JP2006216740A - Soi wafer and manufacturing method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method for an SOI wafer capable of preventing the generation of a thermal strain, a peeling, a crack or the like resulting from the difference of the coefficients of thermal expansion of a transparent insulating substrate and an SOI layer. <P>SOLUTION: In the manufacturing method for the SOI wafer, an ion implanting layer is formed in a wafer by implanting at least one of hydrogen ions or rare-gas ions from the surface of a single-crystal silicon wafer, and the ion-implanting surface of the single-crystal silicon wafer and/or the surface of the transparent insulating substrate are treated with a plasma and/or ozone. In the manufacturing method, the ion-implanting surface of the single-crystal silicon wafer and the surface of the transparent insulating substrate are stuck fast and joined at a room temperature while using the treated surfaces as joint surfaces, the joint surfaces are irradiated with ultraviolet rays from the transparent-insulating substrate side, and a bonding power is increased. In the manufacturing method, an impulse is applied to the ion implanting layer, the single-crystal silicon wafer is peeled mechanically, and the SOI layer is formed on the transparent insulating substrate. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an SOI wafer manufacturing method and an SOI wafer, and more particularly to an SOI wafer manufacturing method and an SOI wafer for forming an SOI layer on a transparent insulating substrate.

  An SOI wafer having an SOI (Silicon On Insulator) structure in which a silicon single crystal layer is formed on an insulator is suitable for manufacturing a high-density semiconductor integrated circuit, for example, a TFT-LCD (Thin Film Transistor-Liquid Crystal Display). And optical devices such as thin film transistor liquid crystal displays).

  For such an optical device, for example, an SOI wafer in which an SOI layer is formed on a transparent quartz substrate is used. In this case, since the substrate is a perfect insulator, the mobility of carriers in the SOI layer is not affected by the substrate and becomes extremely high, and the effect when driven at a high frequency is remarkable. Moreover, in such an SOI wafer, a drive circuit can be integrally formed around the TFT region, and high-density mounting is possible.

  In an SOI wafer used for such an optical device, the thickness of the SOI layer must be reduced to, for example, about 0.5 μm or less. Therefore, the quartz substrate and the SOI layer are bonded firmly so as to withstand the thermal and mechanical stress applied to the SOI layer at the time of grinding and polishing to reduce the thickness of the SOI layer to such a thickness and device fabrication. Therefore, it was necessary to increase the bonding strength by high-temperature heat treatment.

  However, since the thermal expansion coefficient is different between the quartz substrate and the SOI layer, stress due to thermal strain is generated during the heat treatment for bonding, cooling, grinding, or polishing after bonding, and the quartz substrate and the SOI layer are cracked. May occur or they may be peeled off and damaged. Such a problem is not limited to the case where the insulating transparent substrate is a quartz substrate, but is a problem inevitably caused when a single crystal silicon wafer is bonded to a substrate having a different thermal expansion coefficient.

  In order to solve this problem, in a method for manufacturing an SOI wafer using a hydrogen ion implantation delamination method, there is a technique for performing the bonding heat treatment step and the thinning step alternately in a stepwise manner to alleviate the influence of thermal stress generated during the heat treatment. It is disclosed (for example, see Patent Document 1).

JP-A-11-145438

  The present invention is a method for manufacturing an SOI wafer in which an SOI layer is formed on a transparent insulating substrate, and it is easy to generate thermal strain, delamination, cracks, and the like due to differences in thermal expansion coefficients between the transparent insulating substrate and the SOI layer. An object of the present invention is to provide an SOI wafer manufacturing method and an SOI wafer which can be prevented by a simple process.

In order to achieve the above object, according to the present invention, an SOI layer is formed on the transparent insulating substrate by thinning the single crystal silicon wafer after bonding the single crystal silicon wafer and the transparent insulating substrate. In the method of manufacturing, at least,
A step of implanting at least one of hydrogen ions or rare gas ions from the surface of the single crystal silicon wafer to form an ion implantation layer in the wafer;
Treating the ion-implanted surface of the single crystal silicon wafer and / or the surface of the transparent insulating substrate with plasma and / or ozone;
Bonding the ion-implanted surface of the single crystal silicon wafer and the surface of the transparent insulating substrate by bringing the treated surface into close contact with each other at room temperature; and
Irradiating the joint surface with ultraviolet light from the transparent insulating substrate side to increase the bonding force;
Impacting the ion-implanted layer to mechanically peel off the single crystal silicon wafer and forming an SOI layer on the transparent insulating substrate;
A method for manufacturing an SOI wafer is provided.

  Thus, if the ion implantation surface of the single crystal silicon wafer and / or the surface of the transparent insulating substrate is treated with plasma and / or ozone, OH groups increase on the ion implantation surface of the wafer and / or the surface of the substrate. Activated. Therefore, in this state, if the ion-implanted surface of the single crystal silicon wafer and the surface of the transparent insulating substrate are bonded together at room temperature using the treated surface as a bonding surface, the bonded surface is bonded by hydrogen bonding. Since it joins firmly, even if it does not give the high temperature heat processing which raises a bonding power after that, it will become sufficiently strong joining. Further, if the bonding surface is irradiated with ultraviolet light from the transparent insulating substrate side after that, the ultraviolet light is absorbed by the silicon wafer surface and converted into heat, so that the vicinity of the bonding surface is heated locally. Can be further enhanced. Since the bonding surfaces are firmly bonded in this way, the single-crystal silicon wafer is mechanically peeled by applying an impact to the ion-implanted layer, and a thin SOI layer is formed on the transparent insulating substrate. Therefore, the film thickness can be reduced without performing heat treatment for peeling. Accordingly, an SOI wafer can be manufactured without causing thermal distortion, peeling, cracking, or the like due to a difference in thermal expansion coefficient between the transparent insulating substrate and the single crystal silicon wafer. Further, since the hydrogen ion implantation separation method is used, it is possible to manufacture an SOI wafer having an SOI layer that is thin and has excellent film thickness uniformity and excellent crystallinity.

In this case, it is preferable that the ultraviolet light irradiation step is performed by laser light irradiation.
As described above, if the ultraviolet light irradiation step is performed by irradiating laser light, the laser light has a high energy density, so that the surface of the silicon wafer, that is, the bonding surface can be locally heated in a short time.

Further, it is preferable that the ultraviolet light irradiation step is performed by irradiation with pulsed light.
As described above, if the ultraviolet light irradiation step is performed by irradiating pulsed light, the pulsed light has a short duration and diffusion of heat generated by absorption is small. Therefore, only the very surface of the single crystal silicon wafer is efficiently heated in a short time, and the thermal stress is not applied to the entire wafer but locally only on the bonding surface, so that thermal strain, peeling, cracking, etc. It can be surely prevented.

Moreover, it is preferable that the wavelength of the ultraviolet light irradiated to the said joint surface shall be 200 nm or less.
As described above, when the wavelength of ultraviolet light applied to the bonding surface is set to 200 nm or less, H ₂ O molecules and OH groups existing at the interface between the single crystal silicon wafer and the transparent insulating substrate absorb ultraviolet light and become more active. And the bonding strength can be further increased.

In addition, after performing the bonding step, simultaneously or continuously with the ultraviolet light irradiation step, the bonding wafer is heat treated at 100 to 300 ° C. to increase the bonding strength, and then the peeling step is performed. Preferred (claim 5).
In this way, in addition to the ultraviolet light irradiation, the bonded single crystal silicon wafer and the transparent insulating substrate are heat-treated at a low temperature of 100 to 300 ° C. so that thermal distortion does not occur at the same time or continuously. If the mechanical debonding process is performed by applying an impact to the ion implantation layer after increasing the thickness, it is possible to more reliably prevent the occurrence of delamination, cracking, and the like of the joint surface due to mechanical stress, thereby manufacturing the SOI wafer.

Further, the heat treatment step can be a flash lamp annealing treatment.
Thus, if the heat treatment step is a flash lamp annealing treatment, the heat treatment can be effectively performed in a short time.

Moreover, it is preferable to perform mirror polishing on the SOI layer surface of the SOI wafer obtained by the peeling step.
As described above, if the surface of the SOI layer of the SOI wafer obtained by the peeling process is mirror-polished, the surface roughness of the SOI layer generated in the peeling process and crystal defects generated in the ion implantation process can be removed. An SOI wafer having a smooth polished SOI layer can be manufactured.

The transparent insulating substrate is preferably a quartz substrate, a sapphire (alumina) substrate, or a glass substrate.
As described above, if the transparent insulating substrate is any one of a quartz substrate, a sapphire (alumina) substrate, and a glass substrate, these are transparent insulating substrates having good optical characteristics. Can produce wafers.
Here, as a glass substrate, white plate glass, borosilicate glass, non-alkali borosilicate glass, alumino borosilicate glass, crystallized glass, etc. can be used besides general blue plate glass. When a glass substrate containing an alkali metal such as blue plate glass is used, it is preferable to form a diffusion prevention film made of spin-on glass on the surface of the glass substrate in order to prevent the alkali metal from diffusing from the surface.

The present invention also provides an SOI wafer manufactured by any one of the above manufacturing methods (claim 9).
As described above, an SOI wafer manufactured by any one of the above manufacturing methods is free from thermal distortion, peeling, cracking, etc. during manufacturing, and is thin and useful for manufacturing various devices. An SOI wafer having an SOI layer on a transparent insulating substrate having good film thickness uniformity, excellent crystallinity, and high carrier mobility.

  In the method for manufacturing an SOI wafer according to the present invention, before the single crystal silicon wafer and the transparent insulating substrate are bonded, the surface to be bonded is treated with plasma and / or ozone to increase the OH groups on the surface and to be active. Therefore, when the single crystal silicon wafer and the transparent insulating substrate are brought into close contact at room temperature and bonded in such a state, the bonded surfaces are firmly bonded by hydrogen bonding. Therefore, a sufficiently strong bond can be obtained without subsequent high-temperature heat treatment for increasing the bonding strength. Furthermore, since ultraviolet light is irradiated to the bonding surface from the transparent insulating substrate side thereafter, the ultraviolet light is absorbed by the silicon wafer surface and the bonding surface is heated, so that the bonding force can be further increased. Since the bonding surfaces are firmly bonded in this way, the single-crystal silicon wafer is mechanically peeled by applying an impact to the ion-implanted layer, and a thin SOI layer is formed on the transparent insulating substrate. it can. Accordingly, a thin film can be formed without performing heat treatment for peeling. In this manner, an SOI wafer can be manufactured without causing thermal strain, peeling, cracking, or the like due to the difference in thermal expansion coefficient between the transparent insulating substrate and single crystal silicon.

  In addition, the SOI wafer of the present invention is free from thermal distortion, peeling, cracking, etc. during production, and has a thin and good film thickness uniformity that is useful for manufacturing various devices. This is an SOI wafer having an SOI layer on a transparent insulating substrate having excellent carrier mobility.

As described above, in the method for manufacturing an SOI wafer in which an SOI layer is formed on a transparent insulating substrate, the occurrence of thermal strain, peeling, cracking, etc. due to the difference in the thermal expansion coefficient between the transparent insulating substrate and the SOI layer. In order to solve this problem, a technique for reducing the influence of thermal stress generated during heat treatment by alternately performing a bonding heat treatment step and a thinning step in a method for manufacturing an SOI wafer using a hydrogen ion implantation delamination method is disclosed. ing.
However, in order to improve the productivity of SOI wafers, there has been a demand for a technique that can solve the above problems in a short time with fewer steps.

Therefore, the present inventors increase the bonding strength without performing heat treatment by performing plasma and / or ozone treatment in advance on the surfaces to be bonded, and then irradiate the bonding surface with ultraviolet light from the transparent insulating substrate side. Thus, the present inventors have completed the present invention by conceiving that the bonding strength is further increased, and that peeling is performed without performing high-temperature heat treatment by performing mechanical peeling at the time of peeling.
Hereinafter, embodiments of the present invention will be described in detail, but the present invention is not limited thereto.

  FIG. 1 is a process diagram showing an example of a method for manufacturing an SOI wafer according to the present invention.

First, a single crystal silicon wafer and a transparent insulating substrate are prepared (step A).
The single crystal silicon wafer is not particularly limited. For example, the single crystal silicon wafer is obtained by slicing a single crystal grown by the Czochralski method. For example, the diameter is 100 to 300 mm, the conductivity type is P type or N type, and the resistivity. Can be about 10 Ω · cm.
Also, the transparent insulating substrate is not particularly limited, but if this is any one of a quartz substrate, a sapphire (alumina) substrate, and a glass substrate, these are transparent insulating substrates having good optical characteristics. An SOI wafer suitable for fabrication can be manufactured.

Next, at least one of hydrogen ions or rare gas ions is implanted from the surface of the single crystal silicon wafer to form an ion implantation layer in the wafer (step B).
For example, the implantation energy is such that the temperature of the single crystal silicon wafer is 250 to 450 ° C. and the ion implantation layer can be formed from the surface to a depth corresponding to the desired thickness of the SOI layer, for example, a depth of 0.5 μm or less. Then, at least one of a predetermined dose of hydrogen ions or rare gas ions is implanted. As conditions at this time, for example, the implantation energy can be 50 to 100 keV, and the implantation dose can be 1 × 10 ¹⁶ to 1 × 10 ¹⁷ / cm ² . Further, if an insulating film such as a thin silicon oxide film is formed in advance on the surface of the single crystal silicon wafer and ion implantation is performed therethrough, an effect of suppressing channeling of implanted ions can be obtained.

Next, the ion-implanted surface of this single crystal silicon wafer and / or the surface of the transparent insulating substrate are treated with plasma and / or ozone (step C).
When processing with plasma, a single-crystal silicon wafer and / or a transparent insulating substrate that has been cleaned such as RCA cleaning is placed in a vacuum chamber, and after introducing a plasma gas, a high-frequency plasma of about 100 W is applied to high-frequency plasma. The surface is subjected to plasma treatment for about 10 seconds. As a plasma gas, when processing a single crystal silicon wafer, when oxidizing the surface, plasma of oxygen gas, when not oxidizing, hydrogen gas, argon gas, or a mixed gas thereof or a mixture of hydrogen gas and helium gas. A mixed gas can be used. When processing a transparent insulating substrate, any gas may be used.

  When processing with ozone, a single crystal silicon wafer and / or a transparent insulating substrate cleaned by RCA cleaning or the like is placed in a chamber introduced with air, and a plasma gas such as nitrogen gas or argon gas is introduced. After that, the surface is subjected to ozone treatment by generating high-frequency plasma and converting atmospheric oxygen into ozone. Either or both of plasma treatment and ozone treatment can be performed.

  By treating with this plasma and / or ozone, organic substances on the surface of the single crystal silicon wafer and / or the transparent insulating substrate are oxidized and removed, and the OH groups on the surface are increased and activated. A surface to be processed is a bonding surface, and a single crystal silicon wafer is an ion implantation surface. The treatment is more preferably performed on both the single crystal silicon wafer and the transparent insulating substrate, but only one of them may be performed.

Next, the ion-implanted surface of the single crystal silicon wafer and the surface of the transparent insulating substrate are bonded together at room temperature with the surface treated with plasma and / or ozone as the bonding surface (step D).
In step C, at least one of the ion implantation surface of the single crystal silicon wafer and the surface of the transparent insulating substrate is subjected to plasma treatment and / or ozone treatment. It is possible to bond strongly with the strength that can withstand mechanical peeling in the subsequent process simply by making it adhere underneath. Therefore, a high-temperature bonding heat treatment such as 1200 ° C. or higher is not necessary, and there is no fear of occurrence of thermal strain, cracking, peeling or the like due to a difference in thermal expansion coefficient that is a problem due to heating.

Next, the joint surface is irradiated with ultraviolet light from the transparent insulating substrate side (step E).
As a result, the ultraviolet light reaches the bonding surface without being absorbed, scattered or the like depending on the transparent insulating substrate, and the ultraviolet light is absorbed by the silicon wafer surface which is the bonding surface and the surface is heated. The binding force of can be further increased. According to the measurement by the present inventors, the light absorption of silicon increases sharply in the ultraviolet region where the wavelength of light is about 400 nm or less, and the extinction coefficient k is about 1.1 or more. Is about 34.5 (μm ⁻¹ ) or more. Therefore, about 97% or more of the irradiated ultraviolet light is absorbed from the surface to a depth of 0.1 μm and converted into heat, so that the silicon wafer surface, that is, the bonding surface is efficiently heated.

In addition, H ₂ O molecules and OH groups absorb light having a peak wavelength λmax of about 167 nm and a peak molecular extinction coefficient εmax of about 1480 (dm ³ · mol ⁻¹ · cm ⁻¹ ) due to the n-σ ^* transition. This light absorption starts from a wavelength of about 200 nm or less. Therefore, if the wavelength of the ultraviolet light applied to the bonding surface is 200 nm or less, H ₂ O molecules and OH groups existing at the interface between the single crystal silicon wafer and the transparent insulating substrate absorb UV light and are further activated. This is preferable because the bonding strength can be further increased.

The ultraviolet light irradiation step is not particularly limited, but if this is irradiated with laser light, the laser light has a high energy density, so that the bonding surface can be locally heated in a short time. In this case, the laser beam is irradiated so as to scan the entire surface of the bonding wafer on the transparent insulating substrate side.
Also, if the pulsed light is irradiated, the pulsed light has a short duration and the diffusion of heat generated by the light absorption of silicon is small, so that only the very surface of the single crystal silicon wafer is heated efficiently in a short time. Therefore, thermal stress is not applied to the entire bonding wafer but locally only to the vicinity of the bonding surface. Therefore, thermal distortion, peeling, cracking, etc. can be prevented more reliably.

As the laser, a gas laser such as an excimer laser or an argon laser, or a laser that generates ultraviolet light by wavelength conversion by combining a YAG laser and a nonlinear optical crystal can be used. These may be either a continuous oscillation type or a pulse oscillation type depending on the characteristics of the laser, manufacturing conditions, and the like. For example, when using a pulse oscillation type excimer laser device on the market, using a XeCl as an excitation gas, the oscillation wavelength 308 nm, it can be the repetition frequency 30 Hz, the energy density and 50mJ ^/ cm ² ~500mJ ^/ cm 2 . If ArF is used as the excitation gas, the oscillation wavelength can be 193 nm, but there is no particular limitation. The beam shape of the laser light may be linear or rectangular.

In addition, you may perform the process which heat-processes the joined wafer at low temperature of 100-300 degreeC, and raises a bond strength simultaneously with this ultraviolet irradiation process or before or after an ultraviolet irradiation process. FIG. 1 shows the case where heat treatment for increasing the bonding force is performed continuously after the ultraviolet irradiation step (step F).
For example, when the transparent insulating substrate is quartz, the thermal expansion coefficient is smaller than that of silicon (Si: 2.33 × 10 ⁻⁶ , quartz: 0.6 × 10 ⁻⁶ ), and a silicon wafer having the same thickness and When bonded and heated, the silicon wafer will break if it exceeds 300 ° C. However, such a relatively low-temperature heat treatment is preferable because there is no fear of thermal distortion, cracking, peeling due to a difference in thermal expansion coefficient. In this heat treatment step, when a batch treatment type heat treatment furnace is used, a sufficient effect can be obtained if the heat treatment time is about 0.5 to 24 hours.

  Further, this heat treatment step can be a flash lamp annealing treatment. Such an annealing process using a flash lamp that emits light having a short duration is preferable because heat treatment can be effectively performed in a short time, and the possibility of occurrence of thermal distortion, cracking, peeling, etc. is further reduced. For the flash lamp annealing treatment, for example, a halogen lamp, an infrared lamp or the like can be used. The heat treatment temperature can be about 150 ° C., and the treatment time can be 1 to 120 seconds.

Next, an impact is applied to the ion implantation layer to mechanically peel off the single crystal silicon wafer, and an SOI layer is formed on the transparent insulating substrate (step G).
In the hydrogen ion implantation delamination method, the bonding wafer is heat-treated at about 500 ° C. in an inert gas atmosphere, and thermal delamination is performed by the effect of crystal rearrangement and the coagulation effect of injected hydrogen bubbles. In the invention, impact is applied to the ion-implanted layer to perform mechanical peeling, so that there is no possibility that thermal strain, cracking, peeling, etc. due to heating occur.
In order to give an impact to the ion-implanted layer, for example, it may be blown continuously or intermittently from the side surface of the wafer joined with a jet of fluid such as gas or liquid. There is no particular limitation.

Thus, an SOI wafer in which an SOI layer is formed on a transparent insulating substrate can be obtained by a peeling step, and it is preferable to perform mirror polishing on the surface of the SOI layer of the SOI wafer thus obtained (Step H).
By this mirror polishing, surface roughness called haze generated in the peeling process can be removed, and crystal defects near the SOI layer surface caused by ion implantation can be removed. As this mirror polishing, for example, polishing called “touch polish” with a polishing margin of 5 to 400 nm being extremely small can be used.

And, the SOI wafer manufactured by the processes A to H is free from thermal distortion, peeling, cracking, etc. during manufacturing, and has a thin and good film thickness uniformity useful for manufacturing various devices. And an SOI wafer having an SOI layer on a transparent insulating substrate having excellent crystallinity and high carrier mobility.
Such an SOI wafer is particularly suitable for manufacturing an optical device such as a TFT-LCD because an SOI layer is formed on a transparent insulating substrate.

  The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has any configuration that has substantially the same configuration as the technical idea described in the claims of the present invention and that exhibits the same operational effects. It is included in the technical idea of the invention.

  For example, since the SOI layer of the SOI wafer after steps A to G or H has already been sufficiently thinned, high-temperature heat treatment (500 ° C. or higher to less than the melting point of silicon) to further increase the bonding strength depending on the purpose May be added.

It is process drawing which shows an example of the manufacturing method of SOI wafer which concerns on this invention.

Claims (9)

In the method for manufacturing an SOI wafer by forming an SOI layer on the transparent insulating substrate by thinning the single crystal silicon wafer after bonding the single crystal silicon wafer and the transparent insulating substrate,
A step of implanting at least one of hydrogen ions or rare gas ions from the surface of the single crystal silicon wafer to form an ion implantation layer in the wafer;
Treating the ion-implanted surface of the single crystal silicon wafer and / or the surface of the transparent insulating substrate with plasma and / or ozone;
Bonding the ion-implanted surface of the single crystal silicon wafer and the surface of the transparent insulating substrate by bringing the treated surface into close contact with each other at room temperature; and
Irradiating the joint surface with ultraviolet light from the transparent insulating substrate side to increase the bonding force;
Impacting the ion-implanted layer to mechanically peel off the single crystal silicon wafer and forming an SOI layer on the transparent insulating substrate;
A method for manufacturing an SOI wafer, comprising:   2. The method for manufacturing an SOI wafer according to claim 1, wherein the ultraviolet light irradiation step irradiates a laser beam.   3. The method for manufacturing an SOI wafer according to claim 1, wherein the ultraviolet light irradiation step is performed by irradiation with pulsed light.   4. The method for manufacturing an SOI wafer according to claim 1, wherein a wavelength of ultraviolet light applied to the bonding surface is 200 nm or less. 5.   5. The method for manufacturing an SOI wafer according to claim 1, wherein after the bonding step is performed, the bonding wafer is heated to 100 to 300 ° C. simultaneously or continuously with the ultraviolet light irradiation step. A method for manufacturing an SOI wafer, comprising: performing a step of increasing the bonding strength by heat treatment, and then performing the peeling step.   6. The method for manufacturing an SOI wafer according to claim 5, wherein the heat treatment step is a flash lamp annealing process.   7. The method for manufacturing an SOI wafer according to claim 1, wherein the SOI layer surface of the SOI wafer obtained by the peeling step is mirror-polished. .   8. The method for manufacturing an SOI wafer according to claim 1, wherein the transparent insulating substrate is any one of a quartz substrate, a sapphire (alumina) substrate, and a glass substrate. Manufacturing method of SOI wafer.   An SOI wafer manufactured by the manufacturing method according to claim 1.

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