US 3563873 A
Description (OCR text may contain errors)
Feb. 16, 1971 I JDQSQBE'YER' 1 3,563,873
METHOD OF PRODUCING THIN TUNGSTEN-SILICON RESISTOR FILMS Filed June 28, 1968 v z Sheets-Sheet 1 osc GAS f l 26 INVENTOR. Egg; 1 DONALD s. BEYER ATTORNEYS Feb. 16, 1971 D. s. BEYER 3,563,873
METHOD OF PRODUCING THIN TUNGSTEN-SILICON RESISTOR FILMS Filed June 28) ;1 aas 3 sheets-'shet 2 LIZ-"1:5- E
, INVENTOR. DONALD s. BEYER ATTORNEYS D. s. BEYER 3,563,873 METHOD OF PRODUCING THIN TUNGSTEN-SILICON;RESISTOR FILMS Feb. 16, 1971 3 Sheets-Sheet 3 i Filed June 28 1968 INVENTOR.
DONALD S. BEYER ATTORNEYS United States Patent 3,563,873 METHOD OF PRODUCING THIN TUNGSTEN- SILICON RESISTOR FILMS Donald S. Beyer, Scottsdale, Ariz., assignor t0 Dickson Electronics Corporation, a corporation of Arizona Filed June 28, 1968, Ser. No. 741,076 Int. Cl. C23c 15/00 US. Cl. 204-192 6 Claims ABSTRACT OF THE DISCLOSURE The production of thin films on a substrate is effected by sputtering the film on .the substrate; sputtering is achieved by subjecting a tungsten-silicon target to ionic bombardment. The ionizing bombardment is achieved in an argon atmosphere by impressing a RF potential between the target and an aluminum electrode; a grounded aluminum shield shrouds the aluminum electrode.
The present invention pertains to methods of producing thin films, and more particularly, to a method of producing a thin film resistor of the type suitable for use in integrated or miniaturized circuits.
Present methods and techniques for the production of thin film resistors frequently utilize sputtering systems for co-sputtering silicon and tungsten onto a silicon substrate. The resulting composition forming the film is a combination of silicon dioxide, tungsten and oxygen, known in the trade as Ceremet. The production of such thin film resistors leaves much to be desired in that the finished product usually varies from the desired resistance value to the extent requiring subsequent alteration. Alteration of these composite film resistor resistances is usually accomplished by trimming the film with an abrasive blasting compound or by such techniques as diamond abrading or laser beam trimming. The reproducibility of such composite films also sufi'ers since the combination of trace oxygen with the sputtering materials is not consistent, resulting in variations in film resistance and concomitant variations in temperature co-efficient of resistance of the resistor.
It is therefore an object of the present invention to provide a method of producing a thin film resistor by sputtering techniques.
It is a further object of the present invention to provide a method of producing a thin film of silicon and tungsten free of oxygen.
It is another object of the present invention to provide a method for producing a thin film, the physical parameters of which may inexpensively and accurately be controlled by simply controlling power per unit time during the sputtering thereof.
It is still another object of the present invention to provide a method of producing a thin composite film of silicon and tungsten having a very hard and durable surface.
These and other advantages of the present invention will become apparent to those skilled in the art as the description thereof proceeds.
Briefly, in accordance with the embodiment chosen for illustration, the present method co-sputters silicon and tungsten by applying a RF potential between a target of tungsten partialy shrouded by silicon and an aluminum electrode. A grounded aluminum shield shrouds the aluminum electrode from the target and from a substrate positioned in the vicinity of the target; the substrate is continuously moved to insure that the entire surface thereof is uniformly subjected to the silicon and tungsten particles dislodged from the target by the ionic bombardment. The present invention may more readily be described by reference to the accompanying drawings, in which:
FIG. 1 is a cross-sectional view, partially schematic, illustrating apparatus suitable for practicing the method of the present invention.
FIG. 2 is a top perspective view of the type of apparatus as shown in FIG. 1.
FIG. 3 is an illustration of a tungsten-silicon target for use in the present method.
FIG. 4 is a perspective view of a portion of the apparatus of FIG. 1 showing an oscillating platform supporting the substrate, the aluminum electrode, and the aluminum shield.
Referring now to the drawings, a chamber 10, formed, for example, of a Pyrex cylinder 11 and metal end plates 12 and 13, supports an aluminum electrode 15. The electrode 15 is attached to arm 16 which is electrically insulated from the plate 12 and connected by means of a suitable conductor 20 to one side of an oscillator 21. A tungsten table 25 is electrically connected through the plate 13 to the other side of the oscillator 21 by conductor 26. A predetermined plurality of silicon wafers 30 are uniformly positioned on the table 25 so that the relative exposed area of tungsten and silicon represent the desired proportion of silicon and tungsten to be sputtered onto the substrate. A'plurality of targets 32 are mounted by any convenient means to the underside of an oscillating platform 35. The platform 35 is supported by a shaft 36 extending through the plate 12 and is driven by a conventional electrical motor 40 through a reciprocating arm 41.
A shield 42 constructed of aluminum is positioned to shroud the electrode 15 from both the target and the substrate wafers 32; further, the shield 42 is supported from the plate 12 and is electrically connected to ground. A source 45 of inert gas, such as argon, communicates through valve 46 to the interior of the chamber 10. Similarly, a vacuum pump 50 communicates with the interior of the chamber 10 so that the pressure therein may be lowered.
The method of the present invention may be implemented by apparatus such as that just described by introducing an inert gas, such as argon, into the chamber 10 and reducing the pressure therein by the vacuum pump 50 to a pressure in the range of 0.1 to 3 microns mer cury. The electrical motor 40 is energized by connecting it to any conventional electrical power source (not shown) and the oscillating platform thereby caused to sweep back and forth immediately over the tungstensilicon target formed by tungsten table 25 and silicon wafers 30. The oscillator 21 is energized to apply RF potential between the aluminum electrode 15 and the tungsten-silicon target. The ionic bombardment of the target by argon ions dislodges silicon and tungsten which subsequently travels to the substrates 32. The aluminum acts as a getter and combines with trace oxygen (either atomic or molecular) remaining in the chamber 10. This gettering action permits the deposition of substantially pure silicon unlike the silicon dioxide deposited by prior art methods. The oscillator 21 supplies electrical energy to the system by a balanced line (i.e., the RF potential is applied directly between the electrode and target and is double-ended with neither side being grounded). The aluminum shield 42 acts as an effective shroud to prevent contamination of the target with aluminum. The resulting film produced by this method is very hard and can be controlled by simply controlling the power per unit time delivered by the oscillator 21. The elimination of the requirement to substantially trim the resistor greatly reduces the cost of the production of such composite film resistors. The potential used may be set in accordance with the other parameters and has been found to be generally in the neighborhood of 200 volts; the frequency of the RF potential may also vary but characteristically is in the range permitted for industrial uses (27+ megacycles).
It is possible using the method of the present invention to deposit a layer of pure silicon on a silicon substrate having a thermally grown layer of silicon dioxide thereon. The structure thus formed may be used as a building block for the production of capacitors and the like. It will therefore be apparent to those skilled in the art that many modifications may be made in the method of the present invention without departing from the spirit and scope thereof. It is therefore intended that the present invention be limited only by the scope of the claims appended hereto.
1. A method of producing a composite thin film resistor comprising the steps of: placing a tungsten target in a chamber; covering a predetermined proportion of said tungsten target with silicon to form a tungsten-silicon target; placing a silicon substrate in said chamber, placing an aluminum electrode in said chamber; placing an aluminum shield in said chamber positioned to shroud said aluminum electrode from said silicon substrate and said tungsten-silicon target; introducing an inert gas into said chamber; reducing the pressure in said chamber to the range of 0.1 to 3 microns mercury; and applying a RF potential between said aluminum electrode and said tungsten-silicon target for a predetermined time to ionically bombard said target and sputter tungsten-silicon onto said substrate.
2. The method set forth in claim 1 wherein said inert gas is argon.
3. The method set forth in claim 1 wherein said substrate is silicon with a silicon dioxide layer thereon.
4. The method of claim 1 wherein said silicon substrate is continuously moved relative to said target.
5. The method set forth in claim 4 wherein said inert gas is argon. l
6. The method set forth in claim 5 wherein said RF potential is applied by balanced line and wherein said shield is grounded.
References Cited UNITED STATES PATENTS 3,450,581 6/1969 Shortes 204l92 3,477,935 11/1969 Hall 204-492 3,481,854 12/1969 Lane 204-192 ROBERT K. MIHALEK, Primary Examiner U.S. Cl. X.R. 75-176; 204-298