JP2827700B2 - Polishing cloth selection method and method for managing semiconductor wafer mirror polishing process - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a mirror surface of a semiconductor wafer.
Selection method of polishing cloth (polishing cloth) used for polishing
The present invention relates to a method for managing a mirror polishing process for a conductive wafer .

[0002]

2. Description of the Related Art Conventionally, the surface of a semiconductor wafer is mirror-finished.
Polishing with a polishing cloth
Have been used. Hereinafter, this will be described. Semiconductor devices, such as ICs, LSIs, VLSIs, UVLSIs, etc., have been required year by year to be miniaturized and highly integrated. These semiconductor devices, on the surface of the semiconductor wafer,
It can be obtained by forming a predetermined structure using various methods such as deposition, diffusion, photolithography, etching, and ion implantation. In that case, the semiconductor wafer as a starting material has a problem in crystal quality such as crystal defects, oxygen concentration and other metal impurities, and the quality of the surface roughness has a great influence on the integration degree and yield of the semiconductor device. It has been known. However, conventionally, semiconductor wafers
No experience to finish wafer surface roughness to a specified value
Polishing was performed by selecting a suitable polishing cloth, determining the pressure and time required for polishing.

[0003]

Conventionally, however, the evaluation of the polishing cloth has been limited to evaluation solely based on its material and physical properties such as apparent hardness, compressibility and elastic modulus. In particular, since the relationship between the microstructure and the surface roughness of the mirror-polished semiconductor wafer obtained by polishing has not been technically grasped, a great deal of trial and error must be performed in determining the polishing conditions on site. In addition, it was impossible to know what kind of polishing cloth was necessary to efficiently perform ideal mirror polishing.

Further , as the polishing time elapses, dressing of the polishing cloth (e.g., grinding and polishing of the polishing cloth with a grindstone to eliminate irregularities due to shaving and settling caused by use, and to prevent clogging of the polishing cloth. Removal and reusable state) or replacement is required, but it has been empirically determined at what point in time dressing or replacement should be performed.

SUMMARY OF THE INVENTION The present invention aims to solve the above-mentioned problems, and has the following objects. (1) The surface of a semiconductor wafer is mirror- finished to a desired surface roughness.
Selection of suitable polishing cloth for polishing, (2) Determination of dressing time of used polishing cloth , (3) Experience and trial of determination of replacement time of used polishing cloth
Do not rely on mistakes and do it based on scientific data
It is to provide a method that can be performed.

[0006]

Means for Solving the Problems The present inventors have developed a polishing cloth.
Surface irregularities are transferred to a replica film.
By measuring the unevenness of the replica film,
The unevenness of the polishing cloth measured in
The surface roughness of the mirror-polished semiconductor wafer is extremely low.
And found that there was a strong correlation
Was. That is, the present inventors set the surface of the polishing cloth
Objective and quantitative understanding of changes in microstructure and state
To develop a polishing cloth surface evaluation method that can be evaluated
In addition, by using this evaluation method, the polishing cloth
Find the relationship between the surface roughness and the surface roughness of the polished wafer,
In addition, the above purpose is achieved by utilizing this correlation.
And, as a result, a good quality
It succeeded in obtaining a mirror-polished product .

[0007] The method for selecting a polishing cloth according to the present invention
Polish the conductor wafer surface to the desired surface roughness by mirror polishing.
When selecting a suitable polishing cloth for polishing, use a polymer
The replica film is
Contact with a solvent capable of swelling or dissolving the
The replica film swelled and softened by the polishing cloth
The surface of the polishing cloth is
Transfer the irregularities to the replica film and evaporate the solvent
After curing the replica film by
Transfer replica film transfer surface roughness (surface
Convexity) and mirror polishing using the above polishing cloth.
By measuring the surface roughness of a polished semiconductor wafer
Transfer replica film surface roughness and mirror polishing
The correlation with the surface roughness of the wafer
Polishing to obtain the desired surface roughness after mirror polishing.
The loss is selected based on the above correlation.
Is what you do.

[0008] In addition, the semiconductor wafer mirror polishing method according to the present invention
Polishing process management method is used for mirror polishing of semiconductor wafer surface.
To determine the dressing time of abrasive cloth after use
At this time, the surface roughness of the transfer replica film is
Between surface roughness and surface roughness of semiconductor wafer after mirror polishing
The polishing cloth after using it for polishing
The measured surface roughness of the transfer replica film
When it becomes coarser than the set value, the dressing of the polishing cloth
Is performed.

[0009] Further, the semiconductor wafer mirror surface according to the present invention
The method of managing the polishing process is mirror polishing of the semiconductor wafer surface.
In deciding when to replace the polishing cloth after using it for
The surface roughness of the transfer replica film and mirror
Calculate correlation with surface roughness of semiconductor wafer after surface polishing
In advance, the polishing cloth used after polishing was determined.
The measured surface roughness of the transfer replica film is
When the polishing cloth becomes rough, transfer the polishing cloth
Another polishing cloth whose film surface roughness measurement value is less than the specified value
It is characterized in that it is exchanged.

The polishing cloth is usually of suede type (Su
ede Type) and velor type (Velour T)
ype).

The suede-type polishing cloth is, as it were, artificial leather for industrial materials and has a base layer and a surface layer. The base layer is made of a three-dimensional non-woven fabric made of synthetic fibers and special synthetic rubber, and is designed to sufficiently withstand mechanical stress and compression deformation during polishing. It has a moderate stiffness to assist most effectively, and at the same time serves as a support for the entire abrasive cloth to withstand various external pressures. The surface layer is formed of a resin having excellent wear resistance, for example, a polyurethane resin. When the surface layer is formed of a polyurethane resin, the urethane resin is wet-formed (a method of applying a urethane solution and wet-solidifying to form a film), and then the surface layer is removed by high-precision grinding. This surface layer is usually composed of bulky pores that form large pores and micropores that are long in the vertical direction. In addition to the characteristics of the raw material resin used, abrasive grains (slurry) ) Retention and respiratory function,
It is designed to enable securing of material removal capability and surface defect-freeness.

[0012] Next, velor type polishing cloth is the so-called non-woven fabric having a single layer structure. This polishing cloth is composed of a synthetic fiber for the main fiber structure and an elastic polymer for filling voids and bonding fibers, and its composite structure is completely different from ordinary two-dimensional fiber products such as knitted and woven fabrics. Further, it is a porous sheet material having a three-dimensional structure. The fiber structure is composed of single or multiple synthetic fibers, and a fiber entangled body (nonwoven web) made by needle-punching this is
It forms the main structure and has a generally felt appearance. Furthermore, the nonwoven web is impregnated and solidified with a polymer such as synthetic rubber or polyurethane to form a nonwoven velor. There is a thing which was raised by the surface and became fluffy on the surface.

As is apparent from the above description, since the surface of the polishing cloth is intricately formed in a three-dimensional network, a stylus type roughness conventionally used for measuring the surface roughness of various materials and articles. Even if an attempt is made to directly measure the roughness of the polishing cloth by using a meter, the needle will be caught in the three-dimensional mesh, making the measurement impossible. Therefore, in the present invention,
Transfer the unevenness of the polishing cloth surface to the replica film,
By measuring the unevenness of the transfer replica film, the surface of the polishing cloth is indirectly evaluated.

In the method of the present invention, the surface state of the polishing cloth is not completely copied, and the shape of the polishing cloth having a small entrance and a large inside (a so-called undercut shape) is not reflected on the replica film as it is. The shape and depth of the hole entrance are not reflected, but are reflected on the replica film as irregularities. At first glance, it can be considered that the measurement method using the polishing cloth directly as the measurement target is excellent, but it is impossible to measure the surface state with the conventional stylus-type roughness meter as described above. Even if the three-dimensional structure of the polishing cloth is directly observed with a microscope, it is not easy to grasp its characteristics and statistically process its properties.

The present inventors have polished by the above-mentioned predetermined method.
Transfer the unevenness of the cloth surface to the replica film, and
As a result of measuring the unevenness of the transfer replica film,
Semiconductors after mirror polishing with this polishing cloth
There is a very strong correlation between wafer surface roughness
It is obtained by reached the present invention that.

The replica film material is preferably soft when it is pressed against the surface of the polishing cloth, and is cured after transferring the irregularities on the surface of the polishing cloth and peeling it off from the polishing cloth. Therefore, in the present invention, the solvent swells and softens.
A replica film made of a polymer material that can be
Is employed in combination with a solvent capable of swelling or dissolving. Examples of such a combination of a polymer material and a solvent include acetyl cellulose and methyl acetate, vinyl chloride and methyl ethyl ketone, vinyl chloride and butyl acetate, ethyl cellulose and cyclohexanone, and the like. Of these, the combination of acetylcellulose and methyl acetate has a track record of being used to observe biological tissues with a microscope,
It has excellent properties to transfer microscopic irregularities accurately. Note that the present invention is not limited to the above-described replica film material, and any other polymer materials and solvents other than those described above can be used as long as they are soft when pressed and can transfer the unevenness of the polishing cloth. is there.

After the transfer replica film on which the unevenness of the polishing cloth has been transferred is sufficiently cured, the unevenness of the transfer replica film is measured. The unevenness of the transfer replica film can be measured by a stylus-type roughness meter or an electron microscope. To measure with a stylus-type roughness meter, attach the transfer replica film after the unevenness transfer to the sample stage with double-sided tape, etc., and scan the stylus-type roughness meter with a predetermined area on the transfer replica film transfer surface, The irregularities are automatically recorded. In some cases, the needle may be scanned in a vertical direction, a horizontal direction, an oblique direction, or the like of the transfer replica film.

[0018] Figure 1 an example of a measurement result by the stylus-type roughness meter
Shown in FIG. 1 shows the results of examining the unevenness of a replica film obtained by transferring the unevenness from a polishing cloth that has never been used for polishing. The most concave portion of the transfer replica film corresponds to the convex portion of the polishing cloth. Then, the convex portion of the polishing cloth corresponds to a so-called "cutting edge" that effectively works for polishing an object to be polished such as a semiconductor wafer.

FIG . 2 shows that the surface of a polishing cloth is rubbed with a grindstone before use for polishing (file seasoning).
Of the replica film on which the irregularities were transferred, were examined by a stylus type roughness meter. For the polishing cloth, Ra = 3.08 μm before seasoning and Ra = 1.02 μm after seasoning, indicating that the method of the present invention properly captures the difference in unevenness of the polishing cloth. Here, the roughness Ra means that a portion of a predetermined measurement length is extracted from the profile in the direction of its center line, and the absolute value of the sag from the center line of the extracted portion to the unevenness of the profile is averaged. The values are expressed in μm.

In order to measure the unevenness of the transfer replica film with an electron microscope, for example, carbon is deposited to impart conductivity to the replica film, and an electron beam is obliquely applied to the transfer replica film on which the carbon deposition layer is formed. The measurement is performed by using an electron microscope having an automatic recording function of the state of the unevenness.

[0021]

According to the present invention, the surface roughness of the polishing cloth can be reduced (indirectly).
2) In the measurement, the unevenness of the polishing cloth surface is transferred to the replica film surface in a very similar manner, so that necessary and sufficient surface morphological information for the surface evaluation can be obtained. The portion with an undercut that protrudes into the replica film is transferred to the replica film without causing an undercut, so that the stylus of the stylus-type roughness meter can be measured smoothly without being stuck during measurement.

In the present invention, a polymer film which can swell or soften by a solvent is brought into contact with a solvent which can swell or dissolve the polymer film, and the polymer film which has been swollen and softened is used as a replica film. When the replica film is overlaid on the cloth and pressed, the unevenness on the polishing cloth surface is transferred well, and the solvent can be volatilized after the transfer to sufficiently cure the replica film.

Further , acetylcell is used as a replica film.
Lurose film, and methyl acetate as solvent
If used, a drop of solvent was deposited on the replica film.
Then, after about one second, a transferable soft state can be obtained and transferred to the replica film in a state very similar to the unevenness of the polishing cloth, and the solvent evaporates quickly after transfer, A hard transfer replica film is obtained.

The transfer replica measured by the above method
Film surface roughness and the origin of this replica film
Surface of the wafer polished using the changed polishing cloth
There is a strong correlation between roughness and, for example, as shown in FIG.
By using this correlation,
A polishing cloth suitable for finishing to the desired surface roughness,
Easy selection without relying on experience or feeling
You.

Further, in the present invention, the polishing after use for polishing is performed.
For the polishing cloth, transfer replica film at the appropriate time
Is measured, and the measured value becomes coarser than a predetermined value.
At the time when the polishing cloth is dressed.
It can be reused.

Further, in the present invention, the polishing after use for polishing is performed.
For the polishing cloth, transfer replica film at the appropriate time
Is measured, and the measured value becomes coarser than a predetermined value.
At the time when the polishing cloth is placed on the surface of the transfer replica film.
Replace with another polishing cloth whose roughness measurement is
With this, it is possible to obtain a polished wafer having a desired surface roughness.
it can.

[0027]

Next, the present invention will be described in more detail with reference to examples. Example 1 As a polishing cloth sample, a polishing cloth was used for mirror-polishing a silicon wafer used for a substrate such as an IC or LSI. This polishing cloth is of a velor type, which is a so-called “non-woven fabric” having a single-layer structure, and has a surface roughness (the maximum value of the distance between the top and the bottom of the surface unevenness).
Is approximately 35 μm.

The raw product is not subjected to seasoning of the polishing cloth and (velor type 1), the seasoning product according rasp seasoning, and transferred to the replica film the surface of each of the following steps. (1) A replica film made of cellulose acetate having a length of 10 mm × 10 mm and a thickness of 80 μm is attached to a glass plate of 13 mm × 13 mm by a double-sided adhesive tape. (2) One drop of methyl acetate as a solvent is dropped on the surface of the replica film, and after one second, the sample of the polishing cloth is uniformly contacted with the surface of the replica film. In this case, care must be taken to prevent air bubbles from entering the end of the sample. (3) A load of 1 kg is applied to the sample for 30 seconds. (4) After evaporating the solvent for several minutes, the replica film is peeled off from the polishing cloth. The thickness of the replica film is preferably larger than the surface roughness of the polishing cloth, and in this embodiment, the surface roughness is about 35 μm. Therefore, a replica having a thickness of about 50 to 100 μm is suitable.

[0029] The transfer surface roughness of the thus transcribed replica film obtained was measured using a stylus-type roughness meter radius of curvature of the tip portion has a stylus of 5 [mu] m. Hereinafter, the measurement results will be described with reference to FIGS.

FIG . 1 shows a profile of a transfer replica film transfer surface of the above-mentioned unprocessed polishing cloth. From this figure, the roughness Ra of the replica film transfer surface was determined to be 3.08 μm.

FIG . 2 shows the profile of the replica film transfer surface of the above polished cross-seasoned product.
In this case, the procedure for measuring the replica film surface roughness was the same as that for the untreated product. This seasoned product is obtained by seasoning the untreated polishing cloth with reference to the profile obtained by measuring the surface roughness of the untreated polishing cloth. From FIG. 2, the roughness Ra of the transfer surface was determined to be 1.02 μm.

From the comparison between FIG. 1 and FIG. 2, it can be seen that the height of the convex portion acting as a cutting edge in the polishing cloth is reduced by seasoning.

Next, the surface roughness Ra of the replica films transferring the polishing cloth untreated and seasoning products
The relationship between the above and the surface roughness Ra (nm) of the silicon wafer mirror-polished with each of the above polishing cloths was examined. The results are shown in FIG.

[0034] Example 2 Example 1 is different from velor type polishing is not subjected to cross seasoning untreated and (velor type 2),
Regarding the seasoned product by the file seasoning, the irregularities were transferred to the replica film in the same manner as in Example 1, and the surface roughness Ra (μm) of the replica film surface and the surface roughness Ra of the wafer mirror-polished with the respective polishing cloths were used. (Nm) was examined. The results are shown in FIG.

The per polishing cloth suede type of embodiments 3 without seasoning, transferring the uneven replica film in the same manner as in Example 1, the replica film surface roughness Ra ([mu] m)
And the surface roughness Ra (nm) of the silicon wafer mirror-polished with this polishing cloth were examined. The results are shown in FIG.

From FIG . 3, it can be seen that Ra (nm) becomes larger or smaller corresponding to the size of Ra (μm).
Considering the conventional knowledge that the wafer surface roughness after polishing is closely related to the polishing cloth surface roughness, FIG. 3 shows that the replica film surface accurately reflects the surface roughness of the polishing cloth. Therefore, FIG. 3 demonstrates that the method of transferring the surface of the polishing cloth to a replica film and evaluating the surface roughness is effective.

[0037]

As is apparent from the above description, according to the present invention, the transfer surface of the replica film accurately reflects the unevenness of the polishing cloth surface and the roughness of the transfer surface is reduced. For example, when measuring with a stylus-type roughness meter,
Measures smoothly and accurately without getting stuck on this transfer surface
can do. Therefore, according to the present invention,
Of polishing cloth with a stylus-type roughness meter
Surface roughness measurement can be performed indirectly and efficiently
Becomes Moreover, the surface of the polishing cloth evaluated by this method
Roughness and semiconductor wafer mirror-polished using this polishing cloth
There is a very strong correlation between the wafer surface roughness and
Therefore, by utilizing this correlation,
Mirror polishing of the surface of the body wafer to the desired surface roughness
Selection of suitable polishing cloth, dressing of polishing cloth after use
Of polishing time or replacement of abrasive cloth after use
Make decisions easily without resorting to experience or trial and error.
It is possible to achieve a great effect practically
You.

[Brief description of the drawings]

FIG. 1 is a graph showing a profile obtained by evaluating the surface roughness of a velor-type polishing cloth without seasoning according to the present invention.

FIG. 2 is a graph showing a profile obtained by evaluating the surface roughness of the velor-type polishing cloth of FIG. 1 subjected to file seasoning according to the present invention.

FIG. 3 shows the surface roughness of a transfer replica film and its transfer.
5 is a graph showing a relationship between a silicon wafer polished by a polishing cloth corresponding to a replica film and a wafer surface roughness.

──────────────────────────────────────────────────続 き Continuing from the front page (72) Hideo Kudo, Inventor 150 Odakura, Odakura, Nishigo-mura, Nishishirakawa-gun, Fukushima Prefecture Inside the Semiconductor Shirakawa Research Laboratory, Shin-Etsu Semiconductor Co., Ltd. Koshishinda 596-2 Naoetsu Electronics Co., Ltd. (56) References JP-A-2-170010 (JP, A) JP-A-61-137005 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01B 21/30

Claims (5)

(57) [Claims] 1. The method according to claim 1, wherein the surface of the semiconductor wafer is mirror-polished.
Select a polishing cloth suitable for polishing to the desired surface roughness
When replicating a polymer film,
With a solvent that can swell or dissolve the replica film
And the replica fill swelled and softened by the contact operation.
Over the surface of the polishing cloth and press
Transfer the unevenness of the polishing cloth surface to the above replica film
And evaporating the solvent to form a replica film.
After curing the transfer replica film,
Measure the surface roughness and use the above polishing cloth
Measuring the surface roughness of mirror-polished semiconductor wafers
Due to the surface roughness of transfer replica film and after mirror polishing
Determine the correlation with the surface roughness of the semiconductor wafer,
Suitable polishing to obtain the target surface roughness after mirror polishing
It is special to select polishing cloth based on the above correlation.
How to select polishing cloth 2. The method according to claim 1, which is used for mirror polishing of a semiconductor wafer surface.
In determining the dressing time of the polishing cloth later,
Table of the transfer replica film according to the procedure of claim 1.
Correlation between surface roughness and surface roughness of semiconductor wafer after mirror polishing
The relationship between the polishing cloth and the polishing cloth used for polishing.
Surface Roughness Measured Value of the Transfer Replica Film
When the roughness becomes coarser than a predetermined value, the drainage of the polishing cloth
Semiconductor wafer mirror polishing characterized by performing
How to manage the polishing process. 3. The method according to claim 1, which is used for mirror polishing of a semiconductor wafer surface.
Claim 1 when deciding when to replace the polishing cloth later
The surface roughness of the transfer replica film
Determine the correlation with the surface roughness of the semiconductor wafer after mirror polishing
First, determine the polishing cloth used after polishing.
The measured surface roughness of the transfer replica film
When the polishing cloth becomes coarser, transfer the polishing cloth to a transfer replica.
If the measured surface roughness of the film is
Mirror polishing of semiconductor wafers, characterized by replacement with
Process management method. 4. The method according to claim 1, wherein the replica film is acetyl cellulose.
That the solvent is methyl acetate
The method for selecting a polishing cloth according to claim 1, wherein: 5. The semiconductor wafer mirror according to claim 2, wherein said replica film is an acetylcellulose film, and said solvent is methyl acetate.
Management method of surface polishing process.