is closed, and the conductance valve 23 is closed.
is fully opened, the inside is evacuated using the vacuum pump 24, the ribbon heater 13 and the heater 11 in the deposition tube 9 are energized, and the temperature of the quartz substrate 1 on the thermostatic table 10 is monitored while monitoring the thermocouple 12. The temperature was adjusted to 250°C. next,
Open the high-speed opening/closing valve 19, introduce hydrogen gas into the deposition tube 9 at a flow rate of 50 sccm, and then open the conductance valve 2.
The pressure inside the deposition tube 9 is adjusted to 1.00 To by adjusting the opening degree of step 3.
Adjusted to rr. In this state, hydrogen gas was continued to flow for about an hour, and at the same time, the current value of the DC constant current power supply 14 was adjusted so that the temperature of the ribbon heater 13 reached 1350°C.
Since the temperature of the quartz substrate 1 rose due to the radiant heat, the temperature of the heater 11 was adjusted to maintain the substrate temperature at 400°C.

Next, the ribbon heater 13 and the quartz substrate 1
When the temperature became stable, microwave power with an output of 500 W was supplied from the microwave power source 21 to the applicator type discharge tube 22 to generate hydrogen plasma in the discharge tube and generate atomic hydrogen. Next, the high-speed opening/closing valve 19 was closed, the atomic hydrogen was discharged from the T-shaped pipe 20 to another evacuation device, and the hydrogen plasma in the applicator type discharge tube 22 was maintained at a pressure of 1.10 Torr. At the same time as closing the high-speed on-off valve 19, the high-speed on-off valve 18 is opened, and silane gas is introduced into the deposition tube 9 from the source gas introduction pipe 15 at a flow rate of 50 sccm, and the opening degree of the conductance valve 23 is adjusted to perform deposition. The pressure inside tube 9 was adjusted to 1.00 Torr. The introduced silane gas is dissociated by the heat of the ribbon heater 13, and as shown in FIG. 2(a), SiH2 precursor 2 and molecular hydrogen 3 having the lowest dissociation energy are produced. These SiH2 precursors 2 reached the quartz substrate 1, and through an insertion reaction in which they replaced Si--H bonds on the film surface, a growth layer 4 of an a-Si:H film was deposited at a deposition rate of 2.1 Å/sec. At this time, a large frame of an irregular network structure peculiar to a-Si:H is completed. Si-H2 on the surface
There are many bonds, and the growth layer 4 itself is in the process of structural relaxation to Si-Si bonds, and due to the natural decomposition of SiH2, Si
It contains a large amount of hydrogen, such as an increase in -H polymers and a large number of micropores with many Si-H bonds on the inner surface. However, due to the high temperature of 400℃, Si-H2
Bonds of multiple atomic hydrogens 5 such as bonds, Si-H polymers, and Si-H bonds in micro-voids are broken to form molecular hydrogen 6, which is condensed in Si-H polymers and micro-voids. Because it passes through gaps such as voids and diffuses to the surface, excess molecular hydrogen 6 is constantly desorbed and released from the deposition surface until it is depleted. As a result, a part of the Si-H polymer is structurally relaxed into Si-Si bonds, and the hydrogen contained in the grown layer 4 is mainly composed of Si-H bonds, and the amount of hydrogen contained in the grown layer 4 is significantly reduced. However, heat release alone is not sufficient to relax the structure to Si-Si bonds as in the conventional example, and the structure contains many structural defects such as dangling bonds and micro-voids with many Si-H bonds on their inner surfaces. It is hard to say that it is a precise structure. Furthermore, as the deposition continues, inside the growth layer 4, solidification begins gradually starting from the layer closest to the quartz substrate 1, so that an inner layer 4' consisting of an irregular network structure in which structural defects are frozen is formed. . Therefore, before this inner layer 4' is formed, a process to remove these structural defects is required.

24 seconds after the introduction of the raw material gas, when the thickness of the growth layer 4 reaches 50 Å and the internal layer 4' begins to form, the high-speed opening/closing valve 18 is closed to stop the supply of the raw material gas. did. Next, when the high-speed opening/closing valve 19 is opened and atomic hydrogen 7 obtained by plasma decomposition of hydrogen gas by microwave discharge is introduced into the deposition tube 9, a grown layer 4 is formed as shown in FIG. 2(b). The surface of will be exposed to this atomic hydrogen. This atomic hydrogen 7 can be further injected and diffused into the film from the surface of the growth layer 4, reaching the interface between the growth layer 4 and the inner layer 4'. The atomic hydrogen 7' injected into the growth layer 4 further breaks the residual Si-H polymer and the Si-H bonds in the micropores to form new atomic hydrogen 5,5'.
It restores the Si-Si bonds while generating ions, condenses them, and releases molecular hydrogen 6,6', and on the other hand, compensates for dangling bonds to create a dense film with few structural defects. The growth layer is modified to contain less hydrogen. That is, these atomic hydrogens are very useful for removing excess hydrogen and structural defects in the film. The time for this atomic hydrogen treatment is preferably about 40 seconds, although it depends on the structure of the deposited film and the treatment conditions.
If exposed to the atomic hydrogen 7 for too long, the implanted atomic hydrogen 7' will also break the Si-Si bonds in the inner layer 4' and remain, causing unpaired electrons to be generated. It becomes impossible to fully demonstrate the effect.

Next, 40 seconds after starting the atomic hydrogen treatment, the high-speed on-off valve 19 is closed, and at the same time, the high-speed on-off valve 18 is opened to introduce silane gas into the deposition tube 9 instead of atomic hydrogen. As shown in FIG. 2(c), the process was returned to the first step (deposition step), and the growth layer 4 was deposited. growth layer 4
When the thickness of the inner layer 4' becomes thick enough to form the inner layer 4', the structure of the grown layer 4 and the inner layer 4' treated with atomic hydrogen becomes solidified and stable, and is dense and has few structural defects as shown in FIG. 2(b). Low hydrogen-containing a-Si:H film with irregular network structure 8
becomes. In this way, by repeating the deposition process and the atomic hydrogen treatment process alternately, a low hydrogen-containing a-Si film with a thickness of 6000 Å was deposited.
: After the H film is deposited on the film forming substrate 1, the high-speed on-off valve 18 is closed to stop the supply of silane gas to complete the deposition, and the high-speed on-off valve 19 is also closed to stop the supply of atomic hydrogen 7. Then, the ribbon heater 13 and the heater 11 were turned off, the quartz substrate 1 was cooled, the butterfly valve 23 was closed, and the deposition tube 9 was returned to atmospheric pressure, and then the door was opened and the quartz substrate 1 was carried out. .

Similarly, infrared absorption spectroscopy (FT-IR
In order to measure the amount of hydrogen contained in the film using the method), an a-Si:H film was deposited using an n+ type single crystal silicon substrate.

FIG. 3 shows the atomic hydrogen treatment time from 0 seconds (no atomic hydrogen treatment) to quartz substrate temperature of 300°C, 400°C, 500°C, and 600°C using the method of the above embodiment. Hydrogen content CH (at.%) in the a-Si:H film obtained by infrared absorption spectroscopy of the a-Si:H film prepared by changing the time up to 70 seconds
The measurement results are shown below. As the amount of hydrogen released increases as the substrate temperature rises, the amount of hydrogen in the film decreases, reaching 6.5 at. %become. When further treated with atomic hydrogen, the amount of hydrogen contained decreases with the treatment time, and the amount of change slows down after about 30 seconds, and at 400°C, it becomes 2.8 at. % has been reached. However, at 600°C, it is 1.7at. %, indicating that atomic hydrogen contributed to the repair of excessively broken Si-H bonds.

[0026] In order to confirm that there is no increase in dangling bonds as the hydrogen content decreases, 400
Unpaired electrons (dangling bonds) measured by constant photocurrent method (so-called CPM) on a-Si:H films fabricated on a quartz substrate at substrate temperatures of 600°C and 600°C for different atomic hydrogen treatment times. The density of the localized level near the center of the band created by
Evaluation was made using the value of S (1/cm3). The results are shown in FIG. Regardless of the substrate temperature, the DOS value decreased with processing time, reached a minimum value around 40 seconds, and was approximately proportional to the decrease in hydrogen content. The DOS value at a substrate temperature of 400° C. and a processing time of 40 seconds was 9×10 14 /cm 3 . However, it has been found that excessive processing actually increases the number of defects. Also, when the substrate temperature reaches 600℃,
Due to the increase in defects due to the breakage of Si--H bonds and the release of the implanted atomic hydrogen, the defects could not be sufficiently compensated for, and the amount of change in the DOS value was small. For this reason, the substrate temperature is preferably about 400° C., and the atomic hydrogen treatment time is preferably about 40 seconds.

FIG. 5 shows the activation energy Ead of a-Si:H films fabricated at substrate temperatures of 300°C, 400°C, 500°C, and 600°C with an atomic hydrogen treatment time of 40 seconds.
(eV), and irradiation light intensity 100 mW/c at AM-1
Bright conductivity σp (s/cm) and dark conductivity σd at m2
(s/cm). The activation energy Ead is 0.67 eV at a substrate temperature of 400°C, which is slightly smaller than that of a film formed by the conventional plasma CVD method, but increases as the substrate temperature increases, and becomes about 8 eV at 600°C. Also, the dark conductivity σd is 10-10
It is on the order of s/cm and decreases as the substrate temperature increases, but the change is small. In comparison, the bright conductivity σp reaches 1.3×10 −4 s/cm at 400° C., which is superior to a film formed by conventional plasma CVD method. This is an increase of nearly four orders of magnitude compared to the film produced by the conventional thermal CVD method (without atomic hydrogen treatment) shown in FIG. 5, and the bright/dark conductivity ratio reaches five orders of magnitude. However, if the substrate temperature is too high, the increase in bright conductivity will be small even if the atomic hydrogen treatment is performed. These measurement results are proportional to the trend of DOS values shown in FIG. Thus, the atomic hydrogen treatment of the present invention was able to reduce excess hydrogen in the film and at the same time reduce structural defects such as dangling bonds and micro voids. For this membrane,
When the above irradiation light was continuously irradiated and the change in bright conductivity was observed, the value after 15 hours was 7.4 × 10-5 s/c
It was m. This is an extremely small amount of deterioration compared to the one-digit decrease in film produced by conventional plasma CVD.

Next, another embodiment of the present invention will be shown.

50 sccm of silane gas and 10 sccm of diborane (B2 H6) gas diluted with hydrogen gas.
is supplied from the raw material gas introduction pipe 15, the pressure inside the deposition pipe 9 is adjusted to 1.00 Torr, and atomic hydrogen treatment is performed in the same manner as in the above embodiment to form an a-Si:H film. I did doping. The doping amount at this time was a concentration ratio of diborane gas and silane gas of 3000 ppm. FIG. 6 shows the relationship between substrate temperature and dark conductivity. The maximum value was 4.3×10 −3 s/cm at a substrate temperature of 360° C. Compared to the substrate temperature dependence of the bright conductivity of a non-doped film, this is shifted to a lower temperature side by about 50°C, and due to the lower activation energy associated with doping, the dissociation energy of Si-H bonded hydrogen atoms is lowered. This is thought to be because of this.

As a method for producing atomic hydrogen or atomic deuterium, decomposition using microwave plasma in the above embodiment has a high electron density and is the most efficient. 7 instead of the microwave power source 21 and applicator type discharge tube 22 connected to
As shown in the figure, a high-frequency discharge tube 26 is used as a hydrogen gas decomposition furnace, in which a capacitively coupled electrode is arranged in a dense alumina ceramic tube, and a high-frequency power source 25 with a frequency of 13.56 MHz is connected to one of the electrodes. Atomic hydrogen introduction tube 1
6 to decompose hydrogen gas. However, in this case, since the electron density of the plasma is lower than in the case of using the microwave discharge, it is preferable to input high-output radio-frequency power, taking into consideration that the decomposition efficiency of hydrogen molecules will be lowered.

Furthermore, in addition to the apparatus of the above embodiment, when atomic hydrogen is also generated using thermal energy without relying on decomposition by glow discharge, the microwave power source 21 and the applicator type discharge tube 22 may be used. Instead of Figure 8
A high temperature image furnace 27 made of a quartz tube can be used as shown in FIG. Since the dissociation energy of hydrogen molecules is high, it is heated to 2000°C or higher.

Furthermore, in the above embodiments, a quartz substrate was used as the film-forming substrate, but it is also possible to use a heat-resistant material, for example, a metal material such as stainless steel.

In the above example, the temperature at which silane gas was thermally decomposed was set at 1350°C. This is because, although the deposition rate becomes faster when the temperature is raised further, precursors other than SiH2 are also produced, which tends to deteriorate the film quality.

[0034]

According to the present invention, a first step of depositing an a-Si:H film on a substrate heated and maintained at 300 to 600° C. by thermally decomposing a silane gas as a raw material; By alternately repeating the second step of exposing the surface to atomic hydrogen and/or atomic deuterium, excess hydrogen on the growth surface and the Si-H polymer in the vicinity and on the inner surface of micro voids is desorbed. , by releasing and reducing the amount of hydrogen contained in the film, and at the same time injecting and diffusing the atomic hydrogen and/or atomic deuterium into the growth layer.
By cutting the -H bond to promote the recovery of the Si-Si bond and compensating for the unpaired electrons of the silicon atom, it is possible to create a dense, low-hydrogen-containing a-Si:H film with few structural defects. , which could not be produced using conventional thermal CVD methods.
Since it is possible to manufacture films with low localized level density, excellent bright/dark conductivity ratio, and less photodegradation, it is possible to produce optical sensors with excellent photoelectric conversion characteristics, solar cells with less photodegradation, and excellent high-speed response performance. It is extremely effective in realizing thin TFTs and the like.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of an apparatus used to practice the invention.

FIG. 2 is a schematic cross-sectional view for explaining the process of the present invention.

FIG. 3 is a diagram showing an example of the characteristics of an a-Si:H film obtained by implementing the present invention.

FIG. 4 is a diagram showing an example of the characteristics of an a-Si:H film obtained by implementing the present invention.

FIG. 5 is a diagram showing an example of the characteristics of an a-Si:H film obtained by implementing the present invention.

FIG. 6 is a diagram showing an example of the characteristics of an a-Si:H film obtained by implementing the present invention.

FIG. 7 is a cross-sectional view of an apparatus used to practice the invention.

FIG. 8 is a cross-sectional view of an apparatus used to practice the invention.

[Explanation of symbols]

1 Film-forming substrate 2 SiH2 precursor 3 Molecular hydrogen 4 Growth layer 4’ Inner layer 5,5' Atomic hydrogen 6,6’ Molecular hydrogen 7,7’ Atomic hydrogen 9　　　　　Deposition tube 10　Thermostatic stand 11 Heater 12 Thermocouple 13 Ribbon heater 14 Heater power supply 15 Raw material gas introduction pipe 16 Atomic hydrogen introduction tube 17 Exhaust pipe 18, 19 High-speed opening/closing valve 20 T-shaped piping 21 Microwave power supply 22 Applicator type discharge tube 23 Conductance valve 24 Vacuum pump 25 High frequency power supply 26 Capacitively coupled high frequency discharge tube 27 High temperature image furnace

Claims (5)

[Claims] 1. A method for producing a hydrogenated amorphous silicon thin film, which comprises depositing a hydrogenated amorphous silicon thin film on the film forming substrate by thermally decomposing a raw material gas consisting of a silane-based gas in the vicinity of the film forming substrate. The film-forming substrate is heated to 300 to 600°C.
a first step of depositing a hydrogenated amorphous silicon thin film by heating and holding; A method for producing a hydrogenated amorphous silicon thin film, the method comprising alternately repeating a second step of exposing a hydrogenated amorphous silicon film. 2. (a) mixing a doping gas with the source gas; (b) heating and holding the film-forming substrate in the first step at a temperature of 250 to 550°C; and (c)
) A method for producing a hydrogenated amorphous silicon thin film, which is the same as the method according to claim 1, except for obtaining a hydrogenated amorphous silicon thin film with controlled valence electrons. 3. The hydrogenated amorphous silicon thin film according to claim 1 or 2, wherein the thickness of the deposited layer deposited in the first step is 10 to 60 Å. Production method. 4. The production of atomic hydrogen and/or atomic deuterium is performed by glow discharge decomposition of molecular hydrogen gas and/or molecular deuterium gas. A method for producing a hydrogenated amorphous silicon thin film according to claim 3. 5. The atomic hydrogen and/or atomic deuterium is produced by thermally decomposing molecular hydrogen gas and/or molecular deuterium gas at a temperature higher than the thermal decomposition temperature of the raw material gas. Claim 1, characterized in that
4. The method for producing a hydrogenated amorphous silicon thin film according to claim 3.