WO1998031847A1

WO1998031847A1 - Crystal holder

Info

Publication number: WO1998031847A1
Application number: PCT/US1998/001043
Authority: WO
Inventors: Kermit Crain; Robert S. Tuchel; Michael J. Holter; Timothy Dietrich
Original assignee: Specialty Coating Systems, Inc.
Priority date: 1997-01-22
Filing date: 1998-01-20
Publication date: 1998-07-23
Also published as: AU6032298A

Abstract

In one embodiment, the present invention provides a crystal holder that includes a crystal, a housing body, a housing cap, a first O-ring and a second O-ring. The first O-ring is disposed between the crystal and the housing cap, and the second O-ring is disposed between the crystal and the housing body. The crystal holder may be included within a vacuum system having a deposition chamber. In another embodiment, the present invention provides a crystal holder that includes a crystal, a housing body and a tubing. The housing body is adjacent the crystal such that a volume is formed between the rear face of the crystal and the housing body. The tubing has a first open end and a second open end, and the tubing is partially disposed within the orifice of the housing body such that the first open end is disposed within the volume between the rear face of the crystal and the housing body. This crystal holder may be incorporated into a vacuum system having a deposition chamber.

Description

CRYSTAL HOLDER

BACKGROUND

1. Field of the Invention

The present invention relates generally to crystal holders for use with depositing layers of materials under vacuum, and more specifically to such crystal holders that may be used with devices designed to monitor and/or control the material deposition rate and/or the material thickness.

2. Discussion of the Related Art

Dielectric films are widely used throughout both the electronics and coatings industries. Due to their relatively high dielectric constants and melting points, there is an increasing interest in forming dielectric layers from parylene polymers having the molecular structure:

wherein X is typically a hydrogen atom or a fluorine atom. G is a nuclear substituent group such as a perfluorinated alkane, a perfluorinated alkene, a perfiuorinated alkyne, chlorine or fluorine, and m has a value of from zero to four.

Parylene polymers are usually formed by chemical vapor deposition processes. One such process is the Gorham process which employs a vacuum system, such as disclosed in U.S. Patent No. 5,538,758, which is hereby incorporated by reference. Fig. 1 shows such a block diagram of one embodiment of a vacuum system 50 disclosed in U.S. Patent No. 5,538,758 and designed for use in the Gorham process. System 50 includes a vaporization zone 52, a pyrolysis zone 54, a post-pyrolysis zone 56 and a deposition chamber 58. Parylene dimer having the molecular structure:

is vaporized in vaporization zone 52. The parylene dimer passes to pyrolysis zone 54 in which the dimer bonds are cleaved to yield parylene monomer having the structure:

The parylene monomer passes through post-pyrolysis zone 56 which is designed to remove undesirable chemical species and moderate the kinetic energy of parylene monomer. The parylene monomer then passes into deposition chamber 58 and deposits onto a surface of substrate 60, which is attached to zone 58 by support mount 59. The parylene monomer undergoes polymerization at this surface to form a layer of parylene polymer. Many properties of the layer of parylene polymer, including the dielectric properties and the stress-induced properties, depend upon the thickness of the layer and/or the rate of monomer deposition, including the dielectric properties and the stress-induced properties. Therefore, vacuum system 50 can include a device 62 which is designed to monitor and/or control the rate of parylene monomer deposition and the thickness of the layer of parylene polymer. Based on the rate of deposition of parylene monomer or the thickness of the layer of parylene polymer, device 62 increases or decreases the rate of parylene monomer flow into deposition chamber 58. In some related art systems, device 62 indirectly measures the rate of parylene monomer deposition by monitoring the pressure within deposition chamber 58, and, in this sense, functions only as a monitor and not a controller of the thickness of the layer of parylene polymer. This arrangement provides only indirect information on the deposition rate and/or layer thickness, resulting in inaccurate measurements of deposition rate and layer thickness.

Fig. 2 shows a different embodiment of a related art device that includes a controller 75, a housing 74, a crystal 72 and a crystal mount 76. Controller 75, housing 74, crystal 72 and crystal mount 76 are designed to control and/or monitor the rate of monomer deposition and control and/or monitor the thickness of the layer of parylene polymer. Housing 74 is disposed along wall 61 of deposition chamber 58. Housing 74 contains crystal 72 which is mounted on crystal mount 76. Crystal 72 has a rear face 71 and a front face 73. Controller 75 includes an electrical circuit designed to drive crystal 72 at its resonant frequency using the piezoelectric effect, such as described in McGraw-Hill Encyclopedia of Physics 835-840, 1982, McGraw-Hill. As the thickness of a layer of parylene polymer disposed on front face 73 increases, the resonant frequency decreases. This change is monitored by controller 75 and used to calculate the thickness of the parylene polymer layer. When the resonant frequency of crystal 72 reaches a certain value, controller 75 reduces or terminates parylene monomer deposition by reducing vaporization of parylene dimer in vaporization zone 52 or closing a valve disposed between vaporization zone 52 and pyrolysis zone 54. The conventional design of device 70 has several shortcomings, however. For example, controller 75, crystal 72, housing 74 and crystal mount 76 are suitably designed to measure relatively thin, dense deposited layers of materials such as gold or silver (e.g., about 0.1 μ). When the relatively thick and less dense layers of parylene polymer (e.g., about 15 μ to about 30 μ) are deposited onto these crystals, overdampening of the oscillation of crystal 72 can occur, resulting in inaccurate deposition rate and layer thickness measurements. Furthermore, there exist no vacuum seals between crystal mount 76, crystal 72 and housing 74. This can allow parylene monomer to enter into the area behind the rear face 71 and deposit onto rear face 71, interfering with the measurement of the thickness of the layer of paryelene polymer on front face 73. The parylene monomer that gets behind rear face 71 can also form a layer of parylene polymer that can interfere with electrical connections during deposition and render such contacts unsuitable for further use. These problems can be overcome by using vacuum seals, but this can result in crystal rupture due to the formation of a pressure differential between front face 73 and rear face 71 since the area behind rear face 71 is not vacuum sealed from the coating environment of deposition chamber 58. Moreover, there are a substantial amount of irregularities in the outer surface of housing 74 and mount 76, decreasing the ease with which the layer of parylene polymer can be removed from housing 74 and mount 76 between deposition cycles.

Therefore, it is desirable within the art to provide an improved crystal holder to be used with a controller for measuring the rate of parylene monomer deposition and/or the thickness of a parylene polymer film or layer. It would be advantageous that such a system has a reduced tendency for crystal rupture and parylene monomer to enter the area behind the crystal.

SUMMARY

In one illustrative embodiment, the present invention provides a crystal holder. The crystal holder comprises a crystal, a housing body, a housing cap and at least two O-rings. The first O-ring is disposed between the crystal and the housing cap, and the second O-ring disposed between the crystal and the housing body. In another illustrative embodiment, the present invention provides a vacuum system that comprises a deposition chamber and a crystal holder vacuum sealed to an exterior of a wall of the deposition chamber. The crystal holder comprises a crystal, a housing body, a housing cap and at least two O-rings. The first O-ring is disposed between the crystal and the housing cap, and the second O-ring disposed between the crystal and the housing body. In yet another illustrative embodiment, the present invention provides a crystal holder.

The crystal holder comprises a crystal, a housing cap, a housing body and a tubing. The tubing has two open ends and is partially disposed within an orifice of the housing body such that one open end is disposed within a volume of space located between the rear face of the crystal and the housing body. The other open end of the tubing is typically in fluid communication with the deposition chamber.

In a further illustrative embodiment, the present invention provides a vacuum system that comprises a deposition chamber and a crystal holder vacuum sealed to the exterior of a wall of the deposition chamber. The crystal holder comprises a crystal, a housing cap, a housing body and a tubing. The tubing has two open ends and is partially disposed within an orifice of the housing assembly such that one open end is disposed within a volume of space located between the rear face of the crystal and the housing body. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a cross-sectional view of a related art parylene vacuum system; Fig. 2 is a cross-sectional view of a another embodiment of a related art vacuum system; Fig. 3 is a cross-sectional view of a parylene deposition system according to one embodiment of the present invention;

Fig. 4 is an exploded cross-sectional view demonstrating the manner in which a crystal is related to a deposition chamber according to one embodiment of the present invention;

Figs. 5A-F are views one embodiment of a housing according to the present invention; Figs. 6A-D are views of a housing cap for the housing of Figs. 5A-F; Figs. 7A and 7B are views of an adaptor plate for use with the housing of Figs. 5A-F;

Figs. 8 A and 8B are views of an access plate for use with the housing of Figs. 5A-F; and Figs. 9A and 9B are a cross-sectional views of a housing for a crystal oscillator controller connected to an adapter flange assembly according to one embodiment of the present invention.

DETAILED DESCRIPTION In one aspect, the present invention relates to a vacuum system 100 designed for use in the Gorham process as shown in Fig. 3. System 100 includes a vaporization zone 120, a pyrolysis zone 140, a post-pyrolysis zone 160 and a deposition chamber 180. System 100 further includes a substrate 200 and a crystal oscillator controller 220 to monitor and/or control the rate of parylene monomer deposition and the thickness of the layer of parylene polymer on the surface of substrate 200. Controller 220 is formed of a suitable electronic circuit, such as a model 360 deposition rate controller (available from Maxtek, Inc., located in Torrance, CA), which is in electrical communication with a quartz crystal 1. Crystal 1 is connected to a housing assembly 14 which is sealed to deposition chamber 180 along the exterior of wall 190 at orifice 195. Fig. 4 shows one embodiment of the manner in which crystal 1 is related to deposition chamber 180. In this embodiment, this connection is made using an aperture control disk 2, a centering O-ring 3, a centering ring 4, an exterior O-ring 5, an interior O-ring 6, head cap screws 7, a clamp 8, a hose fining 9, a wire hook-up 10, pogo probes 11, pogo sockets 12, a housing O- ring 13, crystal housing and flange assembly 14, an access plate 15, a piece of tubing 16, a housing cap 17, a screw 18, a panel receptacle 19, cap screws 20, an adapter flange assembly 21. Assembly 21 is formed of an adapter plate 23 and a QF adaptor 502 for adapter plate 23. Assembly 14 is formed of a crystal housing body 500 and a QF flange 501 for crystal housing body 500.

As parylene monomer is deposited onto substrate 200 (Fig. 3), it also deposits onto crystal 1. The rate of deposition onto crystal 1 is monitored by measuring the change in the frequency at which crystal 1 oscillates as a function of time. This measurement is made by using crystal 1 as the basic transducing element of the electrical circuit of controller 220. Crystal 1 is excited into mechanical motion (i.e., oscillation) by an external oscillator in the electrical circuit of controller 220. The change in the frequency of oscillation of crystal 1 is monitored by controller 220 which interprets the change in frequency as an increase in the thickness of the parylene polymer layer deposited on crystal 1. The monitored thickness and/or deposition rate is electronically compared to predetermined thickness and/or deposition rate set points in the electrical circuit of controller 220. Electrical signals are sent to controller 220 to increase, decrease or terminate the flow of parylene monomer into chamber 180 by increasing or decreasing the temperature of parylene dimer in vaporization zone 120 and/or controlling the flow of gaseous parylene dimer between vaporization zone 120 and pyrolysis zone 140, such as disclosed in U.S. Patent No. 5,538,758.

In some related art systems, parylene monomer can access the volume behind crystal 1 , resulting in deposition of parylene monomer on the rear face of crystal 1 between crystal 1 and housing body 500. Such deposition on the rear face of crystal 1 is undesirable since it leads to incorrect measurement of the thickness of the parylene polymer layer on the front face of crystal 1. Therefore, it is desirable to provide a vacuum seal that substantially prevents parylene monomer from reaching the rear face of crystal 1. However, it is also desirable to reduce the pressure in the volume behind crystal 1 to substantially the same pressure of deposition chamber 180 to prevent a pressure differential from forming across crystal 1 which could result in rupture of crystal 1. With the arrangement shown in Fig. 4, as deposition chamber 180 is pumped out, the pressure behind crystal 1 is also reduced by pumping this volume out through tubing 16 which provides a pressure relief pathway. This reduces or entirely eliminates problems such as crystal rupture due to a pressure differential across crystal 1. According to the present invention, one end of tubing 16 is connected by a series of pathways to the volume behind crystal 1. In some embodiments, hose fitting 9 can be used to place this open end of tubing 16 in fluid communication with the volume behind crystal 1. The other open end of tubing 16 is in fluid communication with deposition chamber 180 such that, as the pressure of chamber 180 is reduced, the pressure of the volume behind crystal 1 is reduced to substantially the same pressure. Preferably, tubing 16 is designed to allow gases behind crystal 1 to pump out through deposition chamber 180 while preventing parylene monomer within chamber 180 from entering behind crystal 1. This is accomplished by making tubing 16 relatively long. The use of O-ring seals 5 and 6 results in a substantial vacuum seal between crystal 1, housing cap 17 and housing body 500 and also decreases the tendency for parylene monomer to enter behind crystal 1.

Housing body 500 and housing cap 17 are preferably formed from polished materials that should have a reduced number of irregularities exposed to the parylene monomer during deposition. This makes it easier to remove paryelene polymer from these surfaces between deposition cycles.

Aperture control disk 2 acts to reduce the amount of parylene monomer reaching crystal 1. This assists in increasing the lifetime of crystal 1.

However, it is to be understood that the present invention is not limited by these listed components. Other examples of each of these components that are capable of functioning in an equivalent fashion are known to those skilled in the art and may be substituted for the listed components.

Figs. 5A-F shows one embodiment of housing body 500.

Figs. 6A-D show one embodiment of housing cap 17 that has appropriate dimensions for use with housing body 500 shown in Figs. 5A-F.

Figs. 7A and 7B show one embodiment of adaptor plate 23 having appropriate dimensions for use with housing body 500 as shown in Figs. 5A-F.

Figs. 8 A and 8B show one embodiment of an access plate 15 having dimensions appropriate for use with housing 22 as shown in Figs. 5A-F. Fig. 9 A shows one embodiment of adaptor flange assembly 21, and Fig. 9B shows this adaptor flange assembly with housing body 500, crystal 1, housing cap 17, rings 3 and 4 and BNC receptacle 19 assembled to chamber 180.

Having thus described certain embodiments of the present invention, various alterations, modifications and improvements will be obvious to those of ordinary skill in the art. Such alterations, modifications and improvements are intended to be part of this disclosure and are intended to be within the spirit and scope of the present invention. The particular dimensions, shapes and materials used may be so long as they accomplish one or more of the aforementioned improved properties provided by the controller of the present invention. Crystal 1 may be formed from a variety of solid materials, as known to those skilled in the art. In some embodiments, system 100 may not include post-pyrolysis zone 160. Alternatively, vaporization zone 120, pyrolysis zone 140 and post-pyrolysis zone 160 may be replaced by a source of parylene monomer. In certain embodiments, the controller of deposition rate controller and/or film or layer thickness of the present invention may be used in conjunction with chemical vapor deposition or physical vapor deposition systems that are not specifically designed for use with parylene. Accordingly, the foregoing description is by way of example only and is not intended as limiting. The present invention is limited only as defined by the following claims and the equivalents thereto .

What is claimed is:

Claims

1. A crystal holder, comprising: a crystal; a housing body; a housing cap; a first O-ring disposed between the crystal and the housing cap; and a second O-ring disposed between the crystal and the housing body.

2. The crystal holder according to claim 1 , wherein the first O-ring forms a vacuum seal between the crystal and the housing cap.

3. The crystal holder according to claim 1, wherein the second O-ring forms a vacuum seal between the crystal and the housing body.

4. The crystal holder according to claim 1, further comprising a controller for monitoring a resonant frequency of the crystal.

5. The crystal holder according to claim 4, wherein the crystal forms a transducer within the controller.

6. A vacuum system, comprising: a deposition chamber having a wall with an exterior; and a crystal holder vacuum sealed to the exterior of the wall, the crystal holder, comprising: a crystal; a housing body; a housing cap; a first O-ring disposed between the crystal and the housing cap; and a second O-ring disposed between the crystal and the housing body.

7. The vacuum system according to claim 6, wherein the first O-ring forms a vacuum seal between the crystal and the housing cap.

8. The vacuum system according to claim 6, wherein the second O-ring forms a vacuum seal between the crystal and the housing body.

9. The vacuum system according to claim 6, further comprising a controller for monitoring a resonant frequency of the crystal.

10. The vacuum system according to claim 9, wherein the crystal forms a transducer within the controller.

11. The vacuum system according to claim 6, further comprising a vaporization zone in fluid communication with the deposition chamber.

12. The vacuum system according to claim 11, wherein the vaporization zone comprises: a container for containing parylene dimer; and at least one heater for heating the container and vaporizing the parylene dimer.

13. The vacuum system according to claim 11, further comprising a pyrolysis zone disposed between the vaporization zone and the deposition chamber, the pyrolysis zone being in fluid communication with the vaporization zone and the deposition chamber.

14. The vacuum system according to claim 13, further comprising a valve disposed between the vaporization zone and the pyrolysis zone to control a flow of a gas between the vaporization zone and the pyrolysis zone.

15. The vacuum system according to claim 13, further comprising a post-pyrolysis zone disposed between the pyrolysis zone and the deposition chamber, the post-pyrolysis zone being in fluid communication with the pyrolysis zone and the deposition chamber.

16. A crystal holder, comprising: a crystal having a rear face; a housing body adjacent the crystal such that a volume is formed between the rear face of the crystal and the housing body, the housing body having an orifice; and a tubing having a first open end and a second open end, the tubing being partially disposed within the orifice of the housing body such that the first open end is disposed within the volume between the rear face of the crystal and the housing body.

17. The crystal holder according to claim 16, further comprising: a housing cap; a first O-ring disposed between the crystal and the housing cap; and a second O-ring disposed between the crystal and the housing body.

18. The crystal holder according to claim 17, wherein the first O-ring forms a vacuum seal between the crystal and the housing cap.

19. The crystal holder according to claim 17, wherein the second O-ring forms a vacuum seal between the crystal and the housing body.

20. The crystal holder according to claim 16, further comprising a controller for monitoring a resonant frequency of the crystal.

21. The crystal holder according to claim 20, wherein the crystal forms a transducer within the controller.

22. A vacuum system, comprising: a deposition chamber having a wall with an exterior; and a crystal holder vacuum sealed to the exterior of the wall, the crystal holder, comprising: a crystal having a rear face; a housing body adjacent the crystal such that a volume is formed between the rear face of the crystal and the housing body, the housing body having an orifice; and a tubing having a first open end and a second open end, the tubing being partially disposed within the orifice of the housing body such that the first open end is disposed within the volume between the rear face of the crystal and the housing body.

23. The vacuum system according to claim 22, further comprising: a housing cap; a first O-ring disposed between the crystal and the housing cap; and a second O-ring disposed between the crystal and the housing body.

24. The vacuum system according to claim 23, wherein the first O-ring forms a vacuum seal between the crystal and the housing cap.

25. The vacuum system according to claim 23, wherein the second O-ring forms a vacuum seal between the crystal and the housing body.

26. The vacuum system according to claim 22, further comprising a controller for monitoring a resonant frequency of the crystal.

27. The vacuum system according to claim 26, wherein the crystal is a transducer within the controller.

28. The vacuum system according to claim 26, further comprising: a vaporization zone; a pyrolysis zone in fluid communication with the deposition chamber and the vaporization zone; and a valve constructed and arranged such that the controller can substantially control a rate of flow of gas between the vaporization zone and the pyrolysis zone by controlling a position of the valve between an open position and a closed position, the position of the valve being selected based upon a comparison of a deposition rate measured by the controller and a predetermined deposition rate set point.

29. The vacuum system according to claim 28, further comprising a heater for vaporizing a gas in the vaporization zone, the heater being constructed arranged such that the controller can substantially control a rate of flow of gas between the vaporization zone and the pyrolysis zone by controlling a temperature of the heater, the temperature of the heater being selected based upon a comparison of a deposition rate measured by the controller and a predetermined deposition rate set point.

30. The vacuum system according to claim 26, further comprising: a vaporization zone; and a heater for heating a gas in the vaporization zone, wherein the controller is constructed arranged such that the controller can substantially control a rate of flow of gas between the vaporization zone and the pyrolysis zone by controlling a temperature of the heater, the temperature of the heater being selected based upon a comparison of a deposition rate measured by the controller and a predetermined deposition rate set point.

31. The vacuum system according to claim 9, further comprising: a vaporization zone; a pyrolysis zone in fluid communication with the deposition chamber and the vaporization zone; and a valve constructed and arranged such that the controller can substantially control a rate of flow of gas between the vaporization zone and the pyrolysis zone by controlling a position of the valve between an open position and a closed position, the position of the valve being selected based upon a comparison of a deposition rate measured by the controller and a predetermined deposition rate set point.

32. The vacuum system according to claim 31 , further comprising a heater for vaporizing a gas in the vaporization zone, the heater being constructed arranged such that the controller can substantially control a rate of flow of gas between the vaporization zone and the pyrolysis zone by controlling a temperature of the heater, the temperature of the heater being selected based upon a comparison of a deposition rate measured by the controller and a predetermined deposition rate set point.

33. The vacuum system according to claim 9, further comprising: a vaporization zone; and a heater for heating a gas in the vaporization zone, wherein the controller is constructed arranged such that the controller can substantially control a rate of flow of gas between the vaporization zone and the pyrolysis zone by controlling a temperature of the heater, the temperature of the heater being selected based upon a comparison of a deposition rate measured by the controller and a predetermined deposition rate set point.