Method of holding substrate and substrate holding system

#The present invention relates to a method of holding a substrate and a substrate holding system to hold a substrate securely during a production process for treating the substrate, such as semiconductor device, while it is being cooled.

#Among substrate treating apparatuses for production of semiconductor devices, there are a lot of substrate treating apparatuses requiring the cooling substrates, such as a plasma treatment apparatus, a sputtering apparatus, a dry etching apparatus, a CVD (chemical vapor deposition) apparatus and a high energy ion implantation apparatus. Since the treating environment in these apparatuses is generally a vacuum, it is difficult to cool a substrate by bringing it into contact with a cooling surface, as in atmospheric pressure, because of the decrease in thermal conductivity which occurs in a vacuum. Although there is abundant literature concerning thermal conductivity in a vacuum (rarefied gas), the amount of heat transferred by contact is small because of the small real contact area when surfaces come into contact with each other. Especially in heat transfer between a substrate and a cooling surface, it is difficult to strongly press the substrate against the cooling surface since there is a possibility to damage the substrate. Therefore, various ideas, such as placing a soft elastomer on the surface contacting the substrate, have been proposed. However, in recent years, it has been more conventional for a gas to be introduced between the substrate and a cooling surface to cool the substrate using the gas as a coolant, when the heat load in the substrate increases or a requirement to cool the substrate to lower the temperature thereof arises.

#There are various types of gas cooled substrate holding systems. They can be roughly categorized as follows: (1) a gas cooling type system where the back surface of a substrate and a cooling surface contact each other and a gas is introduced into the gap between the surfaces formed by the surface roughness, and (2) a gas cooling type system where the back surface of a substrate and a cooling surface do not contact each other and a gas is introduced into the gap between the surfaces.

#FIG. 1 is a vertical cross-sectional view showing an outline of a substrate treatment apparatus to which a substrate holding system in accordance with the present invention is applied.

#FIG. 2 is a vertical cross-sectional view showing an embodiment of the substrate holding system in FIG. 1.

#FIG. 3 is a vertical cross-sectional view showing another form of the substrate holding system to be used in the apparatus of FIG. 1.

#As a first embodiment according to the present invention, FIG. 1 shows substrate treatment apparatus employing an electrostatic adhering circuit for fixing a substrate 1 to a substrate holding system 9. In FIG. 1, a microwave plasma etching apparatus is used for treating the substrate 1. A substrate holding system 9 mounting the substrate 1 is placed in an etching chamber 10. The etching chamber 10 is exhausted using a vacuum pump 11, and a gas for etching is supplied from a gas supply unit. The substrate holding system 9 is connected to a high frequency power source 12 and a direct current power source 13. Microwave energy is introduced into the etching chamber 10 from a quartz glass window 15 through a waveguide 14. When the high frequency power source 12 is switched into operation or the microwave is introduced, a plasma 16 is produced in the etching chamber 10. At that time, an electrostatic adhering circuit 17 is formed by the potential of the direct current power source 13 through the substrate holding system 9, the substrate 1, and the plasma 16. In this state, the substrate 1 is fixed to the substrate holding system 9, that is, fixed by the electrostatic force produced in the substrate holding system 9.

#FIG. 2 shows a cross-section of the substrate holding system 9 in FIG. 1. A substrate 1 is mounted on protruding portions 3 and 20 of a holding member 2 for holding the substrate, the protruding portion 3 of the holding member 2 being connected in the electrostatic adhering circuit 17, the substrate 1 being fixed to the holding member 2 at the portions 3 and 20. A flow passage for supplying a coolant 4 is provided in the holding member 2 to cool the substrate 1. The coolant is supplied from a supplying unit to an inlet portion 5, schematically illustrated, and flows out from an outlet portion 6 to control the temperature of the holding member 2. Further, a flow passage for a cooling gas 7 is provided in the center of the holding member 2 to supply and exhaust the cooling gas 7. The temperature control of the substrate 1 is attained by the cooling gas 7 which flows into the indented portion 8 of the holding member 2 so as to perform a heat transfer between the holding member 2 and the substrate 1. The electrostatic adhering force is generated by a dielectric material 18 attached to or formed on the surface of the holding member 2.

#Aluminum oxide, or mixture of aluminum oxide added to titanium oxide, may be used as the dielectric material 18. A voltage of several hundred volts is applied to the holding member as a direct current voltage for generating the electrostatic force. Therewith, the substrate is electrostatically fixed to the protruding portion 3 of the holding member 2 shown in FIG. 2. The electric potential for electrostatic adhering is applied from the direct current power source 13, the potential being uniform over the holding member 2, over the protruding portion 3 and over the outer periphery of the substrate 1. Therefore, the potential difference produced over the surface of the substrate 1 is caused by the distribution of electrons or ions irradiated on the substrate 1, and is not so high that the potential difference may cause damage to the substrate 1. On the other hand, in a method where positive and negative electric poles are formed in the holding member 2 to cause the substrate to adhere electrostatically with the electric poles, there is a possibility that a high voltage difference in the substrate 1 will give rise to damage to the substrate.