JP6510356B2 - Wafer support device - Google Patents

Description

The present invention relates to a wafer support apparatus used in a semiconductor or liquid crystal manufacturing process.

An electrostatic chuck is widely used as an apparatus for fixing a wafer when performing dry etching, PVD (physical vapor deposition) or the like in a process of manufacturing a semiconductor or liquid crystal.

The electrostatic chuck is, for example, as shown in FIG. 2, a conductor electrode 3 for electrostatic chucking on the surface of an insulating base material formed by coating the periphery of a graphite plate 1 with an insulating layer 2 such as PBN (pyrolytic boron nitride). Are arranged in a predetermined pattern, and conductor electrodes 4 for a heater are arranged in a predetermined pattern on the back surface, and these electrodes 3 and 4 are covered with an insulating coating layer 5. Although not shown, both ends of the electrodes 3 and 4 are connected to a power source through terminals.

In the electrostatic chuck having such a configuration, when the wafer 7 is placed on the surface 6 of the insulating film layer 5 and a voltage is applied between the terminals of the electrode 3, a coulomb force is generated and the wafer 7 is electrostatically chucked. Do. In the configuration of FIG. 2, since the heater electrode 4 is provided, the wafer 7 can be chucked while uniformly heating the object 6 to an optimum temperature at which an appropriate chuck suction force is exerted.

FIG. 2 shows a configuration example of the bipolar electrostatic chuck. In the case of a single-pole electrostatic chuck, a configuration in which a single conductor electrode is disposed on an insulating substrate is covered with the insulating coating layer 5, and the chuck electrode 3 and the surface 6 of the insulating coating film 5 The wafer 7 is chucked by applying a voltage between it and 7 placed thereon.

The insulating coating layer 4 in the electrostatic chuck preferably has an electrical resistivity in the range of 10 ⁸ to 10 ¹³ Ω · cm. When the electrical resistivity of the insulating coating layer 5 is in this range, a very weak current is allowed to flow between the electrode and the wafer, and the chuck attraction force is greatly increased by the Johnson-Labeck effect.

From this point of view, the present applicant gives the electrical resistivity in the above-mentioned range by forming the insulating coating layer 4 with C-PBN in which a slight amount of carbon is contained in PBN using CVD (chemical vapor deposition). A method was proposed (Patent Document 1). Specifically, a trace amount of carbon is added by adding a gas (for example, methane) necessary for carbon addition to a reaction gas (for example, boron trichloride + ammonia) for PBN molding, and introducing into a reduced pressure high temperature CVD furnace. The insulating film layer 5 which consists of a PBN molded object to contain can be formed.

Patent No. 2756944

However, although the electrostatic chuck having the insulating film layer 5 formed of PBN (including C-PBN containing a trace amount of carbon, the same applies hereinafter) can generally exhibit satisfactory performance, PBN is crystalline. Because of this, under high temperature use conditions, crystals of PBN are detached from the PBN insulating film layer 5 to generate particles, which adhere to the back surface of the wafer to significantly reduce the product value.

When the inventor conducted an experiment on this point, it was confirmed that a large number of particles were generated on the chuck electrode pattern of the electrostatic chuck. From this, it is presumed that when the wafer 7 directly mounted on the surface 6 of the insulating film layer 5 is adsorbed to the chuck electrode 3, the surface 6 of the soft PBN is scratched to generate particles.

An object of the present invention is to solve the disadvantages of the prior art described above and to provide a wafer support apparatus capable of suppressing the generation of particles. The generation of particles is particularly noticeable during chucking at high temperatures, but a small amount of particles may be generated when chucking at normal temperature or simply bringing the wafer into contact with the PBN surface. It can be recognized as a problem common to wafer support devices in general as well as the electric chuck.

In order to solve the above-mentioned problems, the present inventor has thought that generation of particles can be suppressed by partially coating pyrolytic graphite (PG) harder than PBN on the surface of the PBN insulating coating layer. As a result of repeated experiments and studies based on the present invention was created.

That is, the invention according to claim 1 of the present application has a main body of which at least the surface is PBN or C-PBN, and a convex portion by PG (pyrolytic graphite) partially formed on the main surface. The upper surface of the PG convex portion is a wafer mounting surface.

The invention according to claim 2 of the present application is characterized in that, in the wafer support apparatus according to claim 1, a plurality of PG convex portions are formed at the same height to provide one wafer mounting surface.

The invention according to claim 3 of the present application is characterized in that, in the wafer support apparatus according to claim 2, a plurality of PG convex portions are dotted at intervals.

The invention according to claim 4 of the present application is the wafer support apparatus according to any one of claims 1 to 3, wherein the main body is such that the conductor electrode is disposed on the insulating base material, and the surface of the conductor electrode is PBN or C-PBN. An insulating coating layer is formed and used as an electrostatic chuck.

According to the present invention, since the wafer is placed on the surface of the convex portion made of PG harder than PBN without contacting the surface of PBN (or C-PBN), the generation of particles is significantly reduced. Effectively prevent particles from adhering to the back of the wafer and reducing product value.

Also, instead of coating the entire surface of PGN with PG, the back surface of the wafer is formed by forming PG in the shape of a dot, line, band, grid, etc. as a convex portion that partially covers the surface of PBN. Since the area in contact with the surface (wafer mounting surface) is reduced, the generation of particles is also prevented or suppressed from this point, and the stress due to the thermal expansion coefficient difference between PBN and PG is divided and released to separate PGs. Can be prevented.

1 is a cross-sectional view of an electrostatic chuck according to an embodiment of the present invention. FIG. 1 is a cross-sectional view of an electrostatic chuck according to the prior art.

FIG. 1 is a cross-sectional view showing an example of an electrostatic chuck according to an embodiment of the present invention. In this electrostatic chuck, conductor electrodes 3 for electrostatic chuck are arranged in a predetermined pattern on the surface of an insulating base material formed by covering the periphery of a graphite plate 1 with an insulating layer 2 such as PBN (pyrolytic boron nitride) At the same time, a conductor electrode 4 for the heater is disposed in a predetermined pattern on the back surface, and these electrodes 3 and 4 are covered with the insulating coating layer 5. Although not shown, both ends of the electrodes 3 and 4 are connected to a power source through terminals. The configuration and operation of this electrostatic chuck is basically the same as the electrostatic chuck according to the prior art (FIG. 2) described above.

However, while the electrostatic chuck according to the prior art described above is used by placing the wafer 7 directly on the surface 6 of the PBN insulating film layer 5, in this electrostatic chuck, the surface of the insulating film layer 5 is used. A plurality of projections 8 made of PG (pyrolytic graphite) are formed so as to partially cover them, and the upper surfaces of the projections 8 are formed substantially flush to provide the mounting surface 9 to the wafer 7 There is a big difference in points. With this configuration, the wafer 7 is placed on the chuck surface 9 by the upper surface of the convex portion 8 made of PG harder than PBN without being in contact with the surface 6 of the PBN insulating film layer 5. Also under the conditions of use, the generation of particles can be prevented or greatly reduced.

The present invention will be further described with reference to the following test examples and the examples of the present invention.

The PBN insulating layer 2 of 300 μm in thickness is formed on the surface of a disk-shaped graphite plate 1 of 10 mm in thickness by thermal CVD, and a PG layer of 50 μm in thickness is also formed on both front and back sides similarly by thermal CVD. Were partially removed to form a chuck electrode 3 of a predetermined pattern, and the back side was also partially removed to form a heater electrode 4 of a predetermined pattern. Next, a carbon-doped PBN (C-PBN) insulating coating layer 5 having a thickness of 100 μm is formed to cover the entire surface of the PBN insulating layer 2 having the electrodes 3 and 4 similarly by thermal CVD. Manufactured electrostatic chuck. This electrostatic chuck is one in which the insulating coating layer 5 is formed of C-PBN in the above-described conventional electrostatic chuck (FIG. 2).

The electrostatic chuck of Test Example 2 was manufactured in the same manner as Test Example 1 except that methane gas was not used when forming the insulating coating layer 5. This electrostatic chuck is one in which the insulating coating layer 5 is formed of carbon-free PBN in the above-mentioned electrostatic chuck (FIG. 2) according to the prior art.

After obtaining the electrostatic chuck of Test Example 1, and further forming a PG layer of 5 μm thickness on the surface of the C-PBN insulating film layer 5 by a thermal CVD method, a cylindrical (1 mm diameter) convex portion by PG An electrostatic chuck (invention according to the present invention) having the configuration shown in FIG. 1 was manufactured by partially cutting a number of 8 at a center distance of 3 mm.

With respect to these electrostatic chucks, when the DC voltages of ± 0.25 kV, ± 0.30 kV and ± 0.50 kV were applied, the chuck force for the silicon wafer 7 was measured, and the results shown in Table 1 were obtained.

As demonstrated also in patent document 1, compared with the electrostatic chuck of the test example 2 which has the PBN insulating film layer 5, the electrostatic chuck of the test example 1 which made the insulating film layer 5 C-PBN is a chucking force. There has been a significant increase. In the electrostatic chuck according to the embodiment of the present invention in which a large number of PG convex portions 8 are scattered on the C-PBN insulating film layer 5, the wafer mounting surface 9 is provided by the upper surface of the PG convex portion 8. Compared with the electrostatic chuck of the test example 2 which does not have the convex part 8, it is separated from the chuck electrode 3 by the height (5 μm in this example) of the PG convex part 8, and the chucking force is thereby reduced. It was confirmed that the decrease was slight and that it could exert a chucking force sufficient for practical use.

In the electrostatic chuck of the embodiment of the present invention, the PG convex portion 8 formed on the surface 6 of the insulating coating layer 5 did not peel off thereafter. In order to support the wafer 7 in a noncontact manner on the PBN of the insulating coating layer surface 6 in a non-contact manner, the PG convex portion 8 is formed in a dot shape, a linear shape, a strip shape, or the like as partially covering the insulating coating layer surface 6 However, it is possible to minimize the contact area on the back surface of the wafer and to further suppress the generation of particles by forming the many PG convex portions 8 so as to be dispersed in a mutually independent state as in the above embodiment. It is preferable for enhancing.

Next, with respect to the electrostatic chuck of Test Example 1 and the electrostatic chuck of the embodiment of the present invention, in the case where the wafer is simply mounted without applying a voltage to the electrodes 3 and 4 of the electrostatic chuck at room temperature (room temperature: wo / When the wafer is simply mounted without applying a voltage to the electrodes 3 and 4 of the electrostatic chuck at 500 ° C. (500 ° C .: 500 ° C .: wo / ESC), and the electrodes 3 and 4 of the electrostatic chuck at 500 ° C. When the voltage is applied to chuck the wafer 7 (500.degree. C .: w / ESC) and the number of generated particles is measured for each size under three conditions, the results shown in Table 2 are obtained. That is, when using the electrostatic chuck according to the embodiment of the present invention in which a large number of PG convex portions 8 are scattered on the C-PBN insulating film layer 5, a test in which the wafer is directly mounted on the surface of the C-PBN insulating film layer 5 As compared with the electrostatic chuck of Example 1, the number of particles generated was significantly reduced in each case. When the electrostatic chuck according to the embodiment of the present invention was used as a wafer support apparatus, it was confirmed that the amount of particles generated having a size of more than 20 μm was zero in any case, and the particle generation suppressing effect was significantly improved.

In the above embodiment, PG convex portions 8 having a center distance of 3 mm and a diameter of 1 mm and a height of 5 μm are scattered, but the ratio of the total surface area of PG convex portions 8 to the total surface area of C-PBN insulating coating layer 5 (PG When the wafer 7 is placed on the upper surface 9 of the PG convex portion 8 if the height of the PG convex portion 8 decreases due to the diameter of the convex portion 8 or the distance between the centers of the PG convex portion 8 being too small The back surface contacts the surface of the C-PBN insulating film layer 5 to increase the particle generation amount. On the other hand, if the ratio of the total surface area of the PG convex portion to the total surface area of the insulating coating layer or the height of the PG convex portion 8 is too large, it is impossible to apply a chucking force sufficient for practical use.

Taking into consideration the above, when the center-to-center distance and height of the PG convex portion 8 and the ratio of the total surface area of the PG convex portion / the total surface area of the insulating coating layer were changed variously, the height of the PG convex portion 8 was obtained. In the case where the distance between the centers is 10 mm and the diameter is 1 mm, when the height is 1 μm, the wafer 7 is bent and the back surface of the wafer is in contact with the C-PBN insulating film layer 5, but when the height is 2 μm I did not touch. In addition, it was found that when the height of the PG convex portion 8 is 20 μm, the chucking force is significantly reduced and it is not suitable for practical use.

In addition, when the chucking force was measured by changing the ratio of the total surface area of the PG convex portion / the total surface area of the insulating coating layer, when this surface area ratio was 64%, it was not possible to secure the chucking power that is practical. The chucking force increased as the surface area ratio decreased, and a chucking force of 4.0 g / cm ² (applied voltage ± 0.5 kV) was obtained at 42%. This value is about 190mm in diameter of the electrostatic chuck that adsorbs the wafer 7 of 8 inches (effective area except for the part that can not exert the chucking force such as bolt holes and patterns: about 198 / cm ² ). This corresponds to a chucking force of 792 g, meaning that chucking can be performed with a safety factor of about 16 times the weight of an 8-inch silicon wafer (about 50 g), which is a practically sufficient chucking force.

From these results, in order to prevent the contact of the back surface of the wafer 7 with the surface of the C-PBN insulating coating layer 5 due to the deflection of the wafer 7 to exert the particle generation suppressing effect remarkably and to secure a chucking force sufficient for practical use. (1) The height of the PG convex portion 8 is preferably 2 μm or more and 20 μm or less, and (2) the ratio of the total surface area of the PG convex portion / the total surface area of the insulating coating layer is 42% or less It confirmed that it was preferable. Also, in order to separate and release the stress due to the thermal expansion coefficient difference between PBN and PG to prevent peeling of PG, the size (diameter) of PG convex portion 8 is preferably 5 mm or less, particularly 3 mm or less. Also confirmed.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited thereto, and can be widely modified or changed within the scope of the invention defined in the claims. For example, it is also within the scope of the present invention to deposit a metal carbide such as TaC, SiC, NbC on the PG convex portion 8. In this case, the surface of the metal carbide film on the PG convex portion 8 becomes flush with each other to provide the wafer mounting surface 9. Moreover, it is preferable that the film thickness of the insulation film layer 5 which consists of PBN or C-PBN is 50-300 micrometers, and it is preferable that carbon addition amount is 0 to 10%.

1 Graphite plate 2 Insulating layer 3 Chuck electrode 4 Heater electrode 5 Insulating coating layer (PBN or C-PBN)
6 Insulating Coating Layer Surface 7 Wafer 8 PG Convex Portion 9 Wafer Mounting Surface

Claims (4)

A main body of which at least the surface is made of PBN (pyrolytic boron nitride) or C-PBN (pyrolytic boron nitride containing a trace amount of carbon), and a convex portion by PG (pyrolytic graphite) partially formed on the surface of the main body And the upper surface of the PG convex portion is a wafer mounting surface. The wafer support apparatus according to claim 1, wherein the plurality of PG convex portions are formed at the same height to provide one wafer mounting surface. 3. The wafer support apparatus according to claim 2, wherein the plurality of PG convex portions are spaced apart from each other. The body is characterized in that a conductor electrode is disposed on an insulating base material, and an insulation coating layer made of PBN or C-PBN is formed on the surface of the conductor electrode, and used as an electrostatic chuck. The wafer support apparatus according to any one of 1 to 3.