US2447789A - Evaporating crucible for coating apparatus - Google Patents

Description

Aug. 24, 1948. BARR 2,447,789

EVAPORATING CRUCIBLE FOR COATING APPARATUS Filed March 23, 1945 INVENTOR.

5 54. BY Z V Patented Aug. 24, 1948 LUNFI TED :srarzas PATENT rrircE :EVABORATING CRUCIBLE FOR COATING APPARATUS --Edgar E. Barr; North Woburn, Mass, as'signor to Polaroid Corporation, Cambridge, Mass a :corporation of Delaware Application March 23, 1945, Serial No. 584,450

. ,1 This invention relates toa'new and'iniproved crucibleparticula-rlyadapted for use in the production of 'optical' elements by the evaporation and deposition of light-transmitting materials in a-vacuum.

-'Ithas recently been discovered that optically homogeneous and useful, light-transmitting films *canbeproduced by the evaporation of a variety 'of" classes of'organic compounds and the deposition of said evaporated compounds on asuitable support-in a vacuum. It appears that in carry- -ingoutthis work it is desirable that the entire charge of material to be evaporated ice-heated to theevaporation point'before any evaporation be- "gins. -Otherwise-there is a tendency for the vat charge-within the crucible and for preventing the -escape therefromof particles greater than a predetermined-size.

A further object is to provide a crucible having *the above'advantages and comprising ablock -'of "heat-conducting metal or other material provided with at least one and preferably a= mul-tiplicity of cavities therein for holding the charge to be evaporated, and provided also with screen or baflie means for preventing the escape from said crucible of particles appreciably greater than molecular size.

Other objects and advantages will in part appear and in part be pointed out in the following description of one or more embodiments of the invention which are given as nonlimiting examples in connection with the accompanying drawings, in which:

Figure 1 is a view in vertical section of a crucible embodying a form of the invention; and

Figure 2 is a plan view, partly broken away, of the crucible shown in Fig. 1.

In the drawings, body member ill comprises a block of steel or any other suitable heat-conducting metal or other material, and is shown as cylindrical but may be of an other desired shape. Annular flange I2 projects upwardly from the outer rim of body member Ill and may be secured thereto in any suitable way but is most conveniently formed integrally therewith as by 2 Claims. (Cl.-'219--19) member .I 0.

boring outthe upper portion of an initially-solid block. Cavitiesorcells il within body'member til are designed to-hold the charge of material tabs-evaporated. Cells Htmaybe of any'desired shape but are most'conveniently made circular-in cross section "by drillinginto the -body There are preferably provided as many'of cells as can conveniently bearranged in honeycomb fashion in body member to, and

'theyshould extend well into-butnot through said body, member.

For example, ii the depth of body member it: is of the orderof one inch, cells *l l 'may-be-one-half inch in depth and a-ccnvcnient 'diameter'is approximately one-eighth of aninch.

."It'is desirable "to provide the-crucible oi the zinventi'onwith suitablescreening -means forpreventing the escape during evaporation of parti- 'cles tappreciably greater than molecular :size.

"This may'be done by-means o'f any-suitable fine meshrscreenbut preferred results a have been ob- 'tained with the use of asolid plate Iii of steel-or other suitable rigid material. As shownin the :drawings, "the 'radius of plate I5 is preferably just suflicientl smaller than the inner radi-us oi "flange 12 'to leave an annular space 46 '(Fig. 2) therebetween. the orderof 0.10 inch in width.

1 *rality-of short studs 20 adapted to support plate l5. Studs 20 ma for example be of the order of one-sixteenth of an inch in height, and this arrangement has the advantage that plate I5 is readily removable to permit access to cells I4 for charging or cleaning the crucible. It is also desirable to provide body member In with some non-heat-conducting mounting means such, for example, as legs 22 of porcelain or similar material.

In use, it is desirable that heat may be applied relatively rapidly to the crucible of the invention and a suitable arrangement for this purpose is shown in Fig. 1. It will be understood that said crucible is intended for use with conventional evacuation apparatus comprising any suitable bell jar means, not shown, and base plate 24. Elements 25 and 25 represent heating filaments of any suitable metal and shape, a convenient shape being spiral as indicated at 25 in Fig. 2. The desirability of bringing the entire charge to the evaporation temperature before appreciable vaporization begins has already been noted. It is greatly facilitated by the crucible of the inven- 3 tion. The honeycomb construction acts to conduct heat uniformly throughout the charge, and this in turn makes it possible to apply heat rapidly with minimum danger of uneven heating or overheating any portion of the charge before the balance has reached the evaporation point. One advantage of these features is a substantial reduction in the time necessary for the evaporation and deposition of a film of any given thickness,

and makes practical the use of the two filaments shown in Fig. 1. On the other hand, any insumciently heated particles which might tend to rise into vapor are effectively prevented from doing so by contact with plate I5, since it is necessary for the vapor to travel first sidewise through space l8 and then upwards through space 16 before leaving the crucible. Plate 15 has the further advantage of shielding the deposited film from any efiects of sputtering within the crucible.

It will be apparent that the above-described construction is subject to considerable variation without departing from the scope of the invention. For example, it has been pointed out that screening means other than plate l5 may be used and that the mounting for said screening means may be varied in many ways. The size of annular space I6 may readily be altered by changing the size or shape of plate 15 to limit the passage from the crucible of particles greater than any predetermined size. It will also be noted that the shape of the crucible or of the cavities for the charge may be altered at will, but the circular configurations are shown because of the ease with which they may be reproduced as Well as their general efiiciency. Many other variations which do not alter the principles of the invention will doubtless be apparent to those skilled in the art, and it is accordingly intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative and not in a limiting sense.

It is also to be understood that the following claims are intended to cover all of the generic and specific features of the invention herein described, and all statements of the scope of the invention which, as a matter of language, might be said to fall therebetween.

What is claimed is:

1. In an evaporation apparatus, the combination comprising a crucible comprising, in combination, a substantially cylindrical body member comprising readily heat-conducting material, means providing a multiplicity of cavities extending into but not through said body member from the upper surface thereof, screen means positioned adjacent said cells and preventing the escape therefrom of particles greater than a predetermined size, and means providing a plurality of filament elements positioned closely adjacent said crucible and adapted to emit radiant heat, one of said filaments being positioned above said body member and another being positioned below said body member.

2. [in an evaporation apparatus, the combination comprising a crucible comprising, in combination, a substantially cylindrical body member comprising a readily heat-conducting metal, mounting means for said body member comprising substantially non-heat-conducting material, means providing a multiplicity of substantially tubular cells extending substantially perpendicularly into but not through said body member from the top thereof, an annular flange member extending upwardly from the outer rim of said body member, a substantially rigid, circular plate member having a radius slightly smaller than the inner radius of said flange member whereby when said plate is positioned within said flange member an annular space remains therebetween, stud means for removably mounting said plate within said flange and in spaced relation with the tops thereof and of said cells, and means providing a plurality of filament elements positioned closely adjacent said crucible and adapted to emit radiant heat, one of said filaments being positioned above said body member and another being positioned below said body member.

EDGAR E. BARR.

REFERENCES CITED Siebertz July 4, 1939 OTHER REFERENCES Strong: Procedures in Experimental Physics, pages 173 and 182. Prentice-Hall, Inc., New York (1946).

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