Gas Supply System

Abstract

An improved gas supply system for supplying nitrogen and/or oxygen or other gases to semiconductor doping systems via liquid, such as water, boiling in a flask in a manner whereby the supply of gas remains consistent as to its characteristics, for example, moisture content, purity, etc. A double check valve arrangement, with one check valve weighted to a closed position, permits a gas, such as oxygen, to be supplied selectively wet or dry to a doping furnace as employed in semiconductor manufacture. The dual check valve arrangement further serves to permit a second source of gas to be employed. Liquid is maintained at a constant level in the boiling water flask by means of a magnetic element carried in the elongated stem of a float riding in the water. The magnetic element serves to activate a reed switch for electrically controlling a solenoid operated water supply valve.

Description

BACKGROUND OF THE INVENTION

This invention pertains to a gas supply system particularly useful in closely controlling the characteristics of gas supplied to a doping furnace in the manufacture of semiconductor materials.

As is known, various gases such as nitrogen and oxygen are employed in the so-called "doping" of semiconductor materials in the course of manufacture of semiconductor materials. With oxygen it is desirable under some circumstances to supply the oxygen to the doping furnace in a so-called "dry" state whereas in other circumstances, it has been found desirable, if not a requirement, to supply the oxygen in a so-called "wet" state as by passing the oxygen first through a water environment.

Heretofore, most systems which have been developed for meeting the foregoing criteria have had difficulty in providing consistent gas characteristics.

SUMMARY OF THE INVENTION AND OBJECTS

In general, a gas supply system has been provided for delivering gas to a doping furnace. The system comprises a closed container adapted to receive liquid, such as water, therein and means to supply and heat water in the container while an output line forms a fluid discharge path from the container. First and second check valves are each oriented to pass fluid into a doping furnace input line, one from the flask and the other from a source of gas, such as oxygen, for example. The discharge side of each check valve is coupled to supply gas under pressure to tend to close the discharge side of the other. A first gas delivery path from the source of gas supply includes one of the check valves and a second gas delivery path includes the container and the other check valve. In addition, there is provided a selector valve coupled to the gas supply line to direct gas from the source to the furnace input line via either the first or second path, depending upon whether or not wet or dry gas is desired. A steam relief valve coupled to the second fluid path is located between the container and that check valve located in the discharge path from the container to the furnace input line. The steam relief valve is selectively operable to vent or contain steam pressure and a control operates both the steam relief valve and the gas supply valve whereby, in one state, it operates the steam relief valve to vent pressure from its path when the gas supply selector valve has been operated to couple the gas source to the furnace via only the first-named check valve. In its other state, the control means reverses the condition of the last-named two valves.

In general, it is an object of the invention to provide an improved gas supply system.

It is another object of the invention to overcome the foregoing and other problems existing in present day gas supply systems.

The foregoing and other objects of the invention will be more clearly understood from the following detailed description of a preferred embodiment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic illustration of a gas supply system according to the invention;

FIG. 2 is an elevation view, partly in section, in enlarged detail showing a float and stopper assembly represented in FIG. 1;

FIG. 3 is an enlarged elevation section view of a reed switch shown in association with the stem of the float;

FIG. 4 is an enlarged elevation view, partly in section, of the system portion labeled "FIG. 4" in FIG. 1.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

A gas supply system 10 includes a source 11 of gas, such as oxygen, for example. Source 11 preferably can include a conventional toggle valve 12, regulator 13, appropriate meter 14, and submicron filter 16 connected in series and feeding into a conventional flow meter 17 whereby oxygen is brought to a normally closed solenoid operated flow valve 18 which, when opened, provides oxygen to the system on the gas supply line 19.

Thus, a pushbutton 21 or other type control serves to energize the solenoid 22 for opening valve 18 from its normally closed state.

A closed container such as the glass flask 23 is adapted to receive liquid, such as water, from the waterline 24 as controlled by the electrically operated valve means 26. The manner of controlling the input supply of water is described further below whereby the volume of water or other liquid is continuously maintained in a given level, notwithstanding losses through vaporization.

Means are provided for heating the water in the container, as by means of the electric heating mantle 27, to boil the water in flask 23.

An output line 28 forms a fluid discharge path from flask 23. Line 28 includes a "Y" junction 29, one branch of which leads to a check valve 31 while the other branch leads to a steam relief valve 32.

Valve 32 is normally open under the action of the spring 33 whereby the spool 34 will be located at the left end of the valve housing as shown in FIG. 1. Energizing solenoid 36 will, however, move spool 34 to a position blocking the output passage of that branch of line 28 leading through valve 32 thereby causing steam pressure to build up within flask 23 or to pass out of check valve 31 and into input line 37 of a diffusion furnace 38.

A selectively operable gas supply valve 39 normally serves to interconnect supply line 19 with a "dry" oxygen line 41 which forms a fluid path via the connection 42 and a second check valve 43 to supply oxygen directly to input line 37. The discharge side of check valve 43 is directly interconnected to the discharge side of check valve 31 whereby the gas pressure of oxygen being delivered to furnace 38 is utilized to prevent steam from being added to the input line 37 at such times. In this manner the oxygen remains dry.

In order to further insure against entry of steam into input line 37, check valve 31 includes means for urging its closure element to a position impeding (or closing entirely) the flow passage of valve 31 in favor of valve 43. The pressure of the oxygen supplied via check valve 43 against the discharge side of check valve 31 is supplemented by the inclusion of a load or weight of small lead balls or "shot" or other relatively heavy material 50 carried within the movable closure element 44 which is formed as a hollow glass blown piece.

Thus, it is evident that the pressure of gas fed from valve 43 plus the action of the weight of the lead shot in the closure element in valve 31 serves to protect the gas from being mixed with gas (or e.g., steam) fed via valve 31 to input line 37.

Closure element 44 rides between a normally lowered position and a raised position within a hollow housing 46, preferably of glass, formed on its interior surface with a ground glass finish in the region 47 so as to provide a relatively tight fit with the lower end of element 44. Pressure or gas directed downwardly against closure element 44, in addition to its weight, keeps a tight seal to the flow passage via housing 46.

On the other hand, when gas enters from below via the tube 51, the closure element is moved longitudinally within housing 46 until arrested short of its upper end by means of a trio of radially inwardly directed stops 52 which keep closure element 44 from seating into the upper opening 53.

Check valve 43 is similarly arranged but its closure element 48 does not carry the weight carried by closure element 44. The upper ends of both housings or valve bodies 46, 49 have been interconnected by means of the tubing 54, such as glass tubing, whereby the output from each of the two check valves 31, 43 can be connected by means of the glass connection fitting 56 to the input line 37 of furnace 38. It will be further evident that the two check valves are each oriented to pass fluid into the furnace input line and are further disposed whereby the discharge side of each of the two check valves is coupled to supply gas under pressure to the discharge side of the other to tend to close the flow passage thereof.

The furnace input line 37 is selectively supplied with gas from source 11 by means forming a first or second fluid path.

A selectively operable gas supply valve 39 is coupled to the gas supply line 19 so as to selectively direct gas from source 11 to furnace 38 via a first or a second path dependent upon the condition of solenoid 58. Thus, when solenoid 58 is deenergized, the spool 59 will be urged upwardly by the spring 61 so as to interconnect gas supply line 19 to line 41.

By energizing solenoid 58, spool 59 will be drawn downwardly against spring pressure so as to connect line 19 to feed oxygen along the connection 57 into flask 23.

Briefly, to this point, it will be readily evident that either one of two paths may be defined for supplying oxygen to the furnace 38. One path runs from source 11 through valve 39 and then along line 41 and connection 42 into check valve 43. From check valve 43 the gas serves to aid in closing the weighted check valve 31 and travels into input line 37. This oxygen is referred to as "dry" oxygen since it does not pick up any steam from flask 23.

However, upon energizing solenoid 58, spool 59 will be shifted so as to preclude the passage of oxygen along line 41 and to redirect the oxygen supply via connection 57 and flask 23 (where the water will be boiling). Oxygen and steam escaping from flask 23 is discharged along output line 28 and thence via the weighted check valve 31 into input line 37.

In this condition of operation, it will be readily evident from the electrical circuit traced from the battery 62 that both solenoids 36 and 58 are energized upon closure of switch 63 whereby the normally open steam relief valve 32 will be closed by movement of spool 34 into a position blocking the output passage of line 28. Pressure in line 28 will be required to overcome the weight of the closure element 44 of valve 31 in order to escape. Simultaneously, of course, oxygen will be fed into flask 23 so that it can become moistened and discharged. Pressure on the discharge side of check valve 31 serves, as above described, to aid in closing the check valve element 48.

In addition to the above, a second source 64 of gas, such as supply of nitrogen, entering from a toggle valve 66 via a regulator 67, meter 68 and submicron filter 69 feeds through flow meter 71 and through the normally open solenoid operated valve 72.

Accordingly, in standby operation, conventionally the nitrogen supply will be discharging along line 41 and connection 42 through check valve 43 whereby the pressure of the nitrogen supply serves to cause check valve 31, in addition to its weight, to insure closure of check valve 31 as the nitrogen enters input line 37. This serves to protect against steam entering and mixing with the flow of nitrogen into furnace 38.

It has been observed that in order to maintain the characteristics of the gas supplied by the system substantially constant at all times, the water level in flask 23 must be maintained relatively constant within a relatively narrow range.

Accordingly, means have been provided for the automatic control of the feeding of water into flask 23 as it is discharged in the form of steam or vapor via line 28.

In general, there has been provided a source of water such as supplied via line 73 into flask 23. Float means for riding in the water in flask 23 operate the solenoid 74 for electrically controlling the operation of valve 26 thereby selectively and variously supplying water to flask 23.

Switch means operably responsive to the position of the float means serves to operate valve 26 in response to the water level within the container as now to be described.

Flask 23 is sealed shut by means of a glass stopper 76 formed at its upper end with a pair of outwardly projecting ears 77 located diametrically opposite each other and adapted to engage the end of a helical spring 78 attached at its other end to similarly projecting ears 79 formed to protrude from the glass flask 23. In this way, stopper 76 is retained firmly seated in the neck of flask 23. Stopper 76 is also formed to include a downwardly extending tubular float guide 81. The float guide 81 is further formed with inwardly protruding nibs 82 variously disposed radially around the inner bore of guide 81. The nibs 82 are located at both the upper ends and lower ends of element 81.

An elongated hollow glass float 83, formed with a relatively small elongated hollow stem 84, is disposed within flask 23 to ride deeply in the volume of water within the flask whereby surface disturbances on the water will not affect its generally stable state. Stem 84 is guided by nibs 82 within guide 81, and in order to minimize any drag which might occur between the moving and stationary surfaces, a Teflon or other smooth plastic sleeve 86 is coated about the length of stem 84.

For purposes which will be described further below, a permanent elongated magnet 87 is positioned in the upper end of the hollow stem 84 and fastened in place by suitable means, such as by an epoxy cement.

Stopper 76 further includes a switch receptacle tube 88 closed at its lower end but open at its upper end to receive an elongated reed switch 89 whereby the proximity of magnet 87 serves to effect closure of the movable tips of pair of elongated relatively thin, flat, resilient leaves 91, 92. Leaves 91, 92 are housed in a separate cylindrical glass tubular capsule 93 and further encased in a cylindrical envelope 94 of protective material. The two terminals 96, 97 extend outwardly from the ends of capsule 93, the lower terminal 96 extending directly longitudinally outwardly, while the upper terminal 97 is bent at a right angle. When terminal 97 is seated properly in a keyway 98, the leaves 91, 92 in the switch receptacle tube 88 will be properly oriented for proper operation.

Thus, it is to be understood that, for example, leaf 92 may be constructed of a nonmagnetic material such as aluminum and the leaf 91 formed of a magnetic material such as iron so that, upon movement into proximity of magnet 87, the iron leaf 91 will be caused to move toward the magnet striking the nonmagnetizable leaf 92 thereby completing a circuit between terminals 96, 97.

Having in mind the foregoing, magnet 87 normally rides above and out of the range of the tips of leaves 91, 92 whereby to indicate that float 83 is riding at a proper level since switch 89 will then be open. Switch 89 controls valve 26.

Accordingly, the solenoid operated valve 26 is opened when solenoid 74 is energized and will be conditioned so as to cause its associated spool 26a to be moved into position to supply water through valve 26 so long as solenoid 74 remains energized by the presence of magnet 87 in the vicinity of the tips of leaves 91, 92 of switch 89.

Ultimately, the water level in flask 23 rises upwardly beyond its effective range and the tips of leaves 91, 92 spring apart due to their generally resilient nature thereby opening the circuit including solenoid 74 so as to permit the spring 99 to urge valve spool 26a to a position closing valve 26 and thereby to cut off delivery of additional water to flask 23.

It has been observed that maintenance of the water level at a constant position serves to aid in providing gas of constant doping characteristics thereby proving more reliable doping of materials.

From the foregoing it will be readily evident that there has been provided an improved gas supply system particular useful for supplying gas with constant characteristics to a diffusion furnace as employed in doping semiconductor materials.

Claims

I claim:

1. A gas supply system for doping semiconductor materials comprising a source of gas, a supply line leading from said source, a closed container adapted to receive water therein, means to supply and heat the water in the container, an output line forming a fluid discharge path from said container, a furnace input line adapted to carry gas into a semiconductor doping furnace, first and second check valves each oriented to pass fluid into said furnace input line and disposed whereby the discharge side of each check valve is coupled to supply gas under pressure to tend to close the discharge side of the other valve, means forming a first and second fluid path to said furnace input line from said source, said first path including said second check valve means and said second path including said container and said first check valve means, selectively operable gas supply valve means coupled to said gas supply line to selectively direct gas from said source to said furnace input line via said first or second path, a steam relief valve coupled to said second fluid path intermediate said first check valve means and said container and selectively operable to vent or contain steam pressure in said second path, and control means operably coupled to means for operating both said steam relief valve and said gas supply valve means and serving in one state to operate the steam relief valve to prevent pressure buildup in said second path when the gas supply valve means has been operated to couple said source to said first path and in a second state to reverse the conditions of the two last-named valve means.

2. A gas supply system according to claim 1 in which there is further included a second source of gas and means serving to selectively couple same to said first path to be delivered to said furnace input line while said second gas urges said first check valve to a closed state.

3. A gas supply system according to claim 1 wherein each of said check valves includes a movable closure element, said closure element for said first check valve being characterized by means for urging same to a position impeding the flow passage of said first check valve in favor of that of said second check valve.

4. A gas supply system according to claim 3 wherein the last-named means comprises additional weight carried by said closure element of said first check valve as compared to that of the closure element of said second check valve, said valves being oriented to dispose their closure elements for movement between lowered and raised positions to respectively close and open a flow passage in their respective check valves.

5. In a system for supplying gas to an input line of a semiconductor furnace from a source of gas, first and second check valves, each of said check valves including a movable closure element, each check valve being oriented to pass gas to said input line and disposed whereby the discharge side of each check valve is coupled to supply gas to the discharge side of the other for closing the flow passage thereof, the closure element for said first check valve being provided with means for urging same to a position closing the flow passage of said first check valve in favor of that of said second check valve whereby the pressure of gas fed to said input line via said second check valve plus the action of said means serves to protect said gas from being mixed with gas fed via said first check valve.

6. In a system for supplying gas according to claim 5 wherein said means consists of a heavier closure element in said first check valve than in said second check valve, the closure elements of both of said check valves being oriented to require upward movement in order to pass gas through their respective valves.

7. In a system for supplying gas according to claim 1 further including a source of liquid for said container, float means riding in said liquid in said container, electrically operated valve means serving to selectively supply said liquid to said container, and switch means operably responsive to the position of said float means for operating said valve means in response to the liquid level within said container.

8. In a system according to claim 1 further including an elongated float element for riding deeply in liquid maintained in said container, electrically operated valve means serving to selectively supply liquid to said container, and switch means operably responsive to the position of said float element for operating said valve means in response to the liquid level within said container, said switch means including a pair of conductive movable leave including a portion of each disposed in closely spaced relation to the other, one of said leaves being nonmagnetic and the other being magnetically responsive, a magnet carried by said float element for movement into and out of proximity with said portions to attract said magnetically responsive leaf into engagement with the other leaf to close the switch, said valve means being operably responsive to closure of the switch to control the flow of liquid into said container.