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Wet cleaning of electrostatic chucksRelated Patent Categories: Cleaning And Liquid Contact With Solids, Liquid Treating Forms And Mandrels, Including Application Of Electrical Radiant Or Wave Energy To WorkWet cleaning of electrostatic chucks description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20060112969, Wet cleaning of electrostatic chucks. Brief Patent Description - Full Patent Description - Patent Application Claims
BACKGROUND [0001] An electrostatic chuck (ESC), a component of semiconductor processing equipment such as plasma etch chambers, can be used for transporting, holding and/or temperature control of a semiconductor wafer or glass substrate (i.e., flat panel display) during processing, for example, in a chemical vapor deposition (CVD), physical vapor deposition (PVD), or etch reactor. ESCs often exhibit short lifetimes resulting in failures including, for example, dynamic alignment failure, high leakage of helium cooling gas between the ESC and the underside of a supported substrate, increased dechucking time, and sticking of the substrate to the ESC or dechucking failure. The early failure of ESCs can cause substrate breakage, impact throughput, lead to particle and defect issues, and increase ownership costs of plasma processing equipment incorporating such ESCs. SUMMARY [0002] Provided is a method of cleaning a new or used electrostatic chuck useful for plasma etching of a dielectric layer on a semiconductor substrate. The chuck includes a ceramic surface on which the semiconductor substrate is supported during the etching. The method comprises contacting at least the ceramic surface of the chuck with (a) isopropyl alcohol; (b) a basic solution that comprises hydrogen peroxide and ammonium hydroxide; (c) a dilute acidic solution that comprises a hydrofluoric acid and nitric acid mixture and/or a dilute acidic solution that comprises a hydrochloric acid and hydrogen peroxide mixture; and/or (d) ultrasonic cleaning, whereby contaminants are removed from the ceramic surface of the chuck. When cleaning a used chuck previously used for supporting a semiconductor substrate during plasma etching of a dielectric layer on the semiconductor substrate, the method preferably further comprises contacting at least the ceramic surface of the chuck with tetramethyl ammonium hydroxide. DETAILED DESCRIPTION [0003] A non-destructive and simple method for cleaning ESCs comprises a wet cleaning process, which does not require stripping or at least partial removal and redepositing a ceramic layer on the ESC. The wet cleaning process comprises cleaning the ESC with organic solvent, basic solution, optionally tetramethyl ammonium hydroxide (TMAH), and dilute acidic solution, as well as ultrasonic cleaning. [0004] Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS) analysis of used ESCs reveals deposition of contaminants on ceramic ESC surfaces following etching. The contaminants change the surface characteristics of the ESCs and cause early failure, as ESC performance greatly depends on the cleanliness of ESC surfaces. Among the contaminants deposited on ESC surfaces during manufacturing of new chucks or when used for dielectric plasma etching are organic impurities, metallic impurities, fluoride impurities, electrode impurities, silicon particles, surface particles, and combinations thereof. More specifically, examples of fluoride impurities include, for example, aluminum fluoride, titanium fluoride, and combinations thereof; examples of metallic impurities include iron, chromium, nickel, molybdenum, vanadium, and combinations thereof; examples of electrode impurities include, tungsten, phosphorus, and combinations thereof; examples of silicon particles include, for example, Si, SiO.sub.2, and combinations thereof. It has been surprisingly discovered that new ESCs can be preconditioned and used ESCs can be recovered by cleaning the contaminants resulting from manufacturing or deposited on the ESCs during etching to refresh the ceramic surface by means of a wet cleaning process. [0005] As used herein, dielectric ESCs refer to ESCs used in dielectric etch processes such as plasma etching silicon oxide and low-k materials. An exemplary dielectric ESC can comprise a metal base (e.g., anodized or non-anodized aluminum alloy) with a ceramic surface on which a semiconductor or substrate such as a wafer is supported. As an example, the ceramic surface may comprise a sintered laminate comprising a patterned refractory (e.g., tungsten or molybdenum) electrode between two ceramic layers (e.g., thin ceramic layers approximately 20 mils thick). The laminate may be bonded to the metal base with a bonding material such as a silicone based material containing conductive powders (e.g., aluminum, silicon, or the like). The metal base, approximately 1.5 inches thick, typically includes RF and DC power feeds, through holes for lift pins, helium gas passages, channels for temperature controlled fluid circulation, temperature sensing arrangements, and the like. [0006] ESCs are typically either Coulombic or Johnsen-Rahbek type. Coulombic type ESCs use a dielectric surface layer having a higher electrical resistance to generate coulombic electrostatic forces. Johnsen-Rahbek type ESCs, which often provide higher electrostatic clamping forces for a lower applied voltage, utilize lower resistance dielectric surface layers such as Al.sub.2O.sub.3 doped with, for example, TiO.sub.2. [0007] According to an embodiment, the ceramic dielectric layer of a Johnsen-Rahbek type ESC may comprise 94% Al.sub.2O.sub.3, 4% SiO.sub.2, 1% TiO.sub.2, and 1% CaO, as well as trace amounts of MgO, Si, Ti, Ca, and Mg. According to another embodiment, for a Coulombic type ESC, the ceramic dielectric layer may comprise greater than or equal to 99% Al.sub.2O.sub.3. Thus, depending on the composition of the ceramic layer, elements such as Ti, Si, Mg, and Ca may not be considered contaminants to be removed by the wet cleaning process. In contrast, contaminants such as metal particles and electrode particles (e.g., tungsten or molybdenum) are preferably removed from the surface of the ESC by the wet cleaning process. [0008] Contaminants such as, for example, organic impurities, metallic impurities, and electrode impurities may be found on new ESCs while contaminants such as, for example, organic impurities, fluoride impurities, and silicon particles, may be deposited on the ceramic surface of used ESCs during dielectric etching. The components of the wet cleaning process, i.e., organic solvent, basic solution, optional TMAH, dilute acidic solutions, and ultrasonic cleaning, serve to remove specific contaminants that may be found on ceramic ESC surfaces. [0009] For example, the isopropyl alcohol (IPA, 100%, conforming to SEMI Specification C41-1101A, Grade 1 or better) serves to remove organic impurities. While it is contemplated that other organic solvents may be used, acetone is preferably avoided, as acetone may attack the ESC bonding material. [0010] The basic solution serves to remove organic impurities, metallic impurities, and titanium fluoride. An exemplary basic solution for use in the wet cleaning process may comprise hydrogen peroxide (H.sub.2O.sub.2) (30%, semiconductor grade, conforming to SEMI Specification C30-1101, Grade 1 or better) and ammonium hydroxide (NH.sub.4OH) (29%, semiconductor grade, conforming to SEMI Specification C21-0301, Grade 1 or better). Hydrogen peroxide is a strong oxidizer with a high standard reduction potential. The hydrogen peroxide can react with metal to form metal ions in the weak basic solution of ammonium hydroxide and hydrogen peroxide, which is stable at least up to 70.degree. C. The standard reduction potential of hydrogen peroxide is: H.sub.2O.sub.2+2H.sup.++2e.sup.-=2H.sub.2O E.degree.=1.776V (versus standard hydrogen electrode (SHE)) and the standard reduction potential of hydrogen peroxide in weak basic solution is: HO.sub.2.sup.-+H.sub.2O+2e.sup.-=3OH.sup.-E.degree.=0.878V (versus SHE). The ammonium hydroxide can form complex ions, such as Cu(NH.sub.3).sub.4.sup.2+ and Ni(NH.sub.3).sub.4.sup.2+, with metallic impurities. Since the use of hydrogen peroxide increases the surface potential of ESC ceramic surfaces, it can reduce the redeposition or surface absorption of metals after previous chemical cleaning of ESC ceramic surfaces. For example, the standard reduction potential of copper is: Cu.sup.2++2e.sup.-=Cu E.degree.=0.337V (versus SHE) and the reduction potential of silicon is: Si+2H.sub.2O+2H.sup.++2e.sup.-=2H.sub.2O E.degree.=-0.857V (versus SHE). Thus, silicon can provide electrons to Cu.sup.2+ to form copper metal, which can be absorbed on the ESC ceramic surface. Hydrogen peroxide can remove electrons from silicon, allowing copper to form Cu(NH.sub.3).sub.4.sup.2+, which can be removed. [0011] The optional TMAH (e.g., 2.38 weight %, CC-238S non-ionic developer from Cyantek, Corp., Fremont, Calif.) serves to remove aluminum fluoride, a contaminant that may be found on used ESCs. Thus, used ESCs are preferably cleaned with TMAH. [0012] An exemplary acidic solution for use in the wet cleaning process may comprise hydrofluoric acid (HF) (49%, semiconductor grade, conforming to SEMI Specification C28-0301, Grade 1 or better) and nitric acid (HNO.sub.3) (67%, semiconductor grade, conforming to SEMI Specification C35-0301, Grade 1 or better). The nitric acid serves to remove metal particles and electrode impurities and the hydrofluoric acid serves to remove silicon particles, such as SiO.sub.2. The reaction of hydrofluoric acid with SiO.sub.2 is as follows: 4HF+SiO.sub.2=SiF.sub.4+2H.sub.2O 6HF+SiO.sub.2=H.sub.2SiF.sub.6+2H.sub.2O There is a low concentration of H.sup.+ and F.sup.- ions in a solution of hydrofluoric acid due to a low reaction constant of k.sub.1=1.3.times.10.sup.-3 mol/liter. The presence of nitric acid, with common H.sup.+ ions, should result in an even lower concentration of F.sup.- ions. As hydrofluoric acid may attack ceramic surfaces at their grain boundaries, special care is preferably taken in applying hydrofluoric acid to ceramic surfaces. While not wishing to be bound by theory, it is believed that the addition of nitric acid is effective for metal and metal ion decontamination. As nitric acid is a strong oxidizer, it can react with active metals such as iron, nickel, aluminum, zinc, as well as inactive metals such as copper. The standard reduction potential of nitric acid is: NO.sub.3.sup.-+4H.sup.++3e.sup.-=NO+2H.sub.2O E.degree.=0.957V (versus SHE) [0013] Another exemplary acidic solution for use in the wet cleaning process may comprise hydrochloric acid (HCl) (conforming to SEMI Specification C28-0301, Grade 2 or better) and hydrogen peroxide. This acidic solution serves to remove metallic impurities and electrode impurities. Metal contaminants on ceramic surfaces may include, for example, copper, iron, nickel, titanium, aluminum, and other metal particles. According to Pourbaix Diagrams (E versus pH), in order to remove copper contaminants from ESC ceramic surfaces, the pH of the cleaning solution should be maintained at less than or equal to 6.0 for Cu.sup.2+ or greater than or equal to 12.5 for Cu(OH).sub.hu 2- and the reaction potential on ESC ceramic surfaces should be controlled at 0.50 volts or higher versus SHE. Using nitric acid and hydrogen peroxide in an acidic solution will provide an appropriate ceramic surface potential to achieve an efficient removal of copper. While hydrofluoric acid alone would not be expected to remove copper contamination from an ESC ceramic surface, a solution of nitric acid with hydrofluoric acid and/or hydrogen peroxide with ammonium hydroxide should provide more effective copper decontamination of ESC ceramic surfaces. Metal particles such as iron, nickel, titanium, etc., can be effectively removed by a solution of hydrochloric acid and hydrogen peroxide, as iron and nickel can dissolve in hydrochloric acid and titanium can be oxidized by hydrogen peroxide and then dissolve in a solution of hydrochloric acid. The acidic solution comprising hydrochloric acid and hydrogen peroxide has demonstrated effective decontamination of metal and metal ions, such as aluminum, iron, nickel, and copper. [0014] The acidic solution for use in the wet cleaning process may comprise a mixture of hydrofluoric acid and nitric acid and/or a mixture of hydrochloric acid and hydrogen peroxide. The acidic solution or solutions used may be based on the type of ESC and the conditions to which it is subjected during dielectric etching. For example, to prevent damage to the ceramic surface of a Johnsen-Rahbek type ESC operated at high power (e.g., 3000-6000 W), such an ESC preferably is not cleaned with hydrofluoric acid and nitric acid. [0015] The ceramic surface of the ESC is preferably contacted with the acidic solution and TMAH by wiping while the ESC is on a fixture, with the ceramic surface facing downward. Use of the fixture allows cleaning with the acidic solution or TMAH without causing the cleaning solution to become trapped in passages of the ESC and damaging the bonding layer. [0016] In addition to contacting the ceramic surface of the ESC with the above-described components of the wet cleaning process, cleaning of local stains may be assisted by careful use of a scouring pad, such as a 3M.TM. white Scotch Brite. The scouring helps to remove deposition and contamination (e.g., polymer buildup) on the ceramic surface of the ESC. [0017] The ultrasonic cleaning serves to remove surface particles, as well as particles trapped inside passages in the ESC, for example, water channels, temperature sensor holes, lift pin holes, and through holes, such as helium supply holes and associated microchannels. A particle density on the ESC ceramic surface of less than 0.17 particles/cm.sup.2 is desired following ultrasonic cleaning. [0018] Chemical attack of the bonding area of an ESC during the wet cleaning process is undesirable. Thus, the corrosion resistance of a ESC bond was systematically studied by exposing the bond to different chemicals, with the results indicated in Table I. TABLE-US-00001 TABLE I Temperature Chemical Weight % 25.degree. C. 40.degree. C. 66.degree. C. 90.degree. C. H.sub.2SO.sub.4 <20 X 20-70 X 70-75 X >75 X HNO.sub.3 <10 * X >10 X HF * * X Acetic Acid X HCl >20 * 20-37 * * NH.sub.4OH .sup. 0-10 10-20 X 20-30 X X H.sub.2O.sub.2 <10 * * X 10-30 * X CO.sub.2 * IPA Acetone .largecircle. .largecircle. X Excellent corrosion resistance or very light corrosion * Depends on the type of bond material used .largecircle. May be used, but with considerable corrosion or damage X Severe corrosion or damage (cannot be used) Coating the bonding area with MicroShield.TM. Masking Aid (Structure Probe, Inc., West Chester, Pa.), drying for 30 minutes, and covering with chemical resistant tape (e.g., Kapton.TM. tape or 3M.TM. Electroplating Tape #470, 484, or 854) was found to be an effective means of protecting the bonding area. [0019] Similarly, contact with water, aqueous chemicals, or acetone, but not IPA, can adversely affect electrical contacts, including contacts with plastic insulators and silver coated contacts, on the backside of the ESC. Accordingly, electrical contacts and exposed bonding material on the ESC are preferably protected by covering with masking material and/or chemical resistant tape [0020] As noted above, ESC surfaces such as the wafer-contacting ceramic surface can be analyzed prior to subjecting the ESC to the wet cleaning process to determine whether contaminants are found on a surface of the ESC. Additionally, ESC surfaces can be analyzed after subjecting the ESC to the wet cleaning process to determine whether contaminants are found on a surface of the ESC. Further, plasma etch chamber performance of the ESC can be tested, prior to subjecting the ESC to the wet cleaning process, and preferably after subjecting the ESC to the wet cleaning process. Continue reading about Wet cleaning of electrostatic chucks... Full patent description for Wet cleaning of electrostatic chucks Brief Patent Description - Full Patent Description - Patent Application Claims Click on the above for other options relating to this Wet cleaning of electrostatic chucks patent application. ###  How KEYWORD MONITOR works... a FREE service from FreshPatents1. Sign up (takes 30 seconds). 2. Fill in the keywords to be monitored. 3. Each week you receive an email with patent applications related to your keywords. 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