CROSS-REFERENCE TO RELATED
BACKGROUND OF THE INVENTION
SPUTTERING METHOD FOR THIN FILM giving an example of the type of substrate which is in
DEPOSITION ON A SUBSTRATE tended for use with the invention. No limitations are
intended by the expression which has only been used for introduction purposes. 5 The invention herein is primarily concerned with the coating of thin flexible substrates arranged in strips or Reference will be made herein to two patent applica- elongate members in an atmosphere of some inert gas tions filed by the applicant and assigned to the same as- such as argon using a thermal phenomenon which is signee as the assignee of this application. known as plasma vapor deposition. The method is corn
One application is Ser. No. 260,848 filed June 8, 10 monly known as sputtering. 1972 and entitled "ELECTRO-PHOTOGRAPHIC Reference made herein to "plasma" will mean an
FILM," now abandoned. ionized gas created in a d.c. or radio-frequency a.c.
The second patent application is Ser. No. 322,968 field for the purpose of sputtering atoms from a target filed concurrently herewith on Jan. 12, 1973, and enti- onto a substrate. The word "vapor" as used herein will tied "THIN FILM DEPOSITION APPARATUS 15 means a cloud of atomic particles created in a low presUSING SEGMENTED TARGET MEANS" now U.S. sure atmosphere by means of ionization or the like, the Pat. No. 3,829,373. vapor condensing on the surface of the substrate. Ac
cordingly, "plasma vapor" means the cloud of particles created by sputtering.
The invention herein relates to the coating of sub- 20 In the sputtering technique, a hermetic vessel is evacstrates such as flexible film which primarily is arranged uated and then filled with an inert noble gas such as arin lengths by moving the substrate through a vessel in gon. The vessel is equipped with a cathode or target which some type of coating is applied, by plasma vapor made of the material to be deposited and a substrate techniques. holder between which a high voltage a.c. or d.c. electri
Many structures in use today comprise thin members 25 cal field is established. The vessel may be made of which have been uniformly coated with one or more stainless steel or heat resistant glass so as not to react substances whose characteristics and properties differ with the sputtered material or the substrate. The target substantially from those of the members. The member usually consists of a disc carefully brazed or otherwise receiving the coating is usually called a substrate and bonded to a target holder which is cooled by a suitable the coating is applied by one of several different tech- 30 COolant such as water to maintain a constant temperaniques. Such structures include photographic film and ture. Various means are used to control temperature, paper, optical articles, other photosensitive structures, Further features of the usual apparatus include high decorative objects and the like. The techniques by voltage conduits to bring either a.c. or d.c. power to the which the coatings are applied include vacuum deposi- target from sources on the exterior of the vessel. The tion and plasma vapor techniques these latter two tech- ^5 voltages fall typically in the kilovolt range. The subniques taking place inside of hemetic vessels whose at- strate holder is in juxtaposition to the target as is also mospheres have been altered, by pumping down to cooled to maintain its own temperature which may difachieve vacuum, by introducing atmospheres of differ- fer from the cathode or target temperature. This holder ent types of gases, etc. will usually have its own electrical connections but also
For the purposes of the discussion and description 40 will normally provide for the adjustment of the space which follow, several definitions should be kept in between the target and the substrate to compensate for mind. The expression "thin film" as used herein is in- the gradual thinning of the target or to vary the depositended to mean a layer of some substance such as a tion rate as a function of distance, semiconductor or ohmic material applied to a surface. Since the electrical field may be either d.c. or a.c,
Such a thin film layer is one which has a thickness that ^ the coating of either single or composite materials is cais measured in several thousands of Angstroms, such as pable of being achieved. D.c. sputtering is normally for example 5,000 A or 0.5 microns. The techniques used for single conductive material targets whereas the and apparatus to be discussed make it feasible to de- deposition of composite materials which may consist of posit thin film layers whose thicknesses can be mea- ^ three or four elements necessitates a.c. sputtering at sured in even smaller fractions of microns. radio frequencies.
Another expression which will be used is "photo- If the vapor pressures of the individual elements in a
graphic film." This means a complete article which in- composite target are substantially different, then the eludes a base of some plastic material such as sheeting, element with the highest vapor pressure can be introcarrying an emulsion coating or the like. The article 5J duced in gaseous form. This technique will result in a which is produced by the methods and apparatus of the reaction of the atoms flying from the target toward the invention can be considered a photographic or electro- substrate with the introduced gas during the flight, thus photographic film which comprises a plastic sheet hav- depositing a stoichiometrically accurate compound as ing one or more thin films deposited thereon. the surface coating. This method is called reactive sput
The word "film" with its generic meaning as a thin 6Q tering. coating or thin article without a modifying adjective The presence of the high voltage electric field ionizes will not be used herein in order to avoid confusion. the inert gas thereby producing ions of a type which While the substrate which is coated with thin film ac- knock atoms from the target in addition to heatcording to the method and apparatus of the invention producing secondary electrons which have no practical may be called a "film" of plastic, since it is preferably 65 value. The atoms knocked from the target are driven to of the order of 0.125 millimeters, it will be referred to the substrate and deposited. The process involves mulherein only as a substrate. Reference has been made tiple collisions and complex physical effects but the net previously to a "flexible plastic film" for the purpose of result is the depositing of the metal or other substance