Papers

AVS1996 Session PS2-WeA: High Density Plasmas II

Wednesday, October 16, 1996 2:00 PM in Room 201B

Wednesday Afternoon

Start	Invited?	Item
2:00 PM		PS2-WeA-1 Linear Slot Antenna Microwave Plasma Source for Large Area Processing D. Korzec, C. Seibert, J. Engemann (University of Wuppertal, Germany) Linear plasma sources are important processing tools for planar substrates. For such applications a homogeneous plasma over a wide area is crucial. Recent examinations of the ring-shaped microwave plasma source SLAN show excellent plasma homogeneity (1). This was achieved by the use of coupling-slots and a resonant cavity. The SLAN-concept was used to develop a long linear plasma source. In this case an annular cavity was replaced with a waveguide cavity. Plasma density and plasma homogeneity in the new source were investigated. Two types of power guiding lines to the source were tested. In the centre of the source prototype (length 80 cm) an ion density of 5.5 x 10\super 11\ cm\super -3\ and an electron temperature of 3.5 eV at a pressure of 0.1 mbar (argon ) with a microwave power of 600 W were measured. Perpendicular to the slots the spread of the plasma is defined by the position of the slots and the form of the cavity. For argon the elongated zones of dense plasma are generated parallel to the slot direction, between each couple of slots. The length of these zones increases with increasing power. Their behavior can be described by use of a surface wave concept similar to that presented in (2). The plasma zone edges are sharply defined at pressure above 1 mbar. A good homogeneity of the plasma along the source especially for low pressures (less than 0.1 mbar) is observed. For oxygen no regular plasma regions at the quartz wall can be established. The plasma ignites and sustains at arbitrary places in the process chamber. A homogeneous plasma can be reached by the use of a remote cage (stainless steel grid), but the ion density outside of the remote cage is 3 times smaller then inside of it. It is possible to build up a linear plasma source with lengths up to two meters by the use of the SLAN-principle. (1) Korzec, D., Werner, F., Winter, R., and Engemann, J. (1996). Scaling of microwave slot antenna (SLAN): A concept for efficient plasma generation, J. Plasma Sources Science and Technol., in press. (2) Werner, F., Korzec, D., and Engemann, J. (1996). Surface wave mode operation of the SLotted ANtenna microwave plasma source, J. Vac. Sci. Technol. A, in press.
2:20 PM		PS2-WeA-2 Electromagnetic Field Patterns in Slot Antenna Microwave Plasma Sources: Numerical Simulation and Measurement J. Engemann, M. Walter, R. Dahlhaus, H. Hutten, D. Korzec (University of Wuppertal, Germany) Microwave plasma sources of slot antenna type (SLAN) (1) are being successfully used for an efficient, homogeneous large volume plasma production. Applications are found in thin film deposition, etching and surface modification. A characteristic feature of all SLAN-sources is the coupling of 2.45 GHz microwave energy usually from a magnetron through waveguides to an annular cavity forming the core part of SLAN's. From the annular cavity the microwave power is radiated through slot antennas into a cylindrical quartz plasma chamber. The source dimensions are critical to an efficient microwave power coupling into the plasma and the ignition characteristics as well. In extension to error and trial the source design has been optimized by electromagnetic field calculations. The numerical simulation package MAFIA (Maxwells Equations Finite Integration Algorithm (2) was used for 3-dimensional calculations of the electromagnetic field pattern in SLAN with and without plasma. Simulated field distributions were compared with experimental data obtained by an electromagnetic probe positioned along the source waveguides and in the volume enclosed by the radiating annular waveguide. The calculated frequency spectrum of the source compares well with experimental data obtained by a spectrum analyzer. Special attention has been paid to the identification of the resonance frequencies. (1) Korzec, D., Werner, F., Winter, R., Engemann, J. (1996). J. Plasma Sources and Technol., in press. (2) Weiland, T. (1985). Particle Accelerators, 17, 227-42.
2:40 PM		PS2-WeA-3 8.3 GHz Microwave Plasma Excitation using a Radial Line Slot Antenna M. Hirayama, T. Ohmi (Tohoku University, Japan); T. Yamamoto, M. Ando, N. Goto (Tokyo Institute of Technology, Japan) High-density, uniform, low-temperature plasma is produced without magnetic field by 8.3 GHz circularly-polarized microwave radiated from a radial line slot antenna. The plasma is uniform within \+-\5% over a diameter of 300 mm, though an inside diameter of a vacuum chamber is only 400 mm. The discharge gap can be narrowed to 20 mm with keeping excellent uniformity. The typical value of ion current is 12 mA/cm\super 2\ at the Ar pressure of 50 mTorr and the discharge gap of 20 mm. The small plasma space makes it possible to immediately remove reaction product gas from wafer surface in RIE and plasma CVD process. The plasma source is quite simple. The radial line slot antenna is placed on a quartz flange. The microwave radiated from the antenna is introduced into the vacuum chamber through the quartz flange. The reflection of microwave on the plasma surface is not large, for the plasma density is lower than a cutoff density of 8.5X10\super 11\cm\super -3\ at 8.3 GHz in our operations. The traveling microwave gradually decreases with accelerating the electrons in the plasma. For the uniform plasma generation in the plasma space the excess dissociation, that deteriorates etching selectivity, does not occur. The slot pattern of the antenna, by which the distributions of microwave power density and phase are decided, was optimized to improve the uniformity of the ion current. The radial line slot antenna is quite appropriate to the plasma source for RIE, plasma CVD and plasma oxidation.
3:00 PM		PS2-WeA-4 Homogeneity Characterization of a Large Microwave Plasma S. B\aa e\chu, C. Boisse-Laporte, P. Leprince (CNRS, France); J. Marec (University Paris-Sud, France) Microwave plasma reactor without magnetic field has been designed for large surface treatment or deposition. Using the surfaguide principle, a 2.45 GHz wave is coupled to the plasma created in a 12cm tube surrounded by a metallic cylinder of 18.8 cm diameter. Wave propagation is limited at the top by a movable short circuit, the tube of 30 cm long emerges at the bottom into a 1 meter diameter metallic vessel for treatment. Aim of this paper is to characterize this plasma, particularly the spatial homogeneity, along the tube and mainly over its cross-section. Argon and oxygen gases have been used. Pressure and microwave power were in the range 0.01 to 1 torr and 300 to 2 000 Watt. Wave propagation has been studied. In our case, at low electron density (\<\ 10\super 11\ cm\super -3\) only guide modes can propagate whereas at higher density only 5 plasma modes can propagate. Electric field measurements have shown that mainly the m=3D3 plasma mode (the azimuthal hexapolar one) propagates. Electrostatic probes provide local plasma parameters as electron and ion densities and electron mean energy. In HF environment and in our range of pressure and electron density, technical and theoretical difficulties have been resolved. In argon gas, densities and electron mean energy (several eV) are quite homogeneous over the plasma section. Emission spectroscopy provides excited states repartition. This external diagnostic does not disturb the plasma but gives spatially integrated values. However, the use of 3 axes measurements leads to quasi local informations. Azimuthally, the excited states are quite homogeneous at low pressure, and weakly modulated (m=3D3) at higher ones. Radially the profile depends on the electric field repartition. Actinometry has showed that the atomic oxygen density is rather homogeneous over the section, promising for future surface treatment applications. These all results can be explained by the efficient spatial diffusion under our experimental conditions.
3:20 PM		PS2-WeA-5 Large Volume, Ultra High Frequency Electron Cyclotron Resonance Plasma for Microelectronics Processing K. Yokogawa, N. Itabashi, S. Tachi (Hitachi, Ltd., Japan); K. Suzuki (Hitachi Ltd., Japan) A large diameter, UHF (915MHz) electron-cyclotron-resonance (ECR) plasma has been developed for achieving $@&U (J12 inch wafer plasma etching. Two types of planer antenna were used to obtain a uniform plasma: one is a line-shaped antenna and the other is a disk-shaped antenna. In the present apparatus, magnetic field for ECR was supplied by solenoid coil, and the distance between the antenna and ECR plane (327 Gauss) was set 10 cm. Discharge was able to ignite even at 50 W input power for both antenna, and stable plasmas were maintained in the experimented power range of up to 2.5 kW. The disk-shape antenna being connected to a 915 MHz power supply through a coaxial cable, has been found suitable to generate a uniform plasma with high density. It was found that the present UHF-ECR make possible to generate plasma with higher efficiency at 1-50 mTorr pressure range. The plasma uniformity measured can be controlled within $@!^ (J10% in the discharge tube. Typical ! electron density and electron temperature measured at 10 cm below the ECR plane were 1-3 $@!_ (J10\super 12\/cm\super 3\ and 2-3 eV for Ar discharge at 10 mTorr with a discharge condition of power range of 0.6-2.5 kW. The fluorocarbon gas discharge in the present apparatus has been applied to etch SiO\sub 2\ films in 5-15 mTorr gas pressure range.
3:40 PM		PS2-WeA-6 A Compact Helicon Plasma Tool for R&D R. Chen, A. Quick, N. Hershkowitz (University of Wisconsin, Madison) A compact helicon plasma tool has been developed. The tool uses a single-loop helicon antenna around a pyrex bell-jar to generate low pressure high density plasmas in a low magnetic field (50 - 100 gauss). The plasma is flared into the vacuum chamber by a modified magnetic cusp field in order to obtain a large and magnetic field free processing area with high processing rates. Preliminarily, a SiO\sub 2\ etch rate of 2400 A/min with a +-2% uniformity in an eight inch wafer area has been obtained at a 3 mTorr CF\sub 4\ plasma, 50 gauss B-field, rf bias of 80 W, and rf power of 2 kW. The helicon reactor possesses good accessibility which is important for R & D. The design of the single-loop antenna plasma source and the design of the modifying coil, which can improve the plasma density and uniformity at the wafer stage, as well as the preliminary characterization (including Oxide/poly-Si selectivity) of the new tool will be presented in detail.
4:00 PM		PS2-WeA-7 Frequency Dependence of Helicon Wave Plasmas Near the Lower Hybrid Frequency S. Yun, J. Kim, H. Chang (Korea Advanced Institute of Science and Technology) The frequency dependence of helicon wave plasmas has been investigated with a 25 cm diameter tube, various antennas and gases such as He, Ne, Ar, and Xe at 1-20 MHz and 200-1150 Gauss. There were optimum frequencies where the electron density was maximum at each magnetic field and there was a mode transition from low-mode to high-mode as power increased. When the low-mode changed to the high-mode, the electron density increased and the electron temperature decreased from 7 eV to 4 eV. The optimum frequencies were 3.0, 4.7, 6.9 MHz at B\sub o\ = 350, 700, 1130 Gauss, respectively with a 30 cm Nagoya type III antenna at 2 mTorr of Ar and 740 W when the plasma was at the high-mode. The optimum frequencies were 2.2, 2.8, 3.6 MHz at B\sub o\= 350, 700, 1130 Gauss at 300 W when the plasma was at the low-mode. The electron density was proportional to the magnetic field above 7 MHz but not below 7 MHz in this experiment. The optimum frequencies were proportional to the magnetic field and inversely proportional to the gas mass. The relations between the density and the magnetic field could not be explained by the helicon wave dispersion relation. The possibility of lower hybrid resonance heating and the reason for the difference in optimum frequencies between the low-mode and the high-mode were discussed.
4:20 PM		PS2-WeA-8 Operational Characteristics of the MORI-200 High Density Plasma Source G. Tynan, A. Bailey, III, D. Hemker, A. Kuthi, C. Lee (Plasma & Materials Technologies); T. Shoji (Nagoya University, Japan) The MORI-200 is an inductively coupled radiofrequency (RF) helicon wave plasma source consisting of an antenna/bell-jar generator immersed in a diverging magnetic field which transports plasma into a field-free downstream process chamber. At low source power (500W) plasma is generated in the upstream volume containing the antenna near-field and then diffuses along B into the low-field (<5G) downstream processing chamber. As source power is increased above 1kW the plasma generation volume is enlarged and begins to encompass the diverging B-field region. Downstream radial profiles demonstrate that plasma uniformity and wafer etch rate can be controlled by varying the divergence of the upstream source magnetic field. Power balance estimates are consistent with this picture of upstream plasma generation and followed by transport to the processing region. RF energy propagation and absorption has also been studied. The RF spatial distribution and wave propagation characteristics obey the theoretical m=0 helicon wave dispersion relation, confirming the operational mode of the source. However, rapid wave absorption occurs near the source and is currently under investigation. Spatially resolved optical emission spectroscopy studies show that chlorine is almost completely dissociated near the plasma center. The atomic chlorine density is slightly higher near the RF source, suggesting localized upstream free radical generation followed by transport into the downstream processing region. Spatially uniform downstream plasma and neutral distributions are then produced, and have been used in a variety of etch applications.
4:40 PM		PS2-WeA-9 Metal Etch Application of Extremely High Density Plasma Generated by Modified Helicon Plasma Tool Y. Ueda, K. Tokashiki, H. Miyamoto (NEC Corporation, Japan); K. Minami, K. Kaneko (ANELVA Corporation, Japan) An Extremely High Density Plasma (EHDP) was successfully obtained with Modified Helicon Plasma Tool. And the etching selectivity of AlCu to photoresist was improved from 2.4 to 5.2 by this new plasma tool. Improvement of etching selectivity to photoresist is one of most important subject for metal etching. Because the process technology for next generation ULSI device needs thin(<1 ) DUV photoresist that is etched faster than i-line resist. Currently commercially available metal etch tools have only realized around factor of 2 for a resist selectivity which would not be sufficient for next generation device fabrication. In our experiment, it was found that the resist selectivity strongly correlated with a plasma ion current density. The selectivity increased from 2.4 to 5.2 with an increase of ion current density ranged from 10 to 60 mA/cm2. In addition, an etching residue was completely suppressed under this range. Then the stacked metal wire (TiN/AlCu/TiN/Ti =500/4500/1000/300 A), 0.25 \mu\m (B line width defined by a chemically amplified resist having 0.8 \mu\m (B thickness, was successfully patterned. Thus, the EHDP has an enough potential for the future metal etching process and we believe the extremely high ion current density of 60 mA/cm2 or more for plasma process tools has never been reported. The EHDP was obtained by modified helicon plasma source. Conventional source, made by PMT Corp., is composed of 200mm long of bell jar and RF antenna, generating m=0 mode helicon wave. By reducing the length of plasma source bell jar to 30mm and 0mm, initially obtained ion current density(8 mA/cm2) was enhanced to 80 mA/cm2 at maximum. This plasma generation mechanism has not been clear. However, helicon wave might be created even though the bell jar length is 30mm or 0 mm 1).1) J. E. Stevens, M. J. Sowa and J. L. Cecchi, J. Vac. Sci. Tech., A13(5), 2476 (1995)