Papers

AVS1997 Session VT+MS-MoA: Contamination-Free Manufacturing II

Monday, October 20, 1997 2:00 PM in Room J1/4

Monday Afternoon

Start	Invited?	Item
2:00 PM		VT+MS-MoA-1 Laser Diode Spectroscopic Study of HCl and Its Application for In Situ Monitoring of a Process Chamber H. Masusaki, S.Q. Wu, T. Satou, J. Dong, A. Ubukata, K. Matsumoto (Nippon Sanso Corp., Japan); H. Kuze, N Takeuchi (Chiba University, Japan) We have developed a 1.74 µm single mode LD (Laser Diode) and measured HCl spectra. So far, it is difficult to conduct a laser spectroscopy between 1.65 µm and 3 µm because of difficulty in availability of a single mode LD to emit light in this region. In this paper, we will present a preliminary study of LD spectroscopic monitoring of HCl gas. The frequency modulation spectroscopy used to obtain a 2nd derivative spectrum was carried out by using an in-house DFB (Distributed Feed Back) LD operating at 1.74 µm which corresponds to the HCl gas absorption line. The detector is an InGaAs photodiode. The sample cell is 50 cm long. Flat parallel windows of the sample cell were used to simulate a process chamber window configuration. The measurement pressure was 10663 Pa (80 Torr). HCl gas was diluted by mixing with N₂. HCl calibration curve was obtained between the concentration of 40 ppm and 1% with good linearity. The LOD (limit of detection) at this condition is estimated at 11 ppm (3 times standard deviation), which is limited by the optical etalon fringe because of the flat parallel windows of the cell. Upper limitation is due to the absorption saturation. It's possible to achieve an overall improvement by 3 orders of magnitude by using the Brewster's angle windows of the sample cell and optimizing other conditions. This system is also applicable to an HF in situ monitor with similar sensitivity and dynamic range, judging from the almost identical absorption cross sections. The above results suggest that this system is promising for an in situ process monitor.
2:20 PM		VT+MS-MoA-2 High Rate Cleaning of Surfaces using Atmospheric Pressure Generation of Reactive Metastable Species G.S. Selwyn, I. Henins (Los Alamos National Laboratory); J.Y. Jeong, S.E. Babayan, R.F. Hicks (University of California, Los Angeles) Plasmas are a rich source of reactive species produced by the interaction of energetic electrons with a stable feedgas. Traditionally, two forms of plasmas have been used for materials processing: nonthermal, or low pressure plasmas and thermal, or high pressure plasmas. For many sensitive applications, such as microelectronics processing, low pressure plasmas are used exclusively because of the non-destructive nature of this discharge. We report on a novel approach that spans these two diverse plasma generation methods: the non-thermal, atmospheric pressure plasma jet (APPJ). Unlike low pressure plasmas used for semiconductor processing, this method generates copious amounts of metastable effluent, reactive species not previously used in materials processing. Generation of metastable O₂ by the APPJ greatly exceeds the generation of this species in conventional, low pressure plasmas. These reactive species are then be impinged onto surface for etching or cleaning. The total absence of ions outside of the source, combined with the high output of reactive metastables provides a degree of chemical selectivity and surface reaction rates unobtainable in low pressure discharges. Etch rates for polyimide are routinely achieved at greater than 10 microns/min. This approach is also environmentally-responsible, because the reactive metastables generated typically degrade to harmless ground state compounds in less than 1 second. New approaches to plasma processing, including differences in the handling, throughput and types of materials capable of surface treatment are possible with this novel approach. Use for a wide variety of surface treatments, ranging from paper, to semiconductors and graffiti removal will be discussed, along with characterization of the source and the downstream effluent. The operation of the atmospheric plasma source for cleaning applications will be demonstrated in a short video tape.
2:40 PM		VT+MS-MoA-3 Detection and Filtration of Large Particle Concentrations in CMP Slurries Z. Lin, G. Vasilopoulos (Millipore Corporation) The use of Chemical Mechanical Planarization (CMP) in semiconductor device manufacturing has become an enabling technology, but it has also posed a new set of challenges for the industry. In an oxide CMP process, silica slurries, which are stabilized suspensions of 0.05 to 0.1 µm particles in aqueous solutions at concentrations ranging from 10 to 30%, are applied to the rotating pad to polish the wafer and achieve wafer planarity. Metal slurries used in tungsten CMP to remove excess metal from the wafer surface, leaving filled contact plugs, are two component solutions consisting of an oxidant and an abrasive with particles ranging in size from 0.1 to 1.5 µm at concentrations ranging from 1 to 10%. Large particles, however, in these slurries which may be formed from agglomeration, local drying of slurry on containers, and gel formation due to pH shocks and temperature fluctuation, have been found to cause scratches on the wafer surface resulting in defective wafers. High particle concentrations on the order of 10¹⁵ counts/ml in slurries present unique challenges in delivery, filtration, and particle measurement. Conventional microporous filters used to remove contaminating particles from semiconductor process chemicals tend to retain the active slurry particles and can plug very rapidly. This paper describes methodology and procedures developed to measure large particles in slurry. It describes the filters that are used to remove large particles from CMP slurries without changing the concentration or size distribution of slurry particles, and the location of these filters in CMP processing. It discusses the effect of filtration on the concentrations of large particles and slurry particle size distribution. The effect of volume of slurry filtered on pressure drop, particle retention and particle size distribution, is also presented. The strategy to implement filtration in CMP processes is described to achieve maximum wafer defect reduction.
3:00 PM		VT+MS-MoA-4 Recent Experiences with In Situ Contamination Monitoring & Control V. Menon, M. Grobely (Texas Instruments, Inc) In situ monitors offer the potential of real time detection and interdiction of contamination events in semiconductor processe equipment. If undetected, such events can result in significant loss of yield and cycletime. However, there are many challenges to implementing such monitors in semiconductor manufacturing. This paper will discuss some recent projects at Texas Instruments using in situ particle sensors for monitoring chemical vapor deposition and plasma etch processes. Critical technical and organizational success factors for implementation in manufacturing will be discussed along with an approach to integration of sensor information to factory computer systems.
3:40 PM		VT+MS-MoA-6 A Study of the Behavior of H₂O at Low Concentrations J.W. Martinez de Pinillos, D.A. Zatco (Air Products and Chemicals, Inc); A.D. Johnson (Air Products and Chemicals, Inc.) Water, with its active oxygen atom and highly polar nature, is one of the most damaging gas impurities encountered in the manufacturing of semiconductor chips. In striving for high yields, chip manufacturers set water impurity specifications at low ppbv levels for all bulk gases, and at less than 1 ppmv for most specialty gases. At the same time, H₂O represents one of the most difficult impurities to measure and to control in the manufacturing environment. Water's strong interaction with the distribution system's surfaces introduces surface and history effects not generally found with other gas impurities such as molecular oxygen. Surface effects include loading of the surface with difference species and different amounts, and desorption (emission) influenced by bonding mechanisms and energetics (the temperature effect). The history of the material's exposures to various water impurity levels can seriously influence the way the system has to be used at the start of a process. The properties of the H₂O molecule will be reviewed and data showing its behavior in low concentration in poorly reactive and very reactive gases will be presented and discussed. The behaviors observed will be correlated with surface phenomena in the components that carry the gases from their source to the analyzers being used.
4:20 PM		VT+MS-MoA-8 Contamination Measurement and Control in Vacuum Systems H.F. Dylla (Jefferson Lab) During March of 1997, the AVS sponsored a workshop on the measurement and control of contamination in vacuum systems. The purpose of the workshop was to examine the common problems and potential common solutions for contamination measurement and control (both particulate and gas phase) that affect practitioners in the fields of microelectronic fabrication and accelerator construction and operation. Topics discussed included (1) the evolution of new cleaning methods (high pressure plasmas, high pressure water rinsing, and the use of new surfactants for acqueous cleaning); (2) extending the limits of laser scattering and surface analysis instrumentation for the measurement of particulates; and (3) new optical methods for accurate residual gas analysis. The author will present a summary of the key findings of the workshop. The event provided numerous examples of technical cross fertilization stimulated by the diverse interests of the workshop attendees. This work supported by the Mid Atlantic Chapter of the AVS and U.S. DOE Contract No. DE-AC05-84-40150.
4:40 PM		VT+MS-MoA-9 Excimer Laser Cleaning of Wafer Backside Metallic Particles F. Beaudoin, M. Meunier (Ecole Polytechnique, Canada); M. Simard Normandin (Nortel, Canada); D. Landheer (NRC, Canada) Particles transferred to the wafer backside from handling equipment introduce significant levels of metallic contamination.^1,2 Since the diffusion of metallic contamination, such as Fe, Cr, Ni, Cu, into the bulk of silicon can seriously harm microelectronics devices, it is essential to remove this contamination before any important thermal step during the front end processing. We have developed an excimer laser cleaning system operating at 248 nm to remove backside metallic particles. Both dry and steam laser cleaning were investigated. In the dry cleaning technique, the strong absorption of silicon at the excimer wavelength causes the surface to expend resulting in the removal of particles by momentum transfer. In the steam cleaning technique, the surface is covered with a micrometer-thick liquid film. The liquid film explosion during laser irradiation results in forces high enough to expel the particles from the surface. The surface photovoltage (SPV) method was used to characterize the cleaning efficiency through the change in diffusion length and iron concentration in the silicon bulk. Deliberate iron contamination has been performed using iron oxide particles (diameter 0.5 - 2 µm). Following an RTA at 1050°C for 4 min., SPV measures initial iron concentrations up to 2x10¹³ cm^-3 corresponding to diffusion lengths below 50 µm. For instance, in initial experiments using the steam cleaning technique with a laser fluence below the silicon threshold damage of 200 mJ/cm², the iron concentration in the bulk is reduced by more than 95%, to an iron concentration of 10¹² cm^-3. Effects of the laser fluence, nature and thickness of the liquid film on the cleaning efficiency will be discussed. The removal of other types of backside metallic oxide particles is currently under investigation. ¹F. Beaudoin, M. Simard-Normandin, M. Meunier. To be published in the proceedings of the advanced workshop on silicon recombination lifetime characterization methods, held June 2-3 1997 in Santa Clara, California. ²M. Simard-Normandin, F. Beaudoin, M. Meunier. Particles on surfaces: detection, adhesion and removal (VI), K. L. Mittal. (in print)
5:00 PM		VT+MS-MoA-10 Clustered Dry Cleaning of Residue from an ICP Oxide Etch A.S. Lawing, O. Kwon, Y.P. Han, H.H. Sawin (Massachusetts Institute of Technology) A totally integrated: oxide etch in an Inductively Coupled Plasma (ICP) reactor, oxygen plasma Post Etch Treatment (PET), and dry cleaning sequence has been demonstrated on blanket oxide film and patterned 4" wafers. This process sequence was performed in a clustered system in our laboratory. In this apparatus, we have the ability to transfer samples between processing chambers and perform surface analysis at a base pressure in the low 10^-8 Torr range. In this manner, we can mimic a clustered process, avoid ambient contamination, and obtain an accurate picture of the evolution of the wafer surface throughout the process sequence. We support our cleaning results with quasi in situ angle resolved X-ray Photoelectron Spectroscopy (XPS). High density plasma oxide etching results in the deposition of a fluorocarbon film on the wafer surface. The thickness and chemical composition of the film is dependent on process conditions including; power input to the plasma and the wafer electrode, gas composition, and process pressure. We have adjusted our processing conditions to obtain contaminating films of varying thickness and composition. Our results on blanket wafers indicate that in most cases, an in situ high density oxygen plasma PET is effective in removing fluorocarbon contamination. The PET results in the growth of an oxide film on the order of 50 Å thick. A vapor phase HF process removes the oxide film resulting in a fairly clean surface. In cases where the PET is not as effective in removing the fluorocarbon contamination, UV excited chemistries, including UV/Cl₂ and UV/O₂, have been utilized in combination with the HF/Vapor process to remove both the oxide film and residual carbonaceous contamination.