High temperature electrostatic chuck

Details High temperature electrostatic chuck High temperature electrostatic chuck

1999-12-22

2002-04-23

Leja, Ronald W. (Department: 2836)

Electricity: electrical systems and devices

Electric charge generating or conducting means

Use of forces of electric charge or field

C279S128000

Reexamination Certificate

active

06377437

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to an electrostatic chuck (ESC) useful for processing substrates such as semiconductor wafers. The ESC can be used to support a semiconductor substrate in a plasma reaction chamber wherein etching or deposition processes are carried out. The ESC is especially useful for high temperature plasma etching of materials such as platinum which are not volatile at low temperatures.
DESCRIPTION OF THE RELATED ART
Vacuum processing chambers are generally used for etching and chemical vapor depositing (CVD) of materials on substrates by supplying an etching or deposition gas to the vacuum chamber and application of an RF field to the gas to energize the gas into a plasma state. Examples of parallel plate, transformer coupled plasma (TCP) which is also called inductively coupled plasma (ICP), and electron-cyclotron resonance (ECR) reactors are disclosed in commonly owned U.S. Pat. Nos. 4,340,462; 4,948,458; and 5,200,232. Vacuum processing chambers are typically designed to meet performance specifications which depend on the process to be carried out therein. Thus, the particular plasma generating source, vacuum pumping arrangement and substrate support associated with the particular processing chamber must be customized or specially designed to meet the performance specifications.
Substrates are typically held in place within the vacuum chamber during processing by substrate holders. Conventional substrate holders include mechanical clamps and electrostatic clamps (ESC). Examples of mechanical clamps and ESC substrate holders are provided in commonly owned U.S. Pat. Nos. 5,262,029 and 5,671,116. Substrate holders in the form of an electrode can supply radiofrequency (RF) power into the chamber, as disclosed in U.S. Pat. No. 4,579,618.
Substrates including flat panel displays and smaller substrates can be cooled by the substrate holder during certain processing steps. Such cooling is performed by the application of an inert gas, such as helium, between the substrate holder and the opposed surface of the substrate. For instance, see U.S. Pat. Nos. 4,534,816, 5,160,152; 5,238,499; and 5,350,479. The cooling gas is typically supplied to channels or a pattern of grooves in the substrate holder and applies a back pressure to the substrate. Electrostatic chucks of the monopolar type utilize a single electrode. For instance, see U.S. Pat. No. 4,665,463. Electrostatic chucks of the bipolar type utilize mutual attraction between two electrically charged capacitor plates which are separated by a dielectric layer. For instance, see U.S. Pat. Nos. 4,692,836 and 5,055,964.
Substrate supports for vacuum processing chambers are typically mounted on a bottom wall of the chamber making servicing and replacement of the substrate support difficult and time consuming. Examples of such bottom mounted substrate supports can be found in U.S. Pat. Nos. 4,340,462; 4,534,816; 4,579,618; 4,615,755; 4,948,458; 5,200,232; and 5,262,029. A cantilevered support arrangement is described in commonly owned U.S. Pat. Nos. 5,920,723 and 5,948,704.
High temperature electrostatic chucks incorporating clamping electrodes and heater elements have been proposed for use in chemical deposition chambers. See, for example, U.S. Pat. Nos. 5,730,803; 5,867,359; 5,908,334; and 5,968,273 and European Patent Publication 628644 A2. Of these, EP'644 discloses an aluminum nitride chuck body having an RF metallic electrode plate which is perforated with holes to form a mesh and a heater embedded therein, the chuck body being supported on an alumina cylinder such that the outer periphery of the chuck body extends beyond the cylinder. The '803 patent discloses a chuck body of silicon nitride or alumina having an electrical grid of Mo, W, W—Mo and a Mo heater coil wire embedded therein, the chuck body being supported by a Mo heat choke cylinder which surrounds a Cu or Al water cooled cooling plate in thermal contact with the chuck body by a thermal grease which allows differential expansion between the chuck body and the cooling plate. The '359 patent describes a chuck operational at temperatures on the order of 500° C., the chuck including sapphire (single crystal Al
2
O
3
) layers brazed to opposite sides of a niobium electrode and that assembly brazed to a metal base plate. The '334 patent describes a chuck for use at temperatures in excess of 175° C., the chuck including polyimide films on either side of a monopolar or bipolar electrode with the lower polyimide film self adhered to a stainless steel platen. The '273 patent discloses a layered chuck body including an aluminum nitride top layer, an electrode, an aluminum nitride layer, a metal plate, a heater, a metal plate and an aluminum composite, the chuck body being supported by a cylinder such that the outer periphery of the chuck body extends beyond the cylinder.
Some ESC designs use a heat conduction gas such as helium to enhance conduction of heat between adjacent surfaces of the wafer support. For instance, U.S. Pat. No. 5,155,652 describes an ESC having layers including an upper pyrolytic boron nitride layer or optionally polyimide, alumina, quartz, or diamond, an electrostatic pattern layer comprised of a boron nitride substrate and a conductive pattern of pyrolytic graphite thereon, a heater layer comprised of a boron nitride substrate and a conductive pattern of pyrolytic graphite thereon, and a heat sink base of KOVAR™ (NiCoFe alloy with 29% Ni, 17% Co and 55% Fe). The heat sink base includes water cooling channels in a lower portion thereof and chambers in an upper surface thereof which can be maintained under vacuum during heatup of the chuck or filled with helium to aid in cooling of a wafer supported by the chuck. U.S. Pat. No. 5,221,403 describes a support table comprised of an upper member which supports a wafer and a lower member which includes a liquid passage for temperature control of the wafer, the upper member including an ESC constituted by a copper electrode between polyimide sheets and a gap between contacting surfaces of the upper and lower members being supplied a heat conduction gas. Commonly owned U.S. Pat. No. 5,835,334 describes a high temperature chuck wherein helium is introduced between contacting surfaces of a lower aluminum electrode and an electrode cap which is bolted to the lower electrode, the electrode cap comprising anodized aluminum or diamond coated molybdenum. A protective alumina ring and O-ring seals minimize leakage of the coolant gas between the electrode cap and the lower electrode. The electrode cap includes liquid coolant channels for circulating a coolant such as ethylene glycol, silicon oil, Fluorinert™ or a water/glycol mixture and the lower electrode includes a heater for heating the chuck to temperatures of about 100-350° C. To prevent cracking of the anodization due to differential thermal expansion, the electrode cap is maintained at temperatures no greater than 200° C. In the case of the diamond coated molybdenum electrode cap, the chuck can be used at higher temperatures.
International Publication WO 99/36956 describes a process for plasma etching a platinum electrode layer wherein a substrate is heated to above 150° C. and the Pt layer is etched by a high density inductively coupled plasma of an etchant gas comprising chlorine, argon and optionally BC
1
3
, HBr or mixture thereof. U.S. Pat. No. 5,930,639 also describes a platinum etch process wherein the Pt forms an electrode of a high dielectric constant capacitor, the Pt being etched with an oxygen plasma.
Although there has been some attempts to provide improved chuck designs for use at high temperatures, the high temperatures impose differential thermal stresses which are detrimental to use of materials of different thermal expansion coefficients. This is particularly problematic in maintaining a hermetic seal between ceramic materials such as aluminum nitride and metallic materials such as stainless steel or aluminum. As such, there is a need in the art for improved chuck designs which can accommodate

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