WO1986006874A1

WO1986006874A1 - Ion beam implant system

Info

Publication number: WO1986006874A1
Application number: PCT/US1985/000929
Authority: WO
Inventors: Shantia Riahi
Original assignee: J.C. Schumacher Company
Priority date: 1985-05-17
Filing date: 1985-05-17
Publication date: 1986-11-20
Also published as: US4855604A; JPS62503059A; DK24187D0; DK24187A; NO870191D0; NO870191L; FI870178A0; EP0221056A1; EP0221056A4

Abstract

A charge forming system and apparatus (20) for introducing ion source materials (24) into the ion source vaporizer (10) of an ion implant instrument.

Description

ION BEAN IMPLANT SYSTEM

ElSlU mml mmhi. 1^^1.^ 1011

This invention relates to ion implantation generally and more specifically relates to the manufacture of semiconductor devices using ion implant techniques.

Background ol iiie Invention Ion implantation is a well-known and widely used process for injecting atoms into a solid material to selected depths and concentrations in selected areas. Ion implant accelerators are similar to isotope separators but typically have an added acceleration stage and field controls for precisely locating the beam of ions and controlling the energy and flux of the beam of ions to cause the desired penetration and concentration. Atoms of the selected chemical element to be ionized are ionized by collisions with electrons in an electrical discharge in a gas at lowpressure and pass through an orifice into a high- vacuum region where they are accelerated by an electric field to a an intermediate energy, typically from 10 to 30 ke V, where they are analyzed by amagnetic field based upon the e/m ratio, i.e. the ratio of electronic charge over mass. The selected ion beam passes through an analyzer slit, and the ions are accelerated to the desired energy, and the beam passes through a refocussing field, typically a quadrupole lens, is deflected by a scanner system, and collimated by a defined aperture and allowed to strike the target. When the ions penetrate the target lattice, they lose energy through collisions with lattice atoms and come to rest as part of the target. There are, of course, a large number of variations between specific ion implant systems but the foregoing principles apply generally to ion implant processes. The ion implant technique is described, inter alia, in United States Patents Nos. 2,750,541, 2,787,564 and 2,842,466, which are incorporated herein. The ion implant method is also described in many texts, encyclopedias and scientific journals; see, e.g. ENCYCLOPEDIA OP SEMICONDUCTOR TECHNOLOGY, "Ion Implantation" pp. 397-410, John Wiley & Sons (1984) and the numerous references cited therein; see also, Kirk Othmer CONCISE ENCYCLOPEDIA OF CHEMICAL TECHNOLOGY, "Ion Implantation", p. 666 et seq., John Wiley & Sons (1985); and ION IMPLANTATION, J.K. Hirvonen, ed., Academic Press, Inc., (1980). Since the equipment and methods of ion implantation are so thoroughly described and widely used in the semiconductor industry, those skilled in the art are familiar with these methods and devices and may refer to any of the many excellent journal, text and patent descriptions for details. Manufacturer's manuals, provided with specific items of equipment are the best source for details as to a given piece of equipment.

Solid source ion material is introduced into the ion implant equipment periodically. This generally requires cooling the implant equipment down, opening the high vacuum to at least some atmospheric exposure, introducing the new charge of ion source material into a receptacle, closing up the equipment, pumping the ion implant and accelorator chambers down to a high vacuum, and placing the equipment into operating again. The procedure is necessarily very expensive in terms of lost production and wasted time in a very expensive piece of equipment. Ion implant devices not infrequently cost over one million dollars and it is necessary to maximize production to recoup the investment in saleable product.

While the ion implant equipment is very precise, elegant and complex in design and operation, the introduction of solid ion source material is a relatively simple, largely manual operation. Basically, the charge of solid ion source material is, according to the prior art, simply pushed, poured or dropped into a small chamber in a Source Vaporizor which is then closed, after which the entire

SUBSTITUTE SHEET system is pumped down using well-known rotory and oil diffusion vacuum pumps. Source vaporizers of the type under consideration are sold by various manufacturers, one of which is described as a Nova NV-10 (TM) Series Source Vaporizer. This, however, is merely exemplary and other source vaporizers are well-known to those skilled in the art.

For more than a decade, ion implantation has been a chief step in the industrial processing of semiconductor devices; in particular, large-scale integrated circuits; see, for example, ION IMPLANTATION IN SEMICONDUCTORS, Sartwell, et al., editors, Plenum Press, New York (1977). It is within this art that the present invention lies and to which it is an improvement. Summary of the Invention

The present invention is an improvement in the ion implantation process and apparatus described above, the improvement comprising a compact, safe system and apparatus for introducing solid ion source material into the source vaporizer of an ion implant instrument.

As an article of manufacture, this invention comprises a charge of ion source material configured and dimensioned to be received in an ion source vaporizer secured to means for inserting the charge into an ion source vaporizer of an ion implant device. As an article of manufacture, trade and commerce, the invention thus, in an exemplary form, comprises, in combination, a charge of ion implant material, charge forming means configuring the charge into a size and shape for being received in a source vaporizer of an ion implant instrument, and endlosure means for enclosing at least a portion of the charge forming means and for positioning the charge forming means in the well of a source vaporizer.

In one exemplary embodiment, the present invention may be described as ion source insertion means for loading

SUBSTITUTE SHEET an ion source into a source vaporizer of an ion implant instrument comprising: (a) source forming means for containing, protecting and configuring source material into a configuration which is substantially the size and configuration of the source receptacle in the source vaporizer, the source forming means having a generally cylindrical wall, a bottom and a top, and optionally including a breakseal hermetically sealing the top against contact with the atmosphere; (b) enclosure means for the source forming means for enclosing at least a substantial portion of the cylindrical wall portions thereof, the enclosure means including means snugly fitting around the cylindrical wall of the source forming means permitting the source forming means to move under applied force reciprocally in the enclosure means; and (c) moving means in the enclosure means for applying moving force to the source forming means for moving the source forming means out of the enclosure means and optionally for rupturing the breakseal on the source forming means, the combination of source forming means, enclosure means and moving means, substantially preventing the source material in the source forming means from contact with the atmosphere.

The invention may, optionally, comprising external container means hermetically sealing the entire source insertion means from contact with atmosphere. The external container means may, optionally for all embodiments, comprise a flexible package formed of a polymer film having thereon a layer of metal hermetically sealing the ion source insertion means from the atmosphere, or a sealed tube with a breakable portion therein to permit the sealed tube to be broken, upon application of force, in the breakable portion, or both of these outer packages.

Where a breakable tube is used, the source forming means further comprises a flange resiliently sealing

SUBSTITUTE SHEET -4a- against the internal wall of the tube.

SUBSTITUTE SHEET -5- There is considerable advantage when the means snugly fitting around the cylindrical wall of the source farming means forms a substantially fluid tight seal therewith. In some embodiments, the enclosure has generally cylindrical internal walls and the moving means comprises a generally discoid piston movably sealing in substantially fluid tight relation with the internal walls of the enclosure means. The invention may, additionally, comprise a semi-rigid ring encircling the tube in contact with the breakable portion to assure that when the tube is broke it breaks cleanly at the breakable portion.

These and other exemplary facets of the invention are more clearly shown and discussed in the drawing and in the specification.

Brief Description of the Drawing

Figure 1 is a perspective, exploded view of a preferred form of the article of manufacture of this invention, a charge for introduction into a source vaporizer of an ion implant instrument, showing a portion of the source vaporizer.

Figure 2 is a side view, enlarged and partially cut away, showing partially in cross-section the article of manufacture of this invention.

Figure 3 is a partial side view of an alternative embodiment of the manufacture of this invention wherein the charge container includes a breakseal.

Figure 4 is another alternative embodiment of the manufacture of the present invention.

Description of the Preferred Embodiment The invention comprises, in the form of an article of manufacture, apparatus for providing iσn source material to the source vaporizer of ion implant equipment, an exemplary source vaporizer being depicted at 10 in

SUBSTITUTE SHEET Figure 1 comprising a body of well-known configuration and a well 12 which is configured, designed and adapted to receive a charge of the ion sourcematerial. Thewell 12 is about 22 mm in depth and 16 mm in diameter and generally cylindrical in configuration. The article of manufacture 20 shown in Figure 1 is one feature of the present invention, providing means for providing ion source material into the source vaporizer.

Referring to Figure 2 next, a preferred, complete article of manufacture is depicted. The assembly 20 comprises a charge forming device 22whichholds the charge 24 of ion source material in its desired configuration and protects it from contamination. The charge forming device 22 is preferrably formed of quartz, although for certain low temperature applications it may be formed of inert polymer or borosilicate glass. The charge forming device 22 is, in the embodiment of Figure 1, an open top right cylindrical vessel being so configured and dimensioned as to be loosely received in the well of the vaporizer. The charge forming device is received in an enclosure

26 which comprises a generally cylindrical receiving body having an opening 28 which includes a sealing ring which fits very εnuggly around and seals against the outer cylindrical walls of the charge forming device 22, permitting the charge forming device 22, upon the application of force, to move recipically in the enclosure 26 with the walls thereof in sealing relationship therewith.

The enclosure 26 is generally in the form of a hollow cylinder formed of suitable inert polymer, preferrably a fluorocarbon or fluorochlorocarbon polymer, such as Teflon (TM) for example, which is self-lubricating and forms an excellent seal with quartz, glass or metal. One end of the cylinder of the enclosure 26 comprises an end cap 30 which has a passage 32 therethrough slidably receiving the shaft 34which, in turn, is part of a plunger or piston, the distal portion being generally discoid in configuration, as shown at 36, and forming a seal against the interior walls of the enclosure 26. The enclosure assembly 26-36 may, then, be described as a piston and cylinder arrangement in which the cylinder is formed by the enclosure 26 and the piston is formed by the shaft or plunger 34 and discoid piston 36. An "0" ring 38 in a groove in the plunger forms a stopagainst excessive travel of thepiston. The enclosure also includes, in apreferred form, a sealing flange 40 which, during shipping and storage, positions the charge forming device and enclosure inside a protective cylinder 42 and which maintains a seal with the walls of the cylinder 42 after the cylinder is opened.

The manufacture may be contained in any number of protective envelopes, but in the preferred embodiment the entire assembly 20 is stored, shipped and handled before use in a glass or quartz cylindrical tube 42 which is hermetically sealedat both ends, enclosing the assembly 20 inside in inert atmosphere, and which includes a scribe mark 44whichpermits the tube to be easily broken, allowing the upperportion46, as shown, to be removed andpermitting removal of the assembly 22. Aprotective ring 48 formed of a semi-rigid, self-lubricating polymer such as Ryton (TM) polysulfide is a desired but non-critical feature of the invention. This ring includes, preferrably, a projection which extends into the scribe 44 to assure a safe, clean break. Finally, the overall assembly 22 and its protective tube 42 is packaged in an inert atmosphere contained in a moisture andvapor impervious flexiblepackage50 formed of a layer of Mylar (TM) polyterephthalate 52 and metal, such as vapor deposited aluminum 54, sealed in any convenient way as shown, simply as an example, at 56. 8

Figure 3 depicts a highly desirable alternative of the assembly of the invention for forming and loading a charge of ion source material which is exceptionally sensitive to contamination or which is to be given ultimate purity protection. In this assembly 120, the charge forming device 122 is the same in all essential features as the device 22 except that it includes a quartz (or in some instances polymeric or borosilicate) seal 123 which hermetically seals the ion source material 124 in the charge shape and size. The enclosure 126 -130 is the same as described respecting enclosure 26-30 andthepiston 134- 136 is the same as described respecting piston134-136, but has the added structure of a breakpoint 137 on the distal side of the piston 136 and may include an additional "O" ring stop 139 to prevent accidental movement of the piston. The operation, whichwill be described, is the same for this embodiment as for that of Figure 2 except that the first "0" ring 139 is removed and the breakpoint 137 contacts and breaks the breakseal 123 in the early stages of movement of the piston in the cylinder.

Figure 4 depicts another alternative embodiment. In this assembly 220, the charge forming device 222 includes a breakseal 223 and is the same as the device 122-123. The charge forming device is recived ina cylindrical enclosure portion 226which seals at 228, as describedwith respect to the opening 28 and 128 in the earlier described embodiments. Projections or keys 129 may be provided in this embodiment for engaging the thermal source evaporator 10 to prevent relative rotation therewith. The enclosure purtion includes threads on the outside and a cap 230 which includes an interior structure 232 for engaging the charge forming device and a breakpoint 233 for contacting and ruptureing the breakseal 223. While not necessary, it is sometimes desirable to include a bottom or distal cap 240 which slips on or screws on to the enclosure portion 226, providing an extra measure of protection. The entire assembly may then be enclosed in a glass or quartz tube as described and in an envelope or, as depicted in Figure 4, simply enclosed in a vapor barrier envelope 250 sealed at 256, of the construction described It is customary to carry out the process of ion implantation by the general steps of (a) evaporating a source material; (b) ionizing at least one component of the source material; (c) accelerating the resulting ions; (d) electro agnetically selecting the ions to be implanted in the target; and (e) accelerating and directing a beam of the selected ions to a predetermined point or location on the target. The improvement of this invention is in the first step of evaporating a source material and in a preliminary step of providing a source material, and, more particularly in the configuration, structure, operation, function and design of an article of manufacture for charging an ion source vaporizer

As background for understanding the significance and importance of this invention, a brief discussion of some factors of great practical and economic, as well as technical, importance is in order.

The ion implant instrument is very expensive, costing a million dollars or more typically, and down-time or non- productive time must, for economic soundness, be avoided and minimized to the greatest possible extent. Down time results whenever it is necessary to shut the instrument down to recharge it with ion source material. In many instances in the prior art, the source vaporizer must be scraped out and a weighed or measured amount of ion source introducted into thewell of the sourcevaporizer. Inmost instances, this requires that the source vaporizer be introduced into a clean-room or glovebox to prevent contamination of the reagents and spread of the reagents, some of which are extremely poisonous or otherwise 10 hazardous. Those who have worked in a glove box will appreciate that this is a very time consuming and inconvenient operation.

After the charge is loaded into the source vaporizer, the instrument, which operates at high vacuum and an ambient operating temperature of from about 100 to 300°C. must be pumped down and brought up to operating temperature, all of which consumes substantial periods of time. The instrument spectrographic and accelerating chamber operates, for example, at vacuums of as low as 10~⁵ torr. The introduction of a charge which requires extensive outgassing or which introduces volatile impurities can slow the start-up of the ion implant instrument εignficantly. In addition, if the instrument is required to operate at high temperatures, e.g. above 300°C. i additional time is requiredto bring the instrument to a stable operating temperature and additional pumping time may be required.

It is, therefore, a highly sought after goal and a long felt need in the industry to find a method which will reduce down-time, minimize start-up time, and extend run-time between recharging the ion source.

Safety is also a very important consideration. It would be desirable to have an ion source which can be handled safely extreme or unusual precautions or undue risk andwhich, upon being used up, is easily removed and safely handled residue.

The article of manufacture is used in the following manner. First, once the source vaporizer is prepared to recieve a charge, the article 20, 120 or 220 is taken from its protective package(s), depending upon the form of packaging used. The article is positioned as shown in Figure 1 with the source defining device 22 adjacent the well 12 in the source vaporizer, the distal end thereof is then inserted into the well and the article 20 is pressed 11 snuggly against the source vaporizer. In the case of the embodiments of Figures 1 and 2, the piston is pressed forcing the charge forming device and charge into the well and, in the case of the article 120, breaking the seal 123 thus opening the charge for use. The article 220 is handled basically in the same way, except that the lid 230 is turned to break the seal 223. This takes only a few seconds and the vaporizer is secured in the ion implant instrument, in the usual and conventional manner, and the ion implant instrument is put back into normal operation. Upon completion of the run, the charge forming device contains the residual material from the charge and the charge forming device is simply poured back into the container and disposed of according to regulations which may apply to the particular facility and material.

Therearemanyand important advantages tothepresent invention, only someofwhichare discussed inany degree or particularity here.

First, itwill beapparent thatthe clean-upof the ion source vaporizer is greatly simplified. Whereas in the prior art it was often necessary tohand-scrape residueout of the well, some of which residues being poisonous or hazardous, the residue and the charge forming means are simplyallowedto fallout of thewellandmaybe returnedto the original container for disposal.

This is a much quicker, simpler and cleaner approach than the prior art, and a very much safer procedure.

The charge forming means permits the very convenient use of fine powders with high surface areas as charge materials, rather than plugs or chunks of material. This results in better, more stable and more controllable ion sourcematerialvaporizationandthe use ofmaterialswhich would otherwise not be acceptable as source materials.

The present invention reduces down-time and permits more rapid start-up after the source is renewed because 12 fewer impurities are introduced, there is virtually no handling of any part of the charge or its associated components. This, of course, is also a safety feature.

Ultra-high purity reagent quality can be maintained since the source material is hermetically sealed from atmospheric and other contamination, and yet is easily and safely handled.

Shipping and handling safety are greatly enhanced. No longer is it necessary to handle open reagents or to use cumbersome gloveboxes to protect reagents from contamination or operators from toxicity.

Purity is assured because the source forming means serves to protect and contain the source material at all stages from packing, which can be in ultimately clean environments, through shipping, storage and even in use. Other advantages will appear to those who have struggled with the prior art apparatus, systems and methods.

While the invention has been described with reference to the semiconducter industry and in the manufacture of semiconductor materials, e.g. boron implanted into silicon, the invention is of general applicablity in, for example, forming corrosion or wear resistant surfaces on bearings, cutting tools, and the like. Furthermore, while the invention has been described in terms of particular materials of composition, construction and configuration, these aremerely exemplary andgreatvariation is permited, as these are not critical, within the scope, concept and claims of the invention without departing from equivalents of examples and principles hereinbefore εetforth.

Industrial Application This invention finds its most direct and immediate application in the manufacture of semiconductor devices, cutting tools, bearings and other metal objects in which 13 surface characteristics are modified by ion implantation.

Claims

14WHAT IS CLAIMED IS:

1. As an article of manufacture, trade and commerce, the combination of a charge of ion source material, charge forming means configuring the charge into a size and shape for being received in a source vaporizer of an ion implant instrument, and enclosure means for enclosing at least a portion of the charge forming means and for positioning the charge forming means in the well of a source vaporizer.

2. An ion source insertion means for loading an ion source into a source vaporizer of an ion implant instrument comprising, in combination:

(a) source forming means for containing, protecting and configuring source material into a configuration which is substantially the size and configuration of the source receptacle in the source vaporizer, the source forming means having a generally cylindrical wall, a bottom and an open top;

(b) enclosure means for the source forming means for enclosing at least a substantial portion of the cylindrical wall portions thereof, the enclosure means including means snuggly fitting around the cylindrical wall of the source forming means permitting the source forming means to move under applied force reciprocally in the enclosure means; and

(c) moving means in the enclosure means for applying moving force to the source forming means for moving the source forming means out of the enclosure means; the combination of source forming means, enclosure means and moving means, substantially preventing the source material in the source forming means from contact with the atmosphere.

3. The invention of Claim 2 further comprising external container means hermetically sealing the entire source insertion means from contact with atmosphere. 15

4. The invention of Claim 3 wherein external container means comprises a flexible package formed of a polymer film having thereon a layer of metal hermetically sealing the ion source insertionmeans fromthe atmosphere.

5. The invention of Claim 3 wherein the external container means comprises a sealed tube with a breakable portion therein to permit the tube to be broken, upon application of force, in the breakable portion.

6. The invention of Claim 5 wherein the source forming means further comprises a flange resiliently sealing against the internal wall of the tube.

7. The invention of Claim 2 wherein means snuggly fitting around the cylindrical wall of the the source forming means forms a substantially fluid tight seal therewith.

8. The invention of Claim 7 wherein enclosure has generally cylindrical internal walls and wherein the moving means comprises a generally discoid piston movably sealing in substantially fluid tight relation with the internal walls of the enclosure means and with the top of the source forming means.

9. The invention of Claim 2 wherein enclosure has generally cylindrical internal walls and wherein the moving means comprises a generally discoid piston movably sealing in substantially fluid tight relation with the internal walls of the enclosure means and with the top of the source forming means.

10. The invention of Claim 9 further comprising external container means hermetically sealing the entire source insertion means from contact with atmosphere.

11. The invention of Claim 10 wherein external container means comprises a flexible package formed of a polymer film having thereon a layer of metal hermetically sealing the ion source insertionmeans fromthe atmosphere.

12. The invention of Claim 10 wherein the external 16 container means comprises a sealed tube with a breakable portion therein to permit the tube to be broken, upon application of force, in the breakable portion.

13. The invention of Claim 12 wherein the source forming means further comprises a flange resiliently sealing against the internal wall of the tube.

14. The invention of Claim 13 wherein means snuggly fitting around the cylindrical wall of the the source forming means forms a substantially fluid tight seal therewith.

15. The invention of Claim 25 further comprising a semi-rigid ring encircling the tube in contact with the breakable portion to assure that when the tube is broke it breaks cleanly at the breakable portion.

16. An ion source insertion means for loading an ion source into a source vaporizer of an ion implant instrument comprising, in combination:

(a) source forming means for containing, protecting and configuring source material into a configuration which is substantially the size and configuration of the source receptacle in the source vaporizer, the source forming means having a generally cylindrical wall, a bottom and a top, and including a breakseal hermetically sealing the top against contact with the atmosphere;

(c) moving means in the enclosure means for applying moving force to the source forming means for moving the source forming means out of the enclosure means 17 and for rupturing the breakseal on the source forming means; the combination of source forming means, enclosuremeans andmovingmeans, substantially preventing the source material in the source forming means from contact with the atmosphere.

17. The invention of Claim 16 further comprising external container means hermetically sealing the entire source insertion means from contact with atmosphere.

18. The invention of Claim 17 wherein external container means comprises a flexible package formed of a polymer film having thereon a layer of metal hermetically sealing the ion source insertionmeans from the atmosphere.

19. The invention of Claim 17 wherein the external container means comprises a sealed tube with a breakable portion therein to permit the tube to be broken, upon application of force, in the breakable portion.

20. The invention of Claim 19 wherein the source forming means further comprises a flange resiliently sealing against the internal wall of the tube.

21. The invention of Claim 16 wherein means snuggly fitting around the cylindrical wall of the the source forming means forms a substantially fluid tight seal therewith.

22. The invention of Claim 21 wherein enclosure has generally cylindrical internal walls and wherein the moving means comprises a generally discoid piston movably sealing in substantially fluid tight relation with the internal walls of the enclosure means.

23. The invention of Claim 16 wherein enclosure has generally cylindrical internal walls and wherein the moving means comprises a generally discoid piston movably sealing in substantially fluid tight relation with the internal walls of the enclosure means.

24. The invention of Claim 23 further comprising 18 external container means hermetically sealing the entire source insertion means from contact with atmosphere.

25. The invention of Claim 24 wherein external container means comprises a flexible package formed of a polymer film having thereon a layer of metal hermetically sealing the ion source insertionmeans from the atmosphere.

26. The invention of Claim 24 wherein the external container means comprises a sealed tube with a breakable portion therein to permit the tube to be broken, upon application of force, in the breakable portion.

27. The invention of Claim 26 wherein the source forming means further comprises a flange resiliently sealing against the internal wall of the tube.

28. The invention of Claim 27 wherein means snuggly fitting around the cylindrical wall of the the source forming means forms a substantially fluid tight seal therewith.

29. The invention of Claim 26 further comprising a semi-rigid ring encircling the tube in contact with the breakable portion to assure that when the tube is broke it breaks cleanly at the breakable portion.

30. An ion source insertion means for loading an ion source into a source vaporizer of an ion implant instrument comprising, in combination: (a) source forming means for containing, protecting and configuring source material into a configuration which is substantially the size and configuration of the source receptacle in the source vaporizer, the source forming means having a generally cylindrical wall, a bottom and a top, and including a breakseal hermetically sealing the top against contact with the atmosphere;

(b) enclosure means for the source forming means for enclosing at least a substantial portion of the cylindrical wall portions thereof, the enclosure means 19 including means snuggly fitting around the cylindrical wall of the source forming means permitting the source forming means to move under applied force reciprocally in the enclosure means; and (c) moving means moveably associated with the enclosure means for applying moving force to the source formingmeans for moving the source forming means out of the enclosure means and for rupturing the breakseal on the source forming means; the combination of source forming means, enclosuremeans andmoving means, substantially preventing the source material in the source forming means from contact with the atmosphere.

31. The invention of Claim 30 further comprising external container means hermetically sealing the entire source insertion means from contact with atmosphere.

32. The invention of Claim 31 wherein external container means comprises a flexible package formed of a polymer film having thereon a layer of metal hermetically sealing the ion source insertionmeans from the atmosphere.

33. The invention of Claim 31 wherein the external container means comprises a sealed tube with a breakable portion therein to permit the tube to be broken, upon application of force, in the breakable portion.

34. The invention of Claim 35 wherein means snuggly fitting around the cylindrical wall of the the source forming means forms a substantially fluid tight seal therewith.

35. The invention of Claim 33 further comprising a semi-rigid ring encircling the tube in contact with the breakable portion to assure that when the tube is broke it breaks cleanly at the breakable portion.