JP3371392B2 - Manufacturing method of bonded SOI substrate - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a bonded SOI.
(Silicon on insulator) The present invention relates to a method for manufacturing a substrate, particularly a method for manufacturing a bonded SOI substrate capable of forming an island-shaped semiconductor layer with a uniform thickness on the entire wafer.

[0002]

2. Description of the Related Art Development of a VLSI using a so-called SOI substrate in which a thin film single crystal silicon layer is formed on the surface of an insulator is under development. Among the various SOI substrate manufacturing methods, the one that is considered to have the best crystallinity and the excellent characteristics is the bonding method of the SOI substrate. FIG. 3 shows the steps of the method for manufacturing the SOI substrate.
It was shown to. A method of manufacturing this SOI substrate will be briefly described with reference to FIG.

As shown in FIG. 3A, a predetermined pattern composed of a plurality of concave and convex portions 2 is formed on the surface of an element forming substrate 1 which is a single crystal silicon wafer having a mirror finished surface by using a photolithography technique. It is formed by steps. An upper insulating film 3A and a lower insulating film 3 are formed on these uneven portions 2.
An insulating film 3 formed continuously with B, for example, Si
An O ₂ film is formed, a flattening layer, for example, a polycrystalline silicon layer 4 is formed on the entire surface to further fill the step, and the surface of the polycrystalline silicon layer 4 is flatly polished.

Next, as shown in FIG. 3B, a supporting substrate 5 of, for example, another mirror-finished silicon wafer is attached to the flattened surface of the polycrystalline silicon layer 4, and the supporting substrate 5 is attached. 5 is ground to a predetermined thickness, and a bonded substrate 7 is manufactured by bonding the element forming substrate 1 and the supporting substrate 5. Then, as shown in FIG. 3C,
Using the upper insulating film 3B of the insulating film 3 as a polishing stopper, the element forming substrate 1 which is a single crystal silicon wafer is polished from the back surface thereof, and a plurality of island-shaped silicon thin films separated by the insulating film 3 of SiO ₂ are formed. A bonded SOI substrate 8 having a layer 6 is obtained.

The bonded SOI substrate 8 in FIG. 3C is shown in a state in which the bonded substrate 7 in FIG. 3B is turned upside down. Therefore, the upper insulating film 3A and the lower insulating film 3B in FIG. 3B become the lower insulating film 3A and the upper insulating film 3B in FIG. 3C, respectively. In order to avoid ambiguity in the description, in the following description, in the state of the bonded SOI substrate 8 of FIG. 3C, the insulating film 3B located above will be referred to as an upper insulating film.

By the way, in the process of manufacturing the bonded SOI substrate 8, polishing of the element forming substrate 1 after bonding the support substrate 5 is performed by forming the island-shaped silicon thin layer 6 in the recess of the SiO ₂ film into a recess. Upper insulating film 3 of peripheral SiO ₂ film
It depends on whether it is finished on the same plane as B and is flat and free from polishing damage.

FIG. 4 shows the laminated substrate 7 in the step shown in FIG. 3B upside down again. The element formation substrate 1 which is a single crystal silicon wafer before polishing
In this case, due to the grinding accuracy before that, a macro thickness unevenness is generated as shown in the figure. For example, the thicker one is 5-1
There is unevenness of about 0 μm, and about 1 μm in the thinner one.

[0008]

Conventionally, in polishing the element forming substrate 1 having such a thickness unevenness as described above, the element forming substrate 1 is subjected to only a partial polishing method or a selective polishing method. It was finished using. The former partial polishing method is a process for eliminating the thickness unevenness of the element forming substrate 1 and making the thickness uniform, and polishing the surface of the element forming substrate 1 part by part with a polishing head while scanning. Then, in the case of polishing the next portion, the method is to sequentially polish so as to overlap a portion of the portion that has just been polished. As the polishing liquid used in this case, a polishing liquid containing free abrasive grains is used, and the free abrasive grains are used for polishing in which physical polishing is superior to chemical polishing. When the surface of the element forming substrate 1 is polished only by this partial polishing method, as shown in FIG. 5, microscopic thickness unevenness 9A due to the overlapping portion of the scanning of the polishing processing head occurs, and the island which is the element forming region is formed. There is a problem in that the silicon thin layer 6 is uneven in thickness. The micro uneven thickness 9
A becomes thinner than other parts by about 10 to 100 nm.

The applicant has applied for the selective polishing method,
Published Japanese Patent Application No. 2-267 published on November 1, 1990
One of the polishing methods is shown in Japanese Patent Laid-Open No. 939 "polishing method", but the entire surface to be polished of the element forming substrate 1 is polished at the same time, and polishing is simultaneously completed on the plane where the upper insulating film 3B is present. Is the way.

A polishing apparatus 10 capable of executing this selective polishing method.
Is shown in FIG. The polishing apparatus 10 is composed of a rotating wafer holder 11 and a rotating polishing platen 14 in which a polishing pad 13 is attached to a flat surface of a polishing platen 12. When the bonded substrate stack 7 is polished by using the polishing apparatus 10, the bonded substrate stack 7 is attached to the wafer holder 11.
Is adhered with wax with the element forming substrate 1 side facing down or fixed by vacuum suction, the surface to be polished of the element forming substrate 1 is brought into contact with the polishing pad 13, and the polishing liquid L is supplied from the nozzle 15. Meanwhile, the entire surface to be polished is polished at the same time. In this case, the polishing liquid L is the upper insulating film 3B of SiO _2.
Does not chemically react with, but uses a polishing solution of an alkaline solution that chemically reacts with single crystal silicon or a polishing solution of an alkaline solution containing free abrasive grains. To do. Further, as the polishing pad 13, various hardnesses such as a super hard surface plate such as a ceramic plate to a soft cloth of suede type foamed polyurethane are used as needed.

As shown in FIG. 6, partial overpolishing caused by macroscopic unevenness in thickness cannot be avoided only by the selective polishing method using the polishing apparatus 10, and uneven thickness 9B,
9C and 9D occurred, and it was not possible to finish on the same plane.

Therefore, since the thickness of the island-shaped silicon thin layer 6 is about 20 nm to 100 nm, when the thickness unevenness 9A or the thickness unevenness 9B, 9C, 9D as described above occurs, a desired good element is formed. There was a problem that I could not do it. Therefore, the present invention is intended to solve such a problem, in which an island-shaped silicon thin layer in a recess of an insulating film such as a SiO ₂ film is flush with the upper insulating film of the insulating film around the recess. Another object of the present invention is to provide a method for manufacturing a bonded SOI substrate which is flat and can be polished and finished without polishing damage.

[0013]

Therefore, in the method for manufacturing a bonded SOI substrate of the present invention, a plurality of concave patterns are formed on the surface of the element forming substrate by the insulating step formed by the upper insulating film and the lower insulating film. Then, in polishing the element forming substrate outside the recess so that the element forming regions remain in the recesses in the form of islands, first, by a partial polishing method, an insulating step outside the concave is formed until just before reaching the upper insulating film. The above problem is solved by polishing the element formation substrate present in 1) and then polishing the remaining element formation substrate using the upper insulating film as a polishing stopper by a selective polishing method.

Therefore, according to the method of manufacturing the bonded SOI substrate of the present invention, the island-shaped silicon thin layer is polished on the same plane as the upper insulating film around the recess so as to be flat and free from polishing damage. Can be finished.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of a method for manufacturing a bonded SOI substrate of the present invention will be described with reference to FIGS. FIG. 1 is a manufacturing process diagram for explaining a method for manufacturing a bonded SOI substrate of the present invention, and FIG.
FIG. 3 is a conceptual diagram of a plasma etching method for explaining an example of a method for manufacturing a bonded SOI substrate of the present invention. The same components as those of the conventional SOI substrate are designated by the same reference numerals in the following description.

In FIG. 1, FIG. 1A shows the laminated substrate 7 of FIG. 3B turned upside down, and is the same laminated substrate 7 as in FIG. As described above, in the bonded substrate 7 before polishing, the thickness of the element forming substrate 1 has in-plane thickness unevenness due to processing accuracy such as grinding. The macro thickness unevenness is, for example, 5-1 for thicker ones.
As described above, the unevenness is about 0 μm and about 1 μm for the thinner one.

It has been found that the following polishing method is optimal for finishing the bonded substrate 7 having such uneven thickness with good in-plane uniformity. That is, first, partial polishing is performed. In this partial polishing process, the surface of the element-formed substrate 1 having partial thickness unevenness before the partial processing is subjected to the above-described partial polishing method, and the element existing outside the insulating step concave portion until just before reaching the upper insulating film. The formed substrate is polished to reduce in-plane macroscopic thickness unevenness. Then, the remaining element formation substrate is polished by the selective polishing method using the upper insulating film as a polishing stopper.

In carrying out the polishing method of the present invention, first, before the partial polishing process is performed, the thickness of the element forming substrate 1 is measured on the entire surface and stored in the computer. After that, the partial polishing process is started. In this partial polishing process, based on the instructions of the computer,
The surface of the element forming substrate 1 is partially scanned by a processing head having a smaller diameter than the element forming substrate 1, and the element forming substrate 1
To polish.

The surface of the element forming substrate 1 is partially scanned and polished by using this small-diameter processing head. In this partial polishing processing, a polishing liquid containing loose abrasive grains is used. When this polishing liquid is used, physical polishing is performed with the abrasive grains rather than chemical polishing. The processing speed of this polishing is automatically controlled, and the uneven thickness is corrected.

This partial polishing process using a polishing liquid containing the above-mentioned loose abrasive grains is a method suitable for correcting macroscopic thickness unevenness, but when viewed microscopically, paragraph [000] is used.
7], the partial polishing process according to the present invention is performed only by removing the macroscopic unevenness in thickness before polishing. That is, as shown in FIG. 1B, in this partial polishing process, the element forming substrate 1 existing outside the insulating step concave portion is polished until just before reaching the upper insulating film 3B, and the micro processing is performed by the overlapping portion of the scanning of the polishing processing head. It is always stopped before the depth of the uneven thickness 9A reaches the upper insulating film 3B.

In the present invention, instead of the partial polishing process using the polishing liquid containing free abrasive grains as described above, a partial process by a plasma etching method or an ion milling method may be performed. Above all, the plasma etching method can be performed by using the plasma etching apparatus 20 as shown in FIG. That is, the plasma etching apparatus 20 is provided in a vacuum chamber (not shown), a plasma processing head 22 having an anode 21 mounted thereon, a cathode 23, and a high-frequency voltage source 24 connected between the anode 21 and the cathode 23.
Etc. In this embodiment, it is assumed that the plasma processing head 22 is a fixed type plasma etching apparatus 20.

Using the plasma etching apparatus 20 having such a structure, the so-called PACE method (Plasma-Assisted Chemic) is used.
al Etching). When the element forming substrate 1 of the bonded substrate 7 is partially processed using this method, the bonded substrate 7 is placed on the surface of the cathode 23 with the surface of the element forming substrate 1 facing upward, and, for example, , CF ₄ or the like is supplied into the vacuum chamber, the inside of the vacuum chamber is set to a high gas pressure of 1 Toll or more, and a high frequency voltage is applied from the high frequency voltage source 24 between the anode 21 and the cathode 23 to generate CF ₄ plasma. Turn into. In FIG. 2, the symbol P indicates the plasma. Then, isotropic plasma etching is performed at an etching rate of 1 to 50 μm / min. During this processing, the bonded substrate stack 7 is sequentially moved in the XY direction within the same plane. By doing so, the entire surface of the element formation substrate 1 can be chemically etched by isotropic plasma.

Even when this plasma etching apparatus 20 is used, the thickness unevenness is almost the same as the thickness unevenness 9A generated when the partial polishing process is performed with the polishing liquid containing the loose abrasive grains. That is, the plasma processing head 22 scans the next strip-shaped etched portion so that one side edge of the strip-shaped portion that has once scanned the surface of the element forming substrate 1 overlaps the next scan. Therefore, the thickness unevenness 9A as shown in FIG. 1B occurs in the overlapping portion of the scanning on the surface of the element forming substrate 1.

Therefore, this plasma etching apparatus 20
Even when the surface of the bonded substrate 7 is partially processed by using, the element forming substrate 1 existing outside the insulating step concave portion until just before reaching the upper insulating film 3B is etched as shown in FIG. 1B, The depth of the microscopic thickness unevenness 9A due to the overlapping portion of the scanning of the plasma processing head 22 is the upper insulating film 3
Be sure to stop before reaching B. The subsequent polishing process is finished by using the selective polishing process. The processing of the surface of the element forming substrate 1 by the plasma etching method can be performed at a relatively high etching rate as compared with the partial polishing processing using a polishing liquid containing loose abrasive grains, so that the partial processing can be processed efficiently. it can.

Further, partial processing may be performed by using an ion milling method. In this case, unlike the partial processing by the plasma etching in which the chemical processing is performed, the physical polishing is performed similarly to the partial polishing by the polishing liquid containing the loose abrasive grains.

In this way, the bonded substrate 7 which has been partially polished is microscopically thin element forming substrate 1.
Although the single crystal silicon layer of No. 1 remains, the macroscopic thickness unevenness is greatly reduced and is corrected to about 0.05 to 0.5 μm.

Next, in the present invention, the selective polishing process is performed on the bonded substrate 7 after the partial polishing process is completed.
In the selective polishing process, since it is necessary to polish only the single crystal silicon layer of the element forming substrate 1 without polishing the upper insulating film 3B, an alkaline polishing liquid containing almost no abrasive grains is used and physical polishing is performed. Even chemical polishing is superior to polishing. For example, ethylenediamine and ammonia can be easily used. Further, as the selective polishing machine, a general one-sided mirror polishing machine may be used.

When the surface of the upper insulating film 3B is polished by this selective polishing process, the microscopic thickness unevenness 9A caused by the partial polishing process can be removed at the same time. Therefore, by performing this selective polishing process, the surface of the upper insulating film 3B is exposed almost at the same time on the entire surface, and as shown in FIG. 1C,
Bonded SOI in which the island-shaped silicon thin layer 6 with extremely little excessive polishing is formed over the entire surface of the bonded substrate 7.
The substrate 8 can be obtained.

[0029]

As described above, according to the method for manufacturing a bonded SOI substrate of the present invention, the island-shaped silicon thin layer in the recess of the insulating film is the same as the upper insulating film of the insulating film around the recess. It is possible to finish the surface on a flat surface so that it is flat and free from polishing damage, and the yield can be improved. Moreover, the introduction of automatic processing by a computer becomes easy. Therefore, cost reduction can be achieved by these synergistic effects.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram for explaining a method for manufacturing a bonded SOI substrate of the present invention.

FIG. 2 is a conceptual diagram of a plasma etching method for explaining an example of a method for manufacturing a bonded SOI substrate of the present invention.

FIG. 3 is a manufacturing process diagram for explaining a method for manufacturing a bonded SOI substrate according to a conventional technique.

FIG. 4 is a cross-sectional view of a bonded SOI substrate for explaining the shape of the bonded substrate stack before manufacturing the bonded SOI substrate.

5 is a cross-sectional view of a bonded SOI substrate for explaining a defect when the bonded substrate shown in FIG. 4 is partially polished by a conventional method.

6 is a cross-sectional view of a bonded SOI substrate for explaining a defect when the bonded substrate shown in FIG. 4 is subjected to selective polishing by a conventional method.

FIG. 7 is a partial cross-sectional view of a conventional polishing apparatus for selective polishing processing.

[Explanation of symbols]

1 element formation substrate 2 uneven parts 3 insulating film 3A Lower insulating film (Fig. 1) 3B Upper insulating film (in FIG. 1) 4 Polycrystalline silicon layer 5 Support substrate 6 Thin silicon layer 7 Laminated substrate 8 Bonded SOI substrate 9A Thickness unevenness due to partial polishing 9B Thickness unevenness due to selective polishing 9C Thickness unevenness due to selective polishing Thickness unevenness due to 9D selective polishing

Front page continuation (58) Fields surveyed (Int.Cl. ⁷ , DB name) H01L 21/762 H01L 21/3065 H01L 27/12

Claims (6)

(57) [Claims] 1. A plurality of recess patterns are formed on the surface of an element formation substrate by an insulating step made up of an upper insulating film and a lower insulating film, and the recesses are formed so that the element forming regions remain in island shapes in the recesses. A method for manufacturing a bonded SOI substrate for processing the element-forming substrate outside, wherein the manufacturing method removes thickness unevenness of the element-forming substrate outside the insulating step recess until just before reaching the upper insulating film. a partial polishing step, subsequent to the partial polishing step, the upper insulating film uniformity is selected polishing step through the process step consisting of the surface within the thickness of removing uneven thickness of the element forming substrate of the residual as a stopper A method for manufacturing a bonded SOI substrate, which comprises obtaining a bonded SOI substrate. 2. The method for manufacturing a bonded SOI substrate according to claim 1, wherein the partial polishing process is mainly performed by chemical polishing. 3. The method for manufacturing a bonded SOI substrate according to claim 2, wherein the partial polishing process step is performed by plasma etching. 4. The method for manufacturing a bonded SOI substrate according to claim 1, wherein the partial polishing process is mainly performed by physical polishing. 5. The method for manufacturing a bonded SOI substrate according to claim 1, wherein the partial polishing process step is performed by ion milling. 6. The method for manufacturing a bonded SOI substrate according to claim 1, wherein the selective polishing process step is performed mainly by chemical polishing.