JP2010186876A - Electrode-plate structure for plasma treatment device, and plasma treatment device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve in-plane uniformity of an etching depth by reducing a temperature difference occurring between the central part and the outer peripheral part of an electrode plate. <P>SOLUTION: An electrode-plate structure 20 is used in a plasma treatment device. The electrode-plate structure comprises: an electrode plate 3 to which a high-frequency voltage is applied; and a cooling plate 14 fixed on the rear face of the electrode plate 3 into a close contact state. The electrode plate 3 is configured such that the thickness t1 of the central part is formed smaller than the thickness t2 of the outer peripheral part. The cooling plate 14 is configured corresponding to the electrode plate 3 such that the thickness of the central part is formed larger than the thickness of the outer peripheral part. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrode plate assembly for a plasma processing apparatus having a through hole through which a plasma generating gas passes, and a plasma processing apparatus including the electrode plate assembly.

 A plasma processing apparatus such as a plasma etching apparatus or a plasma CVD apparatus used in a semiconductor device manufacturing process has, for example, an electrode plate connected to a high frequency power source and a frame placed in a chamber facing each other in a vertical direction, and silicon is placed on the frame. With the wafer placed, plasma is generated by applying a high-frequency voltage from a through-hole formed in the electrode plate toward the silicon wafer, and processing such as etching is performed on the silicon wafer. ing.

The electrode plate used in this plasma processing apparatus is formed into a disk shape by, for example, single crystal silicon, a large number of through holes are formed on the entire surface, and a cooling plate is provided on the back surface.
For example, in Patent Document 1, a cooling plate made of a metal such as aluminum whose surface is anodized is provided on the back surfaces of the inner and outer members made of silicon single crystal. In Patent Document 2, a silicon electrode plate is used. A cooling plate is fastened and fixed to the back surface of the metal plate via a metal film.

JP 2003-332314 A JP-A-11-256370

By the way, in the plasma processing apparatus configured as described above, the diameter of the wafer is increased from 200 mm to 300 mm, and strict process control that does not allow dimensional variations of several nanometers has been required. High in-plane uniformity has become essential for etching.
In order to realize this requirement, it is desirable to keep the temperature at the center and the outer periphery of the electrode plate constant during plasma etching, but at present, there is a variation in the temperature at the center and the outer periphery of these electrode plates, It was an obstacle to ensure in-plane uniformity of etching.

  The present invention has been made in view of such circumstances, and a plasma processing apparatus capable of reducing in-plane uniformity of etching depth by reducing a temperature difference generated between the central portion and the outer peripheral portion of an electrode plate. It is an object of the present invention to provide an electrode plate structure for a plasma and a plasma processing apparatus including the electrode plate structure.

  The electrode plate structure for a plasma processing apparatus of the present invention is an electrode plate structure used in a plasma processing apparatus, and is fixed in close contact with an electrode plate to which a high-frequency voltage is applied and a back surface of the electrode plate. A cooling plate, and the electrode plate is formed such that the thickness of the central portion is smaller than that of the outer peripheral portion, and the thickness of the cooling plate is larger than that of the outer peripheral portion corresponding to the electrode plate. It is characterized by that.

 In this electrode plate structure, the electrode plate is formed such that the thickness of the central portion that is difficult to dissipate is smaller than the outer peripheral portion that easily dissipates heat, and the cooling plate that contacts the central portion is conversely the central portion compared to the outer peripheral portion. Therefore, the heat generated at the central portion of the electrode plate is quickly transmitted to the central portion of the large capacity cooling plate and is released to the outside through the cooling plate. Therefore, the temperature of the electrode plate is uniform from the center to the outer periphery, and the in-plane uniformity of the etching depth can be improved.

In the electrode plate structure for a plasma processing apparatus of the present invention, the back surface of the electrode plate is formed in a concave conical surface, and the front surface of the cooling plate is formed in a convex conical surface corresponding to the conical surface of the electrode plate. It is good to have.
By forming the contact surface between the electrode plate and the cooling plate as a conical surface, the thickness of the electrode plate and the cooling plate is gradually changed, and there is no sudden change in the radial temperature distribution. In-plane uniformity can be further improved.
Moreover, the plasma processing apparatus of this invention attaches the said electrode plate structure.
The difference in thickness between the central portion and the outer peripheral portion of the electrode plate is, for example, about 5 mm for an outer diameter of 300 mm.

 According to the present invention, the thickness of the central portion of the electrode plate is made smaller than that of the outer peripheral portion, and the cooling plate is formed in correspondence with the electrode plate so that the thickness of the central portion is made larger than that of the outer peripheral portion. Heat is quickly transmitted from the central portion of the plate to the central portion of the cooling plate having a large capacity, and is discharged from the cooling plate to the outside. Therefore, the in-plane uniformity of the etching depth can be improved by reducing the temperature difference between the central portion and the outer peripheral portion of the electrode plate.

It is a longitudinal cross-sectional view which shows embodiment of the electrode plate structure for plasma processing apparatuses of this invention, (a) has shown 1st Embodiment, (b) has shown 2nd Embodiment. It is a longitudinal cross-sectional view which shows a plasma etching apparatus as embodiment of the plasma processing apparatus with which the electrode plate structure of this invention is applied. It is a longitudinal cross-sectional view which shows the conventional electrode plate structure.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
First, a plasma etching apparatus will be described as an embodiment of a plasma processing apparatus in which this electrode plate structure is used.
As shown in the schematic cross-sectional view of FIG. 2, the plasma etching apparatus 1 includes an electrode plate 3 provided in the upper part of the vacuum chamber 2, and a gantry 4 that can be moved up and down in the lower part. Are provided in parallel. In this case, the upper electrode plate 3 is supported by an insulator 5 in an insulated state with respect to the wall of the vacuum chamber 2, and an electrostatic chuck 6 is provided on the gantry 4. A wafer 8 is placed together with a support ring 7 on the substrate. Further, an etching gas supply pipe 9 is provided in the upper part of the vacuum chamber 2, and the etching gas sent from the etching gas supply pipe 9 passes through the diffusion member 10 and then passes through the through hole 11 provided in the electrode plate 3. It is configured to flow toward the wafer 8 and to be discharged to the outside from the discharge port 12 on the side of the vacuum chamber 2. On the other hand, a high frequency voltage is applied between the electrode plate 3 and the gantry 4 by a high frequency power source 13.

 The electrode plate 3 is formed in a disc shape having a diameter of, for example, 300 mm using single crystal silicon, columnar crystal silicon, or polycrystalline silicon, and a cooling plate 14 made of aluminum or the like having excellent thermal conductivity is provided on the back surface thereof. The through holes 15 are also formed in the cooling plate 14 at the same pitch as the through holes 11 so as to communicate with the through holes 11 of the electrode plate 3. The electrode plate 3 and the cooling plate 14 constitute an electrode plate structure 20 as will be described later.

In this plasma etching apparatus 1, when an etching gas is supplied by applying a high-frequency voltage from a high-frequency power source 13, the etching gas passes through the diffusion member 10, passes through the through-hole 11 provided in the electrode plate 3, and returns to the electrode plate. 3 is released into the space between the gantry 3 and the gantry 4 and becomes plasma in this space, hits the wafer 8, and the surface of the wafer 8 is etched by sputtering, ie, physical reaction, and chemical reaction of the etching gas. The
Further, for the purpose of uniformly etching the wafer 8, the generated plasma is concentrated on the central portion of the wafer 8, and is prevented from diffusing to the outer peripheral portion, thereby generating a uniform plasma between the electrode plate 3 and the wafer 8. In order to generate it, the plasma generation region 16 is normally surrounded by a shield ring 17.

Next, an embodiment of the electrode plate assembly 20 described above will be described. FIG. 1A shows the first embodiment, and FIG. 1B shows the second embodiment.
In the electrode plate assembly 20 of the first embodiment shown in FIG. 1A, the electrode plate 3 has a thickness (t1) of the central portion C in a range of 100 mm in diameter with respect to an outer diameter of 300 mm, for example. It is formed smaller than the thickness (t2) of the outer peripheral portion D. In this case, the entire front surface of the electrode plate 3 is formed as a flat surface, but the back surface is a circular recess 21 having a flat central portion C. On the other hand, the cooling plate 14 fixed to the back surface of the electrode plate 3 is formed so that the thickness of the central portion C is larger than the outer peripheral portion D contrary to the electrode plate 3. The entire surface is formed as a flat surface, but the front surface corresponds to the shape of the back surface of the electrode plate 3 and the central portion C is a flat circular convex portion 22. Then, in a state where the convex portion 22 on the front surface of the cooling plate 14 is fitted in the concave portion 21 on the rear surface of the electrode plate 3, both are brought into close contact with each other to form the electrode plate structure 20.

Moreover, in the electrode plate structure 25 of 2nd Embodiment shown in FIG.1 (b), the electrode plate 26 is formed so that thickness may become large gradually toward the center from an outer periphery, In this case The front surface is formed as a flat surface as in the first embodiment, and the back surface is formed as a concave conical surface 27 having the center as a vertex. Therefore, the thickness of the electrode plate 26 is the smallest at the center (t1), the largest at the periphery (t2), and gradually increases from the center to the periphery. On the other hand, the entire rear surface of the cooling plate 28 is formed as a flat surface, and the front surface is a convex conical surface 29 having the center as a vertex. Then, in a state where the convex conical surface 29 on the front surface of the cooling plate 28 is fitted to the concave conical surface 27 on the back surface of the electrode plate 26, both are brought into close contact with each other to form the electrode plate structure 25.
In any of the embodiments, the difference in thickness (t2-t1) between the central portion and the outer peripheral portion of the electrode plates 3 and 26 is when the outer diameter is 300 mm and the outer peripheral portion thickness (t2) is 10 mm. 5 mm, and the cooling plates 14 and 28 are formed with a central portion 5 mm thicker than the outer peripheral portion. In the embodiment of FIG. 1, the electrode plates 3 and 26 and the cooling plates 14 and 28 are combined. The total thickness of the structural bodies 20 and 25 is set to the same thickness from the central part to the outer peripheral part.

  By using such electrode plate structures 20 and 25, heat at the center of the electrode plates 3 and 26, which is difficult to dissipate heat, is quickly transmitted to the center of the cooling plates 14 and 28 having a large thickness and a large capacity. The temperature difference between the central portion and the outer peripheral portion of the electrode plates 3 and 26 can be reduced, thereby making the temperature uniform in the surface and improving the in-plane uniformity of the etching depth. Can be made.

Next, an example of such an electrode plate structure will be described together with a conventional comparative example.
In the following description, as shown in FIG. 1A, the electrode plate structure in which “Example 1” is joined in a state where the convex portion 22 of the cooling plate 14 is fitted in the flat circular concave portion 21 of the electrode plate 3. 20, “Example 2” is an electrode plate assembly 25 joined in such a manner that the convex conical surface 29 of the cooling plate 28 is fitted to the concave conical surface 27 of the electrode plate 26 as shown in FIG. The “comparative example” is an electrode plate assembly 31 in which a flat cooling plate 33 is joined to a flat electrode plate 32 as shown in FIG.

<Manufacture of electrode plates>
“Example 1”, “Example 2”, and “Comparative Example” were both produced by the following method. First, a single crystal silicon ingot having an outer diameter of 300 mm was pulled up by the chocolate ski method (CZ method), and this ingot was cut into a 10 mm thickness by a diamond band saw to produce a single crystal silicon disk. In this single crystal silicon disk, pores having an inner diameter of 0.5 mm to be through-holes 11 were formed at a pitch of 8 mm. This drilling process may be either a non-contact process using a laser or a machining process using a diamond drill. The processing area of the pores was in the range of 200 mm in diameter from the center of the disk.
Thereafter, the following processing was performed on the upper surface of the electrode plate thus formed. That is, with respect to the electrode plate 3 of “Example 1”, the central portion is formed in a concave shape with a diameter of 100 mm and a depth of 5 mm (= t1), and a step is formed with respect to the thickness of the outer peripheral portion of 10 mm (= t2). Provided. As for the electrode plate 26 of “Example 2”, as shown in FIG. 1B, the depth of the center is set to 5 mm (that is, the remaining thickness t1 is 5 mm), and gradually from the center toward the periphery. The concave conical surface 27 was processed so as to be shallow, and remained at a thickness of 10 mm (= t2) at the peripheral edge. The processing for forming such a concave portion is performed by a diamond end mill or the like. On the other hand, as for the electrode plate 32 of the “comparative example”, as shown in FIG. 3, a flat disk having a total thickness of 10 mm was used as it was.

<Manufacture of cooling plate>
The aluminum plate was processed into a disk shape by processing to a diameter of 300 mm and a thickness of 25 mm with a lathe. Then, the cooling plate corresponds to the shape of the back surface of each electrode plate, and the cooling plate 14 of “Example 1” has a circular protrusion at the center as shown in FIG. In the cooling plate 28 of “Example 2”, the convex conical surface 29 having the center at the apex was formed as shown in FIG. As the cooling plate 33 of “Comparative Example”, as shown in FIG. 3, a disk-shaped aluminum plate processed by a lathe was used as it was.
In addition, on each cooling plate, pores with an inner diameter of 3 mm that became the through holes 15 were formed by drilling at the same positions as the through holes 11 of the electrode plate, and then the surface was anodized.

 Then, the electrode plates produced as described above and the corresponding cooling plates are screwed to form the electrode plate structures 20, 25, 31 shown in FIGS. 1 (a), 1 (b) and FIG. . Each electrode plate assembly was set so that the total thickness of the electrode plate and the cooling plate (the whole including the central portion and the outer peripheral portion) was 35 mm.

Next, the attaching this way each electrode plate structure body obtained in the plasma etching apparatus as shown in FIG. 2, mounted to face the wafer outer diameter 200mm that SiO ₂ layer was formed in advance by CVD, An etching test was performed under the following conditions.
Pressure in chamber: 10 ⁻¹ Torr (13.33 Pa)
Etching gas composition: 90 sccm CHF ₃ +4 sccm O ₂ +150 sccm He
High frequency power: 2kW
Frequency: 20kHz
Note that sccm is an abbreviation for standard cc / min and refers to a flow rate (cc) per minute normalized at a constant temperature such as 0 ° C. or 25 ° C. at 1 atm (atmospheric pressure 1013 hPa).

Under such conditions, plasma etching of the SiO ₂ layer on the wafer surface is performed, and the surface temperature of the electrode plate is measured every 5 seconds after power charging, and the wafer surface at the time when a predetermined time has elapsed from the start of etching. The maximum etching depth (= A) and the minimum etching depth (= B) of each SiO ₂ layer were measured. A value of (A−B) / A × 100 (%) was obtained from the measured values of the etching depth, and the etching uniformity of the wafer surface was evaluated. Table 1 shows the transition of the surface temperature depending on the etching elapsed time, and Table 2 shows the etching uniformity.

According to the results of Table 1, the temperature of any electrode plate assembly increases as the power charge time elapses. In Example 1 and Example 2, even if the temperature difference between the central part and the outer peripheral part is maximum. In contrast to the temperature of 8 ° C., in the comparative example, a large temperature difference of 115 ° C. occurred after 40 seconds, and in both examples, it was confirmed that the temperature difference was kept small.
The etching depth of the SiO ₂ layer of such a wafer surface is also deepest small ones of the difference of the depth of the etched portion and the shallowest etched portions embodiment, a comparative example the uniformity of etching It was confirmed that there was an improvement.

  As described above, according to the electrode plate structure for a plasma processing apparatus of the present embodiment, the thickness of the central portion of the electrode plate is made smaller than that of the outer peripheral portion, and the thickness of the central portion of the cooling plate corresponding to the electrode plate is set. By making the thickness larger than the outer peripheral part, the heat generated at the center part of the electrode plate can be quickly absorbed at the center part of the thick and large capacity cooling plate and radiated to the outside. The temperature difference between the central portion and the outer peripheral portion can be reduced, the entire temperature can be made uniform, and the in-plane uniformity of the etching depth can be improved.

In addition, this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.
For example, in each embodiment, the thickness of the central portion of the electrode plate is 5 mm and the outer peripheral portion is 10 mm. However, the dimensions are not limited to this. However, it is preferable that the thickness of the thinnest part of the central part be 3 mm or more in order to prevent the plasma from wrapping around the back part of the electrode plate.
In addition, although the total thickness of the electrode plate and the cooling plate is set to be constant, the total thickness of each portion may be adjusted, for example, by making the central portion of the cooling plate thicker.
Furthermore, in the electrode plate shown in FIG. 1A, a step portion of 90 ° is formed between the central portion and the outer peripheral portion, but the step portion may be formed in a tapered shape. Further, a plurality of step portions may be provided concentrically so that the thickness changes stepwise.

DESCRIPTION OF SYMBOLS 1 Plasma etching apparatus 2 Vacuum chamber 3 Electrode plate 11 Through-hole 13 High frequency power supply 14 Cooling plate 15 Through-hole 20 Electrode plate structure 21 Recess 22 Convex part 25 Electrode plate structure 26 Electrode plate 27 Conical surface 28 Cooling plate 29 Conical surface

Claims (3)

An electrode plate structure used in a plasma processing apparatus,
The electrode plate is composed of an electrode plate to which a high-frequency voltage is applied and a cooling plate fixed in close contact with the back surface of the electrode plate, and the electrode plate is formed with a central portion smaller than the outer peripheral portion, and the cooling plate Is an electrode plate structure for a plasma processing apparatus, wherein the thickness of the central portion is larger than that of the outer peripheral portion corresponding to the electrode plate.   2. The plasma according to claim 1, wherein the back surface of the electrode plate is formed in a concave conical surface, and the front surface of the cooling plate is formed in a convex conical surface corresponding to the conical surface of the electrode plate. An electrode plate assembly for a processing apparatus. A plasma processing apparatus to which the electrode plate structure according to claim 1 or 2 is attached.

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