Papers

AVS1996 Session PS2-ThA: Deposition III - Metals and Sputtering

Thursday, October 17, 1996 1:30 PM in Room 201B

Thursday Afternoon

Start	Invited?	Item
1:30 PM		PS2-ThA-1 Ionized Physical Vapor Deposition using a DC Magnetron Sputtering System Coupled with Secondary Plasma Sources D. Hayden, D. Ruzic, K. Green, D. Juliano (University of Illinois, Urbana); C. Weiss, A. Lantsman (Materials Research Corporation) Using an industry-caliber circular planar magnetron with a 33 cm aluminum target, a DC plasma is coupled with a secondary plasma source to ionize the sputtered metal neutrals. Radio-frequency (RF) and microwave plasmas are each investigated. The RF plasma is created through a two-turn coil located approximately halfway between the target and substrate. The microwaves are transmitted through a waveguide and microwave window perpendicular to the cylindrical axis of the chamber just below the RF coil. The secondary plasma increases the electron density, thereby increasing the probability of the ionization of the metal ions. Applying a small negative bias to the substrate makes a voltage gradient relative to the plasma which draws the metal ions in to the substrate orthogonally. Silicon wafers with patterned trenches are used to study the deposited layer thickness and profile. Comparing experiments with and without an applied bias shows the effect of ionizing the metal on the thin film growth. Increased ability to fill high aspect ratio trenches without the regular effects of isotropic sputtering (such as overhang) is discussed. A weak magnetic field coil of 16 turns is added around the outside of the vacuum chamber between the target and substrate to produce an axial field component of up to eight Gauss. This field confines some electrons and enhances the electron-metal atom collisions, thereby increasing the metal ionization fraction. Tuning the frequency of the RF plasma to the appropriate electron cyclotron frequency of the coil (2.8 MHz per gauss) increases the electron tempteratures and yields increased ionization for the RF plasma experiments in certain pressure regimes.
1:50 PM		PS2-ThA-2 Sputtering Apparatus with External Plasma Injection and with Target/Source Focusing of Deposition Material A. Hershcovitch, V. Kovarik, K. Frederick (PLD Advanced Automation Systems, Inc.) A novel plasma sputtering device which utilizes external plasma injection, and curved targets to focus sputtered atoms unto substrates is being developed at P.L.D. Present day sputtering devices have some shortcomings. Target bias can be set to either optimize the discharge or the sputtering rate but not both (the sputtering coefficient as well as the discharge performance depend on the target bias, but, their optimal voltages do not coincide). Additionally, there is no flexibility for adjusting the background pressure which is determined by discharge optimization. Devices like planar magnetrons, have non-uniform discharge distribution across the target resulting in non-uniform sputtering and poor target utilization. The problem of non-uniformity was adequately addressed with the rotatable magnetron cathode, but the angular dispersion of the sputtered material is worse due to the convex geometry of the cathode; therefore, much of the sputtered material does not reach the substrate. In this device, a plasma, which provides ions for sputtering, is generated external to the target. The injected plasma is formed into a thin uniform sheet across a target by a special magnetic field configuration. The target is concave to focus sputtered atoms unto the substrates. Hollow cathode discharges are used for plasma generation, and a modified Yin- Yang magnetic field forms the plasma into a sheet across the target. Experimental program is in progress. Sputtering and deposition rates will be presented, and the numerous advantages will be discussed.
2:10 PM		PS2-ThA-3 The Effect of Metal on Ionization Mechanism in Magnetron Sources Operating in Self-Sputtering Mode Z. Radzimski, O. Hankins, J. Cuomo (North Carolina State University); W. Posadowski (Technical University of Wroclaw, Poland) It is generally understood that the presence of an inert gas is essential to the operation of magnetron sources. However, often neglected are the effects of metal ions or neutrals originating from the target on the plasma formation. The metal may significantly change the ionization efficiency within the plasma and as a result the overall phenomenon of the sputtering process. For example, it was shown that introduction of sputtered species with low ionization potentials reduces the electron temperature. On the other hand, the ability to sputter deposit in the self-sustained mode without an inert gas indicates that a purely metal ion plasma can be formed using magnetron source. It is interesting to investigate which mechanism is responsible for such effective ionization of species leaving target. Three parameters: the initial pressure of argon, the power density delivered to the magnetron source and the target material have to be considered. In this paper we discuss the operation of a high power density magnetron source during sputtering of a copper target both in standard mode with argon as well as in self-sputtering mode without argon. Light emission spectra were taken in the wavelength range of 300 to 900 nm for various conditions of magnetron operation to understand the transition from standard to self-sputtering mode. We offer explanation on the factors which may be responsible for effective ionization of copper species leaving target. The effect of metal species on the plasma temperature and electron density is discussed based on Maxwellian energy distribution and electron-impact ionization mechanism.
2:30 PM		PS2-ThA-4 Determination of Ionization Fraction and Ion Energy using a Quartz Crystal Oscillator and Gridded Energy Analyzer K. Green, D. Ruzic (University of Illinois, Urbana) Using a quartz crystal oscillator with an attached gridded energy analyzer, the ion to neutral ratio has been determined for a variety of pressures, DC power, and RF power regimes in a DC magnetron sputtering device. The Materials Research Corporation donated this magnetron system to the University of Illinois Plasma Material Interaction group for the purpose of developing new techonologies for filling high aspect ratio trenches and vias. By varying the voltage applied to the grids, the plasma potential and the ion energy distribution have been measured. Comparing the total deposition rate with and without a bias that screens out the ions, but leaves the plasma undisturbed, allows for the determination of the ion to neutral ratio.Additional features of this sensor include an externally controlled shutter which protects the sensor from the initial sputter cleaning. To measure uniformity in the deposition and ionization throughout the plane of the wafer, the sensor is mounted on a linear motion feedthrough and embedded in a slot in the wafer chuck. The sensor can be moved across the entire width of the wafer during normal magnetron operation. For example a magnetron configuration having a pressure of 36-37 mTorr, a DC power of 1 kW, and a net RF power of 140 W at an RF frequency of 13.5 MHz yielded 40-50 % ionization and a plasma potential of 15-20 V.
2:50 PM		PS2-ThA-5 Optical and Film-related Diagnostics of Relative Ionization Uniformity in Ionized Magnetron PVD (I-PVD) System J. Joo (Kunsan National University, Korea); S. Rossnagel, S. Hamaguchi, A. Mayo (IBM T.J. Watson Research Center) Ionized magnetron sputter deposition, also known as I-PVD, utilizes in-flight ionization of atoms sputtered from a conventional magnetron cathode followed by deposition of these metal ions on a surface by means of a small sample bias. This technique results in normal-angle deposition under controlled energy conditions and may be suitable for semiconductor applications for the lining and filling of moderate aspect ratio surface features. The uniformity of the relative ionization of the metal across the discharge is critical because it can result in differing degrees of relative directionality and variations of the effective kinetic energy of the deposition flux across the wafer. Optical emission measurements of the relative ion to neutral ratio have been made spatially across the 30cm cathode diameter. Samples for cross-sectional SEM analysis were also taken as a function of position across the wafer. The relative ionization measured by OES couples well with the relative ionization determined by comparison of the deposited film profiles calibrated by a deposition computer model described previously. Variations in chamber pressure, applied rf power to the inductively-coupled plasma, and chamber geometry all show a definite correlation between measured plasma properties and film topography. This approach can be used to optimize system geometries, operating conditions, and lifetime issues within a system without the expense and difficulty of wafer topography measurements.
3:10 PM		PS2-ThA-6 Crystallographic and Electrical Properties of Sputter-deposited Ta Thin Films formed under Various Ion Bombardment Conditions K. Ino, T. Shinohara, T. Ushiki, T. Ohmi (Tohoku University, Japan) We have clarified the relationship between the crystal structure of sputter-deposited Ta thin film(bcc or \beta\ phase) and the ion bombardment condition during film growth by using dual-frequency-excitation plasma process, which can independently control film growth rate, ion bombardment energy and ion flux to the substrate with high precision. So far, many researchers have studied the relationship, however, it is not clear enough because ion bombardment conditions, especially ion flux, have not been precisely controlled or they are different from researcher to researcher. Therefore we have systematically examined the role of energetic ions in Ta thin film growth by independently controlling film growth rate, ion energy and flux, and by introducing a new parameter, "normalized ion flux" which is defined as the number of ions bombarding a Ta atom. The crystal phase and resistivity of deposited Ta thin film are strongly dependent on normalized ion flux as well as ion bombardment energy. When normalized ion flux is low, the film properties do not depend on ion energy, and all films indicate \beta\-phase and resistivities are around 140\mu\\Omega\.cm. On the contrary, when normalized ion flux is high, the film properties strongly depend on ion energy. In the case of ion energy higher than 30eV, all of the deposited Ta films also indicate \beta\-phase. However, in the case of ion energy lower than 30eV, the lower the ion energy, the larger the amount of bcc-Ta and the lower the resistivity is. The low resistivity of 17\mu\\Omega\.cm has been achieved at ion energy of 10eV and normalized ion flux of 15. In conclusion, the relationship between sputter-deposited Ta film property and ion bombardment condition during film growth has been clarified, and low resistivity bcc-Ta thin film has been successfully formed at low energy and high flux ion bombardment condition.
3:30 PM		PS2-ThA-7 Ta Metallization using an Electron Cyclotron Resonance Plasma Source Coupled with Divided Microwaves H. Nishimura, T. Ono, M. Oda, S. Matsuo (NTT LSI Laboratories, Japan) An advanced ECR plasma source for conductive film deposition has been developed\super 1\. In this source, 2.45-GHz microwaves are divided into two directions and transported into the composer through quartz windows. The windows are in a region where the magnetic field is higher than that of the ECR condition, and are arranged in the blind space from a cylindrical target located below the plasma extraction window. We can deposit Al films stably for over 100 h with no quartz window exchange. Ta film deposition on SiN film has been investigated by ECR sputter deposition. In this technique, we can obtain high-quality films because of enhancement of the sputtering and film formation reaction by highly ionized ECR plasma. A columnar-structure \beta\-Ta with high compressive stress and high resistivity (150 \mu\\Omega\cm) was obtained by Ar plasma. By using Xe, however, \alpha\-Ta with resistivity of 13 to 18 \mu\\Omega\cm was obtained at temperatures higher than 150C, which was achieved by the moderate ion bombardment effect of Xe\super 2\. The compressive internal stress decreased with increasing temperature or film thickness. The stress change in air was less than 10 MPa even 10\super 3\ h after deposition. The Xe in films could not be detected by SIMS. Fine patterns with 100 nm width have been etched into 400 nm thick Ta by ECR ion stream etching. We can obtain low-stress, low-resistivity, and stable Ta films using ECR sputter deposition by controlling the ion bombardment effect. ECR sputter deposition can be used for deposition of Ta film as absorbers of X-ray masks and as diffusion barriers in LSI devices. \super 1\T. Ono, et al., J. Vac. Sci. Technol. A12(1994)1281. \super 2\R. A. Roy, et al., J. Vac. Sci. Technol. B11(1993)1921.
3:50 PM		PS2-ThA-8 Compositional Variations of Sputter Deposited Ti/W Barrier Layers on Substrates with Pronounced Surface Topography C. Hedlund, L. Jonsson, I. Katardjiev, S. Berg (Uppsala University, Sweden) Sputter deposited Ti/W barrier layers have been found to be Ti deficient with respect to the target composition, which is attributed to the preferential re-sputtering of Ti from the deposited films by energetic neutrals or ions from the discharge. On the other hand, the sputterering yield of most materials is known to be strongly dependent on the angle of incidence of the bombarding species. Due to this angular dependence the resputtering rate of Ti/W films will also be a function of the local orientation of the surface. If the films are deposited by bias sputter deposition this preferential resputtering effect will be even more pronounced. The substrates of the IC circuits onto which the Ti/W barrier layers are deposited normally possess a pronounced surface topography. The purpose of this work is to study the deviation of the expected Ti/W concentrations at sloped surfaces as a function of the energy of the bombarding species as well as the atom to ion flux arrival ratio. It is shown that the Ti concentration in the films as a result of the preferential sputtering does exhibit substantial concentration variations accross sloped surfaces at constant discharge parameters. The experiments are done in an Ar r.f. discharge, using a Ti/W target with 50 at.% Ti and 50 at.% W. The films have been analysed by RBS, AES and EDS. The experimental results are discussed and compared with dynamic TRIM simulations, which indicate that the loss of Ti in the deposited films is primarily due to ballistic preferential sputtering effects.
4:10 PM		PS2-ThA-9 Reactive Sputtering Deposition of Aluminum Nitride and Aluminum Oxide Thin Films using Pulsed Techniques C. Guarnieri (IBM T.J. Watson Research Center); Z. Radzimski, N. Williams, J. Cuomo (North Carolina State University) Magnetron sputtering is a powerful technique for thin metallic= film deposition, however, it suffers from some setbacks when it comes to reactive deposition of dielectric films. Since the reaction during sputtering takes place not only on the substrate but also on the target and surfaces in the vicinity of the magnetron source, process stability is affected by the formation of arc discharges. They in turn lead to particle formation and reduction of deposition rate. Another serious disadvantage is disappearing anode effect. Recent development in power supplies for magnetron sources focus on the operation in the range of 10-100 kHz. It has been shown that many existing restrictions related to charging effects can be overcome at these frequencies. Two approaches are generally used: pulsed DC sputtering and AC sputtering with unipolar pulses when applied to one magnetron source. Also, a dual magnetron sputtering has been proposed which practically eliminates charges and disappearing anode effect. In this work we investigate reactive magnetron sputtering of aluminum nitride and aluminum oxide thin films deposited by pulsed technique. We have used the ETERNA81 Magnetron Power Supply which offers two frequency modulated modes of operation: alternating current mode and unipolar current mode. Power Supply generates a series of 75 kHz pulses modulated with 2.5 kHz frequency. The amplitude of the pulses is constant and equal to 7 A. The unipolar mode was compared with a standard DC sputtering. The alternating current mode was used to power two identical magnetron sources for dual magnetron operation.
4:30 PM		PS2-ThA-10 Reactive Sputter Deposition of TiO/sub X/ Thin Films D. Guerin (University of Delaware); S. Shah (E.I. du Pont de Nemours and Company) Titanium oxide thin films were deposited on a variety of substrates using dc sputtering of Ti metal target with an Ar/O/sub 2/ sputtering gas mixture. The gas composition was varied in order to obtain a series of films with varying chemical and physical properties. The hysteresis curve for metallic-non-metallic- metallic mode reactive sputtering was obtained. There is an anomalous increase in the deposition rate just before the transition from metallic to non-metallic mode. The system can be tuned to this high deposition rate condition and operated with the flow rate feed back loop. Proper process parameter control can also lead to a high deposition rate stoichiometric TiO2 thin film growth. A model explaining the anomalous deposition rate will be presented. Films deposited under various deposition conditions were analyzed by x-ray diffraction and x-ray photoelectron spectroscopy to understand the effects of the process parameters on the structure and properties of the film. These results will be presented with special emphasis on the sub- oxide to stoichiometric TiO/sub 2/ formation as a function of partial pressure of oxygen in the sputtering gas mixture.