US3466424A

US3466424A - Evaporant source for vapor deposition

Info

Publication number: US3466424A
Application number: US665679A
Authority: US
Inventors: George D Adams
Original assignee: National Aeronautics and Space Administration NASA
Current assignee: National Aeronautics and Space Administration NASA
Priority date: 1967-08-31
Filing date: 1967-08-31
Publication date: 1969-09-09
Anticipated expiration: 1986-09-09

Description

Sept. 9, 1969 ADAMS 3,466,424

EVAPORANT SOURCE FOR VAPOR DEPOSITION Filed Aug. 31, 1967 2 Sheets-Sheet 1 g I d 2 i ig a I 27 I 1 -29 29 r I 29 27 fl g.

I l I I l :9 I9 I9 ilmmmm: MINIMUM/3 FIG. I

INVENTOR($) GEORGE D. ADAMS BY 5 Q 7 Sept. 9, 1969 ADAMS 3,466,424

EVAPORANT SOURCE FOR VAPOR DEPOSITION Filed Aug. 51, 196'? 2 Sheets-Sheet 2 GEORGE D. ADAMS 5y q 9. 3 2

NW N.

ATTOR S United States Patent 3,466,424 EVAPORANT SOURCE FOR VAPOR DEPOSITION George D. Adams, Huntsville, Ala., assignor to the United States of America as represented by the Administrator of the National Aeronautics and Space Administration Filed Aug. 31, 1967, Ser. No. 665,679 Int. Cl. F22b 1/00; C23c 11/00 US. Cl. 219275 7 Claims ABSTRACT OF THE DISCLOSURE A spatterproof evaporant source for use in vacuum depositing of thin solid films upon a substrate. A metallic cartridge for containing evaporable material has a vapor exit opening formed in the central region of the upper side of the cartridge. An inwardly depressed dimple is formed in a metallic strip beneath the vapor exit opening and the dimple has small perforations in an area offset from vertical alignment with the vapor exit opening. Vapors pass through the perforations and are initially deflected by the portion of the upper side of the cartridge around the vapor exit opening and subsequently re-evaporated or deflected upward through the vapor exit opening to the substrate. Any gross particle spattering through the perforations will be trapped in the dimple cavity or else reflected through the vapor exit opening at such a low trajectory that it will not reach the substrate to damage the film being deposited.

The invention described herein was made by an em- BACKGROUND OF THE INVENTION This invention relates generally to vacuum deposition of thin solid films on substrates and more particularly to evaporant sources for use in vacuum deposition operations.

The art of vacuum coating is very important in the field of microelectronics since many of the critical electronic components are formed by the vacuum deposition process wherein extremely thin films of dielectric and conductive materials are deposited in the desired arrangement on a substrate. A continuing problem encountered in the vacuum deposition process has been that known in the art as spattering of the evaporation source material. This spattering occurs when the solid evaporant material explodes during heating because of occluded gases. Relatively large solid particles of evaporant leave the evaporant source at high velocities and strike the thin film being deposited on the substrate with suflicient energy to pierce the film and leave pin holes therein. This type of film damage has been particularly bothersome in the formation of dielectric films in thin-film capacitors. These explosions will also empty the source of evaporant material before the evaporation begins unless a means is provided to trap the material in the source.

Efforts to solve the spattering problem have been directed toward designing the evaporant sources or containers so that the detrimental microscopic particles will be separated from the vapor before striking the substrate. This is done by directing the vapor toward the substrate while rebounding the harmful particles in the vapor off of a reflecting surface in a direction that misses the substrate, this being possible since the vapor is reflected from a smooth surface at random directions, having no relation to the angle of incidence, while the microscopic particles are reflected specularly, meaning that the angle of reflec- 3,466,424 Patented Sept. 9, 1969 tion of the particles will approximate the angle of incidence.

Although certain of the evaporant sources recently introduced have proved somewhat successful in alleviating the spattering problem, all of these sources are unduly complex in design, involving several components such as a separate and distinct reflecting hood and reflecting box in addition to the crucible or cartridge that contains the evaporant. Such elaborate sources are rather difficult and expensive to fabricate and require an excessive amount of power for operation.

Summary of the invention Briefly described, the invention comprises an evaporant source that is very simple and may be made from two strips of metal foil. The source comprises a cartridge evaporant container having a vapor exit port in the upper side thereof. Beneath the upper side of the cartridge is a metallic strip having a depressed or dimpled area positioned in opposed relationship to the vapor exit port with the dimpled area being directed inwardly of the cartridge. The dimpled area is larger than the area occupied by the vapor exit port and small perforations are provided in the peripheral zone of the dimpled area which perforations are offset from vertical alignment with the vapor exit port. Vapor rises from the cartridge through the perforations in the dimpled portion and is reflected off of the inner surface of the upper side of the cartridge around the vapor exit port and is subsequently reflected or reevaporated off of the dimpled surface and out through the vapor exit port toward the substrate. Since harmful microscopic particles cannot escape from the cartridge in a vertical direction, most of them will be trapped in the cartridge. The particles that do escape through the perforations must strike the portion of the cartridge that covers the perforations in the dimpled area and bounce off this surface at an angle approximating the angle of incidence. Thus, most of these particles will be trapped in the dimple cavity and will never reach the substrate. If occasional ones of the particles do escape through the vapor exit port their trajectories will likely be at such a low angle that they will miss the substrate.

Accordingly, it is a general object of the present invention to provide an improved spatterproof evaporant source.

A more specific object of the invention is to rovide a spatterproof evaporant source that is very simple and inexpensive to make and which is durable and reusable and susceptible of operating on low power supply.

Another object of the invention is to provide an evaporant source that separates high velocity miscroscopic particles from the vapor being evaporated from the source by using an extremely simple yet highly effective baflie arrangement.

These and other objects and advantages of the invention will become apparent upon reference to the following specification, attendant claims and drawings:

Brief description of the drawing FIGURE 1 is an elevational view, partially broken away, of a vacuum evaporation chamber containing a plurality of spatterproof evaporant sources.

FIGURE 2 is a perspective view of a spatterproof evaporant source such as contained in the vacuum evaporation chamber shown in FIGURE 1.

FIGURE 3 is a cross sectional view taken along line 3-3 of FIGURE 2.

FIGURE 4 is a cross sectional view taken along line 44 of FIGURE 3.

FIGURE 5 is an exploded perspective view showing the metallic sheet elements of the evaporant source prior to folding and assembly of the elements.

FIGURE 6 is a cross sectional view of a modified evaporant source.

Description of the preferred embodiments Referring to FIGURE 1, therein is shown a vacuum chamber 11 comprising a base 13 and a bell jar 15 partially broken away to reveal a portion of the inside of the vacuum chamber 11. Within the vacuum chamber 11 are a plurality of vertical plates 17 radiating from the center of the chamber to divide the chamber into a series of triangular compartments 19. The upper ends of the plates 17 are covered by a circular plate 21 that has a series of openings (not shown) aligned with each of the compartments 19. Supported above the plate 21 is a revolving substrate carrier plate 23 that is designed to support a substrate over either or all of the aforesaid openings in the plate 21 such that the respective substrates are exposed to the respective compartments 19. Each compartment 19 has an evaporant source 25 at the bottom thereof mounted on

electrodes

27 and 29. In forming an electronic component, such as a thin film capacitor, the sources 25 in the respective compartments 19 may alternatively, from one compartment to the next, contain a dielectric evaporant material and a conductive evaporant material and the substrate carrier plate 23 is adapted to revolve and position the substrate over the compartments for the appropriate vacuum deposition of the dielectric and conductive films.

As is well understood in the art, the evaporable material in sources such as source 25 is resistance heated to a vaporizing temperature through the

electrodes

27 and 29 and the material evaporates from the sources 25 and is deposited on the substrate carried by the substrate carrier 23. Since the details and operation of the vacuum chamber 11 forms no part of the present invention, this apparatus will not be further described.

A novel evaporant source 25 is illustrated in FIGURES 2 through 5, being shownin perspective in FIGURE 2, and comprises a cartridge 31 that is made by folding the blank 33 shown in FIGURE along the broken lines such that the portion 35 constitutes the bottom of the cartridge, and portion 37 forms the top. Portion 39 forms one side,

portions

41 and 43 cooperate to form another side, and

portions

45 and 47 press together to form a seam '48 (FIGURE 2) that is welded. One end of the cartridge is pressed and welded at 49 as indicated in FIGURE 2. The other end is left unwelded for filling the cartridge with evaporable material.

In the center of the top of the cartridge 31 is a vapor exit port 51 and in the bottom of the cartridge directly opposite the exit port 51 is a dimple 53, the purpose of which will be explained hereinafter. Coextensive with the top of the cartridge 31, disposed on the inside of the cartridge and contiguous with the top of the cartridge is a metallic strip 55 that is welded to the top of the cartridge. The strip 55 is provided with a dimple cavity 57 that is vertically aligned with the vapor exit port 51 in the top of the cartridge with the dimple cavity 57 being larger in dimension than the vapor exit port 51. The dimple cavity 57 is provided with a series of perforations 59 extending around the peripheral zone of the dimple 57 and thus offset from vertical alignment with the vapor exit port 51 and with the axes of the openings 59 disposed diagonally with respect to the cartridge 31 and converging generally in the space above the cartridge. The cartridge 31 is adapted to contain an evaporant material 61 such as sicilon monoxide.

When the evaporant source 25 is resistance heated to operating temperature by electric power supplied to

electrodes

27 and 29, the material 61 begins to vaporize and the vapor rises through the openings 59. Since there is no direct line between the interior of the cartridge 31 and the vapor exit port 51 through which the vapor can pass, the vapor must pass through the openings 59 and rebound on the interior surface of the top of the cartridge around the vapor exit port 51 and subsequently rebound from the bottom of the dimple cavity 57 and out through the vapor exit port 51 onto the substrate. Moreover, any high velocity microscopic particles that would be detrimental to the thin film being deposited on the substrate must pass through the openings 59 and, therefore, most of such particles will not escape from the cartridge 31. The particles that do escape will bounce off the surface of the top of the cartridge 31 around the vapor exit port 51 and, since these particles will bounce off the surface at an angle approximating the angle of incidence, most of these particles will become trapped in the dimple cavity 57. Any microscopic particles that do bounce off of the dimple cavity 57 and through the vapor exit port 51 will likely be directed in a trajectory so low as to miss the substrate.

The purpose of the dimple 53 in the bottom of the cartridge 31 is to reduce the amount of evaporable material disposed directly underneath the dimple cavity 57 so that the exit port region of the cartridge will be maintained somewhat hotter than the rest of the cartridge. Also, the seam 48 of the cartridge is necked down slightly at 65 to create a hot spot in the area of the dimple cavity 57 and the vapor exit port 51 so as to prevent clogging of the openings 59 during the vapor deposition operation.

FIGURE 6 illustrates a cross section of an evaporant source that provides an even more complete trapping of high velocity microscopic particles than that shown in FIGURES 2 through 5. In FIGURE 6 a cartridge 67 has a vapor exit port 69 and a dimple 71 in the bottom of the cartridge 67 in vertical alignment with the vapor exit port 69. The top of the cartridge 67 has a downwardly directed rim 73 around the vapor exit port 69. A baffie strip 75 is welded to the top of the cartridge 67 and has a depression or cavity 77 the bottom of which is generally flat. The cavity 77 has a series of perforations 79 located around the cavity 77 near the top thereof with the axes of these openings directed toward the rim 73. With the configuration of the vapor exit port and dimple cavity shown in FIGURE 6, it would be virtually impossible for any high velocity particles to pass through an opening 79 and subsequently emerge through the vapor exit port 69 before dissipating all of its energy. The vapor, however, which is reflected at random off of the reflecting surfaces will pass through the openings 79 and reflect off of the rim 73 and the surface of the cavity 77 and be passed or reevaporated through the vapor exit port 69 onto the substrate.

Obviously, many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore, to be understood that within the scope of the appended claims the invention may be practiced other than as specifically described herein.

I claim:

1. An evaporant source for the vapor deposition of thin solid films upon a substrate comprising:

(a) a cartridge having an interior space for containing evaporable material;

(b) said cartridge having a vapor exit opening formed in the upper side thereof;

(c) a strip substantially coextensive with and underlying said upper side of said cartridge;

(d) the area of said strip underlying said opening and the portion of said upper side defining said opening being depressed inwardly of said cartridge to form a cavity in the region of said cartridge beneath said opening;

(e) said depressed area of said strip having a series of regularly spaced perforations therethrough extending around the peripheral zone of said depression with said perforations being offset from vertical alignment with said opening;

(f) said strip being bonded to said upper side of said cartridge in the area of said strip around said depression.

2. The invention as defined in claim 1 wherein said perforations are disposed in said depression above the bottom of said depression.

3. The invention as defined in claim 2 wherein said depression is of concave cross section.

4. The invention as defined in claim 1 wherein said evaporant source is necked down in the region of said exit opening.

5. The invention as defined in claim 1 wherein said cartridge comprises a depression in the side of said cartridge opposite'said vapor exit opening, said depression being directed inwardly of said cartridge toward said opening whereby the quantity of evaporable material that may be disposed directly beneath said opening is reduced.

6. The invention as defined in claim 2 wherein a rim extends at least partially around said vapor exit opening, said rim being directed inwardly of said cartridge.

7. The invention as defined in claim 6 wherein the central axes of said perforations coincide with lines intersecting a portion of said rim.

References Cited UNITED STATES PATENTS 2,793,609 5/1957 Shen et al. 2,998,376 8/1961 Smith 11849 X 3,129,315 4/1964 Radke et al. 219271 3,210,525 10/1965 Liben 219-271 3,244,857 4/1966 Bertelsen et al. 219-275 3,344,768 10/1967 Jennings 2l9-275 JOSEPH V. TRUHE, Primary Examiner PETER W. GOWDEY, Assistant Examiner US. Cl. X.R. 11848, 49.1