JP3632531B2 - Manufacturing method of semiconductor substrate - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a semiconductor substrate that is generally used for semiconductor devices including composite ICs and LSIs.
[0002]
[Prior art]
2. Description of the Related Art An SOI (silicon on insulator) semiconductor device in which a semiconductor layer is disposed on a semiconductor substrate via an intermediate insulating film is a device in which a plurality of types of elements such as bipolar, MOS, and power elements are mounted on a single chip, for example, a composite It is suitable for use in ICs, high voltage ICs, and LSIs for portable devices that require high speed and low power consumption.
[0003]
In order to manufacture an SOI semiconductor device, a so-called SOI substrate in which a high-quality crystalline semiconductor layer is formed on a very high resistance layer made of an insulator such as SiO ₂ is required as a substrate. Conventionally, a bonding method has been known as a method for manufacturing such an SOI substrate. This method uses a base wafer made of a first semiconductor substrate having at least a main surface mirror-polished and a bond wafer made of a second semiconductor substrate having at least a main surface mirror-polished, and at least one of the two is used. After forming an oxide film on the main surface, the main surfaces of the two wafers are bonded together in a clean atmosphere, and after bonding the two wafers by performing high-temperature bonding heat treatment, bonding of the bonded wafers The SOI substrate is manufactured by surface grinding and mirror polishing the side and back surfaces to obtain a predetermined SOI layer thickness required for device characteristics.
[0004]
[Problems to be solved by the invention]
However, in the conventional method for manufacturing a bonded SOI substrate, as shown in FIG. 6, after two mirror wafers 51 and 52 that have been previously molded to a target wafer diameter are bonded via an oxide film 53 ( 6 (a)), an edge of several mm from the periphery of the bond side wafer 52 is removed to the vicinity of the bonding interface by edge grinding (FIG. 6 (b)), and then immersed in an alkaline solution such as NaOH for oxidation. The film 53 (SiO ₂ ) surface was exposed (FIG. 6C), and the bond-side wafer 52 was surface ground (FIG. 6D) and mirror-polished (FIG. 6E). However, this method requires steps such as edge grinding and alkali etching, which increase the number of steps in the manufacturing process of the SOI substrate and increase the cost due to a decrease in throughput.
[0005]
In another SOI substrate manufacturing method according to the prior art shown in FIG. 7, two mirror wafers 61 and 62 previously formed to have a target wafer diameter are bonded together via an oxide film 63 (FIG. )), One of the wafers 62 is ground to the vicinity of a predetermined SOI thickness (FIG. 7B), leaving a few millimeters from the outer periphery of the wafer, and covering the SOI side surface with an acid-resistant masking tape 64. It was immersed in a mixed solution of oxynitric acid to remove Si at the end to expose the surface of the oxide film 63 (SiO ₂ ) (FIG. 7C), and mirror polishing (FIG. 7D) was performed. However, in this method, masking tape sticking or the like is required, and, like the method shown in FIG. 6, the man-hours in the manufacturing process of the SOI substrate are increased, and the cost is increased due to the decrease in throughput.
[0006]
Furthermore, SOI wafers manufactured by these conventional methods have a terrace structure in which the base wafer protrudes outward at the outer periphery. This is not only a problem that the effective area on the bond wafer side that can be used for device formation is reduced, but also due to various deposited films remaining in the terrace structure part during the device formation process or due to element isolation. When the trench etching is performed, the silicon at the edge of the base wafer is exposed to induce the generation of black silicon. If it is severe, they will be peeled off in a later process, causing contamination and particle sources to reduce the yield. There is a problem of becoming.
[0007]
The present invention has been made in view of the above problems, and an SOI semiconductor capable of reducing the manufacturing cost of an SOI wafer and suppressing a decrease in yield due to generation of particles during the device formation process. An object of the present invention is to provide a method for manufacturing a substrate.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, a base wafer (1) comprising a first semiconductor substrate having at least a main surface mirror-polished, and a second semiconductor having at least a main surface mirror-polished. A bond wafer (2) made of a substrate is prepared, and a step of forming an oxide film (3) on at least one main surface of the base wafer and the bond wafer is arranged so that the main surfaces of the base wafer and the bond wafer face each other. A bonding process including a step of bonding a base wafer and a bond wafer through an oxide film to form a bonded wafer, and a step of surface grinding and mirror polishing the back surface of the bonded wafer on the bond wafer side to obtain a predetermined SOI layer thickness. In the method for manufacturing a bonded SOI wafer, after the bonding step is completed, at least one of a base wafer and a bond wafer And removing at the end dilute hydrofluoric acid formed oxide film, after the step of removing the oxide film, possess a step of subjecting the beveling process to the end of the bond wafer, further, the oxide film In the removing step, an oxide film formed on the back surface of at least one of the base wafer and the bond wafer is left.
[0009]
In this way, by performing the beveling process after the end of the bonding heat treatment, it is possible to reduce the steps of edge grinding or masking tape application and alkali etching, which are necessary in the manufacturing process of the conventional bonded SOI wafer. Manufacturing costs can be reduced. Further, it is possible to eliminate the terrace structure at the outer periphery of the wafer, which was unavoidable with the conventional SOI wafer manufacturing method, and the occurrence of contamination or particles due to the presence of the terrace structure during the device formation process is suppressed. There is an effect that a decrease in yield can be prevented. Further, by removing the oxide film formed on at least one of the base wafer and the bond wafer before the beveling treatment, it is possible to prevent the grindstone from being seized or worn. Further, if the oxide film formed on the back surface of at least one of the base wafer and the bond wafer is left in the step of removing the oxide film, the wafer is affected by the stress of the oxide film between the two wafers. The occurrence of warping can be suppressed.
[0010]
In addition, as shown in claim 2, if a semiconductor substrate having an outer diameter larger than the outer diameter of the finally obtained SOI wafer is used as the first and second semiconductor substrates, the diameter by beveling processing is used. Can be expected to shrink.
[0011]
For example, as shown in claim 3, the beveling process applied to the end portion of the bonded wafer can be performed after the bonding process and before the surface grinding. Moreover, as shown in Claim 4, it can carry out after a surface grinding and before mirror polishing. Further, as shown in claim 5, it may be performed after the completion of mirror polishing.
[0015]
In addition, the code | symbol in the bracket | parenthesis of each said means shows the correspondence with the specific means as described in embodiment mentioned later.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
A first embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a manufacturing process of an SOI substrate. Hereinafter, a method for manufacturing an SOI substrate according to the present embodiment will be described with reference to FIG.
[0017]
[Step shown in FIG. 1 (a)]
First, a base wafer 1 as a first semiconductor substrate having at least one main surface mirror-polished and a bond wafer 2 as a second semiconductor substrate having at least one main surface mirror-polished are prepared. Then, after heat treatment at, for example, 1050 ° C. in an oxidizing atmosphere is performed on at least one main surface of both wafers to form an oxide film (SiO ₂ ) 3 of about 1 μm, the main surfaces of the two wafers are Bonding is performed in a clean atmosphere so as to face each other, and for example, bonding heat treatment is performed at about 1100 ° C. and about 1 Hr in an oxidizing or nitrogen atmosphere to form a bonded wafer 4.
[0018]
[Step shown in FIG. 1B]
Next, surface grinding is performed from the back surface (main surface on the side opposite to the bonding surface) of the bond-side wafer 2 in the bonded wafer 4, and the surface is thinned to a thickness near the target SOI thickness. At this time, it is desirable that the grinding is performed by appropriately changing the count of the grindstone from rough grinding to finish grinding so that the crushed layer is not left as deep as possible.
[0019]
[Step shown in FIG. 1 (c)]
Next, beveling processing (chamfering processing) is performed on the end of the bonded wafer 4 after the surface grinding using a grindstone. This beveling process is performed using a grindstone 5 having a substantially circular recess as shown in FIG. At this time, the portions of the oxide film 3 located at the end and back surface of the bonded wafer 4 are previously removed by means such as dilute hydrofluoric acid solution dipping in order to prevent the grindstone 5 from being seized or worn. However, when the oxide film 3 in the buried portion of the bonding interface is thick, the wafer 4 is warped due to the influence of stress. Therefore, it is desirable to intentionally leave the oxide film 3 on the back surface. For this purpose, for example, a jig such as a pot chuck may be used to remove only a portion of the oxide film 3 located at the end of the base wafer 2 and leave the oxide film on the back surface.
[0020]
[Step shown in FIG. 1 (d)]
When the beveling process is completed, mirror polishing is performed next. Thereby, an SOI wafer is formed. In addition, as usual, this mirror polishing is performed in the order of primary polishing, secondary polishing, and finish polishing to obtain a device-grade mirror surface with a predetermined SOI thickness. Finally, cleaning is performed to complete the SOI substrate.
[0021]
In the above embodiment, the outer diameters of the base wafer 1 and the bond wafer 2 as the first and second semiconductor substrates to be used first are larger than the outer diameter of the completed SOI wafer (required after the bonding wafer 4 is beveled). It is desirable to use a large semiconductor substrate. This is because in the beveling process (see FIG. 1C), the wafer outer diameter may be reduced as a result of chamfering the wafer edge.
[0022]
Moreover, in the said embodiment, what has not performed the beveling process is used for the edge part of the base wafer 1 and the bond wafer 2 as a 1st and 2nd semiconductor substrate used initially. That is, using a wafer that has been lapped, etched, and washed on a wafer sliced from an ingot, the two wafers 1 and 2 are bonded together, and then the combined wafer 4 is integrally beveled. Thereby, the beveling process of each of the first and second semiconductor substrates which has been conventionally performed can be reduced.
[0023]
Further, in the above embodiment, the beveling process is performed after the wafer bonding, and both the bond wafer and the base wafer are chamfered so that the diameter becomes maximum at about half the thickness of the finally obtained SOI substrate. Therefore, the bonded SOI substrate that has been thinned by surface grinding or mirror polishing has the same cross-sectional shape as that of a single mirror wafer, particularly on the polishing surface of the surface, and the peripheral portion also has an appearance. A gentle chamfering is made and a so-called terrace structure is not formed. In addition, an SOI substrate having the same structure can be formed using a bond wafer and a base wafer having substantially the same diameter.
[0024]
As described above, according to the present embodiment, by performing the beveling process after the end of the bonding heat treatment, the steps of edge grinding or masking tape application and alkali etching, which are necessary in the manufacturing process of the conventional bonded SOI wafer, are reduced. Therefore, the manufacturing cost of the SOI wafer can be reduced. Further, it is possible to eliminate the terrace structure on the outer periphery of the wafer, which cannot be avoided by the conventional SOI wafer manufacturing method. As a result, when the device is actually formed on the bond wafer side, particles deposited due to the peeling of the deposited film from the terrace structure part or the generation of black silicon in the terrace structure part due to the presence of the terrace structure part are generated. Generation | occurrence | production etc. can be suppressed and there exists an effect that the fall of a yield can be prevented.
[0025]
(Second Embodiment)
FIG. 3 shows a manufacturing process of the SOI substrate in the second embodiment of the present invention. The difference of this embodiment from the first embodiment is the step shown in FIG. 3B, in which the beveling process after bonding is performed after the bonding heat treatment and before surface grinding. In this case, beveling is performed in such a shape that the diameter becomes maximum at about half the thickness of the finally obtained SOI substrate. Even if it does in this way, the effect similar to 1st Embodiment is acquired.
[0026]
The process shown in FIG. 3A corresponds to the wafer bonding process shown in FIG. 1A, and the processes shown in FIGS. 3C and 3D are the surface grinding and FIG. This corresponds to each step of mirror polishing 1 (d).
[0027]
(Third embodiment)
FIG. 4 shows a manufacturing process of an SOI substrate in the third embodiment of the present invention. The difference of the present embodiment from the first embodiment is the step shown in FIG. 4D, in which the beveling process after bonding is performed after the mirror polishing is completed. Even if it does in this way, the effect similar to 1st Embodiment is acquired.
[0028]
Each process shown in FIG. 4 corresponds to the process shown in FIG. 1 in which the order of the process shown in FIG. 1C and the process shown in FIG.
[0029]
(Fourth embodiment)
FIG. 5 shows an SOI substrate manufacturing process according to the fourth embodiment of the present invention. In this embodiment, the difference from the first embodiment is the process shown in FIG. 5A. As the first and second semiconductor substrates to be used first, a substrate that has been subjected to a beveling process as usual is used. It is a point to use. Even if the beveling process has been performed in advance, if the outer diameter of the wafer is large, the same effect as in the first embodiment can be realized by performing the beveling process with the bonded wafer as a unit after the bonding heat treatment. The steps after FIG. 5B are the same as the steps after FIG. 1B, but of course the order of the steps of beveling, surface grinding, and mirror polishing as in the second to fourth embodiments. You may make it replace.
[Brief description of the drawings]
FIG. 1 is a diagram showing a manufacturing process of an SOI substrate in a first embodiment of the present invention.
FIG. 2 is a diagram illustrating a state of a beveling process.
FIG. 3 is a diagram showing a manufacturing process of an SOI substrate in a second embodiment of the present invention.
FIG. 4 is a diagram showing a manufacturing process of an SOI substrate in a third embodiment of the present invention.
FIG. 5 is a diagram showing a manufacturing process of an SOI substrate in a fourth embodiment of the present invention.
FIG. 6 is a diagram showing a manufacturing process of a conventional SOI substrate.
FIG. 7 is a diagram showing a manufacturing process of a conventional SOI substrate.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Base wafer, 2 ... Bond wafer, 3 ... Oxide film, 4 ... Bonded wafer.

Claims (5)

A base wafer (1) made of a first semiconductor substrate having at least a main surface mirror-polished and a bond wafer (2) made of a second semiconductor substrate having at least a main surface mirror-polished are prepared, and the base wafer and A step of forming an oxide film (3) on at least one main surface and an end of the bond wafer; and the base wafer via the oxide film so that the main surfaces of the base wafer and the bond wafer face each other. And bonding the bond wafer to form a bonded wafer;
In the manufacturing method of the bonded SOI wafer, including a step of performing a surface grinding and mirror polishing the back surface on the bond wafer side of the bonded wafer to a predetermined SOI layer thickness,
Removing the oxide film formed at the end of at least one of the base wafer and the bond wafer with dilute hydrofluoric acid after finishing the bonding step;
After the step of removing the oxide film, it possesses a step of subjecting the beveling process to an end of the coupling wafer,
Furthermore, in the step of forming the oxide film, the oxide film is also formed on the back surface of at least one of the base wafer and the bond wafer,
In the step of removing the oxide film, the oxide film formed on the back surface is left . 2. The semiconductor substrate manufacturing method according to claim 1, wherein the first and second semiconductor substrates are semiconductor substrates having an outer diameter larger than an outer diameter of an SOI wafer finally obtained. Method. 3. The method of manufacturing a semiconductor substrate according to claim 1, wherein the beveling process performed on the end portion of the bonded wafer is performed after the bonding process and before the surface grinding. 4. 3. The method of manufacturing a semiconductor substrate according to claim 1, wherein the beveling process applied to the end portion of the bonded wafer is performed after the surface grinding and before the mirror polishing. 4. The method for manufacturing a semiconductor substrate according to claim 1, wherein the beveling process performed on the end portion of the bonded wafer is performed after the mirror polishing is completed.

Images