JPH0548130A - Semiconductor device and its manufacture - Google Patents

Abstract

PURPOSE:To manufacture such a semiconductor device that is free from the deterioration of optical sensitivity caused by misfitting of a grating at the interface of a heterojunction and provided with a high-quality film having no defect by providing a taperlike band profile and making the band coupling continuous at the boundaries between a p-type layer and i-type layer and between the i-type layer and an n-type layer. CONSTITUTION:In this non-single-crystal silicon semiconductor device having a pin type structure, a p-type layer 105, i-type layer 104, and n-type layer 103 are formed so that they can have a taper-like in-film hydrogen-concentration profile and taper-like band profile. In addition, the band coupling is made continuous at the boundaries between the layers 105 and 104 and between the layers 104 and 103. The continuous band coupling can be obtained by forming the layers 105, 104, and 103 while the in-film hydrogen concentration is controlled so that the optical band gaps between each of the layers can be formed under a taper-like condition. Therefore, the occurrence of an band offset which is produced when the layers are deposited in the conventional method can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device and a manufacturing method thereof, and more particularly to a semiconductor device using non-single crystal silicon as a semiconductor layer and a manufacturing method thereof.

[0002]

2. Description of the Related Art In recent years, semiconductor devices using non-single crystal silicon (hydrogenated amorphous silicon, etc.) have been actively developed. Especially for the development of solar cells that can be manufactured in a large area and at low cost, and p for solid-state imaging devices for facsimiles that can be made lightweight and compact.
In-type photodiodes are being actively developed.

For example, as a method of depositing hydrogenated amorphous silicon (hereinafter abbreviated as a-Si: H) used in these semiconductor devices, an RF plasma CVD method using SiH ₄ or Si ₂ H ₆ as a film forming gas, and A microwave plasma CVD method or a reactive sputtering method in which a Si target is sputtered in Ar plasma in the presence of hydrogen gas has been used. In addition to this experimentally, light C
There are reports of VD method, ECRCVD method, vacuum deposition method of Si in the presence of hydrogen atoms, etc., and there are successful examples of thermal CVD method using Si ₂ H ₆ or the like.

A-Si: H obtained by these methods
The film is a film containing almost 10% or more hydrogen. The most popular method for depositing such an a-Si: H film is a plasma CVD method, and in many cases, S
iH ₄ , Si ₂ H ₆ gas is used, diluted with hydrogen gas as necessary, and 13.56 MHz or 2.54 GHz
Plasma is generated at a high frequency of, and the film-forming gas is decomposed by the plasma to form reactive active species.
Deposit a Si: H film.

In addition, PH ₃ , B ₂ H ₆ , and BF are used as film forming gases.
Mixing a doping gas such as _{3 with} n-type or p-type a
Since -Si: H films can be formed, these films can be used to make such amorphous silicon devices.

It is also possible to produce hydrogenated amorphous silicon carbide as a wide gap material by further utilizing a gas such as CH ₄ . If appropriate conditions are selected, micro crystal silicon (hereinafter abbreviated as μ-cSi) can be formed by these film forming methods.

[0007]

However, an a-Si: H film or a μ film obtained by the above-mentioned conventional film deposition method is used.
When a device is formed using a non-single crystal film of a -cSi film, there are the following problems.

For example, in the case of making a pin type solar cell or a photodiode, B ₂ H ₆ and BF ₃ are used.
When the mold layer is formed, the optical band gap becomes narrower than that of the intrinsic a-Si: H film.

When the p-type layer is used as the window layer, a material having a wide optical band gap such as p-type amorphous silicon carbide may be used. In the case of such a layer structure, the interface between the p-type layer and the intrinsic layer becomes a heterojunction, and as a result, a lattice misfit occurs at the interface, many interface states are generated, and the generated carriers in the interface are generated. There was a problem that the photosensitivity decreased due to recombination.

Conventionally, in order to eliminate such misfit, compositional modulation is performed with an alloy material added with a material such as carbon or germanium, the optical band gap is designed in a taper shape, and the band joining at the interface is performed. Attempts have been made continuously. However, such compositional modulation with an alloy system causes a number of defects inside the film, and there is a problem that it is difficult to obtain a good quality film even though band design is possible.

Therefore, an object of the present invention is to provide a pin type film having a good quality film with no defects, in which the optical bandgap of the p type layer is not narrow, the photosensitivity is not decreased due to the misfit of the lattice at the heterojunction interface. To realize a semiconductor device such as a solar cell and a photodiode and a method for manufacturing the same.

[0012]

In order to solve the above-mentioned problems, the present invention has the following means.

In a non-single-crystal silicon semiconductor device having a pin structure, the p-type layer and / or the i-type layer,
And / or the n-type layer has a tapered hydrogen concentration profile in the film and a tapered band profile, and band coupling is continuous at the interfaces of the p-type layer, the i-type layer, and the n-type layer. There is a semiconductor device.

Further, a step of depositing a non-single-crystal silicon layer on a substrate as the p-type layer and / or the i-type layer and / or the n-type layer, and then irradiating the non-single-crystal silicon layer with hydrogen plasma As one step, film formation is performed while repeating a plurality of the steps, and in at least a part of the steps, the deposition time and / or the hydrogen plasma irradiation time is changed for each step to taper the hydrogen concentration in the film. A method for manufacturing a semiconductor device, comprising forming a semiconductor layer having a tapered band profile by controlling the shape of the semiconductor layer.

[0015]

According to the present invention, by forming the film while controlling the hydrogen concentration in the film, it is possible to obtain the band continuity at the interface portion by tapering the optical band gap.

As a result, band offsets (conduction band energy difference ΔEc and valence band energy difference ΔE at the heterojunction surface) that occur when the above-mentioned conventional method is used for deposition.
v) does not occur.

Further, according to the present invention, since the band gap is designed by controlling the hydrogen concentration in the film, unlike the conventional composition modulation described above, a high-quality film can be obtained without increasing defects in the film.

[0018]

EXAMPLE 1 FIG. 1 is a cross section of an example in which an intrinsic hydrogenated amorphous silicon layer is formed by using the film forming method according to the present invention, and a pin type photodiode or a solar cell is produced. It is a figure (a) and its band profile (b).

In the figure, 101 is a glass substrate and 10 is a glass substrate.
2 is a lower electrode, 103 is an n-type layer, 104 is an i-type layer, and 105
Is a p-type layer, 106 is a transparent electrode, and 107 is an upper electrode.

FIG. 1B is a schematic diagram showing the band profile, and FIG. 5 is a band profile diagram when the film is formed by the conventional film forming method and conditions. As shown in the conventional example of FIG. 5, the optical band gap of the p-type layer is i
It is narrower than the layer, and band offset occurs at the p / i interface to form a heterojunction. On the other hand, FIG.
In (b), the band profile of the i layer is continuous in the p / i layer interface without causing band offset because the i layer portion is tapered and is continuous with the p layer. For this reason, there is no fear that the photosensitivity will decrease due to the misfit of the lattice, which has occurred at the interface of the conventional heterojunction.

Next, a method for manufacturing such a semiconductor device of the present invention will be described below.

FIG. 3 is a diagram for explaining a procedure for forming an a-Si film by the method of the present invention. As shown in FIG. 3, the method of the present invention comprises a set of steps of depositing an a-Si: H layer for time t _D and then irradiating the deposited film with hydrogen plasma for time t _A. Film formation is repeated. In the present invention, the times t _D and t _A are changed at each step to form a film.

As a result, the Si network can be rearranged. This deposited deposited film surface during deposition time t _D during the hydrogen plasma irradiation time t _A,
While being exposed to hydrogen plasma, atomic hydrogen in hydrogen plasma diffuses into the deposited film or on the surface of the deposited film to some extent while drawing out excess hydrogen,
It is considered that the network has been rearranged.

FIG. 7 is a diagram for explaining the effect of hydrogen plasma at that time. When the deposition time t _D and the hydrogen plasma irradiation time t _A are kept constant, the hydrogen concentration in the film and the substrate are The relationship with the temperature T _S is shown. As shown in the figure, the hydrogen concentration in the film of the i layer when the hydrogen plasma irradiation time t _A is set sufficiently long (b) is generally lower than the hydrogen concentration by the normal GD method (a). It has a hydrogen concentration. As described above, the hydrogen concentration in the film can be lowered by the method of performing the deposition while sufficiently irradiating the hydrogen plasma.

FIG. 8 shows the dependence of the hydrogen concentration in the film on the hydrogen plasma irradiation time t _A. a is the film thickness at each step is 50Å
And b is the case where the film thickness is 100Å. It can be seen that, if the film thickness in each step is 100 Å or more, the hydrogen abstraction effect is difficult to appear, the hydrogen concentration does not decrease, and the structural relaxation does not proceed no matter how many times hydrogen plasma irradiation is performed.

Further, a-S deposited during the deposition time t _D
The film thickness of i: H is preferably 2 atomic layers or more, and practically 10 Å or more. This is because if the newly deposited layer is only one atomic layer, the amorphous structure cannot be kept stable, and crystallization is promoted by hydrogen plasma irradiation. It is considered that the cause of this is that the abstraction of hydrogen by atomic hydrogen triggers an excessive network rearrangement. To prevent excessive network reorganization due to hydrogen plasma irradiation and to promote hydrogen abstraction with good controllability, a-Si of 10 Å or more:
Deposition of the H layer is required.

Therefore, the film thickness deposited during the deposition time t _D must be 10 Å or more and 100 Å or less, preferably 50 Å or less, as described above.

FIG. 9 shows the relationship between the deposited film thickness l and the in-film hydrogen concentration during the deposition time t _D. It can be seen that when the deposited film thickness during the deposition time t _D is 50 Å or more, the effect of hydrogen plasma irradiation decreases, and the hydrogen concentration does not decrease even when hydrogen plasma irradiation is performed.

Therefore, it is understood from FIGS. 8 and 9 that the hydrogen concentration in the film can be controlled by controlling the deposition time t _D and the hydrogen plasma irradiation time t _A.

The film forming conditions in these figures are the same as those of the i layer of the following pin type photodiode prepared by the apparatus of FIG.

FIG. 4 is a schematic configuration diagram showing an example of a film forming apparatus for realizing the present invention.

In FIG. 4, 400 is a reaction chamber,
401 is a substrate, 403 is an anode electrode, 402 is a cathode electrode, 404 is a substrate heating heater, 405 is a grounding terminal, 406 is a matching box, and 407 is 13.5.
6 MHz RF power source, 408 and 414 are exhaust pipes, 409 and 415 are exhaust pumps, 410 is hydrogen gas introduction pipe, 411 and 412 are film formation gas introduction pipe, 4
13 is a three-way valve, 420, 430, 440, 450,
460, 422, 432, 442, 452 and 462
Are valves, 421, 431, 441, 451 and 4
Reference numeral 61 indicates a mass flow controller. A three-way valve 413 is attached to the film-forming gas introduction pipe 411,
The film forming gas is turned on / off by switching the three-way valve 413. Hydrogen (H ₂ ) from the 462 side, silane (SiH ₄ ) from the 422 side, diborane (B ₂ H
₆ ) is introduced from the 432 side, phosphine (PH ₃ ) is introduced from the 442 side, and methane (CH ₄ ) is introduced from the 452 side.

In this apparatus, hydrogen is constantly flowing. Further, by simply ON / OFF controlling the flow of only SiH ₄ or Si ₂ H ₆ which is a film forming gas at the time of depositing an a-Si: H film, both the a-Si: H film deposition and hydrogen plasma irradiation can be easily performed. You can switch.

If the ratio of the film forming gas to the hydrogen gas is too low, crystallization tends to occur during hydrogen plasma irradiation. Therefore, the film forming gas concentration is preferably 10% or more, preferably 20% or more. In this case, it is possible to leave the plasma unbroken in both the step of depositing the a-Si: H film and the step of irradiating with hydrogen plasma. Can be prevented from being deposited. In this case, it is also preferable to add Ar for plasma stabilization.

Next, an example of a manufacturing process of a pin type photodiode having an intrinsic a-Si: H layer having a tapered optical bandgap formed by the film forming method of the present invention is shown in FIG. It will be described below with reference to the drawings and the manufacturing apparatus of FIG.

First, after forming the lower electrode 102 using a metal film such as Al on the glass substrate 101 whose surface is polished,
It is attached to the cathode 402 in the reaction chamber 400, exhausted sufficiently by the exhaust pump 409, and 10 ⁻⁶ Tor
r. The substrate temperature was 300 ° C.

Next, SiH ₄ gas was flowed at 30 sccm to generate H
₂ gas was flowed at 30 sccm, and PH ₃ gas diluted to 1% with H ₂ gas was flowed at 30 sccm. Set the chamber pressure to 1.0 torr and apply 10 W of RF power.
After discharging for a minute, the n-type a-Si: H layer 103 was deposited at 400 Å. After stopping the gas supply, the inside of the chamber is 10 ^-6 T
Evacuated below orr.

Next, the i-type a-Si is formed by the film forming method according to the present invention.
Deposit layer 104. The substrate temperature was kept at 300 ° C.

First, 30 sccm of H ₂ gas was flown into the reaction chamber 400. After the three-way valve 413 was connected to the film-forming gas introduction pipe 411 and the exhaust pipe 414, the valves 420 and 422 were opened, and SiH ₄ gas 30 scc
m was passed through the film-forming gas introduction pipe 411. In this state, RF power of 20 W was applied to start hydrogen plasma discharge.

Next, by switching the three-way valve 413, film formation (deposition) and hydrogen plasma irradiation are repeated as one step. Film formation time (deposition time) t _{D in} this example
Was constant for 40 seconds, and the film thickness at this time was 50Å.

The hydrogen plasma irradiation time t _A is as shown in FIGS.
Using FIG. 10, the optical band gap was set to 1.7 eV on the n-type layer side and 1.60 eV on the p-type layer side, and the opening / closing of the three-way valve was controlled by a computer during actual film formation. The total number of steps is 120 and i-type layer 10
The film thickness of No. 4 was 6000Å.

The hydrogen plasma irradiation time t _A is 1 second for the first to fifth steps and 2 for the sixth to 17th steps.
Seconds, 18th to 29th steps are 3 seconds, 30th to 4th
4 seconds for 1 step, 5 seconds for 42nd to 53rd steps,
Steps 54 to 65 are 6 seconds, Steps 66 to 77 are 7 seconds, Steps 78 to 89 are 8 seconds, 9th
0 to 101st step is 9 seconds, 102nd to 120th
The step was 10 seconds.

By setting t _A in this way, the hydrogen concentration in the film can be tapered, and the occurrence of defects can be suppressed at the interface portion where defects are likely to occur in film formation by the ordinary method.

Next, a p-type a-Si layer 105 was deposited.
The degree of vacuum in the chamber 400 was evacuated to 10 ⁻⁶ Torr or less, the substrate temperature was changed to 250 ° C., and then the SiH ₄ gas 3 was used.
B ₂ H ₆ gas 3 diluted to 0% with 0 sccm and H ₂ gas
0 sccm, RF power of 40 W was applied, plasma discharge was performed for 5 minutes, and a p-type layer 105 of 500 Å was deposited. The optical bandgap of the single-layer p-type layer formed under these conditions was 1.60 eV.

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

Since the band is continuously formed at the interface between the p-type layer and the i-type layer of the pin type photodiode thus formed and no heterojunction is formed, the generation of interface defects is small. As a result, recombination of carriers at the interface was suppressed, and when light was introduced from the p-type layer, improvement in photosensitivity was observed. In addition, there were few carriers trapped at the joint surface and the response was improved. Further, in the solar cell prepared by the method of this example, the improvement in efficiency was recognized due to the similar effect.

[0047] While conditions were set so as to vary the t _A at each step in the present embodiment, the i layer forming the initial steps to change the t _A, such that a constant t _A in the second half of the step Conditions can also be set.

(Second Embodiment) As a second embodiment, a pin photodiode in which p-type hydrogenated amorphous silicon carbide is deposited by the film forming method according to the present invention will be described. As the film forming apparatus, the apparatus shown in FIG. 4 was used, and the film forming method of the present invention was applied to the p-type layer.

First, a lower electrode 102 is formed by using a metal film such as Al on a glass substrate 101 whose surface is polished, and then attached to a cathode in a reaction chamber 400, and exhausted by an exhaust pump 409 to 10 ⁻⁶ Torr. And
The substrate temperature was 300 ° C. SiH ₄ gas at 30 scc
m ₂ flow, 30 sccm H ₂ gas flow, 1% H ₂ gas
PH ₃ gas diluted to 30 sccm was flowed. The chamber internal pressure was set to 1.0 Torr, 10 W of RF power was applied, and discharge was performed for 3 minutes to deposit an n-type a-Si: H layer of 400 liters.

Next, the i layer was deposited. The degree of vacuum in the chamber is evacuated to 10 ^-6 Torr or less and the substrate temperature is 250 ° C.
After changing to SiH ₄ gas 30sccm and H ₂ gas 30
Sccm was flown and RF power of 20 W was applied to perform plasma discharge for 100 minutes to deposit an i-type layer of 6000 Å.
At this time, the optical band gap of the monolayer i layer is 1.80e.
It was V.

Next, a p-type amorphous silicon carbide layer is deposited by the film forming method according to the present invention. Three-way valve 41
3 is connected to the film-forming gas introduction pipe 411 and the exhaust pipe 414, and then the valves 420, 422, 430, 43
Open 2, 450, 452, SiH ₄ gas 30scc
m, 20 sccm of CH ₄ gas and 30 sccm of B ₂ H ₆ gas diluted to 1% with H ₂ gas were introduced into the introduction pipe 611,
The chamber pressure was kept at 0.5 Torr. The substrate temperature was 300 ° C., and RF power of 80 W was applied in this state to start hydrogen plasma discharge.

Next, the film formation and hydrogen plasma irradiation are repeated by switching the three-way valve 413. In this example, the film formation time t _D was fixed at 20 seconds and the film thickness was 20Å. The hydrogen plasma irradiation time t _A has an optical band gap of 1.80 eV on the i-type layer side and 2.00 eV on the upper electrode side.
The computer controlled opening / closing of the three-way valve during the actual film formation. The total number of steps was 50, and the film thickness of the p-type layer was 1000Å.

The hydrogen plasma irradiation time t _A is 5 seconds for the first to ninth steps, 3 seconds for the tenth to 19th steps,
The 20th to 29th steps were fixed at 2 seconds, the 30th to 39th steps at 1 second, and the 40th to 50th steps were fixed at 0 second.

These times were determined from the same relationship as in FIGS. 7-10 for p-type hydrogenated amorphous silicon carbide.

By setting t _A in this way, the hydrogen concentration in the film can be tapered, and the occurrence of defects can be suppressed at the interface portion where defects are likely to occur in the film formation by the ordinary method.

The optical band gap of the single p-type layer formed under these conditions was 2.00 eV.

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

FIG. 2 is a band diagram of the pin type photodiode thus manufactured. In the conventional film, the p layer has an optical band gap of 2.
0 eV, which is larger than that of the i layer, but in this embodiment, the band gap is continuously joined at the interface between the p type layer and the i type layer by tapering the band gap of the p type layer as shown in FIG. Since there is no heterojunction, the generation of interface defects is small.

As a result, recombination of carriers at the interface was suppressed, and when light was introduced from the p-type layer, improvement in photosensitivity was observed. In addition, there were few carriers trapped at the joint surface and the response was improved.

Further, in the solar cell prepared by the method of this example, the improvement of efficiency was recognized due to the similar effect.

[0061] Incidentally, as in the present embodiment has been set a condition so as to vary the t _A for each step, and constant t _A in p layer deposition initial step, of changing the t _A in the second half of the step It is also possible to set various conditions.

Further, when the n-type layer is used as the window layer, the tapered n-type layer can be obtained by carrying out the present invention in the same manner.

Also, when applying a microcrystal silicon layer to these semiconductor layers, the present invention can be carried out and the same effect can be obtained.

As a method of hydrogen plasma irradiation, any method can be used as long as it efficiently generates atomic hydrogen, and capacitive coupling type or inductive coupling type high frequency glow discharge can be used. That is, a-Si deposited on the substrate:
By placing the H film together with the substrate in a glow discharge of hydrogen gas or in the vicinity of plasma, atomic hydrogen is a-Si:
H film can be supplied. In addition, there is a method of generating atomic hydrogen by microwave plasma and diffusing it to the a-Si: H surface, and a method of generating atomic hydrogen by ECR plasma. If the plasma CVD method is adopted as the method of depositing the a-Si: H film, hydrogen plasma can be generated by the same method, and the film forming method of the present invention can be realized very easily.

[0065]

According to the present invention, by forming the film while controlling the hydrogen concentration in the film, the optical band gap is tapered so that the continuity of the band at the interface can be obtained. ..

As a result, the band offset (energy difference ΔEc of the conduction band at the heterojunction surface, energy difference ΔE of the valence band at the heterojunction surface) that occurs when the above-mentioned conventional method is used for deposition.
v) does not occur, the p / i interface in the semiconductor device,
Alternatively, the effect of eliminating the band discontinuity at the n / i interface and improving the device characteristics can be obtained.

Further, according to the present invention, since the band gap is designed by controlling hydrogen in the film, unlike the conventional composition modulation described above, a high quality film can be obtained without increasing defects in the film.

As a result, in the pin type photodiode or the solar cell using the semiconductor device of the present invention, the photosensitivity does not decrease due to the misfit of the lattice at the heterojunction interface, and it has a good quality film without defects. A semiconductor device such as a pin solar cell or a photodiode can be obtained.

Further, in the photodiode and the like of the present invention, the recombination of carriers at the interface was suppressed, the improvement of the photosensitivity was recognized, and the trapping of carriers at the bonding surface was small and the response was also improved.

Further, in the solar cell produced by the method of the present invention, improvement in efficiency was recognized due to the same effect.

[Brief description of drawings]

FIG. 1 is an example 1 produced by a film forming method according to the present invention.
FIG. 3 is a diagram showing a cross-sectional view of the structure of a pin photodiode or a solar cell and its band profile.

FIG. 2 is a diagram showing a band profile of Example 2;

FIG. 3 is an explanatory diagram of a film forming method according to the present invention.

FIG. 4 shows a film forming apparatus suitable for producing the semiconductor device of the present invention.

FIG. 5 shows a band profile of a conventional example.

FIG. 6 shows a band profile of a conventional example.

FIG. 7 is a diagram comparing the relationship between the substrate temperature and the in-film hydrogen concentration between the case of the present invention and the case of a normal GD method.

FIG. 8 shows the relationship between the hydrogen concentration in the film and the hydrogen plasma irradiation time t _A.

FIG. 9 shows the relationship between the hydrogen concentration in the film and the film formation film thickness l at each step.

FIG. 10 shows the relationship between the band gap and the hydrogen concentration in the film.

[Explanation of symbols]

 101 glass substrate 102 lower electrode 103 n-type layer 104 i-type layer 105 p-type layer 106 transparent electrode 107 upper electrode

Claims (6)

[Claims] 1. A non-single-crystal silicon semiconductor device having a pin-type structure, wherein the p-type layer and / or the i-type layer and / or the n-type layer has a tapered hydrogen concentration profile in the film, A semiconductor device having a tapered band profile, wherein band coupling is continuous at an interface between the p-type layer, the i-type layer, and the n-type layer. 2. The semiconductor device according to claim 1, wherein the semiconductor device is a photodiode having a pin structure. 3. The semiconductor device according to claim 1, wherein the semiconductor device is a solar cell having a pin structure. 4. The method for manufacturing a semiconductor device according to claim 1, wherein after the non-single-crystal silicon layer is deposited on the substrate as the p-type layer and / or the i-type layer and / or the n-type layer, The step of irradiating the non-single-crystal silicon layer with hydrogen plasma is defined as one step, and the plurality of steps are repeated to form a film. In at least some of the steps, the deposition time and / or the hydrogen plasma irradiation time are changed. A method of manufacturing a semiconductor device, wherein a semiconductor layer having a tapered band profile is formed by controlling the hydrogen concentration in the film in a tapered shape by changing the hydrogen concentration in each step. 5. The method of manufacturing a semiconductor device according to claim 4, wherein the semiconductor device is a photodiode having a pin structure. 6. The method for manufacturing a semiconductor device according to claim 4, wherein the semiconductor device is a solar cell having a pin structure.