Spatter proof evaporant source design for use in vacuum deposition of solid thin films on substrate

Adams, G. D.

English

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 
WASHINGTON, D.C. 20546 
REPLY TO 
FROMt G P / O f f i c e  of Assistant General Counsel f o r  
Patent Matters 
SUBJECT: Announceme& of NASA-Owned U. S.  Patents i n  STAR 
In  accordance w i t h  the procedures agreed upon by Code GP 
and C o d e  USI, the attached NASA-owned U. S. Patent is being 
folawakded f o r  abstracting and announcement i n  NASA STAR. 
The following information is providedt 
U. S.  Patent No. ‘ t  
GOVeKIMIent o r  
Corporate Anployee t Government 4 
Supplementary Corporate 
Source ( i f  applicable 1 : 
NASA Patent C a s e  No .  e . 
NOTE - If  th i s  patent covers an invention made by a 
employee of a NASA Contractor, the llowing is  applicable: 
Pursuant t o  Section 305(a) of the N onal. Aeronautics and 
Space A c t ,  the name of the Administrator of NASA appears on 
the first page of the patent; however, the name of the actual  
inventor (author) appears a t  the heading of Column No. 1 of 
‘the Specification, following the words M e  . e with res 
Yes 0 NO 
Copy of Patent o i ted  above 
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EVAPORANT SOURCE FOR VAPOR DEPOSITION 
31 
3 
INVENTOR. (S) 
GEORGE D. ADAMS 
B Y  
. D. S 
EVAPORANT SOURCE FOR VAPOR DEPOSITION 
Filed Aug. 31, 1967 2 Sheets-Sheet 2 
45 
GEORGE D 
'IG. 5 
IMVElV TOR 
AOAMS 
FIG. 6 B Y  
ite Patente 
1 
3,466,424 
E ~ A P O R A ~  SOURCE FOR VAPOR DEPOSITION 
George D. Adarns, 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 /OO; C23c I 1  /00 
US. CL 219-275 7 Claims 
A ~ $ ~ R A C T  OF THE DISCLOSURE 
A spatterproof evaporant source fox use in yacuum de- 
positing 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'suhsequently re-evap- 
orated or deflected upward through the vapor exit open- 
ing 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 itwill not reach the substrate to  dam- 
age the film being deposited. 
The invention described herein was made by an em- 
ployee of the United States Government and may be 
manufactured and used by or for the Government for 
governmental purposes without the payment of any royal- 
ties thereon or therefor. 
BACKGROUND O F  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 opera- 
tions. 
The art of vacuum coating is very important in the 
field of microelectronics since many of the critical elec- 
tronic components are formed by the vacuum deposition 
process wherein extremely thin films of dielectric and 
conductive materials are deposited in the desired arrange- 
ment 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 mate- 
rial. 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 sufficient 
energy to pierce the film and leave pin holes therein. This 
type of film damage has been partidularly 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 di- 
rected toward designing the evaporant sources or con- 
tainers 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 sub- 
strate, this being possible since the vapor is reflected from 
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tion of the particles will approximate the angle of in- 
cidence. 
Although certain of the evaporant sources recently in- 
troduced 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 posi- 
tioned 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 perfora- 
tions 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 re- 
evaporated 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 inven- 
tion to provide an improved spatterproof evaporant 
source. 
A more specific object of the invention is to provide a 
spatterproof evaporant source that is very simple and in- 
expensive 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 evap- 
orant source that separates high velocity miscroscopic 
particles from the vapor being evaporated from the source 
by using an extremely simple yet highly effective baffle 
arrangement. 
These and other objects and advantages of the inven- 
tion 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 eva- 
porant source such as contained in the vacuum evapora- 
tion 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 
4-4 of FIGURE 3. 
a smooth surface at random directions, having no relation 70 
to the angle of incidence, while the microscopic particles 
are reflected specularly, meaning that the angle of reflec- 
FIGURE 5 is an exploded perspective view showing the 
metallic sheet elements of the evaporant source prior to 
folding and assembly of the elements. 
3,466,424 
4 
FIGURE 6 is a cross tional view of a modified 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 velo- 
city microscopic particles that would be detrimental to 
in is shown a vacuum the thin film being deposited on the substrate must pass 
and a bell jar 15 par- through the openings 59 and, therefore, most of such 
tially broken away to reveal a portion of the inside of the particles will not escape from the cartridge 31. The par- 
vacuum chamber 11. Within the vacuum chamber 11 are ticles that do escape will bomce off the surface of @e 
a plurality of vertical Plates 17 radiating from the center top of the cartridge 31 around the vapor exit port S1 and, 
of the chamber to divide the chamber into a series of since these particles will bounce off the surface at an angle 
triangular compartments 19. The upper ends of the plates approximating the angle of incidence, most of these par- 
17 are covered by a circular plate 2% that has a series of tides will become trapped in the dimple cavity 57. Any 
openings (not shown) aligned with each of the compartc microscopic particles that do bounce off of the dimple 
ments 19. Supported above the plate 21 is a revolving cavity 57 and through the vapor exit port 51 will likely be 
substrate carrier plate 23 that is designed to support 8 15 directed in a trajectory so low as to miss the substrate. 
substrate over either or all of the aforesaid openings in The purpose of the dimple 53 in the bottom of the 
the plate 21 such that the respective substrates are exposed cartridge 31 is to reduce the amount of evaporable mate- 
to the respective compartments 19. Each compartment 19 rial disposed directly underneath the dimple cavity 57 so 
has an evaporant source 25 at the bottom thereof mounted that the exit port region of the cartridge will be maintained 
on electrodes 27 and 29. In forming an electronic compo- 20 somewhat hotter than the rest of the cartridge. Also, the 
nent, such as a thin film capacitor, the sources 25 in the seam 48 of the cartridge is necked down slightly at 65 to 
respective compartments 19 may alternatively, from one create a hot spot in the area of the dimple cavity 57 and 
compartment to the next, contain a dielectric evaporant the vapor exit part 51 so as to prevent clogging of the 
material and a conductive evaporant material and the openings 59 during the vapor deposition operation, 
substrate carrier plate 23 is adapted to  revolve and POSi- 25 FIGURE 6 illustrates a cross section of an evaporant 
tion the substrate over the compartments for the appro- source that provides an even more complete trapping of 
priate vacuum deposition of the dielectric and conductive high velocity microscopic particles than that shown in 
films. FIGURES 2 through 5. In FIGURE 6 a cartridge 67 has 
AS is well understood in the art, the evaporable mate- a vapor exit port 69 and a dimple 71 in the bottom of the 
rial in sources such as source 25 is resistance heated to a 30 cartridge 67 in vertical alignment with the vapor exit port 
vaporizing temperature through the electrodes 27 and 29 69. The top of the cartridge 67 has a downwardly di- 
and the material evaporates from the Sources 25 and is de- rected rim 73 around the vapor exit port 69. A baffle strip 
posited on the substrate carried by the substrate carrier 15 is welded to the top of the' cartridge 67 and has a de- 
23. Since the details and operation of the vacuum cham- pression or  cavity 77 the bottom of which is generally 
ber 11 forms no part of the present invention, this appa- 35 flat. The cavity 77 has a series of perforations 79 located 
ratus will not be further described. around the cavity 77 near the top thereof with the axes 
A novel evaporant source 25 is illustrated in FIGURES of these openings directed toward the rim 73. With the 
2 through 5, being shown in perspective in FIGURE 2, configuration of the vapor exit port and dimple cavity 
and comprises a cartridge 31 that is made by folding the shown in FIGURE 6, it would be virtually impossible for 
blank 33 shown in FIGURE 5 along the broken lines such 40 any high velocity particles to pass through an opening 
that the portion 35 constitutes the bottom of the cartridge, 79 and subsequently emerge through the vapor exit port 
and portion 37 forms the top. Portion 39 forms one side, 69 before dissipating all of its energy. The vapor, how- 
portions 41 and 43 cooperate to  form another side, and ever, which i s  reflected at randam off of the reflecting 
portions 45 and 47 press together to form a Seam 48 surfaces will pass through the openings 79 and reflect 
(FIGURE 2) that is welded. One end of the cartridge is 45 off of the rim 73 and the surface of the cavity 77 and 
pressed and welded at  49 as indicated in FIGURE 2. The be passed or reevaporated through, the vapor exit port 
other end is left unwelded for filling the cartridge with 69 onto the substrate. 
evaporable material. Obviously, many modifications and variations of the 
In the center of the top of the cartridge 31 is a vapor present invention are possible in the light of the above 
exit port 51 and in the bottom of the cartridge directly 60 teachings. It is therefore, to be understood that within 
opposite the exit port 51 is a dimple 53, the purpose of the scope of the appended claims the invention may be 
which will be explained hereinafter. Coextensive with the practiced other than as specifically described herein. 
top of the cartridge 31, disposed on the inside of the I claim: 
cartridge and contiguous with the top of the cartridge is a 1. An evaporant source for the vapor deposition of 
metallic strip 55 that is welded to  the top of the cartridge. 55 thin solid films upon a substrate comprising: 
The strip 55 is provided with a dimple cavity 57 that is (a)  a cartridge having an interior space for contain- 
vertically aligned with the vapor exit port 51 in the top ing evaporable material; 
of the cartridge with the dimple cavity 57 being larger (b) said cartridge having a vapor exit opening formed 
in dimension than the vapor exit port 51. The dimple in the upper side thereof; 
cavity 57 is provided with a series of perforations 59 ex- 60 (c) a strip substantially coextensive with and under- 
tending around the peripheral zone of the dimple 57 and lying said upper side of said cartridge; 
thus offset from vertical alignment with the vapor exit (d) the area of said strip underlying said opening and 
port 51 and with the axes of the openings 59 disposed the portion of said upper side defining said opening 
diagonally with respect to the cartridge 31 and converging being depressed inwardly of said cartridge to  form 
generally in the space above the cartridge. The cartridge 65 a cavity in the region of said cartridge beneath said 
31 is adapted to contain an evaporant material 51 such opening; 
as sicilon monoxide. (e) said depressed area of said strip having a series of 
When the evaporant source 25 is resistance heated to regularly spaced perforations therethrough extend- 
operating temperature by electric power supplied to elec- ing around the peripheral zone Qf said depression 
trodes 27 and 29, the material 61 begins to vaporize and 70 with said perforations being offset from vertical 
the vapor rises through the openings 59. Since there is alignment with said opening; 
no direct line between the interior of the cartridge 31 and (f) said strip being bonded to said upper side of said 
the vapor exit port 5P through which the vapor can pass, cartridge in the area of said strip around said de- 
the vapor must pass through the openings 59 and rebound pression, 
on the interior surface of the top of the cartridge around 75 2. The invention. as defined in claim 1 wherein said 
evaporant source. 
Description of the preferred embodiments 
3,466,424 
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. 
cartridge comprises a depression in the side of said car- 3 y 1 2 9 ~ 3 1 5  4/1964 Radke et -------- 219-271 
tridge opposite said vapor exit opening, said depression lo Liben ------------- 219-271 
being directed inwardly of said cartridge toward said 31244~857 4/1966 Bertelsen et ----- 219-275 
opening whereby the quantity of evaporable material Jennings ---------- 219-275 
that may be disposed directly beneath said opening is 
reduced. 
6.  The invention as defined in claim 2 wherein a rim 15 PETER W. GOWDEY, Assistant Examiner 
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 cen- 
tral axes of said perforations coincide with lines inter- 
secting a portion of said rim. 
References Cite 
UNITED STATES PATENTS 
2,793,609 5/1957 Shen et aI. 
5. The invention as defined in claim 1 wherein said 2,998,376 811961 Smith ------------ 118-49 x 
3,2109525 
3~344,768 
JOSEPH V. TRUHE, Primary Examiner 
US.  C1. X.R. 
1 1 8 4 8 ,  49.1 


Evaporant source for vapor deposition Patent

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