Vacuum coating apparatus

Abstract

Vacuum coating apparatus having isolatable coating and vacuum chambers whose volumes are correlated to each other to minimize contamination and pump-down time, with the coating chamber having a closure means mounting a substrate holder for positioning substrates in an evaporant stream from a vapor source contained in the vacuum chamber.

Description

FIELD OF THE INVENTION

This invention relates to coating apparatus, and more particularly, to an improved apparatus for coating substrates with an evaporant stream from a suitable source material in a vacuum system.

BACKGROUND OF THE INVENTION

Vacuum coating of substrates from a suitable source material is extensively used for various applications. Typically, such applications involve, among others, the deposition of non-metallic coatings on optical lenses, coatings on paper, and in particular, the coating of electrically conductive metal and dielectric films on semiconductor substrates for enabling subsequent delineation of conductor patterns in the fabrication of semiconductor devices.

Typical of such apparatuses to which this invention is directed are those described in U.S. Pat. No. 3,524,426 and 3,641,973. Such systems comprise a main vacuum or evaporation chamber containing a source of coating material to be evaporated in a stream to a substrate supported in a coating chamber which is controllably placed in communication and isolation with respect to the evaporation chamber. A vacuum gate valve is included intermediate the chambers to either, in the open position, place them in communication with each other or, in the closed position, to isolate each from the other. In any event, a vacuum source, such as a diffusion pump, is normally connected to the evaporation chamber to maintain a continuous vacuum therein.

For loading of the system, the gate valve is moved in the closed position to isolate the evaporation and coating chambers, the latter of which is provided with means of access for insertion of substrate holders in an evaporant stream. On insertion of the substrate holders and resealing and rough evacuation of the coating chamber, the gate valve is moved to the open position to place the chambers in communication with each other. On development of a common vacuum atmosphere in the chambers, an evaporant stream, of a source material from an E-beam source, is directed from evaporation chamber into the coating chamber and onto the substrates, generally by removal of a shutter placed in the evaporant stream.

SUMMARY OF THE INVENTION

It has been found that the foregoing vacuum systems can be improved to minimize pump-down time and ambient contamination and conversely increase through-put of substrate coatings. Briefly, this can be effected by correlating the volumes of the coating and evaporating chambers to each other wherein the former comprises a substantially smaller volume of the latter, generally in the range of about 3 percent to 10 percent. In view of the reduced size of the coating chamber relative to the evaporation chamber, pump-down time of the apparatus is substantially reduced. In addition, the resulting pressure rise of the evaporation chamber is reduced to minimize defocusing of the E-beam and backstreaming of diffusion pump.

In addition, the coating chamber is also provided with an access port whose cross-sectional opening is also substantially reduced to minimize ingress of ambients during loading of substrates. Generally, the ratio of area of the port to the volume of the coating chamber will be in the range of about 1:20 to about 1:30.

Also, to minimize ambient contamination, the coating chamber is provided with means to introduce an inert gas flow (eg. nitrogen, argon, and the like) to flow through the chamber and out of the port during removal and loading of substrates.

Also, to minimize pump-down time of the coating apparatus, the coating chamber is connected through valving to a roughing pump to generate a vacuum therein prior to placing it in communication with the evaporation chamber.

Another feature of the invention includes a door or closure member for the access port and having mounted thereon a holder for substrates which are positioned within the evaporant stream in the coating chamber. This feature provides the capability for automatic loading/unloading of the substrates.

A further feature of the invention includes an additional gating means (such as a poppet valve) in the evaporation chamber for sealing with an access port to the vacuum pump to obtain isolation therebetween, and access to the chamber without need to shut down the vacuum pump.

Other features, objects and advantages will become more apparent from the following more detailed description of the invention in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing in cross-section, of one embodiment of a vacuum coating apparatus in accordance with this invention.

FIG. 2 is a diagrammatic view of a substrate holder for use in the embodiment of FIG. 1.

FIG. 3 is a partial schematic drawing, in cross-section, of a coating chamber in accordance with another embodiment of this invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

Although the vacuum coating apparatus of this invention has a wide variety of applications, they will be described below in conjunction with the coating of electrically conductive metal films on semiconductor substrates for subsequent photolithographic delineation of conductor patterns in device fabrication.

Referring to the drawings, the vacuum coating apparatus comprises a coating chamber 1 and an evaporation chamber 2 operatively in communication with each other under a common vacuum environment generated by a vacuum pump 3 (eg. a diffusion pump) through a vacuum access duct 4 in the lower wall of the chamber enclosure 5.

Included between coating chamber 1 and evaporation chamber 2 is a valve housing 6 for a conventional vacuum gate valve 7 which is movable in the housing 6 by means of a pneumatic or hydraulic cylinder 8 mounted at one end of housing 6 and having a reciprocable extending rod 9 attached to valve plate 7. The gate valve is shown in the closed position in FIG. 1 to isolate or seal the coating and evaporation chambers 1 and 2, respectively, from each other to allow access to the coating chamber 1 while maintaining a continuous vacuum in the evaporation chamber 2. The mounting of this valve is such that its sealing surface faces upward, thereby inherently shielding said surface from evaporant deposits.

Activation of cylinder 8 to retract rod 9, will move the valve plate 7 to the open position to place coating chamber 1 and evaporation chamber 2 in communication with each other for development of a common vacuum environment.

The evaporation chamber 2 includes a conventional vapor or ion source 10 of the type shown in U.S. letters Pat. No. 3,710,072 which may be referred to for details of construction. Source 10 will normally comprise a water cooled crucible 11 having coolant passages 12 through which a coolant may be circulated by suitable means, not shown. Crucible 11 contains a molten pool 14 of evaporant material from which vapor of the coating is produced, as for example aluminum or copper aluminum alloy for coating of an electrically conductive film of semiconductor substrates 13 (see FIG. 2) in device fabrication. The molten pool 14 is heated by an electron beam 15, deflected in an arcuate path by suitable magnetic field, from an electron beam gun 16.

Mounted in evaporation chamber 2, about vacuum source 10, is an enclosing evaporant shield 17 having an opening 18 in top wall 19 thereof, for shaping the evaporant stream 20 of the coating material from source 10.

In order to prevent the coating of valve plate 7 in the closed position, a shutter 21 is provided between the source material 10, at the shaping port 18, and the coating chamber 1. The shutter 21 is mounted on a pivot shaft 22 extending through shield 17, the bottom wall 23 (of evaporation chamber 2) and in a vacuum tight bushing 24 secured thereto.

Also included in evaporation chamber 2 is a poppet valve 25 having a sealing plate 26 disposed opposite vacuum access duct 4, for sealing engagement therewith when ram 27 is extended by actuation of a pneumatic or hydraulic cylinder 28.

Coating chamber 1 includes an access port 29 which serves to load and unload substrates 13 into and out of the chamber. A second access flange is provided opposite the access port for maintenance purposes. The access port 29 is adapted to be opened and closed by a door or cover member 30 pivotally mounted to a bracket 31 and having an annular groove 32 for mounting of an O-ring 33 or other suitable sealing means.

Mounted on the exterior of closure member 30 is a bracket 34 to which is secured a motor 35 having a drive shaft 36 extending through closure member 30 into the coating chamber 1. Secured to the free end of drive shaft 36 is a substrate holder 37 for supporting substrates in a coating position with respect to the evaporant stream in coating chamber 1. Motor 35 is used to rotate the holder 37 and secure substrates 13 in the evaporant stream in order to provide an more uniform coating on the substrates.

Holder 37 comprises a support base 38 having a plurality of finger grips 39 having pivoted clamping lips 40 positioned over the support face of base 38 by means of compression springs 41 which are secured between annular seats 42, secured to the back side of support base 38, and like registered annular seats 43 secured to lateral extensions 44, of grips 39, pivotally mounted to brackets 45, also secured to the back side of support base 38. As will be noted, the lips 40 are formed with an angular configuration 46 to facilitate camming of grips 39 open if a tool is desired to be employed for positioning substrate 13 on holder 37.

Also provided in communication relationship with coating chamber 1 is a roughing line 50 extending through valve 51 to a vacuum roughing pump (not shown) in order to evacuate coating chamber 1 down to a safe level for opening valve plate 7 to place the chamber into communication with evaporation chamber 2 without drastic equilization therebetween.

Also provided in communicating relationship with coating chamber 1 is an inert gas line 52 extending through valve 53 to an inert gas source, not shown, of nitrogen, argon and the like, for purposes of establishing a flowing atmosphere of the inert gas through the chamber 1 and out of the access port 29 when the closure member 30 is in the open position. The flow of inert gas out of access port 29 will minimize ingress of ambients into the chamber and thus conversely minimize contamination thereof.

Mechanical movement of the closure member or lid 30 can be effected by pivotally connecting mounting bracket 34 to a clevis member 60 on the end of a piston rod 61 of a pneumatic or hydraulic cylinder 62 suitably mounted (not shown) in any convenient manner to the vacuum coating apparatus.

As indicated previously, in order to minimize pump-down time, the volume of coating chamber 1 is substantially smaller than the volume of the evaporating chamber. Generally, the practical ratios of the volume of the coating chamber 1 to the volume of the evaporating chamber 2 will be in the range of from about 1:10 to about 1:30. In one unit fabricated in accordance with this invention, the volume of coating chamber 1 was 5 liters while the volume of the evaporation chamber 2 was 150 liters.

Also as indicated previously, to minimize ingress of contaminating ambients when closure member 30 is open, the cross-sectional area of acess port 29 is also correlated to the volume of coating chamber 1. Generally, the practical ratios of the cross-sectional area of access port 29 to the volume of coating chamber 1 will be in the range of from about 1:20 to about 1:30. Such a restricted access port 29 also serves to throttle the flow of inert gas out of coating chamber 1 and retain temperature control of internal tooling surfaces. In the above indicated fabricated unit having a coating chamber 1 volume of about 5 liters (310 in.sup.3), the access port 29 had a cross-sectional area of about .apprxeq.10 in.sup.2.

FIG. 3 shows a variation of the coating chamber 1 of the apparatus of this invention. In this embodiment an access port 29A to the coating chamber 1A is provided in an enclosure wall 71 formed on an angle to the evaporant stream form the source 10 in evaporation chamber 2. Pivotally mounted to a bracket 72 on the enclosure wall is the closure member or lid 30A provided on its outer surface with a motor 35A with a drive shaft 36 extending through a vacuum seal into the coating chamber 1A, and having secured to its free end a rotatable substrate holder 37 to support a substrate at an angle within the evaporant stream in the coating chamber 1A. Also contained in coating chamber 1A are heating elements 70 for heating substrates to deposition temperatures. The heater elements are protected from the evaporant stream by a shield 75.

In operation, for loading of substrates, the valve plate 7 (FIG. 1) is moved to the closed position to isolate coating chamber 1 from evaporation chamber 2 in which a vacuum (eg. of about 3 to 9 .times. 10.sup.-.sup.7 TORR) is continued to be maintained by virtue of its communication through vacuum port 4 to the vacuum pump 3. Prior to opening of closure member 30, valve 53 is opened in inert gas line 52 to connect coating chamber 1 to an inert gas source, whereupon closure member 30 is opened. At this point, any substrate on holder 37 may be removed and a new substrate 13 (e.g. a semiconductor wafer) mounted thereon followed by closure of lid 30. The inert gas flow is stopped by closure of valve 53, and the coating chamber connected to a roughing pump by opening of valve 51 is roughing line 50. When the coating chamber 1 is evacuated to a suitable level (eg. about 50 microns), the roughing line valve 51 is closed, followed by moving valve plate 7 to the open position. After statilization of the unit, the shutter 21 will be rotated out of in front of the shaping port 18, to permit the evaporant stream from vacuum source 10 in the evaporation chamber 2, to flow into the coating chamber 1 onto the substrate 13 mounted on holder 37. Substrate rotation, heating, and source rise and soak can be started after communication is established between the coating and evaporation chambers. For photolithographic delineation of conductor patterns on semiconductor devices, the vacuum source can comprise a molten pool of 70 aluminum/30 copper alloy to coat the electrically conductive metal film on the wafer (eg. substrate).

For servicing of the evaporation chamber 2, without shutting down vacuum pump 3, the poppet valve 28 is extended into a closed position with vacuum port 4, and both coating and evaporation chambers vented to the atmosphere when suitable servicing access can be obtained to both chambers.

It is to be understood that while the invention has been particularly shown and described with reference to the preferred embodiments thereof, it will be understood by those skilled in the art that the foregoing and other changes in form and detail may be made therein without departing from the spirit and scope of the invention.

Claims

What is claimed is:

1. A vacuum coating apparatus comprising:

A. an evaporation chamber;

B. a coating chamber in communication with said evaporation chamber;

C. gate means reciprocally movable between an open and closed position intermediate said coating and evaporation chambers for selectively isolating each from the other;

D. a vapor source means in said evaporation chamber for generating an evaporant stream of coating material into said coating chamber;

E. a port in a wall of said coating chamber for access thereto and wherein the ratio of the area of said port to the volume of said coating chamber is in the range from about 1:20 to about 1:30;

F. door means pivotally mounted on said wall for movement into open and closed positions relative to said port with said closed position securing said door means in sealing relation with said coating chamber;

G. substrate holder means mounted on an inner surface of said door means for supporting substrates in a coating position within said evaporant stream in said coating chamber;

H. means for rotating said substrates on said holder means;

I. means for maintaining said evaporation chamber under a continuous vacuum;

J. a second vacuum means for roughing a vacuum in said coating chamber when isolated from said evaporation chamber by said gate means;

K. means for isolating said second vacuum means from said coating chamber when said gate means is to be moved to the open position;

L. gas means for controllably introducing an inert gas flow in said coating chamber when isolated from said evaporation chamber, when said gate means is in the closed position, to minimize ingress of ambients into said coating chamber when said door means is in the open position; and

M. valve means for shutting off the flow of said inert gas to said coating chamber; wherein the ratio of the volumes of said evaporation chamber to said coating chamber is in the range from about 10:1 to about 30:1.

2. A vacuum coating apparatus comprising:

A. an evaporation chamber;

B. a coating chamber in communciation with said evaporation chamber;

C. gate means reciprocally movable between an open and closed position intermediate said coating and evaporation chambers for selectively isolating each from the other;

D. a vapor source means in said evaporation chamber for generating an evaporant stream of coating material into said coating chamber;

E. a port in a wall of said coating chamber for access thereto and wherein the ratio of the area of said port to the volume of said coating chamber is in the range from about 1:20 to about 1:30;

F. door means pivotally mounted on said wall for movement into open and closed positions relative to said port with said closed position securing said door means in sealing relation with said coating chamber;

G. substrate holder means mounted on an inner surface of said door means for supporting substrates in a coating position within said evaporant stream in said coating chamber;

H. means for rotating said substrates on said holder means;

I. means for maintaining said evaporation chamber under a continuous vacuum; wherein said holder means supports said substrates within and at an angle to said evaporant stream;

J. a second vacuum means for roughing a vacuum in said coating chamber when isolated from said evaporation chamber by said gate means;

K. means for isolating said second vacuum means from said coating chamber when said gate means is to be moved to the open position;

L. gas means for controllably introducing an inert gas flow in said coating chamber when isolated from said evaporation chamber, when said gate means is in the closed position, to minimize ingress of ambients into said coating chamber when said door means is in the open position; and

M. valve means for shutting off the flow of said inert gas to said coating chamber; wherein the ratio of the volumes of said evaporation chamber to said coating chamber is in the range from about 10:1 to about 30:1.

3. A vacuum coating apparatus comprising:

A. an evaporation chamber;

B. a coating chamber in communication with said evaporation chamber;

C. gate means reciprocally movable between an open and closed position intermediate said coating and evaporation chambers for selectively isolating each from the other;

D. a vapor source means in said evaporation chamber for generating an evaporant stream of coating material into said coating chamber;

E. a port in a wall of said coating chamber for access thereto and wherein the ratio of the area of said port to the volume of said coating chamber is in the range from about 1:20 to about 1:30;

F. door means pivotally mounted on said wall for movement into open and closed positions relative to said port with said closed position securing said door means in sealing relation with said coating chamber;

G. substrate holder means mounted on an inner surface of said door means for supporting substrates in a coating position within said evaporant stream in said coating chamber;

H. means for rotating said substrates on said holder means;

I. means for maintaining said evaporation chamber under a continuous vacuum; wherein said holder means supports said substrates within and at an angle to said evaporant stream; wherein said holder means supports said substrates within and at an angle to said evaporant stream;

J. heater means in said coating chamber within said evaporant stream for heating said subtrates to deposition means;

K. an evaporant shield for said heater means in said coating chamber;

L. a second vacuum means for roughing a vacuum in said coating chamber when isolated from said vacuum chamber by said gate means;

M. means for isolating said second vacuum means from said coating chamber when said gate means is to be moved to the open position;

N. gas means for controllably introducing an inert gas flow in said coating chamber when isolated from said evaporation chamber, when said gate means is in the closed position, to minimize ingress of ambients into said coating chamber when said door means is in the open position; and

O. valve means for shutting off the flow of said inert gas to said coating chamber; wherein the ratio of the volumes of said evaporation chamber to said coating chamber is in the range from about 10:1 to about 30:1.

4. A vacuum coating apparatus comprising:

A. an evaporation chamber;

B. a coating chamber in communication with said evaporation chamber;

C. gate means reciprocally movable between an open and closed position intermediate said coating and evaporation chambers for selectively isolating each from the other;

D. a vapor source means in said evaporation chamber for generating an evaporant stream of coating material into said coating chamber;

E. a port in a wall of said coating chamber for access thereto and wherein the ratio of the area of said port to the volume of said coating chamber is in the range from about 1:20 to about 1:30;

F. door means pivotally mounted on said wall for movement into open and closed positions relative to said port with said closed position securing said door means in sealing relation with said coating chamber;

G. substrate holder means mounted on an inner surface of said door means for supporting substrates in a coating position within said evaporant stream in said coating chamber;

H. means for rotating said substrates on said holder means;

I. mans for maintaining said evaporation chamber under a continuous vacuum;

J. a valve means in said evaporation chamber reciprocally movable between an open and closed position relative to the first said vacuum means for selectively placing said evaporation chamber and the first said vacuum means in communicating and isolating relationship with each other;

K. a second vacuum means for roughing a vacuum in said coating chamber when isolated from said evaporation chamber by said gate means;

L. means for isolating said second vacuum means from sad coating chamber when said gate means is to be moved to the open position;

M. gas means for controllably introducing an inert gas flow in said coating chamber when isolated from said evaporation chamber, when said gate means is in the closed position, to minimize ingress of ambients into said coating chamber when said door means is in the open position; and

N. valve means for shutting off the flow of said inert gas to said coating chamber; wherein the ratio of the volumes of said evaporation chamber to said coating chamber is in the range from about 10:1 to about 30:1.

5. A vacuum coating apparatus comprising:

A. an evaporation chamber;

B. a coating chamber in communication with said evaporation chamber;

C. gate means reciprocally movable between an open and closed position intermediate said coating and evaporation chambers for selectively isolating each from the other;

D. a vapor source means in said evaporation chamber for generating and evaporant stream of coating material into said coating chamber:

E. a port in a wall of said coating chamber for access thereto and wherein the ratio of the area of said port to the volume of said coating chamber is in the range from about 1:20 to about 1:30;

F. door means pivotally mounted on said wall for movement into open and closed positions relative to said port with said closed position securing said door means in sealing relation with said coating chamber;

G. substrate holder means mounted on an inner surface of said door means for supporting substrates in a coating position within said evaporant stream in said coating chamber;

H. means for rotating said substrates on said holder means;

I. means for maintaining said evaporation chamber under a continuous vacuum; wherein said holder means supports said substrates within and at an angle to said evaporant stream;

J. a valve means in said evaporation chamber reciprocally movable between an open and closed position relative to the first said vacuum means for selectively placing said evaporator section and the first said vacuum means in communicating and isolating relationship with each other;

K. a second vacuum means for roughing a vacuum in said coating chamber when isolated from said evaporation chamber by said gate means;

L. means for isolating said second vacuum means from said coating chamber when said gate means is to be moved to the open position;

M. gas means for controllably introducing an inert gas flow in said coating chamber when isolated from said evaporation chamber, when said gate means is in the closed position, to minimize ingress of ambients into said coating chamber when said door means is in the open position; and

N. valve means for shutting off the flow of said inert gas to said coating chamber; wherein the ratio of the volumes of said evaporation chamber to said coating chamber is in the range from about 10:1 to about 30:1.

6. A vacuum coating apparatus comprising:

A an evaporation chamber;

B. a coating chamber in communication with said evaporation chamber;

C. gate means reciprocally movable between an open and closed position intermediate said coating and evaporation chambers for selectively isolating each from the other;

D. a vapor source means in said evaporation chamber for generating an evaporant stream of coating material into said coating chamber;

E. a port in a wall of said coating chamber for access thereto and wherein the ratio of the area of said port to the volume of said coating chamber is in the range from about 1:20 to about 1:30;

F. door means pivotally mounted on said wall for movement into open and closed positions relative to said port with said closed position securing said door means in sealing relation with said coating chamber;

G. substrate holder means mounted on an inner surface of said door means for supporting substrates in a coating position within said evaporant stream in said coating chamber;

H. means for rotating said substrates on said holder means;

I. means for maintaining said evaporation chamber under a continuous vacuum;

wherein said holder means supports said substrates within and at an angle to said evaporant stream;

J. heater means in said coating chamber within said evaporant stream for heating said substrates to deposition means;

K. an evaporant shield for said heater means in said coating chamber;

L. a valve means in said vacuum chamber reciprocally movable between an open and closed position between said evaporation chamber and the first said vacuum means for selectively isolating each from the other;

M. a second vacuum means for roughing a vacuum in said coating chamber when isolated from said evaporation chamber by said gate means;

N. means for isolating said second vacuum means from said coating chamber when said gate means is to be moved to the open position;

O. gas means for controllably introducing an inert gas flow in said coating chamber when isolated from said evaporation chamber, when said gate means is in the closed position, to minimize ingress of ambients into said coating chamber when said door means is in the open position; and

P. valve means for shutting off the flow of said inert gas to said coating chamber;

wherein the ratio of the volumes of said evaporation chamber to said coating chamber is in the range from about 10:1 to about 30:1.