United States Patent [191
`Matthews
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,548,688
`Oct. 22, 1985
`
`[54] HARDENING 0F PHOTORESIST
`[75] Inventor:
`J01!!! C. Matthews, Columbia, Md.
`[73] Assignee: Fusion Semiconductor Systems,
`Rockville M d
`’
`'
`
`[21] APPL NQ; 497,465
`'
`[22] F1led:
`
`May 23, 1983
`
`[51] Int. (31.4 ............................................ ...B32B 27/10
`[52] US. Cl. ..
`.
`.... .. 204/159.18, 204/159.14,
`430/325; 430/326; 430/330
`[58] Field of Search ..................... .. 430/153, 330, 348;
`204/158, 159.11, 159.14, 159.16, 159.17, 159.19,
`592’ 159'18
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
`
`-
`
`3,415,648 12/1968 Certa ................. .Q. ................. .. 96/36
`3,549,366 12/1970 Margerum .............. ..
`96/ 35.1
`gig?!“ ett 211' '
`1'... 430/302
`4:264:712 4/1981 Kress
`....
`4,429,034 1/1984 Keane et a1. ................. .. 204/159.18
`4,439,516 3/1934 Cernigliaro et a1. .............. .. 430/323
`
`FOREIGN PATENT DOCUMENTS
`
`54-92808 7/1979 Japan .
`
`55402427 g/isso Japan .
`55-1024 8
`/ 980 Ja an .
`5402469 8/1980 Jagan _
`55402470 8/1980 Japan '
`55-103722 8/1980 Japan .
`55-103721 8/1980 Japan .
`58-8573 1/ 1983 Japan .
`58-125354 8/1983 Japan .
`58-223340 12/1983 Japan .
`861871 3/1961 United Kingdom .
`974837 11/1964 United Kingdom Q
`1103865 M968 United Kingdom ‘
`1170495 11/1969 United Kingdom .
`1492620 11/1977 United Kingdom ,
`2019593 10/1979 United Kingdom .
`Primary Examiner—Howard S. Williams
`Attorney, Agent, or Firm-Pollock, Vande Sande &
`Priddy
`
`_
`ABSTRACT
`'[57]
`photoresist is hardened by exposing it to UV radiation
`while subjecting it to elevated temperatures upon an
`increase i“ th‘? ‘legree of p°lymerizati°n due 1° eXPP'
`Sure to the Iadlatlon- The temperature Ofthe photoreslst
`can be controlled by a thermal chuck which contains a
`thermal ballast of heat conducting material.
`
`10 Claims, 3 Drawing Figures
`
`CONDITION "I" -RESIST IS MAINTAINED AT AMBIENT TEMPERATURE
`DURING THE EXPOSURE.
`
`CONDITION "2" -RESIST IS MAINTAINED AT A CONSTANT ELEVATED
`TEMPERATURE BELOW THE INITIAL RESIST FLOW
`TEMPERATURE DURING THE EXPOSURL
`
`CONDITION "3" -RESIST TEMPERATURE IS ALLOWED TO RISE DURING
`UV EXPOSURE , BUT IS MAINTAINED BELOW THE FLOW
`TEMPERATURE OF THE RESIST. FINAL RESIST TEMPE
`RATURE EXCEEDS INITIAL FLOW TEMPERATURE OF
`
`THE RESIST _
`
`SAMSUNG-1008.001
`
`

`
`US. Patent Oct. 22, 1985
`
`S_heet10f2
`
`4,548,688
`
`HG]
`
`aw Bis
`
`Al»). 4
`
`SAMSUNG-1008.002
`
`

`
`U. S. Patent Oct. 22,1985
`
`Sheet2 of2
`
`4,548,688
`
`TAMBIENT
`
`EXPOSURE
`sum
`
`|
`|
`I
`'.
`T's
`
`T2
`
`Tl TIME
`
`CONDITION "I" -RESIST IS MAINTAINED AT AMBIENT TEMPERATURE
`DURING THE EXPOSURE_
`
`CONDITION "2" -RESIST IS MAINTAINED AT A CONSTANT ELEVATED
`TEMPERATURE BELOW THE INITIAL RESIST FLOW
`TEMPERATURE DURING THE EXPOSURE
`
`CONDITION "3" -RESIST TEMPERATURE IS ALLOWED TO RISE DURING
`UV EXPOSURE , BUT IS MAINTAINED BELOW THE FLOW
`TEMPERATURE OF THE RESIST. FINAL RESIST TEMPE
`RATURE EXCEEDS INITIAL FLOW TEMPERATURE OF‘
`THE RESIST
`
`F I G . 3
`
`SAMSUNG-1008.003
`
`

`
`1
`
`HARDENING OF PHOTORESIST
`
`4,548,688
`
`2
`dioxide is etched to remove the unprotected oxide re
`gions.
`Likewise, photoresist materials are used to de?ne
`other regions of such devices such as polycrystalline
`silicon regions and metallic type interconnections.
`Many of the commonly used photoresists are not
`especially resistant to ?ow or distortion when exposed
`to relatively high temperatures encountered in more
`recently employed processing techniques such as
`plasma etching. In addition, it is desired to use the pho
`toresist remaining after de?ning for instance the oxide
`regions, in many applications as a protecting layer in the
`processing such as the doping. This also exposes the
`photoresist to elevated temperatures including that
`above about 200° C.
`In order to be suitable for such purposes, materials
`which are resistant to flow at higher temperatures have
`been developed and used as photoresists. In addition, it
`has been suggested to subject certain positive photore
`sists to exposure to deep UV radiation to cross-link and
`stabilize the material against elevated temperatures after
`the pattern in the photoresist has been developed. Ex
`amples of such discussions of the use of deep UV radia
`tion to cure or cross-link positive photoresists can be
`found in Yen, et al., Deep UV and Plasma Hardening of
`Positive Photoresist Patterns, Integrated Circuit Labo
`ratory, Xerox Palo Alto Research Center, Palo Alto,
`Calif. Hiraoka, et al., High Temperature Flow Resis
`tance of Micron Sized Images in AZ Resists, AZ Re
`sists, Vol. 128, No. 12, pages 2645-2647; and Ma,
`Plasma Resist Image Stabilization Technique (PRIST)
`update, SPIE Vol. 333, Submicron Lithography, 1982,
`pages l-23.
`The use of deep UV radiation for such stabilization is
`not entirely satisfactory since the time of exposure for
`many of the commonly used photoresists has been re
`ported as being about 10-30 minutes, which is relatively
`long.
`
`15
`
`DESCRIPTION
`1. Technical Field
`The present invention is concerned with a method
`and apparatus for hardening of photoresist materials. In
`particular, the present invention is directed to an im
`proved method for hardening positive photoresist mate
`rial employing UV radiation and especially deep to mid
`UV radiation. The present invention is particularly
`advantageous in the fabrication of integrated circuits.
`The present invention is also concemed with a device
`capable of controlling the temperature of the photore
`sist during exposure to UV radiation.
`2. Background Art
`In the fabrication of various articles, it is often neces
`sary to protect preselected areas of the surface while
`other areas of that same surface are exposed to particu
`lar treatments and/or process procedures. For instance,
`in the fabrication of semiconductor devices wherein, for
`example, an oxide layer is formed on a semiconductor
`substrate, it is often necessary to remove selected por
`tions of the oxide layer so as to allow diffusion of a
`suitable impurity through the oxide layer openings into
`25
`the underlying semiconductor substrate. Exemplary of
`such procedures is the fabrication of semiconductor
`devices, such as single crystal ?eld effect transistors.
`The above type of devices are formed by vapor dif
`fusing a suitable impurity into a wafer of a single silicon
`crystal to form suitably doped regions therein. In order
`to provide distinct P or N regions which are necessary
`for the proper operation of the device, diffusion should
`occur through only a limited portion of the substrate.
`Usually, this is accomplished by masking the substrate
`with a diffusion resistant material, such as silicon diox
`ide, which is formed into a protective mask to prevent
`diffusion through preselected areas of the substrate.
`The silicon dioxide mask is typically provided by
`forming a uniform oxide layer over the wafer substrate
`and thereafter creating a series of openings through the
`oxide layer to allow the passage of the impurity directly
`into the underlying surface within a limited area. These
`openings are readily created by coating the silicon diox
`ide with a material known as a photoresist. Photoresists
`can be negative photoresist or positive photoresist ma
`terials. A negative photoresist material is one which is
`capable of polymerizing and insolubilizing on exposure
`to light. Accordingly, when employing a negative pho
`toresist material, the photoresist layer is selectively
`exposed to light, causing polymerization to occur above
`those regions of the silicon dioxide which are intended
`to be protected during a subsequent operation. The
`unexposed portions of the photoresist are removed by a
`solvent which is inert to the polymerized portion of the
`resist and a suitable etchant for the silicon dioxide, such
`as hydrogen ?uoride or plasma is applied to remove the
`unprotected oxide regions.
`The positive resist material is one that upon exposure
`to light is capable of being rendered soluble in a solvent
`in which the unexposed resist is not soluble. Accord
`ingly, when employing a positive photoresist material,
`such is selectively exposed to light, causing reaction to
`occur above those regions of the silicon oxide which are
`not intended to be protected during the subsequent
`processing. The exposed portions of the photoresist are
`removed by a solvent which is not capable of dissolving
`the unexposed portion of the resist. Then the silicon
`
`45
`
`SUMMARY OF THE INVENTION
`The present invention provides a process for harden
`ing positive photoresist materials by UV radiation
`which makes it possible to signi?cantly reduce the nec
`essary exposure time. For instance, the present inven
`tion makes it possible to effect stabilization of many
`positive photoresists using exposure times for UV radia
`tion containing wavelenghts of up to 320 nm of less than
`one minute. In addition, the present invention makes it
`possible, in many instances, to eliminate postbaking or
`to postbake at higher temperatures and/or shorter
`times.
`i
`In particular, the present invention is concerned with
`hardening a positive photoresist by exposing a film of I
`photoresist material to UV radiation while subjecting
`the ?lm to elevated temperatures upon an increase in
`the degree of polymerization of the photoresist due to
`exposure to the UV radiation. The elevated temperature
`is maintained below the ?ow temperature of the ?lm.
`The ?ow temperature as used herein refers to that tem
`perature which causes the photoresist to distort when
`applied to the photoresist for 30 minutes. The resist
`during the exposure to the UV radiation is heated to an
`elevated temperature which is greater than the ?ow
`temperature of the photoresist at the start of the expo
`sure to the UV radiation.
`The present invention is also concerned with a ther
`mal chuck for use in the above described process to
`
`SAMSUNG-1008.004
`
`

`
`4,548,688
`3
`control the temperature of the photoresist during expo
`sure to UV radiation. The thermal chuck contains a
`thermal ballast which supports the substrate and which
`is composed of a thermally conductive material for
`transferring heat during exposure to the light to and
`from the substrate and photoresist. The mass of the
`thermal ballast is selected so that the temperature of the
`photoresist is raised above the flow temperature of the
`photoresist which existed at the start of the exposure to
`the UV radiation, but below the ?ow temperature of the
`photoresist at the time the temperature is raised.
`The present invention is also concerned with appara
`tus for hardening a photoresist which comprises the
`thermal chuck described hereinabove and a lamp capa
`ble of emitting UV radiation and heat.
`
`15
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 is a schematic diagram of apparatus suitable
`for carrying out the present invention.
`FIG. 2 is a schematic diagram of a lamp suitable for
`supplying UV radiation for use in the present invention.
`FIG. 3 is a graph illustrating flow temperature versus
`exposure time for different temperature conditions dur
`ing exposure to UV radiation.
`
`20
`
`4
`to mid UV radiation, also emits IR irradiation suf?cient
`to supply the necessary heat to the photoresist for car
`rying out the process of the present invention. Lamp 5
`is a microwave powered electrodeless lamp comprising
`two separate microwave powered electrodeless lamps 6
`having an elongated lamp envelope 8 within housing 7.
`Since the lamps are fully described in US. patent appli
`cation Ser. No. 393,856 to Ury, et al., ?led June 30, 1982
`now US. Pat. No. 4,504,768, entitled “Electrodeless
`Lamp Using a Single Magnetron and Improved Lamp
`Envelope Therefore”, disclosure of which is incorpo
`rated herein by reference; a more detailed discussion
`thereof is not deemed necessary. The basic difference
`between the disclosure of Ser. No. 393,856 and the lamp
`illustrated in FIG. 2 is that two separate individually
`microwave powered lamps 6 are contained in housing 7
`as contrasted to one such lamp explicitly described in
`said Ser. No. 393,856. The lamps 6 are at at angle of
`about l9°-20° to each other. The lamps include an elon
`gated envelope and elliptical re?ector as described in
`Ser. No. 393,856. Two lamps are employed in this em
`bodiment merely as a precaution to insure uniform irra
`diation of the wafer and photoresist. However, as un
`derstood, any lamp capable of providing the needed
`irradiation can be used.
`A lamp as disclosed is available from Fusion Semi
`conductor Systems Corporation, a subsidiary of Fusion
`Systems Corporation under the trademark “Microlite
`126A Resist Stabilizer Unit”.
`The exposure time required is signi?cantly reduced
`according to the present invention by maintaining the
`resist at an elevated temperature during the exposure to
`the UV radiation. The temperature must be below the
`?ow temperature of the resist which would cause defor
`mation or distortion of the coating or of any pattern
`therefrom. Although the photoresist need not be sub
`jected to elevated temperatures throughout the expo
`sure to the radiation, it is preferred that elevated tem
`peratures be used during at least substantially the entire
`exposure to radiation. During the exposure to the radia
`tion the photoresist is heated to elevated temperature
`which is above the flow temperature of the resist at the
`start of the exposure to the radiation.
`The ?ow temperature of the photoresist steadily in=
`creases throughout the duration of the radiation as re
`sult of an increase in the degree of polymerization or
`cross-linking of the photoresist. Accordingly, the tem
`perature to which the photoresist can be heated without
`distortion increases as the cross-linking or polymeriza
`tion due to the radiation procedes.
`In a preferred embodiment of the present invention,
`the temperature of the photoresist is controlled during
`the exposure to radiation so that it rises at approxi
`mately the same rate as does the ?ow temperature while
`insuring that the temperature of the photoresist never
`equals or exceeds the ?ow temperature. The exposure is
`continued until the flow temperature exceeds the de
`sired hard bake temperature of the photoresist.
`Another embodiment of the invention involves a
`two-step process which includes a ?rst step of exposing
`the photoresist to said UV irradiation at a temperature
`below the flow temperature of the unexposed resist, and
`a second step of exposing the resist to said UV irradia
`tion at a temperature substantially exceeding the ?ow
`temperature of the unexposed photoresist. If desired,
`the source of the UV irradiation of the ?rst step can
`differ from that of the UV irradiation of the second step.
`
`35
`
`45
`
`25
`DESCRIPTION OF PREFERRED AND VARIOUS
`MODES FOR CARRYING OUT INVENTION
`A wide variety of photoresist materials can be em
`ployed in the process of the present invention. Among
`those photoresist materials found to be especially suit
`30
`able are the positive photoresists which are cross-linka
`ble when exposed to UV radiation of up to 320 nm, and
`particularly, those photoresists sensitized with diazo
`compounds. Examples of such diazo sensitizers are dis
`cussed on pages 48-55 of DeForest, Photoresist Materi
`als and Processes, McGraw-Hill Book Company, 1975,
`disclosure of which is incorporated herein by reference.
`Some diazo compounds are benzoquinone 1,2-diazide-4
`sulfochloride; 2-diazo-l-naphthol-S-sulphonic acid es
`ter; naphthoquinone-l,2-diazide-5-sulfochloride; naph
`thoquinone- l ,2-diazide-4-sulfochloride;
`naphthoqui
`none-2,l-diazide-4-sulfochloride; and naphthoquinone
`2,l-diazide-5-sulfochloride.
`The preferred photoresist materials employed are the
`phenolic-formaldehyde type novolak polymers sensi
`tized with a diazo compound. The phenols include phe
`nol and substituted phenols such as cresol. A particular
`example of such is Shipley 1350 which is an m-cresol
`formaldehyde novolak polymer composition. Such is a
`positive resist composition and includes therein a dia
`zoketone, such as Z-diazo-l-naphthol-S-sulphonic acid
`ester. In such a composition, the ortho-diazoketone
`during the photochemical reaction is converted to a
`carboxylic acid. Other commercially available photore
`sists are suitable for carrying out the process of the
`present invention, including other novolak types.
`The UV radiation employed must contain suf?cient
`dosage of deep to mid UV radiation having wave
`lengths about 320 nm and below to cause the polymer to
`cross-link; preferably about 180 to 320 nm and more
`usually, about 190-260 nm. In many instances, the dos
`age to the photoresist of the UV radiation of wave
`length of 320 nm and below is at least about 10 Jou
`le/cmz.
`Although the present invention can be carried out
`with any deep UV output lamp, a particularly suitable
`lamp is schematically illustrated as numeral 5 in FIG. 2.
`This lamp 5 in addition to providing the necessary deep
`
`60
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`SAMSUNG-1008.005
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`

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`5
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`25
`
`40
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`4,548,688
`5
`When used in the fabrication of integrated circuits,
`the photoresist is usually applied in thicknesses of
`10,000 angstroms to about 20,000 angstroms.
`The diazo-sensitized phenolic-formaldehyde type
`photoresist of the type referred to hereinabove are usu
`ally heated to at least about 100° C., preferably at least
`about 120° C., and most preferably, to at least about
`200° C. in practicing the present invention. A typical
`range therefor being about 100°-200° C. and more usu- "
`ally, about 120° to about 200° C. Of course, the particu
`lar preferred temperature will depend upon the speci?c
`photoresist and thickness of the ?lm employed.
`Reference to FIG. 1 schematically illustrates appara
`tus suitable for carrying out the present invention. In
`particular, as discussed hereinabove, numeral 5 refers to
`the lamp system which supplies the UV irradiation of
`up to 320 nm and the IR irradiation for heat to the
`photoresist 1A and wafer 1 located beneath the output
`of the lamp at the quartz plate 10. For a typical applica
`tion of a wafer having a diameter of about 2 to 6 inches
`with a resist thickness of about 10,000 to about 20,000
`angstroms thereon, the distance between the wafer
`resist combination from the output of the‘ lamp at the
`quartz plate 10 is about one-eighth inch. The wafer and
`resist are supported by a thermal ballast 2.
`The material and mass of the thermal ballast 2 is
`selected so that the rise in the temperature of the photo
`resist due to heat from the lamp which will be supplied
`to the photoresist 1A and the thermal ballast 2 will be
`such as to raise the temperature of the photoresist 1A
`30
`above the ?ow temperature of the photoresist which
`existed at the start of the exposure to the radiation, but
`below the ?ow temperature of the photoresist 1A at the
`time the temperature is raised.
`The heat ballast 2 acts to transfer heat both to and
`from wafer 1. In particular, heat ballast 2 is preheated to
`about 100°-120° C. to transfer heat to wafer 1 prior to
`and at the start of the exposure to the UV radiation. As
`the exposure to the UV radiation proceeds, heat ballast
`2 actually removes heat from the wafer to prevent the
`temperature from exceeding the ?ow temperature.
`The thermal ballast 2 is a material capable of conduct
`\ing heat such as a metal or metal alloy.
`Examples of such materials are aluminum and stain
`less steel. The mass of the thermal ballast 2 should usu
`45
`ally be at least as large as that of the wafer 1 and in many
`instances, up to about 30 times the mass of the wafer 1.
`In a typical application the thermal ballast is about
`one-eighth to about one-sixteenth of an inch thick hav
`ing a diameter of about 2 to about 6 inches correspond
`ing to the diameter of the wafer and weighing about 50
`to about 100 grams. If desired, a vacuum (not shown)
`can be applied to the thermal ballast 2 in order to assure
`intimate contact between the wafer and ballast. A vac
`uum can be applied by providing small grooves in the
`top surface of the thermal ballast 2 and connecting a
`vacuum source via lines attached through the back of
`the thermal ballast 2. The exact mechanism by which
`the wafer is secured and positioned, if desired, has not
`been shown since there are many techniques in the prior
`art in which to accomplish such.
`Moreover, although this embodiment illustrates sup
`plying the heat from the lamp itself and using a thermal
`ballast, there are other methods in which heat can be
`supplied to the photoresist other than the lamp such as
`supplying heat to the support 2 by external means and
`employing a control to raise the temperature to the
`desired level after exposure to the light for a predeter
`
`6
`mined period of time. However, the means disclosed
`herein provides a very convenient and relatively simple
`means to automatically control the temperature of the
`photoresist within the desired limits. The temperature
`to be employed for any particular photoresist at any
`particular thickness after exposure for any length of
`time can be determined by determining the flow tem
`perature of such from previous testing without undue
`experimentation.
`The thermal ballast as employed will limit the tem
`perature rise automatically by drawing away a certain
`amount of heat due to the particular mass of the ballast
`and the amount of time in which the ballast is exposed
`to the infrared light from the lamp. Accordingly, by
`selecting the material and mass as mentioned herein
`above, the temperature rise of the wafer and photoresist
`can be readily regulated within the desired limits. Al
`though the presence of non-heat conductors on the
`wafer such as silicon dioxide may have some effect on
`the transfer of heat, the ?lms are so thin that the effect
`would be minimal as contrasted to the predominant
`effects caused by the heat source and heat reflective
`capacity of the heat ballast 2.
`Extending downward from the thermal ballast 2 are
`insulating stand-offs or pins 3 which extend into and
`through heat sink 4. The pins 3 at their lower end can be
`connected to mechanical arrangement (not shown) to
`move the pins and in turn, thermal ballast 2 away from
`or in contact with heat sink 4. The pins can be made of
`a non-heat conductor and non-re?ector such as quartz.
`Upon completion of the exposure, the wafer and photo
`resist is removed from a thermal ballast 2 and thermal
`ballast 2 is then contacted by manually moving pins 3
`down into heat sink 4 to thereby have the thermal bal
`last 2 contact heat sink 4 in order to cool thermal ballast
`2 back down to about 100° C. or less. Heat sink 4 can
`also be made of a heat conducting material such as
`aluminum or stainless steel and readily removes heat
`from the heat ballast 2. Heat sink 4 can be cooled by
`supplying cool air or other cooling media thereto. At
`this point, a new wafer can be applied to the thermal
`ballast 2 and then the thermal ballast 2 can be moved by
`manually moving the pins 3 upward in order to disen
`gage contact with the heat sink 4 and in position for
`exposure to the light.
`Reference to FIG. 3 illustrates the relative times
`required to obtain a T bake or stabilization for 200° C.
`for positive photoresists of the type discussed herein
`above. Curve 1 illustrates the values for the condition
`wherein the resist is maintained at normal ambient tem
`peratures of about 20°—40° C. during the exposure. The
`temperatures are kept at this level by not employing the
`heat ballast, but instead, just using the wafer on’ the heat
`sink 4.
`Curve 2 illustrates the values for the resist which is
`maintained at a temperature of about 100°-120° C. dur
`ing the exposure. These temperatures are not above the
`flow temperature of the resist at the start of the expo
`sure. The temperature is maintained at this level by not
`employing the heat ballast, but using the heat sink as for
`Curve 1 and preheating the sink to about 100° C. before
`exposure.
`Curve 3 illustrates conditions wherein the tempera
`ture of the resist is permitted to rise during the exposure
`to UV, but maintained below the flow temperature of
`the resist. The ?nal resist temperature is 200° C. which
`is above the initial ?ow temperature of the resist.
`
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`SAMSUNG-1008.006
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`

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`Photoresist
`Temperature
`2040’ C.
`
`Time to
`Stabilize
`90 sec.
`
`IOU-120° C.
`
`50 sec.
`
`100-180" C.
`
`30 sec.
`
`No thermal ballast,
`heatsink at ambient
`No thermal ballast,
`preheat heatsink to 100° C.
`4" thermal ballast
`5" thick, 67 grams
`aluminum
`
`4,548,688
`8
`7
`subjected to elevated temperature during the exposure
`Using the arrangement illustrated in FIG. 1 with
`HPR 204 from Phillip A. Hunt (a Novolak type) photo
`to the UV radiation which is greater than the initial
`resist at thickness of about 14,000 angstroms on a 4"
`?ow temperature of the resist at the start of the expo
`diameter wafer, an aluminum thermal ballast of 4" di
`sure to the UV radiation, and to thereby harden said
`ameter, the following results are obtained for the fol
`positive photoresist.
`lowing conditions:
`2. The method of claim 1 wherein said UV radiation
`contains wavelengths of about 180-320 nm.
`3. The method of claim 1 wherein said UV radiation
`has wavelengths of about 190-260 nm.
`4. The method of claim 1 wherein said elevated tem
`perature is above about 100° C.
`5. The method of claim 1 wherein said photoresist is
`a diazo sensitized polymer composition.
`6. The method of claim 5 wherein said polymer is a
`phenolic-formaldehyde novalak type.
`7. The method of claim 1 wherein said elevated tem
`perature is above about 120° C.
`8. The method of claim 1 wherein the photoresist is
`heated to elevated temperature of about 200° C.
`9. The method of claim 1 wherein the ?lm of positive
`photoresist material is about 10,000 to about 20,000
`angstroms.
`10. The method of claim 1 which further comprises
`controlling the temperature of the photoresist during
`the exposure to radiation so that it rises at approxi
`mately the same rate as does the flow temperature while
`insuring that the temperature of the photoresist never
`equals or exceeds the ?ow temperature.
`* Ii
`*
`1‘
`*
`
`15
`
`The above illustrates that the procedure of the pres
`ent invention signi?cantly reduces the time required to
`subject the photoresist to exposure to UV radiation.
`What is claimed is:
`1. A method of hardening a positive photoresist
`which comprises exposing a ?lm of positive photoresist
`material to UV radiation containing suf?cient dosage of
`wavelengths of about 320 nm or below to cause said
`25
`photoresist to harden while subjecting the ?lm to ele
`vated temperature upon increase in the degree of poly
`merization due to exposure to said UV radiation
`wherein said elevated temperature, at any instant during
`the said exposing, is below the flow temperature of the
`?lm at the particular instant, and wherein the resist is
`
`35
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`SAMSUNG-1008.007