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`5,091,047
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`Feb. 25, 1992
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`Ulllted States Patent
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`Cleeves et al.
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`[19]
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`US005091047A
`[11] Patent Number:
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`[45] Date of Patent:
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` .
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`[54] PLASMA ETCHING USING A BILAYER
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`MASK
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`[75]
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`Inventors:
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`James M. Cleeves, Redwood City;
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`James G. Heard; Zoilo c. H. Tan,
`both Of Cupertino, all of Calif.
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`[73] A5513"66' Sggmégffémndmm corp" sama
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`[21] Appl‘ No" 733,473
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`[22] Filed:
`Jul. 22, 1991
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`Related US. Application Data
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`Division of Ser No 210‘ 2“ Jun‘ 17 1988 Pat No
`5,045,150
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`'
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`’
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`’
`'
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`’
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`[62]
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`[51]
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`Int. Cl.5 ...................... .. B44C 1/22; c03C 15/00;
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`C03C 25/06; C23F'1/00
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`[52] US. Cl. .................................. .. 156/643; 156/646;
`156/653; 156/656; 156/657; 156/659.1;
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`l56/661.1; 156/904; 204/ 192.37
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`[58] Field of Search ............. .. 156/643, 646, 653, 656,
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`156/657, 659.1, 661.1, 904; 204/192.32, 192.37;
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`252/79.l; 427/38, 39
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`[56]
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`References Cited
`US, PATENT DOCUMENTS
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`5/1978 Hoepfner ..................... 156/661.1X
`4,092,210
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`4,484,978 11/1984 Keyser ................................ 156/643
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`Primary Examiner——-William A. Powell
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`Attorney, Agent, or Firm—Townsend and Townsend
`
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`ABSTRACT
`[57]
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`A bilayer mask is utilized for etching a primary layer,
`which may be either an aluminum metallization layer or
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`a dielectric layer. The bilayer mask includes both a thin
`resist layer and a metal imaging layer. The thin resist
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`layer provides for high resolutiOn patterning of the
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`metal imaging layer. The metal imaging layer, in turn,
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`provides for durability to withstand subsequent plasma
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`etching of the underlying primary layer.
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`7 Claims, 1 Drawing Sheet
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`Page 1 0f 4
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`TSMC Exhibit 1034
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`TSMC v. IP Bridge
`IPR2016-01379
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`TSMC Exhibit 1034
`TSMC v. IP Bridge
`IPR2016-01379
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`US. Patent
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`Feb. 25, 1992
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`5,091,047
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`Page 2 of 4
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`PLASMA ETCHING USING A BILAYER MASK
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`1
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`5,091,047
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`This is a division of application Ser. No. 07/210,211
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`filed June 17, 1988, now US. Pat. No. 4,045,150.
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`BACKGROUND OF THE INVENTION
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`1. Field of the Invention
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`The present invention relates generally to the field of
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`semiconductor fabrication, and more particularly to a
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`method for plasma etching using a bilayer mask in order
`to define very small geometries on a semiconductor
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`substrate.
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`2. Description of the Background Art
`As the drive to increase device density continues, it
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`becomes increasingly necessary to be able to define
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`very small geometries on the surface of a semiconduc-
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`tor substrate. To form such small geometries, it is highly
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`. desirable to use very thin resist layers which provide for
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`precise replication of the projected masking pattern.
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`Image resolution and definition are lost as‘the thickness
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`of the photoresist layer increases.
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`The ability to utilize very thin photoresist layers,
`however, is limited by the need to provide a resist layer
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`25
`which is sufficiently thick to withstand the etching of
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`the underlying layer which is being patterned through
`the resist mask. In particular, plasma etching often re-
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`quires a relatively thick resist layer since it is a relatively
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`lengthy process and many etchant gases directly attack
`the resist material. For that reason, the resist layers used
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`as masks in plasma etching processes are often too thick
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`to allow for submicron geometries, as is frequently
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`desired.
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`For the above reasons, it would be desirable to pro-
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`vide methods which would combine the advantages of
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`a thin resist layer, i.e., high image resolution, definition,
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`and control, with the ability to withstand the relatively
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`harsh conditions associated with plasma etching.
`SUMMARY OF THE INVENTION
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`The present invention provides for high resolution
`plasma etching of a primary layer on a semiconductor
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`substrate and is particularly suitable for forming submi-
`cron geometries. The present invention utilizes a bilayer
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`mask, including a metal image layer formed over the
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`primary layer and a very thin resist layer formed di-
`rectly over the metal image layer. The thin resist layer
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`is patterned by conventional
`techniques, where the
`thinness of the layer allows for a very high resolution
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`and definition of the desired pattern. The resist mask is
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`then used to etch the metal image layer under condi-
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`tions which are highly selective for the metal over the
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`resist. The metal image layer mask is then used to pat-
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`tern the primary layer under more rigorous plasma etch
`conditions.
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`In a first exemplary embodiment, the primary layer is
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`aluminum and the metal image layer is chromium. The
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`chromium layer is patterned using the resist mask and a
`conventional wet chromium etchant, such as ceric am-
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`monium sulfate-based etchants. The resulting chromium
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`mask is then used to pattern the underlying aluminum
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`layer, typically with a chlorine plasma etch.
`In a second exemplary embodiment,
`the primary
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`layer is an organic or inorganic dielectric and the metal
`image layer is aluminum. The aluminum is wet or dry
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`etched using the thin layer resist as a mask, and the
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`patterned aluminum layer in turn acts as a mask for
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`plasma etching the dielectric. A fluorine plasma etch is
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`typically used with inorganic dielectric layers, such as
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`silicon oxide and silicon nitride, while an oxygen plasma
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`may be used with organic polymeric dielectrics.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`FIG. 1 illustrates a conventional semiconductor sub-
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`strate having a primary layer, a metal image layer, and
`a resist layer formed successively over its surface.
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`FIG. 2 illustrates the structure of FIG. 1, wherein the
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`resist layer has been patterned.
`FIG. 3 illustrates the structure of FIG. 2, wherein the
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`metal image layer has been patterned using the resist
`layer as a mask.
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`FIG. 4 illustrates the structure of FIG. 3, wherein the
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`primary layer has been patterned using the metal image
`layer as a mask.
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`DESCRIPTION OF THE PREFERRED
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`EMBODIMENTS
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`Referring generally to FIGS. 1—4, specific methods
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`will be described for fabricating semiconductor devices
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`according to the method of the present invention.
`Semiconductor devices are fabricated on silicon
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`wafer substrates 10 (a portion of one being illustrated in
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`FIGS. 14). Usually, the wafer will include a variety of
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`features (not illustrated) formed on its upper surface,
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`including transistors, resistors, capacitors, and the like.
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`According to the present invention, a primary layer
`12, which is either an aluminum layer or a dielectric
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`layer, will be formed over the substrate 10 using con-
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`ventional techniques. The primary layer 12 is patterned
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`using a bilayer mask including a metal imaging layer 14
`and a resist layer 16, which is specifically intended to
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`provide for high resolution plasma etching of the pri-
`mary layer.
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`In a first embodiment of the invention, the primary
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`layer 12 is an aluminum layer formed by conventional
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`techniques, such as sputter deposition or evaporation.
`Usually, the aluminum layer 12 will be a metallization
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`layer intended for interconnecting the various features
`formed on the substrate 10.
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`When the primary layer 12 is aluminum, the metal
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`imaging layer will be chromium, typically applied by
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`sputter deposition or evaporation. The chromium layer
`14 must be sufficiently thick to withstand the subse-
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`quent plasma etching of the primary layer 12, as de-
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`scribed hereinafter. Thicknesses in the range from 100
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`to 1009 A, more usually in the range from about 500 to
`1000 A, are suitable.
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`In an alternate embodiment, the primary layer 12 is a
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`dielectric layer,
`including both inorganic dielectrics
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`such as silicon oxide and silicon nitride as well as or-
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`ganic dielectrics, such as polyimides. The dielectric
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`layer 12 is formed by conventional techniques. In the
`case of inorganic dielectrics, such techniques include
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`thermal oxidation (for silicon oxides) and chemical
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`vapor deposition (CVD). In the use of organic dielec-
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`trics, a liquid resin may be applied by conventional
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`spin-on techniques.
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`For dielectric primary layers 12, the metal imaging
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`layer 14 will be aluminum. Again, the aluminum layer
`14 will be sufficiently thick to act as a mask during
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`subsequent plasma etching of the primary dielectric
`layer 12. Thicknesses in the range from about 100 to
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`1000 A, more usually in the range from about 200 to 500
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`A, are suitable.
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`The nature of the resist layer 16 is not dependent on
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`the nature of the primary layer 12, but must be able to
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`Page 3 of 4
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`

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`5,091,047
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`3
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`protect the underlying metal imaging layer 14. Suitable
`resist materials include photoresists, electron beam re-
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`sists, and x-ray resists. The thickness of the resist layer
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`will depend both on the desired image resolution and on
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`the need to cover irregular surface topographies. With
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`planarized surfaces, resists as thin as 0.2 pm may be
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`employed, providing for etched geometries of 0.5 pm
`and below. In the case of irregular surface topogra-
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`phies, resist layers having a thickness in the range from
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`about 1 to 2 pm may find use. The resists are applied by
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`conventional spin-on techniques to the desired thick-
`ness, and cured.
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`Referring now to FIG. 2, the resist layer 16 is pat—
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`terned by conventional techniques, such as light expo-
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`sure for photoresists, electron beam exposure for elec-
`tron beam resist, and x-ray exposure for x-ray resists.
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`After exposure, the resists are developed to provide a
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`desired mask for subsequent etching of the underlying
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`metal imaging layer 14.
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`Once the resist layer 16 has been patterned, it is used
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`as a mask for etching the metal image layer 14, as illus-
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`trated in FIG. 3. The chromium metal imaging layer 14
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`may be etched using conventional wet etchants, such as
`ceric ammonium sulfate-based etchants, at room tem-
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`perature. The aluminum metal imaging layer 14 may be
`wet etched using a phosphoric/nitric acid mixture, or
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`may be dry etched using a chlorine plasma, such as
`CCI3, CC14, HCl, C12, or BCI3.
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`After patterning, the metal imaging layer 14 is used as
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`a mask for plasma etching the primary layer 12. In the
`case of an aluminum primary layer 12, a chlorine plasma
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`i employed as described above. In the case of a dielec-
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`tric primary layer, the nature of the plasma will depend
`on the nature of the dielectric. In the case of organic
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`dielectrics, such as polyimides, an oxygen plasma is
`suitable. In the case of inorganic dielectrics, such as
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`silicon dioxide and silicon nitride, fluorine plasmas such
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`as CF4, CHF3, and the like, will find use.
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`After etching, the substrate will appear as illustrated
`in FIG. 4, with the resist layer 16 having been removed '
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`during' the plasma etch of the primary layer. If desired,
`the metal imaging layer 14 may be removed by conven-
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`tional techniques. The chromium imaging layer can be
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`removed by wet etching with ceric ammonium sulfate—
`based etchants or with an oxygen plasma. An aluminum
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`metal imaging layer 14 can be removed by wet etching
`using a phosphoric acid/nitric acid mixture at an ele-
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`vated temperature, typically about 70° C., or by dry
`etching with a chlorine-based plasma.
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`10
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`15
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`20
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`25
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`35
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`4
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`Use of the present invention provides for high resolu-
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`tion plasma etching of both aluminum metallization
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`layers and organic and inorganic dielectric layers. By
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`employing a bilayer mask including both a metal imag-
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`ing layer and a resist layer, very thin resist layers pro-
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`viding for high resolution and definition can be utilized.
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`By then using the photoresist to pattern the metal imag—
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`ing layer, a mask combining both the high resolution of
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`a thin photoresist and the durability of a metal
`is
`achieved.
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`Although the foregoing invention has been described
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`in some detail by way of illustration and example for
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`purposes of clarity of understanding, it will be obvious
`that certain changes and modifications may be practiced
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`within the scope of the appended claims.
`What is claimed is:
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`l. A method for etching a silicon dioxide dielectric
`layer on a semiconductor substrate, said method com-
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`prising:
`forming a layer of aluminum having a thickness in the .
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`range from about 100 to 1000 A over the dielectric
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`layer;
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`forming a thin resist layer having a thickness in the
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`range from about 0.2 to 2 pm over the aluminum
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`layer;
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`photolithographically patterning the resist layer to
`form a first mask;
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`etching the aluminum layer through the first mask to
`form a second mask;
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`plasma etching the dielectric layer through the sec—
`ond mask with a fluorinated hydrocarbon or oxy—
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`gen plasma, wherein said plasma etching removes
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`the resist layer from the aluminum layer.
`2. A method as in claim 1, wherein the resist is a
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`photoresist having a thickness in the range from about
`0.2 to 2 pm.
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`3. A method as in claim 1, wherein the resist is an
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`electron beam resist having a thickness in the range
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`from about 0.2 to 2 pm.
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`4. A method as in claim 1, wherein the resist is an
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`x-ray resist having a thickness in the range from about
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`0.2 to 2 pm.
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`5. A method as in claim 1, wherein the aluminum
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`layer is formed by sputtering or evaporation.
`6. A method as in claim 1, wherein the aluminum
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`layer is wet etched.
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`7. A method as in claim 1, wherein the aluminum
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`layer is dry etched. t
`t
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`i
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`45
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`50
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`55
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`65
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`Page 4 of 4
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`Page 4 of 4
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