JP3091882B2 - Semiconductor device and manufacturing method thereof - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial applications]

According to the present invention, +
The present invention relates to a photoelectric conversion device in which a P-type region serving as an electrode and an N-type region serving as a negative electrode are selectively provided.

2. Description of the Related Art Conventionally, regarding a photoelectric conversion device, a solar cell in which a PN or PIN junction is formed on a silicon substrate or an insulating substrate using a single crystal silicon semiconductor, a polycrystalline silicon semiconductor, or an amorphous silicon semiconductor, or Photocells are known. However, this PN or PIN junction has a positive electrode or a negative electrode on the front and back surfaces of a semiconductor layer laminated on a single crystal silicon substrate or an insulating substrate, and the junction surface is formed on the main surface of the semiconductor layer or the substrate. They are provided substantially parallel to each other, and are merely devised so that a large amount of light is irradiated on the bonding surface. In these conventional photoelectric conversion devices, a bonding surface is provided in parallel with the main surface of the semiconductor layer or the semiconductor substrate. Therefore, the direction of the electric field generated inside the semiconductor due to the PN or PIN junction provided in the semiconductor and the light irradiation surface Became vertical, the light irradiation intensity was not uniform in the direction in which the electric field was applied, and electrons and holes were generated efficiently and could not be extracted to the outside. Further, the single crystal substrate has many drawbacks, such as being extremely sensitive and expensive, difficult to process, and incapable of integrating a plurality of photoelectric conversion devices and arranging them in series or in parallel. In addition, in the case of a photoelectric conversion device using an amorphous semiconductor, the carriers generated by light irradiation have a short extension length of the semiconductor material itself, so that the carriers generated by light irradiation cannot be effectively extracted to the outside. There was a problem to say. On the other hand, in a photoelectric conversion device using a single crystal semiconductor or a polycrystalline semiconductor, since the light absorption coefficient of the semiconductor layer itself is small, the thickness of the semiconductor layer itself has to be increased, and thus there is a problem in manufacturing time and manufacturing cost. Was.

Configuration of the Invention

The present invention is a photoelectric conversion device having a P-type or N-type impurity region selectively in the same semiconductor film on a substrate,
The photoelectric conversion device is characterized in that the direction of the electric field formed by the P-type or N-type impurity region is parallel to the light irradiation surface. In addition, this semiconductor film has a large diffusion length that cannot be obtained with an amorphous semiconductor by being formed of a semi-amorphous or semi-crystalline semiconductor, and has a large light absorption coefficient that cannot be obtained with a single crystal or polycrystalline semiconductor. With this, a photoelectric conversion device with a thin semiconductor film and a long diffusion length can be realized. In the photoelectric conversion device configured as described above, the carrier generated in the photoelectric conversion region between the P-type diffusion region and the N-type diffusion region is efficiently extracted to the outside by the long diffusion length of the semiconductor layer. Can be. Further, since the P-type region and the N-type region are formed in the depth direction of the semiconductor from the light irradiation surface of the same semiconductor film, the electric field between the P-type region and the N-type region in the direction of the electric field is reduced. The light intensity becomes constant, so that the photoelectric conversion efficiency can be improved. The mechanism of the semi-amorphous or semi-crystalline semiconductor used in the present invention will be briefly described. The semi-amorphous or semi-crystalline semiconductor film of the present invention can be obtained by performing a thermal crystallization treatment after forming a film by an LPCVD method, a sputtering method, a PCVD method or the like. The following description will be made using the sputtering method as an example. That is, when sputtering is performed using a mixed gas of hydrogen and argon with a single-crystal silicon semiconductor as a target in the sputtering method, sputtering of heavy atoms of argon (impact)
Atomic silicon also leaves the target and flies over the substrate having the surface to be formed, but at the same time, a cluster of tens to hundreds of thousands of atoms solidifies away from the target as a cluster and flies to the surface to be formed. Let's do it. During this flight, hydrogen combines with the dangling bonds of silicon outside and around the cluster to form a relatively highly ordered region on the formation surface. That is, a mixture of pure amorphous silicon and clusters having a high order on the surface on which the film is formed and having Si—H bonds in the periphery is used. This is heat-treated in a non-oxidizing gas at 450 ° C. to 700 ° C., so that the Si—H bonds around the cluster react with other Si—H bonds to form Si—Si bonds. However, as this bond pulls together, the more ordered clusters attempt to shift phase to a more ordered state, namely crystallization. However, between adjacent clusters, Si-Si bonded to each other pulls between the clusters. As a result, the crystal has lattice distortion, and the crystal peak in laser Raman is measured shifted from the single crystal of 520 cm ⁻¹ to a lower wave number side. Further, since the Si-Si bond between the clusters anchors (connects) each other, the energy bands in each cluster can be electrically connected to each other via the anchoring points. Therefore, it is fundamentally different from polycrystalline silicon in which a crystal grain boundary acts as a carrier barrier, and a carrier mobility of 10 to ²⁰⁰ cm ² / V Sec can be obtained. That is, as in the present invention, a semi-amorphous or semi-crystal based on such a definition can be expected to have a state in which it has apparent crystallinity but has substantially no crystal grain boundary electrically. Of course, if the annealing temperature is 45
When crystallization accompanied by crystal growth of 1000 ° C. or more is performed instead of medium-temperature annealing at 0 ° C. to 700 ° C., oxygen and the like in the film precipitate at the grain boundaries due to the crystal growth, thereby forming a barrier. This is a material having the same crystal and grain boundaries as a single crystal. When the degree of anchoring between clusters in this semiconductor is increased, the carrier mobility is further increased. For this purpose, the amount of oxygen in this film is reduced to 7 × 10 ¹⁹ cm ^−3.
If it is preferably 1 × 10 ¹⁹ cm ⁻³ or less, crystallization can be further performed at a temperature lower than 600 ° C., and high carrier mobility can be obtained. Hereinafter, the present invention will be described according to examples. Embodiment 1 FIG. 1 is a longitudinal sectional view showing a manufacturing process of the present invention. In FIG. 1A, a conductive or insulating substrate can be used as the substrate (1). It is a requirement that this substrate be inexpensive and have mechanical strength and heat resistance for the subsequent film forming process. For this reason, in this embodiment, a ceramic, ceramic, or glass substrate is mainly used. In FIG. 1, magnetron RF is placed on a glass that can withstand heat treatment at about 600 ° C., such as AN glass or Pyrex glass.
A silicon oxide film (2) as a blocking layer was formed to a thickness of 1000 to 3000 ° by (high frequency) sputtering. The process conditions were a 100% oxygen atmosphere, a film formation temperature of 150 ° C., an output of 400 to 800 W, and a pressure of 0.5 Pa. The deposition rate using quartz or single crystal silicon as the target was 30 to 100 ° / min. Further, a silicon film (3) was formed thereon by LPCVD, sputtering, or plasma CVD. When formed by the reduced pressure gas phase method, 100 to 2
00 ° C. lower 450 to 550 ° C., for example 530 ° C. In disilane (Si ₂ H ₆₎
Alternatively, trisilane (Si ₃ H ₈ ) was supplied to a CVD apparatus to form a film. The pressure in the reactor was 30 to 300 Pa. Film formation speed 50-250
Å / min. When performing the sputtering method, the back pressure before sputtering is 1 × 10 ^-5
The pressure was set to Pa or less, and the reaction was performed in an atmosphere in which hydrogen was mixed with argon to 20 to 80% using single crystal silicon as a target. For example, argon was 20% and hydrogen was 80%. The film formation temperature was 150 ° C., the frequency was 13.56 MHz, and the sputter output was 400 to 800 W. The pressure was 0.5 Pa. When a silicon film is formed by a plasma CVD method, the temperature is, for example, 300 ° C., and monosilane (SiH ₄ ) or disilane (Si ₂ H ₆ ) is used. These were introduced into a PCVD apparatus, and a film was formed by applying a high frequency power of 13.56 MHz. The film formed by these methods has oxygen of 7 ×
The concentration is preferably 10 ¹⁹ cm ^-3 or less, and more preferably 1 × 10 ¹⁹ cm ^-3 or less. This is because, when the silicon film is crystallized in such a range, the degree of crystallization can be promoted. For example, in SIMS (secondary ion mass spectrometry) method, oxygen has an impurity concentration of 8 × 10 ¹⁸ cm ⁻³ and carbon of 3 × 10 ¹⁶ cm ⁻³ , hydrogen has an impurity concentration of 4 × 10 ²⁰ cm ⁻³ and silicon has an impurity concentration of 4 × 10 ²⁰ cm ^−3. × 10 ²² cm ^-3
Was 1 atomic%. Thus, the amorphous silicon film is formed in a thickness of 2,000 to 2 μm.
m, for example, 1 μm in thickness, and then subjected to a medium-temperature heat treatment in a non-oxide atmosphere at a temperature of 450 to 700 ° C. for 12 to 70 hours. For example, it was kept at a temperature of 600 ° C. in a nitrogen or hydrogen atmosphere. Since a silicon oxide film in an amorphous state is formed on the surface of the substrate below the silicon film, no specific nucleus is present in the silicon film by this heat treatment, and the whole is uniformly heat-annealed. That is, it has an amorphous structure at the time of film formation, and hydrogen is simply mixed therein. By this annealing, the silicon film shifts from an amorphous structure to a highly ordered state, and a part of the silicon film exhibits a crystalline state. In particular, a region having a relatively high order at the time of forming a silicon film is particularly likely to be crystallized to be in a crystalline state. However, since the silicon existing between these regions is bonded to each other, silicon mutually pulls each other. When the crystal is measured by laser Raman spectroscopy, a peak shifted from the single crystal silicon peak 522 cm ^-1 to a lower frequency side is observed. Its apparent particle size, calculated from the half width, is 50
It is like a micro crystal with ~ 500 mm,
Actually, there are many such high crystallinity regions having a cluster structure, and a film having a semi-amorphous structure in which each cluster is bonded to each other by silicon (anchoring) can be formed. As a result, the coating exhibits a state substantially free of grain boundaries (GB). Carriers can easily move from one cluster to another through anchored locations, resulting in higher carrier mobility than so-called GB polycrystalline silicon. That is, hole mobility (μh) = 10 to ²⁰⁰ cm ² / Vsec and electron mobility (μe) = 15 to 300 cm ² / Vsec are obtained. Similarly, the diffusion length of the carrier is several μm to several tens μm, which is equivalent to or larger than that of the polycrystalline semiconductor. On the other hand, instead of annealing at medium temperature as described above, 900-1
When the film is polycrystallized by high-temperature annealing at a temperature of 200 ° C, segregation of impurities in the film occurs due to solid phase growth from the nucleus, and GB contains a large amount of impurities such as oxygen, carbon, and nitrogen. Mobility is high, but barrier in GB (barrier)
To hinder the movement of carriers there. As a result, it is difficult to obtain a mobility of 10 cm ² / Vsec or more. That is, in the embodiment of the present invention, as described above, the silicon semiconductor (3) having a semi-amorphous or semi-crystalline structure is used. Next, in FIG. 1 (B), a mask (4) made of a photoresist is formed using the photomask, and a dose of 1 × 10 ¹⁵ cm ⁻² of boron is applied to the P-type impurity region (5). It was added by ion implantation. Next, as shown in FIG. 1C, a photoresist mask (6) was formed using the photomask. Then, phosphorus is added to the N-type impurity region (7) in an amount of 1 × 10 ¹⁵ cm ⁻² ,
It was added by ion implantation. The distance between the P-type impurity region and the N-type impurity region is 2 to
It is preferable to make the width as narrow as 20 μm, especially 5 to 7 μm, and make it 1/4 to 1/2 shorter than the diffusion distance of carriers of electrons and holes generated by reexcitation in the semiconductor. Next, heat annealing again at 600 ° C. for 10 to 50 hours,
The P-type and N-type impurity regions were activated. Thermal annealing was performed twice in FIGS. 1A and 1C. However, the annealing in FIG. 1A may be omitted depending on the desired characteristics, and both may be combined by the annealing in FIG. 1C to shorten the manufacturing time. Next, as shown in FIG. 1D, the insulator (8) was formed into a silicon oxide film by the above-mentioned sputtering method. This silicon oxide film may be formed by an LPCVD method or an optical CVD method. For example, it was formed to a thickness of 0.2 to 0.4 μm. Thereafter, a window (9) for an electrode for the P-type and N-type impurity regions was formed by etching using a photomask. Further, aluminum was formed on the whole by sputtering, and the lead (10) was manufactured using a photomask, thereby completing the photoelectric conversion device of this example. As for the characteristics of such a photoelectric conversion device, a conversion efficiency of 11.5% was obtained in an area of 1.05 cm ² , and the diffusion length of carriers in this semiconductor film was 10.5 μm. As a feature of the present invention, since the + and-electrodes do not exist in the semiconductor film stacking direction with the semiconductor layer interposed therebetween as in the conventional device, a short circuit between the two electrodes due to a pinhole formed at the time of manufacturing the semiconductor film. Thus, a photoelectric conversion device having a good fill factor (FF) value could be obtained. Embodiment 2 As shown in FIG. 2A, this embodiment has a structure similar to that of Embodiment 1. However, an amorphous silicon semiconductor film (11) having a thickness of 3000 mm is formed on the light irradiation side of the semiconductor film (3).
Other forming methods and the like are almost the same as those in the first embodiment. The amorphous silicon semiconductor film (11) has a larger light absorption coefficient than the underlying semiconductor film (3). Therefore, in this embodiment, the carrier is changed to the semiconductor film (11) by light irradiation.
After a large amount is generated, it drifts to the semiconductor film (3), moves through the semiconductor layer (3) as a passage, and is taken out from the + and-electrodes. At the same time, carriers are also generated by light irradiation in the semiconductor film (3). However, since the light sensitivity of the semiconductor film has wavelength dependency, it is possible to convert light in a wide wavelength range into electricity by the structure of this embodiment. Becomes possible. Further, the semiconductor film (11) has a wider energy band width than the semiconductor film (3), so that carriers generated in the semiconductor film (3) are prevented from drifting to the semiconductor film (11), and the semiconductor film (11) is prevented from drifting. The carriers generated by the film (11) move to the semiconductor film (3) along the gradient of the energy band, so that the generated carriers can be taken out more efficiently. This is shown in FIGS. 4 (A) and 4 (B). Fig. 4 (A)
4A is an energy band diagram along the line AA 'in FIG. 2A, and FIG. 4B is an energy band diagram along the line BB' in FIG. 2A. I have. Embodiment 3 This embodiment shows an example in which amorphous silicon is provided on the light irradiation side, as in Embodiment 2. FIG. 2 (B) shows a sectional view thereof. Unlike the second embodiment, the light irradiation surface is provided on the substrate side and the extraction electrode is provided on the opposite side. In the present embodiment, in exactly the same steps as in the first embodiment,
The fabrication of the photoelectric conversion device will proceed, but the thickness of the semiconductor film (3) before thermal crystallization treatment must be 1.5 μm in order to provide the amorphous silicon semiconductor film portion (12) below the semiconductor film (3).
And a heat treatment is performed at a temperature of 500 ° C. lower than that of the first embodiment, under such conditions that all the semiconductor films (3) are not completely thermally crystallized, and an amorphous semiconductor film (12) is formed on the substrate side. Was formed. Therefore, in FIG. 2 (B), a boundary (dotted line) is shown between the semiconductor film (3) and the semiconductor film (12), but there is actually no clear boundary, and the thickness direction is higher than the substrate side. A semiconductor film was formed such that the degree of crystallization was different. As a result, as shown in FIG. 4 (C), FIG.
In the energy band diagram along the line CC ′, the semiconductor film (12) is continuously connected to the semiconductor film (3).
The carriers generated in the semiconductor film (12) are guided to the semiconductor film (3) according to the continuous gradient of the energy band, and reach the external extraction electrode through the semiconductor film (3). When a continuous energy band structure is formed, carbon and nitrogen are actively added to the substrate side of the semiconductor film to form a wide gap, so that the gradient of the energy band can be further increased, and carrier To the semiconductor film (3). Embodiment 4 A schematic sectional view of a photoelectric conversion device corresponding to this embodiment is shown in FIG.
Shown in the figure. The manufacturing method of this embodiment is exactly the same as that of the first embodiment.
It has a configuration in which a plurality of mold or N-type regions are provided. Since the P-type or N-type impurity region and the electrode connected thereto are formed on one main surface of the semiconductor film, the + and-electrodes can be arbitrarily connected according to required power. In addition, since the light irradiation surface can be on the substrate side, it is possible to perform arbitrary power only by changing the mask pattern without reducing the area of the photoelectric conversion region for connection of the electrodes. Was. [Effects of the Invention] By adopting the configuration of the present invention, a photoelectric conversion device having a long diffusion length of a thin film on a substrate and a large light absorption coefficient can be realized. In addition, carriers generated by light irradiation diffuse in the planar direction of the semiconductor film, and are efficiently extracted to the outside without being affected by an interface formed in the thickness direction by the formation of the semiconductor film. Another feature is that since the external extraction electrode is formed on the substrate, a plurality of photoelectric conversion devices on one substrate can be integrated and connected directly and in parallel, and the backflow prevention diode is also made of the same semiconductor on the same substrate. Can be made. Since the + electrode and the-electrode are formed only on one surface,
When manufacturing a semiconductor, it is not necessary to consider the thermal stress. Inexpensive substrates, especially insulating substrates such as ceramics, ceramics, and glass, are used.
Since it is formed with a thickness of μ, the material cost is low.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing a manufacturing process of a photoelectric conversion device having a structure according to the present invention. 2 (A), 2 (B) and 3 are longitudinal sectional views of another embodiment of the present invention. FIG. 4 is an energy band diagram corresponding to FIG. 3 ... Semiconductor film 5 ... P-type impurity region 7 ... N-type impurity region 10 ... Electrode 11,12 ... Amorphous semiconductor film

Claims (3)

(57) [Claims] 1. A substrate, a silicon oxide film provided on the substrate, and an I-type semiconductor film provided on the silicon oxide film and having a crystallinity including an oxygen amount of 1 × 10 ¹⁹ cm ⁻³ or less. P-type and N-type regions provided in the I-type semiconductor film so that a bonding surface is substantially perpendicular to the substrate; and the I-type semiconductor film provided in the I-type semiconductor film receiving light irradiation. A semiconductor device comprising an amorphous semiconductor film having a larger light absorption coefficient and a larger energy band width than the film. A step of forming a silicon oxide film acting as a blocking layer on the substrate;
A step of forming a crystalline I-type semiconductor film containing an oxygen amount of ¹⁹ cm ^-3 or less, and sequentially and selectively ion-implanting the I-type semiconductor film so that a bonding surface is substantially perpendicular to the substrate; Forming a P-type and N-type region, and heat-treating the I-type semiconductor film at a temperature of 450 to 700 ° C. in a non-oxidizing atmosphere. 3. A step of forming an amorphous semiconductor film having a larger light absorption coefficient and a larger energy band width than the I-type semiconductor film on the silicon oxide film or the I-type semiconductor film to be irradiated with light. 3. The method for manufacturing a semiconductor device according to claim 2, wherein: