JPH0738112A - Semiconductor device, manufacture thereof and diamond thin film forming method - Google Patents

Abstract

PURPOSE:To form a thin film semiconductor device by conducting a pressure- reduced chemical vapor phase deposition method by differentiating the chemical composition of the semiconductor film for film thickness direction. CONSTITUTION:After a silicon dioxide film 202 and a source/drain region 203 have been formed on a substrate 201, an intrinsic silicon film is deposited using an LPCVD device, and then a silicon film is formed by implanting phosphoric ions. When the intrinsic silicon film, which becomes a source/drain region, is deposited by an LPCVD device, the intrinsic silicon film is preferentially oriented on a [220] surface perfectly. Then a semiconductor film 204, which becomes a transistor active layer, is deposited by the LPCVD device. Subsequently, when a silicon film is deposited as a first semiconductor film under the same condition as the intrinsic silicon film, the crystal condition of the first semiconductor film is preferentially oriented on the [220] surface. When the second semiconductor film is formed continuously without a break, the crystal condition is substantially oriented to [111] surface. When a channel part 205, which becomes an active layer, is formed by patterning, a semiconductor device of high mobility can be formed at a low temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film semiconductor device and a method for forming a diamond thin film, which are applicable to active matrix liquid crystal displays and the like.

[0002]

2. Description of the Related Art In recent years, with the increase in screen size and resolution of liquid crystal displays, the drive system is shifting from the simple matrix system to the active matrix system, and it is becoming possible to display a large amount of information. The active matrix method enables a liquid crystal display having more than several hundred thousand pixels, and forms a switching transistor for each pixel. As a substrate for various liquid crystal displays, a transparent insulating substrate such as a fused silica plate or glass that enables a transmissive display is used.

However, in order to expand the display screen and reduce the price, it is essential to use inexpensive ordinary glass as an insulating substrate. Therefore, there has been a demand for a technique capable of forming a thin film transistor for operating an active matrix type liquid crystal display on an inexpensive glass substrate with stable performance while maintaining the economical efficiency.

A semiconductor film such as amorphous silicon or polycrystalline silicon is usually used as an active layer of a thin film transistor. However, when a thin film transistor is to be integrated with a driving circuit, polycrystalline silicon having a high operating speed is advantageous. Is.

As described above, there is a demand for a technique for producing a thin film semiconductor device in which a semiconductor film such as a polycrystalline silicon film is used as an active layer on a normal glass substrate. However, when a large normal glass substrate is used, In order to avoid the deformation of the substrate, there is a big restriction that the maximum process temperature is about 570 ° C. or less. That is, a technique for forming a thin film transistor capable of operating a liquid crystal display in a low temperature process and an active layer of a thin film transistor capable of operating a driving circuit at high speed is desired.

In order to deposit the semiconductor film by the conventional LPCVD method, first, a semiconductor film such as a silicon film is deposited at a deposition temperature of about 600 ° C. with a deposition pressure of about 1 mtorr using a high vacuum type LPCVD apparatus. It was deposited. (Inter
national Electron Devices
Meeting 1991 technicaldi
best p. 559) In order to form an active layer semiconductor film by another method, as a second method, for example, a semiconductor film such as an amorphous silicon film is deposited on an insulating substrate at a temperature of 570 ° C. or less by a normal type low pressure CVD method. Then, heat treatment is performed at a temperature of 640 ° C. or lower for about 24 hours to form a crystallized semiconductor film,
The characteristics of thin film transistors are improved (Japanese Patent Laid-Open No. 63-3 / 1988).
07777). The third method is to deposit an amorphous silicon film at a temperature of about 300 ° C. or lower by RF magnetron sputtering or plasma CVD method, and then irradiate various lasers to form a silicon film, which is used as an active layer of a thin film transistor. (Jpn.J.App
l. phys. 28 . P1871 (1989) and IEICE Technical Report EID-88-58).

The semiconductor film deposited by these conventional techniques had a uniform film composition and crystal state with respect to the film thickness. Further, conventionally, the diamond thin film has been formed by the plasma CVD method.

[0008]

However, various problems are inherent in each of the above-mentioned prior arts. In the method of performing the heat treatment after depositing the second amorphous silicon film, the heat treatment temperature is too high to use the glass substrate, and if the treatment temperature is set to about 600 ° C. or less, the treatment time may take several tens of hours or more. , Again, glass substrates cannot be used. In addition, as compared with the first high vacuum LPCVD method, there is a problem that the manufacturing process becomes redundant, resulting in a decrease in productivity and an increase in product price. In the method of performing laser irradiation after depositing the third silicon film, there is a problem in that there are large variations in semiconductor characteristics, and it is not possible to produce many thin film semiconductor devices uniformly over a large area. In addition, as compared with the first high-vacuum LPCVD method, the manufacturing process is remarkably complicated and redundant as in the second method, resulting in a decrease in productivity, purchase of expensive processing equipment, and an increase in product price. There is a problem.

On the other hand, in the conventional method for forming a semiconductor film such as a silicon film by the high vacuum LPCVD method, when the deposition temperature is set to about 570 ° C. or below at which large normal glass can be used without problems, the semiconductor characteristics are unsatisfactory. There is a problem that it is sufficient and still unsuitable for use as a switching element or a driving circuit of a high-definition, high-quality liquid crystal display. Further, it was known that a high quality semiconductor film can be obtained by depositing a semiconductor film by lowering the partial pressure of the source gas, but if the pressure is lowered at a temperature of about 570 ° C. or less, the film is not deposited at all and eventually 570 ° C. There was a problem that a high-quality semiconductor film could not be obtained below a certain level.

Therefore, the present invention aims to solve these problems, and an object thereof is to form a good thin film semiconductor device at a temperature of 570 ° C. or lower at which a large ordinary glass can be used.
The purpose is to provide a simple method in which only the VD method is used. Further, conventionally, the diamond thin film is formed by the plasma CVD method, and there are problems such as the generation of fine particles (particles) and the problem of uniformity. Therefore, another object of the present invention is to provide a method for forming a diamond thin film by LPCVD in order to solve these problems.

[0011]

According to the present invention, a thin film semiconductor device in which a semiconductor film is formed on an insulating material of a substrate having at least a part of the surface made of an insulating material and the semiconductor film is used as an active layer of a transistor. In the above, the chemical composition of the semiconductor film is different in the film thickness direction.

The present invention also provides a thin-film semiconductor device in which a semiconductor film is formed on the insulating material of a substrate, at least a part of the surface of which is an insulating material, and the semiconductor film serves as an active layer of a transistor. The crystalline state of the semiconductor film is different in the film thickness direction.

The present invention also relates to a method of manufacturing a thin film semiconductor device in which a semiconductor film is formed on an insulating material of a substrate, at least a part of the surface of which is an insulating material, and the semiconductor film is used as an active layer of a transistor. At this time, when depositing the semiconductor film by a low pressure chemical vapor deposition method (LPCVD method), a compound containing a semiconductor element forming the semiconductor film is used as at least one of source materials, and a first semiconductor film is formed. The method is characterized by including a step of continuously depositing a second semiconductor film under different deposition conditions from the first semiconductor film deposition condition to form the semiconductor film.

Further, according to the present invention, a thin film semiconductor device in which a semiconductor film containing silicon is formed on a substrate of which at least a part of the surface is made of an insulating material and the semiconductor film is used as an active layer of a transistor. In the method for manufacturing the semiconductor device, monosilane (SiH ₄ ) is used as at least one of the raw materials when the semiconductor film is deposited by a low pressure chemical vapor deposition method (LPCVD method). It is characterized in that it includes a step in which the pressure is 0.1 mtorr or less.

In the method for forming a diamond thin film according to the present invention, silane and CH ₄ are used as source gases when the diamond thin film is deposited by a low pressure chemical vapor deposition method.
The flow rate ratio of CH _{4 to} silane during thin film deposition increases with the progress of deposition, and is 100% at least immediately before the end of deposition.
The feature is that CH ₄ is introduced into the reactor.

[0016]

(Embodiment 1) FIGS. 2A to 2E are sectional views showing a manufacturing process of a thin film semiconductor device for forming a MIS field effect transistor. In the sixth embodiment, a thin film semiconductor device having a non-self-aligned staggered structure is taken as an example, but other than this, the present invention is also effective for a thin film semiconductor device having an inverted staggered structure and a self-aligned thin film semiconductor device. There is.

In the first embodiment, the substrate 201 is 235 m.
Although quartz glass of m □ was used, the type and size of the substrate are not limited as long as the substrate can withstand the silicon film deposition temperature. First, the atmospheric pressure chemical vapor deposition method (A
A source / drain region 20 is formed by forming a silicon dioxide film (SiO ₂ film) 202 serving as a base protection film by a PCVD method) or a sputtering method, and then forming a silicon film containing an impurity serving as a donor or an acceptor and then patterning it.
Create 3. (FIG. 2A) In the first embodiment, a high vacuum type L having a volume of 184.5 l
After depositing an intrinsic silicon film of about 1500 Å at a deposition temperature of 555 ° C. using a PCVD apparatus, phosphorus was selected as an impurity element and phosphorus was implanted by an ion implantation method to form a silicon film containing impurities. The intrinsic silicon film, which will later become the source and drain regions, was deposited in a high vacuum LPCVD apparatus at a deposition temperature of 555 ° C. for 4 hours and 50 minutes by flowing 100 silane of monosilane (SiH ₄ ) as a source gas. The pressure in the reaction chamber immediately after introducing the source gas SiH ₄ into the reaction chamber at 555 ° C. was 1.21 mtorr, and it was 1.27 mtorr 4 hours and 49 minutes after the introduction of the source gas immediately before the completion of deposition. The thickness of the intrinsic silicon film thus obtained is 15
It was 65Å. According to the X-ray diffraction method, the silicon film thus obtained was completely preferentially oriented in the {220} plane. Subsequently, phosphorus element was added to the intrinsic silicon film by using a bucket type mass non-separation type ion implanter. As a raw material gas, phosphine having a concentration of 5% diluted in hydrogen was used, and a high frequency output of 38 W and an acceleration voltage of 80 kV gave 5 ×.
Implanted to a density of 10 ¹⁵ 1 / cm ² . After that, when heat treatment was performed at 350 ° C. for 1 hour in a nitrogen atmosphere, the sheet resistance value of the silicon film containing impurities thus obtained was 880.
It was Ω / □. The source / drain regions 203 are formed by patterning this film.

Next, using the same high vacuum type LPCVD apparatus as described above, a semiconductor film 204 to be an active layer of a transistor was deposited. (FIG. 2B) In Example 1, SiH ₄ was used as a source gas, and a silicon film was deposited at a deposition temperature of 555 ° C. The substrate was inserted into the reaction chamber kept at 400 ° C. with the front side facing down. After inserting the substrate, the turbo molecular pump was started to operate, and after reaching a steady rotation, a leak test was performed for 2 minutes. The leak rate of degassing at this time is 3.9 × 10.
^{It was -5} torr / min. After that, the temperature was raised from the insertion temperature of 400 ° C. to the deposition temperature of 555 ° C. for one hour. During the first 10 minutes of heating, no gas was introduced into the reaction chamber and the temperature was raised in vacuum. The minimum background pressure reaching the reaction chamber 10 minutes after the start of temperature increase was 5.7 × 10 ⁻⁷ torr. During the remaining 50 minutes of heating, nitrogen gas with a purity of 99.9999% or higher is used for 30 minutes.
I continued to flow 0 SCCM. At this time, the equilibrium pressure in the reaction chamber is 3.0.
It was × 10 ^-3 torr.

After reaching the deposition temperature, SiH ₄ which is a source gas
At 100 SCCM, and a silicon film as a first semiconductor film was deposited for 30 minutes. The pressure immediately after introducing the raw material SiH ₄ into the reaction chamber was 1.21 mtorr, and the pressure 29 minutes after the introduction of the raw material gas was 1.26 mtorr. The monosilane partial pressure during this period is 1.15 mtorr. This is deposited under exactly the same conditions as the deposition of the intrinsic silicon film that will become the source and drain regions after being described above. Therefore, the crystalline state of the silicon film as the first semiconductor film is preferentially oriented to the {220} plane. From the investigation of the deposition rate, the silicon film has a thickness of about 70Å after 30 minutes of deposition. After depositing the first semiconductor film for 30 minutes, a silicon film as a second semiconductor film was continuously deposited for 2 hours and 5 minutes without a break. At this time, SiH ₄ as a raw material gas was introduced into the 5SCCM reaction chamber, and pure nitrogen having a purity of 99.9999% or more was used as a diluting gas.
5 SCCM were run at the same time. Total pressure during deposition is 3.02 mt
Therefore, using Dalton's partial pressure law, the partial pressure of monosilane during deposition is 50.3 μtorr (0.05
03 mtorr). Thus, the film thickness of the silicon film obtained by continuously depositing the first semiconductor film and the second semiconductor film under different conditions was 309Å. Also, when this film was analyzed by an X-ray diffraction method, the whole semiconductor film including the first semiconductor film and the second semiconductor film was {111} plane, {2}
The diffraction intensity from each of the 20} plane and the {311} plane is 927.
9, 4717 and 1942, which were relatively oriented in the {111} plane. Since the first semiconductor film has a complete preferential orientation on the {220} plane, it can be said that the second semiconductor film has a preferential orientation on the {111} plane. That is, the lower layer portion 70Å of the obtained silicon film is in a crystalline state in which the {220} plane is preferentially oriented, and the upper layer portion is in a crystalline state in which the {111} plane is preferentially oriented. Next, pattern this silicon film,
A channel portion 205, which will be the active layer of the transistor, was created. (FIG. 2C) After that, the gate insulating film 206 is formed by the ECR-PECVD method or the APCVD method. In the first embodiment, a SiO ₂ film is used as the gate insulating film, and the SiO ₂ film is formed by ECR-PECVD
It was deposited to a film thickness of 500Å. (FIG. 2D) Subsequently, a thin film to be the gate electrode 207 is deposited by the sputter method vapor deposition method or the CVD method. In the first embodiment, chromium (Cr) is selected as the gate electrode material, and the sputtering method is used.
500Å accumulated. After depositing a thin film to be a gate electrode, patterning is performed, further 5000 Å of an interlayer insulating film 208 is deposited, contact holes are opened, and source / drain extraction electrodes 209 are formed by a sputtering method or the like to complete a thin film semiconductor device. (FIG. 2 (e)) Transistor characteristics of the thin film semiconductor device prototyped as described above were measured. Is defined as ON current ION, and 95
% Confidence coefficient ION = (2.62 + 0.23, -0.2
1) It was × 10 ^-6 A. Also, Vds = 4V, Vgs =
The off current when the transistor is turned off at 0V is IOFF
= (0.045 + 0.018, -0.012) * 10
^-12 A. Here, the measurement was performed at a temperature of 25 ° C. for a transistor having a channel portion length L = 10 μm and a width W = 10 μm. Effective electron mobility (J. Levinson et al. J,
Appl, Phys. 53 , 1193'82) is μ =
12.48 ± 0.70 cm ² / v. It was sec. Thus, according to the present invention, it has a high mobility and a gate voltage of 1
Ids fluctuate by about 8 digits for 0V modulation. A low temperature process in which a high quality thin film semiconductor device with a process maximum temperature of 555 ° C. or less is maintained for a few hours or less. It became a reality for the first time.

Example 2 A thin film semiconductor device was manufactured by the same steps as in Example 1 except for the step of depositing a channel portion silicon film. In the second embodiment, the deposition temperature of 555 ° C. is used for depositing the channel portion silicon film.
The silicon film as the first semiconductor film was deposited under the same conditions as in Example 1, but the silicon film as the second semiconductor film had a silane flow rate and a diluted pure nitrogen flow rate of 10 SCCM and 290.
SCCM, 15SCCM and 285SCCM, 25SCC
M and 275 SCCM, 45 SCCM and 255 SCCM,
Deposition was performed by changing to 70 SCCM and 230 SCCM. At this time, the deposition time of the second semiconductor film is 1 hour 1
It was 8 minutes, 1 hour 8 minutes, 55 minutes, 47 minutes and 40 minutes.
As a result, the partial pressures of monosilane during the deposition of the silicon film as the second semiconductor film were 0.100 mtorr and 0.150, respectively.
mtorr, 0.251mtorr, 0.451mto
rr was 0.701 mtorr. The thickness of the obtained silicon film is 263Å, 269Å,
It was 264Å, 276Å, 272Å. Using the silicon film thus deposited, a thin film semiconductor device was prepared in the same process as in Example 1, and the transistor characteristics were measured. Figure 1
For the monosilane partial pressure during the second semiconductor film deposition,
The value of the on-current defined in Example 1 is illustrated. Error bars in the figure represent the interval estimates with a 95% confidence coefficient. From this figure, the monosilane partial pressure is 0.1 m
It can be seen that the transistor characteristics are significantly improved when the pressure is lower than torr.

(Embodiment 3) In order to clarify the superiority of the present invention described in Embodiment 1 and Embodiment 2, comparison with the prior art will be made. In the third embodiment, the thin film semiconductor device is manufactured by the same steps as the first embodiment except for the step of depositing the channel portion silicon film. In the third embodiment, the channel portion silicon film was deposited under the conditions for depositing the first semiconductor film of the first embodiment, except for the deposition time. That is, at a deposition temperature of 555 ° C., SiH ₄ as a raw material gas was flowed at 100 SCCM to deposit a silicon film for 58 minutes and 23 seconds. The pressure inside the reaction chamber immediately after the start of deposition was 1.21 mtorr, and the pressure immediately before the end of deposition was 1.27 mtorr. The monosilane partial pressure during deposition is 1.15 mtorr. The silicon film thickness obtained was 199Å. This silicon film is {22
The crystalline state is preferentially oriented on the 0} plane, and the state does not change with the film thickness. When a thin film semiconductor device was manufactured using this silicon film in the same process as in Example 1, the on-current was 95% with a reliability coefficient of ION = (1.45 + 0.08,
It was −0.07) × 10 ⁻⁶ A. The definition of the on-current and the measurement conditions are the same as in Example 1. The effective electron mobility was μ = 9.30 ± 0.39 cm ² / v · sec. Comparing Example 3 with Example 1 and Example 2,
It is understood that when the channel portion silicon film has a multi-layer structure of the first semiconductor film and the second semiconductor film and the monosilane partial pressure is 0.1 mtorr or less in the silicon film deposition process, the transistor characteristics are remarkably improved. Examples 1 and 2
Then, the semiconductor film is divided into two layers, but this may have a multilayer structure of three layers and four layers.

Next, it will be explained that the present invention is indispensable for producing a good thin film semiconductor device with a relatively low deposition temperature of 555 ° C. and a thermal process of several hours. Example 2
As described in detail in 1., good characteristics are obtained when a thin film semiconductor device is manufactured by depositing a channel silicon film with a partial pressure of monosilane of 0.1 mtorr or less. It can be realized only by In fact, in the same high vacuum type LPCVD apparatus used in Examples 1 and 2, a deposition temperature of 555 ° C., a monosilane flow rate of 10 SCCM, and a pure dilution were applied to a quartz glass substrate having a silicon dioxide film (SiO ₂ film) as a base protection film. Nitrogen flow rate 290SCCM, monosilane partial pressure 0.100mtor
Attempting to deposit for 2 hours at r, no silicon film was deposited at all. That is, if the monosilane partial pressure is extremely low, a good-quality silicon film may be deposited, and a thin-film semiconductor device having good characteristics may be created. It is not done. The continuous multilayer deposition according to the present invention is the only effective means for depositing and forming a good-quality semiconductor film at an extremely low pressure, and is realized only for the first time by the present invention. In this embodiment, the deposition temperature was set to 555 ° C. and monosilane was used as the source gas. However, ultra-low pressure deposition is preferable to obtain a good quality semiconductor film by the LPCVD method regardless of the deposition temperature and the source gas. Alternatively, in order to shorten the deposition time, a deposition method of first depositing the first semiconductor film and then continuously depositing the second semiconductor film is effective. This is because, generally, when ultra low pressure deposition is attempted, there is a so-called "incubation time" at which no deposition occurs. This incubation time tends to increase as the deposition pressure decreases. In the above example, 555 ° C., monosilane partial pressure 0.100 mt
At orr, the incubation time is more than 2 hours. Therefore, in order to deposit a good-quality semiconductor film in a realistic deposition time, or to enhance the process productivity, after depositing the first semiconductor film, a high-quality second semiconductor film is deposited under the condition that a high-quality film can be deposited. The only effective method is to form a semiconductor film by depositing. Therefore, at this time, it is usual that the first semiconductor film and the second semiconductor film have different chemical compositions or crystal states. This matter will be described in another embodiment.

Example 4 A thin film semiconductor device was manufactured by the same steps as in Example 1 except for the step of depositing a channel portion silicon film. In Example 4, the high vacuum LPCVD apparatus described in Example 1 was used to deposit a semiconductor film to be a channel portion. Deposition temperature is 550 ° C
Then, a silicon-germanium film was deposited as the first semiconductor film. As a source gas, SiH ₄ was flowed at 85 SCCM, and GeH ₄ was flowed at 15 SCCM at the same time. The deposition time was 20 minutes, and the pressure immediately after the start of deposition was 1.21 mtorr.
The pressure immediately before the end of deposition was 1.30 mtorr. The silicon-germanium film has a thickness of about 70Å in this first deposition. After depositing the first semiconductor film, the silicon film as the second semiconductor film is continuously formed for 2 hours without interruption.
Deposited for 7 minutes. Deposition temperature is 550 ° C and SiH ₄ is 10S
CCM and pure nitrogen were flown at 290 SCCM. The total pressure and the silane partial pressure during the deposition of the second semiconductor film are 3.01 mtorr each.
And 0.100 mtorr. The obtained semiconductor film has a film thickness of 275Å, the lower layer is a silicon-germanium film and the upper layer is a silicon film. This semiconductor film was in a polycrystalline state. Using the thus obtained double-layered semiconductor film, a thin-film semiconductor device was manufactured in the same process as in Example 1, and the transistor characteristics were measured. As a result, the on-current defined in Example 1 was ION with a 95% reliability coefficient. = (2.75 + 0.31,
-0.30) × 10 ⁻⁶ A, which was lower than the conventional thin film semiconductor device shown in Example 3 and showed high characteristics. In addition, the lower layer of silicon deposited in Example 4
Germanium is represented by the chemical composition formula Si _1-x Ge _{x x}
The value of is approximately 0.25. In the fourth embodiment, the channel portion has two layers of the lower layer Si _0.75 Ge _0.25 film and the upper layer Si film, but it is also possible to have a multi-layer structure. For example, the channel part has a five-layer structure, the bottom layer is a Ge film, the second layer from the bottom is a Si _0.25 Ge _0.75 film, and the third layer from the bottom is a Si _0.5 layer.
The Ge _0.5 film, the fourth from the bottom may be the Si _0.75 Ge _0.25 film, and the uppermost layer may be the Si film. Furthermore, the number of layers and the chemical composition in each layer can be freely set. Further, the boundary between layers does not necessarily have to be clear, and the chemical composition and crystal state may continuously change in the film thickness direction. In Example 4, a silicon-germanium film, which is easily crystallized at a relatively low temperature of about 550 ° C., is used as a lower layer, and polycrystalline silicon having stable off-leakage current and low transistor leakage characteristics is continuously deposited at a very low pressure. A high-performance thin-film semiconductor device was created at a lower temperature than before. In the case of a thin film as in the present embodiment, the entire film thickness is attributed to the characteristics of the channel portion, and therefore it is desirable that the lower layer film also has as high quality as possible.
Silicon-germanium, which is easily crystallized even at 50 ° C., is preferable to a silicon film which is hard to crystallize at 550 ° C. However, when considering problems such as mass production, safety, and pollution, the lower layer film may be a silicon film. Thus, the chemical composition and crystal structure of the semiconductor film can be changed according to the purpose.

In addition, a silicon film is used as the lowermost layer, and the silicon film is changed to silicon carbide (Si
It continuously changes to _1-x C _x ), and it is possible to use a diamond film as the lowermost layer. In this case, SiH ₄ and CH ₄ etc. are used as source gases in the LPCVD furnace, and only SiH ₄ is introduced into the reaction furnace at the initial stage of semiconductor film deposition, and the flow rate ratio of CH ₄ to SiH _{4 is} gradually increased until the final deposition. Specifically, only CH ₄ is introduced into the furnace to form a diamond film. The reaction efficiency and the quality of the deposited semiconductor film can be improved by changing the deposition temperature and pressure as the flow rate of CH ₄ increases during the deposition. Specifically, it is preferable to raise the deposition temperature as the flow rate of CH ₄ increases. Or CH ₄
It is also preferable to lower the deposition pressure as the flow rate increases. Of course, both may be applied at the same time. According to such a deposition method, the film deposited on the upper layer inherits the state of the lower silicon film having the SP3 hybrid orbit, and the diamond thin film is easily deposited. In Examples 1 and 2 and the like, different semiconductor films were deposited in the lower layer and the upper layer by suddenly changing the deposition conditions to obtain a good thin film semiconductor device.
Here, the diamond thin film can be easily obtained by continuously changing the deposition conditions. In addition, since the diamond thin film was formed on the insulating substrate in Example 4, the lowermost layer was a polycrystalline silicon film formed by thermal decomposition of SiH ₄ , but a single crystal silicon substrate was used as the substrate. In this case, a mixed gas of SiH ₄ and CH ₄ may be introduced into the reaction furnace from the initial stage of deposition to gradually increase the flow rate of CH ₄ . Due to this, a uniform diamond thin film can be obtained by the LPCVD method without the generation of particles.

[0025]

As described above, according to the present invention, a high quality semiconductor film made of a polycrystalline silicon film or the like can be easily formed at a low temperature of about 570 ° C. or less, and the characteristics of a thin film semiconductor device can be obtained. Has been dramatically improved, the manufacturing time has been shortened, and stable mass production has been realized. Accordingly, when the present invention is applied to an active matrix liquid crystal display or the like, an inexpensive glass substrate or the like can be used, and also when applied to other electronic devices, element deterioration due to heat is reduced. Thus, the present invention has the great effect of realizing high performance and low cost of electronic devices such as active matrix liquid crystal display devices and integrated circuits.
Further, the present invention has an effect that a diamond thin film can be easily formed by the LPCVD method.

[Brief description of drawings]

FIG. 1 is a diagram showing an effect of the present invention.

2A to 2E are cross-sectional views of elements in respective steps of manufacturing a thin film semiconductor device showing an embodiment of the present invention.

[Explanation of reference numerals] 201 ... Substrate 202 ... Underlayer protection film 203 ... Source / drain region 204 ... Semiconductor film 205 ... Channel portion 206 ... Gate insulating film 207 ... Gate electrode 208 ... Interlayer insulating film 209 ... Source / drain extraction electrode

Claims (9)

[Claims] 1. A thin film semiconductor device in which a semiconductor film is formed on an insulating material of a substrate, at least a part of the surface of which is an insulating material, and the semiconductor film serves as an active layer of a transistor. Thin film semiconductor device characterized by having different chemical composition in the film thickness direction. 2. A thin film semiconductor device in which a semiconductor film is formed on an insulating material of a substrate, at least a part of the surface of which is an insulating material, and the semiconductor film serves as an active layer of a transistor. The thin film semiconductor device is characterized in that the crystal state of is different in the film thickness direction. 3. A method of manufacturing a thin film semiconductor device, wherein a semiconductor film is formed on the insulating material of a substrate, at least a part of the surface of which is an insulating material, and the semiconductor film serves as an active layer of a transistor. When the semiconductor film is deposited by the low pressure chemical vapor deposition method (LPCVD method), a compound containing a semiconductor element forming the semiconductor film is used as at least one of the source materials, and after depositing the first semiconductor film. A method of manufacturing a thin film semiconductor device, comprising the step of continuously depositing a second semiconductor film under a deposition condition different from the first semiconductor film deposition condition to form the semiconductor film. 4. The thin film according to claim 3, wherein when forming the second semiconductor film, the partial pressure of the compound containing a semiconductor element is lower than the partial pressure when depositing the first semiconductor film. Manufacturing method of semiconductor device. 5. Silicon is used as one of the semiconductor elements constituting the semiconductor film, and silane (Si _n H _{2n + 2} : n = 1, 2, 3) is used as one of the compounds containing the semiconductor element.
The manufacturing method of the thin film semiconductor device according to claim 3, wherein 6. The method of manufacturing a thin film semiconductor device according to claim 5, wherein the silane partial pressure when depositing the second semiconductor film is lower than the silane partial pressure when depositing the first semiconductor film. . 7. A method of manufacturing a thin film semiconductor device, wherein a semiconductor film containing silicon is formed on a substrate of which at least a part of the surface is made of an insulating material, and the semiconductor film is used as an active layer of a transistor. In this case, when the semiconductor film is deposited by the low pressure chemical vapor deposition method (LPCVD method), monosilane (SiH ₄ ) is used as at least one kind of the raw material, and the monosilane partial pressure is 0 during the semiconductor film deposition. A method of manufacturing a thin film semiconductor device, which comprises a step of 1 mtorr or less. 8. The method of manufacturing a thin film semiconductor device according to claim 6, wherein the partial pressure of monosilane at the time of depositing the second semiconductor film is 0.1 mtorr or less. 9. A method for forming a diamond thin film, comprising:
When depositing the diamond thin film by low pressure chemical vapor deposition, silane and CH ₄ are used as source gases, and the flow rate ratio of CH _{4 to} silane during the thin film deposition increases with the progress of deposition, and at least immediately before the end of deposition. Is a method for forming a diamond thin film, wherein 100% CH ₄ is introduced into the reaction furnace.