JP2003037089A - Method for polishing wafer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for polishing a wafer to obtain a mirror polished wafer having a high flatness by shortening a polishing time without bringing about a scratch on the wafer. SOLUTION: The method for polishing the wafer comprises a finish-polishing step of the wafer W of finish-polishing the wafer W via a plurality of continuously polishing steps, by setting so that polishing pressures are lowered at a final stage side than a starting stage side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wafer polishing method, and more particularly to a finish polishing method for removing haze components.

[0002]

2. Description of the Related Art For mirror-polishing a wafer such as a semiconductor wafer typified by a silicon wafer, rough polishing whose main purpose is to adjust flatness, and surface roughness having a wavelength of several to several tens nm (so-called It consists of finish polishing whose main purpose is to improve haze.

The mirror polishing process will be described in more detail. Rough polishing is called primary polishing, which is polishing for improving the flatness of the wafer surface after the etching process or surface grinding process, and is for correcting the shape. To be done. Generally, a polishing cloth used for rough polishing is, for example, an Asker C hardness (Asker rubber hardness tester C type, which is a kind of spring hardness tester, obtained by impregnating polyester felt (structure is a random structure) with polyurethane. A relatively hard material having a measured value of about 80 is used. By sticking a polishing cloth on a rotatable surface plate, using an abrasive containing colloidal silica in an aqueous solution of alkali base, and rubbing it while supplying the abrasive between the wafer and the polishing cloth. Polished. Since the polishing pad is hard under the conditions used for rough polishing such as primary polishing, minute scratches on the wafer surface called scratches may occur.

On the other hand, the final polishing is a final step of wafer polishing, which is a step of obtaining a mirror surface in which level irregularities called haze are removed and scratches generated by rough polishing. In finishing polishing, a suede-like artificial leather made of soft urethane foam is pasted on a rotatable surface plate, and the wafer containing the colloidal silica-containing abrasive in the alkaline base aqueous solution is applied to the wafer. It is made by rubbing.

Since the polishing cloth used for finish polishing is generally softer than the polishing cloth used for rough polishing, scratches are less likely to occur, but even if the polishing pressure is increased, scratches are likely to occur, so that the polishing Polishing is generally performed at a relatively low polishing pressure.

[0006]

In rough polishing, although the wafer shape is improved, a haze-free polished surface cannot be obtained, and scratches occur relatively frequently. Therefore, it is necessary to improve these surface conditions by a final polishing step, but if the polishing pressure is lowered, the polishing rate will decrease, and therefore it will take time to obtain a polished surface with less haze. Therefore, productivity is reduced and cost is increased. The present invention has been made in view of such problems of the prior art, and provides a polishing method for obtaining a mirror-polished wafer with high flatness without causing scratches on the wafer and also shortening the polishing time. The purpose is to do.

[0007]

According to the method for polishing a wafer of the present invention, in the final polishing step of a wafer such as a semiconductor wafer, the polishing is performed in a plurality of continuous polishing steps, and the polishing is performed from the starting side to the final side. The polishing pressure is set so as to be low, and the polishing is performed. In other words, when finishing polishing the wafer, first polish with high polishing pressure,
Then, the same polishing apparatus is used for polishing at a low polishing pressure.

By doing so, a high-pressure polishing at the initial stage of polishing produces a polished surface with less haze in a short time. The scratches generated by the high pressure polishing are removed by the low pressure polishing that is subsequently performed. As a result, a polished surface with less haze and scratches can be obtained in a short time.

The polishing of the wafer of the present invention is applicable to finish polishing. The qualities of concern in the present invention are haze and scratch. For example, in rough polishing (generally referred to as primary polishing) for correcting the shape of a wafer, a hard polishing cloth is used. Therefore, even if the pressure is changed during polishing, haze or It is not very effective in reducing scratches. It is important to change the pressure only in the final polishing, which is the final polishing step in which haze and scratch are problems. Therefore, the polishing cloth used in this polishing step is preferably a polishing cloth for the purpose of removing haze, for example, a suede-like finish polishing cloth for finish polishing. The suede-like polishing cloth refers to, for example, a polyester nonwoven fabric impregnated with a polyurethane foam composition and foamed to remove the surface of the sheet on which a foamed layer has been formed to open the surface partial bubbles to form a fluffy surface. It is a polishing cloth used as the surface.

In order to improve the haze and prevent the occurrence of scratches, the above-mentioned method may be carried out. In order to maintain the stability of polishing with time, a polishing cloth having a laminated structure is particularly used. Things are preferred.

When a commonly used single-layer finish polishing cloth is used, especially after frequently using the polishing cloth, the polishing cloth is creep-deformed by the polishing load, and the polishing load is changed to a light load. Deformation remains even if changed by, and if the outer peripheral portion of the wafer is excessively polished or if the polishing cloth has irregular creep deformation residual portions, in-plane polishing unevenness occurs and sagging occurs on the outer peripheral portion of the wafer. May occur or the haze level may become uneven.

That is, at the start of using the polishing cloth (early life)
Then, when the sinking of the polishing cloth during polishing changes from the state during high pressure polishing to the state during low pressure polishing, it immediately shifts (recovers)
Therefore, while the haze level is uniform within the wafer surface, as the usage time increases, the sinking of the polishing cloth at the end of use (end of life) remains creep-deformed in a state close to that during high pressure polishing. Is. If low-pressure polishing is performed in this state, the outer peripheral portion of the wafer comes into strong contact with the polishing cloth, and it is considered that unevenness of haze occurs in the wafer surface.
In particular, sagging may occur in the outer peripheral portion of the wafer, resulting in poor flatness.

Therefore, in order to prevent such a state, the present invention further provides at least a polishing cloth used in the finishing polishing step in which the polishing pressure is set so that the polishing pressure on the final stage side is lower than that on the final stage side. It is characterized in that it is a laminated polishing cloth formed of a surface layer made of a polishing cloth for removing haze and an elastic sheet softer than the surface layer portion. The laminated polishing cloth is a polishing cloth prepared by sticking a foam sponge or the like, which is softer and has less creep deformation than the finishing polishing cloth, under a generally used finishing polishing cloth.
Most of the subsidence when pressure is applied to the laminated polishing cloth is due to compression of foam sponge with less creep deformation, so comparing under the same polishing cloth life, compared to when using a general finish polishing cloth Can suppress haze unevenness on the wafer surface. Further, at this time, a laminated polishing cloth of three or more layers in which a flexible elastic sheet is laminated on the back surface side of the surface layer via a hardness sheet may be used.

Particularly, the polishing cloth having a laminated structure has a surface layer made of a suede-like polishing cloth for the purpose of removing haze, an intermediate layer made of a hard plastic sheet, and an elastic layer having independent foaming and having a hardness lower than that of the surface layer. It is preferably a polishing cloth composed of a lower layer composed of a sheet. A polishing cloth having such a technical idea is disclosed in the polishing cloth described in Japanese Patent Application Laid-Open No. 11-277408, whereby unevenness of the polishing cloth can be prevented, and a flatter wafer without sagging on the outer periphery can be manufactured. The noise is also improved and scratches can be prevented.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below with reference to the embodiments shown in the drawings. However, unless otherwise specified, the dimensions, shapes, materials, relative arrangements, etc. of the products described in this embodiment are not intended to limit the scope of the present invention thereto but merely as examples.

The polishing apparatus is not particularly limited, but a single-wafer polishing apparatus was used. The polishing apparatus may be a batch system.

FIG. 1 is a schematic view of an example of a polishing apparatus used in the polishing method of the present invention. Explaining the details of the polishing device,
As shown in FIG. 1, the polishing cloth 2 is attached to the surface of the polishing platen 8 having a flat surface to form a polishing surface. The polishing platen 8 is rotationally driven by a platen drive unit. The polishing apparatus is a wafer W
Has a polishing head 1 for holding. The polishing head 1 has an up-and-down mechanism that separates and contacts the surface of the polishing platen 8, and is rotationally driven by a polishing head drive unit.

The polishing head is not particularly limited, but a head having a structure capable of changing the polishing pressure is used. In this example, an airbag pressurizing type polishing head was used.
However, the air bag pressurization method may not be used.

In FIG. 1, a polishing head 1 has a hard work holding plate 16 of high flatness such as SiC having a large number of through holes h for suction, and an upper surface of the work holding plate is capped with an inner cover. A vacuum chamber 20 is formed between the work holding plate 16 and
A vacuum passage 17 extends from the center of the inner cover 19 to the vacuum chamber 20 and extends above the center of the rotary shaft 15 to connect to a vacuum device (not shown). Work W is
The vacuum generated by the vacuum device is sucked and held. Further, the polishing pressure adjusting section adopts an air bag pressurizing method, and the holding plate 16 is attached to the outer peripheral portion of the upper end thereof by the annular elastic body 3 at the lower end portion of the inner peripheral portion of the outer cover 18 so as to be vertically and horizontally movable. Annular elastic body 3
The pressurizing chamber 23 is formed in a space surrounded by the inner cover 19 and the outer cover 18. The pressurizing chamber 23 penetrates from the central portion of the outer cover 18, and a pressurized air supply path 21 extends upward near the center of the rotary shaft 15 and is connected to a pressurized air supply device (not shown). The polishing pressure can be adjusted by adjusting the pressure of the pressurized air supply device.

Further, a polishing agent supply means (not shown) for supplying the polishing agent to the polishing cloth 2 side is arranged on the surface side of the polishing platen 8, and the polishing agent is dropped on the center of the polishing platen 8. The polishing pressure control device (not shown) includes a platen drive unit, a polishing head drive unit,
It automatically controls the polishing pressure adjustment part, etc., and is electrically connected to them.

The polishing pressure, the polishing time, the relative speed between the polishing platen and the polishing head, etc. in the final polishing step are set on the basis of data such as the type of polishing agent, polishing cloth and the shape and material of the wafer. The polishing pressure control device is configured to automatically control the polishing platen, the polishing head, the polishing pressure adjusting unit, etc. based on them.

Particularly, the polishing pressure is 5 at the initial stage and the final stage of polishing.
It is preferable to change it by about 0%. Although it depends on the polishing cloth, scratches are significantly reduced when finally set to 15 kPa or less. If the pressure is too low, the etching effect due to the alkaline component of the polishing agent may be increased and the haze may be deteriorated. Therefore, the pressure is preferably 5 kPa or more. Usually, about 10 kPa is preferable.

In this embodiment, the finishing polishing step is performed at the polishing pressure P.
₀ polishing pressure P and the polishing step carried out at high load polishing time T _0
1 (P ₁ <P ₀ ) and at least two polishing steps are performed with a low load for the polishing time T ₁ . The wafer is first pressed against the finish polishing cloth with the polishing pressure P ₀ , and the time T _{0 is applied.}
After the polishing is performed only, the same apparatus is continuously used to perform low-load polishing for a polishing time T ₁ at a polishing pressure P ₁ lower than the polishing pressure P ₀ for finishing.

Specific comparative examples and examples will be described below. The wafers used in the examples and comparative examples are Si single crystals of P-type crystal orientation <100> and a diameter of 200 mm. Used a single-wafer mirror polishing apparatus having the above-mentioned mechanism. The wafer was subjected to the final polishing of the present invention after the steps of primary polishing and secondary polishing. In the primary polishing, a hard velor type cloth / colloidal silica-based polishing agent (Asker C hardness of polishing cloth 85, compression rate 4.0
%) In the secondary polishing, a soft bellows type cloth / colloidal silica-based abrasive (Asker C hardness of polishing cloth 75, compression rate 9.0%) was used for polishing.

[0025]

[Comparative Example 1] Finish polishing was performed on a wafer which had been subjected to the above-mentioned primary polishing and secondary polishing. In the final polishing, polishing was performed only at a low polishing pressure. As a polishing cloth, a suede-like polishing cloth CIEGAL 7355 (manufactured by Toray Cortex; Asker C hardness 61) was used.
The polishing cloth used had been used for about 200 minutes. The polishing pressure was 10 kPa. The polishing time was changed at four levels of 4, 6, 10, and 15 minutes, and the polishing state of the wafer surface was confirmed. Under this condition, 200 sheets were evaluated for each level.

The polishing state of the wafer surface was evaluated by the occurrence of scratches and the haze level. The haze has different values depending on the evaluation device, but in the present invention, the haze level and scratch evaluation method polishes a predetermined number of wafers,
The measurement was performed using a light scattering type particle measuring device (SP1 manufactured by KLA-Tencor). For scratches, the rate of wafers in which scratches occurred was evaluated.

Explaining the evaluation method in more detail,
For the haze level, compare the average value on the wafer surface and the haze map when the range is set to 0.005 ppm and compare the maximum value-minimum value (MAX-MIN) of the in-plane haze value.
Value) was evaluated. Note that the haze of this device is the percentage of scattered light with respect to the incident light irradiated on the wafer (ppm).
Is displayed. The average value of the wafers polished this time is about 0.035 ppm at the haze level, and if it is smaller than this, the surface condition is good. In-plane MAX-MI
When the N value exceeds 0.02 ppm, it is determined that there is haze unevenness.

As a result, with the comparatively low polishing pressure as in Comparative Example 1, the finished polished surface could not be obtained until the polishing time was 10 minutes. (That is, the haze level is 0.035 on average.
It was above ppm. )

The average haze level in 15-minute polishing was 0.028 ppm. Scratch rate is 2
%Met.

[0030]

Comparative Example 2 As in Comparative Example 1, CIEGA was used as a polishing cloth.
L 7355 (manufactured by Toray Cortex) was used. The polishing cloth used had been used for about 200 minutes. The polishing pressure was set to 20 kPa, which is higher than that in Comparative Example 1. Polishing time is 4, 6,
The polishing conditions on the wafer surface were confirmed in the same manner as in Comparative Example 1 by changing the levels at 10 levels for 10 and 15 minutes. Each level 2 under this condition
It was evaluated by 00 sheets each.

As a result, a finish polished surface was obtained after a polishing time of 6 minutes. In other words, the haze level is 0.
028ppm, 0.027ppm after polishing for 10 minutes, 15
At the time of minute polishing, it was 0.026 ppm, which was almost the same level. The scratch occurrence rates were 12, 14 and 10%, respectively, independent of the polishing time. Thus, although the time required to obtain the finished polished surface is shortened as compared with Comparative Example 1, the occurrence of scratches increases, which is a problem.

[0032]

Example 1 As in Comparative Example 1, CIEGA was used as a polishing cloth.
L 7355 (manufactured by Toray Cortex) was used. The polishing cloth used had been used for about 200 minutes. Polishing pressure is first 20 kPa for 6 minutes, then pressure is adjusted to 10 kP
It was changed to a and polished for 1 minute. Then, as in Comparative Example 1, the polishing state of the wafer surface was confirmed. 200 under these conditions
The number of sheets was evaluated. Also, the usage of polishing cloth (polishing cloth life)
In order to see the effect of the above, the polishing cloth used after about 1000 minutes, about 2000 minutes, about 3000 minutes, and about 6000 minutes was used in addition to the above-mentioned polishing cloth that had been used for 200 minutes.

Result: 20 kPa, 6 minutes → 10 kP
a, a finish-polished surface was obtained under the condition of 1 minute. When a polishing cloth with a polishing cloth life of 200 minutes was used, the haze level was 0.026 ppm.

As the influence of the polishing cloth life, the haze level until the polishing cloth is used for about 3000 minutes is 0.02.
The level was 6 to 0.034 ppm and there was no problem. At a polishing cloth life of 6000 minutes, a level difference of 0.01 ppm or more between the wafer periphery and the surface, and an average value of 0.03 in the surface.
The proportion exceeding 5 ppm reached 24%. MAX-MI
Haze unevenness of about 0.032 ppm in N value was observed.
The scratch rate is 2 to 2 regardless of the polishing cloth life.
It was 4%.

From Example 1, in the finish polishing step,
By changing the polishing load from high pressure to low pressure and polishing,
While maintaining the scratch level equivalent to that at the low polishing pressure (Comparative Example 1), the finished polishing surface was obtained in the same polishing time as at the high polishing pressure (Comparative Example 2), and the productivity was improved. The polishing cloth used in Example 1 has a usage limit of 3000 to 60 because uneven haze occurs in about 6000 minutes.
You can see that it is about 00 minutes.

[0036]

Example 2 As a polishing cloth, a laminated polishing cloth (surface layer ... CIEG
AL 7355 (manufactured by Toray Cortex), lower layer ... HN
400 (foamed nitrile rubber sheet, made by Sun Polymer; Asker C hardness 43), the surface layer and lower layer are plastic sheet ST-416P (double-sided tape of PET base of 50 μm,
The one bonded with Sumitomo 3M) was used. Polishing cloth is about 20
The one that had been used for 0 minutes was used. 20k for polishing pressure first
The pressure was adjusted to 10 kPa by adjusting the pressure for 6 minutes and then polishing was performed for 1 minute. Then, as in Comparative Example 1, the polishing state of the wafer surface was confirmed. Under this condition, 200 sheets were evaluated. Further, in order to see the influence of the usage condition (polishing cloth life) of the polishing cloth, in addition to the polishing cloth that has been used for 200 minutes, about 1000 minutes, about 2000 minutes, about 3000 minutes, about 6000 minutes.
The same polishing was performed using the polishing cloth after the minute use.

As a result, the haze level up to a polishing cloth life of 6000 minutes was 0.026 to 0.030 ppm, which was a problem-free level. Also, polishing cloth life 6000
Even for the minute, the haze unevenness seen in Example 1 was not observed,
The MAX-MIN value was less than 0.02 ppm. The scratch rate is 2 to 4 regardless of the life of the polishing cloth.
%Met.

From Example 2, by using such a laminated polishing cloth and further changing the polishing load from a high pressure to a low pressure in the final polishing step, the polishing is performed in the same manner as in the low polishing pressure (Comparative Example 1). While maintaining the scratch level, the final polishing surface was obtained in the polishing time equivalent to that under the high polishing pressure (Comparative Example 2), and the productivity was improved. Further, by using the laminated polishing cloth, the life of the polishing cloth is improved as compared with the first embodiment, and stable quality can be maintained for a long time.

[0039]

Example 3 Using the same polishing cloth as in Example 2, the polishing pressure was first set to 30 kPa for 1 minute and then the pressure was adjusted to 10
It was changed to kPa and polished for 30 seconds. Polishing cloth is about 200
It has been used for a minute.

The polishing condition of the wafer surface was confirmed as in Comparative Example 1. As in Example 2, the haze level is 0.02.
It was about 6 ppm, and Heismura was not observed. Under this condition, the polishing time can be further shortened.

[0041]

[Example 4] Laminated polishing cloth (surface layer ... CIEG as a polishing cloth
AL 7355 (manufactured by Toray Cortex), lower layer ... HN
400 (foamed nitrile rubber sheet, made of Sun Polymer),
The surface and lower layers are plastic sheets ST-416P (50
A μm PET-based double-sided tape adhered with Sumitomo 3M) was used. The polishing cloth used had been used for about 200 minutes. The polishing pressure was first 30 kPa for 4 minutes, and then the pressure was adjusted to 20 kPa to polish for 15 seconds.
Then, as in Comparative Example 1, the polishing state of the wafer surface was confirmed. Under this condition, 200 sheets were evaluated. Also, polishing pressure,
In particular, in order to see the effect of a low polishing pressure, polishing was similarly performed at 15, 10 and 5 kPa in addition to the above 20 kPa.

Result: 30 kPa, 4 minutes → 20 kP
Even under the condition of "a" and 15 seconds, a finish-polished surface was obtained in a short time. In other words, the haze level is 0.026-0.030p
The level was pm and there was no problem. Although the scratch occurrence rate was lower than that of the single stage of 30 kPa, it was as high as 8%. When the low polishing pressure was set to 15 kPa or less, the occurrence of scratches was 2 to 4%, which was a level with no problem.
In addition, the haze level is 0.026- even at 15 kPa or less.
There is no problem because it is 0.030 ppm.

According to the fourth embodiment, in the finish polishing step, by changing the polishing load from high pressure to low pressure and polishing, the scratch occurrence rate can be lowered as compared with the case of high polishing pressure.
It can be seen that it is necessary to change the polishing pressure so that the polishing pressure is preferably lowered to 15 kPa or less.

The polishing time is not limited to the above example, and it is preferable to set the polishing time as short as possible under arbitrary conditions. Further, the polishing time can be adjusted by changing the relative speed between the polishing platen (polishing cloth) and the polishing head.

[0045]

According to the present invention, it is possible to form a good finished surface without lowering the productivity and further suppress the occurrence of scratches. Further, by using the laminated polishing cloth together, the life of the polishing cloth can be extended while suppressing the occurrence of scratches.

[Brief description of drawings]

FIG. 1 is a schematic view of an example of a polishing apparatus used in a polishing method of the present invention.

[Explanation of symbols]

1 polishing head 2 polishing cloth 3 Elastic support 8 Polishing surface plate 15 rotation axis 16 Work holding board 17 Vacuum Road 18 Outer cover 19 inner cover 21 Pressurized air supply path 23 Pressure chamber h Through hole W wafer

Claims (3)

[Claims] 1. In a final polishing process of a wafer, polishing is performed in a plurality of successive polishing steps, and
A method for polishing a wafer, wherein polishing is performed such that the polishing pressure on the final stage side is lower than that on the initial stage side. 2. The polishing cloth used in the final polishing step of setting and polishing so that the polishing pressure on the final stage side is lower than that on the initial stage side is a suede-like polishing cloth. Method for polishing wafers. 3. A polishing cloth used in a finish polishing step of setting and polishing so that the polishing pressure on the final stage side is lower than that on the initial stage side, and a surface layer made of a polishing cloth for at least haze removal, 2. A laminated polishing cloth formed of an elastic sheet that is softer than the surface layer portion.
A method for polishing a wafer according to claim 1.