1. Field
The present invention relates to the field of semiconductor manufacturing, specifically a composite sputter target for depositing alloy films on semiconductor substrates.
2. Description of Related Art
Sputtering is a semiconductor manufacturing process used to deposit pure metal or alloy films on substrates for semiconductor process applications such as vias, plugs, and metal recesses. Sputtering may also be used for advanced applications such as salicide deposition, tungsten adhesion, Ta/TaN barrier, Cu seed, C4 metallization, and backside metallization. Currently, sputtering is accomplished by the use of sputtering targets, whereby ions are attracted to the sputtering target at a force that disassociate metal atoms from the target unto a substrate.
Manufacturing sputter targets conventionally involves a molten metal casting and thermo-mechanical processing (TMP) manufacturing process. However, some materials melt at a very high temperature and can not be easily cast. Other materials are very brittle and can not survive the TMP process without cracking or breaking. These materials which can not be easily casted or survive the TMP process normally require a powder metallurgy manufacturing process.
Powder metallurgy involves consolidating elemental or pre-alloy powders. However, consolidating some metal powders for manufacturing bimetallic sputter targets may result in arcing, in-film defects, brittleness, high porosity, and higher impurity levels which are undesirable for sputtering high quality metal films.
The present invention is a composite sputter target comprised of a plurality of first metal pieces bonded to a plurality of second metal pieces. The sputter target may be used to sputter deposit alloy films of the first and second metals. For example, in order to form a sputter target to deposit a AlCu alloy film, a plurality of Al pieces are bonded to a plurality of Cu pieces. In one embodiment, the bonded first and second metal pieces form an inter-metallic compound between them, which has an elemental composition of both first and second metal pieces. The sputter target is ideal for sputter depositing inter-metallic compounds such as TiAl, which are generally too brittle to manufacture into sputter targets using normal casting and thermo-mechanical processes. By bonding individual metal pieces, a sputter target may be manufactured with high purity, low defect density, and void free targets by which high purity, void free films may be sputter deposited on a substrate.
In an embodiment of the present invention, the sputter target is formed from a plurality of first metal pieces, such as Al, and second metal pieces, such as Cu, which together form an inter-metallic compound, AlCu. Typically, sputter targets comprised of inter-metallic compounds are too brittle to enable the fabrication of a sputter target through powder metallurgy because the TMP process would cause the brittle alloys to crack or break. Accordingly, individual metal components that form inter-metallic compounds are bonded together, which can be easily processed by casting and TMP. By bonding individual components of the inter-metallic compound together, each of the segments of metal pieces remain ductile, enabling fabrication of a ductile target. In an embodiment of the present invention, the bonded region is sufficiently large to ensure each of the pieces are sufficiently bonded to one another, but is not too large that the target becomes brittle. In an embodiment the bonded region has a width on the order of microns. In an embodiment, the bonded region has a width in the range of 10-500 microns.
In the embodiment of
Sputter target 100 may be used to sputter films of varying alloy content, but is generally used to sputter films with at least an alloy concentration greater than 10%. The size of the first and second metal pieces are manufactured to a size such that uniform distribution of the individual elements in the deposited film is achieved. Additionally, the first and second metal pieces are manufactured to a size small enough to achieve the desired elemental uniformity without compromising manufacturability. In an embodiment, the first and second metal pieces have an area of approximately 42 in2 and a thickness of 0.5 inches. In an embodiment, metals are chosen according to the metal's respective sputter rate to achieve the desired alloy concentration for the sputtered film.
In an embodiment, a composite sputter target can be used to sputter deposit a tri-metallic alloy (XYZ) on a substrate. In an embodiment such composite sputter target comprises homogeneous metal pieces X, homogeneous metal pieces Y, and homogeneous metal pieces Z. Alternatively, composite sputter target may comprise of homogeneous metal pieces X and alloy metal pieces YZ. For example, a composite sputter target of the present invention may be comprised of Al, Cu, and Ti for sputter depositing an Al—Cu—Ti film.
The first and second metal pieces of the sputter target 100 may be manufactured in a variety of shapes. For example, embodiments of the present invention may have various metal piece shapes such as pie-slice, circular, semi-circular, rectangular, semi-rectangular, triangular, and semi-triangular. In an embodiment, both first metal and second metal pieces are pie slice shaped as illustrated by first metal piece 102 and second metal piece 106 in
Sputter target 100 may be manufactured to a shape that is suitable for sputter deposition equipment. In an embodiment, sputter target 100 is manufactured into a round, planar shape as shown in
Sputter target 100 may be manufactured by any suitable process when the individual metal pieces can be adequately bonded together such as, but not limited to diffusion bonding. In an embodiment of the present invention, the composite sputter target 100 is formed by a Hot Isostatic Press (HIP) process as shown by the flowchart in
To manufacture sputter target 100 by a HIP process, first and second metal pieces must be provided. According to an embodiment of the present invention as illustrated in
Next, first metal piece 402 and second metal piece 406 are positioned for bonding. In an embodiment, first and second metal pieces are positioned one at a time in alignment can 403 until completely filled as shown in
Next, first metal pieces and second metal pieces are bonded together by HIP process. Alignment can 403, containing first and second metal pieces, are placed within a Hot Isostatic Press chamber 407. Next, within Hot Isostatic Press chamber 407, process conditions are set for high temperature and high pressure to induce diffusion bonding of the first and second metal pieces. The temperature within Hot Isostatic Press chamber 407 is purposefully set below the melting point of each metal piece. Typically, the temperature is set in a range between 400-600° C. However, the temperature set within Hot Isostatic Press chamber 407 is dependent upon the composition of metals within the chamber. For example, if the first metal pieces and second metal pieces are made of titanium and aluminum respectively, chamber temperature must be set below 660° C. to avoid melting because the melting point of titanium and aluminum are 1660° C. and 660° C. respectively. The pressure is set within the chamber to form a good contact between the first metal pieces and second metal pieces to induce diffusion bonding. In an embodiment of the present invention, the pressure is approximately 10 atmospheres. In the embodiment of
In an embodiment of the present invention as illustrated in
After diffusion bonding the first and second metal pieces in the HIP, a sputter target 400 according to the present invention is formed.
The sputter target of the present invention can be used within a sputtering apparatus such as sputter apparatus 600 illustrated in
Sputter target 100 may be used to sputter high purity, void free metal films on a substrate for a variety of semiconductor process applications such as, but not limited to vias, plugs, and metal recesses. For example, sputter target 100 may be manufactured to sputter deposit a high purity, void free TiAl film on a substrate to form a metal via. In an embodiment, substrate 700 may comprise a semiconductor substrate 711, dielectric 709, and opening 713 whereby sputtered alloy film 708 is formed in opening 713 as shown in