JP2000141208A - Polishing method for wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To polish wafers such as silicon wafers while the generation of foreign matter caused by abnormal friction between a polishing member and a wafer, and the generation of a scratch considered to be mainly caused by the foreign matter, are suppressed as much as possible. SOLUTION: When a wafer is polished, the rotation of a polishing surface plate and a polishing carrier and the loading of polishing load are gradually raised up to a specified speed of rotation and a specified polishing load while frictional resistance between the polishing cloth, a wafer, and the polishing carrier is maintained lower by performing ramp-up of the loading of polishing load and ramp-up of the rotation of the polishing surface plate and the polishing carrier independently, or the polishing surface plate and the polishing carrier are allowed to be familiar with a lubricant before the above mentioned ramp-up, or the ramp-up is performed while the lubricant is supplied to the polishing surface plate and the polishing carrier, or the polishing operation after completion of the above ramp-up is performed while the lubricant is supplied to the polishing surface plate and the polishing carrier, or these above processes are suitably combined with each other.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for polishing a wafer, and particularly to the generation of foreign matter due to abnormal friction between a polishing member and a wafer during polishing, and to the main reason for this foreign matter. The present invention relates to a method of polishing a wafer while minimizing generation of scratches.

[0002]

2. Description of the Related Art As the production of devices using various types of wafers such as silicon wafers has become more and more dense, requirements for the surface flatness and the number of particles remaining on the surface of these wafers have become increasingly severe. Therefore, 200m
In the case of a large wafer exceeding m, for example, a 300 mm silicon wafer, a double-side polishing method for simultaneously polishing both surfaces of the wafer has become common.

[0003] The double-side polishing method uses a polishing cloth (artificial leather).
Wafers were loaded into the respective holes of the polishing carrier arranged on the lower polishing plate attached with the polishing pad, and a polishing cloth (artificial leather) was adhered from above while rotating the lower polishing plate. This is a method of polishing while holding down the polishing upper platen under a predetermined load and supplying colloidal silica as a polishing aid slurried with an alkaline solution. By the above operation, the wafer can be polished without leaving processing strain and particles on the surface of the wafer by a combined action of mechanical polishing with silica abrasive grains and chemical etching with an alkaline solution. Thus, a mirror-finished wafer having optical gloss and no processing distortion can be manufactured.

However, in this double-side polishing method, since the polishing carrier as well as the wafer comes into contact with the polishing cloth, the frictional resistance against rotation of the rotary platen is larger than that of the single-side polishing method. Tend to be. In particular, during a so-called ramp-up until a predetermined number of revolutions is reached, that is, during a period until the start-up is completed, an abnormal sound called a chatter is generated due to a polishing load or a vibration of the carrier. Sometimes. Due to the polishing load and the vibration of the carrier, particles removed from the material constituting the polishing cloth due to direct dust generation from the carrier and the pin sleeve or abnormal friction generated between the carrier, the pin sleeve and the wafer. There is a problem that scratches are often formed on the wafer surface during the polishing operation due to foreign matter generated as nuclei.

By the way, in double-side polishing, the load of the polishing load and the ramp-up of the rotation of the polishing platen and the polishing carrier are simultaneously performed, and special attention should be paid to the vibration of the polishing carrier caused by this. At present it is not paid. Before the ramp-up of the load of the polishing load and the start of the ramp-up of the rotation of the polishing platen and the polishing carrier, the wafer placed in the carrier hole keeps the polishing cloth wet. In order to rotate this wafer from this state, it is necessary to apply a considerable force because it is held by the surface tension of the pure water applied to the polishing cloth. The frictional resistance between them must inevitably increase.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a double-side polishing method in which abnormalities between a polishing member and a wafer are caused. It provides a method for polishing various wafers such as silicon wafers, gallium arsenide wafers, and glass wafers while minimizing the generation of foreign matter due to friction and the like, and the generation of scratches that are thought to be mainly due to this foreign matter. is there.

[0007]

Means for Solving the Problems That is, as a result of various studies to solve the above-mentioned problems, the present inventor has found that the first
During the polishing of the wafer, the load of the polishing load is ramped up, and the ramping of the rotation of the polishing platen and the polishing carrier is performed independently, so that the polishing load is applied between the polishing cloth and the wafer and the polishing carrier. Gradually or linearly gradually increasing to a predetermined rotation speed and a predetermined polishing load while keeping the frictional resistance as low as possible; secondly, a polishing platen and a polishing carrier prior to the ramp-up. Third, the frictional resistance is further reduced by sufficiently accommodating with a lubricant, and thirdly, the above-mentioned ramp-up is performed while supplying a lubricant to the polishing platen and the polishing carrier. Fourth, the frictional resistance is further reduced, and fourthly, the polishing platen and the polishing carrier are lubricated even during the polishing operation after the end of the ramp-up. Is obtained and completed the present invention found that it is possible to solve the above problems by performing while supplying.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION In order to minimize the frictional resistance between a polishing cloth and a wafer and a polishing carrier during double-side polishing, the present invention uses various methods for double-side polishing methods to increase the frictional resistance. Firstly, when the ramp-up of the polishing load at the start of polishing and the ramp-up of the rotation of the polishing platen and the polishing carrier are performed at the same time, remarkable frictional resistance is obtained. Therefore, a method for double-sided polishing of a wafer is provided, which disperses as much as possible the start-up operation causing the rapid increase in frictional resistance to achieve a gentle increase in frictional resistance. .

Second, before the start of the polishing operation, the wafer placed in the carrier hole is held by the surface tension of pure water added to hold the polishing cloth in a wet state. Therefore, it is necessary to apply a considerable force to rotate the wafer from this state, and therefore, the frictional resistance between the polishing cloth and the wafer and the polishing carrier is necessarily increased. First, in order to keep the surface as low as possible, first, a polishing member such as a polishing platen and a polishing carrier at the time of start-up and a wafer to be polished are sufficiently fitted with a lubricant so that a gap between them can be obtained. The third is to minimize the frictional resistance at startup, especially the sharp increase in frictional resistance at the time of startup, and thirdly, to increase the frictional resistance until the start of full-scale polishing work as much as possible. Fourth, in order to supply a lubricant to the polishing platen and the polishing carrier during the operation, and fourthly, to keep the frictional resistance as low as possible during a full-scale polishing operation, the polishing platen and the polishing carrier are provided. A double-side polishing method for a wafer, wherein the method is performed while supplying a lubricant to the wafer.

First, a polishing cloth, a wafer, and a polishing carrier are formed by independently performing ramp-up of a polishing load during polishing of a wafer and ramp-up of rotation of a polishing platen and a polishing carrier. Step by step while keeping the frictional resistance between
Alternatively, a method of linearly and gradually increasing the rotation speed to a predetermined rotation speed and a predetermined polishing load will be described in detail. As shown in FIG. 1, the load is gradually or linearly applied gradually to the initial load F0 which is the allowable minimum load of the polishing machine to be used, and when the load reaches F0, the polishing platen is used. While gradually increasing the number of revolutions gradually or linearly, the revolution number is increased to the target number of revolutions N, and when this level is reached and the revolution is stabilized, the polishing load is further increased stepwise or linearly. Gradually increase to a predetermined level.

Next, a description will be given of a method for further lowering the frictional resistance by sufficiently adjusting the polishing platen and the polishing carrier with a lubricant prior to the ramp-up. A carrier for polishing is arranged on a lower polishing table to which a polishing cloth is attached, and in this state, a lubricant is uniformly applied on the polishing table. Next, only the lower platen is rotated to sufficiently penetrate the lubricant between the polishing carrier and the polishing cloth. Subsequently, a wafer is loaded into each hole of the polishing carrier, and after loading, a lubricant is uniformly applied on the loaded wafer. Of course, the wafer may be polished in combination with the above method. In this case, the ramp-up of the load of the polishing load and the ramp-up of the rotation of the polishing platen and the polishing carrier may be performed independently after the lubricant has been adjusted.

Next, a method of performing the ramp-up while supplying a lubricant to the polishing platen and the polishing carrier will be described. As soon as the upper surface plate for polishing comes into contact with the lower surface plate, the supply of the lubricant is started. The supply may be performed while pouring between the upper and lower polishing plates. Thus, an increase in frictional resistance at the time of ramp-up can be suppressed low. Of course, even during the polishing operation after the end of the ramp-up, by performing while supplying the lubricant between the upper and lower polishing plates and the polishing carrier, the occurrence of scratches on the surface of the wafer is further prevented. It is preferable because it can be used.

In the present invention, the lubricant refers to a solution containing a polishing slurry and a surfactant. Here, the polishing slurry refers to a slurry of alkaline colloidal silica usually used for polishing a wafer, and a surfactant containing polyethylene oxide as an active ingredient, for example, Polyox (manufactured by Union Carbide, USA) (Registered trademark) and the like can be suitably used. When this surfactant is used, it may be used by diluting it to such an extent that a sufficient reduction in frictional resistance can be exhibited. The amount of the lubricant to be flowed during the polishing is preferably about 2 to 5 times the flow rate of the polishing slurry. If the flow rate is excessively large, a problem occurs in the treatment of wastewater, which is not preferable.

Next, the present invention will be further described with reference to examples. However, it goes without saying that the present invention is not limited at all by the following examples.

[0015]

[Embodiment] The evaluation after double-side polishing is performed by observing the polished wafer with the naked eye in a dark room under condensing light, counting the number of scratches formed on the surface per mirror surface, and determining the number of scratches. Was. (Example 1) Double-side polishing was performed using a silicon wafer having a diameter of 300 mm under the following conditions. As shown in FIG. 1, a load was gradually applied to the initial load F0 of 100 kg, and when the load reached this F0 value, the rotation speed of the polishing platen was gradually increased while the rotation speed was 26 rpm. When the rotation was stabilized and the polishing load was stabilized, the polishing load was increased to a predetermined level while increasing the load divided into three times. When the state of the normal polishing operation was reached, polishing was performed under normal polishing conditions. After polishing, the occurrence of scratches was checked.
The average was 3.5 lines per mirror surface, and satisfactory results were obtained.

Example 2 A surfactant (trade name: Polyox (registered trademark); manufacturer: Union Carbide Co., USA) having a concentration of 0.036% was added between the polishing carrier and the polishing pad during ramp-up. A lubricant prepared in addition to the polishing slurry was supplied at a rate of 6.44 liters per minute so that the lubricant was sufficiently penetrated, and the wafer was inserted into each hole of the polishing carrier. Then, polishing was performed under the same conditions as in Example 1 except that the above-mentioned lubricant was sufficiently applied on the wafer. After the polishing was completed, the occurrence of scratches was examined. The average number of scratches per mirror surface was 0.1, and extremely satisfactory results were obtained.

Comparative Example Double-side polishing was performed using a silicon wafer having a diameter of 300 mm under the following conditions. As shown in FIG. 2, the polishing load and the rotation of the polishing platen were ramped up according to the conventional method, and then the polishing was performed while supplying only the polishing slurry at a rate of 1.26 liters per minute. . After the polishing was completed, the occurrence of scratches was examined. The average number of scratches per mirror surface was 21.7, which was extremely unsatisfactory.

[0018]

As is clear from the above description, according to the polishing method of the present invention, there is an effect that the number of scratches formed on the wafer surface due to foreign matters or the like generated during polishing can be significantly reduced.

[Brief description of the drawings]

FIG. 1 is a diagram schematically showing a polishing load and a ramp-up state of a polishing platen according to a method of the present invention.

FIG. 2 is a diagram schematically showing a polishing load and a ramp-up state of a polishing platen according to a conventional method.

[Explanation of symbols]

F: Polishing load, N: Number of revolutions of the lower polishing table, F0: Initial polishing load.

Claims (4)

[Claims] 1. A method of polishing a wafer, wherein a ramp-up of a polishing load and a ramp-up of rotation of a polishing platen and a polishing carrier are independently performed during polishing of the wafer. 2. The method according to claim 1, wherein prior to the ramp-up, the polishing platen and the polishing carrier are sufficiently adjusted with a lubricant. 3. The method according to claim 1, wherein the ramp-up is performed while supplying a lubricant to the polishing platen and the polishing carrier. 4. The polishing method according to claim 1, wherein the polishing is performed after supplying the lubricant to the polishing platen and the polishing carrier during the polishing after the completion of the ramp-up. the method of.