United States Patent [19]
`Pan et al.
`
`USOO5533634A
`[11] Patent Number:
`[45] Date of Patent:
`
`5 533 634
`9
`9
`Jul. 9, 1996
`
`[54] QUANTUM CHROMELESS LITHOGRAPHY
`
`[75] Inventors: Hong-Tsz Pan, Chang-hua;
`Ming-Tzong Yang; Shyi-Long Shy,
`
`5,194,345
`5,194,346
`5,208,125
`5,217,830
`
`3/1993 Rolfson ..................................... .. 430/5
`3/1993 Rolfson et al.
`430/5
`5/1993 Lowrey 6t 31-
`430/5
`6/1993 Lowrey . . . . .
`. . . . .. 430/5
`
`both of Hsinchu,
`
`of
`
`
`
`ROlfSOIl ................................. .. OTHER PUBLICATIONS
`
`[73] Assignee: United Microelectronics Corporation,
`Hsinchu, Taiwan
`
`[21] Appl. No.: 299,458
`[22] Filed;
`Sep_ 1, 1994
`
`6
`[51] Int. Cl. ...................................................... ..
`[52] US. Cl. ................................ .. 216/12; 216/24; 216/67
`[58] Field of Search ................................ .. 216/11, 12, 24,
`216/45’ 67; 156/6431, 657-1’ 659-11’ 345;
`430/5, 323
`
`B44C 1/22
`
`[56]
`
`_
`References Clted
`Us PATENT DOCUMENTS
`
`,
`
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`Taneya 6t
`gkahnilgm
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`
`“Lithography’s Leading Edge—-Pa1t I: Phase-Shift Technol
`ogy” pub. in Semiconductor International Feb. 1992 pp.
`4247
`Primary Examiner——-William Powell _
`Attorney, Agent, or F zrm—George 0. $3116; Larry J. Prescott
`
`ABSTRACT
`1571
`This invention describes the use and methQd of fabrication
`of a chromeless quantum phase shift mask and of a chrome
`less quantum phase shift build-0n blank. The build-on blank
`can be readily inspected, stored for future use, and com
`pleted with a feature pattern when needed. The quantum
`phase shift mask provides improved image resolution and
`depth of focus tolerance. The quantum phase shift mask
`requires
`or no
`or computer
`design, modi
`?cation over that used for conventional masks.
`
`5,190,836
`
`3/1993 Nakagawa et al. . . . . .
`
`. . . . . . . . . . .. 430/5
`
`5,194,344
`
`3/1993 Cathey, Jr. et al. ...................... .. 430/5
`
`28 Claims, 7 Drawing Sheets
`
`111
`
`27
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`1141 1
`29\
`
`21
`
`

`

`US. Patent
`
`Jul. 9, 1996
`
`Sheet 1 0f 7
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`5,533,634
`
`FIG.1
`
`27
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`MMWM
`4
`
`FIG. 2
`
`

`

`US. Patent
`
`Jul. 9, 1996
`
`Sheet 2 0f 7
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`5,533,634
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`29..
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`/
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`233295
`
`FIG.
`
`3
`
`A
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`4-7
`
`4-9
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`51
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`Em m ._
`
`FIG.
`
`4
`
`FIG.
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`5
`
`55
`
`/53
`
`

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`US. Patent
`
`Jul. 9, 1996
`
`Sheet 3 of 7
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`5,533,634
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`33
`25
`27
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`2
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`21
`
`FIG. 6
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`?mmmmmmmmmrjg
`
`\27
`
`‘ 2
`
`21
`
`' FIG. 7
`
`29
`
`2% FLELE] Fl Fl K 27
`21
`(
`
`FIG. 8
`
`

`

`US. Patent
`
`Jul. 9, 1996
`
`Sheet 4 of 7
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`5,533,634
`
`FIG. 9
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`i
`
`2
`
`21
`
`FIG. 10
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`/-—35
`
`27
`
`

`

`US. Patent 1
`
`Jul. 9, 1996
`
`Sheet 5 of7
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`5,533,634
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`29
`
`A
`
`W
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`33
`
`,/77
`(
`
`FIG. 11
`
`ii
`
`I‘
`
`7
`
`FIG. 12
`
`

`

`US. Patent
`
`Jul. 9, 1996
`
`Sheet 6 of 7
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`5,533,634
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`55
`25
`27
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`27
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`&\\\\\\\\\\\\\\\\\\\\\\\\‘9‘
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`2
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`21
`
`FIG. 13
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`2
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`21
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`FIG. 14
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`31
`FIG. 15
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`\
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`* ‘?
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`

`

`U.S. Patent
`U.S. Patent
`
`Jul. 9, 1996 »
`Jul. 9, 1996 >
`
`Sheet 7 of 7
`Sheet 7 of 7
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`5,533,634
`5,533,634
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`ala-
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`FIG. 16
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`76
`
`DSS-2001 /Page 8 of 12
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`

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`5,533,634
`
`1
`QUANTUM CHROMELESS LITHOGRAPHY
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`The invention relates to the use of a phase shifting mask
`to improve resolution in the fabrication of sub-micron
`integrated circuits and more particularly to the fabrication
`and use of a quantum phase shift mask without chrome and
`a quantum phase shift build-on blank without chrome. The
`quantum phase shift build—on blank is readily inspected and
`can be easily stored for later completion and use.
`2. Description of Related Art
`As optical lithography advances to 0.5 to 0.35 microns
`and below new technologies are needed to improve the
`resolution of the imaging lens. Phase-shifting photomasks
`have been used to improve resolution as well as depth of
`focus. The use of phase-shiftinglphotomasks are described in
`a number of places, for example U.S. Pat. No. 5,045,417 to
`Okamoto or U.S. Pat. No. 5,268,244 to Yoo. A transparent
`coating of thickness t=0.5L/(n-1) (L=wavelength, n=index
`of refraction) is placed on a mask. The phase of the electric
`?eld of the light passing through the coated area is delayed
`180° compared to the electric ?eld of light passing through
`uncoated regions. At the boundary between the coated and
`uncoated regions the electric ?elds cancel producing an
`electric ?eld null as well as an intensity null. This intensity
`null produces a sharper image as well as improved depth of
`focus at the integrated circuit wafer.
`Phase shifting techniques have been described using
`several con?gurations. U.S. Pat. No. 5,190,836 to Nakagawa
`et a1 describes a re?ection type photomask using phase
`shifting techniques. U.S. Pat. No. 5,194,345 to Rolfson
`describes rim phase shifters wherein phase shifting material
`is deposited on top of opaque material and extends beyond
`the opaque material in an overhang con?guration thereby
`improving image resolution. U.S. Pat. No. 5,194,344 to
`Cathey, Jr. et al, U.S. Pat. No. 5,194,346 to Rolfson et al,
`U.S. Pat. No. 5,208,125 to Lowrey et al, U.S. Pat. No.
`5,217,830 to Lowrey, and U.S. Pat. No. 5,225,035 to Rolf
`son describe various types of phase shifting masks and
`techniques. “LITHOGRAPHY’S LEADING EDGE, PART
`1: PHASE-SHIFT TECHNOLOGY” published in Semicon
`ductor International February 1992 pages 42-47 shows a
`number of phase shifting masks and techniques including a
`chromeless shifter.
`While improvements have been made in image resolution
`and depth of ?eld, the linear dimensions used in integrated
`circuit technology call for even greater improvements in
`resolution and increased depth of ?eld.
`
`SUMMARY OF THE INVENTION
`
`It is a principle object of this invention to provide a
`quantum phase shift build-on blank without chromium
`which can be readily inspected. Masks are then formed from
`these build-on blanks for use in the fabrication of integrated
`circuits where superior image resolution is required. The
`build-on blanks can be easily and accurately inspected and
`they can be formed and stored until they are needed for mask
`formation.
`It is a further object of the invention to provide a quantum
`phase shift mask without chromium for use in the fabrication
`of integrated circuits where superior image resolution is
`required.
`
`2
`It is a further object of the invention to provide a method
`for forming a quantum phase shift build-on blank without
`chromium.
`It is a further object of the invention to provide a method
`of forming a quantum phase shift mask without chromium
`for use in fabrication of integrated circuits where improved
`image resolution is required. The CAD, or computer aided
`design, modi?cations required to form the quantum phase
`shift mask rather than a conventional photomask are easier
`than modi?cations required to form a conventional phase
`shift mask.
`It is a further object of the invention to provide a method
`of forming a quantum phase shift mask without chromium
`from a quantum phase shift build-on blank which has been
`previously formed, inspected, and stored. The CAD, or
`computer aided design, used for conventional masks can be
`used with little or no change in forming this mask.
`These objectives are accomplished by forming a build~on
`blank comprised of a layer of an array of areas of phase
`shifting material adjacent to areas of no phase shifting
`material on a quartz substrate. The areas of phase shifting
`material and areas of no phase shifting material are about 0.1
`to 0.5 microns by 0.1 to 0.5 microns. These blanks have the
`advantage of being easily inspected due to the regular nature
`of the array and can be stored until needed. Then a mask is
`formed by forming a feature pattern in the layer of an array
`of areas of phase shifting material adjacent to areas of no
`phase shifting material. When the mask is used light is
`projected through the mask onto an integrated circuit wafer
`using a 5X stepper so that the pattern is reduced by ?ve
`times. The areas of phase shifting material and no phase
`shifting material project areas of about 0.02 to 0.1 microns
`by 0.02 to 0.1 microns at the wafer surface. Interference
`between the light passing through areas of phase shifting
`material and light passing through adjacent areas of no phase
`shifting material causes an intensity null corresponding to
`the feature pattern at the wafer surface. The image resolution
`is improved by about 30% compared to that achieved using
`a conventional mask.
`The objectives are also achieved by forming a mask
`comprising a feature pattern of an array of areas of phase
`shifting material adjacent to areas of no phase shifting
`material on a quartz substrate. The use of the mask in the
`fabrication of integrated circuit wafers then proceeds as
`described above.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`FIG. 1 shows the top view of a part of the quantum phase
`shift mask showing a part of the feature pattern.
`FIG. 2 shows a cross sectional view at 2—2' of the
`quantum phase shift mask.
`FIG. 3 shows the amplitude of the light passing through
`the quantum phase shift mask.
`FIG. 4 shows the intensity of the light at the integrated
`circuit wafer.
`FIG. 5 shows the resulting positive photoresist pattern on
`the surface of the integrated circuit wafer.
`FIG. 6 shows a cross section of the build-on blank prior
`exposing the photoresist.
`FIG. 7 shows a cross section of the build-on blank after
`the photoresist has been exposed and developed.
`FIG. 8 shows a cross section of the build-on blank after
`the pattern has been formed in the phase shifting material.
`FIG. 9 shows a top view of the completed build~on blank.
`
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`5,533,634
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`3
`FIG. 10 shows a cross section of the build-on blank with
`photoresist formed on the surface prior to forming a quan
`tum phase shift mask.
`FIG. 11 shows a cross section of the build-on blank with
`photoresist which has been exposed and developed on the
`surface.
`FIG. 12 shows a cross section of a completed quantum
`phase shift mask formed from a build-on blank.
`FIG. 13 shows a cross section of the quantum phase shift
`mask prior to exposing the photoresist.
`FIG. 14 shows a cross section of the quantum phase shift
`mask after the photoresist has been exposed and developed.
`FIG. 15 shows a cross section of the completed quantum
`phase shift mask.
`FIG. 16 shows the top view of the completed quantum
`phase shift mask.
`
`DESCRIPTION OF THE PREFERRED
`EMBODIMENTS
`
`Refer now to FIG. 1 through FIG. 5, there is shown an
`embodiment of the quantum phase shift mask without chro
`mium. FIG. 1 shows a top view of the mask with a feature
`pattern 31 of a layer of alternating areas of phase shifting
`material such as SiO2 27 with a thickness between about
`3000 Angstroms and 5000 Angstroms adjacent to areas of no
`phase shifting material 29. FIG. 2 shows a cross section of
`this feature pattern showing the areas of SiO2 adjacent to
`areas of no phase shifting material. The areas of SiO2 and of
`the no phase shifting material areas are about 0.1 to 0.5
`microns by 0.1 to 0.5 microns. Light 45 is projected through
`the quantum phase shift mask onto the surface of the
`integrated circuit wafer. FIG. 3 shows the amplitude of the
`light passing through the SiO2 47 and the amplitude of the
`light passing through no phase shifting material 49 at the exit
`of the mask. FIG. 4 shows the light intensity 51 at the surface
`of the integrated circuit wafer. A 5>< stepper is used so that
`the pattern is reduced ?ve times at the surface of the wafer.
`An intensity null is caused by the interference between the
`phase shifted light and the non phase shifted light. FIG. 5
`shows a cross section of the resulting positive photoresist
`pattern 55 on the surface of the integrated circuit wafer 53.
`The quantum phase shift mask produces improved image
`resolution and depth of focus tolerance at the wafer surface.
`Refer now to FIG. 8 and FIG. 9, there is shown an
`embodiment of the quantum phase shift build-on blank
`without chromium. FIG. 8 shows a cross section of the
`build-on blank showing a layer of etching stopper material
`23 such as A1203 with a thickness between about 100
`Angstroms and 500 Angstroms formed on a quartz substrate
`21 with a thickness between about 1 mm and 10 mm. A layer
`of alternating areas of phase shifting material 27 such as
`SiO2 and no phase shifting material 29 is formed on the layer
`of A1203 with a thickness of SiO2 between about 3000
`Angstroms and 6000 Angstroms. The dimensions of the
`SiO2 27 and non phase shifting material 29 areas are
`between about 0.1 and 0.5 microns by between about 0.1 and
`0.5 microns. When focused on the surface of the integrated
`circuit wafer the pattern will be reduced ?ve times. FIG. 9
`shows the top view of the build-on blank showing the areas
`of SiO2 27 and non phase shifting material 29. The regular
`array of the phase shifting material 27 and no phase shifting
`material 29 greatly simpli?es the inspection of the build-on
`blank. The build-on blank can be stored until needed for
`integrated circuit fabrication at which time a feature pattern
`is formed in the layer of alternating areas of phase shifting
`
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`material and areas of no phase shifting material. The mask
`is then used to project a pattern on an integrated circuit wafer
`surface as described in the previous embodiment.
`Refer now to FIG. 6 through FIG. 9, there is shown an
`embodiment of a method of forming the quantum phase shift
`build-on blank. FIG. 6 shows cross section of the build-on
`blank prior to exposing the photoresist 33. A layer of etching
`stopper material 23 such as A1203 with a thickness between
`about 100 Angstroms and 500 Angstroms is formed on a
`quartz substrate 21 with a thickness between about 1 mm
`and 10 mm. A layer of phase shifting material 27 such as
`SiO2 with a thickness of between about 3000 Angstroms and
`5000 Angstroms is formed on the layer of etching stopper
`material. A layer of antistatic material 25 such as A1203 with
`a thickness between about 100 Angstroms and 500 Ang
`stroms is formed on the layer of SiO;. A layer of photoresist
`33 is formed on the layer of antistatic material 25.
`As shown in FIG. 7 the photoresist layer 33 is then
`exposed using electron beam techniques and developed. As
`shown in FIG. 8 the alternating areas of SiO2 27 and no
`phase shifting material 29 are etched in the layer of SiO2 27
`by means of reactive ion etching, the photoresist is stripped,
`and the build-on blank is ready to be used or stored. FIG. 9
`shows the top view of the build~on blank. The areas of phase
`shifting material and no phase shifting material are between
`about 0.1 and 0.5 microns by between about 0.1 and 0.5
`microns. A 5X stepper will be used to focus the pattern on the
`surface of an integrated circuit so that the pattern will be
`reduced ?ve times at the surface of the integrated circuit.
`Refer now to FIG. 10 through FIG. 12, there is shown an
`embodiment for forming the quantum phase shift mask
`starting with the build-on blank. FIG. 10 shows a cross
`section of the build-on blank with photoresist 33 formed
`over the entire surface. As shown in FIG. 11 the photoresist
`33 is exposed using electron beam techniques and devel»
`oped. The feature pattern is then etched in the alternating
`areas of SiO2 27 and no phase shifting material 29 by means
`of reactive ion etching as shown in FIG. 12 and the quantum
`phase shift mask has been completed. Little or no modi?
`cation to the CAD, computer aided design, used for a
`conventional mask is necessary.
`Refer now to FIG. 13 through FIG. 16, there is shown an
`embodiment of a method of forming the quantum phase shift
`mask. FIG. 13 shows cross section of the mask prior to
`exposing the photoresist. A layer of etching stopper material
`23 such as A1203 with a tlu'ckness between about 100
`Angstroms and 500 Angstroms is formed on a quartz sub
`strate 21 with a thickness between about 1 mm and 10 mm.
`A layer of phase shifting material 27 such as SiO2 with a
`thickness of between about 3000 Angstroms and 6000
`Angstroms is formed on the layer of etching stopper material
`23. A layer of antistatic material 25 such as A1203 with a
`thickness between about'lOO Angstroms and 500 Angstroms
`is formed on the layer of SiO2. A layer of photoresist 33 is
`formed on the layer of antistatic material 25. As shown in
`FIG. 14 the feature pattern is exposed on the photoresist 33
`using electron beam techniques and the photoresist 33 is
`developed. As shown in FIG. 15 the feature pattern is then
`etched in the layer of SiO2 27 by means of reactive ion
`etching and the photoresist is stripped completing the mask.
`FIG. 16 shows the top view of the completed mask. The
`feature pattern 31 is comprised of alternating areas of phase
`shifting material 27 adjacent to areas of no phase shifting
`material 29. The areas of phase shifting material and no
`phase shifting material are between about 0.1 and 0.5
`microns by between about 0.1 and 0.5 microns. The mask
`will be focussed on the surface of an integrated circuit wafer
`
`

`

`5,533,634
`
`5
`using a 5X stepper so the pattern will be reduced ?ve times
`at the surface of the wafer.
`While the invention has been particularly shown and
`described with reference to the preferred embodiments
`thereof, it will be understood by those skilled in the art that
`various changes in form and details may be made without
`departing from the spirit and scope of the invention.
`*What is claimed is:
`1. A method of forming a quantum phase shift mask,
`comprising the steps of:
`providing a transparent substrate;
`forming a layer of etching stopper material on said
`transparent layer;
`forming a layer of phase shifting material on said layer of
`etching stopper material;
`forming a layer of anti-static material on said layer of
`phase shifting material;
`forming a layer of photoresist on said layer of anti-static
`material;
`forming a photoresist feature pattern in said photoresist
`layer by means of exposing said photoresist using
`electron beam techniques and developing said photo
`resist, wherein said feature pattern is comprised of
`alternating areas of photoresist material adjacent to
`areas of no photoresist material;
`etching a phase shifting feature pattern in said phase
`shifting layer using said photoresist feature pattern as
`an etching mask, wherein said phase shifting feature
`pattern is comprised of alternating areas of phase
`shifting material adjacent to areas of no phase shifting
`material; and
`stripping said photoresist material.
`2. The method of claim 1 wherein said transparent sub
`strate is quartz with a thickness between about 1 mm and 10
`mm.
`3. The method of claim 1 wherein said phase shifting
`material is SiO2 with a thickness between about 3000
`Angstroms and 6000 Angstroms.
`4. The method of claim 1 wherein said phase shifting
`material is Si3N4 with a thickness between about 2000
`Angstroms and 5000 Angstroms.
`5. The method of claim 1 wherein said areas of phase
`shifting material are between about 0.1 and 0.5 microns by
`between about 0.1 and 0.5 microns.
`6. The method of claim 1 wherein said areas of no phase
`shifting material are between about 0.1 and 0.5 microns by
`between about 0.1 and 0.5 microns.
`7. The method of claim 1 wherein said layer of etching
`stopper material is A1203 with a thickness between about
`100 Angstroms and 500 Angstroms.
`8. The method of claim 1 wherein said layer of anti-static
`material is A1203 with a thickness of about 200 Angstroms.
`9. The method of claim 1 wherein said layer of anti-static
`material is FeO with a thickness of about 200 Angstroms.
`10. The method of claim 1 wherein said etching of said
`phase shifter feature pattern is accomplished by means of
`reactive ion etching.
`11. A method of forming a quantum phase shift build-on
`blank, comprising the steps of:
`providing a transparent substrate;
`forming a layer of etching stopper material on said
`transparent layer;
`forming a layer of phase shifting material on said layer of
`etching stopper material;
`forming a layer of anti-static material on said layer of
`phase shifting material;
`
`6
`forming a layer of photoresist on said layer of anti-static
`material;
`forming a pattern in said photoresist layer by means of
`exposing said photoresist using electron beam tech
`niques and developing said photoresist, wherein said
`pattern is comprised of alternating areas of photoresist
`material adjacent to areas of no photoresist material;
`etching a pattern in said phase shifting layer using said
`pattern in said photoresist layer as an etching mask,
`wherein said pattern in said phase shifting layer is
`comprised of alternating areas of phase shifting mate
`rial adjacent to areas of no phase shifting material; and
`stripping said photoresist material.
`12. The method of claim 11 wherein said transparent
`substrate is quartz with a thickness between about 1 mm and
`10 mm.
`13. The method of claim 11 wherein said phase shifting
`material is SiO2 with a thickness between about 3000
`Angstroms and 6000 Angstroms.
`14. The method of claim 11 wherein said phase shifting
`material is Si3N4 with a thickness between about 2000
`Angstroms and 5000 Angstroms.
`15. The method of claim 11 wherein said areas of phase
`shifting material are between about 0.1 and 0.5 microns by
`between about 0.1 and 0.5 microns.
`16. The method of claim 11 wherein said areas of no phase
`shifting material are between about 0.1 and 0.5 microns by
`between about 0.1 and 0.5 microns.
`17. The method of claim 11 wherein said layer of etching
`stopper material is A1203 with a thickness between about
`100 Angstroms and 500 Angstroms.
`18. The method of claim 11 wherein said layer of anti
`static material is AlZO3 with a thickness of about 200
`Angstroms.
`_
`19. The method of claim 11 wherein said layer of anti
`static material is FeO with a thickness of about 200 Aug
`stroms.
`20. The method of claim 11 wherein Said etching of said
`pattern in slid phase shifting layer is accomplished by means
`of reactive ion etching.
`21. A method of forming a quantum phase shift mask,
`' comprising the steps of:
`providing a quantum phase shift build-on blank com
`prised of a transparent substrate, a layer of etching
`stopper material formed on said transparent substrate,
`and a layer of alternating areas of phase shifting
`material adjacent to areas of no phase shifting material
`formed on said layer of etching stopper material;
`forming a layer of photoresist on said build-on blank;
`forming a feature pattern in said layer of photoresist by
`means of exposing said photoresist using electron beam
`techniques and developing said photoresist;
`forming said feature pattern on said build-on blank by
`means of etching away said phase shifting material not
`covered by said feature pattern in said layer of photo
`resist; and
`stripping said layer of photoresist.
`22. The method of claim 21 Wherein said transparent
`substrate is quartz with a thickness between about 1 mm and
`10 mm.
`23. The method of claim 21 wherein said phase shifting
`material is SiO2 with a thickness between about 3000
`Angstroms and 6000 Angstroms.
`24. The method of claim 21 wherein said phase shifting
`material is Si3N4 with a thickness between about 2000
`Angstroms and 5000 Angstroms.
`
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`8
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`stopper material is A1203 with a thickness between about
`25. The method of claim 21 wherein said areas of phase
`100 Angstroms and 500 Angstroms.
`shifting material are between about 0.1 and 0.5 microns by
`28. The method of claim 21 wherein said etching of said
`between about 0.1 and 0.5 microns.
`feature pattern in said phase shifting layer is accomplished
`26. The method of claim 21 wherein said areas of no
`phase shifting material are between about 0.1 and 0.5 5 by means of reactive ion etching.
`microns by between about 0.1 and 0.5 microns.
`27. The method of claim 21 wherein said layer of etching
`
`* * *
`
`* *
`
`