JP3578975B2 - High-speed mirror polishing method for silicon wafer - Google Patents

Description

【００３２】
【発明の効果】
以上説明したように、本発明によるシリコンウエハの高速鏡面研磨方法によれば、シリコンウエハを表面粗さＲａが１５０ｎｍ以下になるまで表面加工し、この加工表面を砥粒が炭酸カルシウム粒子及び／又は炭酸マグネシウム粒子である研磨材を用いて湿式研磨条件の下で鏡面研磨したことにより、鏡面研磨中に被研磨加工物表面にスクラッチ傷等の加工ダメージを与えることなく、加工変質層の形成もなく、高速で鏡面研磨することが可能となる。
このため、この研磨方法を実施することにより、ラッピング加工や研削加工後、直ちに表面粗さＲａが例えば0.5ｎｍ程度の鏡面研磨加工が可能となり、従来のシリカスラリーによる２次鏡面研磨と同等以上の品質を持つシリコンウエハが１行程で得られ、もってスループットが向上し、シリコンウエハを高生産性と低コストとを両立させて鏡面研磨仕上げすることができる。
また、エッチング廃液の処理問題もなく、さらにアルカリ廃液等の処理問題や研磨装置および冶具が損傷する不具合もない。
さらに、硬質の研磨パッドを使用可能であるため、エッジ部ダレの発生が少なく、加工精度も向上する。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-speed mirror polishing method for a silicon wafer capable of mirror polishing a silicon wafer at a high speed.
[0002]
[Prior art]
Conventionally, as a mirror polishing method for a silicon wafer, for example, using a slurry containing silica particles and an alkali such as KOH or colloidal silica as an abrasive, and using a nonwoven fabric type or suede type soft pad in two to three steps in multiple steps. A multi-stage polishing method for polishing is known.
[0003]
〔problem〕
However, in the conventional polishing method, the polishing rate is extremely low and the number of steps is large. Therefore, it takes a long time to obtain a target mirror surface, and the productivity is extremely low.
That is, as a pre-process of mirror finishing, after lapping, an etching treatment with an acid or alkali solution is required to remove a processing damage layer, and then, as a mirror polishing process, at least two to three stages under different polishing conditions. Must be performed, the number of steps is extremely large, and the mirror polishing process has a low throughput.
In addition, since silica is harder than silicon, it is easy to damage the wafer such as scratches, and the polishing method using a soft cloth tends to cause edge sagging and reduce the usable area of the wafer. , Cost was high.
Furthermore, since the abrasive contains an aqueous solution of an alkali such as KOH, there is a problem that the waste liquid is treated and the polishing apparatus and the jig are damaged.
Furthermore, the etching solution also has a problem of waste liquid treatment.
[0004]
[Problems to be solved by the invention]
The present invention has been made in view of the above-mentioned problems of the related art, and a problem specifically set for solving the problem is that the mirror polishing speed is significantly improved, and the mirror polishing is performed in a short time with a small number of steps. By improving the throughput, the silicon wafer can be processed at high speed without damaging the wafer, such as scratches and damaged layers, and without causing problems such as waste liquid treatment and damage to polishing apparatuses and jigs. An object of the present invention is to provide a mirror polishing method.
[0005]
[Means for Solving the Problems]
As a means specifically configured to effectively solve the above-mentioned problem, the method for polishing a silicon wafer at a high speed according to claim 1 of the present invention is characterized in that the silicon wafer is surface-polished until the surface roughness Ra becomes 150 nm or less. It is characterized in that it is machined, and the machined surface is mirror-polished under wet polishing conditions using an abrasive whose abrasive grains are calcium carbonate particles and / or magnesium carbonate particles.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be specifically described.
However, this embodiment is specifically described for better understanding of the spirit of the invention, and does not limit the contents of the invention unless otherwise specified.
[0007]
The high-speed mirror polishing method for a silicon wafer according to the present embodiment includes a step of processing the surface of the silicon wafer in advance so that the surface roughness Ra becomes 150 nm or less by a conventional known method (hereinafter, referred to as a processing step). A step of mirror-polishing the processed silicon wafer under a wet polishing condition using an abrasive containing only calcium carbonate particles and / or magnesium carbonate particles as abrasive grains (hereinafter, referred to as a polishing step). I have.
In this specification, “surface roughness Ra” refers to the average of the steps between the convex portions and the concave portions on the surface of the polishing body measured by a contact indicator type surface roughness meter or the like.
[0008]
Hereinafter, each step will be described in detail.
"Processing process"
Conventionally known surface processing methods for processing the surface of a silicon wafer so that the surface roughness Ra is 150 nm or less are not particularly limited, and examples thereof include a lapping method and a grinding method. Among them, the grinding method is preferred. The reason that the grinding method is preferable is that the wafer formed by the grinding method has a thin damage layer and is not always clear, but the mechanochemical reaction between the silicon wafer and the calcium carbonate particles and / or the magnesium carbonate particles is likely to proceed. .
[0009]
"Polishing process"
In the polishing step, the silicon wafer having been subjected to the surface processing so that the surface roughness Ra becomes 150 nm or less is further wet-polished with an abrasive containing calcium carbonate particles and / or magnesium carbonate particles as abrasive grains, and a mirror surface is obtained. This is a polishing step to obtain.
[0010]
The following steps can be exemplified as specific examples of the polishing step.
{Circle around (1)} While supplying an abrasive slurry or paste containing calcium carbonate particles and / or magnesium carbonate particles as abrasive grains between the silicon wafer and the polishing pad, the silicon wafer and / or the polishing pad are rotated. A step of wet polishing a silicon wafer (hereinafter, referred to as a polishing step A).
{Circle around (2)} A polishing pad (hereinafter, referred to as a polishing body) in which calcium carbonate particles and / or magnesium carbonate particles as abrasive grains are formed into a grindstone or fixed in a foam such as polyurethane resin is brought into contact with a silicon wafer. A step of wet polishing by rotating (hereinafter, referred to as a polishing step B).
[0011]
The particle size of the calcium carbonate particles and / or magnesium carbonate particles is not particularly limited, but the particle size usually used as abrasive grains, for example, about 0.1 to 100 μm is used. Is preferred.
[0012]
"Polishing process A"
The abrasive slurry used in this polishing step contains, for example, calcium carbonate particles and / or magnesium carbonate particles as abrasive grains and water.
The addition amount (amount of abrasive grains) of the calcium carbonate particles and / or magnesium carbonate particles in the abrasive slurry is not particularly limited, but if the addition amount is too small, the polishing rate is too low, and the practicality is lacking. Also, if the amount of the abrasive particles is too large, the amount of the abrasive particles that do not contribute to the polishing process increases, and the polishing liquid cost increases, causing an increase in the polishing processing cost. It is not preferable because a problem occurs in supplying the slurry to the surface of the silicon wafer. For this reason, a practical amount of abrasive grains is generally desirably 2 to 80% by weight.
[0013]
In order to prepare an abrasive slurry (polishing liquid) in which the calcium carbonate particles and / or magnesium carbonate particles are added and dispersed, a surfactant such as a polycarboxylate is added, and the calcium carbonate particles and / or This is preferable because the dispersibility of the magnesium carbonate particles is improved.
[0014]
As the polishing pad, a polishing pad conventionally used for polishing a silicon wafer can be used. However, a hard pad such as a polishing pad made of foamed polyurethane such as IC1000 or MHS15A (both manufactured by Rodel Nitta) can be used. The use of a pad is preferable because the pressure at the point of true contact with the abrasive grains is increased and the polishing rate is improved.
The polishing pressure at the time of polishing by bringing the polishing pad and the silicon wafer into contact with each other is not particularly limited, and is usually about 9.8 to 39.2 kPa (100 to 400 gf / cm ² ). However, it is preferable that the polishing processing pressure be higher, because the pressure at the true contact point with the abrasive grains is increased and the polishing rate is improved.
[0015]
"Polishing process B"
The polishing body is made of a grindstone or a polishing pad.
In order to form the calcium carbonate particles and / or magnesium carbonate particles as abrasive grains into a grindstone shape, the whole grindstone is formed by the calcium carbonate and / or magnesium carbonate, or the contact portion of the grindstone with the silicon wafer is partially formed. In some cases, the above-mentioned calcium carbonate particles and / or magnesium carbonate particles are also solidified by heat treatment or the like without using a binder (bondless whetstone), and the grindstone is bonded with a resinoid bond or the like. There may be one that is solidified and molded using an agent (resinoid bond grindstone). The abrasive grain ratio (volume ratio of the abrasive grains in the grindstone) in the grindstone is not particularly limited, and is, for example, 70 to 100%.
[0016]
The resinoid bond used for forming the resinoid bond grindstone is not particularly limited, and a simple substance or a mixture of a thermosetting resin, a thermoplastic resin, and a water-soluble polymer resin can be used.
The molding of the resinoid bond grindstone or the bondless grindstone can be performed by using a commonly used known molding technique.
[0017]
Examples of the polishing pad containing calcium carbonate particles and / or magnesium carbonate particles include the following.
{Circle around (1)} Nonwoven fabric type prepared by impregnating a nonwoven fabric of a chemical fiber such as polyester with a polyurethane solution containing the calcium carbonate particles and / or magnesium carbonate particles.
{Circle around (2)} A suede type produced by foaming a polyurethane containing the above-mentioned calcium carbonate particles and / or magnesium carbonate particles on a non-woven fabric of chemical fibers such as polyester with a foaming agent.
(3) A foamed polyurethane type produced by independently foaming a polyurethane solution containing the calcium carbonate particles and / or magnesium carbonate particles with a foaming agent.
[0018]
The polishing pressure when the polishing body and the silicon wafer are brought into contact with each other and polished is not particularly limited, and is usually about 9.8 to 39.2 kPa (100 to 400 gf / cm ² ). However, it is preferable that the polishing processing pressure be higher, because the pressure at the true contact point with the abrasive grains is increased and the polishing rate is improved.
Polishing is performed while dropping a solution containing an acid or an alkali component appropriately between the polishing body and the silicon wafer.
[0019]
"Action"
Although the mechanism of polishing a silicon wafer by this high-speed mirror polishing method is not always clear, the silicon and calcium carbonate particles and / or magnesium carbonate constituting the silicon wafer are efficiently subjected to a mechanochemical reaction in a wet and pressurized state. It is presumed that mirror polishing is possible even though the abrasive grains (calcium carbonate and / or magnesium carbonate) are softer than silicon.
[0020]
【Example】
Hereinafter, embodiments will be described in detail.
[Example 1]
(Adjustment of abrasive slurry)
After mixing and stirring 2,000 g of calcium carbonate particles having a particle size of 0.5 μm or less and 8000 g of water, the mixture was stirred in an ultrasonic disperser for 10 minutes to obtain an abrasive slurry.
[0021]
(Polishing test)
For a silicon wafer previously ground to a surface roughness Ra of 140 nm using a # 800 diamond grindstone, a polishing pad (Rodel Nitta IC 1000) using a mechanical rotary polishing apparatus (rotational speed: 60 rpm), Polishing was performed under a polishing condition of 29.4 kPa (300 gf / cm ² ), a drop amount of the abrasive slurry of 20 ml / min, and a polishing time of 30 minutes. Table 1 shows the results of the polishing test.
[0022]
The polishing rate was calculated from the measured value of the silicon wafer thickness before and after polishing using a digital micrometer and the polishing time, and the surface roughness and edge sag were measured using a contact pointer type surface roughness meter, respectively. The presence or absence of scratches was determined by observation with an optical microscope.
The presence or absence of the affected layer is determined by immersing the polished silicon wafer in an etchant, etching it diagonally, and processing it in the depth direction by a rocking curve measurement method using an X-ray diffraction device with a 4-crystal monochromator. The thickness of the altered layer was measured, or the cross section of the silicon wafer was confirmed by observing the presence or absence of the altered layer using a transmission electron microscope.
[0023]
[Example 2]
A polishing test was performed in the same manner as in Example 1 except that the silicon wafer used was changed to a silicon wafer that had been processed in advance to have a surface roughness Ra of 60 nm by a grinding method using a # 1000 diamond grindstone. The results are shown in Table 1.
[0024]
[Example 3]
(Adjustment of abrasive slurry)
An abrasive slurry was prepared according to Example 1, except that the abrasive grains were changed to magnesium carbonate.
(Polishing test)
A polishing test was performed in the same manner as in Example 1 except that this abrasive slurry was used. The results are shown in Table 1.
[0025]
[Example 4]
After lapping the silicon wafer, a polishing test was performed in the same manner as in Example 1 except that the silicon wafer was changed to a silicon wafer that was processed in advance so that the surface roughness Ra became 140 nm by an etching method. The results are shown in Table 1.
[0026]
[Example 5]
(Production of whetstone)
3600 g of calcium carbonate particles having a particle size of 0.5 μm or less and 400 g of a phenol resin (manufactured by Sumitomo Durez) were mixed to form a grindstone having a polishing platen of 15 inches φ.
(Polishing test)
Using this grindstone, 10 ml of water was added between the silicon wafer and the grindstone under the conditions of a polishing pressure of 29.4 kPa (300 gf / cm ² ), a grindstone-attached platen rotation speed of 60 rpm, and a work rotation speed of 40 rpm. The silicon wafer was wet-polished using a mechanical rotary polishing apparatus while dripping at a drop rate of 1 / min. The silicon wafer is the same as that used in the first embodiment. Table 1 shows the results of the polishing test.
[0027]
[Comparative Example 1]
A polishing test was performed in the same manner as in Example 1 except that the silicon wafer used was changed to a silicon wafer that had been processed in advance so that the surface roughness Ra was 170 nm by a grinding method using a # 600 diamond grindstone. The results are shown in Table 1.
[0028]
[Comparative Example 2]
A polishing test was performed according to Example 5, except that the silicon wafer used in Comparative Example 1 was used. The results are shown in Table 1.
[0029]
[Comparative Example 3]
(Adjustment of abrasive slurry)
500 g of colloidal silica particles having a particle size of 0.03 μm were added to 9500 g of water as abrasive grains, and an abrasive slurry was prepared by adjusting the pH to 10 with KOH.
(Polishing test)
A silicon wafer was polished according to Example 1 except that this abrasive slurry was used. The results are shown in Table 1.
[0030]
[Comparative Example 4]
Using the grindstone of Example 5, mechanical polishing by a dry method under the conditions of a polishing pressure of 29.4 kPa (300 g / cm ² ), a grindstone-attached platen rotation speed of 60 rpm, and a work rotation speed of 40 rpm. The silicon wafer was polished using the apparatus. The silicon wafer is the same as that used in the first embodiment. Table 1 shows the results of the polishing test.
[0031]
[Table 1]

[0032]
【The invention's effect】
As described above, according to the method for high-speed mirror polishing of a silicon wafer according to the present invention, the silicon wafer is subjected to surface processing until the surface roughness Ra becomes 150 nm or less, and the processed surface is made of calcium carbonate particles and / or By performing mirror polishing under wet polishing conditions using an abrasive that is magnesium carbonate particles, there is no processing damage such as scratches on the surface of the workpiece to be polished during mirror polishing, and no formation of a damaged layer Mirror polishing can be performed at high speed.
Therefore, by performing this polishing method, it becomes possible to perform mirror polishing with a surface roughness Ra of, for example, about 0.5 nm immediately after lapping or grinding, which is equal to or more than that of the conventional secondary mirror polishing using silica slurry. A high quality silicon wafer can be obtained in one process, thereby improving the throughput and mirror polished the silicon wafer while achieving both high productivity and low cost.
In addition, there is no problem of processing the etching waste liquid, and there is no problem of processing the alkaline waste liquid or the like, and there is no problem that the polishing apparatus and the jig are damaged.
Furthermore, since a hard polishing pad can be used, the occurrence of edge sag is small and the processing accuracy is improved.

Claims (1)

A silicon wafer is surface-processed until the surface roughness Ra becomes 150 nm or less, and the processed surface is mirror-polished under a wet polishing condition using an abrasive whose abrasive grains are calcium carbonate particles and / or magnesium carbonate particles. A high-speed mirror polishing method for a silicon wafer, characterized in that: