Apparatus And Method For Securing A High Vacuum For Particle Coating Process

Abstract

A vacuum coating apparatus is provided with valves wherein the volumes containing the coating material emitter and high-vacuum pump can be isolated from the substrate table to preserve the high vacuum of the system. A wide-throated valve between the coating material emitter and the substrate table permits vacuum sealing of the coating material emitter and high-vacuum pump when the substrate is replaced, throttling of the gases within the volume of the system containing the substrate table to reduce the roughing cycle required to attain the requisite high vacuum, and complete opening between the coating emitter apparatus and substrate table to provide an unobstructed particle path for efficient high-vacuum coating.

Description

This invention relates to an apparatus and method for securing a high vacuum for a molecular coating process. More particularly, an improved valve construction is illustrated for isolating the volumes between the substrate on one hand and coating material and high-vacuum pump on the other hand. Moreover, use of the improved valve construction permits an improved process for evacuating the volume surrounding the substrate table.

Modern molecular coating machines contain high-vacuum ambients. Typically, a substrate to be coated is placed within this high-vacuum ambient and bombarded with high-velocity molecular particles discharged from a coating material emitter. As the presence of any appreciable amount of gas between the emitter and substrate retards the passage of the high-velocity molecular particles through intermolecular collisions, all such machines have elaborate vacuum pumps for maintaining the required near-perfect high vacuums.

To place substrates within the apparatus for coating and to remove the substrates after coating, the vacuum interior of such coating machines must be broken. Heretofore, the vast majority of coating systems have required interruption of the vacuum around both the coating material emitter, the substrate table area and the molecular pump used to attain the high vacuum. This interruption results in loss of vacuum within comparatively large volumes of the entire system. Before coating can occur, these large volumes must be evacuated. Moreover, the surfaces interior of such coating machines when exposed to the atmosphere, adsorbs molecules of atmospheric gas, moisture, and other contaminants. These adsorbed molecules must be purged from the system before efficient coating can occur.

In addition to the interruption of the vacuum necessitated by the replacement of the substrate, the high-vacuum molecular pumping systems conjoined to such apparatus must be protected from exposure to appreciable amounts of gas. Typically, these pumps, either of the diffusion or ion variety, cannot tolerate the presence of gases in vapor pressures above 100 microns of mercury in the case of diffusion pumps and 50 microns of mercury in the case of ion pumps. When these pumps are subjected to gas in pressures above these limits, they are "shocked" or "swamped" and their pumping efficiency wholly lost, often with resultant damage to their pumping media.

Heretofore when substrates have been replaced, the volumes containing these substrates typically have been evacuated by mechanical pumps to a gas pressure range wherein the high-molecular pumps can efficiently operate. Unfortunately, the use of mechanical pumps alone to reach the low-pressure limits where the molecular pumps operate is highly inefficient; as the molecular density within the chamber approaches a perfect vacuum, the mechanical pumps become increasingly more inefficient.

To eliminate the inefficient use of mechanical or "roughing" pumps to reach the vacuums required for the operation of the molecular pumps, separate piping and valve systems have been provided to throttle gases to the high-vacuum molecular pumping systems at a pressure where the molecular pumps can operate. While this throttling can take advantage of the improved efficiency of the molecular pumps, it has the disadvantage of incorporating elaborate piping, valving, and controls into the vacuum coating systems. Moreover, the piping associated with these systems provides an inefficient channel for the desired molecular conductance to the high-vacuum pump.

It is an object of this invention to provide a vacuum coating apparatus wherein the high-vacuum molecular pump alone or the coating material emitter and high-vacuum pump can be maintained in a vacuum during changing of the substrate. Accordingly, the coating apparatus of this invention is confined within an enclosed cylinder having the substrate table located at one end thereof and the coating material emitter at the opposite end thereof. A valve with a pivoted disc having a diameter substantially coextensive with the cylinder cross section is positioned to isolate the coating material emitter and high-vacuum pump from the substrate in the closed position and permitted to pivot clear of the cylinder to provide an unobstructed coating material path in the open position.

A further object of this invention is to disclose a chamber configuration wherein the high-vacuum molecular pump can be isolated from both the substrate table and coating material emitter to permit changes to be made to the emitter apparatus without interrupting the high-vacuum state of the molecular pump or damaging its molecule-entraining materials.

An advantage of the valve construction between the substrate table and coating material emitter is that the volume about the substrate table is reduced to an absolute minimum; consequently, pumping time and energy necessary to achieve a high-vacuum state is conserved.

A further object of this invention is to disclose a valve assembly for insertion between the substrate table and high-vacuum molecular pump, which valve has three operative positions; these operative positions include a seated position for sealing the molecular pump to preserve its high-vacuum state, a throttling position for throttling gases from the substrate table to the high-vacuum pump and a fully open position to permit the unrestricted passage of coating materials when the coating is commenced.

An advantage of the throttling position of this valve is that a substantial reduction in the time necessary to evacuate the volume containing the substrate table is attained.

Yet another advantage of the throttling position of this valve is that the substrate chamber need only be evacuated to a pressure range exceeding by a factor of two that pressure range at which the molecular pump is swamped. In the case of a diffusion pump the pressure of evacuation can be as high as 200 microns of mercury; in the case of an ion pump the pressure range can be as high as 100 microns of mercury.

A further advantage is that the throttling function of the valve eliminates the need for complex and expensive auxiliary throttling piping, valves and controls.

An additional advantage is that the throttling valve provides an improved path for molecular conductance between the volume containing the substrate table and the high-vacuum pump. This path is effectively free of recesses and occluded areas where molecules which might otherwise spoil the high-vacuum can accumulate.

A still further advantage of this invention is that the wide throat of the valve permits an essentially unrestricted molecular flow path for evacuating the area around the substrate table and permits emitted coating materials to pass through the valve seat and onto the substrate table.

Other objects, features and advantages will be more apparent after referring to the following specification and attached drawings in which:

FIG. 1 is a side elevation section schematically illustrating the chambers containing the substrate table, the coating material emitter and the high-vacuum pump;

FIG. 2 is a side elevation section illustrating the improved valve construction between the substrate table on one hand and the coating material emitter and high-vacuum pump on the other hand;

FIG. 3 is a plan view of the improved valve construction of this invention along lines 3--3 of FIG. 2; and

FIG. 4 is an expanded side elevation section illustrating the valve in a view similar to that shown in FIG. 2 with the disc of the valve in its throttling position.

With reference to FIG. 1, substrate chamber A is illustrated overlying an emitter chamber C with a throttling gate valve B therebetween. Emitter chamber C is in turn communicated through poppit valve D into cold trap E and molecular pump F. Both the molecular pump F and the substrate chamber A are shown communicated by piping to a roughing pump G.

In operation, substrate 22 is typically inserted within substrate chamber A. Thereafter, the chamber is sealed and roughing pump G, through connected piping, evacuates the chamber to a range approaching a perfect vacuum, typically in the order of 100-150 microns of mercury pressure. Thereafter, disc 14 of valve B is actuated to move to the throttling position shown in FIG. 4. The atmosphere remaining in the partially evacuated substrate volume A is throttled around the periphery of disc 14 of valve D into emitter chamber C and to molecular pump F. Typically, the throttled rate of molecular flow or conductance is maintained between the disc 14 and valve seat 16 at a flow rate wherein molecular pump F is now "swamped" or "shocked." When the molecular densities in chambers A and C has substantially equilibrated, disc 14 is pivoted on arm 18 to a position out of registry with seat 16 (see FIG. 2). In this position, emitter 20 is provided with an unobstructed path to discharge coating material onto substrate 22 within substrate chamber A.

When the coating of substrate 22 is completed, typically disc 14 of valve B will be pivoted to the closed position, then sealed by pressurizing bellows 42. Thereafter, the chamber A will be flooded with atmospheric gas by piping (not shown), substrate chamber A opened, and the coated substrate 22 removed and replaced with uncoated substrate material.

Substrate chamber A and emitter chamber C are formed in the shape of a cylindrical vessel 25, which vessel is closed at the top and bottom thereof by circular walls 26 and 27. Chamber 25 above valve B is cut into two separate sections at annular flanges 30 and 31, flange 30 being attached to the top portion of chamber A and flange 31 being attached to the bottom portion of chamber A. As here shown, the top and removable portion of cylindrical 25 is pivotal about a hinge 32 towards and away from a sealed position between flanges 30 and 31. When the chamber is opened, substrate 22 can be removed and replaced; when the chamber is closed, its interior can be evacuated and coating commenced.

Intermediate of chambers A and C, valve B is disposed. Valve B can be best illustrated with reference to FIGS. 2, 3 and 4.

Valve B is contained within a hollow cardiod or heart-shaped housing 34. Housing 34 is attached integrally to chamber C at the top and bottom housing walls overlying seat 16. These connections in cooperation with seat 16 define through housing 34 an aperture which is effectively a continuation of the cross section of cylinder 25. Housing 34 is hollow and extends beyond seat 16 transversely outward of cylinder 25. Disc 14 pivotally moves into this concavity when valve B is in the open position.

Within the interior of housing 34 at the pointed portion of its heart-shaped plan profile, disc 14 is pivotally mounted about a shaft 36 on arm 18. Arm 18, at its end opposite from shaft 36, has attached thereto disc 14.

With reference to FIG. 3, rotation of shaft 36 is actuated by a pneumatic cylinder 37 to pivot valve disc 14 towards and away from its position of registry with seat 16. As is shown in broken lines in FIGS. 2 and 3, disc 14 pivoted on arm 18, can move from a position overlying valve seat 16 to a position where seat 16 is completely unobstructed. Vacuum is maintained interior of valve housing 34 by a seal (not shown) where shaft 36 penetrates the bottom housing wall.

In addition to the pivotal movement of disc 14 on arm 18, this disc is movable towards and away from a position of sealing engagement with seat 16. Such movement is provided by leaf spring 40 and bellows 42 and guided by pins 43 of disc 14 passing through apertures 44 in pivoted arm 18.

Arm 18 has drilled therein two apertures 44. Typically, disc 14 of valve B has protruding upwardly therefrom and into registry with apertures 43 of arm 18 two pins 44. These pins 44 simultaneously locate disc 14 radially from the pivot point of arm 18 provided by shaft 36 and additionally maintain disc 14 in a horizontal plane as it moves towards and away from seat 16.

Leaf spring 40 functions to bias disc 14 away from seat 16. This leaf spring fastens to disc 14 at its medial portion and extends transversely of arm 18 fastening to disc 14 at its two outer ends.

Bellows 42 are located between the lower surface of arm 18 and the upper surface of a bellows aperture 46 configured within disc 14. Inflation of the bellows through connected tubing 47 overcomes the bias of leaf spring 40 moving disc 14 downwardly in sealing relation onto seat 16. Conversely, release of the pressure within bellows 42 permits the bias of spring 40 to move disc 14 upwardly from sealing engagement with seat 16. Typically, bellows 42 overlie only a relatively small area of the total area of disc 14. This relatively small size is operable as only relatively small motive forces are required to effect movement of the disc.

Typically, actuation of bellows 42 and the compression of disc 14 downwardly onto seat 16 will cause the end of arm 18 remote from shaft 36 to flex upwardly and away from seat 16. To arrest such movement, an angle bar 50 is provided. This bar has its vertically extending surface limiting the pivotal movement of the end of arm 18 remote from shaft 36 and its horizontally extending surface preventing the upward flexure of the end of arm 18.

It will be noted that valve disc 14 is movable upwardly from seat 16 by only a relatively small spatial interval. This spatial interval is chosen to provide a desired throttling of pressure between substrate chamber A and emitter chamber C. As is apparent, such movement can be adjusted by the insertion of shims between disc 14 and arm 18, the shims being placed typically about pins 43.

Referring again to FIG. 1, emitter apparatus 20 is located on the bottom surface 27 of chamber C. As here shown, emitter apparatus 20 is adapted for the thermal coating of substrate 22. Typically, pot 53 defines a concavity 54 in which the coating material 55 is placed. Thermal energy supplied to the material 55 causes its molecular particles to be discharged upwardly and in the direction of substrate 22. Typically, the pot is surrounded by a cylindrical shield 56, which shield confines the emitted particles of coating material 55 to an emitted pattern wherein they will impact the substrate 22 without coating or contaminating other surfaces within the chamber.

Extending transversely outwardly of emitter chamber C underlying housing 34 of valve B there is a duct 60. Duct 60 provides a passage between emitter chamber C on one hand and cold trap E and molecular pump F on the other hand.

Duct 60 is communicated to cold trap E and molecular pump F through poppet valve D. Poppet valve D includes a disc 62 movable towards and away from a seat 63 by means of the pneumatic cylinder 64. Typically, cylinder 64 attaches to disc 62 at rod 65. When communication between duct 60 and cold trap E and molecular pump F is desired, disc 62 is actuated to the position shown in FIG. 1. Conversely, when cold trap E and molecular pump F are to be isolated from duct D, disc 62 is seated on seat 63. Actuation of pneumatic cylinder 64 through tubing (not shown).

Cold trap E and molecular pump F are apparatuses well known in the art. Typically, cold trap E functions to immediately freeze all water vapor within the system and to prevent the oil from molecular pump F from backing into the high-vacuum maintained within substrate chamber A and emitter chamber C. Molecular pump F can be of any known variety; as here illustrated, pump F is of the diffusion variety wherein a stream of oil entraps and entrains the molecules and causes the molecules to be discharged. Alternatively, molecular pump F can be of the ion variety.

Roughing pump G is a mechanical pump. Typically, this pump operates to mechanically displace the atmosphere interior of the coating system. Inlet 73 of roughing pump G is connected to the outlet of molecular pump F through valve 75 and piping 74. Additionally, inlet 73 of pump G is connected to substrate chamber A through valve 76 and piping inlet 77.

Assuming that the entire apparatus herein illustrated is at atmospheric pressure, the operating cycle of the coating apparatus will be as follows: Initially, valve B will be moved with disc 14 into registry with seat 16. With valve 76 closed and valve 65 open, roughing pump G will be actuated to evacuate the entire system to a level wherein the molecular pump F can be actuated. When this state of evacuation is attained, molecular pump F is activated and emitter chamber C, duct 60, cold trap E and molecular pump F placed in an essentially atmosphere-free environment.

Assuming that substrate 22 has been placed within substrate chamber A and the substrate chamber closed by the sealing of flanges 30 and 31, the system will be "roughed." This will occur by closure of valve 75 and opening of valve 76 to the inlet 73 of roughing pump G. Pump G will typically evacuate the interior of roughing chamber A and valve housing 34 until a pressure sufficient for the operation of the molecular pump is attained. This pressure will be approximately 100-200 microns of mercury in the case of the illustrated diffusion pump F or 50-75 microns of mercury of an ion pump.

When such pressure is attained, valve B is moved from its seated position to its throttling position. Such movement is actuated by releasing pressure on bellows 42 and allowing leaf spring 40 to bias disc 14 upwardly relative to seat 16.

In the throttling position, the periphery of disc 14 of valve B overlying seat 16 will define a channel through which molecular conductance or throttling will occur.

Typically, the spatial separation of disc 14 relative to seat 16 as well as the length of overlap between the outside periphery of the disc and the inside periphery of the seat will determine the flow desired. In the case of a sixteen inch valve provided with a three-eighth of an inch overlap between the outside periphery of the disc and the inside periphery of the seat a valve clearance of three-sixteenth inches has been found sufficient. Dependent upon the pump used and atmospheric content desired, the position of disc 14 relative to seat 16 can be varied to move in the range of four-thousandths of an inch to 1 inch.

With disc 14 in the throttling position, substrate chamber A will typically equilibrate with emitter chamber C, molecular pump F effecting the desired evacuation. Thereafter, when complete equilibration has occurred, disc 14 will be pivoted on arm 18 out of registry and clear of seat 16 and coating commenced.

Generally all materials used for the construction of the chamber are either of stainless steel or other vacuum compatible materials. That is to say, all surfaces interior of the coating apparatus have no substantial vapor pressure which will interfere with the near perfect vacuum within the chamber.

It should be apparent that the throttling function provided by valve B could be used between a single chamber in which the entire coating apparatus was confined and a cold trap E and molecular pump F. Likewise, other modifications of my invention may be practiced, it being understood that the form of my invention as described above is to be taken as a preferred example of the same. Such description has been by way of illustration and example for purposes of clarity and understanding. Changes and modifications may be made without departing from the spirit of my invention.

Claims

What is claimed is:

1. A vacuum coating apparatus comprising: a chamber; a valve seat intermediate two ends of said chamber defining a valve aperture substantially coextensive with the cross section of said chamber and dividing said chamber into first and second portions; a valve disc for engagement with said seat; a sealed housing adjoining said seat, communicated to said chamber, and extending outwardly of said chamber for receiving said disc clear of said seat; molecular pump means communicated to one of said portions of said chamber; first disc moving means for moving said disc between a first position overlying said seat and a second position within said housing clear of said seat; and, second means for moving said disc when overlying said seat towards and away from said seat between a first overlying position where said disc seals said seat closing said valve between said first and second portions and a position where said disc permits throttled molecular conductance between said first and second portions.

2. The invention of claim 1 and wherein, said chamber, valve seat, and disc are of circular section.

3. The invention of claim 1 and including valve means between said molecular pump means and said chamber for sealing said molecular pump means from said emitter portion.

4. The invention of claim 1 and wherein said first moving means includes: an arm connected to said disc at one end and to said housing at said opposite end; and, means for pivotally moving said arm with respect to said housing to move said disc between said first and second positions.

5. A process for evacuating a first portion of a vacuum coating chamber by a molecular pump communicated to a second portion of said vacuum coating chamber, said molecular pump operable only below a predetermined gas pressure limit maintained within said second portion, said processing comprising the steps of: providing a valve disc and seat intermediate said chamber ends, said seat defining an opening substantially coextensive with the intermediate section of said chamber; seating said disc on said seat to seal said substrate portion of said chamber from said molecular pump; evacuating said substrate portion of said chamber to a pressure in the range between said predetermined pressure limit and twice said predetermined pressure limit; lifting said disc overlying said seat to permit throttling molecular conductance of gas within said substrate portion to said pump portion at a rate wherein said molecular pump is not swamped; and, moving disc clear of said seat after said throttling has substantially equilibrated gas within said chamber portions.

6. The process of claim 5 and wherein, said molecular pump is an ion pump and said evacuating step evacuates said chamber to a pressure limit between 50 and 100 microns of mercury gas pressure.

7. The process of claim 5 and wherein, said molecular pump is a diffusion pump and said evacuating step evacuates said chamber to a pressure range between 100 and 200 microns of mercury gas pressure.

8. In a vacuum coating chamber having a first portion for mounting a substrate and a second portion for mounting a coating material emitter and molecular pump, and means for vacuum sealing said substrate mounting from said coating emitter and molecular pump therebetween, the improvement in said vacuum sealing means comprising: a valve seat attached to the sidewalls of said chamber intermediate said substrate portion and coating material emitter portion, said seat defining aperture substantially coextensive with the section of said chamber; a valve disc configured for engagement with said seat; a sealed housing adjoining said seat, communicated with said chamber and extending outwardly of said chamber for receiving said disc clear of said seat; first disc moving means for moving said disc between a first position overlying said seat and a second position within said housing clear of said seat; and, second disc moving means for moving said disc when overlying said seat towards and away from said seat between a first position where said disc on said seat seals said emitter portion from said substrate portion and a second position where disc provides throttled molecular conductance between substrate portion and said emitter portion.

9. Apparatus according to claim 8 and wherein, said second disc moving means includes first biasing means for continuously biasing said disc away from said seat to said throttling position and second biasing means for overcoming said first biasing means to seat said disc.