US3748089A - Treating articles for a controlled duration - Google Patents

Abstract

In a method and apparatus for baking photoresist on semiconductor slices, the length of baking time is controlled independently of the number of slices being baked or the position of the first slice placed on a rotary baking table. The position of the first slice is detected photoelectrically and marked with a magnet. The magnet actuates a combination selector-stepping switch each revolution of the rotary table. Continuity through the switch after a preselected number of revolutions initiates slice removal and, thereby, controls the baking time.

Description

United States Patent 11 1 Boyer et al.

11 1 3,748,089 1451 July 24, 1973 TREATING ARTICLES FOR A CONTROLLED DURATION Inventors: Lynn F. Boyer, Reading; Charles R. Fegley, Laureldale; Anderson F. Johnson, Jr.,Sinking Spring, all of Pa.

Assignee: Western Electric Company, In-

corporated, New York, NY.

Filed: May 15, 1972 Appl. No.: 253,601

U.S. Cl. 432/52 Int. Cl. F27b 9/16 Field of Search 432/51, 52, 57

References Cited UNITED STATES PATENTS 6/1934 Fausel 432/57 X 3,105,678 10/1963 Van Houten ..432/52 Primary Examiner-John J. Camby Attorney-W. M. Kain et al.

[57] ABSTRACT In a method and apparatus for baking photoresist on semiconductor slices, the length of baking time is controlled independently of the number of slices being baked or the position of the first slice placed on a rotary baking table. The position of the first slice is detected photoelectrically and marked with a magnet. The magnet actuates a combination selector-stepping switch each revolution of the rotary table. Continuity through the switch after a preselected number of revolutions initiates slice removal and, thereby, controls the baking time.

18 Claims, 10 Drawing Figures Patented July 24, 1973 6 Sheets-Sheet 1 Patented July 24, 1973 3,748,089

6 Sheets-Sheet 5 Patented July 24, 1973 3,748,089

v 6 Sheets-Sheet 4 Patented July 24, 1973 3,748,089

6 Sheets-Sheet 6 TREATING ARTICLES FOR A CONTROLLED DURATION BACKGROUND OF THE:INVENTION 1. Field of the Invention This invention relates to methods and apparatus for treating articles for a controlled duration and, more particularly, for baking photoresist on semiconductor slices for a predetermined time.

2. Description of Prior Art In the manufacture of semiconductor devices, slices of semiconductor material must be coated with a pho tosensitive material or a photoresist which is exposed to an image of the device or devices to be reproduced in or on the semiconductor slice. The photoresist is then developed and baked so that the portions remaining after development become a very adherent mask. This mask protects portions of the semiconductor slice in the shape of a desired image. In prior methods, the photoresist was baked on the slices by placing the slices on a baking means, such as a hot plate which had reached a predetermined stable temperature and setting a buzzer to signal the time when the slices should be removed from the hot plate. That is, the slices were manually loaded on the hot plate, manually timed, and manually unloaded.

Such manual handling of ,slices is undesirable because of potential damage that may be caused by it. Also, this manual handling is costly and manual timer setting is subject'to mistakes. It is desirable, therefore, to automate the loading of slices onto the baking means, the control of the baking time, and the unloading of the slices. This is most easily done by making the baking means rotate and yield the advantage of automatically returning any slices placed on it to the'starting point to be removed.

Some prior art methods control the'number of revolutions or length oftime by means of a magnet fixed to a disc, a sealed contact, and a counter-timer. The magnetoperates the sealed contact and a counter counts during the time "interval which a timer permits. However, where it is possible to rotate a baking means at constant speed, the length of baking time may be governed by controlling the number revolutions of the baking means- This yields the further advantage of eliminating the timer as such.

Asiswell known in. thesemiconductor and thin film art, the photoresist must be baked to achieve the adherence and toughness necessary to withstand the processing involved in the manufacture of thin film and semiconductordevices. The adherence and toughness improve with length ofgbaking time; so much so, that the photoresist becomes difficult to remove if baked too long. There is an advantage, therefore, to limiting the baking to some predetermined amount which provides the best compromise between adherence and ease of removal. This advantage is achieved by identifying the location of the first slice placed on the baking means so that the baking time of it and all other slices following it in sequence, may be precisely controlled.

SUMMARY OF THE INVENTION Accordingly, an object of the invention is to provide new and improved methods and apparatus for treating articles for a controlled duration.

With this and other objects in view, the present invention contemplates a method for treating articles,

such as semiconductor slices coated with photoresist. The articles are automatically loaded on a heated, endless, constant-speed conveyor and the location of the first article on the conveyor is detected. Then, a marker is positioned on the conveyor in response to the detection and in relation to the first article. Next, a selectorstepping switch is actuated by the marker and continuity is established through the actuated switch after a preselected number of cycles of the endless conveyor and, therefore, a preselected treating time has occurred. Finally, both the marker and articles are removed in response to the continuity to terminate the treatment after the controlled duration.

A suitable apparatus for practicing the contemplated invention provides a rotary table for transporting the slices through a predetermined number of heat treating cycles. A photocell detector and relay are provided adjacent the table to detect the location of the first slice loaded on the table. A magnet holder, responsive to the photocell detector and relay, is provided for placing the magnet on the table in relation to the first slice to mark or identify it. The magnet actuates a combination selector-stepping switch which is provided for energizing the magnet holder to remove the magnet and initiating slice removal to end the treatment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 3 is a plan view of the apparatus showing how some of the parts are arranged around the center of the apparatus;

FIG. 4 is a plan view of a load station and baking position showing how the slices are conveyed to their baking position on a rotary table;

FIG. 5 is a cross section along line 55 of FIG. 4, of the load station and baking position;

FIG. 6 is an electrical schematic showing how a selector switch and stepping switch are'connected to form a combination selector-stepping switch, how a sealed contact operates the steppingswitch, and how the combination operates to remove the slices and the marker magnet to end the baking; i

' FIG. 7 is a partial cross section, along line 7-7 of FIG. 3, showing a marker magnet and magnet holder in elevation, for placing the magnet on and lifting it off a rotary table;

FIG. 8 is a partial cross section, along the line 8-8 of FIG. 3, showing the marker magnet on the table and an adjacent sealed contact which operates the stepping switch;

FIG. 9 is a plan view of an unload station and baking position; and

FIG. 10 is a cross section of the unload station and baking position along the line 10-10 of FIG. 9.

DETAILED DESCRIPTION Methods and apparatus embodying the invention will be described in connection with baking photoresist on semiconductor slices. However, it is to be understood the invention may be used for other articles.

Referring now to FIG. 1, asilicon slice 18 is coated with a photoresist 20 to form a coated slice designated generally by thenumeral 22. Thephotoresist 20 may be that sold by the Eastman Kodak Company under the trade designationKPR.

Thephotoresist 20 may be baked best with a rotary apparatus, refer to FIG. 2, in which abase 23 supports a rotary table 24 having anupper level 25 and alower level 26. Theupper level 25 is indirectly heated from below by convection and radiation and its proximity to a plate 27 which is directly heated by aheater 28, e.g., a 1,000 watt Chromalox No. A-90 ring heater. In this way, the coatedslices 22 are heated from the bottom and thephotoresist 20 is baked outward from its contact with theslice 18 so that gas bubbles are not trapped in it. Theupper level 25 is Teflon coated and is rotated at a constant speed, e.g., one rpm. The constant speed provides uniform heating of theupper level 25 by the plate 27 and permits the number of revolutions to determine the total heating or baking time in minutes. For example, 20 revolutions will yield a 20 minute total baking time.

Both theupper level 25 andlower level 26 are fixed to avertical shaft 30 so that they rotate together as a unit, i.e., the table 24, when theshaft 30 is revolved by a drive motor 31.

Referring now to FIGS. 3, 4 and 5, there is shown aload station 34, which is part of a stationary table 35, for loading photoresist coatedslices 22 intobaking positions 36 on theupper level 25 of the table 24. Theslices 22 are handled incarriers 38 and one of these carriers, having the slices to be baked, is inserted in the vertical indexing mechanism of a load station sender, designated generally by the numeral 39, of the type sold for that purpose by the Industrial Modular Systems Corporation. Theslices 22 are evenly spaced in thecarrier 38 and are removed therefrom by anair conveyor 40 which includesplenum 42,nozzles 44 facing toward the center of rotation, and asolenoid valve 46.

There are a plurality ofbaking positions 36, e.g., twenty-five, only some of which are shown. The baking positions 36 includeguides 48; stops 50; and three plenums, oneplenum 52 havingnozzles 54 directed toward the center of rotation and twoplenums 56 havingnozzles 58 directed away from the center of rotation.

Air is admitted to theload station plenum 42 and baking .position plenum 52 by thesolenoid valve 46 viaconnections 60 and 61,orifice 62 andport 64;'and it flows out through thenozzles 44 and 54, respectively. This air is preheated by passage throughtubing 65, attached to the plate 27, refer to FIG. 2, so that it will not cool theupper level 25. Since thenozzles 44 and 54 are directed toward the center of rotation, theslice 22 is conveyed by air from thesender carrier 38 to thebaking position 36 where it lodges against thestop 50. Thestop 50 is off center, as shown, in order to prevent bouncing of theslice 22. Further understanding of this may be had from L. F. Boyer and A. F. Johnson, Jr. Air Bearing Stop," technical digest, Western Electric Company,Issue 20, October [970, pages 13 and I4.

Sequential loading of theslices 22 onto theupper level 25 of the table 24 may start at anybaking position 36. However, thebaking position 36, into which thefirst slice 22 is loaded, must be identified so taht the start of baking and the number of revolutions of the table 24, and thereby the total baking time, may be controlled.

The location of thefirst slice 22 and itsbaking position 36 may be determined by means of aphotocell detector 66. Thedetector 66, refer to FIGS. 2, 3 and 6, projects light downward toward theupper level 25 and receives any light reflected back again. If enough light is reflected back, as when aslice 22 passes beneath thedetector 66, the reflected light activates thedetector 66 which operates aphotoelectric relay 67, FIG. 6, and causes amagnet 68 to be dropped on thelower level 26 of the table 24. Thus, themagnet 68 marks the position of thefirst slice 22 above on theupper level 25.

The total baking time for thephotoresist 20 is obtained by processing theslice 22 through enough bake cycles (revolutions of the table 24) to add to the total baking time desired. Controlof the number of revolutions of the table 24 and thereby, the total baking time is achieved, preferably, by a switching device in the form of a combination selector-steppingswitch 70.

Referring to FIG. 6, aselector arm 72 of the switch may be set to contact any one of the plurality ofselector contacts 74; e.g., a contact 74h as in FIG. 6, which will yield the correct number of revolutions as determined from the desired baking time and known speed of the table 24. The contacts 74a to 74j are connected in parallel to like stepping contacts 76a to 76j, i.e., the selector contact 74a is connected to the stepping contact 76a, the selector contact 74b is connected to the stepping contact 76b, etc.

A steppingarm 78 is fixed to aratchet wheel 80 or the equivalent, and apawl 82, actuated by asolenoid 84, moves theratchet wheel 80 and, thereby, the stepping arm 7 8. Each time thesolenoid 84 is energized thearm 78 steps from onecontact 76 to another.

Themagnet 68, refer to FIG. 8, which is placed on thelower level 26 of the table 24 to mark the position of thefirst slice 22 may be a disc or ring of permanent magnet material, preferably a ring of Alnico V or the like about /a inch O.D. X as inch ID; x V4 inch thick, magnetized axially.

When thelower level 26 rotates and themagnet 68 is resting on it, the magnet passes asealed'contact 86 which is sensitive to the flux of the magnet. The sealedcontact 86 is a hermetically-sealed, normally-open,

flux-sensitive switch, sometimes called a dry reed switch in the art, which is closed by the magnetic flux when themagnet 68 is adjacent to it. Switch closure occurs which thefirst slice 22 is above thesealed1contact 86, because thefirst slice 22 is on theupper level 25 of the table 24,above themarker magnet 68. Since thecontact 86 is positioned along the same radius as an unloadstation 88, refer to FIG. 3, each closure of thecontact 86 signals both: thatone revolution of the table 24, and therefore one bake cycle, has been completed; and that thefirst slice 22 is at the proper location to be conveyed from itsbaking position 36 into thecarrier 38 at the unloadstation 88.

Themagnet 68 is picked up from and dropped into agroove 89 in thelower level 25 of the table 24 by amagnet holder 90. Themagnet holder 90, refer to FIG. 7, includes asolenoid 92 having a vertically movingplunger 94, and anonmagnetic separator plate 96. Theholder 90 is in radial alignment with thedetector 66, refer to FIG. 3, and itssolenoid 92 lifts theplunger 94 from or drops it onto thenonmagnetic separator plate 96. Theplunger 94 is magnetic but not permanently magnetizable. When theplunger 94 is on theplate 96, themagnet 68 resting in theannular groove 89 of thelower level 26 of the table 24 will attract itself to the plunger'and lift itself a short distance up against the underside of thenonmagnetic separator plate 96. Thus, themagnet 68 will remain suspended free of thelower level 26 as long as thesolenoid 92 remains unenergized. When thesolenoid 92 is energized, such as when thephotocell detector 66 detects aslice 22 and actuates the associated electrical circuit, the solenoid lifts theplunger 94 far enough to make the space between the end of the plunger and theseparator plate 96 so large that the force of attraction between themagnet 68 and the plunger becomes too weak to support the magnet. Consequently, themagnet 68 drops into thegroove 89 on thelower level 26 of the table 24.

For best results,solenoid 92 should be supplied with the current connected so that the magnetic field of the solenoid is in the opposite direction to' that of the magnet 68'. This may be accomplished with arectifier 93. Themagnet 68 may be placed at any position in thegroove 89 around thelower level 26 by energizing and de-energizing thesolenoid 92 at the appropriate time.

It is to be noted that themagnet 68 could be placed on and removed from theupper level 25. However, the use of thelower level 26 removes thecontact 86 and magnet holder90 from the heat above the upper level net 68 as desired. In addition, a disc with a. reflective.

surface may be substituted for the magnet68' and" a photocell detector substituted for the sealedcontact 86 to achieve results similar to the. much less costly sealed contact and magnet.

In any case, when the presence of thefirst slice 22 loaded on theupper level 25 of the table 24-is detected, themagnet 68, or its equivalent, is dropped on thelower level 26 at the same angular position as the slice, refer to FIG. 3, because theholder 90 is aligned along the same radiusv as thedetector 66. Themagnet 68 remains in this position marking-oridentify'ing the location above, ofthe'slice 22 on the upper level.25.

The steppingarm 78 of theswitch 70 is connectedto one side ofa voltage source l00, refer.to FIG. 6, andtheselector arm 72 is connected to the other sidethroughzxa solenoid valve 102, atime delay relay 104, and a sealedcontact 106; and a relay 108'. When' theselector arm 72 is set to contact 74h, as in FIG. 6, and

thertable 24 revolved eight times to cause themagnet 68 to close the sealedcontact 86 eight times, thesteppingarm 78 is on' contact 76h,relay 108 is actuated, normallyopen contacts 113 are closed, and thesolenoid valve 102 isin condition'to be operated by closure of the sealedcontact 106. Thecontact 106 may be located any whole number ofbaking positions 36 away from the center line of the. unloadstation 88. Also, whenarms 72 and. 78 are on contacts 74h and 76h, respectively, continuity ensues and therelay 108 opens its normally-closedcontacts 110 to disconnect themagnet solenoid 92 from the source of voltage. This dropszthe: plunger 94-onto theseparator plate 96 so that the:magnet 68 attaches itself-to-the underside of"the plate. Thus, theholderr90removes themagnet 68 in response.. to continuity through the selector-stepping switch'170;

Thevalve 102, refer to FIGS. 9 and 10, admits preheated air both to: an unload station conveyor 111, having aplenum 112 withnozzles 114 directed toward thecarrier 38, through aconnection 116; and the twoplenums 56 in theupper level 25 through twoconnections 117, twoorifices 118 and twoentrance ports 120. The air is preheated by passage throughtubing 121 attached to the underside of the plate 27. Eachorifice 118 aligns with itsrespective port 120 at the same time that thebaking position 36 aligns with the unloadstation 88. Consequently, air flowing out thenozzles 58 and 114 conveys theslice 22 from thebaking position 36 to thecarrier 38 which is indexed vertically by the index mechanism of an unload station receiver, generally designated by the numeral 122, identical to thesender 39.

A plurality ofmagnets 123, refer to FIG. 3, are fixed to theupper level 25, one at eachbaking position 36 approximately on its centerline. Themagnets 123 may be ,/a inch diameter by 1 inch long rod magnets such as type CR-4OO -1 sold by Indiana General Corporation. Eachmagnet 123 closes the sealed contact 106'as eachbaking position 36 aligns with theunloadstation 88. Theair valve 102 is made to operate at the precise time that theorifices 118 are aligned with theports 120 and. thebaking position 36 is aligned with the unloadstation 88, by adjusting thetime delay relay 104. Thus, the

,slices 22 are conveyed one after the other, i.e., sequenthe microswitches. Thus, carn lobes and microswitches will replace magnets and sealed contacts but, of course, are subject to much more wear.

OPERATION The operation ofthe bakingapparatus maybe understood best by: referring to FIGS. 2, 3 and'6; assuming that the speed of rotation of the table 24 is 1 rpm; and assumingthatthep'hotoresist 20 must be baked for five minutes. The schematic diagram of 'FIG. 6doesnot show the circuits for the-drive motor'3l orheater 28* because these. are well known inthe'art.

Thearm 72 oftheselector-stepping switch is set to contact 74c, the fifth contact from OFF; theheater 28 and motor 31' are energized; and theupper level 25 of the table 24 is allowed to rotate in the directionof the arrow until thermal equilibrium is reached.

When equilibrium'is reached, asender switch 124 is closed so that thesender 39 and. solenoid valve-46 are connected to the voltage source through sealedcontacts 126 and 128, respectively. Thecontact 128 is closed by one of themagnets 123 and operates thevalve 46 admitting air totheload station 34 andbaking position 36. This removes thefirst slice 22 from thesender carrier 38. Precise timing so that thevalve 46 operates when theload station 34 andbaking position 36 are aligned, is achieved by adjustment of atime delay relay 129.

Contact 126 closes, following closure ofcontactl 28, and indexes thesender 39 mechanism one step down ward. This lowers thenext slice 22 into position to be conveyed or sent into thenext baking position 36. The closure ofcontact 126 occurs after closure ofcontact 128 because the sealedcontact 126 is located one and onehalf baking positions 36 beyond thecontact 128 in the direction of rotation (see FIG. 3). However, if theswitch 124 is closed when the table 24 rotation is such that two of the magnets 123'are between the sealedcontacts 128 and 126, thecarrier 38 in thesender 39 may index downward and break aslice 22 before air is admitted to thesender conveyor 40. This may be prevented by a sealedcontact 130,time delay relay 132 and arelay 134 having contacts 136. Whenswitch 124 is closed, the contacts 136 ofrelay 134 are open until the sealedcontact 130 is closed by amagnet 123. This sealed contact is located adjacent the upper level 25 a few degrees in advance ofcontact 128, e.g., about (or any even number of baking positions plus 5). Closure ofcontact 130 energizes thetime delay relay 132 which, in turn, energizes therelay 134 for about 1.4 seconds. During this interval the orientation of themagnets 123 with respect to the sealedcontacts 128 and 126 is such that they will be operated in that order, i.e., the proper sequence. Thus, theslices 22 are sequentially removed from thesender carrier 38 and placed in adjacent baking positions 36, by sequentially operating the sealedcontact 128 first and thecontact 126 second. Baking then takes place at the temperature of theupper level 25.

Theposition 36 of thefirst slice 22 loaded on theupper level 25 is detected by light reflected from the slice back into thephotocell detector 66, which is a part of aphotoelectric relay 67. Reflected light seen by thephotocell detector 66 causes therelay 67 to energize the magnet-holder solenoid 92 and theplunger 94 to be lifted. Themagnet 68, as a consequence, drops to thelower level 26 and marks the position of thefirst slice 22.

Thefirst slice 22 will have been carried through essentially one revolution and one baking cycle when it arrives at the unloadstation 88. The sealedcontact 86, positioned adjacent thelower level 26 in line with thestation 88, is closed by themarker magnet 68 and energizes the stepping-switch solenoid 84 to move thearm 78 to the first contact 76a. This is repeated as the table 24 rotates until, at the end of five minutes, thearm 78 establishes electrical continuity from one side of thevoltage source 100 through therelay 108, thearm 78 itself, the contact 76a, the contact 74c and theselector switch arm 72 to the other side of the source. This energiies therelay 108 which opens the normally closedcontacts 110, de-energizes the magnet-holder solenoid 92, drops theplunger 94 and lifts;themagnet 68 from thelower level 26. At the same time, therelay 108 resetsphotoelectric relay 67 and closes its normallyopen contacts 113 to connect the unloadsolenoid valve 102 to the voltage source. Thus, each time one of themagnets 123 closes the scaledcontact 106, thevalve 102 admits air to thebaking position 36 and the unloadstation 88. This conveys thefirst slice 22 into thereceiver carrier 38 and ends the baking of thephotoresist 20 for that slice. Shortly thereafter, one of themagnets 123 closes a sealedcontact 138, refer to FIG. 3, which energizes the indexing mechanism of thereceiver 122 once and raises thereceiver carrier 38 one step into position to receive thenext slice 22. This is repeated until all slices are removed in sequence. Then, the selectorstepping switch is reset so that the next lot of slices may be baked.

It is to be noted that the slices may be baked starting with the table 24 in any position and a wide range in baking times may be had by proper choice of the speed of the table and the number of contacts for the selector-steppingswitch 70.

Thus, a method and apparatus for carrying out the method have been disclosed for treating articles for a controlled duration independently of the number of articles or where the first one is placed on the apparatus.

While specific embodiments have been described in the foregoing specification to illustrate the invention, it will be understood that the invention is not limited to these embodiments. Various changes and modifications may be made without departing from the spirit and scope of the invention.

What is claimed is:

1. A method of treating articles, wherein the duration of treatment is controlled by a marker, which comprises the steps of:

a. placing a series of the articles on an endless conveyor for treatment;

b. detecting the location of the first article of the series of articles placed on the conveyor;

c. positioning the marker on the conveyor in response to the detection of the location to identify such location;

(1. actuating a switching device by means of the marker to count the number of cycles completed by the endless conveyor and to establish continuity through the switching device when a predetermined number of cycles has been completed; and

e. removing the marker and the articles from the conveyor to terminate the treatment, in response to the continuity and beginning with the first article as identified by the marker.

2. The method ofclaim 1 wherein the marker is dropped on the conveyor.

3. The method of claim 2 wherein the marker is magnetic.

4. The method ofclaim 1 wherein there is only one article in the series.

5. The method ofclaim 1 wherein the switching device is a combination selector-stepping switch.

6. The method ofclaim 5 wherein the articles are semiconductor slices coated with photoresist and the treatment is baking the photoresist.

7. The method of claim 6 wherein the endless conveyor is a rotating table.

8. The method of claim 7 wherein the magnetic marker operates a sealed contact to actuate the switch ing device.

9. A method of baking photoresist on semiconductor slices, wherein the length of baking time is controlled by a magnetic marker, which comprises of steps of:

a. positioning a selector portion of a selectorstepping switch to a preselected contact representing the number of revolutions of a rotary table which will yield the desired length of baking time;

b. rotating the table to sequentially receive a plurality of slices from a carrier;

c. conveying the slices sequentially from the carrier into each of a plurality of slices positions on the rotary table;

d. heating the table to bake the photoresist on the slices;

e. detecting the position of the first slice;

f. dropping a magnetic marker on the rotary table in alignment with the first slice to mark its position;

g. positioning a magnetic flux sensitive switch adjacent the rotary table, the switch being aligned with a carrier at an unload station and capable of operating the stepping portion of the selector-stepping switch;

h. actuating the flux-sensitive switch by means of the magnetic marker to operate the stepping portion of the selector-stepping switch each revolution of the table until continuity is established through the preselected contact;

. lifting the magnetic marker from the table in response to the continuity; and

j. removing the slices from their positions on the table in response to the continuity, starting with the first slice, to terminate the baking of the photoresist on each slice at the end of the preselected length of time.

10. An apparatus for treating articles, which comprises:

a. means for transporting the articles through a predetermined number of treating cycles;

b. means for loading the articles sequentially on the transporting means;

c. means for detecting the first article loaded on the transporting means;

d. means for marking the location of the first article;

e. means, responsive to the detecting means, for placing the marking means on the transporting means at the beginning of treatment, to mark the location of the first article, and for removing the marking means at the end of treatment;

f. means, responsive to the marking means, for controlling the number of treating cycles the first article makes and thereby the total duration of the treatment of the articles; and

g. means, responsive to the cycle controlling means, for removing the articles sequentially from the transporting means beginning with the first article marked by the magnet.

11. An apparatus, as recited inclaim 10, wherein the means for markingthe location of the first article comprises a permanent magnet positioned in' relation to the first article.

l2. An apparatus, as recited on claim 11, wherein the transporting means comprises a rotary table.

13. An apparatus, as recited in claim 12, wherein the means for detecting the first slice comprises a photocell and a photoelectric relay.

14. An apparatus, as recited in claim 13, wherein the means responsive to the detecting means comprises a solenoid having a plunger which may be raised or lowercd to position the marking means in relation to the first article.

15. An apparatus, as recited in claim 14, wherein the means responsive to the marking means comprises a sealed contact and combination selector-stepping switch.

16. An apparatus, as recited in claim 15, wherein the articles are photoresist coated semiconductor slices and the treatment comprises baking the photoresist.

l7.'An apparatus for baking photoresist on semiconductor slices, which comprises:

a. a base;

b. a rotary table supported by the base and having baking positions for baking the photoresist on the slices;

c. a loading station for loading the slices sequentially into each baking position;

d. a photocell detector to determine the baking position of the first slice;

e. a combination selector-stepping switch for selecting the number of revolutions through which the table is to be rotated, and for counting the revolutions of the table to control the baking time;

f. a marker, positionable on the table to mark the location of the first slice;

g. a switch, operated by the marker once each revolution, to actuate the stepping portion of the selectorstepping switch and count the revolutions of the table;

h. a marker holder, aligned with and responsive to the photocell detector for positioning the marker on the table in line with the first slice and responsive to the selector-stepping switch for removing the marker from the table after the preselected number of revolutions;

i. an unloading station adjacent the table to receive the baked slices; and

j. means for removing the slices sequentially from the table, beginning with the first slice, and conveying the slices into the unloading station in response to the selector-stepping switch, thereby ending the slice baking.l p v 18. An apparatus for baking photoresist on semiconductor slices, which comprises:

a. a base;

b. a rotary table supported by the base for baking the photoresist on the slices, the table having a heated upper level and a lower level;

c. a loading station adjacent the upper level of the table for loading slices sequentially into a baking position for each slice on the table;

d. a photocell detector adjacent the upper level of the table to determine the baking position of the first slice;- s

e. a combination selector-stepping switch for selecting the number of revolutions through which the table is to be rotated and counting the revolutions to control the baking time, continuity therethrough being established when the preselected number of revolutions have been counted;

f. a magnet, positionable on the lower level of the table,'to mark the location of the first slic'e;

g. a flux-sensitive switch, adjacent thelower'level of the table, the switch being closed by the flux of the magnet once each evolution of the table to actuate the stepping portion of the selector-stepping switch to count the number of revolutions;

h. a magnet holder adjacent the lower level of the table and aligned with the photocell detector, the holder being responsive to the photocell detector for depositing the magnet on the lower level of the table, and responsive to continuity through the combination selector-stepping switch for removing the magnet from the table after the preselected number of revolutions;

i. an unload station adjacent the upper level of the table to receive the baked slices; and

j. means for removing the slices sequentially from the table, beginning with the first slice, and conveying the slices into the unloading station in response to continuity through the selector-stepping switch, thereby ending the slice baking.

Claims (18)

1. A method of treating articles, wherein the duration of treatment is controlled by a marker, which comprises the steps of: a. placing a series of the articles on an endless conveyor for treatment; b. detecting the location of the first article of the series of articles placed on the conveyor; c. positioning the marker on the conveyor in response to the detection of the location to identify such location; d. actuating a switching device by means of the marker to count the number of cycles completed by the endless conveyor and to establish continuity through the switching device when a predetermined number of cycles has been completed; and e. removing the marker and the articles from the conveyor to terminate the treatment, in response to the continuity and beginning with the first article as identified by the marker.

2. The method of claim 1 wherein the marker is dropped on the conveyor.

3. The method of claim 2 wherein the marker is magnetic.

4. The method of claim 1 wherein there is only one article in the series.

5. The method of claim 1 wherein the switching device is a combination selector-stepping switch.

6. The method of claim 5 wherein the articles are semiconductor slices coated with photoresist and the treatment is baking the photoresist.

7. The method of claim 6 wherein the endless conveyor is a rotating table.

8. The method of claim 7 wherein the magnetic marker operates a sealed contact to actuate the switching device.

9. A method of baking photoresist on semiconductor slices, wherein the length of baking time is controlled by a magnetic marker, which comprises of steps of: a. positioning a selector portion of a selector-stepping switch to a preselected contact representing the number of revolutions of a rotary table which will yield the desired length of baking time; b. rotating the table to sequentially receive a plurality of slices from a carrier; c. conveying the slices sequentially from the carrier into each of a plurality of slices positions on the rotary table; d. heating the table to bake the photoresist on the slices; e. detecting the position of the first slice; f. dropping a magnetic marker on the rotary table in alignment with the first slice to mark its position; g. positioning a magnetic flux sensitive switch adjacent the rotary table, the switch being aligned with a carrier at an unload station and capable of operating the stepping portion of the selector-stepping switch; h. actuating the flux-sensitive switch by means of the magnetic marker to operate the stepping portion of the selector-stepping switch each revolution of the table until continuity is established through the preselected contact; i. lifting the magnetic marker from the table in response to the continuity; and j. removing the slices from their positions on the table in response to the continuity, starting with the first slice, to terminate the baking of the photoresist on each slice at the end of the preselected length of time.

10. An apparatus for treating articles, which comprises: a. means for transporting the articles through a predetermined number of treating cycles; b. means for loading the articles sequentially on the transporting means; c. means for detecting the first article loaded on the transporting means; d. means for marking the location of the first article; e. means, responsive to the detecting means, for placing the marking means on the transporting means at the beginning of treatment, to mark the location of the first article, and for removing the marking means at the end of treatment; f. means, responsive to the marking means, for controlling the number of treating cycles the first article makes and thereby the total duration of the treatment of the articles; and g. means, responsive to the cycle controlling means, for removing the articles sequentially from the transporting means beginning with the first article marked by the magnet.

11. An apparatus, as recited in claim 10, wherein the means for marking the location of the first article comprises a permanent magnet positioned in relation to the first article.

12. An apparatus, as recited on claim 11, wherein the transporting means comprises a rotary table.

13. An apparatus, as recited in claim 12, wherein the means for detecting the first slice comprises a photocell and a photoelectric relay.

14. An apparatus, as recited in claim 13, wherein the means responsive to the detecting means comprises a solenoid having a plunger which may be raised or lowered to position the marking means in relation to the first article.

15. An apparatus, as recited in claim 14, wherein the means responsive to the marking means comprises a sealed contact and combination selector-stepping switch.

16. An apparatus, as recited in claim 15, wherein the articles are photoresist coated semiconductor slices and the treatment comprises baking the photoresist.

17. An apparatus for baking photoresist on semiconductor slices, which comprises: a. a base; b. a rotary table supported by the base and having baking positions for baking the photoresist on the slices; c. a loading station for loading the slices sequentially into each baking position; d. a photocell detector to determine the baking position of the first slice; e. a combination selector-stepping switch for selecting the number of revolutions through which the table is to be rotated, and for counting the revolutions of the table to control the baking time; f. a marker, positionable on the table to mark the location of the first slice; G. a switch, operated by the marker once each revolution, to actuate the stepping portion of the selector-stepping switch and count the revolutions of the table; h. a marker holder, aligned with and responsive to the photocell detector for positioning the marker on the table in line with the first slice and responsive to the selector-stepping switch for removing the marker from the table after the preselected number of revolutions; i. an unloading station adjacent the table to receive the baked slices; and j. means for removing the slices sequentially from the table, beginning with the first slice, and conveying the slices into the unloading station in response to the selector-stepping switch, thereby ending the slice baking.

18. An apparatus for baking photoresist on semiconductor slices, which comprises: a. a base; b. a rotary table supported by the base for baking the photoresist on the slices, the table having a heated upper level and a lower level; c. a loading station adjacent the upper level of the table for loading slices sequentially into a baking position for each slice on the table; d. a photocell detector adjacent the upper level of the table to determine the baking position of the first slice; e. a combination selector-stepping switch for selecting the number of revolutions through which the table is to be rotated and counting the revolutions to control the baking time, continuity therethrough being established when the preselected number of revolutions have been counted; f. a magnet, positionable on the lower level of the table, to mark the location of the first slice; g. a flux-sensitive switch, adjacent the lower level of the table, the switch being closed by the flux of the magnet once each evolution of the table to actuate the stepping portion of the selector-stepping switch to count the number of revolutions; h. a magnet holder adjacent the lower level of the table and aligned with the photocell detector, the holder being responsive to the photocell detector for depositing the magnet on the lower level of the table, and responsive to continuity through the combination selector-stepping switch for removing the magnet from the table after the preselected number of revolutions; i. an unload station adjacent the upper level of the table to receive the baked slices; and j. means for removing the slices sequentially from the table, beginning with the first slice, and conveying the slices into the unloading station in response to continuity through the selector-stepping switch, thereby ending the slice baking.

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