Support table for plate-like body and processing apparatus using the table

Abstract: A wafer support table (20) is provided in a vacuum chamber (10) of a magnetron plasma etching apparatus. This support table (20) includes a first member (22) having a mechanism (23, 23a, 23b) for adjusting the temperature of a wafer (1), a second member (21) having an electrostatic chuck (24) for supporting the wafer (1) on its upper surface, and a gas supply mechanism (25, 25a) for supplying a gas between the first and second members (22, 21).

Description: The present invention relates (1) to a processing apparatus for performing a predetermined processing for an object to be processed in a vacuum atmosphere, relates (2) to a support table apparatus for supporting an object for processing same in a processing apparatus in a vacuum atmosphere, and (3) relates to a process for controlling the temperature of an object supported on a split type support table in a vacuum processing chamber. Document JP-A-59-170 268 discloses a solution for a problem which occurred when a target is soldered to the upper surface of a water-cooled backing plate. Firstly, at the high current density usually employed for sputtering, the solder between the target and the backing plate tends to be melted. Secondly, the target has to be replaced periodically, since it provides the material to be sputtered and is eventually consumed. This requires a considerable amount of labor when the target is soldered to the water-backing plate. For solving these problems, it is suggested that the target should be screw-fastened to the backing plate, such that no solder is provided, and that a small clearance is provided between the target and the backing plate, and a gas of reduced pressure is supplied into this small clearance for cooling. The clearance should be larger than the mean free parts of the gas sealed in the clearance, and for example for helium gas at a pressure of 10 Torr the mean free part is approximately 10 µm, resulting in that the width of the clearance should be 10 µm at least. The target has a stepped portion at its periphery where screws for fastening the target to the backing plate are provided, and the screws are made of materials like Ta or Nb which are not likely to be sputtered. Nb and Ta are bad heat conductors since they have a rather low thermal conductivity. For facilitating to understand the subject matter according to the present invention, the technical background thereof will be briefly described hereinafter. In a plasma etching apparatus, a support table called a "susceptor" is used to support a wafer. Since the temperature of the wafer is increased by a plasma during etching, the susceptor incorporates a temperature adjusting mechanism for cooling the wafer at predetermined temperature. The susceptor acts as lower electrode of the plasma etching apparatus. In recent years, since the diameters of wafers become large and the diameters of wafers are increased in accordance with increasing bypass of wafers, susceptors corresponding to the respective wafer sizes must be provided. Published Unexamined Japanese Patent Application No. 59-115521 discloses an apparatus which can use susceptors corresponding to various types of wafers. In addition, since a damage is caused on the surface of a wafer support table for use in, for example, plasma etching, the support table must be replaced as consumable. If the support table has, e.g., for example, an electrostatic chuck sheet, the electrostatic chuck must also be replaced. For the above reasons, a demand has arisen for a support table which can be split into two members or portions, that is, a stationary portion and a removable portion so that replacement can be performed by only removing the removable portion in accordance with the size of a wafer or when the surface is damaged. That is, when the support table is split into two portions, while the stationary portion having a temperature adjusting function is constantly set, a plurality of types of removable portions can be prepared in accordance with the sizes of wafers, thereby processing wafers of various sizes. In addition, since only the removable portion need be removed in the replacement of the support table surface or the electrostatic chuck, the replacement can be easily performed. When the above split structure is adopted in the support table, however, since the removable portion and the stationary portion are always joined with each other with a gap formed therebetween or dust sandwiched therebetween, the heat conduction characteristic between the stationary and removable portions is degraded. Therefore, the temperature of an object to be processed cannot be efficiently adjusted. Especially when the support table is used in a vacuum processing apparatus such as an etching apparatus, a portion defined between the stationary and removable portions is in a vacuum state. Therefore, no heat conduction is caused by a gas, but only solid contact heat conduction near bolt-fastened portions between the two portions can be expected. In this case, since the bolt connection portion is present in a peripheral portion of the support table, no effective heat conduction can be expected in the central portion of the table. Therefore, it is very difficult to perform a uniform temperature adjustment of a wafer. The present invention has been made in consideration of the above situation and has as its object to provide a split-type support table for plate-like objects, which can effectively adjust the temperature of an object to be processed supported thereon. It is another object of the present invention to provide a vacuum processing apparatus using the support apparatus. It is still another object to provide a process for controlling the temperature of an object supported on a split type support table. The present invention provides a support table apparatus according to claim 8. In addition, the present invention provides a processing apparatus for performing a predetermined processing for an object to be processed in a vacuum atmosphere according to claim 1. Further, the present invention provides a process for controlling the temperature of an object supported on a split type support table in a vacuum chamber according to claim 19. Preferred embodiments of the invention are indicated in the dependent claims. According to the present invention the support table or electrode is of the split type, and a gas can be supplied between the first and second members. Therefore, since heat conduction between the two members can be efficiently performed by the gas, the temperature can be controlled with high precision. This invention can be more fully understood from the following detailed description when taken in conjunction with the accompanying drawings, in which: Fig. 1 is a schematic view showing an arrangement of a magnetron plasma etching apparatus using a support table according to an embodiment of the present invention; Fig. 2 is a sectional view showing the support table used in the apparatus shown in Fig. 1 in detail; Fig. 3 is a sectional view showing an electrostatic chuck for supporting a wafer for use in the support table of the apparatus shown in Fig. 1; Fig. 4 is a schematic view showing a mechanism for controlling the pressure of a heat conduction gas; and Fig. 5 is a graph for explaining an effect of the heat conduction gas. An embodiment in which the present invention is applied to a support table of an electrostatic chuck type for use in a plasma etching apparatus will be described below. Fig. 1 is a schematic view showing an arrangement of a magnetron plasma etching apparatus using a support table according to the embodiment of the present invention. This apparatus comprises a vacuum chamber 10, an upper wall of which acts as a second electrode, a support table 20, acting as a first electrode, for supporting a wafer 1 provided in the chamber 10, a magnet section 30 above the chamber 10, and an RF power supply 40. The vacuum chamber 10 has upper and lower chambers 11 and 12. An exhaust port 13 is formed in the lower side wall of the upper chamber 11, and the vacuum chamber 10 is evacuated by an exhaust pump (not shown) connected to the exhaust port 13. The apparatus is designed so that the vacuum chamber 10 is evacuated to about 10 -6 Torr (1 Torr = 133,3 Pa). A plurality of gas inlet ports 14 for supplying an etching gas are formed in the upper wall of the upper chamber 11. A gas supply pipe 14a for supplying the etching gas from a gas supply source (not shown) is connected to the inlet ports 14. Since the support table 20 is arranged on the lower chamber 12 via an electrically insulating ceramic member 15, the lower chamber 12 and the support table 20 are electrically insulated from each other. The support table 20 has an upper member 21 having a wafer support portion and a lower member 22 including a liquid passage 23 for performing temperature adjustment for a wafer. The structure of the support table 20 will be described in detail later. The RF power source 40 is connected to the upper member 21 of the support table 20, and the upper chamber 11 is grounded. Therefore, when RF power is supplied to between the supporting table 20 and the chamber 10, the upper wall of the upper chamber 11 acts as an upper electrode, and the upper member 21 acts as a lower electrode, thereby generating a plasma therebetween. The magnet section 30 applies a magnetic field between the electrodes in the direction perpendicular to the electric field therebetween. The section 30 has a horizontally set support member 31, a permanent magnet 32 supported by the support member 31, and a motor 33 for rotating these members in a direction indicated by an arrow in Fig. 1. In the magnetron plasma etching apparatus having the above arrangement, an etching gas is supplied to the chamber 10, and RF power is applied between the upper and lower electrodes, while a magnetic field is applied between the electrodes by the rotating permanent magnet 32. Therefore, electrons present between the electrodes perform cyclone motion to collide against molecules by crossed fields, thereby increasing the number of times of ionization of the molecules. As a result, a high etching rate of 1 pm/min. can be obtained even at a comparatively low pressure of 10 -2 to 10 -3 Torr. Therefore, processing can be completed within a short time period per wafer and reliability of etching is improved. In addition, since the average energy of ions is decreased, a wafer is damaged less. The support table 20 for a wafer as an object to be processed will be described in detail below. Fig. 2 is a sectional view showing the support table 20 in detail. The support table 20 has the upper and lower members 21 and 22 as described above, and an electrostatic chuck 24 for chucking a wafer by an electrostatic force (Coulomb force) is arranged on the upper surface of the upper member 21. The chuck 24 generates electrostatic chucking force when treatment of the wafer 1 is conducted via a plasma by plasma generation. While the lower member 22 is stationary, the upper member 21 and the electrostatic chuck 24 are replaceable. The upper member 21 is a disk member having a step portion on its peripheral portion, and the lower member 22 is a simple disk member. Bolt insertion holes 28 are formed with equal intervals therebetween in the peripheral portion of the upper member 21 along its circumference. Screw holes 28a are formed in the lower member 22 at positions corresponding to the bolt insertion holes 28. Bolts 29 are inserted in the insertion holes 28 to fasten the upper member 21 on the lower member 22. By removing the bolts 29, the upper member 21 can be removed from the lower member 22. As shown in Fig. 3, the electrostatic chuck 24 is constituted by two insulating sheets (for example, polyimide sheets) 24a and 24b and an electrically conductive sheet 24c formed between the insulating sheets 24a and 24b and consisting of, for example, copper. After the wafer 1 is mounted on the electrostatic chuck 24, a high voltage is applied between the wafer 1 and the electrically conductive sheet 24c from a power suply (not shown) via a plasma, thereby chucking the wafer 1 by Coulomb force. The upper member 21 and the wafer are electrically insulated from each other by the electrostatic chuck 24. The lower member 22 has the annular liquid passage 23 as described above, and liquid inlet and outlet passages 23a and 23b are connected to the liquid passage 23. The temperature of the wafer 1 is adjusted by supplying a liquid at a predetermined temperature to the liquid passage 23 at a proper flow rate. The temperature of the liquid is arbitrarily set in accordance with the type of wafer to be processed. That is, if it is difficult to perform a predetermined etching because an unnecessary reaction except for an etching chemical reaction is caused by the heat of a plasma during the etching operation, a cooling medium such as an anti-freeze at a temperature of, e.g., -25°C is circulated in the liquid passage 23 to hold the wafer temperature at about -15°C. On the other hand, a preferable temperature of the wafer 1 is sometimes about 70°C to 80°C in accordance with the type of etching processing. In this case, a heating medium such as hot water is circulated in the liquid passage 23 to control the temperature of the wafer 1. An O-ring groove 26a is formed in a peripheral portion on the upper surface of the lower member 22 along its circumference, and a gas filling ring groove 25a is formed inside the O-ring groove 26a along the circumference of the lower member 22. A gas inlet passage 25 is connected to the groove 25a, and a heat conduction gas is supplied from a gas supply source (not shown) to the groove 25a via a control mechanism (to be described later) and the inlet passage 25, thereby filling the gas between the upper and lower members 21 and 22. An O-ring 26 is fitted in the O-ring groove 26a to prevent a leakage of the heat conduction gas from between the upper and lower members 21 and 22. However the heat conduction gas may leak if little. The pressure of the heat conduction gas between the upper and lower members 21 and 22 is controlled by a mechanism 60 as shown in Fig. 4. In the mechanism 60, the gas inlet passage 25 extends upward from an intermediate portion of a gas supply pipe 50. A regulator 52 and a throttle valve 54 are arranged on the IN side of the gas supply pipe 50, and a throttle valve 56 is arranged on its OUT side. A gauge pressure measured by the regulator 52 is fed back to a valve drive unit 58 for driving the throttle valve 56 on the OUT side, and opening/closing of the valve 56 on the OUT side is controlled such that the measured gauge pressure is maintained constant. Alternatively, an operator may adjust the valve while monitoring the gauge pressure without using the valve drive unit 58. In a conventional support table in which no heat conduction gas is flowed, a void is formed between the upper and lower members 21 and 22 due to, for example, a difference of smoothnesses, a surface roughness, or dust therebetween. If the temperature adjustment is performed on the lower member 22 side while the void is formed as described above, almost no heat conduction is caused by a gas between the upper and lower members 21 and 22 because the vacuum chamber is evacuated, but only solid contact heat conduction around the bolts 29 fastening the two members can be expected. On the contrary, when a heat conduction gas is held at a predetermined pressure between the upper and lower members 21 and 22 as in the present invention, the heat conduction characteristic between the two members can be improved. Therefore, the temperature of a wafer as an object to be processed can be efficiently adjusted. Although the type of gas used as the heat conduction gas is not particularly limited, a gas having a high heat conductivity is preferred for this purpose. Preferable examples of the gas are He, O 2 , Ar, and N 2 , and He is most preferred. When the pressure of the heat conduction gas is at a predetermined value or more, the effect of the gas can be obtained. For this reason, the gas pressure is controlled as described above. When the gas pressure is at a predetermined value or more, heat conduction caused by the gas does not depend much on the gas pressure but depends largely on a void distance between the upper and lower members 21 and 22. That is, the effect of the heat conduction gas is enhanced as the void between the two members is decreased. Therefore, when the void between the two members is minimized, heat conduction caused by the gas can be improved to realize highly precise temperature control. The void distance can be decreased to be 10 µm or less by finishing the mating surfaces of the two members with high precision. As a result, heat is conducted at a high efficiency to realize highly precise temperature control. Fig. 5 shows the effect of the heat conduction gas. Fig. 5 is a graph showing the relationship between the pressure of the heat conduction gas between the upper and lower members 21 and 22 and the temperature difference between the upper and lower members obtained when He and O 2 were used as heat conduction gases, in which the abscissa indicates the gas pressure and the ordinate indicates the temperature difference. The temperature difference shown in Fig. 5 was obtained between a temperature measured at a point A of the upper member 21 and that at a point B of the lower member 22 shown in Fig. 2. An anti-freeze at a temperature of -25°C was used as a coolant to be flowed through the lower member. The pressure in the chamber 10 was set at 3.5 × 10 -3 Torr. As shown in Fig. 5, a temperature difference of 15°C or more was obtained before supply of a gas was standed regardless of the type of gas. In addition, the temperature reducing effect was saturated at a gas pressure of 150 Torr. The temperature reducing effect changes in accordance with the type of gas. That is, while the temperature difference was reduced to be at most about 10°C when O 2 gas was used, it was reduced to be about 4°C when He gas was used. A heat conduction gas was supplied between the wafer 1 and the electrostatic chuck 24 from a gas inlet passage 27 to further improve the temperature control precision of the wafer 1. Although the type of gas is not particularly limited, He, O 2 , Ar, N 2 , and the like can be preferably used as is the case with the above heat conduction gas. The operation of the magnetron etching apparatus having the above arrangement will be described below. Firstly, the chamber 10 is evacuated to a predetermined degree of vacuum. Thereafter, a wafer to be etched is supplied on the electrostatic chuck sheet 24 from a load lock chamber (not shown) by a robot, and a high electrostatic voltage of, for example 2 kV is applied between the upper chamber 11 and the electrically conductive sheet 24c of the electrostatic chuck 24. When a plasma is generated by a step to be described later, since wafer 1 is conducted via the plasma, static electricity is generated on chuck 24 and wafer 1 is chucked on the electrostatic chuck 24 by a Coulomb force. Subsequently, the vacuum chamber 10 is evacuated to about 0.1 mTorr to 10 mTorr, and an etching gas such as O 2 gas, Cℓ gas, or SF 6 gas is supplied from the gas inlet ports 14 at a flow rate of 50 cc/s (at room temperature and atmospheric pressure). RF power is supplied between the upper wall of the upper chamber 11 as an upper electrode and the upper member 21 as the lower electrode from the RF power source 40, thereby generating a magnetron discharge by crossed fields formed between the two electrodes and forming a plasma between the two electrodes. As a result, radicals and ions are generated to cause reactive ion etching on the surface of the wafer 1. In this etching, since electrons between the electrodes are caused to perform cyclone motion by the magnetic force from the permanent magnet 32 as described above, plasma conversion of the etching gas is accelerated. Therefore, a high etching rate of 1 µm/min can be obtained even at a comparatively low pressure of 10 -2 to 10 -3 Torr. In this case, since a heat conduction gas is supplied between the upper and lower members 21 and 22 of the support table 20 to improve the heat conduction characteristic between the members 21 and 22, the temperature difference between the two members can be minimized. Therefore, temperature control of the wafer can be reliably performed by flowing a liquid for temperature control through the liquid passage 23 of the lower member 22. As a result, regardless of the split structure of the support table, the wafer temperature control can be performed substantially equally as in a support table of a single unit type. In addition, since the support table 20 is of the split type in which the upper member 21 can be removed from the stationary lower member 22, only the upper member 21 need be replaced when the inch size of the wafer 1 is changed. Also, in replacement of the electrostatic chuck 24 as a consumable member, the upper member 21 having a new electrostatic chuck need only be replaced. In the above embodiment, an upper wall of vacuum chamber 10 is used as a second electrode, and the second electrode may provide isolation from the chamber 10. The support table according to the present invention is applied to a magnetron plasma etching apparatus. However, the present invention can be similarly applied to any vacuum processing apparatus without departing from the invention. Examples of the vacuum processing apparatus are, in addition to the magnetron plasma etching apparatus described above, an RIE plasma etching apparatus, other plasma processing apparatuses such as a sputtering apparatus, a CVD apparatus, and an ion injection apparatus, and non-plasma processing apparatuses such as a thermal CVD apparatus. The present invention can also be applied to vacuum apparatuses for use in various other fields. In addition, the present invention can be applied to the apparatus including an electrode, temperature of which is controlled. Such apparatus include an ion source apparatus and the above-mentioned apparatus, and the support table or the electrode can be controlled at either a high or low temperature. A plate-like body is not limited to a semiconductor wafer but may be, for example an LCD substrate. Furthermore, as the gas to be supplied between the upper and lower members, various types of gases capable of improving the heat conduction characteristic can be used in accordance with the type of process.

Claims: A processing apparatus for performing a predetermined processing for an object (1) to be processed in a vacuum atmosphere, comprising a vacuum chamber (1); a support table (20) provided in said vacuum chamber (1) and including a first member (22) having a mechanism (23, 23a, 23b) for adjusting the temperature of said object (1) by means of a temperature control liquid flowing at a predetermined temperature in a liquid passage (23) provided in said first member (22); said support table (20) further including a second member (21) for supporting said object (1); said second member (21) being removably provided on said first member (22) and in heat conduction contact with said first member (22); said first and second members (22,21) having opposedly arranged mating major surfaces finished with high precision such that said mating major surfaces are in solid heat conduction contact, except for a narrow void formed between said mating major surfaces caused by surface roughness, unevenness or dust; gas supply means (25, 25a, 60) for supplying a heat conduction gas to said void between said first and second members (22, 21) for improving the heat conduction between said first and second members (22, 21); said gas supply means (25, 25a, 60) being adapted to supply said gas to said void at a pressure which is sufficient to reduce the temperature difference between said first and second members; and processing means (20, 30, 40) for performing said processing of said object (1). A processing apparatus according to claim 1, characterized in that said gas supply means 25, 25a, 60) is adapted to supply said gas at a pressure which is sufficient to reduce the temperature difference between said first and second members (22, 21) to 10° C or below. A processing apparatus according to claim 2, characterized in that said gas supply means (25, 25a,60) is adapted to supply a heat-conduction gas to said void between the first and second members (22, 21) at a pressure greater than 2x10 4 Pa (150 Torr). A processing apparatus according to claims 1, 2 or 3, characterized in that said processing means (20, 30, 40) includes plasma generating means (20, 40) for performing plasma etching processing by a generated plasma of an etching gas around said object (1). A processing apparatus according to any one of claims 1 to 4, characterized in that said second member (21) includes an electrostatic chuck (24) for holding said object by Coulomb force. A processing apparatus according to claim 5, further comprising gas supply means (27) for supplying a heat conduction gas between said electrostatic chuck (24) and said object (1). A processing apparatus according to any one of claims 4 to 6, further comprising magnetic field applying means for applying a magnetic field to a region where the plasma is generated. A support table apparatus for supporting an object (1) for processing same in a processing apparatus in a vacuum atmosphere, comprising a support table including a first member (22) having a mechanism (23, 23a, 23b) for adjusting the temperature of said object (1) by means of a temperature control liquid flowing at a predetermined temperature in a liquid passage (23) provided in said first member (22); said support table further including a second member (21) for supporting said object (1) and removably provided on said first member (22) in heat conduction contact therewith; said first and second members (22,21) having opposedly arranged mating major surfaces finished with high precision such that said mating major surfaces are in solid heat conduction contact, except for a narrow void formed between said mating major surfaces caused by surface roughness, unevenness or dust; and gas supply means (25, 25a, 60) for supplying a heat conduction gas to said void between said first and second members (22, 21) for improving the heat conduction between said first and second members (22,21); said gas supply means (25, 25a, 60) being adapted to supply said gas to said void at a pressure which is sufficient to reduce the temperature difference between said first and second members. A support table apparatus according to claim 8, further comprising an O-ring for preventing a leakage of the heat-conduction gas, provided between said first and second members. A support table apparatus according to claims 8 or 9 further comprising bolts for fastening said second member to said first member. A support table apparatus according to any one of claims 8 to 10, characterized in that said second member (21) includes an electrostatic chuck (24) for holding said object (1) by Coulomb force. A support table apparatus according to any one of claims 8 to 11, characterized in that said first member (22) is fixed to said processing apparatus, and said second member (21) can be removed therefrom. A support table apparatus according to any one of claims 8 to 12, characterized in that said gas supply means (25, 25a, 60) includes a gas inlet passage (25) for supplying the heat conduction gas between said first and second members (22, 21). A support table apparatus according to any one of claims 8 to 13, characterized in that said gas supply means (25, 25a, 60) is adapted to provide a gas pressure between said first and second members (22, 21) sufficient to reduce the temperature difference therebetween to 10° C or below. A support table apparatus according to claim 14, characterized in that said gas supply means (25, 25a, 60) is adapted to provide a gas pressure greater than 2x10 4 Pa (150 Torr). A support table apparatus according to any one of claims 8 to 15, characterized in that said mechanism for adjusting the temperature includes a mechanism (23, 23a, 23b) for cooling said object (1) to be processed. A support table apparatus according to any one of claims 8 to 15, characterized in that said mechanism for adjusting a temperature includes a mechanism (23, 23a, 23b) for heating said object to be processed. A support table apparatus according to any one of claims 11 to 17, further comprising gas supply means (27) for supplying a heat conduction gas between said electrostatic chuck (24) and said object (1). A process for controlling the temperature of an object supported on a split type support table (20) in a vacuum processing chamber, said support table (20) having a first member (22) and a second member (21) in close heat conducting contact, said first and second members (22,21) having opposedly arranged mating major surfaces finished with high precision such that said mating major surfaces are in solid heat conduction contact, except for a narrow void formed between said mating major surfaces caused by surface roughness, unevenness or dust; comprising the steps of: supporting said object on said second member, adjusting the temperature of said object by conducting a temperature control liquid at a predetermined flow rate through a liquid passage provided in said first member; and supplying to said void a heat conducting gas at a predetermined pressure sufficient for improving the heat conduction between said first and second members of said support table, such that the temperature difference between said first and second members is reduced. A process according to claim 19, characterized in that the heat conduction gas is one member selected from the group consisting of He, O 2 , Ar, and N 2 . A process according to claims 19 or 20, characterized in that said temperature difference is adjusted to 10° C or below. A process according to claim 21, characterized in that said predetermined pressure is greater than 2x10 4 Pa (150 Torr).

Inventors: ARAMI JUNICHI, HASEGAWA ISAHIRO, NOZAWA TOSHIHISA, OKANO HARUO, ARAMI, JUNICHI, HASEGAWA, ISAHIRO, NOZAWA, TOSHIHISA, OKANO, HARUO, HASEGAWA, ISAHIRO, C/O INTELLECTUAL PROPERTY DIV., Okano, Haruo, c/o Intellectual Property Division
Applicants: TOKYO ELECTRON LTD, TOSHIBA KK, KABUSHIKI KAISHA TOSHIBA, TOKYO ELECTRON LIMITED
Application year: 1991
Main classification: C23C14
IPC codes: C23C16, C23C14, H01L21, H01J37