JP5019852B2 - Method for manufacturing strained silicon substrate - Google Patents

Description

  The present invention relates to a method for manufacturing a strained silicon substrate, and more particularly to a method for forming a strained silicon layer by a bonding method.

  Conventionally, improvement in performance of a semiconductor device has been promoted by high integration by miniaturization in accordance with a scaling law. However, in recent years, there has been a demand for higher performance based on guidelines different from such miniaturization and higher integration, and one of such approaches is the use of strain effect and three-dimensional device structure. There is.

  Among these, there is the use of a “strained silicon substrate” as a technique for utilizing the strain effect. The “strained silicon substrate” is a Si substrate having a silicon (Si) layer having lattice strain on the substrate surface. It is known that when tensile strain (stress) is applied to the Si crystal, the mobility of electrons conducted through the strain region is improved. If a channel layer is formed in the strained Si region using this phenomenon, It is possible to increase the speed of the Si transistor. For this reason, devices using strained Si have attracted attention from the viewpoints of high speed and low power consumption.

  Various types of strained Si substrates are known, and some modes of applying strain to Si include those by applying external stress and those using strained Si substrates. As a typical example, a SiGe crystal (Ge concentration of 15 to 20 mol%) having a lattice constant slightly larger than that of the Si crystal is epitaxially grown on the Si substrate, and Si is further epitaxially grown thereon to form the Si epitaxial layer. This is a “bulk strained Si substrate” in which lateral tensile strain (Biaxial strain) is introduced.

  For example, assuming that the molar content of Ge is about 20%, when Si is heteroepitaxially grown on this SiGe, the lattice spacing of Si is increased by about 0.8% and a large tensile stress of about 1.4 GPa is applied. Result.

  In addition, a SiGe layer is formed by diffusing Ge into the Si layer of an SOI (Silicon on Insulator) substrate in which an insulating film (silicon oxide film) is previously formed on the silicon substrate, and Si is crystal-grown thereon to cause strain. There is also an “SGOI (silicon germanium on insulator) substrate” in which a silicon layer is provided.

Further, the above-mentioned “bulk strained Si substrate” and a substrate having an insulating film are bonded together to transfer the strained Si layer, and then the SiGe is removed to obtain a strained Si layer “SSOI (Strained Silicon on Insulator) substrate” (For example, refer to Patent Document 1). In the case of this SSOI substrate, the above-described transfer of the strained Si layer is performed by injecting hydrogen ions into the main surface side of the strained Si substrate in advance and bonding it to the Si substrate with an oxide film as the support substrate, and heat treatment at around 500 ° C. In general, a method is used in which peeling is performed at the ion implantation interface.
US Pat. No. 6,603,156

  While strained Si technology is a very promising technology for improving the performance of semiconductor devices, high-density dislocation generation at a high Ge concentration, abnormal diffusion of Ge in SiGe, low heat dissipation of SiGe, Problems such as reduced flatness have also been pointed out.

Regarding crystal defects, threading dislocations from the SiGe layer to the substrate surface are as high as about 10 ⁵ per cm ² , and the critical film thickness is determined by the strained Si layer thickness depending on the Ge composition ratio of SiGe. If exceeded, misfit dislocations will occur, so the thickness of the strained Si layer is limited to about 15 nm.

  As for the abnormal diffusion of Ge in SiGe, it has been confirmed that Ge is diffused from the SiGe layer into the strained Si layer during the heat treatment in the transistor manufacturing process, and this diffusion Ge becomes the scattering center of the carrier. Or cause a significant decrease in the reliability of the oxide film.

  The present invention has been made in view of such problems, and the object of the present invention is conventional, such as high-density dislocation generation, abnormal diffusion of Ge, low heat dissipation of SiGe, and lower flatness of the substrate surface. A silicon substrate with a strained Si layer that can solve any of the technical problems pointed out in the strained Si substrate, has excellent film thickness uniformity and crystallinity, and is suitable for manufacturing a high-performance Si semiconductor element. It is in.

  In order to solve such a problem, the present invention provides a strained silicon substrate manufacturing method comprising: a first step of implanting hydrogen ions from a main surface side of a silicon substrate; A second step of subjecting at least one main surface of the silicon substrate and a support substrate having a smaller thermal expansion coefficient than the silicon substrate to a surface activation treatment, and the main surfaces of the silicon substrate and the support substrate are set to 100 ° C. Third step of bonding at a temperature of 400 ° C. or less, and applying an external impact to the bonding interface between the silicon substrate and the support substrate to peel the silicon along the hydrogen ion implantation interface of the silicon substrate and And a fourth step of forming a silicon layer on the main surface of the substrate.

  According to a second aspect of the present invention, in the method for manufacturing a strained silicon substrate according to the first aspect, the third step is a temperature of less than 100 ° C. after the bonding, and again the silicon substrate and the support A sub-step of heat treatment at a temperature of 100 ° C. or higher and 400 ° C. or lower with the substrates attached to each other is provided.

According to a third aspect of the present invention, in the method for manufacturing a strained silicon substrate according to the first or second aspect, the thermal expansion coefficient of the support substrate is 1.3 × 10 ⁻⁶ K ⁻¹ or less.

  According to a fourth aspect of the present invention, in the method for manufacturing a strained silicon substrate according to any one of the first to third aspects, the support substrate is a quartz substrate or a glass substrate.

According to a fifth aspect of the present invention, in the method for manufacturing a strained silicon substrate according to any one of the first to fourth aspects, the implantation amount (dose amount) of hydrogen ions in the first step is 1 × 10. ^{16 to} 5 × 10 ¹⁷ atoms / cm ² .

  A sixth aspect of the present invention is the strained silicon substrate manufacturing method according to any one of the first to fifth aspects, wherein the surface activation treatment of the second step is at least one of plasma treatment or ozone treatment. Is executed.

  The invention according to claim 7 is a method for manufacturing a strained silicon substrate, wherein the silicon layer is formed on the principal surface of the strained silicon substrate obtained by the method according to any one of claims 1 to 6. A sixth step of implanting hydrogen ions into the substrate, a seventh step of performing a surface activation process on at least one main surface of the strained silicon substrate and the second silicon substrate, the strained silicon substrate, and the second step. Applying an external impact to the bonding interface between the strained silicon substrate and the second silicon substrate in an eighth step of bonding the main surfaces of the silicon substrates while being heated at a temperature of 100 ° C. to 400 ° C. A ninth step of peeling the silicon along the hydrogen ion implantation interface of the strained silicon substrate to form a silicon layer on the main surface of the second silicon substrate.

  According to an eighth aspect of the present invention, in the method for manufacturing a strained silicon substrate according to the seventh aspect, the second silicon substrate has an oxide film on the main surface of the substrate.

  According to the present invention, as a technique for imparting strain to the silicon layer, instead of using the lattice constant difference between Si and SiGe as in the conventional technique, the difference in thermal expansion coefficient between Si and the support substrate is used. Furthermore, since the strained silicon layer is formed by bonding the silicon substrate and the support substrate, high-density dislocation generation at a high Ge concentration, abnormal diffusion of Ge in SiGe, or low heat dissipation of SiGe or the substrate Various problems such as reduction in surface flatness are solved, and a high-quality strained silicon substrate can be provided.

  Further, according to the present invention, a strained silicon substrate can be produced without making epitaxial growth indispensable as in the conventional method, which contributes to cost reduction of silicon semiconductor device manufacturing.

  As described above, according to the present invention, any technical problem pointed out in the conventional strained Si substrate can be solved, and it is excellent in film thickness uniformity and crystallinity, and suitable for manufacturing a high-performance Si semiconductor element. A silicon substrate with a strained Si layer is provided.

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

  In the method for producing a strained silicon substrate of the present invention, as a method for imparting strain to a silicon layer, the difference between the lattice constants of Si and SiGe is not used as in the conventional method, but the Si and support substrate (handle wafer) are not used. Use the difference in thermal expansion coefficient.

1A to 1C are conceptual diagrams for explaining the principle of introducing strain into a silicon layer by the method of the present invention. In these drawings, reference numeral 10 denotes a silicon substrate whose main surface has been previously subjected to hydrogen ion implantation, and 20 denotes a support substrate such as a quartz substrate or a glass substrate. As the support substrate 20, one having a thermal expansion coefficient smaller than that of the silicon substrate 10 is selected, and preferably a substrate made of a material having a thermal expansion coefficient of 1.3 × 10 ⁻⁶ K ⁻¹ or less is used. . The silicon substrate 10 may be a silicon substrate having an oxide film on the main surface.

  The main surfaces of the silicon substrate 10 and the support substrate 20 are bonded to each other at a temperature of 100 ° C. to 400 ° C. (FIG. 1B). At this time, the silicon substrate 10 is bonded in a state of relatively large thermal expansion as compared with the support substrate 20. If necessary, the temperature is once lower than 100 ° C. after bonding, and heat treatment at a temperature of 100 ° C. or more and 400 ° C. or less is repeated in a state where the silicon substrate 10 and the support substrate 20 are bonded again.

  Thereafter, when the two bonded substrates are returned to room temperature, tensile strain is introduced into the crystal due to the tensile stress generated at the bonding interface in the silicon crystal having a relatively large thermal expansion coefficient ( FIG. 1C). As described above, in the present invention, hydrogen ions are implanted in the vicinity of the bonding surface of the silicon crystal 10, and an external impact is applied to peel the silicon along the ion implantation interface, thereby supporting the substrate 20. A strained silicon layer is formed on the main surface.

  The process example of the manufacturing method of the strained silicon substrate of the present invention will be described below with reference to examples.

  FIG. 2 is a diagram for explaining a first process example of the method for producing a strained silicon substrate of the present invention. In this embodiment, the support substrate 20 is a quartz substrate. In addition, the Si substrate 10 is a commercially available Si substrate grown by, for example, the CZ method (Czochralski method). The electrical property values such as the conductivity type and the specific resistivity, the crystal orientation, and the crystal diameter are as follows. The strained silicon substrate manufactured by the method of the invention is appropriately selected depending on the design value and process of the device provided with the strained silicon substrate or the display area of the manufactured device.

  The diameters of these substrates are substantially the same, and the support substrate 20 is provided with an OF similar to the orientation flat (OF) provided on the Si substrate 10 for the convenience of the subsequent device formation process. It is convenient that these OFs can be matched and bonded together in a later step.

  First, hydrogen ions are implanted into the main surface (later bonding surface) of the Si substrate 10 to form a hydrogen ion implanted layer (FIG. 1A). By this hydrogen ion implantation, an ion implantation layer (damage layer) 11 is formed at a predetermined depth (average ion implantation depth L) near the surface of the Si substrate 10, and the average ion implantation depth in the surface region of the Si substrate 10. An ion implantation interface 12 is formed in a region corresponding to the length L.

The depth of the ion implantation layer 11 from the surface of the Si substrate 10 (average ion implantation depth L) is controlled by the acceleration voltage at the time of ion implantation, and is determined depending on the thickness of the silicon layer to be peeled off. The For example, the average ion implantation depth L is 0.5 μm or less, and the ion implantation conditions are a dose of 1 × 10 ^{16 to} 5 × 10 ¹⁷ atoms / cm ² and an acceleration voltage of 50 to 100 keV.

  Note that an insulating film such as an oxide film is formed in advance on the ion implantation surface of the Si substrate 10 as is normally done in order to suppress channeling of implanted ions in the ion implantation process into the Si crystal. Ion implantation may be performed through the film.

  Plasma treatment and ozone treatment for the purpose of surface cleaning, surface activation, and the like are performed on the bonding surfaces of the Si substrate 10 and the support substrate 20 on which the ion implantation layer 11 is formed in this way (FIG. 2B). ). Such surface treatment is performed for the purpose of removing the organic substances on the surface to be the bonding surface or increasing the OH group on the surface to achieve surface activation. The surface treatment of the Si substrate 10 and the support substrate 20 is performed. It is not always necessary to perform treatment on both joint surfaces, and the treatment may be performed only on one of the joint surfaces.

  When this surface treatment is performed by plasma treatment, a surface-clean Si substrate 10 and / or support substrate 20 that has been subjected to RCA cleaning or the like is placed on a sample stage in a vacuum chamber, and the plasma is placed in the vacuum chamber. The working gas is introduced so as to have a predetermined degree of vacuum. Examples of the plasma gas used here include oxygen gas, hydrogen gas, argon gas, or a mixed gas thereof, or a mixed gas of hydrogen gas and helium gas, for surface treatment of the Si substrate 10. It can be appropriately changed depending on the surface state and purpose of the Si substrate 10.

  When the surface treatment is intended to oxidize the surface of the Si substrate 10, a gas containing at least oxygen gas is used as the plasma gas. Note that when the support substrate 20 is a substrate whose surface is in an oxidized state, such as a quartz substrate, there is no particular limitation on the selection of the plasma gas species. After the introduction of the plasma gas, high-frequency plasma with a power of about 100 W is generated, the surface of the Si substrate 10 and / or the support substrate 20 to be plasma-treated is subjected to treatment for about 5 to 10 seconds, and the process is terminated.

  When performing the surface treatment by ozone treatment, the surface-cleaned Si substrate 10 and / or the support substrate 20 that has been subjected to RCA cleaning or the like in advance are placed on the sample stage in the chamber containing an oxygen-containing atmosphere. After introducing a plasma gas such as nitrogen gas or argon gas into the chamber, high-frequency plasma of a predetermined power is generated, oxygen in the atmosphere is converted into ozone by the plasma, and the Si substrate 10 to be processed and / or support The surface of the substrate 20 is processed for a predetermined time.

  The main surfaces of the Si substrate 10 and the support substrate 20 that have been subjected to such surface treatment are brought into close contact with each other as a bonding surface, and heat treatment is performed at a temperature of 100 ° C. or higher and 400 ° C. or lower (FIG. 2C). As described above, at least one main surface (bonding surface) of the Si substrate 10 and the support substrate 20 is activated by being subjected to surface treatment by plasma treatment, ozone treatment, or the like. Even with heat treatment, it is possible to obtain a bonding strength at a level that can sufficiently withstand mechanical peeling and mechanical polishing in the subsequent process. When it is desired to give higher bonding strength, if necessary, the temperature is once lower than 100 ° C. after bonding, and the Si substrate 10 and the support substrate 20 are again bonded to each other at 100 ° C. or more and 400 ° C. The heat treatment at a temperature of 0 ° C. or lower is repeated.

  The reason why the above heat treatment temperature is set to 400 ° C. or lower in the present invention is that when heat treatment is performed at a temperature exceeding 400 ° C., a minute cavity called a microcavity is generated at the hydrogen ion implantation interface, and this is thermally separated. As a result of this phenomenon, the surface of the silicon layer after peeling and the substrate crack are caused.

When the support substrate 20 is a quartz substrate, the upper limit value of the heat treatment temperature is preferably set to 350 ° C. This is in consideration of the difference in thermal expansion coefficient between Si and quartz, the amount of strain resulting from the difference in thermal expansion coefficient, and the amount of strain and the thickness of the Si substrate 10 and the quartz substrate 20. When the thicknesses of the Si substrate 10 and the quartz substrate 20 are approximately the same, there is a large difference between the thermal expansion coefficient of Si (2.33 × 10 ⁻⁶ ) and the thermal expansion coefficient of quartz (0.6 × 10 ⁻⁶ ). Due to the difference, when heat treatment is performed at a temperature exceeding 350 ° C., cracks due to thermal strain or peeling at the joint surface may occur due to the difference in rigidity between the two substrates. It may occur that the Si substrate or the quartz substrate is broken. For this reason, the upper limit of the heat treatment temperature is selected to be 350 ° C., and more preferably heat treatment is performed in a temperature range of 100 to 300 ° C.

  FIG. 3 is a diagram illustrating an example in which a hot plate is used for the above-described bonding heat treatment. In this figure, reference numeral 30 denotes a heating part, a heating plate 32 having a smooth surface is placed on a hot plate 31, and the smooth surface of the heating plate 32 is placed on the back surface of the support substrate 20 bonded to the Si substrate 10. It is trying to adhere. In this embodiment, a dummy silicon substrate is used for the heating plate 32, but there is no particular material limitation as long as a smooth surface can be easily obtained (semiconductor substrate or ceramic substrate). Silicone rubber or the like can also be used as a heating plate material, but since the heat-resistant temperature is considered to be about 250 ° C., it is not suitable for use at higher temperatures. In addition, if the surface of the hot plate 31 is sufficiently smooth, the hot plate 31 itself may be a “heating plate” without using the heating plate 32.

  Subsequently, external impact is applied to the bonding interface, and silicon is peeled along the hydrogen ion implantation interface 12. Various methods for applying an impact are conceivable. For example, a fluid such as a gas or a liquid is jetted from the tip of the nozzle in a jet form and sprayed from the side surface of the Si substrate 10, or a blade is applied. For example, the tip may be pressed against a region near the ion implantation layer 11 to apply an impact.

  A “microbubble layer” localized in a region corresponding to the average ion implantation depth L is formed on the bonding surface side of the Si substrate 10 by hydrogen ion implantation. Si atoms having a pair bond and high-density “Si—H bond” are generated, and the bonding state of elements in the “microbubble layer” and in the vicinity of the region is locally weakened. Therefore, when the external impact as described above is applied, the chemical bonding of Si atoms having dangling bonds in the ion-implanted layer 11 that is a damaged layer and the breakage of the Si—H bond are easily generated. Silicon peeling occurs along the ion implantation interface 12 corresponding to a predetermined depth in the vicinity of the surface (average ion implantation depth L), and a strained silicon layer 13 is obtained on the support substrate 20 (FIG. 1D). .

  Finally, if the surface of the strained silicon layer 13 is subjected to final surface treatment (CMP polishing or the like) to remove damage caused by hydrogen ion implantation, an SOQ (Silicon on Quartz) substrate having the strained silicon layer 13 as an SOI layer. Is obtained (FIG. 1E).

  FIG. 4 is a diagram for explaining a second process example of the method for manufacturing a strained silicon substrate according to the present invention. The substrate illustrated in FIG. 4A is the strained silicon substrate manufactured in the first embodiment. is there.

  Hydrogen ions are implanted from the strained silicon layer 13 side of the strained silicon substrate to form a hydrogen ion implanted layer in a region near the bonding surface with the support substrate 20 (FIG. 4A). As described in the first embodiment, by this hydrogen ion implantation, an ion implantation layer (damage layer) 14 is formed at a predetermined depth (average ion implantation depth L) of the strained silicon layer 13, and an ion implantation interface is formed. 15 is formed. The ion implantation conditions at this time are also determined depending on how thick the silicon layer is peeled off.

  For the purpose of surface cleaning, surface activation, etc. on at least one main surface (bonding surface) of the strained silicon substrate on which the ion-implanted layer 14 is formed in this way and the silicon substrate (supporting substrate) 40 to be a handle wafer later. The plasma treatment or ozone treatment described above was performed (FIG. 4B). Such a surface treatment has already been described in detail in the first embodiment, and therefore will not be repeated.

  The main surfaces of the two substrates subjected to such surface treatment are brought into close contact with each other and subjected to heat treatment at a temperature of 100 ° C. or higher and 400 ° C. or lower (FIG. 4C). Also here, if necessary, the temperature is once lower than 100 ° C. after bonding, and the heat treatment at a temperature of 100 ° C. or more and 400 ° C. or less is repeated in the state where the Si substrate 10 and the support substrate 40 are bonded again.

  Subsequently, an external impact is applied to the bonding interface, and silicon is peeled along the hydrogen ion implantation interface 15 to obtain a strained silicon layer 16 (FIG. 4D). When surface treatment (CMP polishing or the like) is performed to remove damage caused by hydrogen ion implantation, a silicon substrate having a strained silicon layer 16 on its surface can be obtained (FIG. 4E).

  FIG. 5 is a diagram for explaining a third process example of the method for manufacturing a strained silicon substrate according to the present invention. The substrate illustrated in FIG. 5A is the strained silicon substrate manufactured in the first embodiment. is there. The difference from the second embodiment is that the support substrate 50 is a silicon substrate having an oxide film 51 on its main surface.

  Hydrogen ions are implanted from the strained silicon layer 13 side of the strained silicon substrate to form a hydrogen ion implanted layer in a region near the bonding surface with the support substrate 20 (FIG. 5A). At least one main surface (bonding surface) of a silicon substrate (supporting substrate) 50 to be a handle wafer later is subjected to plasma treatment or ozone treatment for the purpose of surface cleaning or surface activation (FIG. 5B). .

  The main surfaces of both substrates subjected to such a surface treatment are brought into close contact with each other, and subjected to heat treatment at a temperature of 100 ° C. or higher and 400 ° C. or lower (FIG. 5C). Also here, if necessary, the temperature is once lower than 100 ° C. after bonding, and the heat treatment at a temperature of 100 ° C. or more and 400 ° C. or less is repeated in the state where the Si substrate 10 and the support substrate 50 are bonded again.

  Subsequently, an external impact is applied to the bonding interface, and silicon is peeled along the hydrogen ion implantation interface 15 to obtain a strained silicon layer 16 (FIG. 5D). When surface treatment (CMP polishing or the like) is performed to remove damage caused by hydrogen ion implantation, an SOI substrate (SSOI substrate) having the strained silicon layer 16 on its surface can be obtained (FIG. 5E).

  As shown in FIGS. 6A to 6C, when a transistor such as a MOSFET is formed using the strained silicon substrate obtained by the method of Examples 1 to 3 and a channel is formed in the strained silicon region, the operation is performed. It is possible to increase the speed.

  The present invention makes it possible to provide a high-quality strained silicon substrate.

It is a conceptual diagram for demonstrating the principle by which distortion is introduce | transduced in a silicon layer by the method of this invention. It is a figure for demonstrating the 1st process example of the manufacturing method of the distortion | strained silicon substrate of this invention. It is a figure which shows the example which used the hotplate for bonding heat processing. It is a figure for demonstrating the 2nd process example of the manufacturing method of the distortion | strained silicon substrate of this invention. It is a figure for demonstrating the 3rd process example of the manufacturing method of the distortion | strained silicon substrate of this invention. 1 is a structural cross-sectional view of a MOSFET manufactured using a strained silicon substrate manufactured by the method of the present invention.

Explanation of symbols

10, 40, 50 Si substrate 11, 14 Ion implantation layer 12, 15 Ion implantation interface 13, 16 Strained silicon layer 20 Support substrate 30 Heating unit 31 Hot plate 32 Heating plate 51 Oxide film

Claims (7)

A method of manufacturing a strained silicon substrate,
A first step of implanting hydrogen ions from the main surface side of the first silicon substrate;
A second step of subjecting a heat treatment to at least one major surface of the small supporting substrate in thermal expansion coefficient than the first silicon substrate and the first silicon substrate,
A third step of bonding main surfaces of the first silicon substrate and the support substrate to each other at a temperature of 100 ° C. or higher and 400 ° C. or lower;
An external impact is applied to the bonding interface between the first silicon substrate and the support substrate to separate the silicon along the hydrogen ion implantation interface of the first silicon substrate, and the first surface is formed on the main surface of the support substrate . A fourth step of forming a silicon layer;
A fifth step of implanting hydrogen ions into the first silicon layer;
A sixth step of subjecting at least one main surface of the first silicon layer and the second silicon substrate to a surface activation treatment;
A seventh step in which the main surfaces of the first silicon layer and the second silicon substrate are bonded together in a state of being heated at a temperature of 100 ° C. or higher and 400 ° C. or lower;
An external impact is applied to the bonding interface between the first silicon layer and the second silicon substrate, and the silicon is peeled along the hydrogen ion implantation interface of the first silicon layer. An eighth step of forming a second silicon layer on the main surface to form a strained silicon substrate;
A method for producing a strained silicon substrate, comprising: The third step is a sub-step in which, after the bonding, the temperature is temporarily set to less than 100 ° C., and heat treatment is performed again at a temperature of 100 ° C. or more and 400 ° C. or less in a state where the first silicon substrate and the support substrate are bonded again. A method for producing a strained silicon substrate according to claim 1. 3. The method for producing a strained silicon substrate according to claim 1, wherein a thermal expansion coefficient of the support substrate is 1.3 × 10 ⁻⁶ K ⁻¹ or less. The method for manufacturing a strained silicon substrate according to claim 1, wherein the support substrate is a quartz substrate or a glass substrate. 5. The strained silicon substrate according to claim 1, wherein a hydrogen ion implantation amount (dose amount) in the first step is 1 × 10 ^{16 to} 5 × 10 ¹⁷ atoms / cm ^2. Method. The strained silicon substrate manufacturing method according to any one of claims 1 to 5, wherein the surface activation process of the second step is performed by at least one of a plasma process and an ozone process. The method for producing a strained silicon substrate according to claim 1, wherein the second silicon substrate has an oxide film on a main surface of the substrate.

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