US3450097A

US3450097A - Vapor deposition apparatus

Info

Publication number: US3450097A
Application number: US486571A
Authority: US
Inventors: Stanley Firestone; John Mccarthy
Original assignee: US Department of Army
Current assignee: US Department of Army
Priority date: 1965-09-10
Filing date: 1965-09-10
Publication date: 1969-06-17
Anticipated expiration: 1986-06-17

Description

June 17, 1969 5' HIRE-STONE ET AL 3,450,097

VAPOR DEPOS IT ION APPARATUS Filed Sept. 10. 1965 Sheet Z of 2 FIG. I

J 4o FEEDER 2 46 CONTROL FEEDER 52 38 I2 IIIBR W l I n l 32% lp iih...

INVENTORS,

STANLEY FIRESTON'E JOHN MC CARTHY ATTORNEYS June 17, 1 969 Filed Sept. 10, 1965 s. FIRESTONE ET AL 3,450,097 VAPOR DEPOSITION APPARATUS Sheet 2 of2 I INVE'NTORS, STANLEY FIRESTONE JOHN MC CARTHY BY 5M A/Z4. C. W ATTORNEYS United States Patent Office 3,450,097 Patented June 17, 1969 US. Cl. 118-49 7 Claims ABSTRACT OF THE DISCLOSURE A vapor deposition apparatus including a compartmented vapor source defining a tortuous flow path for the evaporant to inhibit particle spatter in the deposition zone and means within the deposition chamber to sequentially feed, to said source, discrete amounts of material to be evaporated.

The invention described herein may be manufactured and used by or for the Government for governmental purposes without the payment of any royalty thereon.

The present invention relates to deposition of thin films on substrates by vaporization and more particularly to the deposition on substrates of a relatively homogeneous film from mixtures of materials which have different vaporization temperatures.

The deposition of films on substrates has become an important technique in the miniaturization of electronic components. Miniature printed electronic circuits and components can be formed on substrates by depositing these circuits or components on the substrate in the form of a film. One particularly critical area is in the formation of resistance elements by film deposition. Due to the extreme thinness of the films, resistance elements normally have to be made relatively long in size. Since, as a practical matter resistance elements in circuits formed by film deposition have taken up a relatively high proportion of the circuit area, recent emphasis has been placed upon finding materials of high electronic resistance in order to form small stable high resistance elements. One type of material that could be used successfully is a cermet. Cermets are a substance consisting of a metal in a ceramic such as metallic oxide, carbide or nitride. One example of a cermet that is particularly useful in the formation of resistance elements is a mixture of chromium and silicon monoxide.

While cermets have the necessary properties to form the desired high resistance film, their deposition as a homogeneous film has presented problems because the elements of a cermet mixture have widely different vapor pressures or thermal evaporation levels. In the past, the existence of these different thermal evaporation levels has caused difficulty in depositing homogeneous films of the cermet material. As is readily apparent, an unevenly deposited film is undesirable because it does not have the desired uniform electrical properties and is electrically unpredictable.

Because of the composition of cermets it is necessary to employ high temperatures often in the order of 1600 2000 C. and perform the actual deposition under conditions approaching a vacuum. Working at such high temperatures amplifies the problem of working with a mix ture of materials of different thermal evaporation levels. Also, the necessity of working in a vacuum increases the difiiculty of handling materials.

In the past, two approaches have been taken. One of these methods has been to preheat a metal surface often called a source and to feed the material to be evaporated in powdered form toward the source. The substrate that was designed to receive the film was placed above the source. In this arrangement, the placement of the feeder and substrate is very critical. Surrounding the heat source is a thermal layer that varies in temperature inversely with the distance from the source. The closer the feeder is positioned to the source, the more likely the powder portion with the lowest vaporization temperature will vaporize within the feeding mechanism. To the extent that vaporization takes place within the feeding mechanism, it will destroy the ability to obtain the desired film consistency. Moving the feeder further away from the heat source creates other disadvantages. When the powder is fed towards the heat source, the convection currents caused by the thermal layer will deflect some of the particles away from the heat zone completely and cause other particles to be propelled upward, or spattered, and eventually deposited on the substrate. The deflection of particles away from the heat zone changes the composition of the film to be deposited on the substrate. The spattering of particles directly onto the substrate also harmfully affects the composition of the film. In an effort to eliminate spattered particles from being deposited on the substrate, the substrate is usually placed quite far from the heat source. This necessitates the use of exceptionally large and expensive equipment and slows down the rate of film deposition. In addition to the above difficulties, the difference in vaporization temperatures causes the following problem. Since there is a temperature gradient around the heat source, the particles Will have to travel varying distances towards the heat source before they are veporized. This distance will depend upon the vaporization temperature. The effect of this difference is to cause the different materials to vaporize at different times.

The second common way of depositing a film is to place the mixture to be deposited on the substrate into an unheated crucible or box and then raise the temperature to a temperature above the vaporization temperature of all of the elements of the material to be deposited. Where the mixture contains materials of widely different thermal evaporation levels, the materials will be deposited sequentially rather than homogeneously since one of the materials will vaporize before the other.

The general purpose of the invention is to provide means for depositing a homogeneous film on a substrate employing feeding and evaporating means possessing none of the aforedescribed disadvantages. To attain this, the present invention contemplates unique means for feeding and vaporizing the material to be deposited.

An object of the present invention is the provision of means for depositing a homogeneous film from materials of different vaporization temperatures.

Another object is to provide a means for making an electrical resistance element by vaporization of cermets.

A further object of the invention is the provision of a simplified heat source for the evaporation of materials in powdered form.

Still another object is to provide a simplified heat source for the evaporation of materials in pellet form.

Yet another object of the present invention is the provision of simplified means for feeding material to be evaporated into a heat source.

The exact nature of this invention as well as other objects and advantages thereof will be readily apparent from consideration of the following specification and the accompanying drawings in which like reference numerals designate like parts throughout the figures thereof and wherein:

FIG. 1 is a diagrammatic view in side elevation of a system for film deposition;

FIG. 2 is an exploded perspective view of a preferred embodiment of a heat source;

FIG. 3 is a perspective view of a modified heat source; and

FIG. 4 is a perspective view of preferred embodiment of a feeding mechanism.

Referring now to the drawings, there is shown in FIG. 1 a vacuum chamber comprising a base housing 12 and a detachable top 14. Base housing 12 and top 14 are designed to provide an air tight chamber except for an orifice 16 to which evacuation means (not shown) may be connected. Extending upwardly from the bottom of base housing 12 are a pair of spaced

cylindrical supports

18 and 20.

Brackets

22 and 24 are respectively fastened to supports 18 and by bolts 26 and 28, said brackets being Z shaped and made of a rigid electrically conductive metal with an extremely high melting temperature. Electrical conductors 30' .and 32 are within

supports

18 and 20 respectively and arranged such that they are in electrical contact with

brackets

22 and 24 when the brackets are secured to the supports. The conductors are connected to a source of electric power (not shown). A heat box source 34 is detachably mounted to

brackets

22 and 24 by

removable fasteners

36 and 38. The heat box source may be one of several embodiments which will be described in detail hereinafter. A feeding mechanism 40, which is controlled from outside the chamber 10 by control means 42, is positioned within the vacuum chamber 10 in such a manner that it can be used to feed the material to be deposited on the film or substrate into the input 44 of heat box source 34. The structural details and position desired in .a feeding mechanism will vary with the type of box source used. A particularly advantageous feeding mechanism will be described in detail later. A rod 46, mounted on base housing 12, has detachably mounted thereon a platform or support 48 which supports the substance 50 on which it is desired to deposit the film. The rod and holder are arranged such that the substance on which it is desired to deposit the film is positioned over the output 52 of the heat box source 34.

Referring now to FIG. 2, there is shown in detail an exploded view of one embodiment of box heat source 34. The base chamber 54 comprises a flat base 56, sidewalls 58, 60 and end

walls

62 and 64. As shown, the

end walls

62 and 64 extend beyond

side walls

58 and 60 and are terminated by respective outwardly extending

flanges

66 and 68. The walls forming the box-shaped chamber 54 are fastened together by welding. A transverse septum 74 extends upwardly from base 56 and is positioned midway between

end walls

62 and 64. The height of septum 74 is made slightly less than the width of

side walls

58 and 60.

Chamber 54 is provided with a complementary top or cover 76 which comprises a plate 78 including downwardly extending side members 80, 82 and upwardly extending

end members

84, 86, which are terminated by outwardly extending

flanges

88, 90. Corresponding apertures or holes 70, 92 and 72, 94 are provided in

flanges

66, 88 and 68, 90 so that the top 76 and base chamber 54 may be properly aligned and fastened together as an integrated device onto supports 18 and 20 (FIG. 1). Spaced circular input and output apertures or holes 96 and 100, respectively, 'are provided in plate 78 as shown. Input hole 96 is bounded by a raised circular lip portion 98 and a chimney 102 is welded around aperture 100 so that both the lip and chimney extend upwardly from base plate 78. Spaced transverse septums 104 and 106 are provided on the underside of plate 78 and are terminated short of the side members 80 and 82 such that when top 76 is positioned over chamber 54, the septums 104 and 106 are on either side of septum 74 and are within the chamber 54. By such an arrangement, a bafiie is provided between input and output apertures 96 and 100. Connecting

studs

108 and 110 are afiixed to sides 80 and 82, respectively, and are respectively welded to

points

112 and 114 shown in phantom on shield 116 in such a manner that the shield is held in spaced relation from top 76 when in position.

Shield 116 comprises a U-shaped member having a base 118 and

arms

120 and 122. Spaced

circular apertures

124 and 126 are provided in base 118 with their respective centers aligned with the centers of apertures 96 and 100 on plate 78, the aperture 124 being slightly smaller than aperture 96 and aperture 126 being slightly larger than aperture 100. Aperture 124 is bounded by an upwardly extending entrance funnel 130 and a downwardly extending lip 128 which together form a passageway with a diameter slightly smaller than the diameter of lip 98. When shield 116 is welded to top 76, chimney 102 passes through and clears hole 126. Chamber 54 is provided with a bottom heat shield 132 which is connected to chamber 54 by means of

studs

134 and 136 which, in turn, are welded to sidewalls 58 and 60 respectively in such a manner that shield 132 is held parallel to and spaced apart from flat base 56.

FIG. 3 illustrates another embodiment of the heat box source shown in FIG. 2. In this embodiment the perpendicular entrance funnel has been replaced by a cylindrical entrance funnel 138 that meets base 118 at an acute angle such as 45". Welded to the free end of funnel 138 is a cone shaped tip 140. The two embodiments differ in that the first (FIG. 2) is particularly adapted for the vaporization of materials in pellet form while the latter (FIG. 3) is best used with powders.

Referring now to FIG. 4, there is shown a feeding mechanism for use in the vaporization or vacuum evaporation of materials in pellet form.

Supports

142 and 144 are afiixed to the base housing 12 of vacuum chamber 10 and a third support 146 which comprises

braces

148 and 150 mounted on base housing 12 with cross bar 152 mounted across the braces. A carriage 154 comprising a channel bar 156 with a pair of outwardly disposed

right angle flanges

158, 160 at one end is mounted in vacuum chamber 10 at this end by screw 162 which passes through aperture 164 in flange 158 and into support 144. The other end of the carriage rests on support 146. The carriage 154 is mounted with the channel facing upward and is positioned so that hole 166 in the center piece of channel member 156 is positioned over the entrance funnel 130 of the heat source box to be used. A rectangular bar 168 rests in channel 156 said bar being provided with a plurality of circular holes 170 along its length and a rectangular slot 172 at one end. Rod 174 is positioned in support 142 and is terminated by tongue 176, said tongue being fastened into slot 172 in bar 168. Rod 174 is so mounted that it may be longitudinally positioned which in turn moves bar 168 along channel bar 156. The movement of rod 174 may be controlled by hand or any suitable control mechanism such as a solenoid (not shown).

The operation of the invention will now be described. The particular heat source box and feeding mechanism that would be best to employ depends upon the form of the material to be deposited on the substrate. While in the past it has been the practice to feed the deposition material in powder form, surprisingly good results have been obtained by preforming the deposition material into pellets particularly when a heat box source of the type described in this application is used. The feeding mechanism shown in FIG. 4 together with the heat box illustrated in FIG. 2 are most suitable for deposition material in pellet form. The heat source box is secured into place as shown in FIG. 1. The pellet feed is mounted in the vacuum chamber so that the hole 166 in carriage 154 is over funnel 130. A pellet of deposition material is placed in each of the holes 170 of rectangular bar 168. The substrate upon which the deposition will take place is positioned on holder 48 and the vacuum chamber 10 is sealed and evacuated. A large electric current is passed from a source (not shown) through conductor 30, bracket 22, the heat source box, bracket 24 and conductor 32. The heat box source which is made of material with an extremely high melting point such as tantalum is brought to the desired temperature, which is preferably higher than the vaporization temperature of each of the materials to be deposited, by

adjusting the size of the current passing through it. Bar 168 is then caused to move along carriage 154 by means of adjusting rod 174 from the outside. Eventually, a pellet in one of the holes 170 will reach hole 166 and drop into entrance funnel 130 and, in turn, into the preheated heat box source. The movement of bar 168 is continued and a solid portion of the bar closes funnel 130. Since the diameter of funnel 130 and lip 128 is smaller than that of lip 98, the pellet will fall directly into the box source. In addition the mass and consistency of a pellet prevents a portion of the deposition mixture from being deflected away from the heat box source. The presence of the heat shield 116 prevents the pellets from being vaporized prior to entering the heat box source and the spacing between lip 98 and lip 1.28 prevents funnel 130 from becoming too hot. When the pellet reaches the inside of the heat box source it is vaporized and the vapor passes around

septums

74, 104 and 106, out chimney 102, and is deposited on substrate 50-. Using a separate exit chimney and entrance funnel together with the blocking of funnel 130 and the use of a baflie means greatly reduces deflection and spattering and as a result increases the consistency of the deposition. Other pellets may be fed as desired.

The heat source box shown in FIG. 3 is best used with powdered deposition mixtures. When powders are used it is considerably more diflicult to obtain spatter free consistent films. When powders are dropped in directly, the light mass of the material increases the occurrence of deflected material and spattering. In addition, the feeding mechanism must be placed very close to the entrance funnel. As noted previously, the further the feeder is placed from the funnel the greater the chance for deflection while the closer it is placed the greater the chance of vaporization prior to the desired time. Another problem is the hardening of portions of the powder to the funnel. The entrance funnel in this embodiment does away with these problems. The angular disposition of the funnel sufliciently removes the feeding mechanism from the heated area to eliminate the problem of prior vaporization in the feeder. In itself, the change in angle would not fully accomplish the desired result because the powder would ordinarily harden to the sides of the funnel as it approached the opening to the heat box source. However, the location of the funnel on the shield spaced away from the heat box source keeps the temperature of the funnel low enough to prevent this. With the exception of this difference in funnels the two box sources are identical and share the same advantages.

Thus, it can be seen that the invention not only provides improved results but its very simplicity makes the deposition of a film on a substrate easier by the elimination of many critical problem areas.

What is claimed is:

1. in a vapor deposition apparatus, a heat box source comprising a base chamber, a transverse wall extending from the base of the chamber and of lesser height than the vertical walls which form said chamber whereby to compartment said chamber, a complementary detachable top for said chamber provided with an entrance aperture for receiving a material to be evaporated, an exit aperture for delivery of such material as an evaporant, said apertures communicating 'with respective ones of said compartments, heat shield means attached to said detachable top, said heat shield means being provided with a first and a second aperture corresponding to said entrance and exit apertures, funnel means mounted on said heat shield bounding said first aperture, electrical means to heat said chamber, and baflie means disposed within respective ones of said compartments and mounted on said top whereby a tortuous flow of evaporant between the compartments and to the exit aperture is etfected without spatter of nonvapor particles at said exit aperture.

2. A heat box source as claimed in claim 1 wherein said funnel means is mounted perpendicular to said heat shield means.

3. A heat box source as claimed in claim 1 wherein said funnel means is mounted at an acute angle with said heat shield means.

4. The apparatus of claim 1 including means to mount said heat shield on said complementary top in spaced relation from said top with the centers of said corresponding apertures aligned, and chimney means mounted around said exit aperture of the top so as to pass through the corresponding aperture of the shield means.

5. A heat box source as claimed in claim 4 wherein said end walls extend further than said side walls and including outwardly disposed flanges mounted on each of said end walls, end members mounted on said plate extending in a direction opposite said side members, corresponding outwardly disposed flanges mounted on each of said end members, said end members contacting said end walls and said corresponding flanges contacting each other when said complementary top is in place.

6. The apparatus of claim 1 wherein said heat box source is disposed in a vacuum chamber, means in said vacuum chamber to support a substrate, means to feed said material to be evaporated and comprising; a fixed track member disposed in an upper section of said vacuum chamber, an aperture in said track member and disposed in alignment with said funnel means, a bar slidable on said track, at least one aperture in said bar whereby to form with the face of the track member a container for storing material to be evaporated, and means to move said bar along the track member whereby to align said bar aperture with the track aperture to deliver said stored material to the funnel means.

7. The apparatus of claim 6 wherein the bar member has a plurality of aligned apertures to form a plurality of containers for storing material to be evaporated and wherein said means to move the bar may sequentially deliver said material to the funnel means.

References Cited UNITED STATES PATENTS 231,038 8/1880 Harris ll848 X 1,930,869 1 0/193 3 Baden 219271 2,053,781 9/ 1936 Reichel ll848 2,940,873 6/ 1960 Toohig ll849 X 3,233,577 2/1966 Allen 11849.1 3,244,857 4/1966 Bertelsen et al 219 -275 3,246,627 4/ 1966 Loeb et al. ll849 3,354,607 11/1967 Lakso 53-08 FOREIGN PATENTS 742,066 12/ 1955 Great Britain.

OTHER REFERENCES IBM Techanical Disclosure Bulletin, Evaporation Bowl for Silicon Monoxide, vol. 2, No. 3 (October 1959), pp. 2728, D. S. West.

MORRIS KAPLA N, Primary Examiner.

US. Cl. X.R. 219-271