United States Patent 1191
`McColgin et al.
`
`[11] Patent Number:
`[45] Date of Patent:
`
`4,931,351
`Jun. 5, 1990
`
`[54] BILAYER LITHOGRAPHIC PROCESS
`[75] Inventors: William C. McColgin, Pittsford;
`Thomas B. Brust, Spencerport;
`Robert C. Daly, Rochester; Joseph
`Jech, Jr., Rochester; Robert D.
`Lindholrn, Rochester, all of NY.
`Eastman Kodak Company,
`Rochester, NY.
`[21] Appl. No.1 378,471
`[22] Filed:
`Jul. 13, 1989
`
`[73] Assignee:
`
`[63]
`
`Related US. Application Data
`Continuation of Ser. No. 2,077, Jan. 12, 1987, aban
`doned.
`
`[51] 1111. C1; ........................ .. o03c 5/00; G03C 5/40
`
`ABSTRACT
`[57]
`A method for producing high resolution patterned resist
`images having excellent etch resistance and superior
`thermal and dimensional stability comprises the steps of:
`(a) forming a planarizing layer resistant to silicon uptake
`on a substrate;
`(b) providing a positive-working photoresist composi
`tion containing ——-OH or -—NH—- groups over the
`planarizing layer,
`(c) imagewise exposing the resist to activating radiation,
`(d) developing the exposed resist,
`(e) contacting the developed resist with a vapor com
`prising a silicon-containing compound to effect silyla
`tion thereof and thereby impart etch resistance, the
`silicon-containing compound having the structural
`formula:
`
`[52] us. c1. . . . . .
`
`. . . . . . . 1 . . . . .. 430/323; 430/313;
`
`430/317; 430/326; 430/328; 156/628; 156/643
`[58] Field of Search ............. .. 430/312, 313, 314, 315,
`430/317, 323, 326, 323; 156/643, 628
`References Cited
`U.S. PATENT DOCUMENTS
`
`[56]
`
`4,521,274 6/1985 Reichmanis et a1. ..
`4,613,398 9/1986 Chiong et al. , . . . . .
`
`156/643
`
`. . . .. 156/628
`
`4,737,425 4/1988 Lin et a1. . . . . . . . .
`. . . . . .. 430/11
`4,782,008 11/1988 Babich et al. ............. ., ...... .. 430/313
`
`FOREIGN PATENT DOCUMENTS
`
`0136130 4/1985 European Pat. Off. .
`2154330 9/1985 United Kingdom.
`
`OTHER PUBLICATIONS
`Follett et al, “Polarity Reversal of PMMA by Treat
`ment with Chlorosilanes”, Electrochemical Sec., vol.
`82-2, Extended Abstracts, Oct. 1982.
`Primary Examiner-Jose Dees
`Attorney, Agent, or Firm--William J. Davis
`
`wherein:
`X1 and X2 are individually chloro or
`
`wherein
`R3 and R4 are individually H or alkyl; and
`R1 and R2 are individually H or alkyl; and
`(t) contacting the planarizing layer with an oxygen-con
`taining plasma so as to preferentially remove portions
`thereof.
`
`7 Claims, No Drawings
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`4,931,351
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`There is a growing need for a lithographic method,
`capable of producing high resolution submicron pat
`terned resist images having excellent etch resistance and
`thermal and dimensional stability, which is compatible
`with existing resist materials and processing facilities
`and affords convenient device processing.
`
`1
`
`BILAYER LITHOGRAPHIC PROCESS
`
`This is a continuation of application Ser. No. 002,077,
`?led Jan. l2, 1987 now abandoned.
`
`FIELD OF THE INVENTION
`This invention relates to a method of forming etch
`resistant polymeric resist images for use in the creation
`of micron and submicron dimension patterns and ?ne
`lines. The method is particularly useful in the fabrica
`tion of electronic devices.
`
`SUMMARY OF THE INVENTION
`In accordance with the present invention, there is
`provided a method for producing high resolution pat
`terned resist images which have excellent etch resis
`tance and superior thermal and dimensional stability.
`The method comprises the steps of:
`(a) forming a planarizing layer resistant to silicon uptake
`on a substrate,
`(b) providing a positive-working photoresist composi
`tion containing —OH or —NH—— groups over the
`planarizing layer,
`(0) imagewise exposing the resist to activating radiation,
`(d) developing the exposed resist,
`(e) contacting the developed resist with a vapor com
`prising a silicon-containing compound to effect silyla
`tion thereof and thereby impart etch resistance, the
`silicon-containing compound having the structural
`formula:
`
`Rl
`
`wherein:
`X1 and X2 are individually chloro or
`
`wherein
`R3 and R4 are individually H or alkyl; and
`R1 and R2 are individually H or alkyl; and
`(f) contacting the planarizing layer with an oxygen-con
`taining plasma so as to preferentially remove portions
`thereof.
`The method is compatible with existing resist materi
`als and processing facilities and affords device process
`ing ‘under convenient conditions. Other advantageous
`features will become apparent upon reference to the
`following description of the preferred embodiments.
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`The invention is hereafter described particularly with
`regard to embodiments featuring certain preferred sily
`lating agents and photoresist compositions and in a
`preferred usage, i.e. in a bilayer resist system. However,
`the silylating agents are also useful in single layer resists
`and with a wide variety of photoresist compositions and
`processing formats.
`Positive-working photoresist compositions which
`can be used in the method of the present invention
`include materials containing sites capable of reacting
`with the silylating agent. These sites preferably com
`prise —OH or --NH— groups and are present in func
`tional groups such as hydroxyl, amine, carboxyl and
`imide. It is believed that the active hydrogens of the
`
`BACKGROUND OF THE INVENTION
`The need for higher resolution lithography in VLSI
`device processing has led to the development of various
`resist processes for fabricating ?ner and more densely
`packed features on silicon wafers. One of these is the
`trilevel process which improves resolution but at a
`considerable cost in process complexity. In the trilevel
`process a thick organic planarizing layer is coated to
`level out the device topography. Next, a thin glass ?lm
`is coated thereon. A thin layer of photoresist, coated
`over the glass, is used to pattern the glass. The glass
`layer then acts as a mask for oxygen plasma etching of
`the planarizing layer. Finally, the pattern is transferred
`into the silicon device.
`Approaches to simplifying the trilevel process are
`being investigated. In one approach, a single thick layer
`of a photosensitive polymer is used. The polymer is
`designed to take up silicon from a vapor-treatment pro
`cess in an imagewise fashion after the polymer has been
`exposed. The silylated portions at the top of the poly
`mer layer act as the etch mask for the portions remain
`ing below. Development is entirely a dry process. Such
`approaches incorporate some of the advantages of the
`trilayer process, but tend to be sensitive to ?are light in
`the patterning exposure tool. Flare light can cause a
`silicon-containing scum which impedes etching.
`Another approach involves replacing silicon in a
`glass layer with silicon in the resist itself for use with a
`planarizing layer in a bilayer process. For example, both
`positive- and negative-working presilylated resist mate
`rials, wherein silicon is formulated as part of the resist
`composition, are known. The silicon in the resist can
`form an SiOz etch mask upon exposure to an oxygen
`plasma. However, the amount of silicon required in
`presilylated resist formulations to achieve good etch
`resistance (up to approximately 15% by weight) lowers
`the glass transition temperature of the resist and renders
`the resist more hydrophobic. This results in poor deve
`lopability in aqueous developers. For positive-working
`materials, thermal and dimensional instability during
`subsequent processing (pattern-transfer and etching
`steps) can result.
`European Patent Application No. 0 136 130 describes
`a method of making articles using a resist formed by
`sorption of an inorganic-containing gas into an organic
`material. The resist is developed by exposure to a
`plasma that forms a protective compound. Example III
`therein describes the use of SiCl4, (CH3)2SiCl2 and
`SnCl4 in a single layer system comprising a negative
`working resist containing an azide sensitizer.
`U.K. Patent Application GB 2154330 A discloses a
`method of fabricating semiconductor devices wherein
`silicon is introduced into novolac resin by exposure to
`an atmosphere of tetrachlorosilane or tetramethylsilane.
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`3
`clohexane, methylisobutyl ketone, mixtures thereof, and
`—OH or —NH— groups are replaced by silicon during
`silylation. Particularly useful materials include novolac
`the like. The developer can contain lower alcohols,
`resins, resoles, polyvinylphenols and poly(hydrox
`ketones, or amines such as alkylamines, cycloalkyla
`yethyl methacrylate). Such polymers can be used alone
`mines and alkanolamines. Etch impeding scum resulting
`or in combination with photoactive compounds to make
`from ?are light is minimized because the resist is devel
`oped prior to silylation. After development, the imaged
`up the photoresist composition. Preferred resists com
`prise a novolac resin and include KMPR 809, available
`bilayer preferably is rinsed in deionized water.
`from Eastman Kodak Co., and I-IPR 204 available from
`As noted, an advantageous feature of the method of
`Hunt Chemical Co. The photoresist composition is
`this invention is that it is compatible with existing resist
`responsive to activating radiation of any kind to pro
`processing facilities and affords convenient device pro
`duce an image after development of the resist. Preferred
`cessing. Inspection, after exposure and development of
`are those that respond to UV or visible radiation and
`the resist is easily performed. Lines and spaces as small
`those that respond to electron beams. The thickness of
`as 0.6 pm and smaller can be inspected for cleanout, for
`the resist layer preferably is less than about 3 pm.
`example, in an optical microscope. After inspection, the
`The resist composition preferably has a glass transi
`resist layer can be stripped, if desired, without affecting
`tion temperature of less than about 75‘ C. It is believed
`the planarizing layer. Furthermore, the pattern can be
`that the uptake and/ or diffusion of the silylating agent is
`conveniently inspected after silylation. The critical
`facilitated by lower glass transition temperatures and by
`lithographic properties of the silylated etch mask
`the presence of —COOH groups.
`formed, such as critical line width and alignment are
`In accordance with the invention, a planarizing layer
`20
`readily measurable, whereas in the case of imagewise
`resistant to silicon uptake is formed on a substrate. As
`silylation of a single layer system, they are not.
`used herein “substrate” includes semiconductor sup
`The developed resist optionally is exposed to a UV
`ports, including, if desired, various levels of, for exam
`light source to enhance silicon uptake prior to contact
`ple, metallization, doped semiconductor material and
`ing the resist with the silicon-containing compound.
`/or insulators. For the manufacture of integrated circuit
`The wafer can be ?ood exposed conveniently for a
`devices, silicon or silicon dioxide wafers, as well as
`fraction of a second up to several minutes to a UV light
`silicon nitride and chromium-coated glass plate sub
`from a suitable exposure source as illustrated in the
`strates are particularly useful. Depending upon the sup
`following examples. In some embodiments of the inven
`port selected, adhesion aids are optionally applied ?rst
`tion, an exposure time from 5 to 40 seconds is preferred.
`as a sub-coating.
`After development, and optionally, exposure to a UV
`The planarizing layer is selected to be resistant to
`light source, the resist is contacted with a vapor com
`silicon uptake. Conventional planarizing layers such as
`prising a silicon containing compound to effect silyla
`thermally crosslinked novolacs, poly(methyl methacry
`tion of the resist and thereby render it etch resistant.
`late), poly(methyl isopropenyl ketone), polyimides and
`Silylation can be conveniently accomplished by placing
`polydimethylglutarimide are useful herein. The thick
`the wafer on a temperature controlled platen in a vac‘
`ness of the planarizing layer preferably is less than 10
`uum oven. The system can be evacuated by conven
`pm. The planarizing layer must be removable with an
`tional means. The silicon-containing compound in
`oxygen plasma but not appreciably dissolve in the sol
`vapor form can then be introduced, optionally, if de
`vent utilized to form the imaging layer.
`sired, with an inert carrier gas such as N2. After silylat
`In addition to the planarizing layer, or admixed there
`ing for the desired time, the system can be flushed, and
`with, there can be present one or more dye-containing
`the wafer removed. As noted, a particularly advanta
`antireflection layers, contrast enhancing layers or etch
`geous feature of the present invention is that convenient
`stop layers.
`device processing is afforded. For example, silylation
`Conventional methods can be used to apply the
`suf?cient to yield good etch resistance can be accom
`planarizing layer to the substrate and the resist to the
`plished in less than 2 hours, and as indicated by the
`planarizing layer. The preferred method is as a coating
`examples which follow, in most instances in 10 minutes
`using an appropriate solvent. Useful coating techniques
`or less.
`include spin-coating, spray coating, and roll coating.
`The silicon-containing compound useful herein pref
`The solvent used to prepare the compositions for coat
`erably has the formula set forth in the summary above,
`ing can be selected from any conventional coating sol
`wherein Xl and X2 are individually chloro or
`vent. Useful solvents include alcohols, esters, ethers,
`ketones, and, particularly, ethanol, 2-ethoxyethyl ace
`tate, n-butyl acetate, 4-butyrolactone, chlorobenzene
`and mixtures thereof.
`The equipment used to imagewise expose the resist is
`conventional. The method is particularly useful in con
`junction with electron beams or exposure sources emit
`ting at from 250 to 450 nm. The exposure times vary
`depending on the desired results and equipment and
`materials used, preferred times being in the range of
`60
`about 1 in sec. to about 90 sec.
`Development of the resist is accomplished by con
`tacting the exposed resist with a suitable developer.
`Suitable developers include tetramethylammonium hy
`droxide, tetraethylammonium hydroxide, methyltrie
`thanol ammonium hydroxide, sodium hydroxide, am
`monium hydroxide, potassium hydroxide, sodium car
`bonate, sodium silicate, sodium phosphate, hexane, cy
`
`wherein R3 and R4 are individually H or alkyl, prefera
`bly containing from 1 to 3 carbon atoms, such as
`methyl, ethyl and propyl; and RI and R2 are individu
`ally H or alkyl, preferably containing from 1 to 3 carbon
`atoms, such as methyl, ethyl and propyl. As noted, these
`silicon-containing compounds (referred to herein also as
`silylating agents) produce high resolution patterned
`resist images which have excellent etch resistance and
`superior thermal and dimensional stability.
`Preferred silylating agents useful in the method of
`this invention include:
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`4,931,351
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`etched for an additional 7 min. to complete etching of
`the planarizing layer. The silylated resist did not flow,
`evidencing superior dimensional stability.
`Example 1 was repeated except that the silylating
`agent was hexamethyldisilazane and the silylating con
`ditions were milder (10 min. at 80 torr.). The resist
`?owed signi?cantly, evidencing dimensional instability.
`
`5
`(a) dichlorodimethylsilane,
`(b) dichloromethylsilane,
`(c) bis(dimethylamino)dimethylsilane,
`(d) bis(dimethylamino)methylsilane,
`(e) dimethylamino chlorodimethylsilane, and
`(f) dimethylamino chloromethylsilane.
`Preferred silylating agents include those having the
`structural formula above wherein at least one of R1, R2,
`R3 and R4 is H. These compounds provide superior
`silylation at lower temperatures and pressures than
`other silanes. Although the mechanism is not well un
`derstood, it is believed that the reactivity and/or ab
`sorptivity of these compounds is facilitated by the pres
`ence of the hydrogen atom. High preferred examples of
`such silylating agents include (b), (d) and (i) noted
`above.
`The imaged bilayer containing the silylated resist is
`contacted with an oxygen plasma so as to preferentially
`remove portions of the planarizing layer by methods
`which are conventional in the art. Pattern transfer can
`be accomplished by an oxygen plasma etch. In a pre
`ferred embodiment, pattern transfer is by an oxygen
`plasma reactive ion etch (Or-RIB). We have found
`that an O2—RIE provides side walls which are
`straighter and more uniform than with a conventional
`wet or oxygen plasma development. Reactive ion etch
`ing and oxygen plasma etching are described by S. J.
`Jonash in “Advances in Dry Etching Processes-A
`Review,” Solid State Technologv, January 1985, pages
`150-158 and the references cited therein.
`
`5
`
`25
`
`EXAMPLE 2
`Example 1 was repeated except that the silylation
`conditions were increased to 93° C. for 135 min. at 150
`torr. Again the silylated 809 resist showed no evidence
`of ?ow either after silylation or after the 3 min. etch.
`The etch rate was reduced to about 110 A/min.
`
`EXAMPLE 3
`Demonstration of Temperature Stability
`Example 1 was repeated except that the silylation was
`at 93° C. for 10 min. at 150 torr. The silylated resist
`showed no evidence of flow after silylation or after the
`etch. The etch rate of the wafer was about 117 A/ min.
`A wafer prepared as described in the preceding para
`graph was placed on a coating-track hot plate for two
`minutes at a time, for an increasing series of tempera
`tures. After each bake, the patterned wafer was ob
`served with an optical microscope. The DCMS-treated
`wafer showed no evidence of flow at hot plate tempera
`tures as high as 160° C.
`
`COMPARATIVE EXAMPLES
`A wafer prepared as described in Example 1 except
`not treated with a silylating agent ?owed at 110° C.
`The silylation of Example 3 was repeated except that
`the silylating agent was chlorotrimethylsilape. The etch
`rate of the silylated resist was over 830 A/min., evi
`dencing poor etch resistance. Furthermore, the resist
`?owed significantly, evidencing dimensional instability.
`EXAMPLES 4-13
`Effect of Flood Exposure
`Example 1 was repeated except that the silylating
`agents were bis(dimethylamino)dimethylsilane and bis(
`dimethylamino)methylsilane. The silylating conditions
`were 90° C. for 15 min. at 100 torr.°The etch rates of the
`silylated resist were 508 and 197 A/min., respectively.
`The resists did not flow. When the wafers were flood
`exposed for 5 seconds to UV light from a Hybrid Tech
`nology Group (HTG) exposure source with the near
`UV mirrors installed (an irradiance of 59 mw/cm2 was
`measured with an HTG Model 100 power meter using
`the 405 nm probe), the etch rates dropped to 326 and 76
`A/min. About the same etch rates resulted from a 40
`second exposure under the same conditions.
`Example 3 was repeated except that the resists were
`?ood exposed in the manner described abovp for 5 and
`40 seconds. The etch rates were 91 and 41 A/ min.
`When the resist of Example 1 was similarly ?ood
`exposed, the etch rate was not appreciably affected.
`
`EXAMPLES 14-16
`Silylation with Dichlorodimethylsilane
`Example 1 was repeated except that the silylating
`agent was dichlorodimethylsilane and the silylation was
`at 100° C., 190 torr. for 90 min. The silylated resist
`(‘Example 14) did not ?ow. The etch rate was 276
`A/min.
`
`r
`
`EXAMPLES
`The following examples further illustrate the inven
`tion.
`
`EXAMPLE 1
`Silylation with Dichloromethylsilane
`A silicon wafer was coated with Kodak KMPR-820
`resist, prebaked, and then hardbaked at 275° C. for 90
`sec. on a track hotplate to produce a planarizing layer
`?lm about 1.0 pm thick. KMPR-809 photoresist (20%
`solids) was then coated over the planarizing layer and
`prebaked at 90° C. for 30 mip. in a convection oven. The
`resist layer was about 4000 A thick. The wafer was then
`repeatedly exposed to the image of a resolution target
`using a Censor SKA-200 wafer stepper (405 nm,
`NA=0.28) in a range of exposures from 55 mJ/cm2 to
`145 mJ/cm2. The wafer was then developed for 40 sec.
`at room temperature in Kodak ZX~934 developer di
`luted to 35% and rinsed in deionized water. Lines and
`spaces as small as 0.6 nm were resolved. The wafer was
`then silylated in a modi?ed vacuum oven as follows:
`The wafer was placed in the oven on a platen main
`tained at 75° C. The oven was pumped down for one
`minute to a pressure of 330 millitorr. Dichloromethylsi
`lane (DCMS) vapor was then admitted into the oven
`and the wafer was silylated for 25 min. at a DCMS
`pressure of 110 torr. The oven was pumped out and
`back-?lled with nitrogen twice, and the wafer was re
`moved. The wafer was then etched for three minutes in
`an O2-RIE etch of a MRC 51 plasma reactor. The
`conditions were 50 sccm of Oz flow, 150 millitorr of
`pressure, and 200 volts DC bias. The etch rate, deter
`mined by ?lm thickness measurements, was about 175
`A/min. Theounsilylated KMPR-809 etch rate is about
`1000-1100 A/min. The etch rate for the planarizing
`layer was also about l000—1l00 A/min. and was essen
`tially unchanged by the treatment. The wafer was
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`7
`Example 14 was repeated except that the wafers con—
`taining the developed resist were ?ood exposed to UV
`light for 5 and 40 seconds, as described above. The etch
`rates were 119 and 126 A/mim, respectively. The sily
`lated resists did not flow.
`
`EXAMPLES 17-19
`
`Effect of Photoresist
`
`wherein:
`X1 and X2 are individually chloro or
`
`Example 3 was repeated except that HPR 204 was
`used in place of KMPR 809. The silylated resist showed
`no evidence of flow after silylation or after the etch.
`The silylated resist (Example 17) had an etch rate of
`about 69 A/min.
`Example 17 was repeated except that wafers contain
`ing the developed resist were flood-exposed to a UV
`light source for 5 and 40 seconds. The etch rates were
`18 and 15 A/min, respectively. The resists did not ?ow.
`
`wherein R3 and R4 are individually H or alkyl
`containing from 1 to 3 carbon atoms; and R1 and
`R2 are individually H or alkyl containing from 1
`to 3 carbon atoms; and wherein at least one of
`R1, R2, R3 and R4 is H; and
`(f) contacting said planarizing layer with an oxygen
`containing plasma so as to preferentially remove
`portions thereof.
`2. The method of claim 1 wherein said developed
`resist is exposed to a UV light source prior to contacting
`said resist with said silicon-containing compound.
`3. The method of claim 1 wherein said silicon-con
`taining compound is selected from the group consisting
`of dichloromethylsilane, bis(dimethylamino)methylsi
`lane, and dimethylamino chloromethylsilane.
`4. The method of claim 1 wherein said resist has a
`glass transition temperature of less than about 75° C.
`5. The method of claim 1 wherein said resist com
`prises a novolac resin.
`5. The method of claim 1 wherein portions of said
`planarizing layer are preferentially removed by an oxy
`gen reactive ion etch.
`7. A method for producing a patterned high resolu
`tion, thermally and dimensionally stable resist image on
`a substrate comprising the steps of:
`(a) forming a planarizing layer resistant to silicon
`uptake on a substrate,
`(b) providing a positive-working photoresist compo
`sition containing —OH or —-—NH—— groups over
`said planarizing layer,
`(0) imagewise exposing said resist to activating radia
`tion,
`(d) developing said exposed resist,
`(e) contacting said developed resist with a vapor
`comprising dimethylamino chlorodimethylsilane
`for a time less than 2 hours to effect silylation
`thereof and thereby impart etch resistance, and
`(f) contacting said planarizing layer with an oxygen
`containing plasma so as to preferentially remove
`portions thereof.
`
`# i i i i
`
`EXAMPLE 20
`Effect of Planarizing Layer
`A planarizing layer of poly(methyl methacrylate)
`subjected to the silylation conditions of Example 3 had
`an etch rate of 1601 A/ min. Under the same conditions,
`the etch rate of the KMPR-820 was 1052 A/min. As is
`evident, excellent etch selectivities can be obtained.
`The invention has been described in detail with par
`ticular reference to preferred embodiments thereof, but
`it will be understood that variations and modi?cations
`can be effected within the spirit and scope of the inven
`tion.
`What is claimed is:
`1. A method for producing a patterned high resolu
`tion, thermally and dimensionally stable resist image on
`a substrate comprising the steps of:
`-
`(a) forming a planarizing layer resistant to silicon
`uptake on a substrate,
`(b) providing a positive-working photoresist compo
`sition containing —OH or —-NH- groups over
`said planarizing layer.
`(c) imagewise exposing said resist to activating radia
`tion,
`(d) developing said exposed resist,
`(e) contacting said developed resist with a vapor
`comprising a silicon-containing compound for a
`time less than 2 hours to effect silylation thereof
`and thereby impart etch resistance, said silicon
`containing compound having the structural for
`mula:
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