JP2014078541A - Semiconductor thin film manufacturing method - Google Patents

Abstract

A semiconductor thin film can be peeled from a thick substrate with a smaller amount of hydrogen ion implantation.
A step of implanting hydrogen ions as a first ion species into a silicon-based crystal substrate containing silicon, a step of implanting a second ion species into the silicon-based crystal substrate, and the silicon-based crystal substrate include: Heating and heating the implantation layer; and a peeling step of peeling the upper side of the silicon-based crystal substrate from the implantation layer to obtain a silicon-based crystal thin plate. Here, the hydrogen ions as the first ion species are uniformly implanted into the silicon crystal substrate, the second ion species are implanted in a periodic linear pattern, and the second ion species implantation region. Do not overlap each other.
[Selection] Figure 1

Description

The present invention relates to a method for producing a silicon-based crystal thin plate containing silicon used as a substrate for power semiconductor devices, solar cells, liquid crystal displays, etc., and particularly relates to a method in which the silicon-based crystal thin film is silicon carbide.

FIG. 4 is an explanatory view of a conventional technique for peeling a thin film from a thick silicon substrate 4 having a thickness of several millimeters by implanting hydrogen ions 9. FIG. 4 shows a cross-sectional view of the substrate 4. In FIG. 4A, hydrogen ions 9 are uniformly implanted from the implantation surface 1 into the surface of the silicon-based substrate 4. The implantation layer 11 is a position where hydrogen ions are implanted. The ion implantation amount is at a level of 1 × 10 ¹⁷ atoms / cm ² . The depth of ion implantation from the surface of the substrate 4 is about several μm or less. 4B to 4C, a support substrate 10 is prepared, and the support substrate 10 is pressed and bonded to the ion implantation side surface. Heat to about 1000 ° C. for bonding. Reference numeral 12 denotes a joint surface between the crystal substrate 4 and the support substrate 10.

 For example, when the silicon-based substrate is the silicon crystal substrate 4, the implanted hydrogen atoms have an effect of converting the Si—Si bond into the Si—H bond and cutting the bond during this heating process. Furthermore, excess hydrogen atoms form vacancies in the silicon crystal in the process of generating hydrogen molecules (hydrogen gas). FIG. 4D shows that the ion implantation layer is separated as the peeling surface 13 by pulling the support substrate 10 from the thick silicon crystal substrate 4. In this way, a substrate in which a silicon-based crystal thin layer is formed on the support substrate 10 can be formed.

  Patent Document 1 discloses a method of manufacturing a semiconductor material film by forming a microbubble layer at an injection site by ion implantation on a semiconductor crystal substrate.

JP-A-5-211128

When the silicon-based crystal substrate is a silicon single crystal, the hydrogen ion concentration for peeling the substrate is at a level of 1 × 10 ²¹ atoms / cm ³ . That is, since the atomic density of silicon atoms is 5 × 10 ²² atoms / cm ³ , it is considered necessary to implant approximately 10% of hydrogen ions of silicon atoms. In the case of implanting ions into a silicon-based substrate, it is known that the range in which implanted ions are distributed increases as the average implantation depth increases. Therefore, in order to peel a layer of about 5 μm to 100 μm by ion implantation, it is necessary to implant more hydrogen ions.
The problem to be solved by the present invention is to peel a semiconductor thin film from a thick substrate with a smaller amount of hydrogen ions.

According to the present invention, in order to solve the above problems,
A step of implanting hydrogen ions as a first ion species into a silicon-based crystal substrate containing silicon; a step of implanting a second ion species into the silicon-based crystal substrate; and heating the silicon-based crystal substrate to A step of heating the injection layer and a peeling step of peeling the upper side from the injection layer of the silicon-based crystal substrate to obtain a silicon-based crystal thin plate are provided.

  Here, the hydrogen ions as the first ion species are uniformly implanted into the silicon crystal substrate, the second ion species are implanted in a periodic linear pattern, and the second ion species implantation region. Are preferably non-overlapping with each other. If they overlap, the amount of ion implantation increases.

  Further, a third ion species is implanted, the third ion species is implanted in a periodic linear pattern, and the implantation regions of the third ion species do not overlap each other and It is preferable that the scanning directions of the third and third ion species intersect each other.

  In addition, the average implantation depth of the first ion species, the second ion species, and the third ion species is 5 μm to 100 μm from the surface of the silicon-based crystal substrate, respectively. The reason why the implantation depth is preferably 5 μm to 100 μm is that the substrate thickness required for a high-withstand-voltage power device (withstand voltage 13 kV) used as a semiconductor thin film is within this range. More preferably, the first ion species, the second ion species, and the third ion species are implanted with a difference in depth of 1 μm or less.

  Furthermore, the first ion species is a hydrogen ion, and the second ion species and the third ion species are the same or different from any one of hydrogen, silicon, carbon, nitrogen, or a rare gas element, Is suitable.

  As a method of forming a thin film, a support substrate is brought into contact with a silicon crystal substrate into which at least a first ion species and a second ion species are implanted, and the silicon crystal substrate and the support substrate are brought into close contact with each other by heat treatment. It is preferable to peel the substrate and the surface side of the silicon-based crystal substrate from the region into which the ion species are implanted from the silicon-based crystal substrate to form a semiconductor thin film.

As the ion species to be implanted, if silicon is implanted into a silicon crystal, the implantation site expands. Further, when carbon is injected into the silicon carbide crystal, the injection site expands. Nitrogen breaks the bond of silicon carbide and also expands in volume. Oxygen also breaks silicon carbide bonds and expands in volume. The rare gas damages the injection site and makes it easy to peel off. As the rare gas, the larger the atomic number, the greater the damage given, which is preferable.
According to the invention as described above, the process of peeling the thin film from the thick silicon substrate (or silicon carbide substrate) is considered to occur as follows.

        The implanted hydrogen ions react with silicon to form a composite structure having Si—H bonds. Generation of the Si—H bond breaks the Si—Si bond, causes embrittlement of the crystal, and becomes easy to peel off.

-Excess hydrogen injected generates hydrogen gas, which generates stress in the crystal due to the expansion of the gas, and forms vacancies, which are easily separated by the expansion force of the vacancies.
In this way, peeling is a process in which Si-Si bonds by hydrogen ions are broken to form minute regions (embrittled regions) with weak bonds, and excessive hydrogen atoms form hydrogen gas and move by heat. The process of growing into macroscopic sized vacancies while agglomerating. In the process of hydrogen gas expansion, the internal pressure of the vacancies increases, and it is thought that separation occurs at the boundary of the layer embrittled by this stress.
The present invention intends to induce separation with a smaller ion implantation amount by effectively arranging a portion having a high hydrogen ion concentration and a portion having a low hydrogen ion concentration in an ion implantation layer.

  According to the present invention, it is possible to easily manufacture a semiconductor thin film from a silicon crystal substrate with a smaller ion implantation amount and an increased throughput of peeling.

The figure which shows the 1st Embodiment of this invention. The figure which shows the 2nd Embodiment of this invention. The figure which shows the 3rd Embodiment of this invention. The figure which shows a prior art. The figure explaining the principle of this invention.

The present invention is to manufacture a semiconductor thin film by reducing the total amount of ion implantation.
For that purpose, hydrogen is ion-implanted,
Si-Si + 2H → 2Si-H
Then, the silicon bond is cut and the film is peeled off.

Also, by implanting hydrogen ions,
2H → H ₂
This reaction is also caused to expand the ion implantation site and peel the film.

  In order to reduce the total amount of ion implantation, the second and third ion species are implanted, the first (hydrogen ion) implantation amount is reduced, the total ion implantation amount is reduced, and a certain location Only increase the amount of ion implantation and increase the throughput of semiconductor thin film peeling. Only a certain part is expanded in volume, and stress is applied to the substrate to peel off.

  As the depth of ion implantation increases, the implantation depth shifts. In the present invention, the ion implantation acceleration voltage (eV) is adjusted so that the deviation of the implantation depth of the first ion species, the second ion species, and the third ion species is within a range of 1 μm or less. To do.

  In order to peel the semiconductor thin film from the ion implantation site, the support substrate is brought into close contact with the crystal substrate. When the support substrate is brought into close contact with the crystal substrate, 1 to 10 atm is generated by electrostatic pressure. Moreover, the force to peel off the semiconductor thin film is only about minus 0.1 atm to minus 1 atm because it only peels off the peeled film.

  The temperature and time conditions for causing the peeling reaction were as follows. The temperature was raised to 500 ° C./min and the temperature was lowered to about −50 ° C./min. In addition, the holding time in the furnace is about 15 minutes.

  As the support substrate, when the crystal substrate is silicon carbide, a silicon carbide with a low price (for example, SiC sintered body) is used. In this way, the thermal expansion coefficient is also the same as that of the SiC of the substrate.

The surface of the crystal substrate and the surface of the support substrate need to be clean in addition to the thermal expansion coefficient in order to improve adhesion. The surface may be oxidized.
FIG. 1 shows a first embodiment of the present invention. FIG. 1A corresponds to the ion implantation step of FIG. 4A of the prior art.
In the present embodiment, the second ionic species is also a hydrogen ion.

First, as a first ion species, hydrogen ions are irradiated at an implantation amount D1 atoms / cm ² so that the entire implantation surface is uniform so that the average depth of the implantation layer 3 is R1 (for example, 15 μm to 20 μm). (FIG. 1A). Thereafter, as the mean depth of the implanted layer 3 is R1, then as a second ionic species which hydrogen ions, hydrogen ions, 1 injection volume on the position of the scanning path (B) D2 atoms / cm ² Irradiate with. Here, the injection amount D2 is higher in concentration than D1. FIG. 1C shows the hydrogen concentration at the depth R1 from the surface at the cross-sectional position 5 in FIG. Examples of the ion implantation amounts D1 and D2 are 1 × 10 ¹⁶ atoms / cm ² and 1 × 10 ¹⁷ atoms / cm ² , respectively. FIG. 1C shows that the widths of the injection amounts D1 and D2 are W1 and W2, respectively. The width of W1 is several μm, and the width of W2 is about one fourth to one fifth of the width of W1. In order to increase the width W2 of the high-density D2 scanning path, the scanning position is slid a plurality of times along the scanning path 6 to perform ion irradiation. However, the scanning positions are not overlapped.

FIG. 2 shows a second embodiment of the present invention, and FIG. 2 (A) corresponds to the ion implantation step of FIG. 4 (A) of the prior art as in FIG. 1 (A).
As a first ion species, hydrogen ions are uniformly irradiated over the entire implantation surface at an implantation amount of D1 atoms / cm ² so that the average depth of the implantation layer is R1 (FIG. 2A), and then implantation is performed. This time, a second ion species different from hydrogen ions is irradiated to the position of the scanning path in FIG. 2B at an implantation amount of D2 atoms / cm ² so that the average depth of the layer becomes R1. Here, the injection amount D2 is higher in concentration than D1.

FIG. 2C shows the hydrogen implantation amount and the implantation amount of the second ion species at the depth R1 from the surface at the cross-sectional position 5 in FIG. The dotted line indicates the hydrogen implantation amount 8 and the solid line indicates the implantation amount 7 of the second ion species.
As shown in this figure, the concentration of the second ion species at the position of the scanning path is higher than the implantation amount of hydrogen ions. Examples of the ion implantation amounts D1 and D2 are 1 × 10 ¹⁶ atoms / cm ² and 1 × 10 ¹⁷ atoms / cm ² , respectively. In order to adjust W1 and W2 in FIG. 2C, the ion irradiation is performed by sliding the scanning position a plurality of times along the ion irradiation scanning path 6 as described in FIG. By doing.

FIG. 3 shows a third embodiment of the present invention, and corresponds to the prior art ion implantation step of FIG. 4A, as in the first and second embodiments. In the present embodiment, as the first ion species, hydrogen ions are uniformly irradiated over the entire implantation surface at an implantation amount of D1 atoms / cm ² so that the average depth of the implantation layer is R1 (FIG. 1A). Then, hydrogen ions or a second ion species different from hydrogen ions are implanted at the position of the scanning path in FIG. 1B so that the average depth of the implanted layer is R1. Irradiate with ² . Here, the injection amount D2 is higher in concentration than D1. As shown in FIG. 3B, the scanning path 6 is composed of vertical and horizontal scanning paths, and represents a case where they are perpendicular to each other. The second ion species implanted along the vertical and horizontal scanning paths is the same hydrogen ion as the first ion species, or the second ion species different from the first ion species, both vertically and horizontally. The second ionic species may be different from hydrogen in the vertical direction and hydrogen in the horizontal direction. Alternatively, hydrogen ions may be uniformly implanted into the crystal substrate 4, and the second ion species may be implanted vertically and the third ion species may be implanted horizontally. In addition, the crossing angle between the vertical and horizontal scanning paths may deviate from 90 °. In addition to the two types of vertical and horizontal scanning paths, a third scanning path may be provided as necessary to perform ion implantation. Examples of the ion implantation amounts D1 and D2 are 1 × 10 ¹⁶ atoms / cm ² and 1 × 10 ¹⁷ atoms / cm ² , respectively. In order to adjust W1 and W2 in FIG. 2C, as described with reference to FIG. 1C, the scanning position is slid a plurality of times along the scanning path 6 to perform ion irradiation.

 Examples of the second ion species and the third ion species include Si, carbon (C), oxygen (O), nitrogen (N), and rare gases (He, Ne, Ar, Xe, Rn). Regarding the order of implantation, the second ion species may be implanted first even when hydrogen is first. In the embodiment, R1 = 15 μm to 20 μm.

  After the ion implantation, a support substrate 10 is prepared as in the prior art, and high-temperature heat treatment is performed in a state where the support substrate 10 is bonded to the surface of the ion-implanted crystal substrate 4. The heat treatment temperature varies depending on the type of silicon substrate, but in the case of silicon, 900 ° C. to 1000 ° C., and in the case of silicon carbide, 900 ° C. to 1300 ° C. are often used. The heat treatment conditions (maximum temperature, temperature rise and temperature fall conditions, etc.) are optimized for the peeling conditions. The support substrate 10 is bonded to the silicon-based crystal substrate 4 by the heat treatment, and at the same time, the ion implantation layer 11 becomes brittle and vacancies are formed. Finally, when a tensile force is applied to the silicon crystal substrate 4 and the support substrate 10, peeling occurs from the portion of the ion implantation layer 11, and the substrate 4 and the support substrate 10 are separated.

FIG. 5 is an explanatory diagram of the principle of the present invention.
FIG. 5 shows a cross section perpendicular to the scanning path of a sample ion-implanted into the silicon-based crystal substrate 4. Here, the principle will be described using the silicon-based crystal substrate 4 as a silicon single crystal substrate.
When hydrogen ions are implanted at a position having an average depth R1 = 15 μm to 20 μm and then heat treatment is performed, the implantation layer 11 becomes brittle and peeling occurs at this position (Si—Si + 2H → 2Si—H). Excess hydrogen aggregates and expands as hydrogen gas (2H → H ₂ ) to form pores. Separation is promoted by an increase in the pressure in the pores due to this expansion (the direction of expansion 16 is indicated by an arrow). As described with reference to FIG. 1C, in the present invention, the injection amount D2 is injected along the scanning path in addition to the uniform ion implantation amount D1 and the uniform ion implantation amount on the substrate surface. .

 The high concentration injection layer 14 in FIG. 5 represents a cross section perpendicular to the scanning direction. When high concentration hydrogen is injected into the scanning path as in the invention of FIG. 1, excess hydrogen is gasified to increase the internal pressure and form vacancies, and is sandwiched between high concentration injection layers 14. The low concentration injection layer 15 (region where the embrittlement of the injection layer due to hydrogen has occurred but no vacancies are generated) is given a force to peel up and down. As a result, there is an effect of inducing peeling even in a low concentration region.

  In the embodiment of FIG. 2, a second ion species different from hydrogen is implanted into the high concentration implantation region along the scanning path. Also in this case, volume expansion occurs in the high concentration injection region, and there is an effect that the region into which the low concentration hydrogen is injected is peeled up and down.

1: Ion implantation surface 2: Ion 3: Ion implantation layer 4: Silicon-based crystal substrate 5: Cross-sectional position 6: Ion irradiation scanning path 7: Second ion species implantation amount 8: Hydrogen implantation amount 10: Support substrate 11 : Ion implantation layer 12: bonding surface 13 between support substrate and crystal substrate: peeling surface 14: high concentration implantation layer 15: low concentration implantation layer 16: direction of expansion

Claims (6)

A step of implanting hydrogen ions as a first ion species into a silicon-based crystal substrate containing silicon; a step of implanting a second ion species into the silicon-based crystal substrate; and heating the silicon-based crystal substrate to A method for producing a semiconductor thin film, comprising: a step of heating an injection layer; and a separation step of peeling an upper side from the injection layer of the silicon-based crystal substrate to obtain a silicon-based crystal thin plate. Hydrogen ions as the first ion species are uniformly implanted into the silicon crystal substrate, the second ion species are implanted in a periodic linear pattern, and the implantation regions of the second ion species are mutually connected. The method for producing a semiconductor thin film according to claim 1, wherein the semiconductor thin film does not overlap.   Further, a third ion species is implanted, the third ion species is implanted in a periodic linear pattern, the implantation regions of the third ion species do not overlap each other, and the second and second ion species are implanted. The method of manufacturing a semiconductor thin film according to claim 1, wherein the ion scanning directions of the three ion species intersect each other.   Average implantation depths of the first ion species, the second ion species, and the third ion species are 5 μm to 100 μm from the surface of the silicon-based crystal substrate, respectively, and the first ion species and the second ion species The method for producing a semiconductor thin film according to claim 3, wherein the third ion species are implanted with a difference in depth of 1 μm or less from each other.   The first ion species is a hydrogen ion, and the second ion species and the third ion species are the same or different from any of hydrogen, silicon, carbon, nitrogen, or a rare gas element, The manufacturing method of the semiconductor thin film of Claim 3 or Claim 4 to do. A support substrate is brought into contact with a silicon crystal substrate into which at least a first ion species and a second ion species are implanted, and the silicon crystal substrate and the support substrate are brought into close contact with each other by heat treatment. 6. The method for producing a semiconductor thin film according to claim 1, wherein the surface side of the region implanted with the ion species is peeled off from the silicon-based crystal substrate to form a semiconductor thin film. .

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