3,461,054
`F. VRATNY
`Aug. 12, 1969
`CATHODIC SPUTTERING PROM A CATHODICALLY BIASED TARGET
`ELECTRODE HAVING AN RF POTENTIAL SUPERIMPOSED
`ON THE CATHODIC BIAS
`Filed March 24, 1966
`
`INVENTOR
`E VRATNY
`BY
`Jj**^ h-4/>
`ATTORNEY
`
`INTEL 1008
`
`

`

`United States Patent Office P_d J ;4^
`
`25
`
`ftSti
`1 ddl
`CATHODIC SPUTTEklNG FROM A CATHOBI-
`CAIXY BIASED TARGET ELECTRODE HAV-
`EVG AN RF POTENTIAL SUPERIMPOSED ON
`THE CATHODIC BIAS
`Frederick Vratny, Berkeley Heights, NJ., assignor to Bell
`Telephone Laboratories, Incorporated, New York,
`N.Y., a corporation of New York
`Filed Mar. 24 1966,^Ser. No. 537,086
`U.S. CI. 204-192I n t"
`
`ponents as needed), the positive pole of the direct-current
`supply and one end of RF supply 20 being connected to
`b ase plate 14, as at 22. Anode member 15 may be con-
`nected to (a) base plate 14, as at 23, (b) the negative
`5 pole 24 of a direct-current source, the positive pole of
`which is connected to base plate 14 (as at 23), (c) the
`positive pole 25 of a direct-current source the negative
`p0ie 0f which is connected to base plate 14 (as at 23),
`(-rf) a s o u r ce of ait e r n ating Curent 26, one side of which
`9 Claims 10 is connected to base plate 14 (as at 23) (e) an RF sup-
`ply 27, one side of which is connected to base plate 14
`(as at 23) or (/) a direct-current high potential supply
`I,.
`28 by m e a ns of
`i n d u c t or 29 a nd an RF ^ P P^ 30 by
`AuoTTjAr-r m? THTT m « rT nsiTWTT
`i n e a ns of c a p a c i t or 3lj o ne e nd of s aid direct-current sup-
`ABSTRACT OF THE DISCLOSURE
`Enhanced deposition rates are attained during conven- 15 ply and said RF supply being connected to base plate 14
`tional cathodic sputtering or dielectric oxide reactive
`(as at 23).
`sputtering in a system wherein a d-c potential and RF
`The present invention may conveniently be described
`excitation are simultaneously applied at the cathode. The
`by reference to an illustrative example wherein it is de-
`resultant increased deposition rates permit operation of
`sired to cathodically sputter manganese or any of the
`the process at substantially lower sputtering pressures than 20 well known fi'm-forming metals, for example, tantalum,
`employed heretofore, so avoiding an apparent source of
`niobium, titanium, zirconium, aluminum, et cetera, in an
`impurities.
`apparatus of the type shown in the figure. Further, the
`inventive technique may be utilized in the preparation of
`any of the oxides, nitridesand carbides thereof.
`_
`The present invention relates to a technique for the
`deposition of thin films by cathodic sputtering.
`Substrate 17 is first vigorously cleaned. Conventional
`cleaning agents are suitable for this purpose, the choice of
`In recent years, considerable interest has been gener-
`a particular one being dependent upon the composition of
`ated in the electronics industry in thin film components
`the substrate itself. Substrate 17 is then placed upon sub-
`and circuits prepared by cathodic sputtering procedures.
`s t r a te holder
`1 5> as s h o wn ln t he figure the latter being
`Although widely practiced, certain limitations have pre-
`eluded total exploitation of the sputtering technique. Thus, 30 composed of a suitable conductor, typically, the material
`limited deposition rates during conventional and reactive
`it is desired to deposit or any material compatible there-
`sputtering, control of thickness uniformity, pressure limi-
`with. The vacuum techniques utilized m the practice of
`tations, et cetera, have adversely affected electrical and
`the present invention are known (see Vacuum Deposi-
`*£** i L- H o lla n d' J- ^
`& S o n s' I n c-'
`stractural parameters.
`<£ ^
`oc ^
`In accordance with the present invention, a technique for ^ New York, 1956). In accordance with such procedures,
`enhancing the deposition rate during conventional or di-
`the vacuum chamber is first evacuated, flushed with an
`electric reactive sputtering is described wherein the afore-
`inert gas, as for example, any of the members of the rare
`mentioned drawbacks are appreciably lessened. The in-
`gas family such as helium, argon or neon and the cham-
`ventive technique involves sputtering in a system in which ^ ber re-evacuated. The extent of the vacuum required is
`there are three electrodes, an anode, a cathode and a 40 dependent upon consideration of several factors which
`third electrode, and in which the cathode member is simul-
`are well known to those skilled in the art. However, for
`taneously biased with a direct-current potential and RF
`the purposes of the present invention, a practical initial
`pressure range is 10-5 to 10-7 torr, while suitable inert
`excitation, the anode member being maintained at ground
`potential or biased at least ±1 volt with respect to the _ or reactive gas pressure during sputtering ranges from
`third electrode. The described technique departs from 45
`IQ-4 to 10-1 torr.
`conventional diode sputtering and bias sputtering as de-
`After the requisite pressure is attained, cathode 16 which
`scribed in copending application Ser. No. 372,537,
`filed m ay be composed of any of the above-noted film-forming
`June 4, 1964, now abandoned, in one major aspect, name-
`metals, or, alternatively, may be covered with any of the
`ly, the simultaneous application of a direct-current po-
`film-forming metals, for example, in the form of a foil,
`tential and RF excitation to the cathode.
`5°
`is m a de e l e c t ric any negative with respect to base plate
`The invention will be more readily understood by ref-
`14 a nd a s o u r ce of ^
`e x cit a t i on simultaneously impressed
`erence to the following detailed description taken in con-
`thereon
`junction with the accompanying drawing wherein:
`minimum voltage necessary to produce sputtering
`.
`0
`J.
`/
`r
`The figure is a schematic representation of an exem-
`.
`°
`plary apparatus suitable for the practice of the present in- 55 is dependent upon the particular film-forming metal em-
`^
`•
`ployed. For example, a direct-current potential of ap-
`^With'reference now more particularly to the figure, there
`proximately 1,000 volts may be employed to produce a
`is shown a vacuum chamber 11 provided with an outlet
`sputtered layer of tantalum suitable for the purposes oi
`12 for connection to a vacuum pump (not shown), an
`this invention, minimum voltages for other film-forming
`inlet 13 for the introduction of either an inert or reactive 60 metals being well known to those skilled in the art. How-
`gas or mixtures thereof during the sputtering process, and
`ever, in certain instances, it may be desirable to sputtei
`a base plate 14 which serves the purpose of a third or
`at voltages greater than or less than the noted voltage,
`ground electrode. Shown disposed within chamber 11 is a
`With regard to the RF excitation, it has been found
`substrate holder or anode member 15 and sputtering shield
`_ ^^
`jn order to produce the desired effect the frequencj
`15c and a cathode member 16 and sputtering shie1d 16a, 6o employed must be at least 0.1 megacycle and may range
`member 16 being comprised of a material described here-
`Up t0 t l le p ia s ma frequency which is defined by the fol
`inbelow. Cathode member 16 is connected to the negative
`lowing equation:
`pole 18 or a direct-current high potential supply by means
`of inductor 19 and to an RF supply 20 by means of ^Q
`capacitor 21 (the inductor and capacitor being of such
`value as to pass and reject RF and direct-current com-
`
`/ n e2Y/2
`Wp=(
`)
`\eoW
`
`Q-
`
`

`

`3,461,054
`
`3
`
`4
`grounded, the cathode was biased at 4 kilovolts negative
`wherein
`with respect to ground and an RF supply of 7.05 mega-
`«=electron density
`cycles was impressed thereon.
`e=electron charge
`A glass microscope slide was used as the substrate. The
`e0=dielectric constant of material sputtering, and
`slide was washed in a nonionic detergent followed by a
`Wi=effective electron mass.
`sequential rinse in water, hydrogen peroxide and distilled-
`The use of frequencies less than 0.1 megacycle fail to
`deionized water. The tantalum cathode was employed in
`significantly enhance the operation of the process since
`theJ°Tm
`of an a rc m e l t ed l nSot s l a b-
`the plasma density is not appreciably increased whereas
`The vacuum chamber was initially evacuated to a pres-
`the plasma frequency, as defined above constitutes the
`t he o r d er of 1 0 _6
`absolute maximum beyond which the system shuts down. 10 s u re of
`torr> flushed with argon and
`The potential of the RF source may range from 1 volt to
`re-evacuated to a partial argon pressure of 20 millitorr.
`The
`s u b s t r a te h o l d er a nd cathode were spaced 3 inches
`10 kilovolts, the limits being dictated by practical con-
`siderations.
`apart, the substrate being placed upon the former. A
`The next step in the invention procedure involves ap-
`direct-current voltage of 4,000 volts was impressed be-
`plying a potential to substrate holder 15 and substrate 17 15 tTe en ^
`c a t l l o de and base plate 14 and an RF supply
`J '?
`m eSa cyc l es at 1 kilovolt impressed upon the
`whereby they are maintained at ground potential or made
`electrically negative or positive with respect to base plate
`cathode. ^
`. sPuttering was conducted for 30 minutes, so resulting
`14, as described above. This end may be attained by ap-
`plying (a) a ground potential, (Z>) a positive or negative
`m a tantalum film 2,830 angstroms thick, the deposition
`direct-current potential, (c) an alternating-current poten- 20
`r a'e b e mg aPProximately 94.2 angstroms/minute. The re-
`tial, (d) an RF potential or (e) an RF and a direct-current
`sultant film evidenced a specific resistivity of 51 mi-
`potential to holder 15 by means described above.
`crohm-cm.
`For the purposes of the present invention, it has been
`F or comparative purposes the procedure described
`found that if holder 15 is to be maintained at a potential
`above was repeated with and without RF and with and
`(with respect to base plate 14) other than ground it may 25 without direct current varying the parameters slightly. The
`be at least ± 1 volt direct-current and range up to +1,000
`results are set forth in the table below.
`TABLE
`
`Example
`
`Cathode Gas
`
`Pressure
`(millitorr)
`
`RF Freq.
`(mc.)
`
`D.C. at
`cathode
`
`Deposition
`rate.
`A./min.
`
`Ar
`Ar
`Ar
`Oj
`Oj
`Oj
`Ar
`Ar
`Oi
`Oj
`
`20
`20
`20
`20
`20
`20
`1.5
`1.5
`20
`20
`
`7.05
`0
`7.05
`0
`7.05
`7.05
`0
`29.7
`0
`7.05
`
`4,000
`4,000
`0
`4,000
`0
`4,000
`4,000
`4,000
`4,000
`4,000
`
`94.2
`80
`0
`0 5
`0
`57 9
`
`76
`5
`100
`
`(1)
`
`— Ta
`1—-
`Ta
`2
`Ta
`3
`Ta
`4
`Ta
`5-
`Ta
`6
`Ta
`7
`Ta
`8—-
`Mn
`9-—
`Mn
`10
`1 No Discharge.
`From the data, it was established that metal films can(cid:173)
`volts on the positive side and approximately —5,000 volts
`not be deposited by the sole application of either low
`on the negative side. Alternatively, an alternating-current
`frequency or RF excitation at the cathode nor can dielec-
`potential ranging up to 5,000 volts may be applied to the
`trie oxide films be deposited by the sole application of low
`ungrounded substrate holder, so attaining similar results.
`frequency excitation at the cathode using an oxygen re-
`The RF requirements in the remaining alternatives are
`45 active atmosphere. On the other hand, the simultaneous
`as previously discussed.
`use of a negative potential and RF excitation at the
`The spacing between the substrate holder (anode) and
`cathode produces higher deposition rates of metal films
`cathode is not critical. However, the minimum separation
`than conventional direct-current cathodic sputtering and
`is that required to produce a glow discharge. For the best
`higher deposition rates of dielectric oxide films than by
`efficiency during the sputtering process, the substrate
`should be positioned immediately without the well known 50 conventional reactive sputtering. As a result of the higher
`Crooke's dark space.
`deposition rate at conventional sputtering pressures (20
`The balancing of the various factors of voltage, pressure
`millitorr) it is possible to decrease sputtering pressures to
`and relatives positions of the cathode and substrate holder
`a magnitude of 0.1 millitorr and obtain conventional dep-
`to obtain a high quality deposit is well known in the
`osition rates,
`sputtering art.
`55 While the invention has been described in detail in the
`With reference now more particularly to the example
`foregoing specification, it will be appreciated by those
`under discussion, by employing a proper voltage, pressure
`skilled in the art that a screen plate or ring assembly and
`and spacing of the various elements within the vacuum
`magnetic field may be employed for further increasing
`chamber, a layer of a film-forming metal is deposited
`the plasma density and sputtering rate,
`upon substrate 17 or a dielectric oxide layer is deposited 60 What is claimed is:
`thereon depending upon the sputtering gas employed.
`1. A method for the deposition of thin films upon a
`Sputtering is conducted for a period of time calculated to
`substrate by cathodic sputtering in a vacuum chamber
`produce the desired thickness.
`in which are disposed a first electrode which is designated
`Several examples of the present invention are described
`a target electrode and serves as a source of material to
`in detail below. These examples are included merely to 65 be sputtered which is conductive in nature, a second
`aid in the understanding of the invention, and variations
`electrode having a substrate positioned thereon and a
`may be made by one skilled in the art without departing
`third electrode which serves as a reference electrode
`from the spirit and scope of the invention.
`which comprises the steps of evacuating the said vacuum
`Example I
`chamber, admitting a sputtering gas thereto and simul-
`70 taneously biasing said first electrode with RF excitation
`having a potential of at least one volt at a frequency of
`This example describes the preparation of a sputtered
`at least 0.1 megacycle and a negative direct current, said
`tantalum
`film.
`first
`electrode being negative with respect to said third
`A cathodic sputtering apparatus similar to that shown
`electrode and biasing the said second electrode and sub-
`in the figure was used to produce the tantalum layer. In
`the apparatus employed, base plate 14 and anode 15 were 75 strate with respect to said third electrode.
`
`

`

`3,461,
`054
`
`2. A method in accordance with claim i wherein said
`second electrode and said third electrode are maintained
`at the same potential.
`3. A method in accordance with claim 1 wherein said
`second electrode is biased positive with respect to said
`third electrode.
`4. A method in accordance with claim 1 wherein said
`second electrode is biased negative with respect to said
`third electrode.
`5. A method in accordance with claim 1 wherein said ^
`second electrode is biased with RF excitation with re-,
`spect to said third electrode.
`6. A method in accordance with claim 1 wherein said
`second electrode is simultaneously biased positive with a
`direct-current potential and RF excitation with respect
`to said third electrode.
`7. A method in accordance with claim 1 wherein said
`second electrode is simultaneously biased negative with
`a direct-current potential and RF excitation with respect
`to said third electrode.
`
`lg
`
`20
`
`6
`8. A method in accordance with claim 1 wherein said
`second electrode is biased with an alternating current
`ranging up to 5,000 volts with respect to said third elec(cid:173)
`trode.
`9. A method in accordance with claim 1 wherein said
`third electrode is a structural member defining the inner
`surface of said vacuum chamber.
`References Cited
`UNITED STATES PATENTS
`7/1965 Pendergast
`3,258,413
`3,347,772 10/1967 Laegreid et al.
`3,287,243 11/1966 Ligenza
`
`204—192
`204—298
`204—192
`
`ROBERT K. MIHALEK, Primary Examiner
`
`204—298
`
`U.S. CI. X.R.
`
`