JP2006269850A - Method for manufacturing soi substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an SOI layer 13 having relatively less unevenness of a film thickness. <P>SOLUTION: The method for manufacturing an SOI substrate includes a process for forming an oxide film 21 on the surface of a first silicon substrate 14, a process for forming an ion implantation region 16 inside the first silicon substrate by implanting hydrogen ions, a process for forming a laminated body 15 by superposing a second silicon substrate 12 on the first silicon substrate, and a process for obtaining the SOI substrate 11 in which the thin SOI layer 13 is formed on the second silicon substrate via the oxide film by separating the first silicon substrate in the ion implantation region. A load F toward the first silicon substrate is applied to the center of the second silicon substrate in the process for forming the laminated body. The load is continuously applied until a bonding area exceeds 0.1% of an area of the main face on the bonding side of the substrate. The load applied to the second silicon substrate 12 is 0.1-5.0 N. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method of manufacturing an SOI (Silicon On Insulator) substrate in which an SOI layer is provided on an oxide film manufactured using a hydrogen ion implantation technique.

  Conventionally, as a method for manufacturing an SOI substrate, after forming an oxide film on the surface of a first silicon substrate, high-concentration hydrogen ions are implanted therein and annealed at a high temperature to form a predetermined depth from the surface of the silicon substrate. An ion-implanted region is formed on the first silicon substrate, and then a second silicon substrate is superimposed on the first silicon substrate to form a laminated body in which both are bonded. The laminated body is heated to a temperature exceeding 500 ° C. There has been proposed a manufacturing method in which a silicon substrate is separated from a second silicon substrate in the hydrogen ion implantation region and a semiconductor SOI layer is formed on the surface of the second silicon substrate (see, for example, Patent Document 1). This method makes it possible to manufacture an SOI substrate having a second silicon substrate, an oxide film formed on the substrate and acting as a buried oxide film, and a semiconductor SOI layer formed on the oxide film. ing.

  Here, in the step of forming a laminated body by superimposing the second silicon substrate on the first silicon substrate, analysis of the progress of the joining to the first silicon substrate results in the following. That is, when the second silicon substrate is overlaid on the first silicon substrate, the second silicon substrate is in a state of floating with respect to the first silicon substrate due to the gas existing therebetween. Then, with the passage of time, the gas existing in the meantime is gradually exhausted from the surroundings, thereby generating a portion where the second silicon substrate partially contacts the first silicon substrate, and from where the second silicon substrate partially contacts. The joining of both is started. As the gas is discharged to the outside at the bonding interface between both substrates, the initially partial bonding area gradually increases, and the bonding area is the bonding side of the first silicon substrate or the second silicon substrate. The joint of both is completed in the state expanded to the whole area of the main surface. By this completion, a laminated body in which the first silicon substrate and the second silicon substrate are joined is obtained.

Therefore, when the second silicon substrate is overlapped with the first silicon substrate and bonded to each other, if the bonding is started from a large number of contact points at the bonding interface between the first silicon substrate and the second silicon substrate, There is a problem that gas remains at the bonding interface of the substrate to generate voids. Also, there is a problem that it takes a relatively long time to leave the second silicon substrate overlaid on the first silicon substrate and to bond them together by the weight of the second silicon substrate.
In order to solve this problem, there has been proposed a bonding processing method in which a second silicon substrate is superimposed on a first silicon substrate and one point of the superimposed substrate is pressed (for example, refer to Patent Document 2). In this bonding processing method, when one point of two superposed substrates is pressed, bonding of the two starts from the pressed point, so that the bonding is started as in the case where bonding is started from a plurality of bonding points. No voids or the like are generated between the bonding interfaces of the single substrates, and it is possible to obtain a good product and shorten the bonding time.
JP-A-5-211128 (Claims) JP 2002-190435 A (specification [0010])

However, in the above conventional bonding processing method, since one point of the two stacked substrates is pressurized, the bonding of both is started so as to expand from the pressurized point to the periphery. If the load is removed before the second silicon substrate is completely bonded, there remains a problem to be solved that the film thickness in the SOI layer becomes uneven. That is, when one point is pressurized, the first and second silicon substrates come into direct contact from the pressurized point, and the gas existing between the first silicon substrate and the second silicon substrate gradually increases from the surroundings over time. As a result, the first and second silicon substrates are joined together so that the outer extension of the area in direct contact with both of them is gradually expanded to the periphery. However, when the load is removed at the stage where the extension of the direct contact area between the first silicon substrate and the second silicon substrate is gradually expanding, the extension of the direct contact area of the two that has continued to expand is temporarily reduced. Then, due to the weight of the second silicon substrate, the extension of the area where the two silicon substrates are in direct contact with each other is expanded again, and finally the entire first silicon substrate and the second silicon substrate are in direct contact with each other to be bonded together. Become. Then, when the SOI layer is measured in a state where the SOI substrate is finally obtained, the film thickness in the SOI layer is still uneven in the extension of the area where the both directly contracted when the load is removed. The problem to be solved remained. This is because when the extension of the area in direct contact between the two is once reduced, the bonding that has progressed in the extension is temporarily stopped, and then peeled once and then joined again, resulting in unevenness in the extension. It is believed that.
An object of the present invention is to provide an SOI substrate manufacturing method capable of obtaining an SOI layer 13 with relatively little film thickness unevenness.

As shown in FIG. 1, the invention according to claim 1 is a step of forming an oxide film 21 on at least the surface of the first silicon substrate 14 and implanting hydrogen ions from the surface of the first silicon substrate 14 to A step of forming an ion implantation region 16 inside the substrate 14 and a laminate in which the first silicon substrate 14 and the second silicon substrate 12 are joined by superimposing the second silicon substrate 12 on the first silicon substrate 14 via the oxide film 21. Forming the body 15 and heat-treating the laminated body 15 at a predetermined temperature, thereby separating the first silicon substrate 14 at the ion implantation region 16 and forming a thin-film SOI on the second silicon substrate 12 via the oxide film 21. And a step of obtaining the SOI substrate 11 on which the layer 13 is formed.
The characteristic point is that a load F directed to the first silicon substrate 14 is applied to the center of the second silicon substrate 12 superimposed on the first silicon substrate 14 in the step of forming the laminated body 15, and the load F is the first silicon substrate 14. The substrate 14 and the second silicon substrate 12 are continuously added until the bonding area of the first silicon substrate 14 or the second silicon substrate 12 exceeds 0.1% of the area of the bonding-side main surface.

In the SOI substrate manufacturing method described in claim 1, since a load toward the first silicon substrate 14 is applied to the center of the second silicon substrate 12, bonding is performed from the center of the second silicon substrate 12 to which the load is applied. Since the process is started, no void or the like is generated between the bonding interfaces of the two substrates as in the case where the bonding is started from a plurality of bonding points, and a good product can be obtained. In addition, since the load is applied to the center of the second silicon substrate 12, the bonding is performed so as to expand radially from the center of the substrate, so that the bonding time is shortened compared with the case where the load is applied to other portions. can do.
In addition, the load F applied to the second silicon substrate 12 is continuously applied until the bonding area exceeds 0.1% of the area of the bonding-side main surface of the substrate. The force that returns to the original shape in the elastic deformation of the wafer is larger, and the extension of the direct contact area between the first and second silicon substrates 12 and 14 is not once reduced. Relatively few SOI substrates 11 can be obtained.

The invention according to claim 2 is the invention according to claim 1, characterized in that the load F applied to the second silicon substrate 12 is 0.1 to 5.0 N.
In the method for manufacturing an SOI substrate according to claim 2, the time until the first silicon substrate 14 and the second silicon substrate 12 are joined is sufficiently shortened without causing damage to the second silicon substrate 12. can do.
In this specification, “bonding” means a state in which the first silicon substrate 14 and the second silicon substrate 12 are in direct contact and there is no gas between them, and “superposition” means the first silicon substrate 14. And the state in which the first silicon substrate 14 and the second silicon substrate 12 are opposed to each other with a gas in between.

  In the SOI substrate manufacturing method of the present invention, since a load toward the first silicon substrate is applied to the center of the second silicon substrate, bonding is started from the center of the second silicon substrate to which the load is applied. A void or the like does not occur between the bonding interfaces of the two substrates as in the case where the bonding is started from the point, and a good product can be obtained. In addition, since the load is applied to the center of the second silicon substrate, the bonding is also performed so as to expand radially from the center of the substrate, so that the bonding time is shortened compared with the case where the load is applied to other parts. be able to. In addition, since the load applied to the second silicon substrate is continuously applied until the bonding area exceeds 0.1% of the area of the bonding-side main surface of the substrate, the area where the first and second silicon substrates are in direct contact with each other. Thus, an SOI substrate with relatively little film thickness unevenness can be obtained in the SOI layer. If the load applied to the second silicon substrate is 0.1 to 5.0 N, the time until the first silicon substrate and the second silicon substrate are joined without causing damage to the second silicon substrate. Can be shortened sufficiently.

Next, the best mode for carrying out the present invention will be described with reference to the drawings.
As shown in FIG. 1 (k), the SOI substrate 11 is made of a second silicon substrate 12 made of a silicon single crystal and a silicon single crystal bonded to the second silicon substrate 12 via a first oxide film 21. And an SOI layer 13. The first oxide film 21 is an electrically insulating silicon oxide film (SiO ₂ film), and shows the case where the oxide film is not formed on the second silicon substrate 12. An oxide film may be formed separately. The thickness of the SOI layer 13 is desirably in the range of 10 to 200 nm, preferably 10 to 70 nm. However, the actual thickness of the SOI layer 13 is according to the requirements of the device manufacturer, and is not limited thereto.

A method for manufacturing such an SOI substrate 11 in the present invention will be described.
First, a first silicon substrate 14 made of a silicon single crystal is prepared, and a silicon oxide film having an electrical insulating property by thermal oxidation on the entire surface including the back surface and side surfaces (not shown) as well as the surface of the first silicon substrate 14 ( A first oxide film 21 made of (SiO ₂ film) is formed (FIG. 1A). The first oxide film 21 is formed to have a thickness of 50 to 300 nm, preferably 100 to 200 nm. Here, the reason why the thickness of the first oxide film 21 is limited to the range of 50 to 300 nm is that if it is less than 50 nm, void disappearance using the fluidity of the oxide film at a high temperature in bonding with the second silicon substrate 12 described later is used. As a result, voids are likely to be generated, and when the thickness exceeds 300 nm, the uniformity of the buried oxide film deteriorates from the device requirement. The first oxide film (SiO ₂ film) may be formed only on the surface of the first silicon substrate by CVD instead of thermal oxidation.

Next, hydrogen ions are implanted from the surface of the first silicon substrate 14 at a dose of 4 × 10 ¹⁶ atoms / cm ² to 10 × 10 ¹⁶ atoms / cm ² and an acceleration energy of 20 to 200 keV. Thereby, an ion implantation region 16 is formed inside the first silicon substrate 14 (FIG. 1B). Here, The reason for limiting the dose of hydrogen ions in the range of ^{4 × 10 16 / cm 2 ~10} × 10 16 / cm 2 can not cleaved by the first heat treatment is less than ^{4 × 10 16 / cm 2,} 10 This is because if it exceeds × 10 ¹⁶ / cm ² , self-peeling of the surface of the first silicon substrate 14 occurs during hydrogen ion implantation, and particles are easily generated. The reason why the acceleration energy is limited to the range of 20 to 200 keV is that if it is less than 20 keV, the SOI layer 13 becomes too thin, and if it exceeds 200 keV, a special ion implantation apparatus is required.

  On the other hand, a second silicon substrate 12 made of a silicon single crystal having the same surface area as the first silicon substrate 14 is prepared (FIG. 1C). The oxide film may or may not be formed on the second silicon substrate 12. The first silicon substrate 14 is overlaid on the second silicon substrate 12 via the first oxide film 21 to form a stacked body 15 (FIGS. 1D and 1E). In the step of forming the stacked body 15, the first silicon substrate 14 is overlaid on the second silicon substrate 12 and the alignment is performed, and then the second silicon substrate 12 overlaid on the first silicon substrate 14 is aligned. A step of applying a load F toward the first silicon substrate 14 at the center is included.

  That is, when the first silicon substrate 14 is overlaid on the second silicon substrate 12, the second silicon substrate 12 is in a floating state with respect to the first silicon substrate 14 due to the gas existing therebetween. For this reason, the friction when the second silicon substrate 12 moves in the horizontal plane with respect to the first silicon substrate 14 is extremely small, and even if there is a slight inclination, the second silicon substrate 12 does not move with respect to the first silicon substrate 14. Will slip out. For this reason, a process of superimposing the first silicon substrate 14 on the second silicon substrate 12 and aligning the first silicon substrate 14 is necessary. The alignment in this embodiment is performed by pressing a plurality of positioning pins (not shown) from around the two overlapping substrates 12 and 14, whereby the second silicon substrate 12 is horizontal with respect to the first silicon substrate 14. The movement of the direction is prohibited, and the second silicon substrate 12 is accurately superimposed on the first silicon substrate 14 (FIG. 1D).

  After alignment with the position of the second silicon substrate 12 superimposed on the first silicon substrate 14, a load F directed to the first silicon substrate 14 is applied to the center of the second silicon substrate 12 (FIG. 1E). ). The load F applied to the second silicon substrate 12 is preferably 0.1 to 5.0N, and more preferably 1.0 to 2.0N. If the load F is less than 0.1, the time until the first silicon substrate 14 and the second silicon substrate 12 are bonded cannot be shortened. If the load F exceeds 5.0 N, the load F is The added second silicon substrate 12 may be damaged. As a specific means for applying the load F, it is relatively simple and preferable to place a weight on the second silicon substrate 12, but a rod-shaped member is projected by an actuator provided with a load sensor, and the load is applied to the tip of the rod-shaped member. May be added. As described above, when a load toward the first silicon substrate 14 is applied to the center of the second silicon substrate 12, the bonding starts from the center of the second silicon substrate 12 to which the load is applied. A void or the like does not occur between the bonding interfaces of the two substrates as in the case where it is started, and a good product can be obtained, and the bonding time can be shortened.

  When a load F is applied to the second silicon substrate 12, the gas existing between the first silicon substrate 14 and the second silicon substrate 12 is gradually discharged from the surroundings to the outside, so that the central portion of the second silicon substrate 14 is discharged. The first silicon substrate 12 is first contacted, and the bonding is started from the contacted central portion. As the gas is discharged to the outside at the bonding interface between the substrates 12 and 14, the actual bonding area generated in the center gradually increases. Here, the load F applied to the second silicon substrate 12 is such that the bonding area of the first silicon substrate 14 and the second silicon substrate 12 is 0 of the area of the bonding silicon main surface of the first silicon substrate 14 or the second silicon substrate 12. Add at least continuously until it exceeds 1%. If the load is removed in a state in which the bonding area is less than 0.1% of the area of the bonding-side main surface, there is a risk that film thickness unevenness may occur in the SOI layer 13 of the obtained SOI substrate 11.

  The numerical value of the area varies depending on the shape of the bonding table. For example, if the bonding table is extremely flat, a bonding area of 0.1% or more is sufficient, but a concave bonding table is used. In the case of (for example, the difference in height between the center and the outer periphery is about 100 μm), it is preferable that the bonding area is continuously added until the bonding area exceeds 0.4% of the area of the bonding-side main surface. On the contrary, in the case of a convex shape (for example, the difference in height between the center and the outer periphery is 500 μm or more), due to the weight of the wafer, bonding proceeds without adding weight, and continuation of weight cannot be controlled. Thick film unevenness occurs in a region corresponding to the convex portion. Regarding the measurement of the bonding area, although not shown in the drawing, infrared rays are irradiated obliquely to the superimposed first silicon substrate 14 and second silicon substrate 12, the reflected infrared rays are incident on the camera, and the output signal of the camera is transmitted. A means for processing by an image processing apparatus and displaying on a monitor is mentioned.

  In the state where the bonding area between the first silicon substrate 14 and the second silicon substrate 12 is expanded to the entire area of the bonding-side main surface of the first silicon substrate 14 or the second silicon substrate 12, the bonding between the two is completed. A laminated body 15 in which the first silicon substrate 14 and the second silicon substrate 12 are joined is obtained. Thereafter, the laminated body 15 is held at 400 to 800 ° C., preferably 450 to 600 ° C. in a nitrogen atmosphere for 1 to 30 minutes, preferably 10 to 30 minutes, and a first heat treatment is performed. As a result, the first silicon substrate 14 is broken at the ion implantation region 16 corresponding to the hydrogen ion implantation peak position, and is separated into a lower thick portion 17 and an upper thin SOI layer 13 (FIG. 1F). The upper SOI layer 13 is in close contact with the second silicon substrate 12 through the first oxide film 21 to become a bonded substrate 18. The lower thick portion 17 is then reused after the separation surface is polished (FIGS. 1H and 1J).

  Next, the bonded substrate 18 is flattened and thinned by a general method until the final film thickness is obtained. For example, after removing a region where damage has occurred during separation by CMP processing, oxidation treatment, or the like, heat treatment for improving the bonding strength is performed. Further, planarization is performed by CMP processing and high-temperature heat treatment in an atmosphere such as hydrogen or argon gas (FIG. 1 (i)), and then thinning is performed by CMP processing or oxidation processing until a predetermined SOI layer 13 thickness is obtained. (FIG. 1 (k)).

  In such a method for manufacturing the SOI substrate 11, since a load toward the first silicon substrate 14 is applied to the center of the second silicon substrate 12, bonding is started from the center of the second silicon substrate 12 to which the load is applied. As in the case where bonding is started from a plurality of bonding points, voids or the like are not generated between the bonding interfaces of the two substrates, and a good product can be obtained. Further, since the load is applied to the center of the second silicon substrate 12, the bonding is also performed so as to expand radially from the center of the substrate, so that the bonding time is shortened as compared with the case where the load is applied to other portions. can do.

  In addition, the load F applied to the second silicon substrate 12 is continuously applied until the bonding area exceeds 0.1% of the area of the bonding-side main surface of the substrate. The force of returning to the original shape due to the elastic deformation of the wafer is larger, and the extension of the area where the first and second silicon substrates 12 and 14 are in direct contact with each other is not once reduced. Can be obtained. If the load F applied to the second silicon substrate 12 is 0.1 to 5.0 N, the first silicon substrate 14 and the second silicon substrate 12 are not damaged without causing damage to the second silicon substrate 12. Time until joining can be shortened sufficiently.

Next, examples of the present invention will be described in detail together with comparative examples.
<Example 1>
As shown in FIG. 1, first, a first silicon substrate 14 made of silicon single crystal and having an outer diameter and thickness of 300 mm and 0.78 mm is subjected to a heat treatment that is held at 1000 ° C. for 5 hours in an oxygen atmosphere. The first oxide film 21 was formed not only on the surface of the silicon substrate 14 but also on the back surface and side surfaces. Next, hydrogen ions are implanted from the surface of the first silicon substrate 14 at a dose of 6 × 10 ¹⁶ / cm ² and an acceleration energy of 50 keV to form an ion implantation region 16 inside the first silicon substrate 14 (FIG. 1 ( b)). On the other hand, a second silicon substrate 12 having the same shape and size as the first silicon substrate 14 is prepared (FIG. 1C), and the first silicon substrate 14 and the first oxide film 21 are formed on the second silicon substrate 12. Then, the laminated body 15 was obtained by superimposing them on each other (FIGS. 1D and 1E).

  In the formation of the laminated body 15, the first silicon substrate 14 is overlaid on the second silicon substrate 12 and aligned, and then the center of the second silicon substrate 12 overlaid on the first silicon substrate 14 is aligned. A load F consisting of 2N toward the first silicon substrate 14 was applied. With this load F, the first silicon substrate 14 and the second silicon substrate 12 started to be bonded from the center, and the bonding area was measured. In the measurement of the bonding area, the first silicon substrate 14 and the second silicon substrate 12 that are superimposed are irradiated with infrared rays obliquely, the reflected infrared rays are incident on the camera, and the output signal of the camera is processed by an image processing apparatus. Was determined by The load F is removed when the bonding area of the first silicon substrate 14 and the second silicon substrate 12 becomes 0.1% of the area of the bonding-side main surface of the second silicon substrate 12, and then the second silicon substrate 12 is removed. After waiting for the whole to come into contact with the first silicon substrate due to its own weight, a laminate 15 was obtained in which the whole was in direct contact and both were joined.

  Next, the laminated body 15 is subjected to a heat treatment at 500 ° C. for 30 minutes in a nitrogen atmosphere, and is split at the ion implantation region 16 so that the upper SOI layer 13 adheres to the second silicon substrate 12 via the first oxide film 21. The obtained bonded substrate 18 was obtained (FIG. 1 (f)). The bonded substrate 18 was subjected to an oxidation treatment to remove the damage layer at the time of peeling, and then subjected to high-temperature heat treatment in an argon gas atmosphere in order to further complete the bonding force at the bonded interface. Then flatten the surface. Next, a thinning process was performed by heat treatment in an oxidizing atmosphere until a predetermined SOI layer thickness was obtained. The SOI substrate 11 obtained in this way was referred to as Example 1.

<Example 2>
With a load F of 2N applied to the center of the second silicon substrate 12, the bonding area of the first silicon substrate 14 and the second silicon substrate 12 becomes 100% of the area of the bonding side main surface of the second silicon substrate 12. Removed later. Except for this, an SOI substrate was fabricated under the same procedure and the same conditions as in Example 1. This SOI substrate was determined as Example 2.
<Comparative Example 1>
The load F composed of 2N applied to the center of the second silicon substrate 12 is set so that the bonding area of the first silicon substrate 14 and the second silicon substrate 12 is 0.08% of the area of the bonding-side main surface of the second silicon substrate 12. Removed when it became. Except for this, an SOI substrate was fabricated under the same procedure and the same conditions as in Example 1. This SOI substrate was referred to as Comparative Example 1.

<Comparison test and evaluation>
The film thicknesses of the respective SOI layers of the SOI substrates in Examples 1 and 2 and Comparative Example 1 were measured. The film thickness was measured with a nanometrics film thickness measuring instrument, and the measurement was performed on the diameter passing through the center of the SOI substrate from the outer periphery toward the opposite outer periphery. The result is shown in FIG.
As is clear from the results of FIG. 2, in Comparative Example 1, the film thickness is remarkably thin at a point of about 5 mm from the center of the SOI substrate, although there is no significant variation in the film thickness of Examples 1 and 2. You can see that there is a part. This is considered to be due to the fact that the time when the load is removed is earlier than that of the embodiment, and it can be seen that the present invention is effectively established.

It is a figure which shows the manufacturing method of the SOI substrate of embodiment of this invention in order of a process. It is a figure which shows the dispersion | variation in the film thickness which is a measurement result in the Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 SOI substrate 12 2nd silicon substrate 13 SOI layer 14 1st silicon substrate 15 Laminated body 16 Ion implantation area | region 21 Oxide film F Load

Claims (2)

Forming an oxide film (21) on at least the surface of the first silicon substrate (14); and implanting hydrogen ions from the surface of the first silicon substrate (14) to form ions in the first silicon substrate (14); A step of forming an implantation region (16); and a second silicon substrate (12) superimposed on the first silicon substrate (14) via the oxide film (21), and the first silicon substrate (14) and the A step of forming a laminated body (15) to which a second silicon substrate (12) is bonded, and a heat treatment of the laminated body (15) at a predetermined temperature, thereby bringing the first silicon substrate (14) into the ion implantation region ( 16) to obtain an SOI substrate (11) in which a thin SOI layer (13) is formed on the second silicon substrate (12) via the oxide film (21). In the manufacturing method,
In the step of forming the laminate (15), a load (F) applied to the first silicon substrate (14) is applied to the center of the second silicon substrate (12) superimposed on the first silicon substrate (14). And
The load (F) is such that the bonding area of the first silicon substrate (14) and the second silicon substrate (12) is the surface of the bonding side main surface of the first silicon substrate (14) or the second silicon substrate (12). A method for producing an SOI substrate, which is continuously added until it exceeds 0.1% of the area. 2. The method for manufacturing an SOI substrate according to claim 1, wherein the load (F) applied to the second silicon substrate (12) is 0.1 to 5.0 N.

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