Method of filling with a metal layer a recess formed in an integrated circuit chip

Abstract: By a method of fabricating an integrated circuit chip including insulated gate field effect transistors, a recess (106) may be formed in the chip under a photoresist layer (102) such that the photoresist overhangs the recess. A metal film (110) is cold-sputtered, filling the recess and covering the photoresist. The metal film in the recess (110) is separated from the metal film (112) covering the recess because of the overhang. A second photo­ resist layer (114) is applied, then etched to expose a corner of the metal film over the overhang. The metal is etched to expose the underlying photoresist (102). Finally the underlying photoresist (102), and the portion of the second photoresist layer (114) over the metal film (110) in the recess, are removed.

Description: The invention relates generally to the field of methods for fabricating MOSFET (metal oxide semi- conductor field effect transistor), more specifically to a method of forming a recess in an integrated circuit chip and filling it with a metal layer. It often becomes necessary in the processing of an integrated circuit chip to fill in a recess in, for example, a dielectric such as an oxide layer with a metal conductor material. In a technique for performing this operation a metal film is deposited on the surface of the chip. The depth of the film is sufficient to at least fill the recess in the dielectric and leave a recess in the upper surface of the metal film. A photoresist coating is applied over the metal film to fill the recess in the metal film and provide a planar upper surface. The photoresist coating is etched by reactive ion etching techniques, leaving the photoresist in the recess in the metal film. A metal etch is then applied, which removes the metal outside the recess. The remaining photoresist is then removed, leaving the metal in the recess. This technique is generally limited to filling recesses having widths of ten microns or less, on chips in which the recesses are of uniform widths. Thus, if the recesses are of significantly diverse widths or if they have widths of greater than about ten microns, the process described in the above-mentioned patent application may not provide satisfactory filling of the recesses. GB-A-2 059 679 and GB-A-1 523 677 also address the problem of filling a recess with a metall layer. The present invention provides a new and improved method of filling a recess in a dielectric with a metal film according to claim 1. The region of the dielectric in which the recess is to be formed is defined by a photoresist, and the region is etched so that the photoresist overhangs the recess slightly. A metal film is then cold sputtered over the entire surface of at least the recess and surrounding photoresist to fill the recess. In this condition, the metal also covers the top of the photoresist and the sidewall thereof bordering the overhang. The metal covering the sidewall of the photoresist is separated from the metal deposited in the recess. The surface of the metal is then covered by a layer of, for example, photoresist, which is partially etched away leavins exposed the edge of metal near the corner of the underlying photoresist layer. The exposed metal is then etched away, exposing the corner of the photoresist therebeneath. The lower photoresist layer is then removed, which also removes the covering metal and upper photoresist layer. Simultaneously, the photoresist covering the metal in the recess is removed. FIGS. 1A through 1F are cross-sectional views detailing the method of filling a recess with a metal film in accordance with claim 1 of the present invention. The invention provides a new and improved method of filling a recess with a metal film layer. As noted above, the process described in connection with FIGS. 1A through 1F can be used in filling recesses 106. With reference to the figures, FIG. 1A depicts an integrated circuit chip having a substrate 100 covered by a layer of photoresist 102. An aperture generally indicated at 104 has been defined in the photoresist layer in a conventional manner and a recess 106 formed in the substrate 100 defined by sidewalls 107. The photoresist thus has a sidewall 103 defining the periphery of the aperture 104. The recess is defined by means of a directional reactive ion etch so as to provide an overhang 108 of the photoresist 102 over the sidewalls 107 defining recess 106. The metal which is desired to fill the recess 106 is then cold-sputtered over the surface of the chip to a depth sufficient to fill the recess 106 (see FIG. 1B). The depth of the metal film 112 over photoresist 102 is approximately the same as the depth in the recess. Near the overhang, as shown in FIG. 1B, the metal covering the photoresist layer curves around the corner defined by sidewall 103 and the top surface of photoresist layer 102. Because of the limited depth of the metal film and the presence of overhang 108, there is a slight concavity in the surface of the film 110 in the recess under the overhang, and so the metal film covering the photoresist does not come in contact with its metal film in the recess. The entire surface of the chip is then covered with a second photoresist layer 114 (FIG. 1C). In the region of the recess 106, the upper surface of the second photoresist layer exhibits a slight concavity so that it is generally thinner in the region near sidewall 103 defining the periphery of aperture 104 than in the rest of the chip. Using a reactive ion etch, a portion of the surface of the photoresist 114 is removed so as to expose the corner of metal film 112 adjacent the periphery of aperture 104 in photoresist layer 102 (FIG. 1D). A wet metal etch is then applied which etches the exposed portions of the metal layer 112 sufficient to expose the photoresist layer 102 therebeneath (FIG. 1E). Since the metal layer 110 in the recess is covered by the remaining photoresist 114 and protected from the wet metal etch by photoresist layer 114 and the overhang 108, the metal layer is 110 is not damaged by the wet metal etch. Finally, the photoresist layer 102 is removed in a conventional manner, taking with it the metal layer 112 and photoresist layer 114 thereover. At the same time, photoresist layer 114 over the metal layer 110 is also removed resulting in the configuration depicted in FIG. 1F. The foregoing description has been limited to the specific embodiment of the various aspects of the invention. It will be apparent, however, that the invention can be practiced in integrated circuit chips having diverse basic construction than is disclosed in the specification, with the attainment of some or all of the advantages of the invention.

Claims: A method of forming a recess in an integrated circuit chip and filling it with a metal comprising the steps of: A. depositing a layer of photoresist on the chip and removing the photoresist in a region in which the recess is to be formed; B. forming a recess in the region of the chip defined by the removed photoresist such that the photoresist overhangs the recess; C. cold sputtering a layer of metal over the recess and on the surface of the photoresist layer, the metal covering the top surface and sidewall of the photoresist, with the metal layer on the photoresist being separated from the metal layer in the recess; D. covering the surface of the chip with a masking material to a depth sufficient to ensure that there is a depression over the recess; E. etching the layer of masking material so as to only expose the portion of the metal layer on the corner of the photoresist layer defined by a portion of the top surface and sidewall thereof; F. etching the exposed metal layer to expose the corner region of the photoresist layer defined by a portion of the top surface and sidewall thereof; G. removing the photoresit layer, the masking material and metal layers only from the top surface of the integrated circuit chip; and H. removing the masking layer over the metal layer in the recess . The method as defined in claimed 1 wherein the masking material is a second photoresist layer so that the photoresist removing step and the masking layer removing step occur together.

Inventors: WU ANDREW L, WU, ANDREW L.
Applicants: DIGITAL EQUIPMENT CORP, DIGITAL EQUIPMENT CORPORATION
Application year: 1985
Main classification: H01L21
IPC codes: H01L21