JP2015023185A - Separation method of epitaxial film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To separate silicide, epitaxially grown on a substrate, simply from the substrate.SOLUTION: An epitaxial film 2 composed of BaSiis epitaxially grown on a Si substrate 1 at 500-600°C. The Si substrate 1 is then taken out from a MBE device, carried in a heating device, and heat-treated under argon gas atmosphere at 700-800°C, for 10-60 sec. Thereafter, it is cooled down to the room temperature. Finally, an adhesive tape 3 is pasted to the surface of the epitaxial film 2, and the epitaxial film 2 is peeled off from the Si substrate 1, together with the adhesive tape 3, by pulling the adhesive tape 3.

Description

  The present invention relates to a method for separating an epitaxial film from a substrate. In particular, the present invention relates to a method for suppressing the occurrence of cracks in the epitaxial film and separating them easily.

  As a method of separating and removing the substrate after forming the epitaxial film on the substrate, a sacrificial layer is provided between the substrate and the epitaxial film, and the sacrificial layer is removed by wet etching or gas etching, thereby removing the epitaxial film from the substrate. A method of separation is known.

  As a technique for separating ITO on a glass substrate, a method of causing separation due to a difference in linear expansion coefficient by cooling the glass substrate after heating is also known (Patent Document 1). In this method, it is described in Patent Document 1 that ITO is obtained in a powder form.

JP 2011-16692 A

  However, in the method using a sacrificial layer, it is necessary to use a material that is lattice-matched to both the epitaxial film and the substrate and is more easily etched than the epitaxial film and the substrate, and the material is severely restricted. Therefore, applicable systems are limited. In particular, when the epitaxial film is silicide that is easily etched by a solvent, the epitaxial film is also etched when the sacrificial layer is removed by wet etching. Therefore, separation using a sacrificial layer is difficult.

  Further, when the method of Patent Document 1 is applied to an epitaxial film made of silicide as it is, many cracks are generated in the epitaxial film, and a wide film-like epitaxial film cannot be obtained.

  As described above, a technology for separating an epitaxial film made of silicide from a substrate has not been established.

  Accordingly, an object of the present invention is to provide a method for separating an epitaxial film made of silicide from a substrate in a simple and suppressed manner.

  The present invention relates to an epitaxial film separation method for separating an epitaxial film epitaxially grown on a substrate from the substrate, wherein the epitaxial film is silicide, and the epitaxial film has a linear expansion coefficient four times or more larger than that of the substrate, After the epitaxial film is formed, the substrate is heat-treated at a temperature of 600 to 800 ° C. for 10 to 60 seconds, thereby causing separation due to the difference in linear expansion coefficient between the substrate and the epitaxial film. It is the isolation | separation method of the epitaxial film characterized by making it isolate | separate.

  For the substrate, any material lattice-matched with silicide can be used, and Si is particularly preferable. The thickness of the substrate is desirably 100 to 1000 μm, and the diameter of the substrate is desirably 1 to 25 cm. This is to make it easier to peel the epitaxial film from the substrate and to obtain an epitaxial film having a large area. A more desirable substrate thickness is 300 to 500 μm, and a more desirable substrate diameter is 5 to 15 cm.

Silicide is a compound of metal and Si, and the like _{BaSi 2, FeSi 2, CoSi 2} , NiSi 2, TiSi 2, MnSi 2, Mg 2 Si, SrSi 2, CaSi 2. In particular, the present invention is suitable for separating the epitaxial film made of BaSi _2. The silicide referred to in the present invention includes a compound in which a part of the metal site or Si site is replaced with another element. For example, the band gap of silicide can be controlled by replacing the metal site with Sr, Ca, Mg, or the like. In addition, impurities may be doped during epitaxial growth in order to control physical properties such as conductivity type. For example, As, Sb, Bi, etc. may be doped.

  In the present invention, the epitaxial film is easily peeled off from the substrate during the heat treatment by setting the linear expansion coefficient of the epitaxial film to four or more times that of the substrate. More desirably, it is 4 to 8 times. If it is less than 4 times, peeling hardly occurs, and if it exceeds 8 times, cracks are likely to occur in the epitaxial film, which is not desirable. More desirable is 5 to 6 times.

  The thickness of the epitaxial film is preferably 0.1 to 1% of the thickness of the substrate. This is because within this range, it becomes easier to separate the epitaxial film without causing cracks. More desirably, it is 0.3 to 1%. The thickness of the epitaxial film is preferably in the range of 0.3 to 5 μm, more preferably 1 to 3 μm.

  As a method for forming the epitaxial film, an RDE method, an MBE method, a CVD method, a sputtering method, or the like can be used. In particular, a high quality and flat epitaxial film can be obtained by epitaxially growing a thin film by using the RDE method and then epitaxially growing by using the MBE method.

  Further, the growth temperature of the epitaxial film is desirably 500 to 600 ° C. Within this temperature range, a high quality and flat epitaxial film can be obtained. More desirably, the temperature is 550 to 580 ° C.

  The heat treatment is more preferably performed at 600 to 800 ° C. for 10 to 60 seconds. If it is this range, peeling of an epitaxial film will become easier. More desirably, it is performed at 700 to 800 ° C. for 20 to 40 seconds. As a heating method, any of a method of heating by heat conduction such as a heater and a method of directly heating the substrate such as induction heating or microwave heating can be used. It is particularly preferable to use flash lamp heating. The heating rate is desirably 10 to 50 ° C./sec. This is because if it is slower than 10 ° C./sec, peeling hardly occurs, and if it is faster than 50 ° C./sec, cracks are likely to occur. More preferably, it is 30-50 degreeC / sec, More preferably, it is 30-40 degreeC / sec. The heat treatment atmosphere is preferably a rare gas atmosphere such as Ar.

  The cooling may be performed by natural heat dissipation, or may be performed by contacting with a cooled solid, attaching to a cooled liquid, or placing in a cooled gas atmosphere. However, the cooling rate is desirably 30 to 50 ° C./sec. If it is this range, it can cool, suppressing that a crack arises in an epitaxial film.

  Further, the heat treatment may be performed by a rapid heating and cooling method such as RTA (rapid thermal annealing).

Further, the thickness of the epitaxial film is x (nm), the temperature of the heat treatment is y (° C.), the heat treatment time is 10 to 60 seconds, and x and y satisfy y ≦ −140 · log ₁₀ x + 1120. It is desirable. If it is this range, a crack can be prevented more.

  According to the present invention, an epitaxial film made of silicide can be easily separated from a substrate without using a sacrificial layer. Moreover, it can isolate | separate, suppressing the crack of an epitaxial film.

FIG. 5 shows steps of an epitaxial film 2 transfer method according to the first embodiment. A photograph of the transferred epitaxial film 2 taken. The graph which showed the attenuation | damping behavior of the photoexcited carrier of the epitaxial film. The figure which showed the thickness dependence of the epitaxial film 2, and the heat treatment temperature dependence of crack generation.

  Specific examples of the present invention will be described below, but the present invention is not limited to the examples.

A method of transferring the epitaxial film 2 made of BaSi ₂ on the Si substrate 1 from the Si substrate 1 and transferring it to another glass substrate 5 will be described below with reference to FIG.

  First, a Si substrate 1 made of Si having a (111) plane as a main surface and a thickness of 500 μm was prepared. Then, the Si substrate 1 was introduced into the MBE apparatus, and the surface protective oxide film was removed by performing thermal cleaning.

[Film formation process]
Next, an epitaxial film 2 made of BaSi ₂ was epitaxially grown on the Si substrate 1. As a growth method, first, epitaxial growth was performed by MBE after epitaxial growth of several tens of nm by RDE (reactive deposition epitaxy) method. The growth temperature was 500 to 600 ° C. The thickness of the epitaxial film 2 was 1.5 μm. In the RDE method, only Ba is used as an evaporation source, and BaSi ₂ is generated by reacting Si on the Si substrate 1 with Ba evaporated on the surface of the Si substrate 1. The deposition rate of Ba was 10 nm / min. In the MBE method, both Ba and Si are used as vapor deposition sources. The deposition rate of Ba was 1.2 nm / min, and the deposition rate of Si was 0.8 nm / min. Further, the degree of vacuum during epitaxial growth was set to the order of 10 ⁻⁷ Torr. The epitaxial film 2 was a crystal in which three different domains were mixed, with the growth axis direction (that is, the direction perpendicular to the main surface of the Si substrate 1) aligned with the a axis. Further, as described above, the epitaxial film 2 grown by the two-stage growth method grown by the MBE method after being grown by the RDE method was high quality and flat.

[Heat treatment process]
Next, the Si substrate 1 was taken out from the MBE apparatus and carried into a heating apparatus. And it heat-processed for 600 to 800 degreeC and 10 to 60 second in argon gas atmosphere. The heating rate was 30 to 50 ° C./sec.

[Cooling process]
Then, it cooled to room temperature by natural heat dissipation. The cooling rate by natural heat dissipation is 30 to 50 ° C./sec.

Here, the linear expansion coefficient of Si is 2.6 × 10 ⁻⁶ (1 / K), and the linear expansion coefficient of BaSi ₂ is 14.8 × 10 ⁻⁶ (1 / K) (both values at 298K). And the linear expansion coefficient of BaSi ₂ is 5.7 times that of Si. Since the difference in coefficient of linear expansion is thus large, a strong stress is applied to the epitaxial film 2 in the plane direction in the heat treatment, and the bonding force is weakened at the interface between the Si substrate 1 and the epitaxial film 2. During cooling, peeling occurs on the entire surface to relieve stress. Moreover, since the heat treatment temperature is set to 600 to 800 ° C. for 10 to 60 seconds, peeling can be caused while suppressing the occurrence of cracks in the epitaxial film 2. Further, since the heating rate is set to 10 ° C./sec or more, peeling does not easily occur, and since the heating rate is set to 50 ° C./sec or less, cracks are hardly generated in the epitaxial film 2.

  Next, the Si substrate 1 is taken out from the heating device, and the adhesive tape 3 is bonded to the surface of the epitaxial film 2 (FIG. 1 (b)). It was peeled off (FIG. 1 (c)). As a result, the epitaxial film 2 having a large area can be separated from the Si substrate 1. The epitaxial film 2 may not be completely separated from the Si substrate 1 in the heat treatment step depending on conditions such as the heat treatment conditions and the thicknesses of the Si substrate 1 and the epitaxial film 2, but only a small part of the region is not peeled off. Since it is a very small region and the bonding force at the interface is weakened, the entire surface can be easily peeled off by the physical force of the adhesive tape 3 and the epitaxial film 2 can be separated.

  Then, the glass substrate 4 which consists of glass was prepared, the adhesive material 5 was arrange | positioned on the glass substrate 4, the epitaxial film 2 was bonded together on the adhesive material 5, and the adhesive tape 3 was bonded together to the glass substrate 4 ( FIG. 1 (d)). The adhesive 5 is an adhesive such as an epoxy resin, a double-sided tape, or the like.

As described above, the epitaxial film 2 having a large area (for example, an area of 1 cm ² or more) could be easily transferred from the Si substrate 1 to the glass substrate 4.

FIG. 2 is a photograph of the transferred epitaxial film 2 when the thickness of the epitaxial film 2 is 1170 nm. A black portion of about 1 cm square is the epitaxial film 2, and a circular transparent portion below it is the glass substrate 4. It can be seen that the epitaxial film 2 made of a wide film of BaSi ₂ has been transferred onto the glass substrate 4.

  FIG. 3 shows photoexcited carriers for the epitaxial film 2 separated from the Si substrate 1 in Example 1 and the epitaxial film 2 grown on the Si substrate 1 and not separated (Comparative Example 1 in FIG. 3). It is the graph which showed the attenuation | damping behavior of. The measurement method is a μ-PCD method using laser light having a wavelength of 350 nm. The heat treatment in the separation step of the epitaxial film 2 was performed at 800 ° C. for 30 seconds, and the thickness of the epitaxial film 2 was 1.17 μm.

  As shown in FIG. 3, it was found that the behaviors of the separated epitaxial film 2 and the epitaxial film 2 as grown on the Si substrate 1 are approximately the same. Therefore, it was found that even if the epitaxial film 2 was separated from the Si substrate 1 by the method of Example 1, the crystal quality of the epitaxial film 2 was not affected at all.

  FIG. 4 is a diagram showing the results of examining the influence of the thickness of the epitaxial film 2 and the heat treatment temperature on the occurrence of cracks in the epitaxial film 2. The heat treatment time was 30 seconds. In FIG. 4, circled plots are those in which no crack was generated in the epitaxial film 2, and square plots were those in which cracks were generated.

As shown in FIG. 4, it was found that the lower the heat treatment temperature or the thinner the epitaxial film 2, the harder cracking occurs in the epitaxial film 2. Further, as shown in FIG. 3, the boundary of whether or not a crack occurs is a straight line of y = −140 · log ₁₀ x + 1120, where the thickness of the epitaxial film 2 is x (nm) and the heat treatment temperature is y (° C.). Assuming that the above is true, if x and y are in a range satisfying y ≦ −140 · log ₁₀ x + 1120, no crack is generated. FIG. 4 shows the result when the heat treatment time is 30 seconds, but it is assumed that the same result is obtained when the heat treatment time is 10 to 60 seconds.

[Modification]
In Example 1, the Si substrate 1 made of Si having the (111) plane as the principal surface was used as the substrate on which BaSi ₂ is grown. However, it can be epitaxially grown in lattice matching with BaSi _2, and is epitaxially grown. Any material having a linear expansion coefficient of the film 2 that is four times or more that of the substrate can be used for the substrate. For example, SiC can be used. The Si substrate 1 preferably has a diameter of 1 to 25 cm. This is because the epitaxial film 2 can be easily peeled off and the epitaxial film 2 having a large area can be obtained. It is more preferably 1 to 15 cm, and further preferably 5 to 10 cm.

In Example 1, BaSi ₂ is grown as the epitaxial film 2, but other silicides whose linear expansion coefficient of the epitaxial film 2 is four times or more that of the Si substrate 1 may be used. For _{example, FeSi 2, CoSi 2, NiSi} 2, TiSi 2, MnSi 2, Mg 2 Si, SrSi 2, CaSi 2 , etc. may be allowed to grow. Further, a compound in which the metal site or Si site of the silicide is replaced with another element may be used. For example, BaSi ₂ Ba may be substituted with 10 to 50%, Sr, Ca, Mg, or the like. By such substitution, the band gap of silicide can be controlled, and the band gap can be optimized when the epitaxial film 2 is used in a solar cell. Further, impurities may be doped to control physical properties such as conductivity type. BaSi ₂ is n-type when undoped.

Even when a substrate other than the Si substrate 1 is used and other than BaSi ₂ is grown as the epitaxial film 2, the linear expansion coefficient of the epitaxial film is desirably four times or more the linear expansion coefficient of the substrate. Within such a range, the epitaxial film can be easily detached from the substrate, and a wide film-like epitaxial film can be isolated. More preferably 4 to 8 times, and even more preferably 5 to 6 times.

  In Example 1, the thickness of the Si substrate 1 is 500 μm and the thickness of the epitaxial film 2 is 1.5 μm. However, the thickness of the Si substrate 1 and the epitaxial film 2 is not limited to this. However, the thickness of the epitaxial film 2 is desirably 0.1 to 1% of the thickness of the Si substrate 1. This is to facilitate peeling from the Si substrate 1 while suppressing cracks in the epitaxial film 2. More preferably, it is 0.3 to 1%.

  In Example 1, a thin film is epitaxially grown on the Si substrate 1 by the RDE method, and then further epitaxially grown using the MBE method. However, the epitaxial film 2 is grown using only the RDE method or only the MBE method. You may let them. Of course, an epitaxial growth method other than the RDE method or the MBE method, such as a CVD method or a sputtering method, may be used.

  Moreover, in Example 1, although the growth temperature of the epitaxial film 2 is 500-600 degreeC, it does not restrict to this. However, by setting the growth temperature within this range, a high quality and flat epitaxial film can be obtained. More desirably, the temperature is 550 to 580 ° C.

  Further, the heat treatment conditions are not limited to those shown in the first embodiment. In Example 1, the heat treatment atmosphere is Ar, but it may be performed in a gas atmosphere that is not reactive with Si or Ba. For example, a rare gas other than Ar, such as He, Ne, or Kr, or an inert gas such as nitrogen can be used. In Example 1, the heat treatment temperature is set to 600 to 800 ° C. and the heat treatment time is set to 10 to 60 seconds. More preferably, the heat treatment temperature is set to 700 to 800 ° C. and the heat treatment time is set to 20 to 40 seconds. . More desirably, the temperature is 750 to 800 ° C. and 30 to 40 seconds. As a heating method, a method of heating indirectly by a heater or the like, or a method of heating directly by induction heating, microwave heating, or the like can be used. In particular, it is preferable to heat by flash lamp heating. Moreover, in Example 1, although the heating rate was 30-50 degree-C / sec, it is more desirable to set it as 30-40 degree-C / sec.

  Further, the cooling method after the heat treatment is not limited to that by natural heat dissipation in Example 1. It may be brought into contact with a cooled solid, immersed in a liquid such as a cooled aqueous solution, or cooled by being placed in a cooled gas atmosphere. However, the cooling rate is desirably 30 to 50 ° C./sec. If it is this range, it can reduce, suppressing the crack of the epitaxial film 2. FIG.

  Further, in the heat treatment in Example 1, a rapid heating and cooling method such as RTA may be used.

  Further, in Example 1, the epitaxial film 2 is peeled off from the Si substrate 1 by the adhesive tape 3, but may be separated by other physical and mechanical methods. For example, the epitaxial film 2 may be peeled off by directly bonding the epitaxial film 2 to another substrate and applying a mechanical impact to the Si substrate 1.

  An epitaxial film such as barium silicide obtained by the present invention can be used as a material for a thin film solar cell.

1: Si substrate 2: Epitaxial film 3: Adhesive tape 4: Glass substrate 5: Adhesive

Claims (9)

In an epitaxial film separation method for separating an epitaxial film epitaxially grown on a substrate from the substrate,
The epitaxial film is silicide;
The epitaxial film has a linear expansion coefficient that is at least four times greater than the substrate,
After forming the epitaxial film on the substrate, the substrate is heat-treated at a temperature of 600 to 800 ° C. for 10 to 60 seconds, thereby causing separation due to a difference in linear expansion coefficient between the substrate and the epitaxial film. And separating the epitaxial film from the substrate,
An epitaxial film separation method characterized by the above.   The method for forming an epitaxial film according to claim 1, wherein the substrate is a Si substrate. The method for separating an epitaxial film according to claim 1, wherein the silicide is BaSi ₂ .   4. The method for separating an epitaxial film according to claim 1, wherein the epitaxial film is formed by epitaxial growth by an RDE method and then epitaxial growth by an MBE method. 5.   5. The method for separating an epitaxial film according to claim 1, wherein the epitaxial film is grown at 500 to 600 ° C. 6. The thickness of the epitaxial film is x (nm), the temperature of the heat treatment is y (° C.), the heat treatment time is 10 to 60 seconds, and x and y satisfy y ≦ −140 · log ₁₀ x + 1120. The method for separating an epitaxial film according to any one of claims 1 to 4.   The thickness of the said epitaxial film is 0.1 to 1% of the thickness of the said board | substrate, The isolation | separation method of the epitaxial film of any one of Claim 1 thru | or 6 characterized by the above-mentioned.   The epitaxial film according to any one of claims 1 to 7, wherein after cooling, an adhesive tape is attached to the epitaxial film, the epitaxial film is peeled off from the substrate, and an epitaxial film is attached to another substrate. Membrane separation method.   The method for separating an epitaxial film according to claim 1, wherein the substrate has a diameter of 1 to 25 cm.