JP6782157B2 - Electrostatic chuck - Google Patents

Description

The present invention relates to an electrostatic chuck for semiconductor manufacturing equipment.

An electrostatic chuck provided with an insulating layer on an electrode applies a voltage between the electrode and an object to be adsorbed such as a semiconductor wafer (hereinafter referred to as a wafer) via the insulating layer, and the wafer is generated by the electrostatic force generated between the two. It is a device that adsorbs an object to be adsorbed.

By using the electrostatic chuck, the entire surface of the wafer can be uniformly processed in the semiconductor manufacturing apparatus for etching, CVD, etc. without using a mechanical holder. Therefore, the electrostatic chuck is widely used as a wafer fixing device such as a susceptor for holding a wafer and controlling the temperature.

As an electrostatic chuck, one is known in which an inert gas such as helium is passed between a wafer and an insulating layer to enhance heat transfer between the two (Patent Document 1).

In the electrostatic chuck disclosed in Patent Document 1, a concavo-convex groove for helium gas is formed in a dielectric layer, and the center line surface roughness Ra (JIS B0601_1994) of the top surface (holding surface) of the convex portion of the concavo-convex groove. Is set to 0.3 μm or less to reduce the amount of gas leakage when the wafer is in close contact with the wafer.

In addition, as an electrostatic chuck that can attenuate the electrostatic force in a short time to speed up wafer attachment / detachment, the electrostatic force residual time and volume specific resistance, relative permittivity, thickness of the insulating layer or protective film can be obtained from the equivalent circuit of the electrostatic chuck. Specifically, it has been proposed that the gap δ between the wafer and the surface of the insulating layer and the maximum height Rmax (JIS B0601_1982) of the surface of the insulating layer are defined in a certain relationship (Patent Document 2). ..

Japanese Unexamined Patent Publication No. 9-23777 JP-A-5-63062

However, even if the surface roughness is defined by the center line surface roughness Ra of the holding surface of the electrostatic chuck as in the technique disclosed in Patent Document 1, the wafer and the electrostatic chuck do not sufficiently adhere to each other, and they The amount of gas leak from the contact interface of the

Further, even if the surface roughness is defined by the maximum height Rz, which is a substitute characteristic of the gap δ between the electrostatic chuck and the wafer, which affects the electrostatic attraction force, as in the technique disclosed in Patent Document 2, the attraction force. However, there is a problem that sufficient adsorption force cannot be actually obtained even if the maximum height Rz is reduced.

The present invention has been made in view of the above problems of the prior art, and an object of the present invention is to provide an electrostatic chuck having a high electrostatic adsorption force. A further object of the present invention is to provide an electrostatic chuck capable of suppressing a gas leak amount from a contact interface with a wafer.

The electrostatic chuck of the present invention includes a ceramic substrate having a first surface and embedding an electrode, and an annular convex portion having a top surface that projects annularly from the outer peripheral edge of the first surface to support the wafer. An electrostatic chuck comprising a plurality of convex portions, each of which is surrounded by the annular convex portion and has a top surface that protrudes from the first surface of the substrate and supports the wafer, and at least the apex of the annular convex portion. surface, said annular protrusion maximum peak height Rp and the arithmetic mean roughness Ra determined from the roughness curve of the top surface of Ri surface der satisfying the relationship of Rp / Ra ≦ 2.8, the top of the annular projection The skewness Rsk obtained from the surface roughness curve is negative, and the top surfaces of the plurality of convex portions are located on the same plane as the top surfaces of the annular convex portions .

In the electrostatic chuck of the present invention, the maximum peak height Rp is preferably Rp ≦ 1.5 μm.

According to the electrostatic chuck of the present invention, the amplitude of the roughness curve of the top surface is set by setting the state of the top surface of the annular convex portion to (maximum mountain height Rp) / (arithmetic mean roughness Ra) ≤ 2.8. The distribution curve becomes asymmetric with respect to the average line (skewness Rsk obtained from the roughness curve is negative), and the cross-sectional area calculated by the product of the arithmetic mean roughness Ra and the circumferential length of the annular convex portion during electrostatic adsorption. Since (the cross-sectional area through which the gas passes) becomes a certain value or less, the amount of gas leakage from the gap between the electrostatic chuck and the wafer in close contact with each other is suppressed.

According to the electrostatic chuck of the present invention, the amount of gas leak can be adjusted more precisely than the conventional electrostatic chuck by finishing the top surface of the annular convex portion using the maximum peak height Rp of the roughness curve. Will be able to.

It is a top view of the electrostatic chuck of embodiment of this invention. It is sectional drawing which follows the AA line of FIG. It is a graph explaining the relationship between the roughness curve before and after surface finishing processing of the holding surface of the electrostatic chuck of embodiment, and the amplitude distribution curve thereof. It is a graph which shows the relationship between the arithmetic mean roughness Ra and the maximum mountain height Rp of a roughness curve with respect to the gas leak amount of an Example and a comparative example. It is a graph which shows the relationship of the ratio of (maximum mountain height Rp of roughness curve) / (arithmetic mean roughness Ra) to gas leak amount of Example and comparative example.

Examples of the present invention will be described below with reference to the drawings.

(Constitution)
FIG. 1 is a plan view of the electrostatic chuck 10 of this embodiment as viewed from the first surface (surface) Ob side, which is a suction surface for sucking and holding a wafer (not shown). The electrostatic chuck 10 includes a substrate 11 formed of a disk-shaped ceramic sintered body. As the material of the ceramics of the substrate 11, aluminum nitride, silicon nitride, sialon, silicon carbide, boron nitride, alumina and the like are preferable.

The substrate 11 has an annular convex portion 11R (hereinafter, also referred to as a rib) protruding from the first surface Ob in an annular shape on the outer peripheral edge portion thereof, and a region surrounded by the annular convex portion 11R of the first surface Ob. A plurality of projecting convex portions 11P (hereinafter, also referred to as pins) are formed.

The substrate 11 is formed with a ventilation passage 13 that is open in the center of the first surface. The ventilation passage 13 is composed of through holes between the first surface and the second surface (back surface) of the substrate 11. The ventilation passage 13 is connected to a heat transfer gas supply device (not shown) such as helium on the second surface side. That is, it is possible to supply the heat transfer gas from the second surface side to the first surface side of the substrate 11 via the ventilation passage 13. The number and opening locations of the ventilation passages 13 are appropriately designed according to the desired flow of the heat transfer gas.

The planar shape of the substrate 11 may be a substantially disk shape, a polygonal plate shape, an elliptical plate shape, or the like. Further, a groove extending in the radial direction from the ventilation passage 13 may be formed on the first surface Ob excluding the annular convex portion 11R and the convex portion 11P.

FIG. 2 is a cross-sectional view taken along the line AA of FIG. 1, but is drawn by omitting a part in the radial direction and the plate thickness direction. In addition, in FIGS. 1 and 2, in order to clarify the configuration of the electrostatic chuck, each of the components such as the convex portion is deformed, and in addition to the aspect ratio in the drawing of each component, the width or height and the mutual. The ratio with the interval may differ from the actual one.

As shown in FIG. 2, an electrode 12 for generating an electrostatic adsorption force is embedded inside the substrate 11. Although omitted in the drawing, the second surface (back surface) Re of the substrate 11 is provided with an electrode terminal electrically connected to the electrode 12, and the electrode terminal and the electrode 12 are electrically connected to each other. The metal wiring to be used is provided in the thickness direction of the substrate 11. That is, it is possible to apply a voltage to the electrode 12 via the electrode terminal.

When the wafer 20 is placed on the first surface Ob, the annular convex portion 11R comes into contact with the outer peripheral region of the wafer 20 and creates a space surrounded by the wafer 20 and the first surface Ob of the substrate 11 from the outside. Functions as a sealing part for sealing. The radial width of the top surface 11RT (contact portion with the wafer) of the annular convex portion 11R is appropriately designed and formed to be, for example, 1000 μm or more so that it can function as a sealing portion. The width of the annular convex portion 11R is preferably narrow in order to secure the area of the heat transfer gas in contact with the wafer.

As shown in FIG. 2, when the wafer 20 is electrostatically adsorbed on the substrate 11, the gap between the wafer 20 and the substrate 11 formed by the wafer 20 being supported by the convex portion 11P and the annular convex portion 11R of the substrate 11 is formed. Form a flow path for heat transfer gas. For the top surface 11RT of the annular convex portion 11R, which affects the function as a sealing portion, the relationship between the maximum mountain height Rp obtained from the roughness curve of the top surface 11RT and the arithmetic mean roughness Ra is Rp / Ra ≦ 2.8. It is formed to be. It is more preferable that the top surface 11RT of the annular convex portion 11R is formed so that the maximum mountain height Rp of the roughness curve is Rp ≦ 1.5 μm.

Furthermore, the skewness Rsk determined from the roughness curve of the top surface 11RT of the annular projection 11R is Ru Makedea. By adjusting the surface state of the top surface 11RT of the annular convex portion 11R, the amount of gas leak from the contact interface with the wafer can be suppressed. The measurement of skewness Rsk conforms to JIS B0601_2001.

The plurality of convex portions 11P are evenly arranged in the circumferential direction and the radial direction of the substrate 11. For example, the plurality of convex portions 11P are regularly arranged in a grid mode such as a regular triangular apex, a square apex, or another grid mode. That is, the intervals or pitches of the convex portions 11P are formed to be constant. To hold without tilting the wafer, the height of the convex portion 11P, the surface of the top face 11PT of the convex portion 11P is, Ru is formed to be positioned on the top surface 11RT flush with the annular convex portion 11R.

Regarding the height of each convex portion 11P and its top surface 11PT (contact portion with the wafer), for example, if the main purpose is to reduce particles, it is desirable to reduce the area of the top surface 11PT. However, if the area of the top surface 11PT is small, the amount of gas leak may increase. In order to increase the attractive force acting on the gap between the wafer and the electrostatic chuck, it is preferable to set the height of the convex portion 11P low.

Each shape of the convex portion 11P may be a truncated cone such as a truncated cone or a truncated cone, as well as a columnar shape such as a columnar shape or a prismatic shape. Further, the shape of the convex portion 11P may be a columnar or pyramidal shape with a step so that the cross-sectional area of the upper portion of the convex portion 11P is smaller than that of the lower portion. The cross-sectional shape of the annular convex portion 11R may be rectangular, but is also formed to have a trapezoidal shape, a semicircular shape, a semi-elliptical shape, or the like so as to gradually narrow in width toward the upper side. You may.

(Manufacturing method)
The electrostatic chuck 10 is manufactured by, for example, the following procedure.

First, a ceramic sintered body for a ceramic electrostatic chuck is prepared. For example, a substantially disk-shaped molded body is produced from the raw material powder, and the molded body is fired to produce a substantially disk-shaped ceramic sintered body.

The ceramic sintered body can be manufactured by the conventional manufacturing method. For example, a hot press sintering method in which electrodes are embedded, a normal pressure sintering method by a green sheet lamination method, or the like is suitable.

After manufacturing the ceramics sintered body, parallel grinding and outer peripheral grinding are performed on both main surfaces of the ceramics sintered body. After that, the ceramic sintered body is subjected to surface finishing processing on the entire surface of the surface of the electrostatic chuck 10 to be the holding surface (top surface 11RT of the annular convex portion 11R and the top surface 11PT of the convex portion 11P). Grinder or lapping machine so that the relationship between the maximum mountain height Rp obtained from the roughness curve and the arithmetic mean roughness Ra is Rp / Ra ≤ 2.8 with respect to the surface to be the holding surface of the ceramic sintered body. The surface is finished with.

According to the grinder or the lapping machine, the flatness can be maintained and the amplitude distribution curve becomes asymmetric with respect to the average line (that is, the skewness Rsk obtained from the roughness curve is negative). However, for example, a processing method such as sandblasting in which the amplitude distribution curve that causes the abrasive grains to collide is symmetrical (or the skewness Rsk is positive) can be excluded from the surface finishing process.

Next, the annular convex portion 11R and the plurality of convex portions 11P of the electrostatic chuck 10 are formed by an appropriate processing method such as blasting, milling, or machining. For example, a predetermined resist pattern corresponding to the annular convex portion 11R and the plurality of convex portions 11P is formed on the surface of the ceramic sintered body after the surface finishing process, and the non-resist forming portion (exposed portion) is sandblasted. This is done to form the annular convex portion 11R and the plurality of convex portions 11P. After that, the resist is removed.

The electrostatic chuck of the present embodiment having an annular convex portion having a top surface having an Rp / Ra ≦ 2.8 and an arithmetic average roughness Ra of, for example, 1 μm or less (preferably Ra 0.7 μm or less) and a plurality of convex portions. Complete.

The amplitude distribution curve with respect to the average line of the roughness curve of the holding surface (top surface 11RT of the annular convex portion 11R and the top surface 11PT of the plurality of convex portions 11P) of the surface-finished electrostatic chuck of the present embodiment is an average line. Not symmetrical with respect to. That is, the skewness Rsk obtained from the surface roughness curve is negative.

FIG. 3 is a graph showing the relationship between the roughness curve and the amplitude distribution curve of the holding surface of the electrostatic chuck of the embodiment before (a) and after (a) surface finishing.

As shown in FIG. 3A, the roughness curve of the surface (first surface) of the ceramic sintered body before the surface finishing process shows that the arithmetic mean roughness Ra is low, but peaks (maximum) protruding from the surroundings in some places. Mountain height Rp, etc.).

After the surface finishing process, as shown in FIG. 3 (b), the peak (maximum mountain height Rp) becomes a relatively uniform height. After this processing, the maximum peak height Rp itself of the roughness curve becomes small, and the amplitude distribution curve becomes markedly asymmetric with respect to the average line. As a result, the gap δ between the electrostatic chuck and the wafer, which affects the attractive force, becomes small, a large attractive force is exhibited, and good adhesion between the wafer and the electrostatic chuck can be realized. In FIG. 3B, the roughness curve and the amplitude distribution curve before processing are drawn by broken lines.

As described above, in the present embodiment, the state of the top surface 11RT of the annular convex portion 11R is defined by using the maximum peak height Rp of the roughness curve in order to sufficiently exert the attractive force of the electrostatic chuck.

Incidentally, the adsorption force is generally determined by the maximum height Rz (the sum of the maximum peak height Rp of the roughness curve and the maximum valley depth Rv) (JIS B0601_2001).

However, in reality, the inventor of the present invention has found that the height distribution of the roughness curve with respect to the average line (probability density function: amplitude distribution curve), that is, the skewness Rsk is affected by the surface processing of the electrostatic chuck. It was.

Due to the surface processing, the surface of the electrostatic chuck becomes a surface whose height distribution is vertically symmetrical with respect to the average line at Rsk = 0. Further, when Rsk> 0, there are many peaks with thin peaks above the average line, but many peaks and valleys are below the average line. Further, when Rsk <0, there are many narrow valleys below the average line, but many peaks and valleys are above the average line. Since it is actually asymmetric (Rsk> 0 or Rsk <0), there has been a case (Rsk> 0) in which sufficient adsorption force cannot be obtained even if the arithmetic mean roughness Ra and the maximum height Rz are adjusted. Was.

Therefore, in the present embodiment, the suction force is sufficiently exerted by adjusting at least the maximum mountain height Rp of the roughness curve of the top surface of the annular convex portion instead of the maximum height Rz, and the maximum mountain height Rp and the arithmetic are performed. An electrostatic chuck capable of adjusting the amount of gas leak is realized by forming a surface form having a parameter combined with the average roughness Ra.

When a certain relationship (Rp / Ra ≦ 2.8) is established between the maximum peak height Rp of the roughness curve of the top surface of the annular convex portion and the arithmetic mean roughness Ra, the wafer does not cause local peeling or the like. Sufficient adsorption of the annular protrusion is ensured, and the outflow of the heat transfer gas to the chamber can be restricted to a certain level or less.

The maximum peak height Rp of the roughness curve is a parameter directly related to the electrostatic attraction force with the wafer on the annular convex portion. The arithmetic mean roughness Ra is a parameter directly related to the conductance regarding the passage of gas through the gap between the electrostatic chuck and the wafer.

(Electrostatic chuck)
An 8-inch diameter (φ200 mm) Al ₂ O ₃ ceramics sintered body was used as the material of the examples. An electrode was embedded 1000 μm below the surface of the ceramic sintered body in advance. The volume resistivity of the ceramic sintered body was 1 × 10 ¹¹ Ω · cm. The flatness of the surface of the ceramic sintered body was 5 μm.

An annular convex portion having an inner diameter of φ190 mm, an outer diameter of φ192 mm, and a height of 25 μm was formed on the surface (first surface) of the ceramic sintered body. In the region inside the inner diameter of φ190 mm, a plurality of convex portions each having a diameter of φ1 mm and a height of 25 μm were formed on the entire surface in a regular triangular apex arrangement with a distance between pitches of 8 mm.

The measurement conditions for the arithmetic mean roughness Ra were a measurement length of 4 mm and a cutoff of 0.8 mm. The arithmetic mean height Ra of each surface uses a commercially available contact type or non-contact type surface roughness meter, and conforms to JIS standards (JIS B0601_2001, JIS B0633_2001, JIS B0031-200 Annex G, F). It was measured. The maximum mountain height Rp was measured under the same measurement conditions using the same surface roughness meter as the arithmetic mean roughness Ra.

(Processing method)
First, as the first surface processing, in the polishing apparatus, the first surface of the ceramic sintered body was polished with free abrasive grains (GC # 1000).

Then, as the second surface processing, polishing is performed by hand using an abrasive containing a diamond having a particle size of 9 μm, so that the maximum peak height Rp of the finished roughness curve is about 1 to 2 μm, particularly 1 μm or less. I tried to achieve it.

(Comparison example)
In the comparative example, if the second surface processing is not performed and the surface is processed by polishing the free abrasive grains (GC # 1000) in the first surface processing and the arithmetic average roughness Ra is about 1 μm. It is an electrostatic chuck obtained by processing in the same manner as in the embodiment except that the processing is completed.

(Leak evaluation method)
An electrostatic chuck was placed in the vacuum chamber.

A bare silicon wafer was placed on the electrostatic chuck, and a potential difference of 400 V was applied between the electrodes of the electrostatic chuck and the bare silicon wafer to electrostatically attract the electrostatic chuck and the wafer.

Helium gas was supplied at 10 Torr (1333.22 Pa) between the electrostatic chuck and the wafer, and the pressure was controlled by the pressure control valve. A gas leak is made by discharging helium gas from the air passage into the gap between the wafer and the electrostatic chuck to fill it, and then discharging a part of the helium gas from between the wafer and the annular convex portion according to the degree of adhesion between them. The amount was measured.

(result)
The maximum peak height Rp, the arithmetic mean roughness Ra, the ratio of Rp / Ra, and the gas leak amount of the roughness curves of the top surfaces of the annular protrusions of Examples 1 to 4 and Comparative Examples 1 to 3 were measured. The results are shown in the table below and in FIGS. 4 and 5. The maximum peak height Rp, arithmetic mean roughness Ra and Rp / Ra of the roughness curve were measured in each Comparative Example after the first surface processing, and in each Example after the second surface processing.

As a result, the relation of Rp / Ra ≦ 2.8 was established on the top surface of the annular convex portion of Example 1, Rp and Ra were the smallest, and the gas leak amount was the smallest. In Example 2, Ra was larger than that of Comparative Example 1, but Rp was small and the amount of gas leak was small. In Example 3, Ra was larger than that of Comparative Example 2, but Rp was small and the amount of gas leak was small. In Example 4, Ra was large, but Rp / Ra was 2.8 or less, and the amount of gas leak was small.

In Comparative Examples 1 to 3, Ra was smaller than in Examples 2 to 4, but the amount of gas leak was large and could not be used in the process.

FIG. 4 is a graph showing the relationship between Ra and Rp with respect to the amount of gas leak in which the results of Examples 1, 2, 3 and 4 and Comparative Examples 1, 2 and 3 are plotted in this order. As is clear from FIG. 4, it can be seen that the correlation with the gas leak amount is stronger in Rp than in Ra.

FIG. 5 is a graph showing the relationship between the ratio of Rp / Ra to the amount of gas leak in which the results of Examples 1, 2, 3 and 4 and Comparative Examples 1, 2 and 3 are plotted in this order. As is clear from FIG. 5, it can be seen that Rp / Ra has a critical significance at the point of 2.8.

As is clear from the above results, in the examples, the amount of gas leak was small in the range of Rp / Ra ≦ 2.8. On the other hand, in the comparative example, the amount of gas leak was large in the range of Rp / Ra> 2.8. Therefore, the effect of the present invention was confirmed.

10 Electrostatic chuck, 11 substrate, 11P convex, 11R annular convex, 11PT, 11RT top surface, 12 electrode, 20 wafer, Ob first surface.

Claims (2)

A ceramic substrate having a first surface and embedding an electrode, and an annular convex portion having a top surface that projects annularly from the outer peripheral edge portion of the first surface to support a wafer, each of which is surrounded by the annular convex portion. An electrostatic chuck comprising a plurality of convex portions having a top surface that protrudes from the first surface of the substrate and supports the wafer.
At least a top surface of the annular convex portion, Ri surface der the maximum peak height Rp and the arithmetic mean roughness Ra determined from the roughness curve of the top surface of the annular convex portion satisfies the relationship of Rp / Ra ≦ 2.8 , The skewness Rsk obtained from the roughness curve of the top surface of the annular convex portion is negative, and the top surface of the plurality of convex portions is located on the same plane as the top surface of the annular convex portion. Electric chuck. The electrostatic chuck according to claim 1, wherein the maximum mountain height Rp is Rp ≦ 1.5 μm.