JP3447305B2 - Electrostatic chuck - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a ceramic electrostatic chuck used for fixing and transporting a silicon wafer or the like in a semiconductor manufacturing apparatus or the like. . 2. Description of the Related Art When processing a wafer such as silicon in a semiconductor manufacturing apparatus, it is necessary to fix the wafer.
As the fixing method, various methods such as a mechanical clamp, a vacuum chuck, and a resin electrostatic chuck have been used, but each has the following advantages and disadvantages. First, the mechanical clamp has the advantage that there is no fear of leakage current because it does not employ an electrical attraction method, and that there is no problem of contamination caused by the clamp member if made of high-purity alumina. However, there is a drawback that the entire surface cannot be uniformly pressed because only the outer periphery of the wafer processing surface is pressed, and the processing yield is reduced because the processing surface is pressed. [0004] Next, the vacuum chuck has a drawback that uneven suction is generated because it is not suction of the entire surface. In addition, many semiconductor manufacturing processes are performed in a high vacuum (10 ⁻³ Torr or less), and it is often difficult to use a vacuum chuck that utilizes a vacuum suction force. [0005] The resin-made electrostatic chuck has abrasion resistance,
Due to low heat resistance and the like, there are problems such as not only a short life but also difficulty in realizing flatness and parallelism of a processing surface required when performing wafer processing. Furthermore, a high voltage must be applied in order to obtain a practical suction force, which may adversely affect the chip after processing. Therefore, in recent years, a ceramic electrostatic chuck excellent in corrosion resistance, wear resistance, accuracy, and the like has been used. As the ceramics, those containing TiO ₂ as a main component of Al ₂ O ₃ (Japanese Patent Application Laid-Open No. Sho 62-62)
No. 264638) and as already proposed by the present applicant (see Japanese Patent Application No. 2-339325), CaTiO
₃ , ferroelectric ceramics such as BaTiO ₃ have been used. [0007] However, the above-mentioned TiO
_The electrostatic chuck made of alumina ceramics containing ₂ has a volume resistivity of about 10 ¹¹ Ω · cm,
The suction force is obtained by a minute leakage current.
Since a leakage current of about A flows, a circuit formed on a silicon wafer may be broken. Further, an electrostatic chuck using ferroelectric ceramics has disadvantages that mechanical strength is low, processing accuracy is difficult to obtain, and adsorption characteristics are not constant in a reducing atmosphere, so that it cannot be used. In view of the above, the present invention provides a ceramic plate to which the content of AlN as a main component is 99% by weight or more and to which carbon is added, an internal electrode, and an object is adsorbed on the surface of the ceramic plate. Surface roughness (Rmax) for
An electrostatic chuck is formed by forming a suction surface of 0.8 s or less and obtaining a suction force by a minute leakage current. According to the present invention, since the base material and the insulating film constituting the electrostatic chuck are made of aluminum nitride, the leakage current is extremely small and the mechanical strength is excellent.
It is possible to solve the above-mentioned problem of the ceramic electrostatic chuck. Further, aluminum nitride has excellent heat radiation properties and is suitably used for an electrostatic chuck used in an etcher or the like. The elements constituting the electrostatic chuck of the present invention include aluminum (Al) and nitrogen (N), and all of these elements adversely affect a wafer such as silicon even when used in a semiconductor device. There is no pollution problem. Embodiments of the present invention will be described below. As shown in FIGS. 1 and 2, the electrostatic chuck of the present invention comprises a ceramic plate 1 made of nitride ceramics, an internal electrode 2, and a base plate 4 made of a bonding agent 3.
It is fixed to. An electrode extraction portion 4a for supplying a current to the internal electrode 2 is formed on the base plate 4. By applying a voltage from a power source 7 between the internal electrode 2 and the object 6 through the electrode extraction portion 4a. Then, a minute current flows through the ceramic plate-like body 1, and the object 6 can be adsorbed on the adsorption surface 1a by the Johnson-Rahbek force. Although a monopolar electrostatic chuck is shown in this embodiment, a plurality of internal electrodes 2 may be formed, and a voltage may be applied between the internal electrodes 2 to form a bipolar electrostatic chuck. The nitride ceramic forming the ceramic plate 1 is mainly composed of AlN,
₂ O _3, Er ₂ O ₃ used, such as aluminum nitride ceramics containing sintering aids such as. Further, in order not to adversely affect the object 6 to be adsorbed such as a silicon wafer, the content of AlN, which is the main component in the nitride ceramics, is set to 99% by weight or more, and other components such as the sintering aid are 1%.
% By weight or less. Further, the suction surface 1a of the ceramic plate 1 is a smooth surface having a surface roughness (Rmax) of 0.8 s or less, and therefore, an excellent suction force can be obtained. The electrostatic chuck according to the present invention obtains an attraction force by a Johnson-Rahbek force due to a minute leakage current in the ceramic plate 1. The volume resistivity value of the state body 1 is important. In view of this, as a result of various experiments, the volume resistivity of the ceramic plate 1 was 10 ¹¹ Ω · c.
If it is smaller than m, the leakage current may be too large and the circuit formed on the silicon wafer may be destroyed. Conversely, if the volume specific resistance is larger than 10 ¹⁵ Ω · cm, it is not possible to obtain a necessary attraction force. Therefore, the volume resistivity value of the ceramic plate 1 is preferably set to 10 ¹¹ to 10 ¹⁵ Ω · cm, preferably 10 ¹² to 10 ¹⁴ Ω · cm. It had sufficient adsorption power for practical use. For example of the electrostatic chuck made of a material having a three volume resistivity in Figure 3, the applied voltage and to indicate the relationship between the attractive force, the volume resistivity 10 ¹² ~10 ¹⁴ Ω ·
cm, it was possible to obtain practically sufficient adsorption power. Further, in order to obtain the above-mentioned volume resistivity of the ceramic plate 1 of the present invention, carbon (C), which is a conductive substance, is added to the aluminum nitride ceramic so that the volume resistivity is preferably adjusted. Adjust to a suitable range. Then, these ceramic raw materials are formed into a plate shape by a tape forming method, a dry press forming method, an isostatic press forming method, or the like, and an inner plate made of silver (Ag), palladium (Pd), platinum (Pt), or the like is formed. After the electrodes 2 are formed, the plate-shaped molded bodies are laminated and integrally fired to form the internal electrodes 2.
Can be obtained. Further, after firing the above-mentioned sheet-shaped ceramic molded body, Ti
It is also possible to join using an active metal made of a base alloy and use this active metal layer as the internal electrode 2. Further, it is not always necessary to embed the internal electrode 2 in the ceramic plate 1, and although not shown, the internal electrode 2 is formed on the surface of the ceramic plate 1 on the side opposite to the suction surface 1 a. It is also possible to fix the base plate 4 via the bonding agent 3 thereon. As the bonding agent 3, an adhesive, glass, silicone resin or the like is used. The base plate 4 is made of a metal material such as aluminum or a ceramic material such as alumina or forsterite. Experimental Example 1 As an example of the present invention, an electrostatic chuck shown in FIGS. 1 and 2 was experimentally manufactured. 99% by weight of S as the ceramic plate 1
A ceramic raw material comprising i ₃ N ₄ and a total of 1% by weight of Y ₂ O ₃ and Al ₂ O ₃ was formed into a plate by a dry press, and this plate was fired in a nitrogen atmosphere (Comparative Example 1). And hot isostatic pressing (HIP) (Comparative Example 2) were prepared. The obtained fired body was bonded with an active metal made of a Ti-based alloy, and this active metal layer was used as an internal electrode 2. Also, 99.5% by weight of Al
N and a ceramic material composed of 0.5% by weight of C are formed into a plate by a dry press, and Ag-Pd is formed on the plate-shaped formed body.
An internal electrode 2 was formed, and another plate-like molded body was laminated and fired and integrated (Example). Further, as Comparative Example 3, a ceramic plate 1 made of ferroelectric ceramics containing calcium titanate (CaTiO ₃ ) as a main component was prepared. In each case, the size was 150 mm in diameter, the distance between the internal electrode 2 and the suction surface 1a was 300 μm, and the suction surface 1a was lapped to have a surface roughness (Ra) of 0.2 μm. As shown in Table 1, the properties of the above various ceramic materials indicate that the nitride ceramics of the present invention have excellent properties such as strength and hardness. In particular, in Examples 1 and 2 using silicon nitride ceramics, it is understood that chipping or the like hardly occurs due to high strength and can be used for a long time. [Table 1] An attraction force test was performed using the electrostatic chucks of the above example and comparative examples 1 and 2. As the conditions, the applied voltage is 0 to 2 kV, the degree of vacuum is 10 ⁻³ Torr, and the temperature is 24 ° C.
And As shown in FIG. 4, the results were all 100 g /
It was possible to obtain an adsorbing force of at least ² cm ² and there was no practical problem. EXPERIMENTAL EXAMPLE 2 Next, the electrostatic chucks of Comparative Examples 2, 3 and Example were tested to determine the attraction force in a nitrogen atmosphere.
Conditions are: applied voltage 1 kV, degree of vacuum 10 ^-2 torr, temperature 15
0 ° C. Fig. 5 shows the relationship between nitrogen concentration and adsorption power.
Shown in From this result, it can be seen that, in Comparative Example 3, as the nitrogen concentration increases, the adsorptive power decreases drastically. This is because, in an active nitrogen atmosphere, the surface resistance of the ferroelectric ceramics decreases, so that a current flows on the surface and the function of the electrostatic chuck itself is lost. On the other hand, in the example using the nitride ceramics and the comparative example 2, such a phenomenon did not occur, and a stable adsorption force was exhibited. Further, when the electrostatic chucks of the above embodiment and comparative example 2 were operated in a single pole and the current flowing between the object 6 and the internal electrode 2 was measured, this leakage current was several tens to It was confirmed that the current value was several μA, which was not a problematic level. EXPERIMENTAL EXAMPLE 3 Next, an experiment was conducted on the heat dissipation of the electrostatic chuck of the example using aluminum nitride and the electrostatic chuck of Comparative Example 3. The upper surface of the object 6 is heated to about 200 ° C. by a light heat source, and the object 6 is adsorbed by an electrostatic chuck.
The temperature rise on the back surface of the electrostatic chuck was measured. The conditions were an applied voltage of 1 KV and a degree of vacuum of 10 ⁻² Torr. As a result, in Comparative Example 3, the steady temperature state on the back surface was about 100 ° C., whereas in the example, the back surface temperature was raised to about 160 ° C. Therefore, the electrostatic chuck using aluminum nitride has good heat dissipation, and is particularly suitable for an electrostatic chuck for an etcher. As described above, according to the present invention, the content of AlN, which is the main component, is set to 99% by weight or more, and the ceramic plate to which carbon is added is provided with the internal electrode, By forming an adsorption surface having a surface roughness (Rmax) of 0.8 s or less for adsorbing an object on the surface of the plate-like body and obtaining an adsorption force by a minute leakage current, an electrostatic chuck is configured. It is possible to obtain a ceramic electrostatic chuck having features such as extremely low leakage current, excellent mechanical strength, stable adsorption power in a reducing atmosphere, and low contamination of an object to be adsorbed such as a silicon wafer. . Further, aluminum nitride is excellent in heat dissipation, so that it is preferably used as an electrostatic chuck used in an etcher or the like.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an electrostatic chuck of the present invention. FIG. 2 is a longitudinal sectional view showing the electrostatic chuck of the present invention. FIG. 3 is a graph showing a relationship between an applied voltage and an attraction force in the electrostatic chuck of the present invention. FIG. 4 is a graph showing a relationship between an applied voltage and an attraction force in the electrostatic chuck of the present invention. FIG. 5 shows the electrostatic chucks of the present invention and a comparative example.
It is a graph which shows the relationship between nitrogen concentration and adsorption power. [Description of Signs] 1 ... Ceramic plate 1a ... Adsorption surface 2 ... Internal electrode 3 ... Binder 4 ... Base plate 6 ... Adsorbed object 7 ... Power supply

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-63-95644 (JP, A) JP-A-62-286247 (JP, A) JP-A-5-13558 (JP, A) JP-A-5-558 13555 (JP, A) JP-A-4-304941 (JP, A) JP-A-4-34953 (JP, A) JP-A-3-183151 (JP, A) JP-A-4-304942 (JP, A) Toshiya Watanabe, Characteristics and Application of Ceramic Electrostatic Chuck, Applied Mechanical Engineering, Japan, May 1989, P129 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/68 B65G 49/06 -49/07 H02N 13/00 B23Q 3/15 C04B 35/581 C04B 35/626

Claims (1)

(57) [Claims 1] The content of AlN as a main component is 99% by weight.
As described above, the ceramic plate to which carbon is added is provided with an internal electrode, and an adsorption surface having a surface roughness (Rmax) of 0.8 s or less for adsorbing an object is formed on the surface of the ceramic plate, An electrostatic chuck characterized in that a suction force is obtained by a minute leakage current.