Improvements in or relating to electrostatic holding systems for holding substrates in processing chambers

Abstract: An electrostatic holding system (10) comprising an electrostatic chuck (20) for holding a substrate (45) is described. The chuck (20) is suitable for mounting on a base (25) , and comprises an electrostatic member (33) having at least two electrodes (50a) , (50b) . The two electrode chuck (20) is used in conjunction with a switching system capable of operating the chuck (20) in either a monopolar mode or in a bipolar mode.

Description: This invention relates to electrostatic chucks used for holding substrates in process chambers. Electrostatic holding systems comprising electrostatic chucks are used to hold semiconductor substrates, such as a silicon wafers, during processing of the substrates. A typical electrostatic chuck includes an electrostatic member on a base, the base capable of being secured to a support in a process chamber. Typically, the electrostatic member has coolant grooves for holding a coolant for cooling the substrate. To use the chuck, a substrate is placed on the electrostatic member, and the electrostatic member is electrically biased with respect to the substrate by an electrical voltage. Process gas is introduced into the process chamber, and in certain processes, a plasma is formed from the process gas. Opposing electrostatic charge accumulates in the electrostatic member and substrate, resulting in an attractive electrostatic force that electrostatically holds the substrate to the chuck. The electrostatically held substrate covers and seals the coolant grooves in the chuck so that coolant substantially does not leak out from the grooves. Conventional electrostatic chucks have certain limitations. Monopolar chucks that have a single monopolar electrode can electrostatically hold a substrate only during the plasma stages of the process. Typically, a positive potential is applied to the monopolar electrode on the chuck, and the substrate is maintained at a negative potential by charges plasma species in the chamber, causing electrostatic charge to electrostatically hold the substrate to the chuck. However, during the non-plasma stages of the process, the substrate is not securely held to the chuck and can move or become misaligned, and/or ineffectively seal the grooves on the chuck causing coolant to leak out. US-A-4,520,421 discloses a semi-conductor fabricating apparatus having a monopolar electrostatic holding system for wafers to be processed. Wafers are supported on a base which carries target attracting portions of semi-conductive dielectric material with electrodes on their under sides. A wafer is disposed on the upper side of the specimen attracting portions and a common voltage is applied to the specimen attracting portions from a power supply to generate a dielectric flux between the specimen attracting portions through the wafer. As a result, an electrostatic attractive force is generated between the wafer and the specimen attracting portions to hold the wafer on the attracting portions. Bipolar electrode chucks that have two or more electrodes can electrostatically hold a substrate for both plasma and non-plasma processes. Bipolar chucks are operated by applying a positive potential to one of the electrodes and a negative potential to the other electrode. However, when a bipolar chuck is used in a plasma process where charged plasma species impinge on the substrate, a complex circuit is necessary to balance the current flow in, and voltage applied to, each electrode. The complex circuit requires a floating power supply that allows the charged plasma species to maintain the substrate either at a negative potential of a few hundred volts or at electrical ground. The complex circuitry renders the chuck more costly to fabricate and maintain. Conventional bipolar electrode chucks are also disadvantageous because the bipolar electrodes provide only about ¼ of the electrostatic clamping force provided by a monopolar electrode having the same electrode area. Lower electrostatic force results because electrostatic clamping force is proportional to the square of the electrode area; and each bipolar electrode has only half the area of a single monopolar electrode. Maximizing electrostatic clamping force is beneficial to reduce movement of the substrate during processing which can result in loss of the entire substrate. Also, higher clamping force allows coolant at higher pressures to be held in the cooling grooves without escaping, thereby allowing better control of the substrate temperature. An object of the present invention is to provide an electrostatic chuck than can be used for both non-plasma and plasma processes without use of complex circuitry, and which allows maximization of the electrostatic clamping force for different process stages. This invention provides an electrostatic holding system for holding a substrate in a process chamber having a voltage supply, the holding system comprising an electrostatic member and at least a pair of electrodes connected to the voltage supply for holding a substrate to the electrostatic member, the holding system including a switch electrically connecting the electrodes to the voltage supply and having a monopolar position for providing a voltage having a potential to the electrodes for operating the electrodes as monopolar electrodes to hold electrostatically the substrate to the electrostatic member with a relatively high force; wherein the switch also has a bipolar position for providing a voltage having opposing potentials to the electrodes for operating the electrodes as bipolar electrodes to hold electrostatically the substrate to the electrostatic member with a relatively low force. The switch may also comprise an open circuit position for connecting the electrodes to an open circuit. In one arrangement according to the invention the voltage supply in the process chamber comprises a single voltage source, the switch in the monopolar mode electrically connecting the electrodes to the voltage source, and in the bipolar mode connecting at least one electrode to ground and another electrode to the voltage source. More specifically the electrostatic member may be supported by a base, and the electrodes in the electrostatic member may be electrically connected to the voltage supply in the chamber via electrical connectors disposed through the base so that when a substrate is held on the electrostatic member, the electrical connectors are substantially covered by the substrate and thereby undergo reduced erosion, each electrode and electrical connector being fabricated from a unitary electrically conductive member. This invention provides a method so as defined by the features of method claims 6 and 8 of using the electrostatic holding system of any of the above arrangements comprising the steps of placing a substrate on the electrostatic member, activating the switch to the monopolar position to electrostatically hold the substrate during a plasma process stage; and before or after the immediately preceding step, activating the switch to the bipolar position to electrostatically hold the substrate during a non-plasma process stage. More particularly in the monopolar position, a first voltage is applied to the electrodes so that the electrostatic charges having substantially identical polarity accumulates in the electrodes, and in the bipolar position, a second voltage is applied to the electrodes so that electrostatic charges having opposing polarities accumulate in the electrodes. The invention also provides a method of holding a substrate in a process chamber during a process comprising plasma and non-plasma stages, the method comprising the steps of securing an electrostatic member comprising at least two electrodes in the process chamber, placing a substrate on the electrostatic member, electrostatically holding the substrate to the electrostatic member during a plasma process stage by applying a first voltage to the electrodes to operate the electrodes as monopolar electrodes, and before or after the immediately preceding step electrostatically holding the substrate to the electrostatic member during a non-plasma process stage by applying a second voltage to the electrodes to operate the electrodes as bipolar electrodes. These and other features, aspects, and advantages of the present invention will become better understood with regard to the following description, appended claims, and accompanying drawings. Operation of an electrostatic holding system 10 comprising an electrostatic chuck 20 according to the present invention is illustrated by the example shown in Figure 1. The electrostatic chuck 20 comprises a base 25 with bores 30a , 30b therethrough. An electrostatic member 33 having at least two electrodes 50a , 50b therein, is supported by the base 25 . Typically, the electrostatic member 33 comprises an insulator 35 having (i) a lower insulative layer 35a and an upper insulative layer 35b enclosing the electrodes 50a , 50b , and (ii) an upper surface 40 for receiving a substrate 45 thereon. Electrical connectors 55a , 55b comprising electrical leads 60a , 60b extend through the bores 30a , 30b of the base 25 and end in electrical contacts 65a , 65b to electrically connect the electrodes to the voltage supply terminals 70a , 70b , respectively, as shown in Figure 2. During its use, the electrostatic chuck 20 is secured on a support 75 in a process chamber 80 . The process chamber 80 includes an electrically grounded surface 95 which forms an enclosure for plasma processing of substrates 45 . The process chamber 80 typically includes a gas inlet 82 for introducing a plasma-forming process gas, and a throttled exhaust 84 for exhausting the reacted plasma and gas products from the process chamber 80 . The support 75 in the process chamber 80 has an insulator flange 77 disposed between the support 75 and the grounded surface 95 to electrically isolate the support from the grounded surface 95. The particular embodiment of the process chamber 80 shown in Figure 1 is suitable for plasma processing of substrates 45 , the plasma being a primary source of erosion of the chuck 20 . However, the present invention can be used with other process chambers and other processes without deviating from the scope of the invention. To operate the chuck 20 , the chuck 20 is secured on the support 75 so that the electrical contacts 65a , 65b of the chuck 20 electrically engage the voltage supply terminals 70a , 70b on the support 75 . The process chamber 80 is evacuated and maintained at a predetermined pressure. A substrate 45 is then placed on the chuck 20 , and the electrodes 50a , 50b of the chuck 20 are activated using the first voltage supply 85 to hold the substrate 45 to the chuck 20 . Thereafter the process gas is introduced into the chamber 80 via the gas inlet 82 , and a plasma is formed for certain stages of the process, by activating the second voltage supply 90 . The electrostatic holding system 10 of the present invention allows use of the chuck 20 in processes having both plasma and non-plasma stages. A switching system uses a switch 140 to operate the electrodes 50a , 50b as monopolar electrodes during plasma stages, and bipolar electrodes during non-plasma stages. The switch 140 has three positions, namely (i) a monopolar position, (ii) a bipolar position, and (iii) an open circuit position. In the monopolar position, the switch connects both electrodes 50a , 50b to the first voltage supply 85 , thereby maintaining both electrodes 50a , 50b at the same electrical potential, so that the electrodes serve as a unitary monopolar electrode. Simultaneously, the second voltage supply 90 is activated to electrically bias the support 75 to form a plasma in the chamber 80 . The electrically charged species of the plasma impinge on the substrate 45 and maintain the substrate 45 at an opposing electrical potential to that of the electrodes 50a , 50b . The opposing electrical potential cause opposing electrostatic charge to accumulate in the substrate 45 and in the electrodes 50a , 50b , thereby resulting in an attractive electrostatic force which holds the substrate 45 to the chuck 20 . In the bipolar position, the switch 140 connects the first electrode 50a to the first voltage supply 85 to maintain the electrode at a first electrical potential, and connects the second electrode 50b to the support 75 . Typically, during bipolar operation, the second voltage supply 90 is deactivated, and the support 75 is electrically grounded. For example, the first electrode 50a is maintained at a positive potential by the voltage supply 85 , and the second electrode 50b is maintained at an opposing electrical potential, namely electrical ground. In his manner, the switchable system allows the electrodes 50a , 50b to be maintained at opposing electrical potentials during the non-plasma stages of the process to operate the electrodes 50a , 50b as bipolar electrodes. The open circuit position of the switch 140 is used to transition the electrodes 50a , 50b between the monopolar and bipolar operational modes. When the process is transitioned from a plasma to a non-plasma stage, the plasma in the chamber 80 cannot be instantaneously evacuated, and some residual electrical charged plasma species remain in the chamber 80 for a short period after, the second voltage supply 90 is turned off. Thus, in between the plasma and non-plasma process stages, the switch 140 is set to the open circuit position, in which no electrical potential is maintained in the electrodes 50a , 50b . The open circuit position delays or stabilizes the transition between the monopolar and bipolar operational modes of the electrodes 50a , 50b . Typically, the first voltage supply 85 includes a high voltage DC power supply 87 and an alternating current filter 89 . Typically, the DC power supply 87 provides a DC voltage ranging from about 1000 to 3000 volts, and more preferably from about 2000 volts. A suitable first voltage supply 85 typically includes a circuit which comprises a DC power supply of about 1000 to 3000 volts, connected to a high voltage readout, through a 10 MΩ resistor. A 1 MΩ resistor in the circuit limits current flowing through the circuit, and a 500 pF capacitor is provided as an alternating current filter. The second voltage supply 90 is connected to the support 75 in the process chamber 80 . At least a portion of the support 75 is typically electrically conductive and functions as a process electrode, or cathode, for forming a plasma in the chamber 80 . The second voltage supply 90 is provided for electrically biasing the support 75 with respect to the electrically grounded surface 95 in the chamber 80 , to form a plasma from process gas introduced into the chamber 80 . The second voltage supply 90 generally comprises an RF impedance that matches the impedance of the process chamber 80 to the impedance of the line voltage, in series with an isolation capacitor. The switchable system is advantageous for processes which comprise both plasma and non-plasma stages. During the non-plasma stage of the process, such as when the substrate 45 is being heated to process temperatures, the switchable system allows the electrostatic chuck 20 to be used in a bipolar mode, with one electrode 50a electrically charged and the other electrode 50b electrically grounded, to electrostatically hold the substrate 45 without use of a plasma. During the plasma stage of the process, the switchable system allows the chuck 20 to be operated in a monopolar mode, which provides increased electrostatic clamping force to prevent movement or misalignment of the substrate 45 . During operation of the chuck, the substrate 45 held on the chuck 20 is cooled using a coolant source 100 that supplies coolant to cooling grooves 105 in the upper surface 40 of the insulator 35 . The substrate 45 held on the chuck 20 covers and seals the grooves 105 preventing leaking of coolant. The coolant in the grooves 105 removes heat from the substrate 45 and maintains the substrate 45 at constant temperatures during processing of the substrate. Typically, the cooling grooves 105 on the insulator 35 are spaced apart, sized, and distributed so that coolant held in the grooves 105 can cool substantially the entire substrate 45 . Typically, the grooves 105 form a pattern of intersecting channels that extend through the entire insulator 35 and electrodes 50a , 50b . More preferably, the cooling grooves 105 are formed in the electrical isolation voids 52 between the first and second electrodes 50a , 50b , that electrically isolate the electrodes from one another, to maintain the electrodes at opposing electrostatic polarities. Preferably, the electrodes 50a , 50b and the electrical isolation voids 52 therebetween are sized and configured so that the electrical isolation voids 52 can serve as cooling grooves 105 for holding coolant for cooling the substrate 45 on the chuck 20 . Particular aspects of the chuck 20 will now be discussed. The base 25 of the chuck 20 supports the electrostatic member 33 , and typically is shaped and sized to correspond to the shape and size of the substrate 45 to maximize heat transfer and provide a wide holding surface. For example, if the substrate 45 is disk shaped, a right cylindrically shaped base 25 is preferred. Typically, the base 25 is of aluminum and has a cylindrical shape with a diameter of about 100 mm to 225 mm, and a thickness of about 1.5 cm to 2 cm. The top and bottom surfaces of the plate are ground using conventional grinding techniques, until the surface roughness of the plate is less than 1 micron, so that the base 25 can uniformly contact the support 75 and the substrate 45 , to allow efficient thermal transfer between the substrate 45 and the support 75 . After grinding, the plate is thoroughly cleaned to remove grinding debris. The base 25 has bores 30a , 30b therethrough, each bore having a slot portion 101 and an enlarged counterbore portion 103 extending from the slot portion 101 , as shown in Figure 2. The bores 30a , 30b are sized sufficiently large to insert the electrical leads 60a , 60b or the electrical lead 60 and integral electrical contacts 65a , 65b therethrough with minimal or substantially no clearance. Preferably, the bores 30a , 30b are sized sufficiently small that when the electrical leads of the connectors 55 are within the bores 30a , 30b , substantially no gas leaks from the bores, a suitable clearance being less than about 5 mm. The electrostatic member 33 comprises an insulator 35 with electrodes 50a , 50b therein. The insulator 35 typically comprises an electrically insulative polymeric material, such as polyimide, polyketone, polyetherketone, polysulfone, polycarbonate, polystyrene, nylon, polyvinylchloride, polypropylene, polyetherketones, polyethersulfone, polyethylene terephthalate, fluoroethylene propylene copolymers, cellulose, triacetates, silicone, and rubber. Preferably, the insulator 35 is resistant to temperatures in excess of 50°C, and more preferably in excess of 100°C, so that the chuck 20 can be used for high temperature processes. Also, preferably, the insulator 35 has a high thermal conductivity so that heat generated in the substrate 45 during processing can dissipate through the chuck 20 , a suitable thermal conductivity being at least about 0.10 Watts/m/K. The insulator 35 can also have dispersed therein a high thermal conductivity powder filler material, such as diamond, alumina, zirconium boride, boron nitride, and aluminum nitride, having an average particle size of less than about 10 µm, to increase the thermal conductivity and erosion resistance. Preferably, the volumetric ratio of the filler to insulator is from about 10% to 80%, and more typically from 20% to 50%. Additionally, a protective coating (not shown) can be applied on the upper surface 40 of the insulator 35 to protect the insulator 35 from chemical degradation when the chuck 20 is used in corrosive and erosive processing environments. The insulator 35 is sized sufficiently large to enclose the electrodes 50a , 50b therein. Typically, the insulator 35 has a resistivity ranging from about 10 13 Ω cm to 10 20 Ω cm, and a dielectric constant of at least about 2, and more preferably at least about 3. The overall thickness of the insulator 35 depends on the electrical resistivity and dielectric constant of the insulative material used to form the insulator 35 . For example, when the insulator 35 has a dielectric constant of about 3.5, the thickness of the insulator 35 is typically about 10 µm to about 500 µm thick, and more preferably from about 100 µm to about 300 µm thick. Polyimide insulative materials have dielectric breakdown strengths of typically at least about 100 volts/mil (3.9 volts/micron), and more typically at least about 1000 volts/mil (39 volts/micron). Typically, the insulator 35 comprises a two layer laminate structure, as illustrated in Figure 1, comprising a lower insulative layer 35a and an upper insulative layer 35b , between which the electrodes are embedded. Preferably, the insulative layers 35a , 35b have substantially equivalent thicknesses of from about 50 µm to about 60 µm thick. The electrodes 50a , 50b are made from an electrically conductive material, such as for example, metals such as copper, nickel, chromium, aluminum, iron, and alloys thereof. The shape, size and number of the electrodes 50a , 50b are selected to maximize the area of the electrodes in contact with the substrate 45 . For example, the electrodes 50a , 50b are disk shaped for disk shaped substrates 45 . Preferably, the electrodes 50a , 50b cover substantially the entire area in the insulator 35 , the total area of the electrodes 50a , 50b being typically from about 50 to about 500 sq. cm., and more typically from 80 to 380 sq. cm. Preferably, the area of each of the two electrodes 50a , 50b is substantially equivalent and typically comprises about one-half of the total area of the top surface of the chuck 20 . Thus, for two electrodes, the area of each electrode 50a , 50b is preferably from about 50 to about 250 sq. cm., and more preferably from 100 to 200 sq. cm. Typically, the thickness of the electrodes 50 is from about 1 µm to 100 µm, and more typically is from about 1 µm to 50 µm. However, in certain bipolar configurations, it is advantageous to utilize thinner electrodes of less about 1 µm, and more preferably less than 0.5 µm thickness, to seal the tips 107 of the cooling grooves 105 at the peripheral edge 110 of the insulator 35 . The electrodes 50a , 50b can either be continuous or patterned with interconnected features, the features sized so that cooling grooves 105 can be formed between the features for holding a coolant for cooling the substrate 45 held on the chuck 20 . The cooling grooves 105 can be formed in the isolation voids 52 between the electrodes, by cutting through the insulator 35 overlying the isolation void 52 so that the cooling grooves 105 extend through the insulator 35 , or the insulator can recede into the isolation voids 52 to form cooling grooves 105 lying between the electrodes 50a , 50b . This configuration allows utilization of the isolation voids 52 between the electrodes 50a , 50b to hold coolant without requiring additional grooves to be cut through the electrodes, thereby maximizing the effective electrostatic force of the electrodes 50a , 50b . For example, Figure 3 shows a double ring electrode configuration comprising an inner electrode ring 50a and an outer electrode ring 50b , with an electrical isolation void 52 therebetween. The electrical isolation void 52 between the two electrodes 50a , 50b is used to form a cooling groove 105 , allowing maximization of the electrode area. Preferably, the electrodes 50a , 50b are coplanar and have substantially equivalent areas so that the electrodes generate equivalent electrostatic clamping forces on the substrate 45 . In a preferred configuration, the electrodes 50a , 50b and isolation voids 52 therebetween are sized and configured so that at least a portion of the electrical isolation voids 52 are positioned at the peripheral edge 110 of the insulator 35 so that coolant held in the tips 107 of the cooling grooves 105 can cool a perimeter 235 of the substrate 45 held on the chuck 20 . For example, in the electrode configuration shown in Figure 4 , the electrodes 50a , 50b are shaped and sized to form electrical isolation voids 52 comprising ring-shaped grooves which are arranged sufficiently close to the peripheral edge 110 of the insulator 35 that when the coolant is held in the grooves 105 , the coolant in the groove tips 107 cools the perimeter 235 of the substrate 45 without leaking out from the grooves 105 . In Figure 4, the first electrode 50b comprises three outer ring electrodes and the second electrode 50a comprises a single solid inner circle. When a substrate 45 is held on the chuck 20 , the substrate 45 presses against the ridges formed by the portions of the insulator 35 overlying the electrodes 50a , 50b and seals the coolant grooves 105 so that coolant does not leak out from the grooves 105. Thus coolant can be distributed evenly and close to the perimeter 235 of the substrate 45 without leaking from the grooves 105 . Another preferred configuration for the multi-electrode chuck 20 comprises two semicircular electrodes 50a , 50b , separated by at least one electrical isolation void 52 that extends radially across the insulator 35 , as illustrated by Figure 5. The radially extending isolation void 52 is used to form a cooling groove 105 which extends close to the peripheral edge 110 of the insulator 35 . The chuck 20 can also include additional radially extending cooling grooves 105 having groove tips 107 which extend close to the peripheral edge 110 of the insulator 35 . The groove tips 107 are positioned close to the peripheral edge 110 of the insulator 35 and define a gap 109 with the edge 110 . The coolant in the tips of the grooves 105 maintains the temperatures at the perimeter 235 of the substrate 45 substantially equivalent to the temperatures at the center 237 of the substrate 45 , the average difference in temperature between the perimeter 235 and center 237 of the substrate 45 being preferably less than about 10°C. Most preferably the coolant maintains substantially the entire substrate 45 at constant temperatures. Two similar electrical connectors 55a , 55b are used to separately electrically connect each of the electrodes 50a , 50b to the first voltage supply 85 . The connectors are substantially identical and each comprise (i) electrical leads 60a , 60b that extend through a bore 30 in the base 25 , and (ii) electrical contacts 65a , 65b . The electrical leads 60a , 60b are fabricated from an electrically conductive metal such as copper or aluminum, the length of the electrical leads 60a , 60b being typically from 10 to 50 mm, and more typically from 20 to 40 mm. The width of the electrical leads 60a , 60b is typically from 2 to 10 mm, and more typically from 4 to 7 mm. Preferably, the electrical leads 60a , 60b , the electrodes 50a , 50b and the electrical contacts 65a , 65b are fabricated from a single unitary conductive member, such as a sheet of metal so that the electrical connector is an integral extension of the electrode. This version is advantageous because it is not necessary to fabricate or assemble a multicomponent assembly for contacting the voltage supply terminal. Typically, a continuous sheet of conductive metal is cut out to form the electrodes 50a , 50b and the electrical connector 55 . The electrical contacts 65a , 65b which are integral with the electrical leads 60a , 60b are shaped and sized sufficiently large to directly electrically engage the voltage supply terminals 70a , 70b on the support 75 , without causing arcing of the high voltage therethrough. Preferably, the area of the electrical contacts 65a , 65b integral with the leads 60a , 60b is at least about the area of the high voltage terminals 70a , 70b , and more preferably substantially equivalent to the area of the high voltage terminals 70a , 70b . Preferably, the area of each of the electrical contacts 65a , 65b is at least about 50 sq. mm, and more preferably at least about 100 sq. mm. Typically, the area of the electrical contacts 65a , 65b is from 50 to 400 sq. mm, and more typically from about 75 to 150 sq. mm. Typically, the electrical contacts 65a , 65b are disk-shaped and have a radii ranging from about 5 mm to about 12 mm to provide sufficient contact area. A method of manufacturing the electrostatic member 33 will now be described. Preferably, the electrostatic member 33 is fabricated as a laminate comprising the insulator 35 with the electrodes 50a , 50b therein, and having electrical connectors 55a , 55b integral with the electrodes 50a , 50b . A suitable method of fabricating the laminate from a multi-layer film comprising an insulative layer and an electrically conductive layer, such as "R/FLEX 1100" film fabricated by Rogers Corporation, Chandler, Arizona, which comprises an electrically conductive copper layer on a 25 to 125 µm thick polyimide insulative layer. The copper layer of the multi-layer film is etched, routed, or milled to form the electrodes 50a , 50b and the integral electrical connectors 55a , 55b . An etching process suitable for forming the electrodes 50a , 50b and integral electrical connectors 55a and 55b comprises the steps of (i) forming a protective resist layer patterned to correspond to the shape of the electrodes 50a , 50b and the electrical connectors 55a , 55b , over the electrically conductive layer of the multi-layer film, and (ii) etching the resist protected multi-layer film using conventional etching processes. The resist layer can be formed using photoresist materials, such as "RISTON" fabricated by DuPont de Nemours Chemical Co., Wilmington, Delaware, applied on the electrode layer. Conventional photolithographic methods, such as those described in Silicon Processing for the VLSI Era, Volume 1: Process Technology, Chapters 12, 13, and 14, by Stanley Wolf and Richard N. Tauber, Lattice Press, California (1986), which is incorporated herein by reference, can be used to pattern the resist layer on the electrically conductive layer. Conventional wet or dry chemical etching methods can be used to etch the multi-layer film. A suitable wet chemical etching method comprises immersing the multi-layer film into an etchant such as ferric chloride, sodium persulfate, or an acid or base, until the unprotected portion of the electrode layer is etched. Suitable dry etching processes are described in Silicon Processing, Chapter 16, supra , which is incorporated herein by reference. After etching the electrically conductive layer to form the electrodes 50a , 50b and integral electrical connectors 55a , 55b ; a second insulative film is adhered over the conductive layer so that the conductive layer is embedded within the insulator 35 to form the laminated electrostatic member 33 . Suitable insulative films include, for example, "KAPTON," a polyamide film manufactured by DuPont de Nemours Co., in Wilmington, Delaware; "APIQUEO" fabricated by Kanegafuchi Chemical Indus., Japan; "UPILEX" manufactured by Ube Indus. Ltd., Japan; "NITOMID" fabricated by Nitto Electric Indus. Co. Ltd., Japan; and "SUPERIOR FILM" fabricated by Mitsubishi Plastics Indus. Ltd., Japan. The electrostatic member laminate is cut to form the electrical connectors 55a , 55b that are each an integral extension of the electrodes 50a , 50b , by stamping, punching, or pressing out the electrical connectors 55a , 55b from the electrostatic member 33 . Preferably, the electrical connectors 55a , 55b are cut out so that the electrical leads 60a , 60b and electrical contacts 65a , 65b of the electrical connectors 55a , 55b are disposed within one of the patterned grooves 105 . Disposing the electrical connector within a segment of the grooves 105 allows fabrication of the electrodes 50a , 50b , the integral electrical connectors 55a , 55b , and the grooves 105 in a single step process. After cutting out the electrical connectors 55a , 55b , residual insulator on the electrical connectors 55a , 55b is removed by peeling off the insulator layer to expose the underlying electrically conductive layer to form the electrical contacts 65a or 65b . The insulated electrical leads 60a , 60b and electrical contacts 65a , 65b are then inserted through the bores in the base 25 so that the electrical contacts 65a , 65b are disposed below the base 25 as shown in Figure 6. The electrostatic member 33 is then adhered to the base 25 of the chuck 20 , using conventional pressure or temperature sensitive adhesives, such as polyimides. Thereafter, the electrical contacts 65a , 65b are adhered to the support member 75 on the base 25 of the chuck 20 . Voltage Supply Terminal The voltage supply terminals 70a , 70b are located on the support 75 at the interface between the base 25 and the support 75 , as illustrated in Figure 2. Typically, each of the voltage supply terminals 70a , 70b includes a spring loaded right circular pin member 170 disposed in a bore 175 through the support 75 . The pin member 170 terminates in a conductive terminal 180 which is preferably gold-plated copper. A high voltage lead 185 extends from the first voltage supply 85 and through the pin member 170 to contact the conductive terminal 180 . A spring is disposed in the bore 175 of the support 7 5 in contact with the pin member 170 to bias the pin member 170 upwardly into contact with the electrical contacts 65a , 65b of the electrodes 50a , 50b . The interface between the base 25 and the support 75 is sealed to prevent any coolant passing through the bores 30a , 30b of the base 25 , from leaking into the process chamber 80 . A sealing member comprising two sealing rings 190a , 190b is disposed in the interface between the base 25 and the support 75 . A first sealing ring 190a is disposed below the base 25 circumferentially about both the electrical contacts 65a , 65b and the bores 30a , 30b of the base 25 . A second sealing ring 190b is disposed circumferentially about the supply bore 175 of the support 75 , and in alignment with the electrical contacts 65a , 65b . Preferably, the two sealing rings 190a , 190b comprise O-ring seals. The electrostatic chuck 20 having features of the present invention has several advantages. The electrostatic holding system 10 allows the chuck 20 to be used in both non-plasma or plasma processes, by operating the chuck 20 in a bipolar or monopolar mode. During the plasma stage of the process, the holding system 10 allows the chuck 20 to be operated in a monopolar mode, which provides increased electrostatic clamping force to prevent movement or misalignment of the substrate 45 . For these reasons, the chuck 20 of the present invention is a significant improvement over prior art chucks.

Claims: An electrostatic holding system for holding a substrate (45) in a process chamber having a voltage supply (85), the holding system comprising an electrostatic member (35) and at least a pair of electrodes (50a,50b) connected to the voltage supply for holding a substrate to the electrostatic member, the holding system including a switch (140) electrically connecting the electrodes to the voltage supply and having a monopolar position for providing a voltage having a potential to the electrodes (50a,50b) for operating the electrodes as monopolar electrodes to hold electrostatically the substrate to the electrostatic member with a relatively high force; characterised in that the switch (140) also has a bipolar position for providing a voltage having opposing potentials to the electrodes for operating the electrodes as bipolar electrodes to hold electrostatically the substrate to the electrostatic member with a relatively low force. An electrostatic holding system as claimed in claim 1, characterised in that the switch (140) further comprises an open circuit position for connecting the electrodes to an open circuit. An electrostatic holding system as claimed in claim 1 or claim 2, characterised in that the voltage supply in the process chamber comprises a single voltage source (85), the switch in the monopolar mode electrically connecting the electrodes (50a,50b) to the voltage source, and in the bipolar mode connecting at least one electrode (50a) to ground (75) and another electrode (50b) to the voltage source. An electrostatic holding system as claimed in any of claims 1 to 3, characterised in that the electrostatic member (35) is supported by a base (25), and the electrodes (50a,50b) in the electrostatic member are electrically connected to the voltage supply (85) in the chamber via electrical connectors (55a,55b) disposed through the base so that when a substrate is held on the electrostatic member, the electrical connectors are substantially covered by the substrate and thereby undergo reduced erosion, each electrode and electrical connector being fabricated from a unitary electrically conductive member. An electrostatic holding system as claimed in any of claims 1 to 4, characterised in that the pair of electrodes (50a,50b) are electrically isolated from one another by an electrical isolation void (52), the electrodes being sized and configured so that the isolation void can form a cooling groove for holding coolant for cooling the substrate. A method of using the electrostatic holding system of claim 1 comprising the steps of: (a) placing a substrate on the electrostatic member; (b) activating the switch to the monopolar position to electrostatically hold the substrate during a plasma process stage; and (c) before or after step (b), activating the switch to the bipolar position to electrostatically hold the substrate during a non-plasma process stage. A method of using the electrostatic holding system of claim 6, characterised in that in the monopolar position, a first voltage is applied to the electrodes so that the electrostatic charges having substantially identical polarity accumulate in the electrodes, and in the bipolar position, a second voltage is applied to the electrodes so that electrostatic charges having opposing polarities accumulate in the electrodes. A method of holding a substrate in a process chamber during a process comprising plasma and non-plasma stages, the method comprising the steps of: (a) securing an electrostatic member comprising at least two electrodes in the process chamber; (b) placing a substrate on the electrostatic member; (c) electrostatically holding the substrate to the electrostatic member with a relatively high force during a plasma process stage by applying a first voltage to the electrodes to operate the electrodes as monopolar electrodes; and (d) before or after step (c), electrostatically holding the substrate to the electrostatic member with a relatively low force during a non-plasma process stage by applying a second voltage to the electrodes to operate the electrodes as bipolar electrodes. A method as claimed in claim 8, characterised in that the electrodes are connected to an open circuit position during the transition between the plasma and non-plasma stages of the process. A method as claimed in claim 8, characterised in that a three-position switch is connected to the electrodes, the switch having (i) a monopolar position for providing the first voltage to the electrodes, (ii) a bipolar position for providing the second voltage to the electrodes, and (iii) an open circuit position for connecting the electrodes to an open circuit. A method as claimed in claim 8, characterised in that the first electrical voltage comprises a direct current voltage of at least about 500 volts, and more preferably from about 500 to about 5000 volts. A method as claimed in claim 8, characterised in that the second electrical voltage comprises at least one of the following: (i) a direct current voltage of at least about 500 volts applied to one of the electrodes, and electrical grounding of the second electrode; or (ii) a direct current voltage having a first electrical potential applied to one electrode, and a direct current voltage having a second electrical potential applied to the other electrode.

Inventors: BIRANG MANOOCHER, CAMERON JOHN F, DESHPANDEY CHANDRA, GOLDSPIEL ALAN, NORTHRUP RON, SHAMOUILLIAN SHAMOUIL, SHERSTINSKY SEMYON, SOMEKH SASSON, BIRANG, MANOOCHER,, CAMERON, JOHN F.,, DESHPANDEY, CHANDRA, GOLDSPIEL, ALAN, NORTHRUP, RON, SHAMOUILLIAN, SHAMOUIL, SHERSTINSKY, SEMYON,, SOMEKH, SASSON
Applicants: APPLIED MATERIALS INC, APPLIED MATERIALS, INC.
Application year: 1995
Main classification: H01L21
IPC codes: H01L21, C23C16, B25J15, H02N13