1, Rachel J. Watters, am a librarian, and the Director of Wisconsin
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`TechSearch (“WTS”), located at 215 North Randall Avenue, Madison Wisconsin,
`
`53706. WTS is an interlibrary loan department at the University of Wisconsin-
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`Madison.
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`1 have worked as a librarian at the University of Wisconsin library
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`system since 1998.
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`I have been employed at WTS since 2002, first as a librarian
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`and, beginning in 201 1, as the Director. Through the course of my employment, I
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`have become well informed about the operations of the University of Wisconsin
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`library system, which follows standard library practices.
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`This Declaration relates to the dates of receipt and availability of the
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`following:
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`Fischl, DS et al. "Etching of tungsten and tungsten silicide
`films by chlorine atoms." J Electrochem Soc: Solid-State
`Science and Technology, v. 135 n. 8, August 1988, p. 2016-
`2019
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`Standard Operating procedures (or periodicals at the Universifl of
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`Wisconsin-Madison. When an individual issue of a periodical was received by the
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`Library, it would be checked in, stamped with the date of receipt, added to library
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`holdings records, and made available to readers as soon after its arrival as possible.
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`The procedure normally took a few days or at most a few weeks.
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`Exhibit A to this Declaration is a true and accurate copy of the Journal of the
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`Electrochemical Society, Volume 135 Number 8, from the University of
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`Wisconsin-Madison Library collection. A date stamp on the cover of this copy
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`1
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`Page 1 of 8
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`Samsung Exhibit 1020
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`Samsung Exhibit 1020
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`

`indicates that this issue of Journal of the Electrochemical Society, published in
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`August 1988, was received by the Kurt F. Wendt Library, College of Engineering,
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`University of Wisconsin, on August 12, 1988.
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`Based on the information in Exhibit A, it is clear that the journal issue was
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`received by the library on or before August 12, 1988, catalogued and available to
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`library patrons within a few days or at most a few weeks after August 12, 1988.
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`I declare that all statements made herein of my own knowledge are true and
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`that all statements made on information and belief are believed to be true; and
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`further that these statements were made with the knowledge that willful false
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`statements and the like so made are punishable by fine or imprisonment, or both,
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`under Section 1001 of Title 18 of the United States Code.
`
`Date: June 8, 2016 WRachel J.
`
`tters
`
`
`
`Wisconsin TechSearch
`
`Director
`
`Wendt Commons Library
`215 North Randall Avenue
`
`Madison, Wisconsin 53706
`
`Page 2 of 8
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`Page 2 of 8
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`

`

`
`
`
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`’
`
`. a NEWS
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`
`VOL. 135, NO. 8
`
`JESOAN 135 (8) 1859-2114, 311‘C-422C
`
`AUGUST 1988
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`f Page 3 of 8
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`SOCIETY OFFICERS AND STAFF
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`SOLID-STATE SCIENCE (Cont)
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`Analytical Study an Interface of Epitaxial Si and Si Substrate Grown by CO;
`Laser CVD
`.................................................................... ..T. Meguro, N. Ikedo, T. Itoh
`
`Dopant Diffusion in Self-Aligned Silicide/Silicon Structures
`................................................................................................ ..M. Wittmer
`
`Chemical Etching of Germanium
`.......................................................................... ..S. K. Clmmli,j. E. Ayers
`
`Contact Resistance Measurements in GaAs MESFETs and MODFETs by the
`Mogneto-TLM Technique
`................................................................................................. ..D. C. Look
`
`Trench Etches in Silicon with Controllable Sidewall Angles
`.................... ..R. N. Curlile, V. C. Liung, O. A. Pulusinski, M. M. Smadi
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`Defect Generation and Gettering during Rapid Thermal Annealing
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`......................................................... ..W. Zugozdzon-Wosik
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`FTIR and UV/VIS Study of the Interface Between PMMA and Dyed Polyimide
`Thin Films
`....... ..j. N. Cox, K. L. Liamv,]. L. Bozarth, C. H. Ting,]. R. Carruthers
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`High Temperature Fuel Cell with Ceria-Yttria Solid Electrolyte
`................................................... ..H. Yohiro, Y. Balm, K. Eguchi, H. Ami
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`EIectro-Optical Investigation of the Potential Drop at III/V
`Semiconductor/Electrolyte Interfaces
`................................................................ ..P. Lr’musson, C. N. Van Huong
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`Carbon Film Oxidation-Undercut Kinetics
`........................................................................... .._]. Bernstein, T. B. Koger
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`The Kinetics of Tungsten Etching by Atomic and Molecular Chlorine
`....................... ..M. 3111006,], I). S. Fischl, I). R. Olunder, W. J. Siekhuus
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`Luminescence of Polycrystalline Cuprous Oxide Films on Copper Metal at 4 K
`and the Effects of Stress
`............................................................. ..R. C. Kaufman, C. D. Dickinson
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`Luminescence Properties of Eu3+ and Tb3+ in Ln30.X Oxyholides (Ln-XzY-CI,
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`....... ..B. Es—Saklii, F. Guillen, A. Garcia, C. Fouussier, P. Hagcnmullcr
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`Investigation of a Ternary Lithium Alloy Mixed-Conducting Matrix Electrode at
`Ambient Temperature
`......................................... ..A. A. Anmu’, S. Crouch—Baker, R. A. Huggins
`
`Fabrication of Silicon Microstructures Based on Selective Formation and Etching
`of Porous Silicon
`....................................................................................................... ..X-Z. Tu
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`Convective Effects in CVD ReactOrs
`..................................................................... ..j. S. Vrcntus, C. M. Vrcntas
`
`Equilibrium Analysis of the VPE-Hydride Method Using a Gallium-Indium Alloy
`Source
`............................................................................................. ..K. P. Quin/(m
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`Thickness Measurement of Aluminum, Titanium, Titanium Silicide, and Tungsten
`Silicide Films by X-Ray Fluorescence
`...................................................................... ..S. Ernst, C-0., Lec,j—]. Lee
`
`ERRATA Vol. 135, pp. 1085-1092 (I988), Vol. 135, p. 1856(I9B8)
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`REVIEWS AND NEWS
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`Page 4 of 8
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`

`

`2016
`
`J. Electrochem. Soc.: SOLID-STATE SCIENCE AND TECHNOLOGY
`
`August 1988
`
`110, 215 (1983).
`3. H. Nakane, M. Nakayama, T. Ayabe, T. Nishimura, and
`T. Kimura, in “Proceedings of Semiconductors and
`Integrated Circuits Technology,” Vol. 1, p. 571 (1978).
`4. M. K. Lee, C. Y. Lu, and C. T. Shih, This Journal, 130,
`2249 (1983).
`5. D. E. Clark, C. G. Pantano, Jr., and L. L. Hench, “Corro-
`
`sion of Glass," Magazines for Industry, New York
`(1979).
`6. W. A. Pliskin and H. S. Lehman, This Journal, 112, 1013
`(1965).
`7. W. A. Pliskin, J. Vac. Sci. Technol., 14, 1064 (1977).
`8. R. J. H. Lin, J. C. Lee, and P. B. Zimmer, ALO-5300-T2,
`US. Department of Energy, Washington, DC (1979).
`
`Etching of Tungsten and Tungsten Silicide Films by
`
`Chlorine Atoms
`
`D. S. Fisch|,*'1 G. W. Rodrigues,2 and D. W. Hess**
`
`Department of Chemical Engineering, University of California, Berkeley, California 94720
`
`ABSTRACT
`
`Thin films of tungsten and tungsten Silicide were etched both within and downstream from a C12 plasma discharge at
`200 mtorr pressure and temperatures below 150°C. When samples were positioned downstream from the discharge, etch-
`ing proceeded solely by chemical reaction of the film with chlorine atoms. Without a discharge, molecular chlorine did not
`etch tungsten or tungsten Silicide. Downstream and in-plasma tungsten etch rates were approximately equal at 110°C, but
`the chlorine atom etch rate dropped more rapidly than the in-plasma etch rate as temperature decreased. The chemical re-
`action between chlorine atoms and the tungsten film was proportional to the gas phase C1 atom mole fraction. A pretreat-
`ment consisting of either a dilute hydrofluoric acid dip or a short plasma etch cycle was necessary for atom etching of
`tungsten Silicide films. The etch rates of tungsten Silicide in C12 plasmas were approximately an order of magnitude higher
`and less temperature sensitive than those in the downstream (atom) configuration.
`
`
`
`The patterning of tungsten and tungsten Silicide for mi-
`croelectronic circuits has been accomplished by a variety
`of halogen-based dry processing etching techniques (1-8).
`Publications on the patterning of these materials using
`chlorine have only summarized the effects that the process
`parameters have on the anisotropy, etch rate, and selectiv-
`ity (5). The limited results suggest that the etch rate of
`tungsten is related to the concentration of chlorine atoms,
`Cl, produced by either laser irradiation (8) or gas-phase
`electron impact dissociation (5) of molecular chlorine, C12.
`However, the etching process was controlled empirically
`and thus is not based on a fundamental understanding of
`the etching mechanism.
`Control of thin film etching processes during microelec-
`tronic device manufacture is often difficult. In large part,
`the difficulties arise from the complexity of RF glow dis-
`charges, coupled with plasma-film interactions. One
`method of simplifying the etch chemistry of these pro-
`cesses is to utilize an upstream discharge to generate reac-
`tive atoms for etching. Since ion, electron, and photon
`bombardment are absent in this configuration, the pure
`atom etch chemistry can be studied. Comparison of down-
`stream etching with in-plasma or discharge etching then
`generates insight into the role of the plasma. Furthermore,
`such investigations yield fundamental information con-
`cerning atom reactions with materials. In this paper we
`present results on the chlorine atom etching (downstream
`or flowing afterglow reactor configuration) and C12 dis-
`charge etching of tungsten and tungsten Silicide thin films.
`
`Experimental
`The reactor used for plasma etching (in the discharge)
`has been described in an earlier publication (5). The flow
`reactor was modified for atom etching by connecting a dis-
`charge and flow tube upstream from the etching reactor. A
`schematic of the system can be found in Ref. (9).
`An upstream RF discharge was used to dissociate C12
`molecules into Cl atoms, which then passed through a
`flow tube into the reactor where they reacted chemically
`with tungsten or tungsten silicide samples without the in-
`fluence of the discharge. Power was supplied by a Tegal
`
`*Electrochemical Society Student Member.
`“Electrochemical Society Active Member.
`'Present address: Air Products and Chemicals, Inc., Applied Re-
`search and Development, Allentown, PA 18195.
`V
`2Present address: Department of Chemical Engineering, Univer—
`sity Wifcgisin, Madison, Wisconsin 53706.
`Page
`0
`
`Corporation 300W RF generator and matching network to
`the upstream discharge via two 1.0 cm wide copper bands
`that were placed around the 3.8 cm diam quartz discharge
`tube. Spacing between the bands was 1.0 cm. A metal box
`enclosed the discharge area to ensure RF shielding and to
`facilitate forced air cooling of the tube. The 3.8 cm diam
`Pyrex flow tube contained two 90° bends to prevent light
`from the upstream discharge from reaching the reactor
`and thus the photomultiplier tube. The flow tube was
`coated with Halocarbon Corporation 1200 wax to minimize
`recombination of C1 atoms. The tubes and reactor were
`connected using MDC Corporation glass to metal Kwik-
`Flange adapters.
`Samples were placed inside the 2.6 liter Pyrex reactor
`chamber on a temperature controlled 2.5 cm diam
`anodized aluminum rod that served as the lower electrode
`for plasma etching experiments. Rod temperature was var-
`ied from 25° to 150°C using heating tape and an Omega En-
`gineering Incorporated Model 650/660 controller. In order
`to reduce the surface area for atom recombination and
`thus increase the atom concentration at the sample sur-
`face, the upper electrode was removed during tungsten
`atom etching experiments.
`Molecular and atomic chlorine traveled approximately
`60 cm from the discharge section to the sample location.
`The chlorine flow rate was controlled by a needle valve
`and measured with a rotameter. Vacuum was provided by
`a liquid nitrogen cold trap and a Busch Corporation Lotos
`corrosion resistant mechanical pump. The pressure in the
`reactor (200 mtorr) was established by a throttling valve at
`the exit from the reactor and was monitored by a capaci-
`tance manometer.
`The gas phase chlorine atom concentration at the posi-
`tion of the sample was measured by titration with nitrosyl
`chloride (10-13). The NOCl titrant (Matheson) entered the
`reactor approximately 7 cm upstream from the sample lo-
`cation through a manifold to disperse gas evenly through-
`out the fiow cross section. Flow rate was regulated by a
`needle valve and measured with a Tylan FM 360 mass flow-
`meter. Monel and Teflon were the materials used for the
`NOCl delivery system. A Hamamatsu R1928 photomul-
`tiplier tube with a Melles Griot 03FIV008 filter was used to
`monitor the 550 nm emission (chemiluminescence) result-
`ing from the recombination reaction of chlorine atoms (9,
`13, 14) at the position of the sample.
`Tungsten films were prepared by sputter deposition and
`had a thickness of 100 nm and resistivity of 500 pin-cm.
`
`Page 5 of 8
`
`

`

`TUNGSTEN AND TUNGSTEN SILICIDE FILMS
`
`2017
`
`Vol. 135, No. 8
`
`0.4
`
`Residence Time in Flow Tube (sec)
`0. 17
`0.08
`0.06
`
`200 m'l‘orr
`
`rates because, at constant power, the number of atoms pro-
`duced decreases when the residence time in the upstream
`discharge becomes too short. Figure 1 also shows that an
`increase in power to the upstream discharge increases the
`chlorine atom mole fraction. This effect is due to increased
`electron impact dissociation of chlorine molecules.
`Figure 2 shows the effect of increasing the RF power to
`the upstream discharge at a constant flow rate of 100 sccm
`C12 and a pressure of 200 mtorr. As expected, an increase in
`power produces an increase in the Cl atom fraction. At
`100W, one-third of the molecular chlorine molecules that
`enter the system remain dissociated when they arrive at
`the sample location. The data shown in Fig. 2 emphasize
`the fact that molecular dissociation is not linearly related
`to the applied discharge power.
`
`Tungsten etching—The effect of temperature on the
`tungsten etch rate at a pressure of 200 mtorr and a total gas
`flow rate of 100 sccm is shown in Fig. 3. Solid symbols rep-
`resent data from plasma etching experiments (5), where
`the sample is positioned within the discharge and subjec-
`ted to ion bombardment. The open squares are results
`from the current study, where etching of the tungsten film
`is solely due to chemical reaction with chlorine atoms. For
`these data points, the gas-phase mole fraction of chlorine
`atoms, C1, is 0.5. Without an upstream or in situ discharge,
`no reaction of tungsten occurs with chlorine molecules,
`C12, at temperatures up to 150°C. However, it should be
`mentioned that thermal dissociation of chlorine molecules
`and subsequent reaction with tungsten occurs at surface
`temperatures above 600°C (8, 17). As the temperature is re—
`duced, etch rates fall and the rate enhancement by ion
`bombardment is greater than at higher temperatures. The
`atom and plasma etch rates are approximately equal at
`110°C. Obviously, in plasma etching, the etch rate is not
`critically dependent on thermal heating which is a control-
`ling factor in atom etching. In the case of plasma etching,
`ion bombardment from the discharge supplies energy to
`break bonds as well as heat the surface. However, experi-
`ments using thermally bonded samples have shown that
`plasma heating does not significantly affect the tungsten
`etch rate (5). If an Arrhenius temperature dependence is
`assumed, the apparent activation energies of the reactions
`are 0.1 and 0.3 eV/molecule for plasma etching and atom
`etching, respectively.
`It was shown in Fig. 2 that the atom concentration in the
`reactor can be varied by changing the upstream discharge
`power. This fact is used to quantitatively determine the ef-
`fect of the gas-phase chlorine atom concentration on the
`tungsten etch rate. The data in Fig. 4 are from experiments
`at three different temperatures with the flow rate and the
`pressure constant at 100 sccm and 200 mtorr, respectively.
`At these temperatures, the etch rate varies linearly with
`the gas-phase chlorine atom mole fraction. The solid lines
`depict the best fit for all data and are described by
`
`l 12
`
`Temperature (C)
`84
`60
`
`40
`
`100 sccm
`
` wEtchRate(nm/min)
`
`mom etching
`
`200 mTorr
`
`2.4
`
`2.6
`
`3.0
`2.8
`lfl‘cmp X1000 (l/K)
`
`3.2
`
`3.4
`
`Fig. 3. Effect of temperature on the atom and in-discharge etch rate
`of tungsten at 200 mtorr pressure and 100 sccm Cl; flow. The chlorine
`atom mole fraction is 0.5 for the atom etching.
`
`t l l i
`
`0.3
`
`0.2
`
`0.l
`
`125 Walls
`
`75 Watts
`
`Fraction 0.0
`ChlorineAtomMole
`
`
`0
`
`100
`Molecular Chlorine Flow Rate (sccm)
`
`200
`
`Fig. I. Effect of Cl; flow rate on the atom yield in the reactor at 200
`mtorr total pressure and for two different powers to the upstream dis-
`charge.
`
`Chemical vapor deposition was used to form the 250 nm
`thick tungsten silicide films which had a resistivity of 1000
`uQ-cm, and an approximate Si/W ratio of 2.5. Both film
`types were deposited onto oxidized silicon wafers, which
`were then broken into samples of approximately 1 cm2 [de-
`tails of film preparation can be found in Ref. (5)]. Etch rates
`were determined from the film thickness and the time re-
`quired for the film to visually clear from the oxide surface.
`Results
`Chlorine atoms—Molecular chlorine gas, C12, is partially
`dissociated into C1 atoms by the upstream plasma. These
`atoms then travel through the flow tube to the reactor with
`some of them recombining by third body (e.g., C12 or wall)
`collisions. The concentration of gas-phase chlorine atoms
`in the reactor at the location of the sample is varied by
`changing the C12 flow rate and the upstream discharge
`power. Titration results yield a linear relationship between
`the C1 atom concentration and the square root of the chem-
`iluminescence intensity (13-15). The C1 atom concentration
`is then easily determined by measurement of the intensity.
`Since all experiments are performed at a constant pressure
`of 200 mtorr, results are presented in terms of the chlorine
`atom mole fraction.
`The effect of chlorine flow rate on the atom yield in the
`reactor is shown in Fig. 1. At constant RF power, a fixed
`amount of C12 is dissociated in the upstream discharge.
`The number of atoms that recombine while traveling to
`the reactor depends on the flow rate, pressure, and recom-
`bination kinetics. These data show that the chlorine atom
`mole fraction increases with an increase in flow rate at con-
`stant pressure. This behavior is consistent with a decrease
`in gas residence time at higher flow rates since shorter resi-
`dence times mean that more of the atoms produced in the
`discharge arrive at the reactor before recombining (16).
`However, the atom mole fraction levels off at higher flow
`
`200 mTorr
`
`100 sccm
`
`Fraction
`ChlorineAtomMole
`
`0
`
`50
`
`100
`
`150
`
`Power (Walls)
`
`Fig. 2. Effect of the upstream power on the atom yield in the reactor
`at 2
`ton pr
`sur
`IOO sccm Cl
`flow.
`age 3 02f“?!j
`2
`
`Page 6 of 8
`
`

`

`
`
`2018
`
`J. Electrochem. Soc.: SOLID—STATE SCIENCE AND TECHNOLOGY
`
`August 1988
`
`200 m'l‘orr
`100 sccm
`
`(nm/min)
`EtchRate
`
`0.0
`
`0.6
`0.4
`0.2
`Chlorine Atom Mole Fraction
`
`0.8
`
`Fig. 4. Effect of chlorine atom mole fraction on the tungsten etch
`rate at 200 mtorr pressure, 100 sccm CI; flow, and three different rod
`temperatures.
`
`Etch rate [nm/min] = 2.3 X 106 Xc] exp (—3900/T)
`
`where X9, is the chlorine atom mole fraction in the gas—
`phase and T is the anodized aluminum rod temperature in
`Kelvin. The pre-exponential constant in the equation does
`not change with flow rate over the range of 20-150 sccm.
`This observation indicates that the reaction is not limited
`by a mass-transport boundary layer. At 200 mtorr pressure
`and XCI = 0.5, kinetic theory predicts that approximately
`1019 chlorine atoms strike a square centimeter of surface
`per second. An etch rate of 40 nm/min requires that ap-
`proximately 1015 tungsten atoms leave a square centimeter
`of surface per second. If the etch product is assumed to be
`WCl4, the reaction probability of Cl atoms is approximately
`10“. This is the predominate product detected by ultra-
`high vacuum experiments with molecular and atomic
`chlorine beams and is also the product predicted by evalu-
`ation of equilibrium vapor pressures of the possible
`tungsten chloride products at these temperatures (17).
`Tungsten silicide etching—Unlike tungsten, tungsten
`silicide that is exposed to air for longer than a few days
`does not etch spontaneously with chlorine atoms. How~
`ever, if the samples are first dipped in a 5% HF solution or
`subjected to a C12 plasma discharge they can be etched
`downstream by chlorine atoms. Apparently, ion bombard-
`ment is necessary to remove the silicon dioxide layer that
`forms on the surface of the samples during exposure to air
`at room temperature. Therefore, tungsten silicide is etched
`by chlorine atoms by first subjecting the samples to a C12
`discharge for 305 (200 mtorr, 150 sccm total gas flow, 10W),
`which is the shortest time found to ensure complete re-
`moval of the native oxide layers. The amount of material
`removed during the 305 is calculated based on plasma
`etching experiments at the same temperature and the re-
`
`Tcmpcrature (C)
`84
`
`112
`
`60
`
`maining film thickness is used in the atom etch rate calcu-
`lation. Althouugh this procedure is not ideal, the error is
`small. Furthermore, the etch rates calculated in this man-
`ner are in agreement with the rates obtained by using an
`HF dip prior to the etch run. Because exposure to air re-
`sults in the growth of an oxide film on the WSiI surface, the
`upper electrode used for the plasma etch remains in place
`during the atom experiments. This electrode offers addi-
`tional surface area for C1 atom recombination compared to
`the electrode configuration for the tungsten etching exper-
`iments. Chlorine atom concentrations are thus lower than
`observed for identical upstream discharge studies when
`etching tungsten (compare Fig. 4 and 6). The plasma pre-
`treatment is preferred over the HF dip because the film
`clears more uniformly and the endpoint is easier to ob-
`serve. Without a discharge, tungsten silicide did not etch
`in molecular chlorine under the conditions investigated.
`The effect of temperature on the etch rate of tungsten sil-
`icide films in the discharge and by C1 atoms is shown in
`Fig. 5, where the data are obtained at 200 mtorr and 150
`sccm C12 flow rate. The solid symbols are the plasma etch-
`ing results and the open symbols are the Cl atom etching
`results with a Cl mole fraction of 0.2. Clearly, tungsten sili-
`cide is etched by C1 atoms, but at a much slower rate than
`that obtained in the discharge when ion bombardment oc-
`curs. However,
`the relatively low atom concentrations
`could also be a major cause of the reduced etch rates in the
`downstream configuration.
`Similar to the tungsten etching results shown in Fig. 3,
`plasma etch rates of tungsten silicide are less temperature
`dependent than atom etch rates. The apparent activation
`energies calculated from the data in Fig. 5 are 0.06 and 0.16
`eV/molecule for plasma etching and atom etching, respec-
`tively.
`The etch rate of silicon is known to be greatly enhanced
`by ion bombardment in C12 discharges (18, 19). Further-
`more, preliminary investigations in our laboratory indicate
`that heavily doped (approximately 1020 cm”) n+ polysili-
`con films are etched by C1 atoms (downstream configura-
`tion) at comparable rates to those observed for W and
`WSiI. Therefore, the large etch rate enhancement due to
`the discharge and the magnitude of the atom etch rate sug-
`gest that the overall etching process of tungsten silicide is
`limited by the presence of silicon in the film. Whether this
`observation is due to volatility considerations, a reduction
`in electron concentration in the solid (resulting in lowered
`etchant adsorption), or the fact that the strong (1.8 eV)
`Si—Si bond is essentially eliminated in the silicide films is
`not clear at this time.
`The variation of WSiI etch rate with the limited range of
`chlorine atom mole fractions achieved is shown in Fig. 6
`for 100°C, 200 mtorr, and 150 sccm. Again, the etch rate in-
`creases with an increase in the Cl-atom mole fraction. Un—
`fortunately, because of the limited range of chlorine atom
`concentrations that could be obtained with our apparatus,
`a general kinetic expression describing atom etching of
`the tungsten silicide films was not formulated.
`
`
`
`200 mTorr
`150 sccm
`100 C
`
`0.0
`
`0.2
`0.1
`Chlorine Atom Mole Fraction
`
`0.3
`
`E\
`
`EE52Nm.
`
`22L
`
`L)
`
`Fig. 6. Effect of chlorine atom mole fraction on the tungsten silicide
`etch rate at 100°C temperature, 150 sccm Cl; flow, and 200 mtorr total
`pressure.
`
`
`
`EtchRate(nm/min)
`
`plasma etching
`
`150 sccm
`
`200 nl'l‘orr
`
`atom etching
`
`2.4
`
`2.6
`
`2.8
`l/Temp. x 1000 (UK)
`Fig. 5. Effect of temperature on the atom and in-discharge etch rate
`of tungsten silicide at 200 mtorr pressure and 150 sccm Cl; flow. The
`708 fraction is 0.2 for the atom etching.
`
`3.0
`
`3.2
`
`Page 7 of 8
`
`

`

`Vol. 135, No. 8
`
`TUNGSTEN AND TUNGSTEN SILICIDE FILMS
`
`2019
`
`Conclusions
`
`Tungsten and tungsten silicide thin films have been
`etched both by C12 plasma discharges and by C1 atoms
`without the influence of the plasma. Molecular chlorine
`did not etch the films at the temperatures investigated.
`Both films could be etched by atomic chlorine, however, a
`native oxide layer present on tungsten silicide had to be re—
`moved before the atoms could attack the film. The results
`show that plasma interactions greatly enhance the Cl atom
`etch rate of tungsten silicide. However for tungsten, the
`etching process proceeds mainly by chemical reaction of
`the film with C1 atoms and is less affected by the plasma.
`
`Acknowledgments
`The authors thank P. Marmillion at IBM Essex Junction,
`Vermont for supplying the tungsten and tungsten silicide
`samples used in this investigation. The corrosion resistant
`pump was supplied by Busch Incorporated, Virginia
`Beach, Virginia and maintained by Semivac Corporation
`in Milpitas, California. This work was funded by Intel Cor-
`poration and the California State MICRO program.
`
`Manuscript submitted Oct. 9, 1987; revised manuscript
`received Jan. 18, 1988.
`
`REFERENCES
`1. S. P. Murarka, Solid State Technol., 181 (Sept. 1985);
`SP. Murarka, “Silicides for VLSI Applications,”
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`2. Y. Pauleau, Solid State Technol, 61 (Feb., 1987); R. S.
`Blewer, ibid., 117 (Nov. 1986).
`
`@m-QODU!
`
`3. T. P. Chow and A. J. Steckl, This Journal, 131, 2325
`(1984).
`4. Workshop on Tungsten and Other Refractory Metals
`for VLSI Applications, Continuing Education in En-
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`. D. S. Fischl and D. W. Hess, This Journal, 134, 2265
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`. G. Koren, Appl. Phys. Lett., 47, 1012 (1985).
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`. M. Rothschild, J. H. C. Sedlacek, J. G. Black, and D. J.
`Ehrlich, J. Vac. Sci. Technol. B, 5, 414 (1987).
`. D. A. Danner and D. W. Hess, J. Appl. Phys, 59, 940
`(1986).
`10. M. A. A. Clyne and W. S. Nip, in “Reactive Interme-
`diates in the Gas Phase,” by D. W. Setser, Editor,
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`Soc., Faraday Trans. II, 68, 153 (1972).
`12. M. A. A. Clyne and H. W. Cruse, ibid., 68, 1281 (1972).
`13. M. A. A. Clyne and D. H. Stedman, Trans. Faraday
`Soc., 64, 1816 (1968).
`14. M. A. A. Clyne and D. H. Stedman, ibid., 64, 2698
`(1968).
`15. M. A. A. Clyne and D. J. Smith, J. Chem. Soc., Faraday
`Trans. 2, 75, 704 (1979).
`16. C. G. Hill, “An Introduction to Chemical Engineering
`Kinetics and Reactor Design," p. 262, John Wiley
`and Sons, Inc., New York (1977).
`17. M. Balooch, D. S. Fischl, D. R. Olander, and W. J. Siek-
`haus, This Journal, 135, 0000 (1988).
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`3. 485 (1985).
`19. R. H. Bruce, Solid State Technol, 64 (Oct. 1981).
`
`Phosphorous Vacancy Nearest Neighbor Hopping Induced
`
`Instabilities in InP Capacitors
`l. Experimental
`
`M. T. Juang, J. F. Wager, and J. A. Van Vechten*
`
`Department of Electrical and Computer Engineering, Center for Advanced Materials Research, Oregon State University,
`Corvallis, Oregon 97331
`
`Variable temperature bias-stress measurements were performed on n-type InP MIS capacitors. Two distinct activa-
`tion energies at 40-50 meV and 1.1-1.2 eV were obtained over a temperature range of 100-350 K. These energies are consist-
`ent with the instability mechanisms of thermionic tunneling into native oxide traps and phosphorous vacancy nearest
`neighbor hopping (PVNNH). The estimated fraction of shift in these particular samples due to PVNNH varies both with
`stress time and with temperature from about 20% for short times at 300 K to about 80% for long times at 350 K.
`
`ABSTRACT
`
`The drain current of an InP metal insulator semicon-
`ductor field effect transistor (MISFET) is often observed to
`decrease as a function of time after the application of a
`positive gate bias which induces an accumulation of elec-
`trons in the channel. Various models have been proposed
`for this drain current drift (DCD) phenomena [see Ref. (1)
`for a critical review of proposed DCD models].
`In this study, we have employed variable temperature
`bias-stress measurements (see the section on Experimen-
`tal Procedure for a description of this technique