Semiconductor contact via structure and method

Abstract: A method is provided for forming an integrated circuit contact structure. A conductive region (12) is formed on a semiconductor device (10). Thereafter an insulating layer (14,16,18) is formed over the conductive region (10). An opening (22) is then formed through the insulating region (14,16,18) to the conductive region (12). A thin barrier layer (26) is deposited over the integrated circuit contact structure. A portion of the thin barrier layer (26) is removed by backsputtering the integrated circuit contact structure so that only a thin barrier sidewall (28) remains. Finally, a conductive metal (30) layer is deposited over the integrated circuit contact structure. In one embodiment, the integrated circuit contact structure is baked before the conductive metal layer (30) is deposited.

Description: The present invention relates generally to semiconductor integrated circuits, and more specifically to formation of a contact structure for such circuits. In fabricating semiconductor integrated circuits, the integrity of various structures on the circuits is of great importance. Undesirable impurities in the wrong portions of a circuit can adversely affect its functioning. One type of structure commonly found on a semiconductor integrated circuit is a contact from an upper level metal interconnect layer to a lower conductive structure through a contact via. An insulating layer though which the contact via is cut often has a reflow glass layer or spin-on glass layer to improve planarity of the chip's surface. These glass layers typically have impurities which can migrate into the metal interconnect in the via and adversely affect its operation. For example, it is known that mobile ion donation from glass layers in contact with metal interconnect can shift data retention voltages in memory circuits. Also, outgassing of solvents in such glass layers can cause voiding in, or oxidation of, sputtered metal interconnect. Since the formation of a reflowable glass layer or a spin-on glass layer improves the planarity of the integrated circuit, it is important to use such material in insulation layers. It would be desirable to provide a technique which allows the planarity improvement of such glass layers without contamination of interconnect by the impurities used in standard glass. Patent Abstracts of Japan, vol. 15, no. 114 (E-1047), 19th March 1991, discloses a contact structure in which a silicon oxide layer is formed over an aluminium layer, and two glass layers formed over the silicon oxide layer. An opening to the aluminium layer is formed through the oxide layer and two glass layers, and a T-W film formed on sidewalls of the opening. A metal layer is then deposited in the contact opening and on the upper glass layer. European Patent Application Publication No. 0165513 discloses a structure in which silicon is formed in the base and on the sidewalls of a contact opening prior to the subsequent deposition of a metal. Electronics, 22nd September 1983, pages 48-49, W.R. Iverson: "Amorphous vias in wafer link chips" discloses a structure in which amorphous silicon serves as an insulator sandwiched between two layers of metal. United Kingdom Patent Application Publication No. 2110876 discloses a structure in which a contact opening has sidewalls of oxide formed thereon. European Patent Application Publication No. 0155699 discloses a multi-layer structure including a BPSG layer. According to one aspect of the present invention there is provided a contact structure for an integrated circuit according to claim 1, comprising: an underlying conductive structure; a first conformal oxide layer overlying the underlying conductive structure, such first conformal oxide layer being undoped or lightly doped; a planarizing oxide layer overlying the first conformal oxide layer; a second conformal oxide layer overlying the planarizing oxide layer, such second conformal oxide layer being undoped; an opening through the second conformal oxide layer, the planarizing oxide layer, and the first conformal oxide layer to expose a portion of the underlying conductive structure; thin sidewalls of amorphous silicon alongside sides of the opening, separating the opening from the first and second conformal oxide layers and the planarizing oxide layer; and a conductive interconnect layer lying on the second conformal oxide layer and extending into the opening, and separated from the planarizing oxide layer and the first and second conformal oxide layers in the opening by the thin amorphous silicon sidewalls. According to a further aspect of the present invention there is provided a method for forming an integrated circuit contact structure according to claim 9, comprising the steps of: forming a conductive region on a semiconductor substrate; forming a first conformal oxide layer over the conductive region and the substrate; forming a planarizing oxide layer over the first conformal oxide layer; forming a second conformal oxide layer over the planarizing layer; forming an opening through the first and second conformal oxide layers and the planarizing oxide layer to expose a portion of the conductive region; depositing a thin layer of amorphous silicon over the second conformal oxide layer and in the opening; backsputtering the integrated circuit contact structure to remove at least a portion of the thin layer over the exposed portion of the conductive region and over the second conformal oxide layer, leaving thin sidewall regions on sides of the opening; and depositing a conductive metal layer over the second conformal oxide layer and in the opening. A method is thus provided for forming an integrated circuit contact structure. A conductive region is formed on a semiconductor device. Thereafter an insulating layer is formed over the conductive region. An opening is then formed through the insulating region to the conductive region. A thin barrier layer is deposited over the integrated circuit contact structure. A portion of the thin barrier layer is removed by backsputtering the integrated circuit contact structure so that only a thin barrier sidewall remains. Finally, a conductive metal layer is deposited over the integrated circuit contact structure. In one embodiment, the integrated circuit contact structure is baked before the conductive metal layer is deposited. The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself however, as well as a preferred mode of use, and further objects and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: Figures 1 - 4 are sectional views of an integrated circuit illustrating a preferred method for forming contact vias according to the present invention. The process steps and structures described below do not form a complete process flow for manufacturing integrated circuits. The present invention can be practiced in conjunction with integrated circuit fabrication techniques currently used in the art, and only so much of the commonly practiced process steps are included as are necessary for an understanding of the present invention. The figures representing cross-sections of portions of an integrated circuit during fabrication are not drawn to scale, but instead are drawn so as to illustrate the important features of the invention. Referring to Figure 1 , a contact is to be formed on a semiconductor substrate 10 . Semiconductor substrate 10 may be simply the substrate on which an integrated circuit is formed, or it may represent multiple lower layers which have already been fabricated. The details of any such multiple lower layers are not important to the present invention. A conductive region 12 is defined and patterned on the semiconductor substrate 10 . Conductive region 12 may be a first metal level interconnect layer, or it may be polycrystalline silicon or a silicided polycrystalline silicon layer. A conformal insulating layer 14 is formed over the surface of semiconductor substrate 10 and conductive region 12 . Conformal insulating layer 14 is an oxide layer, undoped or lightly doped as known in the art. Conformal insulating layer 14 is typically deposited using chemical vapor deposition (CVD) or low pressure chemical vapor deposition (LPCVD). A planarizing insulating layer 16 is next formed over the conformal insulating layer 14 . Planarizing insulating layer 16 may be a spin-on glass layer or a reflowable glass layer. As known in the art, a reflowable glass layer may be comprised of phospo-silicate glass or boro-phospo-silicate glass. An undoped oxide layer 18 is then formed over planarizing insulating layer 16 . Now referring to Figures 1 and 2 , a photoresist mask 20 is used to define and etch an opening or contact via 22 . Photoresist mask 20 is then removed. Contact via 22 provides an opening through conformal insulating layer 14 and planarizing insulating layer 16 to conductive region 12. Contact via 22 is formed by first performing an isotropic etch partially through undoped oxide layer 18 . The isotropic etch causes the sidewalls of contact via 22 to be curved as illustrated at 24 . Those skilled in the art will recognize that this isotropic etch removes sharp corners which can cause step coverage problems. An anisotropic etch is then performed through contact via 22 to conductive region 12 . Referring now to Figure 3 , a thin barrier layer 26 of amorphous silicon is deposited over the integrated circuit. Thin barrier layer 26 forms a thin barrier sidewall 28 along the sidewall of contact via 22 . The horizontal portions of thin barrier layer 26 are then removed by backsputtering the integrated circuit, thus leaving only thin barrier sidewall 28 . This backsputtering step can be simply the normal backsputtering typically performed to clean exposed surfaces prior to deposition of a next conductive layer. In this manner, no additional etching is necessary to remove thin barrier layer 26 and leave only thin barrier sidewall 28 . With reference to Figure 4, a conductive metal layer 30 , comprising a metal such as aluminum, is deposited over the integrated circuit. Planarizing insulating layer 16 is completely isolated from contact via 22 by thin barrier sidewalls 28 . Conductive metal layer 30 is completely isolated from planarizing insulating layer 16 . Thus, conductive metal layer 30 is protected from impurities contained within planarizing insulating layer 16 . In another embodiment of the present invention, the integrated circuit is baked before conductive metal layer 30 is deposited. The baking process may occur at 250 - 450 C for 15 - 60 minutes, reducing the amount of moisture present within spin-on glass layer 16 . This helps to achieve a better step coverage in contact via 22 . As will be appreciated by those skilled in the art, the method described above, and the structure formed thereby, provides for isolation of a conductive metal layer and contact from a planarizing insulating layer comprised of spin-on glass or reflowable glass. Formation of thin barrier sidewall 28 is completed with no need for additional etching to remove thin barrier layer 26 other than backsputtering. This technique is compatible with standard process flows currently in use and allows for improved contact formation while retaining the advantages of using a reflow and spin-on glass for planarization.

Claims: A contact structure for an integrated circuit, comprising: an underlying conductive region (12); a first conformal oxide layer (14) overlying the underlying conductive region (12), such first conformal oxide layer (14) being undoped or lightly doped; a planarizing oxide layer (16) overlying the first conformal oxide layer (14); a second conformal oxide layer (18) overlying the planarizing oxide layer (16), such second conformal oxide layer (18) being undoped; an opening (22) through the second conformal oxide layer (18), the planarizing oxide layer (16), and the first conformal oxide layer (14) to expose a portion of the underlying conductive region (12); thin sidewalls (28) of amorphous silicon alongside sides of the opening, isolating the opening from the first (14) and second (18) conformal oxide layers and the planarizing oxide layer (16); and a conductive interconnect layer (30) lying on the second conformal oxide layer (18) and extending into the opening (22),and isolated from the planarizing oxide layer (16) and the first (14) and second (18) conformal oxide layers in the opening (22) by the thin amorphous silicon sidewalls (28). The structure of claim 1, wherein the underlying conductive region (12) comprises an interconnect structure. The structure of claim 1, wherein the underlying conductive region (12) is formed on a semiconductor substrate (10). The contact structure according to any one of claims 1 to 3 wherein the planarizing oxide layer (16) comprises a layer of spin-on glass. The contact structure according to any one of claims 1 to 3 wherein the planarizing oxide layer (16) comprises a layer of reflow glass. The contact structure according to claim 5 wherein the layer of reflow glass comprises phospo-silicate glass. The contact structure according to claim 5 wherein the layer of reflow glass comprises boro-phospo-silicate glass. The contact structure according to claim 4, wherein the layer of spin-on glass comprises regions having a lesser water content. A method of forming an integrated circuit contact structure, comprising the steps of: forming a conductive region (12) on a semiconductor substrate (10); forming a first conformal undoped or lightly doped oxide layer (14) over the conductive region (12) and the substrate (10); forming a planarizing oxide layer (16) over the first conformal oxide layer (14); forming a second conformal undoped oxide layer (18) over the planarizing layer (16); forming an opening (22) through the first and second conformal oxide layers and the planarizing oxide layer to expose a portion of the conductive region (12); depositing a thin layer (28) of amorphous silicon over the second conformal undoped oxide layer (18) and in the opening; backsputtering the integrated circuit contact structure to remove at least a portion of the thin layer (28) over the exposed portion of the conductive region (12) and over the second conformal undoped oxide layer (18), leaving thin sidewall regions (28) on sides of the opening (22); and depositing a conductive metal layer (30) over the second conformal oxide layer (18) and in the opening (22). The method according to claim 9 wherein the step of forming a planarizing oxide layer (16) comprises the step of depositing a layer of spin-on glass. The method according to claim 9 wherein the step of forming a planarizing oxide layer (16) comprises the step of depositing a layer of reflow glass. The method according to any one of claims 9 to 11 wherein the step of forming an opening further comprises the steps of: performing an isotropic etch partially through the second conformal oxide layer (18); and performing an anisotropic etch through the remainder of the second conformal oxide layer (18), the planarizing oxide layer (16), and the first conformal oxide layer (14) following the isotropic etch, wherein a portion of the conductive region (12) is exposed. The method according to any one of claims 9 to 12 further comprising the step of, before the step of depositing a conductive metal layer (30), baking the integrated circuit contact structure to form a region having a reduced water content within the planarizing oxide layer (16) adjacent to the opening (22).

Inventors: CHEN FUSEN E, DIXIT GIRISH A, WEI CHE-CHIA, CHEN, FUSEN E., DIXIT, GIRISH A., WEI, CHE-CHIA
Applicants: SGS THOMSON MICROELECTRONICS, STMICROELECTRONICS, INC.
Application year: 1993
Main classification: H01L21
IPC codes: H01L21, H01L23