JP3433736B2 - Method for manufacturing semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a thin film semiconductor device applicable to an active matrix liquid crystal display, VLSI, etc., and a low pressure chemical vapor deposition apparatus for depositing a semiconductor layer forming a part of the semiconductor device.

[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.

Amorphous silicon or polycrystalline silicon is usually used as the active layer of the thin film transistor, but polycrystalline silicon, which has a high operating speed, is advantageous when a thin film transistor is to be integrated with a driving circuit.

Thus, there is a demand for a technique for producing a thin film semiconductor device having a polycrystalline silicon film as an active layer on a normal glass substrate. However, when a normal glass substrate is used, the maximum process temperature is about 600. There is a large restriction that the glass strain point temperature is not higher than about 0 ° C.

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 form such an active layer silicon film, firstly, in addition to the technique of depositing by the LPCVD method, for example, a silicon film is deposited on the insulating substrate by the LPCVD method at a temperature of 570 ° C. or lower, and then at 640 ° C. As a technique (Japanese Patent Laid-Open No. 63-307776) for improving the characteristics of a thin film transistor by performing heat treatment for about 24 hours at the following temperature, and as a third method, RF magnetron sputtering or plasma CV
A technique of forming an active layer of a thin film transistor by depositing an amorphous silicon film at a temperature of about 300 ° C. or less by the method D and then performing various laser irradiations (Jpn. JA.
ppl. Phys. 28 , 1871, '89 and the Institute of Electronics, Information and Communication Engineers Technical Research Report EID-88-58).

[0008]

However, various problems are inherent in each of the above-mentioned prior arts. After depositing the second and third silicon thin films, heat treatment or laser irradiation is used to improve the characteristics of the active layer.
Compared with the manufacturing method by the PCVD method, there are problems that the manufacturing process becomes remarkably complicated and redundant, resulting in a decrease in productivity, purchase of expensive processing equipment, and an increase in product price. On the other hand, in the conventional method of depositing a silicon film to be an active layer by the LPCVD method, the LPCVD apparatus is unsuitable for depositing a good-quality silicon film, and the deposition technique itself is unsatisfactory, so that the characteristics as a transistor are insufficient. However, there is a problem that it is still unsuitable for switching elements and driving circuits of high-definition and high-quality liquid crystal displays.

Therefore, the present invention is aimed at solving these various problems, and an object thereof is to form a thin film semiconductor device having good transistor characteristics by a simple process of forming only an active layer by an LPCVD method. It is intended to provide a method of manufacturing a thin film semiconductor device capable of doing so, and to provide a low pressure chemical vapor deposition apparatus suitable for such a purpose.

[0010]

According to the method of manufacturing a semiconductor device of the present invention, in the method of manufacturing a semiconductor device having a silicon thin film, a substrate is inserted into a reaction chamber, the temperature is raised to a deposition temperature, and the temperature is increased to the deposition temperature. After reaching, a silicon film is deposited on the substrate by low pressure chemical vapor deposition (LPCVD),
It is characterized in that the temperature is lowered from the deposition temperature to a predetermined temperature in a hydrogen atmosphere. This makes it possible to suppress the phenomenon in which hydrogen present in the deposited silicon film is desorbed and an unpaired electron pair is generated. Further, the method for manufacturing a thin film semiconductor device of the present invention is, in the method for manufacturing a semiconductor device having a silicon thin film, the substrate is inserted into a reaction chamber and heated to a deposition temperature, and after reaching the deposition temperature, the substrate is attached to the substrate. A silicon film is deposited by a low pressure chemical vapor deposition method (LPCVD method), and the temperature of the substrate is lowered from the deposition temperature to a predetermined temperature in a mixed atmosphere of an inert gas and hydrogen. This makes it possible to suppress the phenomenon in which hydrogen present in the deposited silicon film is desorbed and an unpaired electron pair is generated. Further, the method for manufacturing a thin film semiconductor device of the present invention is, in the method for manufacturing a semiconductor device having a silicon thin film, the substrate is inserted into a reaction chamber and heated to a deposition temperature, and after reaching the deposition temperature, the substrate is attached to the substrate. Low pressure chemical vapor deposition (LP
It is characterized in that the substrate is deposited by the CVD method), the substrate is returned from the pressure at the deposition to the atmospheric pressure in a reducing atmosphere, and the temperature is lowered from the deposition temperature to a predetermined temperature in the reducing atmosphere. This makes it possible to suppress the phenomenon in which hydrogen present in the deposited silicon film is desorbed and an unpaired electron pair is generated.

[0011]

EXAMPLES Example 1 Examples of the present invention will be described below, but the present invention is not limited to the following examples.

FIGS. 1A to 1E are sectional views showing a manufacturing process of a polycrystalline silicon thin film transistor forming an MIS type field effect transistor.

In the first embodiment, the substrate 101 is 235 m.
Quartz glass with m holes was used. However, as long as the substrate can withstand a thermal environment of 600 ° C. for 4 to 5 hours, the type and size of the substrate need not be questioned. First, a base protective film 102 is formed on a substrate 101 that has been organically washed or acid washed. In Example 1, a silicon dioxide film (SiO ₂ film) of 2000 angstrom was deposited by atmospheric pressure chemical vapor deposition (APCVD method). As the base protective film 102, a silicon nitride film (SiNx) or the like can be used instead of the SiO ₂ film, and any forming means having a process temperature of 600 ° C. or less such as a plasma CVD method (PECVD method) or a sputtering method is effective. It is. Subsequently, the source / drain regions 103 are formed.

(FIG. 1A) Since the n-type semiconductor device was manufactured in the first embodiment, phosphorus was selected as the impurity and LPC was selected.
Phosphine (PH ₃ ) and monosilane (SiH ₄ ) by VD method
After depositing a polycrystalline silicon film containing phosphorus using the source gas as a source gas, the source / drain region 10 is formed by patterning.
Formed 3. The deposition temperature of the polycrystalline silicon film containing phosphorus is 600 ° C. and the deposition rate is 30 Å / min.
Was deposited to a film thickness of 1500 Å to form source / drain regions.

Next, a silicon film 104, which will later form the channel portion, is deposited by the LPCVD method. (Fig. 1
(B)) An outline of the LPCVD apparatus used in the first embodiment is shown in FIG. The LPCVD apparatus has a reaction chamber 201 having a volume of 184.5 l, and the substrate 202 is horizontally installed near the center of the reaction chamber. The raw material gas and a diluent gas such as helium, nitrogen, argon, hydrogen, etc. are introduced into the reaction chamber 201 from the lower part of the reaction chamber and exhausted from the upper part of the reaction chamber as needed.
A heater 203, which is divided into three zones, is provided outside the reaction chamber made of quartz glass, and by adjusting them independently, a soaking zone is formed near the center of the reaction chamber at a desired temperature. This soaking zone spreads out at a height of about 350 mm,
The temperature deviation within that range is within 0.2 ° C. when set at 600 ° C., for example. Therefore, the spacing between the insertion boards is 5
If it is mm, it is possible to process 70 substrates in one batch.

In the first embodiment, 17 substrates were installed in the soaking zone at intervals of 20 mm. Exhaust is rotary pump 2
04 and the mechanical booster pump 205 were directly connected. Therefore, the difference in pumping speed due to the difference in gas type does not appear. The pressure was measured by a diaphragm type pressure gauge that does not depend on the gas species. When an inert gas such as helium is flown into the reaction chamber 201 with both pumps operating at a furnace temperature of 600 ° C., the equilibrium pressure P _{(mtorr) in the} reaction chamber and the gas flow rate Q
_The following relational expression holds with _(SCCM) .

P = 2.260 + 0.3100 × Q 10 _SCCM ≦ Q ≦ 1
00 _SCCM P = 24.04 + 0.1626 × Q 200 _SCCM ≦ Q ≦
900 _{SCCM In} this Example 1, the silicon film 104 was deposited using the above LPCVD apparatus. (FIG. 1B) The substrate in which the source / drain regions were formed and the native oxide film on the region surface was removed was inserted into the reaction chamber of the LPCVD apparatus with the front side facing downward. The temperature of the reaction chamber at the time of insertion is 395 to 400
The temperature is between 0 ° C and the reaction chamber is kept in a nitrogen atmosphere.
A nitrogen curtain of about 6 _SLM is formed near the entrance of the reaction chamber to minimize the flow of oxygen and moisture into the reaction chamber when the substrate is inserted. When water and oxygen in the air are mixed in the reaction chamber, they are adsorbed on the silicon layer on the wall of the reaction chamber or react with silicon and remain in the reaction chamber, and are degassed during the deposition of the silicon film which becomes the channel part. It appears and causes instability such as deteriorating the film quality of the deposited silicon film and increasing fluctuation of the film thickness.

After inserting the substrate, perform vacuuming and leak inspection,
If there is no abnormality, raise the temperature of the reaction chamber from the insertion temperature of 400 ° C to the deposition temperature. In Example 1, the deposition temperature is 600 ° C.
It took 2 hours to heat up. Normally, an inert gas such as nitrogen or helium having a purity of about 99.99% or more is flown during this temperature rising period, but in this embodiment 1, hydrogen 3% argon 97
% _SC of argon / hydrogen mixed gas was continuously flowed at 700 _SCCM to _{raise the} temperature. At this time, the equilibrium pressure in the reaction chamber was 138 _mtorr . In the present Example 1, for safety reasons, the hydrogen concentration was set to 3% and the reaction chamber was maintained in a reducing atmosphere during the temperature rising period.
Of course, the hydrogen concentration does not matter. In addition, if the purpose is to increase the temperature in the reaction chamber from 400 ° C. to the deposition temperature, one hour is sufficient for raising the temperature, but oxygen and moisture from the side wall of the reaction chamber should be maintained by maintaining a reducing atmosphere during the temperature raising period. In order to remove the degassing and to bring out a clean deposition environment, a temperature rising period of about 2 hours or more is preferable.

Immediately after the end of the temperature rising period based on the reducing atmosphere, a predetermined amount of silane (SiH ₄ ) -disilane (Si ₂ H ₆ )
A raw material gas such as the above and a diluent gas as necessary are introduced into the reaction chamber to deposit the silicon film 104. In Example 1, silane having a purity of 99.999% or more was flowed at 11.25 _SCCM to deposit a silicon film. The equilibrium pressure in the reaction chamber during the deposition of the silicon film was 7.65 _mtorr . Silicon film 104 is 2
Deposition was performed by continuously flowing silane into the reaction chamber for 0 minutes and 39 seconds.
After the deposition of the silicon film was completed, the reaction chamber was immediately evacuated to prevent unreacted silane from remaining in the reaction chamber. This evacuation was performed for 4 minutes. Immediately after the deposition of the silicon film, the heater set temperature is 600 to 400 ° C.
Was changed to.

After the evacuation was completed, the reactive gas line such as silane and the inside of the mass flow controller were replaced with nitrogen by spending 3 minutes. During this time, 97% hydrogen 3% argon in the reaction chamber.
% Of the argon-hydrogen mixed gas continued to flow 700 _SCCM, maintained the reaction chamber equilibrium pressure of about 140 _{mt orr.} After the completion of nitrogen substitution in the reactive gas line and the mass flow controller, the reaction chamber is returned to atmospheric pressure by an argon / hydrogen mixed gas, and after that, it takes about one and a half hours to allow the temperature of the reaction chamber and the substrate to drop to about 400 ° C. I was waiting. About 1 _SLM of argon / hydrogen mixed gas was flown into the reaction chamber during this cooling period.
The reaction chamber was kept at atmospheric pressure. In the present Example 1, a reducing atmosphere was created with a gas composition of 3% hydrogen and 97% argon during this cooling period, but the hydrogen concentration and the inert gas species are not limited to these. For example, helium, nitrogen or the like may be used as the inert gas instead of argon, and the hydrogen concentration may be 100%. In the present Example 1, 3% was selected for safety reasons so that the lower limit of hydrogen explosion would not be exceeded.

By lowering the substrate temperature in the reducing atmosphere as described above, it is possible to suppress the phenomenon that hydrogen existing in the deposited silicon film is released and an unpaired electron pair is generated. It is generally recognized that the temperature at which hydrogen is desorbed from a silicon film is 450 ° C or higher. Therefore, even when the substrate temperature is lowered in a reducing atmosphere, the environment surrounding the substrate is reduced until the substrate temperature becomes 450 ° C or lower. It is preferable to maintain a sexual atmosphere. However, in order to lower the substrate temperature from the deposition temperature to about 450 ° C. or lower, a temperature lowering period of 1 hour or more is required as shown in the first embodiment, which causes a decrease in work efficiency.

On the other hand, the desorption phenomenon of hydrogen from the silicon film complies with Boltzmann statistics. Therefore, the desorption rate of the hydrogen rapidly decreases as the temperature decreases. For these reasons, it is desirable to keep the environment in which the substrate is contained in a reducing atmosphere at least until the substrate temperature becomes about 500 ° C. or lower.

In this way, the substrate temperature 4
After the temperature was lowered to about 00 ° C., the substrate was taken out of the reaction chamber. In Example 1, since the hydrogen concentration was 3%, the exhaust in the reaction chamber was omitted and the atmosphere was directly opened to the atmosphere. However, when the hydrogen concentration is high, the exhaust is indispensable. The film thickness of the silicon film 104 obtained in Example 1 was 244 Å.

The silicon film thus deposited was patterned with a resist and then etched by a mixed plasma of carbon tetrafluoride (CF ₄ ) and oxygen (O ₂ ) to form a channel part silicon film 105. (FIG. 1C) Subsequently, the gate insulating film 106 is formed. In the first embodiment, S
The iO ₂ film was deposited to a film thickness of 1500 Å by the electron cyclotron resonance plasma CVD method (ECR-PECVD method). (FIG. 1 (d)) After that, after forming the gate electrode 107, an interlayer insulating film 108 is deposited if necessary, and after opening a contact hole, a source / drain extraction electrode 109 is formed to complete the transistor.
(FIG. 1 (e)) When the characteristics of the thin film transistor (TFT) manufactured as described above were measured, the effective electron mobility μo and the trapping density N obtained from the saturation current region at the source / drain voltage V _ds = 4V.
t (J. Levinson et al. J. App.
l. Phys. 53 , 1193, 1982) are μo respectively.
= 5.3 ± 0.15 cm ² /v·secNt=(6.9
It was ± 0.26) × 10 ¹¹ l / cm ² . 25 measurements
The transistor channel portion had a length L of 10 μm and a width W of 100 μm, which were measured at 0 ° C. Also V _ds =
When the transistor is turned on at 4 V and gate voltage V _gs = 10 V, the source / drain current is I _ON = 13.4 ± 1.
When the transistor is turned off at V _ds = 4V and V _gs = 0V, the off current is I _OFF = 0.87 ± 0.
05pA, good on / off ratio of 7 digits or more
Was created.

Example 2 A TFT was manufactured by the same steps as in Example 1 except for the step of depositing a channel portion silicon film. The second embodiment corresponds to a conventional technique of forming a channel portion silicon film by the LPCVD method and can be compared with the present invention of the first embodiment.

In Example 2, the same LPCVD apparatus as in Example 1 was used to deposit the silicon film in the channel portion, but the temperature rising conditions and the temperature decreasing conditions were different from those in Example 1. When depositing the silicon film on the channel part, first insert the substrate,
After evacuation and leakage inspection, the temperature was raised from the insertion temperature of 400 ° C. to the deposition temperature of 600 ° C. This temperature rising condition was performed by the conventional technique.

That is, in the second embodiment, the purity is 99.9999.
% _Or more of helium was continuously flowed at 350 _{SCCM to} provide an hourly heating period. The equilibrium pressure in the reaction chamber during the temperature rising period was 81.
It was 5 _{mt orr} . Immediately after the temperature was raised by helium for one hour, 11.25 _SCCM of silane having a purity of 99.999% or more was flown into the reaction chamber in the same manner as in Example 1 to deposit a silicon film. The equilibrium pressure in the reaction chamber during silicon film deposition is 7.67.
_{It was mtorr} . The silicon film was deposited by continuously flowing silane into the reaction chamber for 20 minutes and 39 seconds. Immediately after the deposition of the silicon film,
The heater set temperature is changed from 600 ℃ to 400 ℃,
The reaction chamber was evacuated for 4 minutes. After the evacuation was completed, the inside of the mass flow controller was replaced with nitrogen for 3 minutes. During this period, nitrogen with a purity of 99.99% or higher is kept in the reaction chamber.
_Continue to flow 00 _SCCM and keep the equilibrium pressure in the reaction chamber at about 140 _mtorr.
Was maintained at. After that, the reaction chamber was returned to atmospheric pressure by nitrogen having a purity of 99.99% or more, and the substrate was taken out directly. The substrate temperature at this time was about 530 ° C. The film thickness of the silicon film obtained in this Example 2 was 250 Å.

TFTs were manufactured through the same steps as those in Example 1 except for the above steps, and the transistor characteristics were measured. As a result, effective electron transfer determined from the saturation current region at the source / drain voltage V _ds = 4V. The degree μo and the trap density Nt are respectively μo = 4.0 ± 0.17 cm ² / v · sec, Nt =
It was (7.8 ± 0.15) × 10 ¹¹ l / cm ² . Also, with a TFT of L = 10 μm and W = 100 μm, V _ds = 4V,
The on-current when the transistor is turned on at V _gs = 10 V is I _ON = 6.24 ± 0.09 μA, V _ds = 4 V, V _gs =
The OFF current when the transistor is turned off at 0V is I _OFF
= 0.94 ± 0.06 pA.

Comparing Example 1, which is an example of the present invention, with Example 2 of the prior art, the present invention is to improve the mobility by 30% or more and reduce the trap density by 10% or more as compared with the prior art. I know that I was successful. As a result, the on-state current is greatly increased by 115% compared with the conventional one, and the off-state current is 1
It is possible to reduce it by almost 0%.

Example 3 A TFT was manufactured by the same steps as in Example 1 except for the step of depositing a channel portion silicon film. Strictly speaking, the second embodiment, which is the prior art, and the first embodiment, which is an example of the present invention, are different in two points of the temperature raising method and the temperature lowering method. Therefore, in the third embodiment, the difference between the temperature lowering methods results. Shown and demonstrate the effectiveness of the present invention.

In the third embodiment, the same LPC as in the first embodiment, which is an example of the present invention, is used for depositing a channel silicon film.
Although a VD device was used, only the temperature lowering condition was different from that of Example 1. In depositing the silicon film on the channel part, first, after inserting the substrate, vacuuming and leak inspection,
The temperature is increased from 00 ° C to 600 ° C which is the deposition temperature. Heating time is two hours, was kept flowing 700 _{SC CM} during this period hydrogen 3% argon 97% argon hydrogen gas mixture. At this time, the equilibrium pressure in the reaction chamber was 139 _mtorr .

Immediately after the temperature rising period, the purity is 99.999.
% Or more silane was flown into the 11.25 _SCCM reaction chamber to deposit the silicon film. The equilibrium pressure in the reaction chamber during the deposition of the silicon film was 7.70 _mtorr . The silicon film was deposited by continuously flowing silane into the reaction chamber for 20 minutes and 39 seconds.

Immediately after the deposition of the silicon film, the heater set temperature was changed from 600 ° C. to 400 ° C., and the reaction chamber was evacuated for 4 minutes. Mass flow for 3 minutes after evacuation
The inside of the controller, etc. was replaced with nitrogen, and during this period, 700 _SCCM of nitrogen having a purity of 99.99% or more was continuously flown into the reaction chamber,
The equilibrium pressure in the reaction chamber was maintained at about 140 _mtorr . After that, the reaction chamber was returned to atmospheric pressure by nitrogen having a purity of 99.99% or more, and the substrate was taken out directly. The substrate temperature at this time was about 530 ° C. The film thickness of the silicon film obtained in Example 2 was 262 Å.

TFTs were manufactured through the same steps as in Example 1 except for the above steps, and the transistor characteristics were measured. As a result, effective electron transfer determined from the saturation current region at the source / drain voltage V _ds = 4V. The degree μo and the trap density Nt are μo = 5.4 ± 0.09 cm ² / v · sec and Nt =
It was (7.9 ± 0.27) × 10 ¹¹ l / cm ² . Also, with a TFT of L = 10 μm and W = 100 μm, V _ds = 4V,
The on-current when the transistor is turned on at V _gs = 10 V is I _ON = 8.89 ± 0.96 μA, V _ds = 4 V, V _gs =
The OFF current when the transistor is turned off at 0V is I _OFF
= 1.16 ± 0.13 pA.

Throughout Examples 1 to 3, 5 transistors on each substrate were measured, and their average and standard deviation were X ± O.
It has been described in the form of n. Example 1 which is an example of the present invention
Although the mobilities agree with each other within an error range from Example 3 performed for comparison, the trap density is obviously reduced when the temperature is lowered in a reducing atmosphere, and as a result, the on-current is increased and at the same time the off-state is turned off. It became possible to reduce the current. This is because lowering the temperature in a reducing atmosphere suppresses hydrogen desorption from the deposited silicon film and minimizes the generation of unpaired electron pairs that cause trap density. This is a demonstration of the effectiveness of the present invention.

(Embodiment 4) FIG. 3 is a diagram showing an outline of a low pressure chemical vapor deposition apparatus (LPCVD apparatus) which is an embodiment of the present invention. The present invention is not limited to the LPCVD apparatus shown in FIG. It is not limited. For example, although the present invention uses the vertical hot wall type as an embodiment, it is effective for all types of LPCVD apparatuses such as a horizontal CVD apparatus and a cold wall type.

The LPCVD apparatus according to the present invention mainly comprises a reaction chamber 301 and a preliminary chamber 302 adjacent to the reaction chamber, and a gate is provided between the reaction chamber 301 and the preliminary chamber 302.
A valve 303 is provided. In the state shown in FIG. 3, the gate valve 303 is open and the substrate 304 is in the reaction chamber. When the gate valve 303 is open, the reaction chamber 301 is sealed by the loader table 305. A gas inlet 306 is provided in the spare chamber 302, and hydrogen or a mixed gas of hydrogen and an inert gas such as helium, nitrogen, or argon, or a single gas of these inert gases is introduced into the spare chamber 302. You can Reserve room 3
The exhaust of 02 is performed by the vacuum pump 307. The vacuum pump can be a rotary pump, a mechanical booster pump, a turbo molecular pump, a dry pump, etc., and is composed of a combination of these. A gate valve 308 is provided between the vacuum pump 307 and the auxiliary chamber 302.
Is provided.

The operation procedure of the LPCVD apparatus according to the present invention and the great effects obtained when a silicon film is deposited by the LPCVD apparatus according to the present invention will be described below.

First, a loader platform 305 descending into a spare chamber 302 opened to the atmosphere and a boat 30 mounted thereon.
The substrate 304 is placed on the substrate 9. In this state, the gate valve 303 is closed and the inside of the reaction chamber 301 is maintained in vacuum. When the spare chamber 302 is open to the atmosphere, the gate valve 303 is closed and the reaction chamber 301 is closed.
It prevents the inside from being polluted from the atmosphere such as oxygen, water, and dust. At this time, the vacuum evacuation system 310 for evacuating the reaction chamber 301 is in operation, and a mixed gas of hydrogen / inert gas containing about 3% hydrogen is flown into the reaction chamber 301.
It is preferable to maintain a reducing atmosphere inside. At this time, the inside of the reaction chamber is maintained at a pressure of about 0.1 to 1 forr, and the temperature of the reaction chamber is kept at about 400 ° C. or higher. At this time, the hydrogen concentration in the mixed gas of hydrogen and inert gas flowing in the reaction chamber can be arbitrarily set between 0% and 100%. However, for safety reasons, the concentration is lower than the lower explosive limit, and a strong concentration is preferable.

After installing the substrate, close the door of the spare room and
The valve 308 is opened, and the vacuum chamber 307 is evacuated by the vacuum pump 307. After the evacuation of the preliminary chamber is completed, a mixed gas of hydrogen and an inert gas is introduced into the preliminary chamber through the gas introduction pipe 306 to the preliminary chamber, and the preliminary chamber is evacuated to a reducing atmosphere. At this time, the hydrogen concentration is preferably as high as possible without exceeding the lower limit of explosion. It is desirable that the hydrogen concentration, the inert gas species, and the like are the same as those of the above-mentioned mixed gas flowing in the reaction chamber, but there is no need to be limited thereto. The pressure in the spare chamber is preferably equal to or slightly lower than the pressure in the reaction chamber. Next, the gate valve 303 is opened, and the substrate 304 is inserted into the reaction chamber 301. (State of FIG. 3) After that, a vacuum drawing leak inspection is performed, and the temperature rising period starts. If the reaction chamber is constantly kept at the deposition temperature, it may take about 30 minutes for the substrate to reach thermal equilibrium at the deposition temperature.
Considering degassing from the substrate 304 and the boat 309, about one hour is preferable. During this heating period, the reaction chamber is kept in a reducing atmosphere as described in detail in Example 1.

Immediately after the temperature rise, a predetermined amount of source gas and, if necessary, a diluent gas are introduced into the reaction chamber to deposit a silicon film. Immediately after the deposition of the silicon film, the reaction chamber is evacuated for about 4 minutes to prevent unreacted source gas from remaining in the reaction chamber. Subsequently, nitrogen replacement in the mass flow controller is performed for 3 minutes. During this time, an appropriate amount of hydrogen / inert gas mixed gas is continuously flown into the reaction chamber and the spare chamber to keep both chambers in a reducing atmosphere vacuum. At this time, the evacuation of the auxiliary chamber is performed by the vacuum pump 307, and the gate valve 308 is open.

In the fourth embodiment, the hydrogen concentration at this time is set to 3%, which does not exceed the lower limit of explosion of hydrogen.
It doesn't matter. However, if the concentration is high, it is necessary to make the hydrogen concentration in the auxiliary chamber below the lower explosion limit before opening the auxiliary chamber to the atmosphere.

The pressure in both chambers during this period is preferably low so that the gas heat capacity in both chambers is as small as possible, but at the same time, considering the volumes of the reaction chamber and the spare chamber, hydrogen and inert gas of several hundreds _SCCM or more are required. It is necessary to keep the gas mixture gas flowing, and it is determined by the balance between these two.

In the fourth embodiment, as in the first embodiment, 700% hydrogen-argon mixed gas containing 3% hydrogen and 97% hydrogen is introduced into both chambers.
_{The SCCM was} kept flowing, and the automatic pressure regulators attached to both chambers were activated to maintain the pressure in both chambers at approximately 140 _mtorr . Reaction chamber 30
In No. 1, the gas inlet is installed in the lower part of the reaction chamber and exhaust is performed from the upper part.
Is provided in the upper part of the spare chamber and is exhausted through the gate valve 308 in the lower part of the spare chamber, but the present invention is not limited to this position combination of the gas inlet and the exhaust.

After the nitrogen replacement is completed, the gate valve 303 is opened, and the loader base 305 and the boat 3 mounted on the loader base 305.
The substrate 304 on the substrate 09 is placed in a preliminary chamber 302 in a reducing atmosphere vacuum.
Take it down. At this time, the wall of the reaction chamber 301 and the substrate 304 have reached thermal equilibrium at the deposition temperature or a temperature slightly lower than the deposition temperature, while the preliminary chamber is equilibrated at room temperature. Therefore, when the pressure in both chambers is high and the speed at which the substrate is lowered from the reaction chamber to the preparatory chamber is high, the thermal shock applied to the substrate becomes large, and when glass is usually used as the substrate, the substrate is broken. When both chambers are at atmospheric pressure, it takes about 45 minutes to move up and down between the reaction chamber 301 and the auxiliary chamber 302 in order to prevent the glass substrate from being cracked by thermal shock. Can be shortened to 40 minutes or less. In this embodiment, the pressure in both chambers is 140
_The substrate was raised and lowered with a _mtorr in 35 minutes.

After the substrate is lowered into the preliminary chamber 302, the gate valve 303 between the reaction chamber 301 and the preliminary chamber 302 is closed, and the hydrogen-inert gas mixed gas containing hydrogen in the preliminary chamber 302 at a concentration below the explosion limit. And let the spare chamber return to atmospheric pressure.
In Example 4, as in Example 1, hydrogen 3%, argon 9
The temperature of the substrate was lowered by returning the preliminary chamber to atmospheric pressure with 7% hydrogen / argon mixed gas. In the present Example 4, since the preliminary chamber was in thermal equilibrium at room temperature, the temperature of the substrate was reduced to about 300 ° C. after the temperature rising period of 10 minutes under the reducing atmosphere atmospheric pressure. During the temperature raising period, about 1 _SLM of hydrogen / argon mixed gas was being flown into the preparatory chamber 302. After that, the preliminary chamber is opened to the atmosphere and the substrate is taken out.

As described above in the fourth embodiment, by using the LPCVD apparatus of the present invention, the good-quality silicon film shown in the first embodiment can be simply deposited without impairing the working efficiency.

That is, in the present invention, since the inside of the reaction furnace is always maintained in a reducing atmosphere, the inside of the reaction furnace is not contaminated by oxygen, moisture, etc., and degassing and thermal equilibrium to the deposition temperature are obtained. The temperature raising period can be shortened by about 1 hour. Also, by keeping the preliminary chamber, which is in thermal equilibrium with the room temperature after deposition, in a reducing atmosphere and lowering the temperature of the substrate in this preliminary chamber, the temperature lowering period can be shortened by one hour or more, and the temperature of the substrate is about 300 ° C. The probability of hydrogen desorption from the silicon film can be further reduced because it is lowered to the maximum. Also, by raising and lowering the substrate between the preliminary chamber and the reaction chamber in a vacuum, the raising and lowering speed can be increased, and the time for loading and unloading the substrate can be shortened by about 20 minutes. As a result, as compared with the case of forming a high-quality silicon film described in the present invention by the conventional LPCVD apparatus as shown in Example 1, the LPCVD apparatus according to the present invention described in Example 4 is used. When forming a high-quality silicon film, the working time per batch can be shortened to about two and a half hours, and the working efficiency is greatly improved.

In addition, in the LPCVD apparatus according to the present invention described in the fourth embodiment, since the reaction chamber is not exposed to the atmosphere, the variation in the deposition rate between lots is small, and accordingly, the lot-to-lot variations are correspondingly. The film quality, and eventually the stabilization of the TFT, was also realized.

[0050]

According to the present invention, in a thin film semiconductor device in which a silicon film serving as an active layer is formed on a substrate, the temperature of the substrate is lowered by keeping the atmosphere containing the substrate under a reducing atmosphere, thereby reducing the silicon temperature. It is possible to suppress the release of hydrogen atoms from the film, reduce the generation of unpaired electron pairs, and manufacture a good thin film semiconductor device.

[0051]

As described above, according to the present invention, a good thin film semiconductor device can be manufactured with good work efficiency and in a stable manner, and high performance and low cost of LSI integration and liquid crystal display using TFTs can be achieved. It has a great effect of bringing about.

[Brief description of drawings]

1A to 1E are cross-sectional views of elements in respective steps of manufacturing a silicon thin film semiconductor device showing an embodiment of the present invention.

FIG. 2 is a diagram showing an outline of a conventional LPCVD apparatus used in an example of the present invention.

FIG. 3 is a diagram showing an outline of an LPCVD apparatus according to the present invention.

[Explanation of symbols]

101 substrate 102 Base protection film 103 source / drain region 104 Silicon film 105 channel silicon film 106 gate insulating film 107 gate electrode 108 Interlayer insulating film 109 Source / drain extraction electrode 201 Reaction chamber 202 substrate 203 heater 204 rotary pump 205 mechanical booster pump 301 Reaction chamber 302 spare room 303 Gate valve 304 substrate 305 loader stand 306 gas inlet 307 vacuum pump 308 Gate valve 309 boat 310 Vacuum exhaust system

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 29/786 H01L 21/336 H01L 21/205 C23C 16/24

Claims (3)

(57) [Claims] 1. A method of manufacturing a semiconductor device having a silicon thin film, wherein a substrate is inserted into a reaction chamber, the temperature is increased to a deposition temperature, and after reaching the deposition temperature, a silicon film is deposited on the substrate under reduced pressure chemical vapor deposition. Method (LPCVD method), and lowering the temperature from the deposition temperature to a predetermined temperature in a hydrogen atmosphere, the method for manufacturing a semiconductor device. 2. A method of manufacturing a semiconductor device having a silicon thin film, wherein a substrate is inserted into a reaction chamber, the temperature is raised to a deposition temperature, and after reaching the deposition temperature, a silicon film is deposited on the substrate under reduced pressure chemical vapor deposition. Method (LPCVD method), and lowering the temperature of the substrate from the deposition temperature to a predetermined temperature in a mixed atmosphere of an inert gas and hydrogen, a method of manufacturing a semiconductor device. 3. A method for manufacturing a semiconductor device having a silicon thin film, wherein a substrate is inserted into a reaction chamber, the temperature is raised to a deposition temperature, and after reaching the deposition temperature, a silicon film is deposited on the substrate under reduced pressure chemical vapor deposition. Method (LPCVD method), the substrate is returned from the deposition pressure to the atmospheric pressure in a reducing atmosphere, and the temperature is lowered from the deposition temperature to a predetermined temperature in the reducing atmosphere. Device manufacturing method.