JP2002141327A - Method for manufacturing crystal thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for manufacturing a crystal thin film by which a crystal thin film formed on a substrate can be separated without being damaged and the substrate can be used several times without being damaged. SOLUTION: In a first step, a silicon substrate 1 with covered periphery is subjected to anode chemical conversion in a first current density for forming a first porous layer 5 on the main region of the substrate 1 except its periphery. Then the cover of the periphery of the substrate 1 is removed and the substrate 1 is subjected to anode chemical conversion in a second current density to form second porous layers 6 and 6' in its periphery and in its main region. After that, in a second step, a crystal thin film 3 is formed by a liquid phase growth method in the main region of the substrate 1. In the first step, after forming the second porous layers 6 and 6', the main region is made more flat and smooth than the periphery by hydrogen annealing. After the second step, in a third step, the crystal thin film 3 is separated from the substrate 1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention belongs to the technical field of manufacturing a crystal thin film, and more particularly to a technique for separating and using a crystal thin film formed on a substrate from the substrate.

[0002]

2. Description of the Related Art A technique is known in which a single-crystal semiconductor thin film is formed on a semiconductor substrate via a release layer such as a porous layer, and then the single-crystal thin film is separated from the substrate. As a method of peeling, a method of etching and a method of mechanically peeling by applying an external force are known. As a method belonging to the latter, Japanese Patent Application Laid-Open No. 7-302889 (Canon) discloses that after forming a porous layer on the surface of a silicon wafer, an epitaxial silicon layer is formed, and another silicon wafer is bonded to the epitaxial silicon layer. Further, it is described that a plate is adhered to each silicon wafer and the epitaxial silicon layer is separated from the silicon wafer by separating the plates.

Japanese Patent Application Laid-Open No. 8-213645 (Sony) similarly discloses that a porous layer is formed on the surface of a single-crystal silicon substrate, and then a pn junction (solar cell layer) is epitaxially grown. The other side of the solar cell layer is adhered to the side of the solar cell layer to be peeled off, while another jig made of, for example, metal or quartz is adhered to the side of the solar cell layer to be peeled off, and then both jigs are separated. From a single-crystal silicon substrate.

[0004]

However, when a crystal thin film is formed by a liquid phase growth method, irregular crystal growth such as burrs has occurred at a peripheral portion including an end face of a substrate. If such irregular crystal growth occurs, there is a disadvantage that the substrate cannot be accommodated in the carrier in a subsequent step. Also,
Crystals generated at the peripheral portion of the substrate are relatively fragile and thus easily peeled off, and this crystal peeling may cause dust.

[0005] In the conventional thin film crystal separation technique, a single crystal film is formed on the entire surface of the substrate, so that the periphery of the porous layer may be covered with the single crystal film. In this case, when the single crystal film is separated, the single crystal film is separated while breaking a part of the peripheral portion thereof, which may damage the single crystal film and the substrate.

Accordingly, the present invention provides a method for separating a crystal thin film formed on a substrate from the substrate without damaging the crystal thin film when obtaining the crystal thin film by separating the crystal thin film from the substrate. It is an object of the present invention to provide a method of manufacturing a crystal thin film that can be reused.

[0007]

According to the present invention, an object of the present invention is attained by anodizing the substrate at a first current density while covering the peripheral portion of the substrate. Forming a first porous layer in a main region other than the peripheral portion of the substrate, removing the coating on the peripheral portion of the substrate, and then anodizing the substrate at a second current density to thereby form a peripheral portion of the substrate. A first step of forming a second porous layer in a portion and a main region, and a second step of forming a crystalline thin film in a main region of the substrate after the first step. And a method for producing a crystalline thin film.

In the present invention, in the first step, after the second porous layer is formed, hydrogen annealing is performed to make the main region smoother than the peripheral portion.

In the present invention, the formation of the crystal thin film is performed by, for example, a liquid phase growth method.

In the present invention, the method may include a third step of separating the crystal thin film from the substrate after the second step.

[0011]

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

The present inventors have found that, with regard to epitaxial film growth on a substrate surface, there are cases where an epitaxial film grows suitably and cases where it does not grow according to the surface condition of the substrate. In particular, when a single crystal silicon thin film is formed on a silicon substrate and the thin film is separated (peeled), a porous layer may be used as a separation layer (peeling layer). In this case, the porous layer is subjected to hydrogen annealing by hydrogen annealing. Its surface is modified and generally smoothed, but not completely smoothed depending on the porosity of the porous layer. Therefore, by utilizing the difference between the substrate surface states, it is possible to prevent the crystal thin film from epitaxially growing on the peripheral portion of the substrate.

1 to 3 are views for explaining the steps of the method for producing a crystalline thin film according to the present invention. FIG. 1 is an explanatory view of forming a porous layer, and FIG. 2 is an explanatory view of forming a crystalline thin film. And
FIG. 3 is an explanatory view of crystal thin film separation. In each of these drawings, (a) is a schematic plan view, and (b) is a schematic cross-sectional view. Hereinafter, each step will be described.

[Formation of Porous Layer] It is known that a porous layer is formed when a silicon substrate is anodized in a hydrofluoric acid solution. In the present invention, the porous layer is used not only as a separation layer of the crystal thin film but also as a crystal growth preventing layer (cover layer) at the periphery of the substrate.

As shown in FIG. 1, first, a peripheral portion 2 of a substrate 1 is formed.
The other region (hereinafter referred to as the main region) is anodized with the first formation current. As a result, the peripheral portion 2 of the substrate 1 is not formed and no porous layer is formed, but the first porous layer 5 is formed in a main region other than the peripheral portion 2. Subsequently, the substrate 1 is anodized with the second formation current including the peripheral portion. As a result, a second porous layer 6 ′ corresponding to the second formation current is formed in the peripheral portion 2, and the second porous layer 6 ′ is provided deep in the first porous layer 5 in a main region other than the peripheral portion. The material layer 6 is formed.

FIGS. 4A and 4B show an example of an anodizing apparatus, wherein FIG. 4A is an overall view and FIG. 4B is a partially enlarged view. The substrate 1 held by the substrate holder 13 is immersed in the chemical liquid 12. As a method for holding the substrate, a vacuum suction (not shown) may be performed between the O-rings 15 and 15 'which are arranged in two layers. The substrate holder 13 also holds an electrode (anode) 14a. An electrode (cathode) 14b is provided at a position facing the substrate 1. A space surrounded by the Si substrate 1 and the anode 14a is filled with an electrolyte 12 '. Chemical solution 12
For example, a mixed solution of hydrofluoric acid and alcohol can be used. The electrolytic solution 12 'may be the same as the chemical solution 12. When a current flows between the electrodes 14a and 14b in this state, a porous layer is formed on the surface of the substrate 1 facing the electrode 14b.

In the present invention, first, anodization is performed with a first formation current while the peripheral portion of the substrate 1 is covered with an annular peripheral retainer 16. Thus, a first porous layer is formed in the main region. Next, remove the edge holder 16,
Anodize with a second formation current. A porous layer corresponding to the second formation current is formed at the periphery, and a porous layer formed in two stages of the first formation current and the second formation current is formed in the main region other than the periphery. Is done.

FIG. 4B is an enlarged cross-sectional view of the peripheral portion of the substrate after the completion of the anodization with the second formation current. The first porous layer 5 is formed only in the main region that has not been covered with the peripheral press. The second porous layers 6, 6 'are formed on both the inner part (6) of the first porous layer 5 and the exposed peripheral part (6'). The “peripheral portion” in the present invention includes, as shown in FIG. 4B, the end surface (or beveling portion) of the substrate 1 in addition to the peripheral portion on the substrate surface.

Next, the substrate anodized as described above is subjected to hydrogen annealing. By properly selecting the first and second anodizing currents, the surface of the main region of the substrate can be smoothed while the surface of the peripheral portion of the substrate is not completely smoothed. For example, the first formation current is set to 5 to 10 mA / cm ² , the differentiation treatment is performed for 10 minutes to 20 minutes, and the second formation current is set to 20 to 20 mA / cm ^2.
Differentiation treatment from 1 minute to 2 at 30 mA / cm ²
% Hydrofluoric acid: Ethanol = 2: 1. The peripheral edge holder 16 is formed of a fluorine resin or the like in the same manner as the substrate holder 13, and is detachable from the substrate holder 13.

[Formation of Crystalline Thin Film] As shown in FIG. 2, an Si single-crystal thin film is formed on the surface of the Si substrate formed as described above and the surface of the peripheral portion 2 is not completely smoothed by the liquid phase growth method. The present inventors have found that, when is formed, the crystalline thin film 3 grows only in the main region.

FIG. 5 is a diagram showing an example of a liquid phase growth apparatus. A crucible 16 containing a solution 17 is provided inside a growth chamber 19 provided with a heater 21. The substrate 1 is held by a substrate holder 22 that can move up and down and rotate forward and backward. A substrate exchange chamber 20 is provided above the growth chamber 19 via a gate valve 18. As the solution 17, tin, indium, copper, aluminum, or the like is used. In the solution 17, Si is dissolved to a saturated amount.

In order to form a Si single crystal thin film using this apparatus, first, with the gate valve 18 closed, the substrate exchange chamber 20
The substrate 1 is loaded into the substrate holder 22 with. After replacing the substrate exchange chamber 20 with hydrogen in the same atmosphere as the growth chamber 19, the gate valve
Open 18 and lower substrate 1 to a position where it is not immersed in solution 17. After annealing at, for example, 1050 ° C. for 10 minutes in a hydrogen atmosphere, the temperature is lowered to a temperature at which the Si dissolved in the solution 17 becomes supersaturated, and then the substrate 1 is immersed in the solution 17, and 0.1 ° C./min.
Slowly cooling at a temperature drop rate of 1.0 ° C
A Si single crystal thin film is grown. If the growth on the back surface is not preferred, the member covering the back surface may be held on the substrate holder 22 so as to overlap the substrate 1. Alternatively, the above-described porous structure of the peripheral portion may be formed on the back surface.

According to the present invention, it is possible to prevent the crystal thin film from growing on the peripheral portion including the end face of the substrate, thereby preventing irregular crystal growth at the peripheral portion.

[Separation of Crystal Thin Film] As shown in FIG. 3, a reinforcing member 4 is attached to the crystal thin film 3 formed as described above, and the crystal thin film 3 is separated from the substrate 1 together with the reinforcing member 4. I do. As described above, the first and second
If the anodizing current is appropriately selected, breakage occurs inside the porous layer in the main region and separation occurs. This separation is performed by the first porous layer 5 and the second porous layer 5 as shown.
In addition to those occurring at the interface with the first porous layer 5, the interface between the first porous layer 5 and the crystalline thin film 3, or the second porous layer 6 and the substrate
It may occur at the interface with 1.

As the reinforcing member 4, a flexible resin such as polycarbonate or polyethylene terephthalate, a metal plate such as stainless steel or aluminum, or quartz or blue plate glass is used, and these are crystal thin films with an adhesive such as an epoxy-based adhesive. Attach to 3. The size of the reinforcing member 4 may be the same as or larger than the crystal thin film 3.

FIG. 6 is a view showing an example of an apparatus for mechanically applying an external force to separate a crystal thin film from a substrate. The crystalline thin film 3 formed on the substrate 1 has a reinforcing member having flexibility in advance.
4 is pasted. After fixing the substrate 1 to the base 25 by vacuum suction or wax bonding, the end of the reinforcing member 4 extending outside the substrate 1 is inserted into the groove 27 of the peeling roller 26 and fixed with the fastener 28. I do. Thereafter, by rotating the peeling roller 26 in the direction of the arrow, the crystalline thin film 3
And is separated from the substrate 1.

According to the present invention, a high-quality crystalline thin film 3 can be obtained because a peeling force that breaks the crystalline thin film 3 is not applied. In addition, since the crystal thin film 3 does not cover the entire surface of the substrate, when separating the crystal thin film 3 from the substrate,
The crystal thin film 3 can be separated without causing breakage of the crystal thin film 3 from the periphery.

In the present invention, the crystal thin film is separated from the substrate 1 by using a reinforcing member 4 having a different coefficient of thermal expansion from that of the substrate 1 by cooling or heating the substrate and the reinforcing member. A known method such as a method of generating a stress in the porous layer using the difference and separating the substrate and the crystal thin film, a method of inserting or injecting a wedge or a high-pressure fluid into the porous layer portion, or the like is appropriately used. be able to.

As shown in FIG. 3, after separation of the substrate and the crystalline thin film, there is a residue of the porous layer on the separation surface, and the surface is not smooth. However, the residue of the porous layer can be removed by a mixed acid of hydrofluoric acid, nitric acid and acetic acid or an alkaline solution such as sodium hydroxide. Alternatively, it may be removed by polishing using a mechanical or chemical mechanical method. The substrate 1 whose surface has been smoothed in this way can be reused to carry out the method of the present invention.

The crystalline thin film obtained by the method of the present invention can be used for producing various electronic devices such as arithmetic elements and storage elements, and photoelectric conversion elements such as light emitting diodes and solar cells.

[0031]

As described above, according to the present invention,
The crystal thin film can be separated from the substrate without being damaged, and the substrate can be used plural times without damaging the substrate when separating the crystal thin film. Therefore, a high-quality crystal thin film can be obtained at low cost.

[Brief description of the drawings]

FIG. 1 is an explanatory view of forming a porous layer in the method for producing a crystalline thin film of the present invention.

FIG. 2 is an explanatory view of forming a crystalline thin film in the method for producing a crystalline thin film of the present invention.

FIG. 3 is an explanatory view of crystal thin film separation in the method for producing a crystal thin film of the present invention.

FIG. 4 is a view showing an anodizing apparatus.

FIG. 5 is a diagram showing a liquid phase growth apparatus.

FIG. 6 is a diagram showing an apparatus for mechanically applying an external force to separate a crystal thin film from a substrate.

[Explanation of symbols]

 1 Substrate 2 Peripheral edge of substrate 3 Crystal thin film 4 Reinforcing member 5 First porous layer 6, 6 ′ Second porous layer

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 33/00 H01L 31/04 X (72) Inventor Takao Yonehara 3-30-2 Shimomaruko, Ota-ku, Tokyo Within Canon Inc. (72) Inventor Kiyofumi Sakaguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo F-term within Canon Inc. (reference) 5F041 CA33 CA63 CA77 5F043 AA02 BB02 DD12 DD14 DD30 FF10 GG10 5F051 AA02 CB09 CB10 CB10 CB30 5F053 AA05 AA25 BB08 DD01 FF01 GG01 HH04 HH10 LL05 PP20

Claims (7)

[Claims] 1. A first porous layer is formed in a main region other than the peripheral portion of the substrate by anodizing the substrate at a first current density while covering the peripheral portion of the substrate. A first step of removing the coating on the peripheral portion of the substrate and thereafter anodizing the substrate at a second current density to form a second porous layer on the peripheral portion and the main region of the substrate;
And a second step of forming a crystal thin film in a main region of the substrate after the first step. 2. The method according to claim 1, wherein in the first step, after forming the second porous layer, hydrogen annealing is performed to make the main region smoother than the peripheral portion. Manufacturing method of crystalline thin film. 3. The method according to claim 1, wherein the crystal thin film is formed by a liquid phase growth method. 4. The method according to claim 1, further comprising a third step of separating the crystal thin film from the substrate after the second step. Wherein said first current density is 5 to 10 mA / cm ^2, characterized in that said second current density is 20 to 30 mA / cm ^2, any one of claims 1 to 4 3. The method for producing a crystalline thin film according to 1. 6. The anodization at the first current density is performed for 10 to 20 minutes, and the anodization at the second current density is performed for 1 to 2 minutes. A method for producing a crystalline thin film. 7. The method according to claim 1, wherein the substrate is a silicon substrate.