JP4615249B2 - Polishing cloth for finish polishing - Google Patents

Description

  The present invention relates to a polishing cloth suitable for finish polishing of semiconductor wafers such as silicon, gallium arsenide, and indium phosphide.

  In a manufacturing process of a general semiconductor wafer, for example, a silicon wafer (hereinafter simply referred to as a wafer), first, a silicon single crystal ingot is sliced to a certain thickness with a wire saw or an inner peripheral blade. A thin disk-shaped wafer is obtained. Since this wafer surface has irregularities caused by slicing and the thickness of individual wafers is not uniform, lapping is performed to flatten the irregularities on the surface and the depth of processing distortion. To make the wafer thickness uniform.

  A processed strain layer is formed on the wafer after lapping due to processing, and particles such as fine metal, polishing powder, and silicon scraps are attached to the processed strain layer. In order to remove these, strong acid and fluoride are removed. Etching is performed by a chemical corrosion method using an acid or the like.

  The wafer after etching is subjected to alkali neutralization of the acid adhering to the surface, washed with water and dried, and then mirror polished on one side. In general, the mirror polishing includes three steps of primary polishing, secondary polishing, and finish polishing. Finally, the finish polishing improves fine surface roughness, and has a haze (Haze, PV value of 10 nm or less). After removing the irregularities on the fine wafer, the process proceeds to a cleaning process (see Patent Document 1).

  In the polishing apparatus, the upper surface plate holding the wafer is placed on the lower surface plate to which the polishing cloth is applied, and the wafer and the polishing cloth are relatively moved while supplying the slurry while the wafer and the polishing cloth are pressurized. Polishing is carried out by sliding the target. The slurry is prepared by dispersing colloidal silica in pure water together with a water-soluble polymer and adjusting the pH to about pH 11 with a pH adjusting agent.

  The polishing cloth used in the above polishing includes a nonwoven fabric type and a suede type, and a suede type polishing cloth is used for the final polishing.

  As shown in FIG. 4A, a conventional suede type polishing cloth is obtained by impregnating a non-woven fabric of synthetic resin fibers such as polyester with a urethane resin as a base material layer 1, and then the base material layer 1 Separately, a DMF solution of urethane resin is coated on the surface. Examples of the urethane resin forming the coating layer 2 include polyether, polyester, polycarbonate, and the like as the long-chain polyol, and polyol and amines are used as the chain extender. In addition, urethane resins include tolylene diisocyanate and methylene diisocyanate as isocyanates (isocyanate esters).

  The DMF solution of urethane resin is a mixture of dimethyl form amide (DMF) as a solvent for the purpose of reducing the viscosity of the urethane resin. The DMF solution may be mixed with carbon paste, epoxy resin, polyvinyl chloride resin, or the like for the purpose of increasing the strength of the urethane after solidification.

  As described above, the base material layer 1 having the urethane resin coating layer 2 is submerged in the coagulation liquid. Then, the coagulating liquid and the solvent contained in the urethane resin solution are replaced, and the urethane resin coating layer 2 is solidified on the base material layer 1 (wet coagulation). As shown in FIG. 4B, many teardrop-shaped pores 3 are formed in the solidified coating layer 2.

  After that, the remaining solvent is removed by washing with warm water or the like, and dried. Since the skin layer 2a is formed on the surface of the urethane resin coating layer 2 so as to cover the pore 3, the skin layer 2a is removed. By grinding and removing by buffing, a layer (nap layer) 4 in which the pores 3 are opened on the surface side as shown in FIG. 4C is formed.

  In the above polishing cloth, the polishing agent held in the pore 3 opened in the nap layer 4 acts between the wafer as the object to be polished and the inner surface of the pore 3, so that polishing progresses and damage is caused. No polished surface is obtained.

By the way, immediately after the polishing cloth is attached to the polishing apparatus, the performance as a polishing cloth is not exhibited at all. When the surface state of the wafer at that time is observed, the measured values of micro defects and haze are measured by the measuring apparatus. It is so bad that it exceeds the measurement upper limit. However, after a fixed-time dummy run (temporary polishing, preliminary polishing), the micro-defects and hazes show low values. It will be able to be used for actual wafer production.
JP-A-10-270392

  The problem with the current polishing cloth for final polishing is that it requires a polishing cloth startup process called a dummy run.

  The time required for the start-up treatment of the polishing cloth for finish polishing is usually about 30 minutes, but in some cases it may take 4 hours or more. Even with the same type of polishing cloth, the start-up processing time varies between lots and between lots. Considering the existence of various polishing cloths when these polishing cloths are used stably for wafer production Then, the start-up process for about 4 hours is performed on all the polishing cloths.

  However, since the life of the polishing cloth for finish polishing is about 24 to 48 hours, a startup process time of about 5-15% is required for the life of the polishing cloth. This is wasteful, and during that time, the final polishing of the wafer as a product cannot be performed, so that productivity is poor.

  As a result of examination by the inventors of the present case, it is estimated that the non-uniformity of the polishing cloth start-up processing time is due to a partial thickness variation of each polishing cloth. Such polishing cloths usually have a thickness variation of about 20 to 30 μm, and this thickness variation creates a pressure non-uniformity between the wafer surface and the polishing cloth surface in finish polishing. . With non-uniform pressure distribution, it is not possible to reduce micro defects and haze required in the finish polishing process. In order for the polishing cloth to exhibit the desired performance, it is necessary that the polishing cloth surface and the wafer surface are in contact with each other in a uniform pressure distribution state.

  For this, it is only necessary to eliminate the variation in the thickness of the polishing cloth, but it is impossible in reality to manufacture a polishing cloth having no variation in thickness. Therefore, conventionally, the non-uniform pressure distribution is attempted to be resolved by the start-up process, that is, the dummy run. The pressure distribution is not uniform.

  Therefore, an object of the present invention is to shorten the time required for the polishing cloth start-up process as much as possible to increase the productivity of the wafer.

  The inventor paid attention to the fact that, even if the polishing cloth has a partial thickness variation, the dummy run makes the entire thickness uniform and exhibits the desired performance. As a result, the following configuration has been conceived.

That is, the polishing cloth for finish polishing according to the present invention is a nap having a teardrop-shaped pore opened on the surface side by separately coating a urethane resin on a base material layer obtained by impregnating a nonwoven fabric of synthetic resin fibers with a urethane resin. In the polishing cloth for finishing polishing in which a layer is formed,
The polishing cloth, when compressed for 30 seconds by applying a surface pressure of 300 g / cm ^2, to release the subsequent compression for 30 seconds, and the repeated compression added under conditions repeating the decompression and the compression 20 min, the polishing the thickness variation from the initial thickness of the entire fabric 15μm or more, characterized in that it is made with 50μm or less.

According to the above structure, and non-woven materials, regardless of the thickness of the substrate layer, when the thickness variation of the entire polishing cloth when subjected to repeated compression of the polishing cloth is 15μm or more, Standing The time required for the lifting process can be as short as 20 minutes, which is shorter than the startup process time with a conventional polishing cloth.
This is presumably because the polishing cloth having a large amount of change in thickness due to repeated compression is flattened early during the start-up process, and the variation in the thickness of each part is reduced. When the thickness change amount exceeds 50 μm, the amount of sinking of the wafer with respect to the polishing cloth increases, and the amount of polishing at the peripheral portion of the wafer increases.

  In the polishing cloth having the above configuration, the amount of change in the thickness of the entire polishing cloth is considered to be mainly due to the thickness of the base material layer, and the thickness of the base material layer is more than 1.2 mm and not more than 2.0 mm. It is desirable.

  When the thickness of the base material layer is more than 1.2 mm and 2.0 mm or less, the thickness change amount due to repeated compression of the entire polishing cloth is within the range of 15 μm or more and 50 μm or less, and the start-up treatment is performed for 20 minutes. Can be done within.

  In the conventional polishing cloth for final polishing, a polyester nonwoven fabric is used for the base material layer. In the present invention, the nonwoven fabric of the base material layer is preferably made of nylon.

  When nylon fiber is used for the nonwoven fabric of the base material layer, the characteristics of absorbing the pressure of the polishing cloth are strengthened, and the amount of change in thickness when the polishing cloth is repeatedly compressed increases, and accordingly, the startup process is required. Time is shortened.

  In addition, since nylon is more hydrophilic than polyester, if the slurry used in the final polishing process penetrates during polishing, the base material layer becomes flexible and the amount of change in thickness due to repeated compression increases. Therefore, it is preferable.

  Nylon fibers used for the nonwoven fabric are preferably those having a fineness of 5 denier or less. When the fiber thickness exceeds 5 denier, the strength of the fiber increases, and when it is repeatedly compressed, the resilience as an abrasive cloth becomes strong.

  According to the present invention, the start-up processing time can be further shortened to 20 minutes or less, compared with the prior art.

  In the present embodiment, a suede-type polishing cloth for final polishing as shown in FIG. 4, specifically, a base material layer 1 formed by impregnating a non-woven fabric of synthetic resin fibers such as polyester with a urethane resin is separately provided. Prepare a number of polishing cloths for finishing polishing, which are coated with urethane resin and have a nap layer 4 having teardrop-shaped pores 3 opened on the surface side. The amount of change was measured. After that, the final polishing of the wafer was actually performed with each polishing cloth, the surface state of the wafer was measured, and the relationship between the amount of change in thickness due to repeated compression and the time required for the start-up process was investigated.

  As a result, when the amount of change in thickness from the initial thickness when repeated compression is applied is 15 μm or more and 50 μm or less, the time required for the start-up process is shorter than the start-up process time of the conventional polishing cloth. It has been found that a short time of 20 minutes is required, and that the wafer can be polished without trouble without causing problems such as sagging of the outer periphery.

  For those having different thicknesses of the base material layer 1, when the thickness of the base material layer 1 is more than 1.2 mm and 2.0 mm or less, the amount of change in thickness due to repeated compression of the entire polishing cloth is 15 μm or more, It has been found that the thickness is 50 μm or less, the start-up process can be completed within 20 minutes, and the wafer can be polished without hindrance.

  When the nonwoven fabric contained in the base material layer 1 is made of nylon, it has been found that the amount of change in thickness due to repeated compression is larger than that of the nonwoven fabric made of polyester, and the time for the start-up process is shorter. It has been found that when the nylon fiber thickness of the nonwoven fabric is 5 denier or less, the thickness change amount by repeated compression of the entire polishing cloth is 15 μm or more and 50 μm or less, and the start-up treatment can be completed within 20 minutes.

Example 1
Finished by forming a nap layer 4 having a teardrop-shaped pore 3 opened on the surface side by separately coating urethane resin on a 1.1 mm thick base material layer 1 obtained by impregnating a polyester nonwoven fabric with urethane resin A polishing cloth for polishing was made. The thickness of the nap layer 4 is 550 μm, and therefore the total thickness is 1.65 mm.

  A large number of the above-mentioned abrasive cloths were prepared, and the compression cloth was repeatedly compressed under predetermined conditions by a repeated compression measuring machine, and then the amount of change in thickness due to repeated compression was measured.

(Conditions for repeated compression)
・ Temperature: normal temperature (25 ℃)
・ Surface pressure: 300 g / cm ²
・ Compression time: 30 seconds ・ Uncompression time: 30 seconds ・ Repetition time: 20 minutes In short, after 30 seconds of compression and 30 seconds of compression are repeated for 20 minutes, the thickness displacement of the polishing cloth is measured. did. Before the measurement, a preload was performed for several minutes at a surface pressure of 300 g / cm ² .

  As a result of the measurement, there was considerable variation in the amount of change in thickness due to repeated compression even with the polishing cloth having the same structure. Of the 14 samples, 1 sample has a thickness variation of less than 10 μm, 9 samples have a thickness of 10 μm or more but less than 20 μm, 1 sample has a thickness variation of 20 μm or more but less than 30 μm, and 1 sample has a thickness variation of 30 μm or more but less than 40 μm. 40 μm or more and 50 μm or less were two points.

  Next, a number of secondary polished wafers are prepared, and the final polishing is actually performed on each of the above polishing cloths, which are the above samples, and the wafer is inspected by the wafer inspection apparatus every 5 minutes. The time until the start-up process was completed, specifically, the time until the haze value fell below 0.04 ppm on the wafer surface was measured.

(Finishing polishing conditions)
・ PH: Uncontrolled ・ Slurry: NP8020 manufactured by Rodel Nitta Co., Ltd.
・ Polisher: Polisher RN20 "manufactured by Rodel Nitta Co., Ltd.
・ Platen speed: 115rpm
・ Slurry flow rate: 300 ml / min ・ Pressure force: 100 gf / cm ²
(Wafer inspection)
-Wafer inspection device: LS6600, manufactured by Hitachi Electronics Engineering Co., Ltd.

  The measurement result is shown in the graph of FIG. 1 in relation to the amount of change in thickness due to repeated compression of each polishing cloth. In FIG. 1, the horizontal axis represents the thickness change amount (μm), the vertical axis represents the startup processing time (minutes), and the measurement points are indicated by black squares.

  From the measurement results shown in FIG. 1, the larger the thickness change amount of the polishing cloth, the shorter the time required for the start-up process. When the thickness change amount is 15 μm or more, the start-up process time It can be seen that it is shorter than 20 minutes, which is shorter than the start-up processing time with the cloth.

  If the thickness change amount exceeds 50 μm, the amount of polishing at the peripheral portion of the wafer increases, so-called peripheral sagging occurs, which is not preferable.

  As a result, a urethane resin nap layer 4 (thickness 550 μm) is formed on a base material layer 1 (thickness 1.1 mm) obtained by impregnating a specific suede type polishing cloth, that is, a polyester nonwoven fabric with urethane resin. As for the finished polishing cloth for finishing polishing, an experiment on a suede type polishing cloth having a base material layer 1 having a different thickness (Example 2 to be described later) and a suede containing a nonwoven fabric of other synthetic resin fibers In consideration of the result of the experiment on the type of polishing cloth (Example 3), when the thickness change amount due to repeated compression is 15 μm or more and 50 μm in general for the suede type polishing cloth, the start-up process is short. It can be completed in time, and it can be said that there is no problem such as a peripheral sag.

(Example 2)
About the base material layer 1 which impregnated the polyester resin nonwoven fabric with the urethane resin, the thickness is varied in the range of 1.1 mm to 2.1 mm to produce a suede type finish polishing cloth, and the thickness of these polishing cloths by repeated compression The amount of change and the start-up processing time were measured. The base material layer 1 is separately coated with a urethane resin to form a nap layer 4. The thickness of the nap layer 4 is constant (550 μm). The conditions for repeated compression, the measurement conditions for the amount of change in thickness, and the method for measuring the start-up processing time are the same as in the first embodiment.

  The measurement results are shown in the graph of FIG. In the graph, the relationship between the thickness of the base material layer 1 and the amount of change in thickness due to repeated compression is indicated by white square measurement points. Moreover, the relationship between the thickness of the base material layer 1 and the start-up processing time is indicated by black square measurement points.

  In the results shown in the graph, each time the thickness of the base material layer 1 is increased from 1.1 mm to 2.1 mm, the amount of change in thickness due to repeated compression of the entire polishing cloth increases, and the thickness of the base material layer 1 is reduced. When the thickness is more than 1.2 mm and not more than 2.0 mm, the thickness change amount by repeated compression is 15 μm or more and 50 μm or less, and the time required for the start-up process is almost 20 minutes or less.

  In consideration of the material cost in addition to the length of the start-up processing time, the thickness of the base material layer 1 is more preferably in the range of 1.3 mm to 1.5 mm. In addition, when the thickness of the base material layer 1 is less than 1.1 mm, the strength of the base material layer 1 becomes extremely low, and it becomes difficult to coat the urethane resin on the top.

(Example 3)
A non-woven fabric made of polyester and a non-woven fabric made of nylon having a fiber thickness of 1 to 6 denier were used as the non-woven fabric contained in the base material layer 1, and a suede-type finished polishing cloth was prototyped. The thickness of the base material layer 1 was 1.1 mm in all cases. The base material layer 1 is separately coated with a urethane resin to form a nap layer 4. The thickness of the nap layer 4 is constant (550 μm).

  For these polishing cloths, the amount of change in thickness due to repeated compression and the start-up treatment time were measured. The conditions for repeated compression, the measurement conditions for the amount of change in thickness, and the method for measuring the start-up processing time are the same as in the first embodiment.

  The measurement results are shown in the graph of FIG. In the graph, the relationship between the thickness of the base material layer 1 and the amount of change in thickness due to repeated compression is indicated by white square measurement points. Moreover, the relationship between the thickness of the base material layer 1 and the start-up processing time is indicated by black square measurement points.

  In the results shown in the graph, as the nonwoven fabric fiber of the base material layer 1, when nylon is used, the thickness change amount by repeated compression is larger than when polyester is used, and accordingly, the start-up processing time is greatly reduced. ing. This is presumably because nylon has higher hydrophilicity than polyester, and the base material layer 1 becomes flexible due to the penetration of the slurry.

  It can be seen that the same nylon non-woven fabric with a fiber finer than 5 denier has a start-up treatment time of 20 minutes or less. When the fiber thickness exceeds 5 deniers, it is considered that the strength of the fibers is increased, the resilience to compression is strong as an abrasive cloth, and the variation in thickness of each part is not eliminated.

The graph which shows the relationship between the amount of thickness changes by repeated compression, and the starting process time of the polishing cloth for final polishing which concerns on the best form of this invention. The graph which shows the relationship between the thickness variation | change_quantity by repeated compression with respect to the thickness of a base material layer, and the starting process time of the polishing cloth for finish polishing of this invention. The graph which shows the relationship between the thickness variation | change_quantity by the repeated compression with respect to the fiber material of a nonwoven fabric, and start-up processing time of the polishing cloth for finish polishing of this invention. Sectional drawing which shows the manufacturing process of the polishing cloth for suede type finish polishing.

Explanation of symbols

1 base material layer 2 coating layer 3 pore 4 nap layer

Claims (4)

In the polishing cloth for finishing polishing in which a base layer formed by impregnating a synthetic resin fiber nonwoven fabric with urethane resin is coated with urethane resin separately to form a nap layer having teardrop-shaped pores opened on the surface side,
The polishing cloth, when compressed for 30 seconds by applying a surface pressure of 300 g / cm ^2, to release the subsequent compression for 30 seconds, and the repeated compression added under conditions repeating the decompression and the compression 20 min, the polishing the thickness variation from the initial thickness of the entire fabric 15μm or more, the final polishing abrasive cloth, characterized in that it is made with 50μm or less.   The polishing cloth for finishing polishing according to claim 1, wherein the thickness of the base material layer of the finishing polishing cloth is more than 1.2 mm and not more than 2.0 mm.   The polishing cloth for finish polishing according to claim 1 or 2, wherein the nonwoven fabric of the base material layer is made of nylon.   The polishing cloth for finish polishing according to claim 3, wherein the nylon nonwoven fabric has a fiber thickness of 5 denier or less.

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