Abstract:
A method of forming an interconnection layer in a semiconductor device is provided that improves the mass productivity and the reliability of the interconnection by forming a sidewall spacer on the sidewalls of a trench that is formed in an insulation film having a low dielectric constant. The sidewall spacer maintains the sidewall profile of the trench during subsequent processing steps.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention is directed to a method for manufacturing a semiconductor device, and in particular to a method for forming an interconnection in a semiconductor device. 
     2. Background of the Related Art 
     FIG. 1 illustrates a crystal structure of a hydrogen silsesquoxane (HSQ) which is a general insulation film with a low dielectric constant. As shown in FIG. 1, the insulation material with the low dielectric constant has a low volume density of atoms. However, if the insulation material is exposed to heat and plasma during a processing step, the insulation material is damaged, and thus cannot maintain its original profile. 
     FIGS. 2A to  2 F are cross-sectional views illustrating a related art method for forming an interconnection in a semiconductor device using HSQ. 
     As depicted in FIG. 2A, a first insulation layer  2  with a first trench  2 A is formed on a semiconductor substrate  1 . The substrate  1  is a silicon wafer on which a semiconductor device has been manufactured, but not the interconnections. The upper portion of the substrate  1  is mostly planarized by chemical mechanical polishing or etchback. The first insulation film  2  is composed of layer insulation materials, such as BPSG, SOG and PE-TEOS. 
     If the first insulation layer  2  has inferior mechanical properties, such that it is difficult to carry out chemical mechanical polishing on a metal to be deposited, an insulation layer (not shown) such as a silicon oxide film may be formed on the first insulation layer  2  to act as an etch stopper during chemical mechanical polishing. 
     Then, a first barrier metal layer  3  is formed at the upper portion of the first insulation layer  2  and in the first trench  2   a . A first metal layer  4  is formed on the first barrier metal layer  3 . As a result, the first trench  2   a  is filled with the first metal layer  4 . The first barrier metal layer  3  is one of Ti, Ti/TiN and TiW, and the first metal layer  4  is copper. 
     As illustrated in FIG. 2B, the first barrier metal layer  3  and the first metal layer  4  are partially removed by chemical mechanical polishing, so that the upper portion of the first insulation layer  2  is exposed, thereby forming a first interconnection layer  5  in the first trench  2   a . Then, a second insulation layer  6 , a third insulation layer  7  and a fourth insulation layer  8  are formed at the upper portions of the first insulation layer  2  and the first interconnection layer  5 . The second insulation layer  6  consists of a silicon nitride which is a metal cap insulation material, the third insulation layer  7  consists of an insulation material with a low dielectric constant, and the fourth insulation layer  8  is composed of a silicon oxide. In general, hydrogen silsesquoxane (HSQ) is employed as the insulation material with the low dielectric constant. 
     As illustrated in FIG. 2C, portions of the third and fourth insulation layers  7 ,  8  corresponding to the first interconnection layer  5  are removed by reaction ion etching using a photoresist film pattern (not shown) as a mask. Thus, a second trench  7   a  is formed in the third insulation layer  7 . The second insulation layer  6  functions as the etch stopper during the etching. 
     As depicted in FIG. 2D, the portion of the second insulation layer  6  exposed by the second trench  7   a  is removed by reaction ion etching using an oxygen plasma. As a result, the sidewalls of the third insulation layer  7  that are exposed to the second trench  7   a  are caved. In other words, when the insulation material with the low dielectric constant, such as the HSQ is used as the third insulation layer  7 , hydrogen elements in the HSQ and oxygen elements in the oxygen plasma are combined, thereby caving the sidewalls of the third insulation layer  7 . 
     As illustrated in FIG. 2E, a second barrier metal layer  9  is formed at the upper portion of the fourth insulation layer  8  and in the second trench  7   a . A second metal layer  10  is then formed on the second barrier metal layer  9 . As a result, the second trench  7   a  is filled with the second metal layer  10 . The second barrier metal layer  9  is generally one of Ti, Ti/TiN and TiW. The second metal layer  10  is generally copper. 
     As depicted in FIG. 2F, the second metal layer  10  is chemically mechanically polished so that the upper portion of the fourth insulation layer  8  is exposed, and thus a second interconnection layer  11  is formed in the second trench  7   a . As a result, the second interconnection layer  11  is connected to the first interconnection layer  5 . However, a void  12  occurs at the center of the second trench  7   a  because the third insulation layer  7  is caved. The fourth insulation layer  8  functions as the etch stopper during the chemical mechanical polishing. 
     The related art method of forming interconnections in the semiconductor device has various disadvantages. For example, as illustrated in FIG. 2D, when the second insulation layer (silicon nitride layer)  6  is partially removed by etching in order to form the interconnection, a bowing occurs, namely the sidewalls of the third insulation layer (HSQ layer)  7  exposed in the second trench  7   a  are caved. Further, as depicted in FIG. 2E, a void  12  occurs at the center of the second trench  7   a  because the third insulation layer  7  is caved, thereby reducing the mass productivity and the reliability of the interconnections. Moreover, when the second barrier metal layer  9 , as well as the second metal layer  10 , are removed by chemical mechanical polishing in order to form the second interconnection layer  11  in the second trench  7   a , two kinds of slurries must be used and two process conditions must be applied, thereby complicating the entire manufacturing process. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to solve at least the problems and/or disadvantages of the related art and prior art. 
     Another object of the present invention is to improve the mass productivity. 
     A further object of the present invention is to improve the reliability. 
     The present invention can be achieved in a whole or in parts by forming a sidewall spacer on the sidewalls of a trench formed in an insulation film with a low dielectric constant, so as to maintain the original sidewall profile of the trench during subsequent processing steps. 
     The present invention may be achieved in a whole or in parts by a method of forming an interconnection in a semiconductor device, comprising the steps of: (1) forming a first insulation layer on a semiconductor substrate; (2) forming a first trench in the first insulation layer; (3) forming a first interconnection layer in the first trench; (4) forming a second insulation layer on the first insulation layer and the first interconnection layer; (5) forming a third insulation layer on the second insulation layer; (6) forming a second trench in the third insulation layer; (7) forming a sidewall spacer on sidewalls of the second trench; (8) removing a portion of the second insulation layer exposed by the second trench; and (9) forming a second interconnection layer in the second trench. 
     The present invention may also be achieved in whole or in part by a method of forming an interconnection in a semiconductor device, comprising the steps of: (1) forming a first insulation layer on a substrate; (2) forming a second insulation layer on the first insulation layer; (3) forming a trench in the second insulation layer that exposes a portion of the first insulation layer; (4) forming a sidewall spacer on sidewalls of the trench; (5) removing the portion of the first insulation layer exposed by the trench; and (6) forming an interconnection layer in the trench, wherein the sidewall spacer is adapted to shield the sidewalls of the trench while the portion of the first insulation layer exposed by the trench is removed. 
     The present invention may also be achieved in whole or in part by a method of forming an interconnection in a semiconductor device, comprising the steps of: (1) forming a first insulation layer on a substrate; (2) forming a second insulation layer on the first insulation layer; (3) exposing a portion of the first insulation layer by forming a trench, having a sidewall profile, in the second insulation layer; (4) removing the portion of the first insulation layer exposed by the trench while maintaining the sidewall profile of the trench; and (5) forming an interconnection layer in the trench. 
     Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objects and advantages of the invention may be realized and attained as particularly pointed out in the appended claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will be described in detail with reference to the following drawings, in which like reference numerals refer to like elements, wherein: 
     FIG. 1 is a three-dimensional view illustrating the crystal structure of hydrogen silsesquoxane (HSQ), which is an insulation material with a low dielectric constant; 
     FIGS. 2A to  2 F are vertical cross-sectional views sequentially illustrating a related art method for forming an interconnection in a semiconductor device; and 
     FIGS. 3A to  3 F are vertical cross-sectional views sequentially illustrating a method for forming an interconnection in a semiconductor device, in accordance with a preferred embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIGS. 3A to  3 F are cross-sectional views illustrating a method for forming an interconnection in a semiconductor device, according to a preferred embodiment of the present invention. 
     As depicted in FIG. 3A, a first insulation layer  22  with a first trench  22   a  is formed on a semiconductor substrate  20 . The substrate  20  is a silicon wafer on which a semiconductor device has been formed, but not the interconnections. The upper portion of the substrate  20  has been substantially planarized, preferably by chemical mechanical polishing or by etchback. The first insulation film  22  is preferably composed of a layer insulation material, suitably an oxide, BPSG, SOG or PE-TEOS, formed by chemical vapor deposition. 
     If the first insulation layer  22  has inferior mechanical properties that makes it difficult to carry out chemical mechanical polishing on a metal to be deposited at a later step, an insulation layer (not shown) such as a silicon oxide film may be formed on the first insulation layer  22  to function as an etch stopper during chemical mechanical polishing. 
     Then, a first barrier metal layer  24  is formed at the upper portion of the first insulation layer  22  and in the first trench  22   a . A first metal layer  26  is then formed on the first barrier metal layer  24 . As a result, the first trench  22   a  is filled with the first metal layer  26 . The first barrier metal layer  24  is preferably one of TiN, Ta, TaN and WNx and combinations thereof, and the first metal layer  26  is preferably copper. 
     As illustrated in FIG. 3B, the first barrier metal layer  24  and first metal layer  26  are partially removed by chemical mechanical polishing, so that the upper portion of the first insulation layer  22  is exposed, and a first interconnection layer  28  is formed in the first trench  22   a . Then, a second insulation layer  30 , a third insulation layer  32  and a fourth insulation layer  34  are formed on the first insulation layer  22  and the first interconnection layer  28 . The second insulation layer  30  is preferably a silicon nitride, which is a metal cap insulation material. The third insulation layer  32  is preferably an insulation material with a low dielectric constant, and the fourth insulation layer  34  is preferably silicon oxide. Hydrogen silsesquoxane (HSQ) is preferably employed as the insulation material with a low dielectric constant (the third insulation layer  32 ). 
     As shown in FIG. 3C, portions of the third and fourth insulation layers  32 ,  34  corresponding to the first interconnection layer  28  are removed, preferably by reaction ion etching using a photoresist film pattern (not shown) as a mask. Thus, a second trench  32   a  is formed in the third insulation layer  32 . The second insulation layer  30  functions as an etch stopper during the etching. Thereafter, a second barrier metal layer  36  is formed on the upper portion of the fourth insulation layer  34  and in the second trench  32   a . The second barrier metal layer  36  is preferably one of TiN, Ta, TaN, WNx and combinations thereof. 
     As depicted in FIG. 3D, the second barrier metal layer  36  is removed, preferably by anisotropic etching, so that the upper portion of the fourth insulation layer  34  is exposed. Thus, a sidewall spacer  36   a  is formed at the sidewalls of the fourth insulation layer  34  and the inner sidewalls of the second trench  32   a.    
     A portion of the second insulation layer  30  exposed by the second trench  32   a  is removed, preferably by reaction ion etching using an oxygen plasma. As a result, the first interconnection layer  28  is partially exposed through the second trench  32   a . The sidewall spacer  36   a  functions as a protective film that prevents the sidewalls of the second insulation layer  30  in the second trench  32   a  from being damaged by the oxygen plasma during the reaction ion etching. 
     As illustrated in FIG. 3E, a second metal layer  38  is formed on the upper portion of the fourth insulation layer  34  and in the second trench  32   a . Accordingly, the second trench  32   a  is completely filled with the second metal layer  38 . 
     As shown in FIG. 3F, the second metal layer  38  is chemically mechanically polished so that the upper portion of the fourth insulation layer  34  is exposed. Thus, a second interconnection layer  40  is formed in the second trench  32   a . The second interconnection layer  40  contacts the first interconnection layer  28 . The fourth insulation layer  34  functions as an etch stopper during the chemical mechanical polishing. 
     Although a two-layer interconnection structure has been illustrated, the present invention is not limited to two-layer structures. It should be recognized that the present invention may also be employed to form a three-layer interconnection, a four-layer interconnection, etc. Generally, interconnections having any number (N) of layers can be formed with the method of present invention. 
     The method of forming an interconnection in a semiconductor device according to the present invention has various advantages. For example, as illustrated in FIG. 3D, the sidewall spacer  36   a  is formed on the inner sidewalls of the second trench  32   a , and the second insulation layer  30  is removed by etching, thereby preventing the sidewalls of the third insulation layer  32  from being caved. Further, as depicted in FIG. 3F, the second trench  32   a  is completely filled with the second interconnection layer  40 , thereby improving the mass productivity and reliability of the interconnection. Moreover, when the second interconnection layer  40  is formed in the second trench  32   a  that contains the sidewall spacer  36   a , only the second metal layer  38  is removed by the chemical mechanical polishing, thus simplifying the entire process. The sidewall spacer  36   a  also makes it easier to fill the second trench  32   a  with metal. 
     The foregoing embodiments are merely exemplary and are not to be construed as limiting the present invention. The present teaching can be readily applied to other types of apparatuses. The description of the present invention is intended to be illustrative, and not to limit the scope of the claims. Many alternatives, modifications, and variations will be apparent to those skilled in the art. In the claims, means-plus-function clauses are intended to cover the structures described herein as performing the recited function and not only structural equivalents but also equivalent structures.