JPH06326030A - Method and apparatus for manufacture semiconductor - Google Patents

Abstract

PURPOSE:To produce a semiconductor device with good film quality by optimizing the conditions of film deposition and hydrogen plasma treatments. CONSTITUTION:A method of semiconductor manufacture comprises the steps of depositing a film of an amorphous silicon alloy on a substrate, and treating the alloy film with a plasma. The two steps are repeatedly carried out while the deposition and the plasma treatment are independently controlled.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor manufacturing method and a semiconductor manufacturing apparatus. In particular, the present invention relates to a semiconductor manufacturing method and an apparatus for manufacturing the amorphous silicon alloy.

[0002]

2. Description of the Related Art In recent years, the development of semiconductor devices using amorphous silicon alloy has been active. In particular, the development of solar cells that can be manufactured in a large area and at low cost, the development of thin film transistors for liquid crystal displays, and the development of solid-state image pickup devices for facsimiles that can be made lightweight and small are active. Conventionally, as a method for producing amorphous silicon alloys used in these semiconductor devices, particularly hydrogenated amorphous silicon, RF plasma CVD method or microwave plasma CVD method using silane SiH ₄ or disilane Si ₂ H ₆ as a film forming gas,
Alternatively, a reactive sputtering method in which a Si target is sputtered in Ar plasma in the presence of hydrogen gas has been used. Experimentally, other than this, photo CVD method, ECR
There are reports of a CVD method, a vacuum vapor deposition method of Si in the presence of hydrogen atoms, etc., and there are also successful examples of a thermal CVD method using Si ₂ H ₆ or the like. The hydrogenated amorphous silicon film obtained by these methods is a film containing almost 10% or more hydrogen.

Plasma C is the most popular method for producing such a hydrogenated amorphous silicon film.
In the VD method, SiH ₄ gas and Si ₂ H ₆ gas are used in most cases, and diluted with hydrogen gas as necessary to obtain 13.56 MH
Plasma is generated at a high frequency of z or 2.54 GHz, the film-forming gas is decomposed by the plasma to generate reactive active species, and a hydrogenated amorphous silicon film is deposited on the substrate. If a deposition gas is mixed with a doping gas such as PH ₃ , B ₂ H ₆ , or BF ₃ , an n-type or p-type hydrogenated amorphous silicon film can be formed.
These films can be used to make such amorphous silicon devices.

However, these films have a problem that the photodegradation (so-called Staebler-Wronski effect) is large, and in order to solve these problems, a method of repeating hydrogen plasma treatment (for example, Proceedings of the Joint Lectures of the Association for Applied Physics, 1990). Spring 31a-2D-8, 31
a-2D-11, Autumn 1988 5p-2F-1, etc.)
Is proposed.

According to this film forming method, after the hydrogenated amorphous silicon film is deposited for the time t _D , the deposited film is subjected to hydrogen plasma discharge for the time t _{A to} generate atomic hydrogen generated at this time. The film is formed by repeating a set of steps of exposing (hereinafter, hydrogen plasma treatment). For this reason, a method is adopted in which the accumulation gas is turned ON / OFF and this process is repeated.

During t _A , the deposited film surface is exposed to atomic hydrogen. The mechanism of the phenomenon occurring on the surface during this period is not necessarily clear, but atomic hydrogen diffuses into the deposited film or on the deposited surface to some extent, and while extracting excess hydrogen, the Si network is recombined (structural relaxation). Is believed to be happening.

First, the effect of exposure to atomic hydrogen will be described.

FIG. 7 shows the dependence of the hydrogen concentration in the film on t _A. a
Shows the case where the film thickness in each cycle is 50Å, and b shows the case where the film thickness is 100Å. c is the case where the atomic hydrogen concentration is increased compared to a (the RF power is increased in this example). It can be seen that if the film thickness at each step is 100 Å or more, structural relaxation does not proceed no matter how much atomic hydrogen exposure is performed. It can be seen that the larger the atomic hydrogen concentration, the shorter the time required to reach the same hydrogen concentration in the film. The film thickness deposited during t _D must be 10 Å or more and 100 Å or less, preferably 50 Å or less.

FIG. 8 shows the relationship between the deposited film thickness during t _D and the hydrogen concentration in the film. It is understood that the hydrogen concentration in the film can be controlled by controlling the atomic hydrogen exposure time or the deposition time. The thickness of the hydrogenated amorphous silicon film deposited during t _D is preferably 2 atomic layers or more, and practically 10 Å or more. This is because if the deposited film has only one atomic layer, the amorphous structure cannot be maintained stably, and crystallization proceeds due to exposure to atomic hydrogen. It is considered that this is caused by excessive abstraction of hydrogen by atomic hydrogen. If the deposited film is thin and hydrogen is extracted too much, structural relaxation will occur extremely, and even crystallization will occur. In order to prevent excessive relaxation due to exposure to atomic hydrogen and promote relaxation with good controllability, it is necessary to deposit a hydrogenated amorphous silicon film of 10 Å or more.

FIG. 9 shows the relationship between the hydrogen concentration in the film and the optical band gap. The hydrogen concentration in the film depends on the atomic hydrogen concentration in the hydrogen plasma.

In this way, hydrogen in the film is controlled during deposition,
That is, by reducing the hydrogen concentration in the film while causing structural relaxation, it is possible to reduce weak bonds in the film, which is considered to be caused by this, and suppress photodegradation due to this.

FIG. 10 shows a manufacturing apparatus conventionally devised to realize such a manufacturing method. In FIG. 10, 300 is a reaction chamber, 301 is a substrate, 302 is an anode electrode, 303 is a cathode electrode, 304 is a substrate heating heater, and 305 is a grounding terminal. 306 is a matching box, and 307 is a 13.56 MHz RF power supply. Reference numeral 308 is a gate valve for pressure control. 309 is a turbo molecular pump, and 310 is a rotary pump. 311 is a deposition gas line, 312 is a hydrogen gas line, and 313 is a waste gas line. 314, 3
Reference numeral 15 is an air valve. These air valves are connected to and controlled by a control sequencer. By switching the air valves 314 and 315, the film forming gas is turned on and off to the chamber. Both the hydrogenated amorphous silicon film deposition and the atomic hydrogen exposure can be easily switched only by controlling ON / OFF of the flow of only the silane gas SiH ₄ which is the deposition gas. FIG. 11 shows the operations during deposition and hydrogen plasma treatment. The flow rates of hydrogen gas and argon gas are constant, and the RF power is also constant throughout film formation and hydrogen plasma treatment.

[0013]

However, when the deposition gas and the hydrogen plasma treatment are alternately performed by turning on and off only the deposition gas as in this conventional example, there are the following problems. Optimum conditions do not always match during deposition and hydrogen plasma processing, and even if we tried to match the gas flow rate, gas ratio, RF power, and pressure, we were unable to do so due to equipment restrictions. For example, as shown in FIG. 11, silane gas SiH ₄ : H
₂ : Ar = 1: 1: 1, but when the silane gas is cut off here, the pressure in the chamber becomes only the partial pressure of hydrogen gas and argon gas, and inevitably becomes half the initial value. In order to increase the amount of atomic hydrogen here, if we try to bring it to an optimal pressure, and if we try to bring it to a higher pressure than this, at present we have to make it hydrogen rich under the initial conditions by changing the flow rate ratio. . However, at this time, the conditions for the deposition are also rich in hydrogen, and as the deposition conditions, there is a problem that microcrystallization is likely to occur. Regarding RF power as well, high power is preferable during hydrogen plasma treatment, but high power during deposition causes problems such as generation of polysilane and easy crystallization. Therefore, the conventional condition is a compromise condition between deposit and hydrogen plasma, and deposit and hydrogen plasma treatment are performed with constant power.

[0014]

[Means for Solving the Problems] In order to solve the above problems,
In a semiconductor manufacturing method and a semiconductor manufacturing apparatus for depositing while alternately repeating a step of depositing an amorphous silicon alloy film on a substrate and a step of subjecting this amorphous silicon alloy film to plasma treatment, during deposition and plasma treatment By providing a semiconductor manufacturing method and a semiconductor manufacturing apparatus characterized by independently controlling process conditions, the above problems are solved and a film having excellent characteristics is formed.

[0015]

In the semiconductor manufacturing apparatus according to the above method, the process conditions during the deposition and the plasma processing can be optimally set. This made it possible to obtain an optimized film.

[0016]

EXAMPLE 1 FIG. 1 shows a semiconductor manufacturing apparatus according to the present invention.

In FIG. 1, 100 is a reaction chamber, 1
Reference numeral 01 is a substrate, 102 is an anode electrode, 103 is a cathode electrode, 104 is a heater for heating the substrate, and 105 is a grounding terminal. 106 is a matching box, 107 is 1
It is an RF power supply of 3.56 MHz. Reference numeral 108 is a gate valve for pressure control. Reference numeral 109 is a turbo molecular pump, and 110 is a rotary pump. 111 is a waste gas line, 119 is a film forming gas line, 120 is a hydrogen plasma processing gas line, 115, 116, 117, 1
18 is an air valve. These air valves are connected to the control computer. 112 is a turbo molecular pump, and 113 is a rotary pump. 114
Is silane gas Si, which is a computer deposition gas for control
Both the hydrogenated amorphous silicon film deposition and the atomic hydrogen exposure can be easily switched only by controlling ON / OFF of H ₄ and hydrogen gas. 121 and 123 are hydrogen gas line valves, 124 and 126 are silane gas line valves, 127 and 129 are hydrogen gas line valves,
130 and 132 are valves of the argon gas line, 13
Reference numerals 3 and 135 are valves of the phosphine gas line. 1
Reference numerals 36 and 138 are diborane gas line valves. 1
Reference numerals 22, 125, 128, 131, 134 and 137 are mass flow controllers for each line.

The operation and operation of the manufacturing apparatus according to the present invention will be described. Generally, as the process conditions during film deposition, if the partial pressure of hydrogen gas increases, microcrystallization easily occurs, so it is better to reduce the partial pressure of hydrogen gas. In that case, if the silane gas partial pressure decreases, the deposition rate also decreases accordingly. In order to prevent this, the flow rate ratio of hydrogen should be kept constant and the overall pressure should be raised, but this will facilitate the production of polysilane. Therefore, in the present embodiment, taking the above into consideration, silane gas 10 sccm and hydrogen gas 1
Flowing at 0 sccm, the total pressure was set at 0.1 Torr. Regarding RF power, it is necessary to avoid RF power because film formation at a high power density also facilitates microcrystallization and polysilane formation. However, it has been found that the greater the RF power, the greater the effect during the hydrogen plasma treatment. 7c is RF
The t _A dependence of the hydrogen concentration in the film is shown when only the power is changed and the other conditions are kept constant. It can be seen that under high RF power conditions, a shorter t _A is required to achieve the same in-film hydrogen. Therefore, according to the method of the present invention, the RF power at the time of thrusting and hydrogen plasma can be independently controlled. Therefore, here, 5 mW / cm ² was used for thrusting and 20 mW / cm ² was used for hydrogen plasma treatment. By doing so, the hydrogen plasma treatment time can be shortened, and the deposition time can be shortened as a whole. This makes it possible to improve the film quality and reduce the cost of accumulation. As a condition for the hydrogen plasma treatment, it has been known that the atomic hydrogen can be increased by appropriately mixing the argon gas. Therefore, the mixing ratio Ar / H ₂ = 1.
As H / 1, 20 sccm of H ₂ gas and 20 sccm of argon gas are caused to flow through the hydrogen gas line. Total pressure is 0.1T
orr.

As can be seen from FIG. 3, a silane gas line is used for the deposition, and the deposition is performed with an RF power of 5 mW / cm ² . A hydrogen gas line is used during hydrogen plasma processing,
Processing is performed with RF power of 20 mW / cm ² . All of these switching operations are performed by the control computer. The flow rate and pressure of silane gas, hydrogen gas, and argon gas, and RF power can be changed as appropriate. The target hydrogen concentration in the film under the above conditions was 4%. t _D = 30Å, t _A = 5se
When the film was formed at c, the deposition rate was 1.5Å / sec. When the hydrogen concentration in the film is similar to the conventional one, the deposition rate was 1.0 Å / sec, which is an improvement of 1.5 times.

Next, a case will be described below in which an intrinsic (i-type) hydrogenated amorphous silicon film is formed by the semiconductor manufacturing apparatus of the present invention, and a solar cell using this i-type film as a photoelectric conversion film is formed. The structure of the solar cell is shown in FIG.

A metal film such as Al is formed on the glass substrate 701.
After the lower electrode 702 is formed by using
Mounted on the anode electrode inside, pumps 109, 110
Exhausted by 10^-6Torr. Valve 121,
Open 123, 124, 126, 133, 135 to Si
H_Four 30 sccm gas, H₂ 30 sccm gas flow
And H₂ PH diluted to 1% with gas₃ Gas 30 scc
m flowed. Substrate with chamber pressure of 0.5 Torr
The temperature was set to 300 ° C. and kept for 1 hour. 50mW /
cm² RF power is turned on and discharged for 7 minutes⁺ Type hydrogenation
A 400 Å microcrystal silicon layer was deposited. Moth
After stopping the gas supply, ^-6Torr or later
Exhausted down.

Next, an i-type hydrogenated amorphous silicon film was deposited by the film forming method according to the present invention. Air valve 11
After closing 6, 118 and opening 115, 117, valves 121, 123, 124, 126, 127, 129 were opened, SiH ₄ gas 10 sccm, hydrogen gas 20 scc.
m to the gas stack line 119, hydrogen gas 20 sccm,
Argon gas of 20 sccm was passed through the hydrogen gas line 120. The chamber pressure was maintained at 0.1 Torr, the substrate temperature was set at 300 ° C., and the temperature was maintained for 1 hour. The switching of the air valve and the RF power supply are all synchronized, and a control computer runs a control program and controls it. RF power of 5 mW / cm ² during film formation and RF power of 20 during hydrogen plasma treatment
Discharge was started at mW / cm ² . Casting time t in this example
The film thickness _D was 30Å. t _A was set to 5 sec. The target hydrogen concentration in the film was 4%. The total number of steps was 200, and the total thickness of the i-type layer was 6000Å. The sequence of thrusting is depicted in FIG. Argon gas was not added at the time of deposition. At the time of hydrogen plasma treatment, the discharge becomes unstable only with hydrogen, for example, at the time of switching, so argon gas was introduced to stabilize the discharge. Further, when argon gas is mixed appropriately (in the case of this embodiment, Ar / H ₂ = 1
/ 1. ) As atomic hydrogen increases, we also aimed at its effect. Further, the RF power was set to a low power at the time of deposition and a high power setting at the time of hydrogen plasma.

Next, a p ⁺ -type hydrogenated microcrystalline silicon film was deposited. The degree of vacuum in the chamber is 10 ^-6 T
Evacuate below orr, valves 121, 123, 124,
126, 127, 129, 136, 138 are opened and Si
1 sccm of H ₄ gas and B ₂ H diluted to 1% with H ₂ gas
Flowing ₆ sccm 1 sccm and H ₂ gas 300 sccm, keeping the chamber pressure at 0.5 Torr and the substrate temperature at 20
After changing to 0 ° C., the temperature was maintained for 1 hour. Then RF power is 5
0 mW / cm ² was charged and plasma discharge was performed for 5 minutes to deposit a p ⁺ type film at 500 Å.

Finally, the upper electrode is covered with a transparent conductive film (ITO).
The film was formed at 700Å.

Since the pin type solar cell thus formed can be formed under optimized conditions as compared with the film formed by the conventional method, the deterioration can be improved. This is shown in FIG. b is the conventional deterioration state, and a is the deterioration state of the device of this embodiment. It can be seen that the optimization is clearly improved by the optimization of the conditions. Furthermore, it was possible to reduce the creation time.

Although only the hydrogenated amorphous silicon film has been described in this embodiment, carbon,
Even if a hydrogenated amorphous silicon alloy containing an element such as nitrogen or germanium is prepared, the same effect can be obtained. Further, not only the hydrogen plasma treatment but also the plasma treatment using a rare gas such as Ar, He, Xe, Ne, or the mixture treatment of these is adopted as the plasma treatment, and the effect of the present invention can be obtained.

In this embodiment, atomic hydrogen is generated only by RF discharge, but microwave discharge plasma is used,
It is also possible to generate atomic hydrogen more efficiently. In this case, a microwave plasma generation tube is attached between the chamber of the hydrogen gas line and the valve 117. Here, atomic hydrogen is generated and introduced into the chamber. Furthermore, the microwave power and RF power are controlled by a computer. For example, the microwave power is reduced during film formation to suppress generation of atomic hydrogen more than necessary, and the microwave power is increased during hydrogen plasma treatment to obtain sufficient atomic hydrogen.

Embodiment 2 In the above embodiment, the air valve is controlled to be opened and closed, but in this embodiment, the process conditions are controlled by controlling the mass flow controller and the air valve. FIG. 2 shows the manufacturing apparatus of this embodiment.

In FIG. 2, 200 is a reaction chamber, 2 is
Reference numeral 01 is a substrate, 202 is an anode electrode, 203 is a cathode electrode, 204 is a substrate heating heater, and 205 is a grounding terminal. 206 is a matching box, 207 is 1
It is an RF power supply of 3.56 MHz. Reference numeral 208 is a gate valve for pressure control. 209 is a turbo molecular pump and 210 is a rotary pump. Reference numeral 211 is a film-forming gas introduction line, and 212 is a control computer. Reference numerals 213, 216 and 219 are air valves.
These air valves are connected to a control computer and automatically controlled. Reference numeral 215 is a silane gas line valve, 218 is a hydrogen gas line valve, 221 is an argon gas line valve, and 222 and 224 are phosphine gas line valves. 225 and 227 are valves of the diborane gas line. 214, 217, 220, 2
23 and 226 are mass flow controllers for each line. Of these, 214, 217, and 219 can automatically control the flow rate, and the control is performed by the control computer.

The principle of operation according to the present embodiment is that, instead of opening and closing the air valve, the silane gas, hydrogen gas, and argon gas are commonly introduced, and the mass flow controller for each gas is controlled to adjust the process conditions to form a film. And hydrogen plasma treatment. With this type, unlike the first embodiment, it is not necessary to prepare a line for exhausting gas and an exhaust system, and the equipment is simplified. Therefore, the cost on the device can be reduced. Further, since the flow rate can be controlled, the adjustment range of process conditions is widened. FIG. 4 shows an example of the operation. Silane 10 sccm, hydrogen gas 10 sccm when forming each film, hydrogen plasma 20 sccm
Shed. Argon is supplied at 20 sccm only when hydrogen plasma is used. These controls are programmed in advance, and these may be run on a computer during film formation. ON / OFF of mass flow controller and flow rate control, RF
Power can be controlled, and optimum conditions can be set.

When a solar cell was prepared and evaluated by the apparatus according to the present invention, good characteristics were obtained.

Although only the hydrogenated amorphous silicon film has been described in this embodiment, carbon, carbon
Even if a hydrogenated amorphous silicon alloy containing an element such as nitrogen or germanium is prepared, the same effect can be obtained. Also in this embodiment, not only the plasma treatment but also the plasma treatment of a rare gas such as Ar, Ne, He, Xe, or the mixture treatment thereof can be used to obtain the effects of the present invention.

In this embodiment, atomic hydrogen is generated only by RF discharge, but microwave discharge plasma is used,
It is also possible to generate atomic hydrogen more efficiently. In this case, a microwave plasma generation tube is attached between the chamber on the gas line 211 and the valve group. Here, atomic hydrogen is generated and introduced into the chamber. Furthermore, the microwave power and RF power are controlled by a computer. For example, microwave power is stopped during film formation so that silane gas is not decomposed in the plasma generation tube, and microwave power is supplied during hydrogen plasma treatment so that sufficient atomic hydrogen is obtained. At the same time, the RF power may be set as in the above embodiment.

[0034]

As described above, the semiconductor manufacturing method in which the step of depositing the hydrogenated amorphous silicon alloy film on the substrate and the step of subjecting the amorphous silicon alloy film to the plasma treatment are alternately repeated Also, in the semiconductor manufacturing apparatus, by providing a semiconductor manufacturing apparatus and a manufacturing method that independently control the process conditions at the time of deposition and plasma processing, the conditions of film formation and deposition plasma processing are optimized, and the film quality is improved. It can be measured.

[Brief description of drawings]

FIG. 1 is a diagram showing a semiconductor manufacturing apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a semiconductor manufacturing apparatus according to a second embodiment of the present invention.

FIG. 3 is a diagram showing an operation of the semiconductor manufacturing apparatus according to the first embodiment of the present invention.

FIG. 4 is a diagram showing an operation of the semiconductor manufacturing apparatus according to the second embodiment of the present invention.

FIG. 5 is a diagram showing the structure of a solar cell prepared by the method according to the present invention.

FIG. 6 is a diagram showing light deterioration characteristics.

FIG. 7 is a diagram showing t _A dependence of hydrogen concentration in the film.

FIG. 8 is a diagram showing the relationship between the in-film hydrogen concentration and the deposited film thickness at each step.

FIG. 9 is a diagram showing the relationship between the concentration in the film and the optical wide band gap.

FIG. 10 is a diagram showing a conventional semiconductor manufacturing apparatus.

FIG. 11 is a diagram showing an operation of a conventional semiconductor manufacturing apparatus.

[Explanation of symbols]

100, 200, 300 Chamber 101, 201, 301 Substrate 102, 202, 302 Anode electrode 103, 203, 303 Cathode electrode 104, 204, 304 Overheating heater 105, 205, 305 Grounding terminal 106, 206, 306 Matching box 107 , 207, 307 RF power source 108, 208, 308 Gate valve 109, 112, 209, 309, 316 Turbo molecular pump 110, 113, 210, 310, 317 Rotary pump 111, 313 Discard gas line 119, 211, 311 Film forming gas Lines 115, 116, 117, 118, 213 216, 219, 314, 315 Air valves 114, 212 Control computers 121, 123, 124, 126, 127 129, 130, 132 133,135 136,138,215,218,221 224,227,318,320,321 323,324,326,327,329 329 330,332 Valve 122,125,128,131,134 137,214,217,220 , 223 226, 319, 322, 325, 328 331 Mass flow controller 701 Glass substrate 702 Lower electrode 703 n ⁺ type film 704 i type film 705 p ⁺ type film 706 Transparent electrode 707 Upper electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masato Yamanobe 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (4)

[Claims] 1. A method for manufacturing a semiconductor, wherein film deposition is performed by alternately repeating a step of depositing a hydrogenated amorphous silicon alloy film on a substrate and a step of exposing the hydrogenated amorphous silicon alloy film to atomic hydrogen. A method for manufacturing a semiconductor, characterized in that the process conditions in the step of depositing a film and the process conditions in the step of performing plasma treatment are controlled independently. 2. The method of manufacturing a semiconductor according to claim 1, wherein the plasma treatment is a treatment of exposing atomic hydrogen generated by at least hydrogen plasma discharge to a film surface. 3. A semiconductor manufacturing method in which a film is deposited by alternately repeating a step of depositing a hydrogenated amorphous silicon alloy film on a substrate and a step of subjecting the hydrogenated amorphous silicon alloy film to a plasma treatment. A semiconductor manufacturing apparatus characterized by having a mechanism for independently controlling the process conditions of the depositing step and the process conditions of the plasma applying step. 4. The semiconductor manufacturing apparatus according to claim 3, wherein the plasma treatment is a treatment in which atomic hydrogen generated by at least hydrogen plasma discharge is exposed to the film surface.