JP3259908B2 - Method for manufacturing semiconductor device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultra-high purity semiconductor manufacturing gas having an extremely low concentration of oxygen or carbon, which is used for PIN.
The present invention relates to a method for manufacturing a semiconductor device having at least one junction. 2. Description of the Related Art Conventionally, oxygen locally forms Si--O--Si in a semiconductor, for example, a silicon semiconductor, and exhibits only insulating properties. However, when a cluster of several to a dozen or so oxygen atoms forms in silicon, it forms a recombination center for electrons and holes and acts as a recombination center for minority carriers generated by light irradiation, that is, a killer. Has been found to be extremely remarkable even in a non-single-crystal semiconductor obtained by a plasma gas phase method to which hydrogen or a halogen element is added. [0003] Further, the dangling bond of oxygen also acts as an N-type donor center, so that a non-single-crystal semiconductor is a semi-amorphous (semi-crystalline) material having a lattice strain more than an amorphous structure and having a structure sensitivity. It turns out that it becomes N-type. For this reason, it is extremely important when considering industrial applications to essentially remove such oxygen as a donor center to produce an intrinsic semiconductor having a structurally sensitive (the Fermi level is almost at the center of the bandwidth). there were. Further, regarding carbon, CmHn (m
In the case of ≧ 2), it is mixed as it is in the semiconductor to generate many recombination centers, resulting in a reduction in the lifetime of carriers, particularly holes. [0005] The present invention provides a P-type semiconductor layer comprising a substrate or a first electrode on the substrate and a non-single-crystal semiconductor layer having at least one PIN junction on the electrode. In a photoelectric conversion device provided by laminating an I-type semiconductor layer and an N-type semiconductor layer, in particular, an intrinsic or substantially intrinsic (P or N-type impurity) which is an active semiconductor layer which generates photovoltaic power by light irradiation is used. artificially it is mixed to a concentration of ^{1 × 10 14 ~5 × 10 17} cm -3, or to entrained) semiconductor background level, oxygen or carbon, especially results in the generation of promoting or recombination centers insulating The purpose of the present invention is to reduce the average concentration to an extremely low concentration of 5 × 10 ¹⁸ cm ⁻³ or less, preferably 1 × 10 ¹⁸ cm ⁻³ or less. According to the present invention, there is provided a method for removing such impurities, a silicon semiconductor containing silicon and hydrogen or fluorine necessary for neutralizing a recombination center as a main component and further shifting a Fermi level. (10 ^{14 -3} × 10 ¹⁷ cm ⁻³ ). Conventionally, silanes have an effective molecular diameter of less than 5 ° (4.8-5 °) and germane has about 6 °. (Polysilane and the like have a larger effective molecular diameter.) However, for example, in silane (monosilane) having the smallest effective molecular diameter, when impurities contained in the reactive gas are examined,
It is as shown in Table 1 below. [Table 1] By examining these facts, especially in the case of this epitaxial growth, the oxides and nitrides are reduced to about 1/30 of Table 1 due to the segregation effect during the gas-solid reaction. Therefore, a substantially intrinsic semiconductor having a specific resistance of 100 Ωcm or more can be obtained. However, in the plasma vapor phase method using glow discharge performed at 100 to 400 ° C., the effect of segregation of impurities as physical purification cannot be expected. For this reason, the impurities shown in Table 1 are directly mixed into the semiconductor.
All react with silane to produce reaction product silicon oxide.
For example, when 99.99% of an epitaxial gas is used, 0.01% of impurities are mixed. Regarding silane itself, activation (ionization) by plasma reaction is 1
-5%, so that it is substantially further concentrated about 20 to 30 times more than the gaseous state, and 2 to 4 × 10 ²⁰ cm ⁻³ is contained in the semiconductor film.
It was found that the concentration was increased and the mixture was found. Therefore, it has been experimentally found that when a reactive gas is used for the plasma gas phase method, it is extremely important to purify the reactive gas in the reactor. Thus, in the present invention, in order to guarantee a conversion efficiency of 10% or more in AM1, oxygen in the I layer is set to 5 × 10 ¹⁸ cm ⁻³ or less, and even in carbon mixed in clusters, 4 × 10 ¹⁸ cm ^-3 or less, preferably 1 × 10 ¹⁸ cm
It is very important that it is less than ^-3 . An object of the present invention is to increase the purity of such a semiconductor. According to the present invention, a reactive gas for semiconductors such as silane, polysilane, silicon fluoride which is a silicide gas and germane which is a germanium gas have an effective molecular diameter of 4.8 mm or more. This is to take advantage of having. That is, using a molecular sheep or zeolite having an effective hole diameter of 2.9 to 4.65Å, 4.5
酸化 物 An oxide gas which is an impurity having the following effective molecular diameter (hereinafter referred to as molecular diameter) such as water (H ₂ O), carbon dioxide gas (CO ₂ ), oxygen (O ₂ ), and a carbide gas such as methane (CH ₄ ) , Ethane (C ₂ H ₆ ), propane (C ₃ H ₈ ), CH ₃ OH
, C ₆ H ₆ and the like. In order to further promote the adsorptive power, the adsorbent for performing the chemisorption is used at room temperature to -100 ° C, preferably -20 to -7 ° C.
It is intended to cool to 0 ° C and further increase its adsorption power by 50 times or more. Thus, conventional non-single-crystal semiconductors having PIN junctions, especially amorphous semiconductors, have AM1 (100mW /
Although the conversion efficiency was only 6 to 8% under the condition of cm ² ), the intrinsic conversion efficiency could be increased to 11 to 14.5%. In particular, in the I layer which is the active semiconductor layer, the oxygen concentration is increased from 5 to 10 × 10 ²⁰ cm ^-3 to 5 × 10 2
¹⁸ cm ^-3 or less, preferably 1 × 10 ¹⁸ to 1 × 10 ¹⁴ cm ^-3 , and further having many CC bonds in the semiconductor, that is,
The density of recombination centers in a semiconductor, for example, a silicon semiconductor, is reduced to 1 × 10 ¹⁸ cm ⁻³ or less, preferably 1 × 10 ¹⁸ to 1 × 10 ¹⁴ cm ⁻³ , to reduce the density of recombination centers.
1 × 10 ¹⁷ cm ^{-3 to} 10 ¹⁸ cm ^-3, preferably 5 × 10 ¹⁴ to 1
It is characterized in that it has been successfully reduced to × 10 ¹⁶ cm ⁻³ and that the so-called Stepler-Lonski effect, in which photoconductivity is degraded by light irradiation, is eliminated. The following is shown according to the drawings. FIG. 1 shows an outline of a manufacturing apparatus used for manufacturing a semiconductor device of the present invention.
As shown in FIG. 1, the reactor (1) (35 mmφ in diameter)
External heating furnace (21), substrate (22), a pair of electrodes (3),
(3 '), high frequency oscillator (2) (e.g. 13.56MHz or 100K
Hz), and 1G to activate and decompose reactive gases
It has a microwave having a frequency of not less than Hz, for example, a microwave oscillator (17) of 2.45 GHz and an attenuator (18). 0.00 from the discharge section protected by ceramics (19)
The microwave was emitted to the reactor (1) held at 1 to 10 torr. The entire reactor is shielded (20) so as not to cause radio interference. When a semiconductor film is formed on the substrate (22) by the reactive gas, the electric energy electric field has a laminar flow parallel to the surface to be formed. Are arranged as follows. As the reactive gas, a carrier gas such as oxygen, and hydrogen containing impurities of 1 ppb or less, preferably 0.1 ppb or less, are introduced from (7). When a silicon film was to be formed, silane as a silicide gas was introduced from (4). Also, 500-5000 depending on hydrogen which is a P-type impurity.
Diborane diluted in PPM was introduced from (5), and phosphine diluted to 500 to 5000 PPM with hydrogen was introduced in (6). These reactive gases are supplied to gas purifiers (11), (1)
4), (12), (15), (13), and (16) were introduced into the reactor at a predetermined flow rate. These gas purifiers were modified on the inlet side of the reaction gas using a molecular sheep or zeolite having an effective hole diameter of 2.7 to 4.65 mm, 3 mm, 4 mm, or 4.5 mm (for example, 4 mm, an effective hole diameter of 3.5 mm to 4.3 mm). . The Molecular sheepshead or _{zeolites, Na (AlO 2) (SiO} 2) 27~30
4% indicates H ₂ O, and 4.5% indicates (K ₄ Zn ₄ ) (AlO ₂ ) (SiO
_{2) 27~30H} using those represented by the ₂ O molecular formula. After this, a gas lean (trade name GC-RX) for deoxidation was connected. These were both made by Nikka Seiko. In order to further improve the chemisorption of these purifiers, the temperature of the electron thermostat is kept at -70 ° C to room temperature, for example, -30 ° C.
It cooled by (8), (9), and (10). For hydrogen diluted phosphine, 3 ヒ ン or 4Å was used because its effective molecular diameter is about 4.3 約. In addition, any of 3%, 4%, and 4.5% was applicable to silane or disilane. Especially for silane, N
In addition to oxygen, which is an easily convertible impurity, the use of 4.5% was particularly effective because phosphine lowers its concentration to 0.01 ppb or less (5 × 10 ¹⁴ cm ⁻³ or less). The exhaust system was evacuated (26) through a needle valve (25), a stop valve (24), and a vacuum pump (23). The pressure in the reactor is 0.001 to 10 torr typically by a needle valve (25).
Controlled between 05 and 0.1 torr. FIG. 2 shows the characteristics obtained from the results of FIG. That is, the substrate temperature is 250 ° C and the pressure in the reactor is 0.1 torr.
When a non-single-crystal semiconductor layer is formed on a substrate such as glass,
Light irradiation (AM1) conductivity and dark conductivity when formed to a thickness of μm. In FIG. 2, when such purification is not performed on silane, the impurities in the cylinder as described above directly enter the semiconductor layer, and particularly, oxygen or carbon has an effect of making silicon amorphous. Thus, a light conductivity curve (29) and a dark conductivity curve (30) were obtained. That is, in the drawing, at a high-frequency output of 20 to 30 W, the photoconductivity is on the order of 10 ^-3 (Ωcm) ^-1 , but at this time, the semiconductor is partially semi-amorphized with some order. Therefore, oxygen, which is an impurity in the semiconductor, becomes a donor center, becomes N-type, and has a dark conductivity (3
0) is also on the order of 10 ^-4 (Ωcm) ^-1 . As a result, when used as an intrinsic semiconductor, the opposite impurity, boron, must be added to a concentration of 1 to 3 × 10 ¹⁷ cm ⁻³ or a low output of 1 to 5 W is required. However, in any case, as apparent from the curve (29), the photoconductivity is reduced to the order of 10 ^-6 to 10 ^-5 (Ωcm) ^-1 . Instead of such a conventional method, the present invention purifies impurities in silane, particularly oxygen, water or hydrocarbon (FIG. 1).
(11) and (14)), and the cylinder is filled with silane after being sufficiently purified. By thus purifying and removing oxygen containing water, a light irradiation conductivity (27) and a dark conductivity (28) as shown in FIG. 2 could be obtained. As apparent from FIG. 2, the photoconductivity is as large as 10 ⁻⁴ (Ωcm) ⁻¹ or more in the region of low plasma energy where the plasma discharge output is ^{1 to} 10 W, and the dark conductivity is 10 ^{−. It} is as small as ¹¹ to 10 ^-10 (Ωcm) ^-1 . That is, the active energy as the intrinsic semiconductor was sufficiently large, and the Fermi level was almost equal to Eg / 2 ⁺ _0.1-0.2 eV. Further examination of this characteristic revealed that in the X-ray diffraction image, weak crystallization was observed in a part of the film obtained at 5 to 10 W, and these were semi-amorphous (semi-non-crystalline) having an intermediate structure between the amorphous structure and the crystallized structure. (Crystalline) semiconductor. That is, an intrinsic semiconductor is formed by a plasma gas phase method.
If the temperature is to be obtained at 100 to 300 ° C., for example, at 250 ° C., the impurity in the silane tends to have a concentration of 30 to 100 times that of a mere CVD or epitaxial growth. For this reason, it is extremely important to use ultra-high-purity silane with as little contamination of the starting material as possible.
Thus, even at a low output of ² to 10 W, the dark conductivity is small and the photoconductivity is close to the single crystal 10 ⁻² (Ωcm) ^−1.
-4 to 10 ^-3 (Ωcm) ^-1 could be obtained. In particular, the reason for obtaining such a low high-frequency output is to clearly define the boundary region as a plane when the PIN junction is gradually laminated with the P layer, the I layer, and the N layer as in the present invention, that is, on the P layer. When laminating the I layer, it is extremely important that the underlayer P layer is hit by the effect of sputtering (damaging) the P layer of the discharge and the mixed layer is prevented from being formed at the interface PI junction interface. . Further, in the reactor shown in FIG.
When microwaves were added, the characteristics were the same in order to increase the ionization rate of the reactive gas, but the growth rate of the coating film was increased about 3 to 5 times and could be increased. For example, silane was introduced at 30 cc / min at 0.1 torr, and high frequency plasma alone was as low as 1 to 3Å / sec.
High-speed growth of Å / sec was achieved. FIG. 3 shows an experiment for confirming the effectiveness of a gas purifier with respect to the purification of the silane of the present invention. FIG.
In the graph, the abscissa indicates the concentration of oxygen or carbon in the film, which was measured by FTIR (infrared absorption spectrum of Fourier transform method), and the ordinate indicates the electric conductivity at the time of light irradiation. Further, the impurity concentration of 1 × 10 ¹⁹ cm ⁻³ or less was measured and examined using SIMS (3F type, manufactured by Kameka). The absolute amount is corrected by adding a specific implantation amount (for example, 1 × 10 ¹⁸ cm ⁻³ ) to the amorphous silicon by an ion implantation method.
This was measured by SIMS and performed based on the ionic strength. When both the deoxygenating purifier (14) and the zeolite (11) are used for the silane system, curves (45) and (46) are obtained. The curve (45) is a characteristic when the oxygen concentration at the time of deoxygenation when the carbon concentration is 3 × 10 ²⁰ cm ⁻³ is used as a parameter, and the curve (46) is the oxygen concentration at 1 × 10 ²⁰ cm ^{−3. 20} cm
^-3 (60), 3 × 10 ²⁰ cm ^-3 (61) When mixed, the conductivity is
It is only 10 ⁻⁵ to 10 ⁻⁶ (Ωcm) ⁻¹ , which indicates that the mixing of oxygen is a factor that causes a decrease in conductivity. Referring to FIG. 3, curves (41) and (42) contain an oxygen concentration of 3 × 10 ¹⁷ cm ⁻³ and a carbon concentration of 4 × 10 ¹⁸ cm ⁻³ , respectively. The oxygen concentration is shown as a parameter. That particular oxygen 5 × 10 ¹⁸ cm ^-3
By setting (43) below, the photoconductivity becomes 10 ⁻³ (Ω
cm) ^-1 and dark conductivity on the order of 10 ^-10 (Ωcm) ^-1 . Substrate temperature from 250 ℃
When the temperature was lowered to 200 ° C and 150 ° C, the conductivity decreased by about 1/3. In order to obtain these oxygen and carbon concentrations, it is extremely important that the oxygen (water) in the silane be 0.03 ppm or less.
Then, the oxygen impurity concentration can be reduced to 0.01 PPM and 0.003 PPM. In addition, the residual water in the reactor is reduced to 0.1 PPM or less (10
^-8 torr or less ultimate vacuum) to further prevent oil back-diffusion. As a result, CmHn could be reduced to 0.1 PPM or less. Furthermore, starting silane (also called raw silane)
If liquefied and vaporized silane is used as the material, it cannot be measured by a mass spectrometer at all. The oxygen and carbon concentrations in the formed semiconductor layer were 5 × 10 ¹⁶ ,
It was 4 × 10 ¹⁷ cm ⁻³ or less, which exceeded the SIMS detection limit. Of course, in order to achieve the above high purity, even in the reaction system shown in FIG. 1, the total leak amount including the reaction furnace is 1 × 10 ⁻¹⁰ cc / sec or less, preferably 1 × 10 ⁻¹⁰ cc / sec.
It is important to keep it below 10 ^-12 cc / sec, and it is also important to devise joints and the like. FIG. 4 shows a film formed using the manufacturing apparatus shown in FIG. 1. FIG. 4A shows a transparent conductive film (3) on a glass substrate (32).
3), and furthermore, P-type silicon carbide (Si _x C _{1 -x} 0 <x <1) (for example, x = 0.8) or a P-type silicon semiconductor (34).
It was formed in thickness. After that, the reaction system was sufficiently evacuated (10 ⁻⁸ torr or less) with a cryopump (62), and then an intrinsic semiconductor layer was formed with purified silane to a thickness of 0.5 μm as (31). Further, the vacuum is drawn again to convert the N-type semiconductor layer (35) into silane by mixing methane with Si _x C.
_1-xx = 0.9, and phosphine was further mixed at a concentration of 1% to form a film having a thickness of 200 mm. Thereafter, a reflective electrode, for example, a known silver or aluminum (36) is provided by vacuum evaporation. The high frequency output was 5 W and the substrate temperature was 200 ° C.
As a result, a conversion efficiency of 10.3% was obtained. In order to further improve the characteristics of the glass substrate, a PIN junction type photoelectric conversion device having a structure as shown in FIG. FIG.
In (B), a P-type semiconductor layer (34), an I-type semiconductor layer (33), and a polycrystalline semiconductor layer (35) having an N-type fiber structure are formed on a stainless steel substrate (32) by the apparatus shown in FIG. 200
Å, 0.5 μm, 150 mm thick. Further, the transparent conductive film (43) is made of ITO (indium oxide [tin oxide 0-10
%]), And aluminum auxiliary electrode (36)
Was provided. FIG. 5 shows the conversion efficiency characteristics of the photoelectric conversion device having the above-described structure of FIG. 4B with the concentration of oxygen mixed into the intrinsic semiconductor layer as a parameter. Oxygen concentration is 5 ×
When the ^{density was} 10 ¹⁸ cm ^-3 or less, particularly 1 × 10 ¹⁸ cm ^-3 or less, the conversion efficiency (49) could exceed 12% with an area of 1 cm ² in AM1. The fill factor (48) also exceeds 0.7,
In particular, a maximum short circuit current (47) of 20 mA / cm ² can be obtained. The open circuit voltage was between 0.86 and 0.93V. Again, the oxygen concentration was reduced, and significant improvement in characteristics was seen by making silicon more silicon-like.
In the embodiment shown in FIG. 4B, the N-type semiconductor layer is made of a polycrystalline semiconductor having a fiber structure and is manufactured at a low temperature of 200 to 250 ° C.
-087801 (57.5.24). FIGS. 6 and 7 show evaluations of extremely important reliability characteristics in consideration of the reliability of the photoelectric conversion device. FIG. 6 shows a curve (50) in which the number of photons added to the sample was 1 × 10 ¹⁵ / cm ² when measuring the constant energy spectral characteristics. The vertical axis indicates the normalized quantum efficiency (efficiency) with the maximum point being “1”. This device is irradiated with AM1 (100 mW / cm ² ) light for 2 hours. After that, the light sensitivity characteristic changes as shown by the curve (51), and the characteristic is extremely deteriorated for light of 350 to 500 nm.
It turned out to be lower. When this is subjected to a thermal annealing treatment at 150 ° C. for 2 hours, a curve (52) is obtained, and the characteristic is
The curve (50) recovers for the short wavelength light of 350 to 500 nm, and does not recover for the long wavelength light of 600 to 800 nm. For this reason, there has been a demand for a highly reliable photoelectric conversion device which is not deteriorated by the light irradiation-thermal annealing treatment, that is, has no Stepler-Lonski effect. FIG. 7 shows that the average oxygen concentration in the I-type semiconductor is 5%.
This shows the characteristics of the photoelectric conversion device in the case of × 10 ¹⁸ cm ^-3 . When the light irradiation (AM1) was performed for 2 hours corresponding to the curve (50) shown in FIG. 6, a curve (51) whose characteristics were almost improved was obtained. Further thermal annealing only slightly changed curve (52). This proved that the concentration of oxygen as an impurity in the I-type semiconductor layer was extremely important for stabilizing characteristics (preventing deterioration). In addition, the oxygen concentration was found to be extremely low at least at 5 × 10 ¹⁸ cm ⁻³ . Further, the light irradiation effect (Stepler-Lonski effect) was able to obtain higher reliability by further reducing the oxygen concentration. In addition, as is clear from FIG. 5, the conversion efficiency (curve (49)) is improved. This is because the number of recombination centers due to dangling bonds of oxygen in the I-type semiconductor layer decreases, the diffusion length of holes increases, and the width of the depletion layer is only 0.1 μm when the oxygen concentration is 1 × 10 ²⁰ cm ^−3. However, when it is 5 × 10 ¹⁸ cm ⁻³ or less, it becomes 0.4 μm or more, and most preferably when divided into the entire thickness of the I-type semiconductor, it is possible to produce a photoelectric conversion device that does not show any deterioration. As described above, the present invention has found that the conversion efficiency and the reliability as a photoelectric conversion device are improved as the oxygen and carbon concentrations, particularly as oxygen as impurities, are reduced, and its practical use is improved. 5 × 10 ¹⁸
cm ^-3 or less, preferably 1 × 10 ¹⁸ cm ^-3 or less. In the above description, a photoelectric conversion device having one PIN junction has been described.
··· It is also important as an application of the present invention to make at least two junctions with a PIN junction, and these may be integrated on a substrate having an insulating surface. In the description so far, silane, particularly monosilane, has been shown as the silicide gas. However, the present invention is also effective for polysilanes such as disilane, and it is possible to physically purify silicide gases because they have a large molecular particle size. Similarly, silicon fluoride such as SiF is effective because its molecular diameter is as large as 5 °. Regarding germanium, it is also possible to use germanium (GeH ₄ ) and use only Si _x Ge _1-x (0 <x <1) or Ge as the non-single-crystal semiconductor for the I-type semiconductor layer of the PIN junction. . In the above description, the photoelectric conversion device having one PIN junction has been mainly described. However, the semiconductor layer has at least one NI or PI junction, ie N (source or drain) I (channel forming region) N (drain or source), an insulated gate field effect semiconductor device having a PIP junction, or a NIPIN, PINIP junction The present invention is extremely effective also for a transistor having

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows an outline of a plasma gas phase reactor for manufacturing a semiconductor device of the present invention. FIG. 2 shows characteristics obtained by the present invention and electric characteristics of a conventional intrinsic semiconductor. FIG. 3 shows changes in electrical characteristics obtained by the reactive gas purification method of the present invention. FIG. 4 shows a photoelectric conversion device of the present invention. FIG. 5 shows various characteristics of the photoelectric conversion device obtained according to FIG. 4 (B). FIG. 6 shows constant energy spectral characteristics of a conventional photoelectric conversion device. FIG. 7 shows a constant energy spectral characteristic of the photoelectric conversion device of the present invention. [Explanation of Signs] 1. Reactor 2. High-frequency oscillator 3, 3 'Electrode 8, 9, 10 Electron thermostat 11, 14, 12
Gas purifier 15, 13, 16 ... Gas purifier 17 ...
Microwave oscillator 18. Attenuator 19.
・ Ceramics 20 ・ ・ Shield 21 ・ ・ External heating furnace 22 ・ ・ Substrate 23 ・ ・ Vacuum pump 24 ・ ・ Stop valve 25 ・ ・ Needle valve

Claims (1)

(57) [Claims] Purified by a gas purifier located on the reaction gas inlet side
Using a silicide gas with a purity higher than 99.99%
Half containing a non-single-crystal silicon semiconductor formed by a vapor phase method
A method for manufacturing a conductor device, comprising : adjusting the oxygen concentration in the non-single-crystal silicon semiconductor to 5 × 10 ¹⁸
cm ^-3 or less and the carbon concentration is 4 × 10 ¹⁸ cm ^-3 or less.
A method for manufacturing a semiconductor device. 2. The semiconductor device includes the non-single-crystal silicon semiconductor and
PIN junction, N-type semiconductor
Including I junction, PI junction, PIP junction or NIN junction
2. The method for manufacturing a semiconductor device according to claim 1, wherein: