JPH0344148B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a plasma gas phase reaction method and an apparatus for producing the same.

[Conventional technology]

Conventionally, in the plasma vapor phase reaction method, a pair of electrodes are arranged in parallel to form a parallel plate type electrode, and a plasma discharge is generated between the electrodes using a glow discharge method to form a semiconductor film, etc. .

Also, the deposits formed at this time are CF ₄ +O ₂ (2~
20%), plasma etching was performed using CF ₂ Cl ₂ , CF ₃ Br, etc.

In addition, in one or more reaction chambers that can be evacuated so that oxygen or silicon oxide does not enter the reaction chamber,
The same main component that is simultaneously formed inside the reaction chamber during the process of forming a film whose main component is amorphous, microcrystalline, or non-single-crystal silicon or silicon carbide, which are oxidized materials. It is extremely important to remove deposits, flakes, coatings, etc.

[Problem that the invention seeks to solve]

However, in such a method, after etching,
Carbon and oxygen remained on the inner walls and surfaces of the hood, as well as chlorine (Cl) and bromine (Br).

When this carbon mixes into amorphous silicon,
This lowers the electrical conductivity and creates recombination centers.

Also, when oxygen is mixed, it reacts with hydrogen and Si-
It forms a CH bond and becomes the cause of deterioration of electrical conductivity due to light irradiation effect (Stebla-Lonski effect).

Furthermore, when chlorine and bromine were mixed in, they formed recombination centers because their atomic radius was larger than that of fluorine.

From these facts, it is clear that non-oxygen, non-carbon, non-chlorine, and non-bromine gases are used in plasma etching to remove deposits mainly composed of silicon and silicon carbide attached to the inner walls of the reaction chamber. It has been found that this is extremely important for improving the properties of a non-single-crystal semiconductor film containing silicon as a main component when forming a non-single-crystal semiconductor film containing silicon as a main component.

In view of the above, the present invention has been made, and when forming a semiconductor film, a film mainly composed of silicon or silicon carbide attached to the inner wall of a reaction chamber is The purpose of etching with bromine gas is to remove deposits adhering to the inner wall so that they do not deteriorate the properties of the silicon or silicon carbide coating.

[Means to solve the problem]

For this purpose, the present invention forms a non-single-crystalline film mainly composed of silicon or silicon carbide in a reaction chamber that can be evacuated, and then removes silicon or silicon carbide that has adhered to the interior of the reaction chamber as its main component. 99.0% of deposits with oxygen content of 1% or less, preferably 0.1% or less
Hydrogen fluoride (also referred to as anhydrous hydrogen fluoride, hereinafter referred to as HF) having the above-mentioned high purity is turned into plasma and removed by dry etching.

Using this HF plasma, we have experimentally discovered that quartz and stainless steel can be etched at an etch rate less than 1/100 of that of amorphous silicon, and that there is virtually no damage to the reaction vessel. What remains after etching is hydrogen and fluorine, both of which are silicon and fluorine.
Since it is a neutralizer (terminator) for the recombination center of a non-single-crystal semiconductor mainly composed of silicon carbide, it does not cause any deterioration of semiconductor characteristics.

Therefore, it has been found that this HF plasma is extremely ideal for cleaning the inside of a reaction chamber for forming a film on a non-single crystal semiconductor.

Embodiments of the present invention will be described below with reference to the drawings.

Example 1 In this example, when a PIN junction is formed on a substrate by laminating a non-single crystal semiconductor layer mainly composed of silicon or silicon carbide with a P-type semiconductor, an I-type semiconductor, and an N-type semiconductor, the reactions of each are evaluated. Using a multi-chamber PCVD method in which containers are connected through a separation part and a plasma etching (hereinafter referred to as PE) method using HF in each reaction chamber, P-type impurities and N-type impurities are removed from each other during PE. This is a method in which etching is performed independently to prevent contamination. This multi-chamber plasma reaction method in which a large number of reaction vessels are connected is a so-called mass production method in which a large number of substrates are grown at a high film growth rate at the same time.

An embodiment of a plasma vapor phase reactor used in the method of the present invention will be described with reference to FIG.

This drawing shows PIN junction, PIP junction, NIN junction,
Semiconductor layers with different conductivity types but different main components or stoichiometric ratios (constituent component ratios) are formed on a semiconductor on a substrate such as a PN junction or PINPIN...PIN junction. This is an apparatus for automatically and continuously forming multiple layers without being influenced (contaminated) by semiconductor layers formed in the previous process.

In the drawing, the three Ps that make up the PIN joint,
Three reaction systems (,,) formed by stacking I- and N-type semiconductor layers, and the first and second
This figure shows a multi-chamber (here, three reaction vessels) type plasma gas phase reactor having several preliminary chambers.

Of course, in the drawing, in order to further reduce the mixing of the reaction chambers between the systems, a buffer chamber is provided between the systems, and a separate part of another buffer chamber is provided between the systems to connect the seven chambers. 1
Semiconductors having two PIN junctions may be stacked.

In this embodiment, P of such a multi-chamber system,
After I and N were formed independently in each reaction chamber, impurities deposited in the reaction chamber were removed by etching.

The system in the drawings has three reaction chambers 6, 7, 8, and gate valves 44, 45, 46, 47 as separation parts between the reaction vessels. In addition, the reactive gas introduction hoods 17', 18', 19' and the exhaust hood 17,
18 and 19, to prevent reactive gas from flowing back from the supply system or exhaust system, or from mixing with reactive gas from other systems.

This apparatus is provided with a first preliminary chamber 5 on the entrance side, and the substrate 4 is first inserted into a substrate holder (also referred to as holder) 74 through the door 42 and placed in this preliminary chamber.

The substrates having the surfaces on which the film is to be formed are arranged so that the back surfaces on which the film is not formed are adjacent to each other, and two of the substrates are arranged in pairs with a distance of 6 cm between them.

An infrared lamp was used to heat the substrate, which was placed approximately parallel to the surface on which the film was formed, with a distance of 2 to 10 cm between the substrates.

When forming 20 substrates of 20 cm x 60 cm at the same time, the reaction space size is 50 cm in height, 70 cm in width, and 70 cm in depth.
Each reaction chamber had a height of 80 cm, a width of 120 cm, and a depth of 120 cm.

Furthermore, in the plasma etching method using HF gas, metals such as aluminum or silicon oxide were etched by less than 200 Å even after one hour of etching, and to be more precise, the etching rate was 3 Å/min.

Among these, regarding silicon oxide, in the Si-O bond part, silicon element is δ ⁺ due to the difference in electronegativity.
is charged with an electric charge. On the other hand, when HF gas is used to generate plasma, HF radicals do not take an electrically biased state like CF ₃ radicals, so the reaction with silicon oxide is difficult to proceed. Furthermore, since HF gas has the property of easily adhering to metal surfaces and forming passive bodies, activated HF gas does not easily reach the metal surface and is not etched.

For this reason, we fabricated a multi-chamber type reaction chamber using quartz and stainless steel. In addition to improving the properties of the film in each reaction chamber, it also prevents unnecessary reaction products from adhering to the inner walls of the chamber as much as possible, and conversely improves the rate at which the supplied reactive gas forms a film. Improving collection efficiency. For this purpose, reactive gas was selectively introduced into a supply hood into a cylindrical space surrounded by an insulating (quartz) holder, in which the substrates were arranged in a chimney shape, and was exhausted through an exhaust hood.
Further, the surface of the substrate to be formed substantially constitutes the inner wall of the chimney, which serves as a reaction space for film formation.

Then, the first preparatory chamber 5 was evacuated using the vacuum pump 35 by opening the valve. Thereafter, the gate valves 44, 45, 46, 47 for separation from the reaction chambers 6, 7, 8, which had been evacuated in advance, were opened and the substrate and holder were transferred. For example, by transferring the substrate 1 and holder 74 from the preliminary chamber 5 to the first reaction vessel 6 and closing the gate valve 44,
It was moved to the reaction chamber 6 of At this time, the substrate 1 held in the first reaction chamber 6 is transferred to the second reaction chamber 7, and the substrate 2 held in the second reaction chamber 7 is transferred to the third reaction chamber 8. 3 reaction chamber 8
The substrate 3 held therein was moved to the second preliminary chamber 9 on the exit side by simultaneously opening the gate valves 45, 46, and 47. After this, gate valves 44, 45, 46,
47 closed. After the gate valve 47 was closed, the substrate transferred to the second preliminary chamber was brought to atmospheric pressure by introducing nitrogen through the gate 41, and was taken out through the door 43.

A P-type semiconductor layer is formed in the first reaction chamber 6 in the system.
The case of forming by PCVD method is shown below.

The reaction system (including reaction chamber 6) was set to 10 ^-3 to 10 torr, preferably 0.01 to 1 torr, for example 0.08 torr.

For the silicide gas 24, the reactive gas is silane (SinH _2o+2 n>1, especially SiH ₄ ), silicon fluoride (SiF ₄ ,
SiF ₂ ), etc., but we used silane, which is easy to handle. In order to form Si _x C _1-x (0<x<1) in this example, methane (CH ₄ ) is used for the carbide gas 23.
was used.

For silicon carbide (Si _x C _1-x 0<x<1),
2000PPM of boron with hydrogen as a P-type impurity
diborane diluted to 25%. In addition, galiyum was treated with TMG (Ga(CH ₃ ) ₃ ) at 10 ¹⁹ ~
It may be added to a concentration of 9×10 ²¹ cm ⁻³ .

These reactive gases pass through a flow meter 33 and a valve 32, respectively, to the reactive gas supply hood 1.
7 and was supplied to the reaction vessel 6 via the negative electrode 61 of the high frequency power source 14. The reactive gas is in this holder 74.
A coating was formed on the substrate 1 constituting this space. Further, electric energy is applied between the negative electrode 61 and the positive electrode 51, for example.
High frequency energy 14 of 13.56 MHz was applied to cause a plasma reaction, and a reaction product formed a film on the substrate.

Furthermore, another second high frequency energy is applied from the power source 84 through the pair of electrodes 71 and 81 in an electric field perpendicular to this first high frequency electric energy to make the formed film uniform.

The substrate can be a conductive substrate (stainless steel, titanium, aluminum, or other metal), a semiconductor (silicon, germanium), an insulator (alumina, glass, organic material), or a composite substrate (aluminum, an insulating film formed on stainless steel). A single layer or a conductive film such as tin oxide or ITO doped with fluorine is formed on the upper surface of a substrate or a glass insulating substrate on which a conductive electrode of a film is formed by separating the flexible substrate with a surface. A two-layer film of SnO ₂ formed on ITO) was used.

The substrate was heated to 100 to 400°C, for example 200°C, using infrared heaters 11 and 11'.

Thereafter, as described above, the above-mentioned reactive gas was introduced into this container, and high-frequency energy 14 and 84 of 10 to 500 W, for example 200 W, was supplied respectively to cause a plasma reaction.

Thus, the P-type semiconductor layer has B ₂ H ₆ /SiH ₄ =0.5%,
A thin film having a thickness of about 100 Å (film thickness variation: 95 to 105 Å) was formed using this reaction system under the conditions of CH ₄ /(SiH ₄ +CH ₄ )=50%. Eg＝
2.0eV, σ=1×10 ^-6 to 3×10 ^-5 (Ωcm) ^-1 .

In this way, a plasma vapor phase reaction was carried out for 1 to 5 minutes, and a silicon carbide film doped with boron or gallium as a P-type impurity was produced to a thickness of about 100 Å. Further, the substrate was transferred to the second reaction chamber 7 on top of the first semiconductor layer according to the above-described operating sequence, where an intrinsic semiconductor layer was formed to a thickness of about 5000 Å.

That is, in the reaction system shown in FIG. 1, silane is used as the reactive gas of the semiconductor, and
In order to add less than 10 ¹⁷ cm ^-3 of boron, B ₂ H ₆ diluted to 0.5 to 30 PPM with hydrogen, silane, etc.
From 7, also add carrier gas to 26 as needed.
Supply hood 18, holder 74, exhaust hood 18
The air was evacuated to the vacuum pump 37. When amorphous silicon is made with silane as a coating,
SiH ₄ 200 c.c./min to 5000 Å thickness, film formation rate 8
Å/sec, substrate (20 pieces of 20cm x 60cm, total area
24000cm ² ), the pressure was 0.08torr, and the total output was 300W.

Thus, in the first reaction chamber, a P-type semiconductor layer was formed by the plasma vapor phase method, and then an I-type semiconductor layer was formed by another PCVD method to form a PI junction.

After forming this I-type semiconductor layer to a thickness of about 5000 Å, the substrate was transferred to the reaction chamber 8 of FIG. 1 according to the operations described above, and an N-type semiconductor layer was formed.
This N-type semiconductor layer was made by PCVD using phosphin at PH ₃ /SiH ₄ = 1.0%, silane from 31, silane from 30, and hydrogen as a carrier gas from 38.
SiH ₄ /H ₂ = 50% was supplied, and an N-type microcrystalline or polycrystalline semiconductor layer with a fibrous structure was formed to a thickness of approximately 200 Å in the same manner as the system, and methane was further added to the top surface of the polycrystalline semiconductor layer with a thickness of approximately 200 Å. ₄ / (SiH ₄ + CH ₄ ) = 0.1 and supply from 29 to form an N-type semiconductor layer represented by Si _x C _1-x (0<x<1) to a thickness of 10 to 200 Å, for example 50
It is formed by laminating layers to a thickness of . Other reaction equipment is the same as the system.

After this process, enter the PIN from the second preliminary room 9.
ITO with a thickness of 100 to 1500 Å is formed on the substrate formed by forming the bond, and an aluminum electrode with a thickness of about 0.3 μm is made as a reflective electrode on top of it by vacuum evaporation method, and then on the glass substrate ( ITO+SnO ₂ ) surface electrode-(PIN semiconductor)-(back surface electrode) was constructed.

Its characteristics as a photoelectric conversion device are 7 to 9%, average 8%, and AMI (100mW/cm ² ) on a 10cm x 10cm substrate.
Under these conditions, it was possible to obtain an effective efficiency of 3 to 5% (3.8% on average) even in a 20 cm x 60 cm glass substrate integrated into a hybrid type.

In this way, coatings were formed at least 50 times in the reaction chamber shown in FIG. As a result, deposits of about 1μ in the reaction chamber 6 of the system, about 80μ in the reaction chamber 7 of the system, and about 2μ in the reaction chamber 8 of the system were formed on the inner walls and the hood surface. Since the temperature inside this reaction chamber is constant, even if a thickness of about 80 μm is formed on the quartz hood and electrode, most of it is flakes (snowflakes).
Not. However, the deposits on the side surfaces generate flakes, and when these adhere to the surface on which they are formed, they promote the generation of pinholes and deteriorate the device.

For this reason, after a maximum of 100 microns of these deposits have adhered, anhydrous hydrogen fluoride (purity of 99.9% or more) is added to the reaction chamber from the doping system at 100 c.c./min from 100 for the system, 101 for the system, and 102 for the system. Introduced flow rate. The internal pressure of reaction chambers 6, 7, and 8 is 0.2 torr.
A total of 500W of pressure at 13.56MHz was applied. The temperature in the reaction chamber was from room temperature to 300°C, and in this example was 150°C. Then, 1000Å/min in the system,
Since an etching rate of 1000 Å/min could be obtained using the system, it was possible to sufficiently clean the inside of the reaction chamber after etching for 5 hours.

Furthermore, if necessary, after the HF was evacuated, plasma hydrogen cleaning was performed using hydrogen (purity of 4N or higher) to further remove F deposits.

On the other hand, if 1% or more of oxygen or oxides, such as 4% oxygen, are mixed into HF, silicon is hardly etched, and even with 1%, amorphous silicon is
The rate was extremely variable at 500 Å/min, and the surface was also highly uneven, making it impossible to put it to practical use. From this, the concentration of oxygen or oxide gas in HF is 1%.
It was important to minimize the following:

In this case, since removal is performed using the same electrode in a high electric field area where a large amount of deposits are formed due to PCVD, the electric field is similarly high, and a faster etch rate can be obtained in areas where thick deposits are formed. For this reason, it was extremely convenient for cleaning to perform PE using the same reaction electrode in the same reaction apparatus.

Furthermore, in the conventional CF ₄ + O ₂ reaction, if there is a local strong electric field region, CF will react more strongly than CF in this region.
Instead of radicals, C itself is further separated and attached. However, to completely remove this carbon, oxygen must be PFed again in the same reaction chamber, and C and O remain in the reaction chamber.

Therefore, C and O impurities, which should be avoided, are mixed into the subsequent film formation.

In the present invention, since the reactive gases are only H and F, the remaining deposits after PE are C, O, Cl,
It has the characteristic that it is essentially impossible for it to be Br, etc., and is ideal for the PE method in a reaction chamber for forming a film mainly composed of silicon.

Furthermore, when this coating was formed in batches of 100 to 300 times, the yield was 20%, and the reaction products that adhered to the inner wall without being exhausted were also formed to a thickness of 10 μ to 5 mm. When the deposits were removed using the HF PE method, even if the deposit was substantially 5 μm, it could be sufficiently removed in 2 hours.

Further, no powder such as carbon remained on the surfaces of the HF PE first reaction chamber and jigs such as the quartz hood, and a sufficiently clean and flat surface could be obtained.

Regarding the type of semiconductor to be formed, as mentioned above, it is not a multiple layer of Si _x C _1-x -Si-Si _x C _1-x , but other groups of Si, Ge, Si _x C _1-x (0<x <1) Si _x
It goes without saying that it may be Ge _1-x (0<x<1), Si _x Sn _1-x (0<x<1), a single layer or a multilayer. The present invention demonstrated a multi-chamber PCVD method using three reaction vessels. But this 1
It is effective to form a semiconductor layer having a PIN junction or other junction by using a single reaction vessel and using the PCVD method.

The non-single crystal semiconductor film formed according to the present invention is also effective for N (source), I (channel forming region), N (drain) junctions or PIP junctions in insulated gate field effect semiconductor devices. More PIN
It is a diode and the energy band width is W-N-
W (WIDE−NALLOW−WIDE) Si _x C _1-x ―Si
-Visible light and light emitting elements may be made using a PIN junction type superstructure with a Si _x C _1-x (0<x<1) structure, or vice versa, a N-W-N type PIN junction type superstructure.
In particular, the so-called W (P or N
type) - N (type I) (WIDE TO NALLOW), and in each reaction chamber, not only the conductivity type but also the product is different, each is independently produced and laminated, and PE can be performed independently. We believe that this will become possible and will be of great industrial importance.

In addition, this embodiment uses a non-single-crystal semiconductor layer doped with hydrogen or fluorine, preferably silicon, germanium, silicon carbide (not only SiC, but in the present invention, Si _x C _1-x 0<x<1). meaning a generic term),
In addition, kermanium silicide (Si _x Ge _1-x 0<x<1) whose main component is silicon, tin silicide ((Si _x Sn _1-x 0
<x<1), and by filling this film with hydrogen or fluorine in an active state, a plurality of semiconductor layers having conductivity types of P, I, and N types with a small recombination center density are formed. A PI junction, NI junction, PN junction, or a combination of these forms a PIP junction, NIN junction, PIN junction, or PNI junction at the layer boundary, and impurities from other adjacent semiconductor layers are mixed into each semiconductor layer. It can be formed without deteriorating the junction characteristics, and it also prevents the formation of an interlayer insulator by exposing a part of the semiconductor to the atmosphere, especially oxygen, during the process of forming the semiconductor layer, which oxidizes a part of the semiconductor. It is also a plasma gas phase reaction for continuous production.

The film formation before the plasma etching of the present invention is not a plasma CVD method, but an optical CVD method that does not use plasma, or a LT CVD method (also referred to as the HOMO CVD method). It is effective to remove the HF using PE method.

〔effect〕

In the present invention, after forming a non-single-crystal coating mainly composed of silicon or silicon carbide, the deposits mainly composed of silicon or silicon carbide deposited inside the reaction chamber can be removed by non-oxygen, non-carbon, non-chlorine, Hydrogen fluoride (also referred to as anhydrous hydrogen fluoride, hereinafter referred to as HF) having a high purity of 99.0% or more with a non-bromine gas of 1% or less oxygen, i.e., 99% or more, preferably 0.1% or less oxygen, is used in plasma. Since the reaction chamber is removed by dry etching, it is possible to clean the inside of the reaction chamber without causing deposits on the inner walls to mix with the silicon and silicon carbide coatings and deteriorate their properties. Ta.

[Brief explanation of drawings]

FIG. 1 schematically shows a manufacturing apparatus for forming a semiconductor film for carrying out the present invention.

Claims (1)

[Claims] 1. After forming a non-single-crystal film mainly composed of silicon or silicon carbide in a reaction chamber that can be evacuated, the deposits mainly composed of silicon or silicon carbide attached inside the reaction chamber are removed by oxygen or A plasma gas phase reaction method characterized in that hydrogen fluoride containing 1% or less of oxide gas is introduced and removed by gas phase etching by applying electrical energy to transform it into plasma.