US00541367OA United States Patent (19) 11 Patent Number: 5,413,670 Langan et al. 45 Date of Patent: May 9, 1995 54 METHOD FOR PLASMA ETCHING OR con Using NF Diluted w/ Ar, Ni, and H2' Proc. 2nd CLEANING WITH DILUTED NFs Intl. Conf. on Elec. Mats, 1990 pp. 439-444. Ianno, Greenberg and Verdeyen "Comparison of the 75) Inventors: John G. Langan, Wescosville; Scott Etching & Plasma Characteristics of Discharges in CF4 E. Beck, Kutztown; Brian S. Felker, and NF3' J. Electrochem. Soc. vol. 128, No. 10, pp. Allentown, all of Pa. 274-21.79. 73) Assignee: Air Products and Chemicals, Inc., Chow, Steckl “Plasma Etching of Sputtered Mo & Allentown, Pa. MoSi2. Thin Films in NF3 Gas Mixtures' J. Appl. Phys. vol. 53, No. 8 Aug. 1982 pp. 5531-5540. 21 Appl. No.: 89,210 Donnelly, Flamm, Dautremont-Smith, Werder, "Ani sotropic Etching of SiO2 in Low-Frequency CF4/O2 22 Filed: Jul. 8, 1993 and NF3/Ar Plasma' J. Appl. Phy. 55(1) 1 Jan. 1984, 51 Int. Cl'................................................ B44C 1/22 pp. 242-252. 52 U.S. C. ..................................... 134/1.2; 134/902; Stenger & Akiki "Kinetics of Plasma Etching Silicon 156/643.1 w/ NF3', Mat. Res. Soc. Symp. Proc vol. 68 pp. 58) Field of Search ................ 156/643, 646; 134/902, 267-272. 134/1, 21 Primary Examiner-R. Bruce Breneman 56 References Cited Assistant Examiner-Joni Y. Chang U.S. PATENT DOCUMENTS Attorney, Agent, or Firm--Geoffrey L. Chase; William F. Marsh 4,412,119 10/1983 Komatsu ............................. 219/121 4,522,681 6/1985 Gorowitz. ... 156/643 57 ABSTRACT 4,654,112 3/1987 Douglas ... ... 156/643 4,711,698 12/1987 Douglas ... ... 156/643 A method has been developed for the removal of silicon 4,904,341 2/1990 Blaugher .. ... 156/643 nitride and silicon dioxide, or other semiconductor ma 4,981,551 1/1991 Palmour ... ... 156/643 terials from a surface of a wafer or CVD reactor. The 5,000,113 3/1991 Wang ........ 118/723 method uses NF3, mixed with an electropositive dilu 5,209,803 5/1993 Powell .. ... 156/345 ent, preferably argon, at a given range of concentration, 5,286,297 2/1994 Moslehi ............................... 118/723 pressure, flowrate, and power to obtain the fastest possi ble etch rates. The etch rates of the film being processed FOREIGN PATENT DOCUMENTS can be caused to increase even as the concentration of 63-11674 1/1988 Japan. NF3 in the diluent is decreased by choosing the proper 1194423 11/1989 Japan. diluent and operating conditions. Not only does this method increase the etch rate, thereby increasing the OTHER PUBLICATIONS throughput of the reactor using this process, it also Barkanic, Hoff, Stach, Golja, "Dry Etching Using accomplishes this task at low concentrations of NF3 NF3/Ar and NF3/He Plasma’ Special Technical Test resulting in a lower cost. ing Publication 850, 1984, pp. 110-123. Tan, Goh, Naseem & Brown, “Plasma Etching of Sili 8 Claims, 4 Drawing Sheets Si3N4 Etching SOOO -o- CF4f02 14000 -o- C2F6/02 12OOO -- 25% NF3 in Ar -- 0% NF3 in Ar 10000 -- 7.8% NF3 in Air BOOO -- 37.8% NF3 in Ar -0- 60% NF3 in Air Ha - 75% NF3 in Ar 2000 -0 - 90% NF3 in Ar O 5OO 1OOO 1500 2OOO Pressure (morr) Si3N4 etch rates obtained at 60W RF power, 50sccm total gas flowrate. U.S. Patent May 9, 1995 Sheet 1 of 4 5,413,670 RF Power Supply and Matching Network Molecular Drag Vacuum Pump Figure 1. Schematic of the plasma etching reactor. U.S. Patent May 9, 1995 Sheet 2 of 4 5,413,670 NF3IAir Etching of SiO2 800 1400 1200 -O- 10% N3 1000 -- 7.8% NF3 800 -- 25% NF3 600 -a - 37.6% NF3 L 400 -o- 50% NF3 200 O O 500 1000 500 2000 Pressure (norr Figure 2. SiO2 etch rates obtained at 60W (l.4W/cm2), 50 scam total gas flowrate U.S. Patent May 9, 1995 Sheet 3 of 4 5,413,670 Si3N4 Etching 16000 -o- CF4 fo2 14000 -o- C2F6fo2 2000 -- 25% NF3 in Ar OOOO --d- 10% NF3 in Ar 8000 -- 17.8% NF3 in Ar 8OOO A. -- 37.6% NF3 in Air s t -0- 50% NF3 in Air 4000 O - -a - 75% NF3 in Ar 2000 -o- 90% NF3 in Air O O 5OO OOO 1600 2000 Pressure (Torr) Figure 3. Si3N4 etch rates obtained at 60W RF power, 50s.ccm total gas flowrate. 5,413,670 1. 2 linear function of inlet gas flow (from 4 to 24 sccm) with METHOD FOR PLASMA ETCHING OR power densities of 0.082, 0.123, 0.163, and 0.204W/cm2. CLEANING WITH DILUTEDNFs “As silicon loading is decreased, loss of fluorine atoms in non-etching reactions will become significant relative TECHNICAL FIELD to those consumed in the etching reaction.' The present invention is directed to the field of etch J. Barkanic, A. Hoff, J. Stach, and B. Golja, "Dry cleaning or removal of semiconductor material, such as Etching Using NF3/Ar and NF3/He Plasmas,” Semi films, on deposition equipment or electronic materials conductor Processing, ASTM STP 850, (1984) pp. substrates using a plasma of low concentration nitrogen 110-123, include research in which experiments were trifluoride in a diluent that is more electropositive than 10 performed in a Plasma Therm PK 2440 Dual Plasma/- nitrogen trifluoride, such as argon. Reactive Ion Etch System with 22 in Dia. electrodes The present invention is particularly appropriate to and electrode spacing of 2.6 inches. Helium and argon the removal of silicon dioxide and silicon nitride at were used as diluents with the NF3 being varied from higher etch rates than previously experienced at lower 10% to 80% of the total flow (by volume). For plasma nitrogen trifluoride concentrations than previously uti 15 etching (PE) experiments a fixed flow of 40 sccm was lized. used and pressure ranged from 60 to 500 microns. For RIE the flow was varied from 10 to 40 scom and the BACKGROUND OF THE PRIOR ART pressure ranged from 15 to 80 microns. Power densities Etching and cleaning of SiO2, tungsten, polysilicon ranged from 0.02 to 0.8 W/cm2. "At low NF3 concen and Si3N4 materials are technologically significant pro 20 trations (<40% NF3/inert) the etch rate in either an Air cesses for microelectronics device fabrication. Faster or He mixture is not significantly different. In addition, etch rates are required to increase the throughput of the the etch rate for low percent NF3 mixtures (10 to 20% process, thus decreasing the total cost. NF3/inert) doesn't vary markedly with power density. In most etching processes, diluting the fluorine This indicates that the NF3 concentration in low per source gas, CF4, C2F6, etc. results in a decrease in SiO2 25 centage NF3 mixtures is low enough such that it doesn't or Si3N4etch rates. The NF3 literature reports the same result in more NF3 being dissociated as power density is result, diluting the NF3 results in lower etch rates. increased.' SiO2 etch rates varied from 30 to 1500 Various attempts have been made to use nitrogen A/min depending upon the mode selected. Loading of trifluoride efficiently in the prior art. the chamber was also noted to have an effect on etch U.S. Pat. No. 4,711,698 describes a plasma etching 30 process for thermally grown or CVD deposited silicon rate with the rate decreasing with increasing number of oxide. This work describes selective etching of silicon wafers. oxide to silicon and refractory metals and their silicides. V.M. Donnelly, D. L. Flamm, W. C. Dautremont The preferred embodiment uses a gas mixture of Smith, and D. J. Werder, "Anisotropic Etching of SiO2 BF3/H2/Ar with the claim that the BF3 gas can be 35 in Low-Frequency CF4/O2 and NF3/Ar Plasmas,” J. replaced by one of the following: NF3, SF6, or SiF4 Appl. Phys., vol. 55, no. 1, (Jan. 1984), pp. 242-252, Hydrogen is supplied to the reactor in a carrier gas of describe a protocol in which during all experiments gas argon in the concentration of 3% hydrogen to 97% pressure was 0.35 Torr and total flow rate was 100 argon. Total flow rates are calculated from the flow sccm. Additionally, three types of electrodes were used: rate of the fluorinated gas (BF3, etc.) and the hydrogen (1) hard anodized aluminum; (2) Stainless steel; and (3) flow rate, with the inert gas component disregarded. silicon covered stainless steel lower electrodes. The inventor claims the percentage in the etchant gas "NF3/Arplasmas generated much higher fluorine atom mixture of all atomic species which form in the glow concentrations than CF4/O2 plasmas . The fluorine discharge molecules and radicals capable of adsorbing atom density is ~ 10 times higher than in CF4/50% O2 onto and reducing silicon oxides in the range of 5% 45 under the same conditions (empty stainless-steel reac atomic to 50% atomic of the etchant gas mixture. The tor, power = 0.35 W/cm2, flow rate = 100 sccm, and pressure range claimed is 100 mTorr to 3 Torr. Also pressure =0.35 Torr).” When the lower electrode was claimed is the atomic ratio of fluorine to hydrogen in covered with silicon the fluorine atom concentration in the etchant gas mixture in the range of 15:1 to 30:1. the NF3 plasma dropped by a factor of ~6. Their results Japanese Unexamined Patent Application 63-1674 is 50 of etch rate vs. fluorine atom concentration suggest that an improved cleaning method for plasma CVD cham the same processes are operative in both CF4/O2 and bers utilizing mixtures of argon and NF3.