US3691053A

US3691053A - Getter-sputtering apparatus

Info

Publication number: US3691053A
Application number: US888493A
Authority: US
Inventors: David W F James; David O Spiller; Harvey D Coltman
Original assignee: Bangor University
Current assignee: Bangor University
Priority date: 1969-01-02
Filing date: 1969-12-29
Publication date: 1972-09-12
Anticipated expiration: 1989-09-12
Also published as: DE2000054A1; FR2027696A1; GB1301653A

Abstract

Apparatus and method for getter-sputtering. Material is sputtered from a cathode onto a substrate at a low pressure in an inert atmosphere. Sputtering is effected in a sputter space to which there is access of gas only by way of a gettering antechamber while sputtering is taking place. The sputter space may be arranged co-axially within the gettering space either in a planar arrangement or an arrangement of co-axial chamber with a dividing wall. Alternatively, the gettering chamber may be arranged above the sputter chamber.

Description

Sept 12, 1972 w, JAMES ET AL 3,691,053

GETTER-SPUTTERING APPARATUS 2 Sheets-Sheet 1 Filed Dec. 29, 1969 DAVID WILLIAM FRANCIS JAMES, DAVID OWEN SPILLER and HARVEY DAVID COLTMAN,

Attorneys p 7 D. w. F. JAMES ETAL 3,691,053

GETTER-SPUTTERING APPARATUS Filed Dec. 29, 1969 2 Sheets-Sheet 2 GC E M DW U l/o DAVID WILLIAM FRANCIS JAMES, DAVID OWEN SPILLER and HARVEY DAVID COLTMAN, Inventors Attorneys United States Patent @fice 3,691,053 GETTER-SPUTTERING APPARATUS David W. F. James, David O. Spiller, and Harvey D.

Coltman, Bangor, Wales, assignors to University College of North Wales, Bangor, Wales Filed Dec. 29, 1969, Ser. No. 888,493 Claims priority, application Great Britain, Jan. 2, 1969, 380/69; Nov. 20, 1969, 56,959/ 69 Int. Cl. C23c 15/00 US. Cl. 204-298 7 Claims ABSTRACT OF THE DISCLOSURE The invention relates to getter-sputtering apparatus and a method of sputtering by establishing a clean atmosphere of inert gas by getter action and depositing material onto a substrate by sputtering. The invention seeks to provide a method andmeans for depositing thin films of conductors and/or insulators for thin film and integrated circuits and the like in materials hitherto difficult to use or in purities hitherto difiicult to obtain because of low sputtering rates or other poor characteristics.

According to one aspect of the invention there is provided getter-sputtering apparatus having a housing within which is a sputter space; means for mounting in the sputter space a substrate on which material is to be sputtered; a sputter cathode in the sputter space; a getter space in the housing, access of gas to the sputter space being by way of the getter space only; and a getter electrode in the getter space.

In one embodiment of the invention the sputter space and getter space are chambers within the housing, which chambers are divided by a dividing wall around which is the only access for gas to the sputter chamber. The sputter chamber may be cylindrical and the getter chamber may be an annular chamber surrounding the sputter chamber, the substrate being supported on a platform which is brought up against the rim of the cylindrical dividing wall.

Alternatively the housing may comprise an open-topped can with a removable lid and a removable transverse partition constituting the dividing wall, the sputter chamber being the space below the partition and the getter chamber being the space above the partition.

In another embodiment of the invention the sputter space and the getter space are defined between a planar cathode assembly and a parallel flat anode surface spaced a short distance therefrom, the planar cathode assembly comprising a shield having a flat face on or near which are mounted sputter and getter cathodes parallel with the face, the getter cathode being annular and surrounding the sputter cathode from which it is spaced. The shield is preferably an earthed metal shield and the getter and sputter cathodes are accommodated in recesses in the flat face thereof.

The getter and sputter cathodes may be energised from a direct current source, the cathodes being held negative with respect to the housing and the substrate, which are 3,691,053 Patented Sept. 12, 1972 earthed, for example. Getter action in the getter space is then effected by discharge between the getter electrode (cathode) and the wall of the housing or the anode surface. Alternatively, the getter and sputter cathodes may be energised by radiofrequency currents. This is particularly suitable for the deposition of insulators.

According to another aspect of the invention there is provided a method of sputtering material onto a substrate comprising the steps of supporting the substrate in a sputter space to which gas may enter only by way of a getter space, introducing an inert atmosphere at sub-atmospheric pressure into the sputter and getter spaces, gettering the gas in the spaces and sputtering material into the substrate from a sputter cathode while maintaining gettering action in the getter space.

The inert gas may be argon maintained at a pressure of about 10- torr. The argon may be pre-purified, if required, before being passed to the enclosure by passage over manganous oxide, thus removing oxygen, which is the major impurity.

The invention will further be described with reference to the accompanying drawings, of which:

FIG. 1 is a perspective view, broken away in part, of apparatus according to the invention;

FIG. 2 is a sectional elevation of a modified form of the apparatus of FIG. 1; and

FIG. 3 is a sectional elevation of further apparatus in accordance with the invention.

Referring to FIG. 1, the apparatus comprises a stainless steel can having a cylindrical body H with a fixed base I. The can has a removable lid A carrying three rods B to which is fixed a platform C which is a sliding fit in the can. The platform divides the can into a lower, sputtering chamber S and an upper, getter chamber T. Within the getter chamber is an annular getter cathode D of copper which is supported on a high quality ceramic lead-through insulator G so as to define an annular gap with the body of the can. The gap lies beneath the rim of the can. The body of the can is earthed and constitutes the getter anode.

The sputtering chamber includes a sputtering cathode E mounted at the end of a high quality lead-through insulator F fixed to the lid A and the platform C. The substrate to be sputtered is mounted on a support K which includes a heater which is energised by leads passing through leadthrough I. A shutter M is controllable manually from outside the can so as to obscure a determined part of the substrate. The shutter is operated via a vacuum seal on a click-stop mechanism. This enables the whole substrate to be uncovered or various parts to be uncovered in sequence thereby making deposition of thin film thermocouples possible.

In a typical sputtering operation in accordance with the invention the following procedure is adopted. Firstly the substrate on which the sputtered film is to be deposited is mounted on support K. Lid A and platform C are then replaced, together with cathodes D and E. The can is mounted in an enclosure (not shown) which may be a vacuum collar arrangement as shown at VC in FIG. 2 (to be described more fully). The enclosure is evacuated to a pressure of 10- torr and back filled with argon several times. A flow of 99.995 argon at about 10- torr is then maintained in the enclosure.

A gettering discharge is then established in the getter chamber at approximately 1.2 kv. and 10 ma. for 30 minutes. The sputtering cathode is then caused to sputter for some time to getter the inner section of the can and also remove surface impurities from the sputtering cathode before opening the shutter M and allowing film deposition to take place. Conditions vary with the material of the sputtering electrode but for molybdenum typical conditions would be approximately 2.3 kv. for 30 minutes at 6 ma. followed by film deposition.

A thermocouple (not shown) is mounted on support K to monitor the temperature of the substrate and thermocouple leads therefor are connected to monitoring equipment through sealed lead-in connections L.

Comparative tests have been carried out on a number of materials producing films both with and without the use of the annular gettering electrode D. Film resistance has been used as a criterion for evaluating any apparent improvement in film quality resulting from the use of the extra gettering electrode. In almost every case there was a most noticeable improvement in film quality. Even in the case of copper, which itself sputters rather quickly, an improvement was obtained. In this case a slight difference in colour in the deposited films was also apparent when the extra electrode was brought into use. The following results indicate the improvement obtained in the case of copper and molybdenum films; the ratio of film resistance without the getter electrode operating to that with the getter electrode operating is, for the case of copper, 12:1 and for molybdenum, 3.5: 1.

Referring now to FIG. 2, there is shown apparatus basically the same as in FIG. 1 but having a sliding support SS for the substrate which allows the substrate to be changed by removal through the wall of the can. There is a gas seal GS in the wall of the can where support SS enters.

FIG. 2 shows a vacuum collar VC surrounding the can, means (not shown) being provided for pumping out the space within the collar by way of a vacuum outlet V and filling it with argon by way of an argon inlet AI. A fiat top is sealed over the collar and supports a radio-frequency matching unit MU which supplies R.F. signals to the getter and sputter electrodes.

Referring now to FIG. 3, there is shown another form of the getter-sputtering apparatus. There is a sputtering chamber S defined by a cylindrical dividing wall DW open at the bottom and sealed at the top to the top of a cylindrical casing CC. The substrate SU is supported on a platform P which is brought up against the rim of wall DW so that there is at most only a small space therebetween. The annular chamber GC surrounding the Wall DW is the getter chamber and includes an annular getter cathode D.

The casing CC is strong enough to withstand atmospheric pressure when exhausted and the space within it is pumped out directly, there being no need for an additional vacuum chamber to include the apparatus as in FIGS. 1 and 2.

The walls of the casing, the getter and sputter electrodes and the platform P are all hollow and are provided with water cooling inlets and outlets. This cooling is eifective to inhibit out-gassing from the metal surfaces.

The invention is not restricted to the details of the above described embodiments. For example, other materials such as certain compound semi-conductors may be sputtered. The film deposited may be amorphous, polycrystalline or a single crystal. Other inert gases than argon may be used. The operating gas pressure may be, for example, in the range 0.1 to 100 microns.

What is claimed is:

1. A getter-sputtering apparatus comprising a housing in the form of a can with a lid, a transverse partition in said can forming a dividing wall dividing the can into a sputter chamber on the side of the wall remote from the lid and a getter chamber on the other side of the wall, the peripheral edge of the dividing wall being spaced from the can to define a passage for gas to pass from the getter chamber to the sputter chamber, whereby access for gas to the sputter chamber is only by way of the getter chamber and said passage past said dividing wall, means for mounting in the sputter chamber a substrate on which material is to be sputtered, a sputter cathode in said sputter chamber, a getter cathode in said getter chamber, a gas inlet in said getter chamber and a gas outlet from said sputter chamber.

2. An apparatus as claimed in claim 1 in which said housing is a cylindrical can and the lid is a removable lid and said transverse partition is removably mounted in said housing.

3. An apparatus as claimed in claim 2 in which the partition, the getter electrode and the sputter cathode are fixed to said lid and are removable therewith.

4. An apparatus as claimed in claim 1 in which said housing is a cylindrical can which is sufficiently strong to withstand atmospheric pressure when the inside is evacuated.

5. An apparatus as claimed in claim 1 in which said substrate mounting means comprises a slide support, the can having an aperture in the side thereof through which said support is inserted and removed, and a gas-tight seal between the support and the aperture.

6. Getter-sputtering apparatus having a housing within which is a sputter chamber; a sputter cathode in the sputter chamber; a platform for mounting in the sputter chamber a substrate on which material is to be sputtered; an annular getter chamber in the housing, the getter chamber surrounding the sputter chamber; a getter cathode in the getter chamber; a gas inlet in said getter chamber and a gas outlet from said apparatus; and a dividing wall dividing the sputter chamber from the getter chamber, the dividing wall having a rim extending close to said platform for defining with said platform a passage for the gas to pass to the sputter chamber, which passage is narrow with respect to the cross-sectional areas of the chambers, whereby access for gas to the sputter chamber is only by way of the getter chamber and past the dividing wall.

7. Apparatus as claimed in claim 6 wherein the housing has a cylindrical casing which defines the getter chamber and which encloses the platform, the casing being sufficiently strong to withstand atmospheric pressure when the inside is evacuated.

OTHER REFERENCES Seeman: Bias Sputtering: Its Techniques and Application, Vacuum, p. 133 (1966).

HOWARD S. WILLIAMS, Primary Examiner S. S. KANTER, Assistant Examiner U.S. C1. X.R. 204192