JP2000077287A - Manufacture of crystal thin-film substrate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To expand the application range of a material which is usable as a support substrate by preventing the support substrate from being exposed to high temps. SOLUTION: This manufacturing method comprises a step (Fig. A) of injecting H ions or He ions in a crystal substrate 2, a step (Fig. B) of heating the crystal substrate 2 to form voids at ion-injected positions 8, while the ion-injected plane 6 of the crystal substrate 2 is pressed to a substrate holder 18 by dead weight, a step (Fig. C) of adhering a support substrate 10 to the ion-injected plane 6 of the crystal substrate 2, using adhesives, and a step (Fig. D) causing the crystal substrate 2 to ped off from the support substrate 10 at the ion-injected positions 8 in the crystal substrate 2 to obtain a crystal thin film 12 on the support board 10.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, as a substrate for a solar cell, a substrate for a liquid crystal display, a substrate for a semiconductor device, etc., and comprises a crystal thin film substrate having a structure in which a crystal thin film is formed on a support substrate. Regarding the method of manufacturing,
More specifically, the present invention relates to a means for preventing a support substrate from being exposed to a high temperature, thereby enabling a wider range of materials that can be used as the support substrate.

[0002]

2. Description of the Related Art For example, in a solar cell, the power generation efficiency when a single crystal silicon substrate is used is higher than that when a polycrystalline silicon or amorphous silicon substrate is used, but the production cost is high. At present, single-crystal silicon substrates are not fully utilized. The main reason for the high production cost is the high cost of the single crystal silicon substrate as a raw material.

[0003] The film thickness required for single crystal silicon of the direct transition type is a BSF structure (Back Surface Field structure, ie,
If the structure is devised by employing an electric field layer on the back surface of the substrate to reduce the recombination loss of carriers),
The thickness may be about 0 to 20 μm, and if the thickness is much larger than this, the probability of electrons and holes disappearing due to trap levels in the silicon substrate increases, and the efficiency is disadvantageously reduced.

However, at present, due to the technical limitations of wire saws used for cutting single crystal silicon ingots,
If the thickness is not more than about 200 μm, cracks and cracks in the substrate occur frequently.
After cutting to about m, each surface damaged by the wire saw is etched by about several tens of μm to finally obtain a single crystal silicon substrate having a thickness of about 120 to 150 μm.

[0005] In such a manufacturing method, a single-crystal silicon ingot having a thickness of 200 to 300 µm is required to be used for a solar cell.
Since only one substrate can be obtained, there is a problem that the material is wasted and the substrate becomes extremely expensive.

[0006] As one of the techniques for solving such a problem, a metal substrate or a glass substrate is provided with a thickness of 0.1 mm on a supporting substrate.
A method of manufacturing a crystal thin film substrate by forming a crystal thin film of several μm to several tens μm, typically a single crystal thin film, has been proposed in, for example, Japanese Patent Application Laid-Open No. 10-93122. Figure 1
This will be described with reference to FIG.

First, a crystal substrate 2 such as a silicon single crystal substrate
And hydrogen ions or helium ions 4 to 40 to 400
Injection is performed at an energy of about keV to a thickness of about 0.5 to 4 μm and about 10 ¹⁶ cm ⁻² or more (implantation step; FIG. 14).
A). 6 is an ion implantation surface, and 8 is an ion implantation position.

Next, the ion implantation surface 6 of the crystal substrate 2
After the supporting substrate 10 is loaded on the substrate (FIG. 14B), high-concentration voids (voids) are formed at the ion implantation position 8 by heating (void forming step, FIG. 14C). The voids are formed to reduce the mechanical strength of the layer and make it easier to peel off the layer later. In general, heating at about 380 to 600 ° C. is required for void formation.

Next, the crystal substrate 2 and the support substrate 1
0 is heated to a high temperature to bond them together (bonding process. FIG. 1).
4D). Generally, the bonding between the two by high temperature heating is 1
000 ° C or higher is required.

Next, the crystal substrate 2 and the supporting substrate 10 are separated at the ion implantation position 8 in the crystal substrate 2, that is, the void formation position, by applying a mechanical force (separation step, FIG. 14E). As a result, the upper layer from the ion implantation position 8 of the crystal substrate 2 shifts to the support substrate 10 side, and a crystal thin film (or a silicon single crystal thin film when the crystal substrate 2 is a silicon single crystal substrate) is formed on the support substrate 10. 12 is obtained. That is, a crystal thin film substrate 16 having a structure in which the crystal thin film 12 is formed on the support substrate 10 is obtained. The thickness of the crystal thin film 12 corresponds to the depth of the ion implantation position 8 and is, for example, about 0.5 to 4 μm.

When it is desired to increase the thickness of the crystal thin film, a crystal thin film 13 is further epitaxially grown on the crystal thin film 12 (epitaxial growth step; FIG. 14F). Thereby, the total (that is, the total of the crystalline thin films 12 and 13) is 10 to
A film thickness of about 20 μm can be obtained. This epitaxial growth is generally performed at 1000 ° C. for silicon.
Before and after heating is required.

The crystalline thin film substrate 16 having the above structure has various uses other than the solar cell substrate. For example, by forming a silicon single crystal thin film having a thickness of about 50 nm to 100 nm on a glass substrate as a supporting substrate, electron mobility about one order higher than that of a polycrystalline silicon (p-Si) thin film can be obtained. Since the leakage current between the source and drain due to the existence of the crystal grain boundary can be drastically reduced, an extremely high-performance and high-speed TFT-LCD (thin film transistor liquid crystal display) can be realized. Further, it can be used as an SOI (Silicon On Insulator) substrate for a semiconductor device.

[0013]

However, in the above-described conventional method of manufacturing a crystalline thin film substrate, the supporting substrate 10
Is about 380 to 600 ° C. in the void forming step,
It is exposed to a high temperature of 1000 ° C. or higher in the bonding step, and about 1000 ° C. in the case of performing the epi-growth step. In the conventional manufacturing method, the supporting substrate 10 is loaded before the void forming step because the supporting substrate 10 is not loaded on the crystal substrate 2 at 380 to 600 ° C.
When it is attempted to form a void layer by heating to about the same level, the void layer is formed due to the pressure of hydrogen gas or helium gas which is rapidly generated in the vicinity of the ion implantation position 8 due to agglomeration and vaporization of implanted ions at the same time as void formation. Since irregularities are generated in the upper layer portion and consequently irregularities are generated on the surface of the crystal substrate 2, the support substrate 10 is stacked before heating to avoid this, and the occurrence of the irregularities is prevented by the support substrate 10. It is thought that it is necessary.

Therefore, the supporting substrate 10 is required not to cause melting, distortion, and the like at the high temperature as described above.
Therefore, the materials that can be used for this are very limited. For example, when the crystal thin film substrate 16 is used for a TFT-LCD substrate, an inexpensive glass substrate having a low softening point, such as ordinary soda glass, cannot be used as the support substrate 10, and the softening point is high but expensive. It is inevitable to use a simple quartz substrate.

Accordingly, an object of the present invention is to prevent the above-mentioned supporting substrate from being exposed to a high temperature and to expand the range of materials that can be used as the supporting substrate.

[0016]

According to one aspect of the present invention, there is provided a method for implanting hydrogen ions or helium ions into a crystal substrate made of silicon or a compound thereof, and then performing ion implantation on the crystal substrate. A void forming step of heating the crystal substrate to form a void at the ion implantation position while being pressed by a pressing unit other than the support substrate, and then using a bonding material to attach the support substrate to the ion implantation surface of the crystal substrate. Bonding step, and then separating the crystal substrate and the support substrate at the ion implantation position in the crystal substrate, a separation step of obtaining a crystal thin film on the support substrate, characterized by comprising (Claim 1).

According to the above manufacturing method, since the support substrate is bonded to the crystal substrate after the void forming step, it is possible to prevent the support substrate from being exposed to the high temperature in the void forming step.

Furthermore, in the void forming step, the crystal substrate is heated while the ion-implanted surface of the crystal substrate is pressed by a pressing means other than the support substrate, so that it is possible to prevent the surface of the crystal substrate from being uneven.

Also, in the bonding step, bonding using an adhesive is employed. Unlike bonding by conventional high-temperature heating, bonding using an adhesive does not require high-temperature heating. Exposure can be prevented.

As described above, according to the present invention, it is possible to prevent the supporting substrate from being exposed to a high temperature, so that the range of materials usable as the supporting substrate can be expanded.

Between the void forming step and the bonding step,
An epitaxial growth step of epitaxially growing a crystal thin film on the ion-implanted surface of the crystal substrate may be provided, and the support substrate may be bonded to the crystal thin film.

Even in the case where the epi growth step is added as described above, since the support substrate is bonded after the epi growth step, the support substrate is exposed not only to the high temperature during the void formation step but also to the high temperature during the epi growth step. This can also be prevented.
Moreover, the thickness of the crystal thin film can be easily increased by adding the epi growth step.

[0023]

FIG. 1 is a process chart showing an example of a method for manufacturing a crystalline thin film substrate according to the present invention. FIG. 2 is a process chart showing another example of the method for manufacturing a crystalline thin film substrate according to the present invention. Portions that are the same as or correspond to those in the conventional example of FIG.

FIG. 1 shows an example in which an epi growth step is not provided, and this example will be described first.

First, hydrogen ions or helium ions 4 are implanted into the crystal substrate 2 (implantation step, FIG. 1A). 6 is an ion implantation surface. The crystal substrate 2 is not limited to a silicon substrate, but may be a silicon compound (for example, SiC, SiGe, Fe
A substrate made of Si ₂ or the like may be used. Hydrogen ions or helium ions 4 even on a silicon compound substrate
It has been confirmed that a void layer is formed by injecting and heating. The crystal substrate 2 is typically a single crystal substrate such as silicon, but may be a polycrystalline substrate. If a polycrystalline substrate is used, the crystalline thin film 12 obtained in a later step will be a polycrystalline thin film.

The energy of the ions 4 determines the ion implantation position 8 in the crystal substrate 2, in other words, the thickness of the crystal thin film 12 obtained in a later step. If the energy of the ions 4 is, for example, 40 to 400 keV, the ion implantation position 8 has a depth of about 0.5 to 4 μm as described above. The implantation amount of the ions 4 is approximately 1 due to void formation.
0 ¹⁶ cm ^-2 or more.

An example of an ion implantation method suitable for implanting the ions 4 will be described later with reference to FIGS.

Next, in this example, the crystal substrate 2 is
The crystal substrate 2 is heated while the ion implantation surface 6 is placed in close contact with the substrate base 18 to form voids at the ion implantation positions 8 in the crystal substrate 2 (void formation step; FIG. 1B). . The heating temperature is, for example, about 380 to 600 ° C. as described above. The heating time is, for example, 10
It is about 30 minutes.

In this example, the crystal substrate 2 presses the ion implantation surface 6 by its own weight, and the crystal substrate 2 itself constitutes a pressing means for pressing the ion implantation surface 6 during heating. According to this, since it is not necessary to use a dedicated pressing device, the process and the apparatus are simplified.

However, the pressing means may be any means capable of pressing the ion-implanted surface 6 of the crystal substrate 2 against the gas pressure from the inside during the heat treatment, and may be other than the above example. For example, as in the example shown in FIG. 3, the pressing substrate 20 may be placed in close contact with the ion-implanted surface 6 of the crystal substrate 2, and the pressing substrate 20 may be removed immediately after the void forming step. Further, at least the ion-implanted surface 6 of the crystal substrate 2 may be filled with a gas or a liquid in a pressurized state, and the ion-implanted surface 6 may be pressed with these. Alternatively, a thin film may be formed on the ion implantation surface 6 of the crystal substrate 2 by, for example, a CVD (chemical vapor deposition) method or a sputtering method, and the ion implantation surface 6 may be pressed by the thin film. Ion implantation position 8
Depending on the depth, specifically, when the ion implantation position 8 is deep, even such a thin film sufficiently functions as a pressing means.

Next, after the temperature of the crystal substrate 2 is lowered to, for example, about room temperature, the supporting substrate 1
No. 0 is bonded using an adhesive (bonding step, FIG. 1C). The adhesive is, for example, an adhesive resin, a metal material having a low melting point, or the like. More specifically, when the support substrate 10 is a transparent substrate such as a glass substrate, for example, an ultraviolet-curing resin is used as an adhesive, and this is applied to the bonding surface and bonded. The ultraviolet curable resin may be cured by irradiating ultraviolet rays from the side and bonded. When the support substrate 10 is, for example, a metal substrate, the above-mentioned metal material having a low melting point may be used as the adhesive. In addition, adhesion may be performed by molecular bonding with water or the like.

Next, the crystal substrate 2 and the supporting substrate 10 are separated at the ion implantation position 8 in the crystal substrate 2, that is, at the void formation position (separation step; FIG. 1D). As a result, the upper layer from the ion implantation position 8 of the crystal substrate 2 shifts to the support substrate 10 side, and the crystal thin film (for example, when the crystal substrate 2 is a silicon single crystal substrate, the silicon single crystal thin film ) 12 is obtained. That is, a crystal thin film substrate 16 having a structure in which the crystal thin film 12 is formed on the support substrate 10 is obtained. The thickness of the crystal thin film 12 corresponds to the depth of the ion implantation position 8 and is, for example, about 0.5 to 4 μm.

As shown in FIG. 4, for example, the crystal substrate 2 and the supporting substrate 10 are separated from each other by a pair of vacuum chucks 22 as shown in FIG.
In the state of being adsorbed at 24, it is sufficient to pull both sides as shown by arrows A and B. By doing so, the crystal substrate 2 and the support substrate 10 can be separated while preventing the occurrence of cracks, chips, and the like.

According to this manufacturing method, since the supporting substrate 10 is bonded to the crystal substrate 2 after the void forming step (FIG. 1B), it is possible to prevent the supporting substrate 10 from being exposed to the high temperature in the void forming step. it can.

Moreover, in the void forming step, the crystal substrate 2
1 is heated in a state where the ion implantation surface 6 is pressed by a pressing means other than the supporting substrate 10 (in the example of FIG. 1 by the weight of the crystal substrate 2), so that the surface (ion implantation surface 6) of the crystal substrate 2 has irregularities. Can be prevented.

In the bonding step (FIG. 1C), bonding using an adhesive is employed. Unlike bonding by conventional high-temperature heating, bonding using an adhesive does not require high-temperature heating.
Also in the bonding step, it is possible to prevent the support substrate 10 from being exposed to a high temperature.

As described above, according to the manufacturing method, the supporting substrate 1
0 can be prevented from being exposed to high temperatures,
The range of materials that can be used as the support substrate 10 can be expanded. That is, various substrates having poor heat resistance can be used as the support substrate 10. For example, the support substrate 10
It is also possible to use an inexpensive glass substrate such as soda glass.

According to the experiment of the present inventor, during the void formation step, the ion implantation surface 6 of the crystal substrate 2 was not pressed by the pressing means at a constant temperature of 380 ° C. or 420 ° C. for 3 hours. When the substrate was heated slowly, the surface of the crystal substrate 2 could be peeled in the subsequent peeling step with almost no irregularities, but when the heating temperature exceeded 450 ° C., irregularities began to appear on the surface of the crystal substrate 2.

However, the method of taking three hours for heating as described above is not preferable because the throughput is greatly reduced. On the other hand, if the pressing means is used as in the present invention, the heating in the void forming step is 10 times as in the conventional example.
Since it takes about 30 minutes, the throughput does not need to be reduced. For example, when heating is performed at 500 ° C. for 10 minutes using the pressing substrate 20 made of a silicon substrate as in the example of FIG. 3, irregularities on the surface of the crystal substrate 2 are of no problem, and After bonding the substrate 10 using an ultraviolet curable resin and applying a force in the peeling direction, the peeling could be performed at the ion implantation position 8.

As in the example shown in FIG. 3, when the ion implantation surface 6 of the crystal substrate 2 is pressed using the pressing substrate 20 during the void forming step, the pressing substrate 20 is pressed against the crystal substrate 2 during heating. In order to prevent adhesion, a material that does not form a chemical bond with water molecules or the like even when heated to about 600 ° C., for example, a thin film of gold or the like is formed on the surface (pressing surface) of the pressing substrate 20 or the like. Substrate 20 made of such a material
It is preferable to use Alternatively, in order to prevent bonding with water molecules, it is also effective to inject fluorine ions into the pressing surface of the pressing substrate 20 or to form a fluorine-based thin film to make the pressing surface hydrophobic. Alternatively, it is also effective to remove the water or oil on the pressing surface by heating or plasma-treating the pressing substrate 20 before pressing.

As in the example shown in FIG. 1, when the ion-implanted surface 6 of the crystal substrate 2 is placed in close contact with the substrate stage 18, the above-described adhesion preventing treatment is applied to the surface (placement surface) of the substrate stage 18. Is preferably applied.

The crystal thin film substrate 16 is, for example, a TFT-L
When used as a substrate for a CD, a single crystal thin film having a thickness of, for example, about 50 to 100 nm may be sufficient as the crystal thin film 12, and thus the manufacturing method of FIG. 1 is sufficient. In the case where a single-crystal silicon thin film having a thickness of about 10 to 20 μm is required, the manufacturing method of FIG.
The ion implantation must be performed at a high energy of V or more, and the method of implanting ions at such a high energy is not practical because the ion implantation apparatus becomes complicated and expensive.

In such a case, it is preferable to use the epitaxial growth together, so that a crystal thin film having the above-mentioned thickness can be easily obtained at low cost.
FIG. 2 shows an example of a manufacturing method in that case.

The manufacturing method of FIG. 2 will be described mainly with respect to differences from the example of FIG. 1. The ion implantation step shown in FIG. 2A and the void forming step shown in FIG. 1B), a crystal thin film 13 is epitaxially grown on the ion-implanted surface 6 of the crystal substrate 2 (epitaxial growth step; FIG. 2C), and then cooled to bond the support substrate 10 to the crystal thin film 13 (FIG. 2C). 2D, which corresponds to FIG. 1C), and then peeled off at the ion implantation position 8 (peeling step, FIG. 2E, which corresponds to FIG. 1D), and the crystal thin film 14 having a predetermined thickness is formed on the support substrate 10. Is obtained. In the above-described epi growth step, in the case of silicon, the crystal substrate 2 is
Heat to around 0 ° C.

The crystal thin film 14 is obtained by laminating the crystal thin film 12 obtained by peeling the upper part of the crystal substrate 2 and the crystal thin film 13 formed by the epitaxial growth. The crystal thin film 13 is formed by the epitaxial growth. Therefore, the crystal thin film 12 has the same crystallinity as that of the crystal thin film 12, and the two crystal thin films 12 and 13 become one integrated crystal thin film 14. When the crystal substrate 2 is a polycrystalline substrate, each of the crystalline thin films 12 to 14 is a polycrystalline thin film.

Even in the case where the epi-growth step (FIG. 2C) is added as described above, the support substrate 10 is bonded after the epi-growth step. Exposure to high temperatures during the epi growth step can also be prevented. In addition, the thickness of the crystal thin film 14 can be easily increased at low cost by adding an epi growth step.

The above-described epitaxial growth is not limited to homoepitaxial, in which the constituent materials of the substrate and the epitaxial thin film are the same, but heteroepitaxial types different from each other may be used.

Next, modified examples of the embodiment shown in FIGS. 1 and 2 will be described.

In applications such as a TFT-LCD substrate and an SOI substrate, when a high-quality crystal thin film free from ion implantation defects is required as the crystal thin film 12 formed on the support substrate 10, the crystal thin film is required after the peeling step. The surface layer of the thin film 12 (this is a portion near the ion implantation position 8 and having many implantation defects) may be ground by etching, polishing, or the like. When the crystalline thin film 13 is formed by epitaxial growth (see FIG. 2E), the entire upper crystalline thin film 12 may be removed by etching or the like. If you do that,
A high-quality crystalline thin film without ion implantation defects can be obtained.

Although it has been described above that a thin film may be formed on the ion-implanted surface 6 of the crystal substrate 2 as a pressing means in the void forming step, the thin film may be made of, for example, a-Si (amorphous silicon). A thin film that has not been crystallized may be formed, and the a-Si layer may be crystallized immediately after the void forming step (that is, before the bonding step) by, for example, heating at about 1000 ° C. or irradiating light such as a laser. . By doing so, even without relying on epitaxial growth,
The thickness of the crystal thin film can be easily increased. Even if the heating is performed, there is no problem regarding the heat resistance of the support substrate 10 because it is before the bonding of the support substrate 10.

When the crystal thin film substrate 16 is used, for example, as a solar cell substrate, an n-type silicon single crystal substrate is used as the crystal substrate 2, and a p-type silicon single crystal thin film is formed as the crystal thin film 13 on the ion-implanted surface 6 by epitaxial growth. Is formed, and the support substrate 10 is bonded thereto and then peeled off at the ion implantation position 8, as shown in FIG. 5, the p-type crystal thin film 13 and the n-type crystal thin film 1 are formed on the support substrate 10.
2 are joined to each other to form a pn junction solar cell.

Further, both crystalline thin films 12 of the solar cell substrate
And 13 are set to, for example, about 0.7 μm and about 20 μm, respectively, and hydrogen ions or helium ions 4 are implanted into the upper crystal thin film 12 at an energy of, for example, about 60 keV and 10 ¹⁶ cm ⁻² or more, followed by heating. Thereby, a void may be formed at the ion implantation position 28 in the crystal thin film 12. If you do so, the literature "Possi
bility of increasingthe efficiency of solar silico
n elements in implanting H ⁺ and He ⁺ ions "; Phyics a
nd Chemistry of Materials Treatment 1994 28 (6) pp.
As detailed in 365-368, the formation of the above voids creates new energy levels in the bandgap of the direct-transition silicon single crystal, and enhances the light absorption coefficient, especially in the long wavelength region. This can dramatically increase the efficiency of the solar cell.

However, if the ion implantation is performed by non-mass separation positive ion implantation, a plurality of implanted layers are formed by a plurality of ion species, and it becomes difficult to form a stable energy level. In the case of injection, it is preferable to perform the injection by mass separation. When the above ion implantation is performed by negative ion implantation of hydrogen (H ⁻ ), in the case of hydrogen, the negative ion becomes H ^−.
, Stable energy levels can be formed even in non-mass separation.

When the crystalline thin film substrate 16 is used for a solar cell, impurities are injected during or after the manufacturing process to impart p-type and n-type properties, or solid-phase diffusion is performed. forming a p-type or n-type amorphous silicon film or the like;
By laminating a thin film, a SiGe thin film, or the like, a photoelectric conversion efficiency may be further increased, or a method of bonding after changing the surface shape by etching may be used as needed.

By applying the crystal thin film substrate 16 to a substrate for a liquid crystal display, a very high performance TFT can be obtained.
-LCDs can be manufactured at low cost. That is, a glass substrate is used as the support substrate 10 and the crystal thin film 12 is formed thereon.
When a silicon single crystal thin film is formed as Nos. To 14, since the silicon single crystal thin film formed on the glass substrate does not have a crystal grain boundary in principle, the electron mobility is almost equal to that of the single crystal substrate, and p-Si (Polycrystalline silicon) A value one order higher than that of a thin film is obtained. For this reason, it becomes possible to manufacture a very high-definition and high-speed TFT-LCD.
In addition, since a step such as laser annealing required for crystallizing p-Si is not required, it can be manufactured at very low cost.

Further, if the above-mentioned crystalline thin film substrate 16 is used,
It is also possible to realize a so-called system-on-panel. That is, since a technology for forming a p-Si thin film at a low temperature has been developed, not only a TFT but also a memory device, a logic device, and the like on a single glass substrate by applying a semiconductor device process. Although the on-panel was temporarily discussed, p-Si has not been realized because of the presence of crystal grain boundaries and a large current flowing along the grain boundaries, resulting in a large leakage current between the source and drain. Also, due to this problem, the TFT structure itself has to adopt a special process and structure such as LDD (Light Doped Drain) at present.

On the other hand, according to the manufacturing method of the present invention, it is possible to manufacture a crystal thin film substrate 16 formed by forming one or more layers of a silicon single crystal thin film on a glass substrate. According to this, it is possible to solve the above problem caused by the crystal grain boundaries. That is, a single-layer or multiple-layer silicon single crystal thin film is formed on one glass substrate, and a TFT, a memory element, a logic element, a photoelectric conversion element (solar cell), or the like is formed thereon and wired. , A system-on-panel can be realized. Moreover, since an inexpensive glass substrate having a low heat-resistant temperature can be used as the glass substrate, the manufacturing cost can be reduced accordingly.

When bonding the support substrate 10 to the ion-implanted surface 6 of the crystal substrate 2 (see FIG. 1C) or the crystal thin film 13 formed by epitaxial growth (see FIG. 2D), If necessary, a technique of forming a barrier layer for preventing impurity diffusion into the crystal thin film 13 and a stress relieving layer for relieving stress caused by the diffusion between the support substrate 10 and the partner may be used.

Although the epitaxial growth of the crystal thin film 13 (see FIG. 2C) may be heteroepitaxial, the following technique is an application example of this. That is, since it is very difficult to make a bulk crystal substrate of a compound semiconductor such as GaAs with a large diameter, it is possible to obtain a large-diameter GaAs film by epitaxially growing GaAs on a large-diameter silicon substrate. Although attempts have been made (see, for example, Japanese Patent Application Laid-Open No. 8-288214), the problem that device characteristics are degraded due to diffusion of silicon atoms into the GaAs film is serious.

In such a case, for example, a silicon substrate is used as the crystal substrate 2 and GaAs is
Is epitaxially grown to form a crystalline thin film 13 made of GaAs (see FIG. 2C), and the support substrate 10 is bonded thereto via the above-described barrier layer (see FIG. 2D), and then separated at the ion implantation position 8 (FIG. 2E). After that, Si)
Is removed by etching, or the crystalline thin film 12 and the crystalline thin film 13 into which silicon atoms have diffused during epitaxial growth are removed, and the surface is flattened to reduce the diffusion of silicon atoms. A crystalline thin film substrate 16 having a GaAs thin film on the surface thereof that has been prevented can be obtained.

Next, an example of an ion implantation technique (apparatus or method) suitable for implanting the hydrogen ions or helium ions 4 will be described. In the following examples, the same or corresponding parts are denoted by the same reference numerals, and differences between the examples will be mainly described.

FIG. 6 shows an example of an apparatus for implanting positive ions of hydrogen or helium by non-mass separation. Plasma chamber 3
A hydrogen or helium plasma 34 is generated in an ion source 30 having an extraction electrode system 36 and a positive ion beam 3 from the plasma 34 by an extraction electrode system 36.
8 is pulled out and injected into the crystal substrate 2 supported on the support 42 in the vacuum vessel 40. This positive ion beam 3
8 corresponds to the ion 4. When hydrogen plasma is generated, positive ions such as H ⁺ , H ₂ ⁺ and H ₃ ⁺ are generated and extracted. When helium ions are generated, H
Positive ions such as e ⁺ and He ₂ ⁺ are generated and extracted.

FIG. 7 shows a plasma immersion (Plasma I).
1 shows an example of an apparatus for implanting positive ions of hydrogen or helium by non-mass separation by a mmersion ion implantation (PIII) method. The plasma 54 is generated near the crystal substrate 2 on the support 42 by the plasma generation means having the high-frequency coil 48, the high-frequency power supply 50, and the matching circuit 52, and the negative pulse bias voltage V is applied to the crystal substrate 2 from the pulse bias power supply 56. By applying _B , positive ions in the plasma 54 are accelerated and injected toward the crystal substrate 2. The pulse bias power supply 56 is a DC power supply 5 in this example.
8 and a switch 60 for turning the output on and off.

FIG. 8 is an improvement of the device of FIG. That is, in this example, a switch 62 is inserted in series with the high-frequency power supply 50, and the switch 62 turns on and off the high-frequency power RF supplied between the support 42 and the high-frequency coil 48 to turn on and off the plasma generation. I have to. Further, the switch 62 and the switch 60 in the pulse bias power supply 56 are periodically turned on and off in synchronization with each other and at a timing (time difference) that the switch 60 is turned on within a predetermined period from the time when the switch 62 is turned on. A timing control circuit 64 is provided.

FIG. 9 shows an example of changes over time of the high-frequency power RF, the emission intensity I _P from the plasma 54, the plasma density N _P and the pulse bias voltage V _{B in} the example of FIG.
Immediately after the high-frequency power RF is turned on, the light emission intensity I _P and the plasma density N _P rapidly increase, and shift to a steady state after a lapse of time t ₃ . The plasma density N _P becomes equal to or higher than the steady state value after time t ₁ from the time when the high-frequency power RF is turned on, and reaches the maximum value after time t ₂ . t ₁ is about 5 to 10 μsec,
t ₂ is about 100 to 200 μsec, t ₃ is about 500 μs
ec to 1 msec.

Accordingly, the time t ₄ from the time when the switch 62 is turned on to the time when the switch 60 is turned on is defined as t ₁ ≦ t ₄ ≦ t
_By setting it to ₃ , specifically, t ₄ is preferably 5
μsec to 1 msec, more preferably 10 μsec to
By setting it to 500 μsec, ions can be extracted from the plasma 54 having a higher density than the steady plasma and can be implanted into the crystal substrate 2. Therefore, the ion implantation amount is increased by about 10 to 30% as compared with the example of FIG. And increase the throughput.

[0067] FIG. 7, FIG. 8, in the apparatus of FIG. 10 further described below, the pulse bias voltage V ion sheath 55 between the plasma 54 crystal substrate 2 is spread upon application of _B, which is the uniformity of energy of the implanted ions In addition, this contributes to limiting the amount of ion implantation. On the other hand, as shown in the example shown in FIG. 12, it is preferable to provide a porous electrode 66 of the ground potential facing the crystal substrate 2 on the support 42 at an interval. The porous electrode 66 may be one having a large number of small holes, a large number of fine metal wires having a diameter of, for example, 1 mm or less arranged in a grid (in a mesh), or such fine metal wires parallel to each other. May be arranged (in a blind).

[0068] The provision of such a porous electrode 66, when the application of pulse bias voltage V _B, since the spread of the ion sheath stops at the position of the porous electrode 66, i.e., the porous electrodes 66
As a result, the spread of the ion sheath can be suppressed, so that the uniformity of the ion energy implanted into the crystal substrate 2 can be improved and the ion implantation amount can be increased.

In any of the above methods, positive ions of hydrogen or helium are implanted into the crystal substrate 2 by non-mass separation. Although a large amount of molecular ions are implanted, the amount of implantation per unit time is large. Since many ion species such as atomic ions and molecular ions are implanted, the implantation depths are different, and the voids may be formed at various depths according to the implantation depth. In addition, when molecular ions having a large mass number are implanted, there is a possibility that the number of crystal defects generated in the upper crystal substrate 2 than the layer in which a void is formed increases. Therefore, the above-described implantation technique is preferably used for applications in which demands on film thickness uniformity and crystal quality are not strict.

The example of FIG. 10 is a modification of the example of FIG. 8, in which negative ions of hydrogen are implanted. In this example for this, the polarity of the DC power source 58 in the pulse bias source 56 to the opposite, a crystal substrate 2 a pulsed bias power supply 57 for applying a positive bias voltage pulse V _B, the pulse bias source 56 Provided instead. Instead of the timing control circuit 64 as described above, the two switches, ie, the switch 62 and the switch 60 in the pulse bias power supply 57 are synchronized with each other and within a predetermined period from the time when the switch 62 is turned off. Switch 60
There is provided a timing control circuit 65 for periodically turning on and off at the timing (time difference) at which is turned on.

[0071] RF power RF in the example of FIG. 10, the electron density N _E in the plasma 54, an example of time change of the negative ion density N _I and the bias voltage V _B shown in FIG. 11. The electron density N in the plasma 54 with the turning off of the high frequency power RF
_E drops rapidly (in about 5 μsec) and becomes a plasma in which low-energy electrons of about 1 to 2 eV are dominant. Molecules or excited molecules are attached to and dissociated from this, generating negative ions. Electron density N _E negative ion density N _I inversely proportional as if decay rapidly (ie negative ion density N _I rapidly increases) after the high-frequency power RF off, about 10μsec
Thereafter, a unique plasma in which positive ions and negative ions are dominant is formed. Negative ion density N _I is a high frequency power RF
The maximum value is reached in about 30 to 40 μsec after the power is turned off, then gradually attenuated, and becomes almost zero about 1 msec after the high-frequency power RF is turned off.

Even if a positive pulse bias voltage V _B is applied to the crystal substrate 2 when the plasma 54 is rich in electrons, most of the electrons that are incident on the crystal substrate 2 are light and have high mobility, and the electrons are negative. Ion implantation cannot be performed. However,
As described above, a unique plasma is formed by turning on / off the plasma generation, and within a period in which the negative ion density N _I is high, specifically, the electron density N _E is reduced to the negative ion density N _I.
More specifically, within 1/10 or less, more specifically, 10 μsec to 1 msec after the high-frequency power RF is turned off.
During a later period, a positive pulse bias voltage V
By applying _B , negative ion implantation can be performed. Therefore, the timing control circuit 65, let me delayed off switch 62 for a time t ₅ switch 6
0 is turned on. The time t ₅ is, 10Myusec～1msec as described above is preferred, 20 [mu]
sec to 200 μsec are more preferable. The latter is
The amount of negative ions implanted into crystal substrate 2 can be further increased.

The example of FIG. 13 is a modification of the example of FIG. 6, in which a hydrogen negative ion beam 70 is extracted from the ion source 30 and implanted into the crystal substrate 2. FIG. 6
In this example, the polarities of the power supplies 44 and 46 are reversed. Electrons extracted together with the negative ion beam 70 heat the crystal substrate 2 and its surroundings and often have an adverse effect. Therefore, for example, as shown in this example, a conductor 72 is provided in the plasma chamber 32 and electricity is supplied to the conductor 72 to weaken it. Preferably, a magnetic field 74 is formed, thereby removing electrons.

In the case of hydrogen, since only negative ions exist as H ⁻ , it is possible to implant a single ion species without providing a mass separator in the case of negative ion implantation of hydrogen. It is possible to uniformly inject into a large area substrate. Therefore, the manufacturing cost can be reduced, and the throughput is very high. The ion species one H ^- since only very accurately it is possible to inject a predetermined depth, yet to atomic ions only be injected, an upper layer of crystalline than the layer voids are formed Crystal defects occurring in the substrate 2 are extremely small. Therefore, the negative ion implantation technique of hydrogen can be applied to a field in which demands on film thickness uniformity and crystal quality are strict.

[0075]

As described above, according to the present invention, it is possible to prevent the supporting substrate from being exposed to a high temperature while preventing the occurrence of irregularities on the surface of the crystal substrate and without lowering the throughput. Can be. As a result, the range of materials that can be used as the support substrate can be expanded. For example, an inexpensive glass substrate with low heat resistance can be used as the support substrate.

According to the second aspect of the present invention, it is possible to prevent the supporting substrate from being exposed not only to the high temperature in the void forming step but also to the high temperature in the epi growing step. Has an additional effect that the thickness of the crystal thin film can be easily increased by the addition.

According to the third aspect of the present invention, since it is not necessary to use a dedicated pressing means, it is possible to obtain a further effect that the process and the apparatus are simplified.

According to the seventh aspect of the present invention, there is an additional effect that the thickness of the crystal thin film can be easily increased without depending on the epitaxial growth.

According to the eighth aspect of the present invention, a further effect is obtained that a high-quality crystal thin film free from ion implantation defects can be obtained.

According to the ninth aspect of the present invention, the following further effects can be obtained. That is, in the case of hydrogen, the negative ions H ^- since there is only, it is possible to inject a single ion species without providing a mass separator, also easily be uniformly injected into a large area substrate Is possible. Therefore, the manufacturing cost can be reduced, and the throughput is very high. The ion species one H ^- since only, it is possible to inject a very accurately predetermined depth, yet to atomic ions only be injected,
Very few crystal defects occur in the crystal substrate above the layer where voids are formed. Therefore, a crystal thin film having excellent film thickness uniformity and crystal quality can be obtained.

[Brief description of the drawings]

FIG. 1 is a process chart showing an example of a method for manufacturing a crystalline thin film substrate according to the present invention.

FIG. 2 is a process chart showing another example of the method for manufacturing a crystalline thin film substrate according to the present invention.

FIG. 3 is a diagram showing another example of the pressing means.

FIG. 4 is a diagram illustrating an example of a peeling unit.

FIG. 5 is a diagram illustrating an example of a solar cell substrate.

FIG. 6 is a diagram illustrating an example of a non-mass separation type ion implantation apparatus.

FIG. 7 is a diagram showing an example of an ion implantation apparatus using a plasma immersion method.

FIG. 8 is a diagram showing another example of the ion implantation apparatus using the plasma immersion method.

FIG. 9 is a diagram showing an example of a time change of a high-frequency power, a plasma emission intensity, a plasma density, and a pulse bias voltage in the apparatus of FIG.

FIG. 10 is a diagram showing another example of the ion implantation apparatus using the plasma immersion method.

11 is a diagram showing an example of a change over time in high-frequency power, electron density in plasma, negative ion density in plasma, and pulse bias voltage in the apparatus of FIG. 10;

FIG. 12 is a view showing an example in which a porous electrode is added to the apparatus shown in FIGS. 7, 8 and 10;

FIG. 13 is a diagram showing another example of a non-mass separation type ion implantation apparatus.

FIG. 14 is a process chart showing an example of a conventional method for manufacturing a crystalline thin film substrate.

[Explanation of symbols]

 2 Crystal substrate 4 Hydrogen or helium ion 6 Ion implantation surface 8 Ion implantation position 10 Support substrate 12-14 Crystal thin film 16 Crystal thin film substrate 18 Substrate base 20 Pressing substrate

Claims (9)

[Claims] 1. A method of manufacturing a crystal thin film substrate having a structure in which a crystal thin film is formed on a support substrate, wherein an implantation step of implanting hydrogen ions or helium ions into a crystal substrate made of silicon or a compound thereof, and then said crystal substrate Forming a void at the ion implantation position by heating the crystal substrate while pressing the ion-implanted surface of the crystal substrate by pressing means other than the support substrate; and then forming a support substrate on the ion-implanted surface of the crystal substrate. Bonding step using an adhesive, and then separating the crystal substrate and the support substrate at the ion implantation position in the crystal substrate, a separation step of obtaining a crystal thin film on the support substrate A method for manufacturing a crystalline thin film substrate, comprising: 2. A method of manufacturing a crystal thin film substrate having a structure in which a crystal thin film is formed on a support substrate, wherein an implantation step of implanting hydrogen ions or helium ions into a crystal substrate made of silicon or a compound thereof, and then said crystal substrate A void forming step of heating the crystal substrate to form a void at the ion implantation position while pressing the ion-implanted surface of the crystal substrate with a pressing means other than the support substrate, and then forming a crystal on the ion-implanted surface of the crystal substrate. An epi-growth step of epitaxially growing a thin film, an adhesion step of bonding a support substrate to the crystal thin film on the crystal substrate using an adhesive, and then bonding the crystal substrate and the support substrate to the ions in the crystal substrate. Peeling at a pouring position of the substrate to obtain a crystalline thin film on the supporting substrate. Law. 3. The pressing means is a pressing substrate placed in close contact with an ion-implanted surface of the crystal substrate, and the pressing substrate is removed immediately after the void forming step.
Or the method for producing a crystalline thin film substrate according to 2. 4. The method of manufacturing a crystal thin film substrate according to claim 1, wherein the crystal substrate is used as the pressing means by placing the ion implantation surface of the crystal substrate in close contact with a substrate table. 5. The method according to claim 1, wherein the pressing means is a gas or a liquid in a pressurized state. 6. The method according to claim 1, wherein the pressing means is a thin film formed on an ion-implanted surface of the crystal substrate. 7. The thin film formed on the ion implantation surface,
7. The method for manufacturing a crystalline thin film substrate according to claim 6, further comprising a crystallization step of crystallizing by heating or light irradiation immediately after said void forming step. 8. The method of manufacturing a crystalline thin film substrate according to claim 1, further comprising an etching step of etching a surface layer of the crystalline thin film on the support substrate by etching after the peeling step. 9. The method according to claim 1, wherein negative ions of hydrogen are implanted in the implanting step.