Coating processes – Coating by vapor – gas – or smoke
Reexamination Certificate
1998-09-03
2001-02-20
Beck, Shrive (Department: 1762)
Coating processes
Coating by vapor, gas, or smoke
C427S255394, C118S729000
Reexamination Certificate
active
06190732
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
This invention relates in general to the field of semiconductor device fabrication, and more particularly to a method and system for dispensing process gas for fabricating a device on a substrate.
BACKGROUND OF THE INVENTION
Microelectronic devices, such as integrated circuit (IC) chips formed on a semiconductor substrate wafer, have grown increasing complex over the past several years. By miniaturizing the circuits of the microelectronic devices, industry has achieved significant performance improvements in terms of increased processing speed and decreased footprint. However, the miniaturized circuits are difficult to form. Minor contamination by impurities and other imperfections have greater and greater effects on the integrity of the devices as the size of circuits within microelectronic devices decrease. As industry transitions from the present 0.25 micron circuit devices to devices having smaller circuits, such as 0.18 and 0.13 microns, device formation techniques will have to provide greater precision using a wider variety of materials and with decreased contamination of the device. One example of a new material designed to reduce device size is the use of copper instead of aluminum to form device interconnects.
Microelectronic devices can be formed on substrates in a number of different ways. Some conventional techniques for forming microelectronic devices include rapid thermal processing (RTP), etch processing, and physical vapor deposition (PVD). PVD occurs in a relatively low pressure environment. A target, comprised of the material to be deposited, and the substrate are disposed in a reaction process chamber with a low pressure plasma gas. The target deposits the material on the substrate by the creation of an electric charge difference between the target and the substrate.
Chemical vapor deposition (CVD) is another example of a conventional and well-known process for depositing materials on a substrate to fabricate a microelectronic device on the substrate, such as in the fabrication of a semiconductor IC chip. To achieve a uniform growth of a thin-film material on a substrate, conventional CVD systems attempt to distribute a precursor gas, sometimes in combination with other reactant gases, in a uniform flow over the substrate. Under predetermined conditions for the precursor, such as predetermined temperature and pressure conditions within the CVD reaction process chamber and the substrate, the precursor deposits a desired material on the substrate as the precursor flows over the substrate. For instance, CVD provides excellent thin-film deposition of copper, tantalum nitride, titanium nitride, barium strontium titanate, and other materials typically used as thin-films for device fabrication on a substrate.
PVD and CVD provide different advantages based upon the material to be deposited. For example, CVD provides significant advantages in the deposition of a uniform thin-film of copper on a substrate. However, it is difficult to manufacture microelectronic devices by combining PVD and CVD processes due to the relatively high pressure of the process gas used in the reaction process chamber for CVD compared to the low pressure used for PVD. Further, the gases used to support CVD tend to damage substrates if the CVD gases are inadvertently introduced during a PVD process.
Typically, CVD occurs in a reaction process chamber that provides a low-conductance, contaminant-free environment for flowing the precursor over the substrate in a uniform manner. Alternatively, CVD can be performed in a high-conductance reaction process chamber that provides a relatively large flow of process gas to achieve a uniform film deposition. High-conductance systems generally have a larger footprint than do low-conductance systems, and use a greater amount of process gas for a given film deposition thickness. After deposition, the precursor is evacuated from the reaction process chamber to allow deposition of a subsequent material film, or to allow transfer of the substrate to another reaction process chamber for deposition of the subsequent material film. CVC, Inc. has a hub system that connects a number of reaction process chambers through a central hub to allow transfer of the substrate. The central hub is maintained at a low pressure to minimize the introduction of contaminants during transfer of substrate wafers through the hub.
Conventional single wafer CVD systems feed gases above and perpendicular to the substrate wafer. The gases deflect from the center of the wafer and flow radially from the center to an exhaust port located below the substrate wafer. In such conventional systems, the center of the substrate tends to receive a higher concentration of process chemicals associated with the gases, resulting in faster thin-film material growth at the center of the substrate than at the edges. This can lead to a bell-shaped film thickness with a thicker film at the center of the substrate than at the edge.
To alleviate this difficulty, conventional CVD systems use a showerhead arrangement. The precursor gas flows from above the showerhead into a centrally-located inlet of the showerhead housing. The showerhead housing has a showerhead gas dispersion plate with several hundred small openings to allow a low-conductance flow of the precursor gas to the CVD reaction chamber for more-uniform distribution across the substrate. To encourage a uniform distribution of the precursor gas from the dispersion plate openings, a deflector plate is typically disposed between the incoming gas flow and the dispersion plate. The deflector plate deflects the incoming gas flow radially from the intake vector to fill the showerhead housing with gas before the gas flows through the openings, thus avoiding an excessive concentration of gas flow over the center of the substrate.
Although a deflector plate and showerhead in a conventional CVD system can aid in the relatively uniform distribution of gas across the substrate, this arrangement creates a number of difficulties in the commercial production of microelectronic devices on a substrate wafer. For instance, the process gas inlet at the top of the showerhead increases the height footprint of the system and vertical thickness of the showerhead housing. This can increase the amount of precursor gas needed for deposition of a given film. Further, the inlet and associated fittings increase the difficulty of showerhead maintenance, and the likelihood of contamination during CVD processing. For example, to allow servicing of the showerhead, flexible hoses are often used between the showerhead inlet and process gas source. These hoses impede access to the showerhead housing, and can include particulate contaminates that can break free during CVD processing to introduce contaminants to the substrate.
Another difficulty associated with conventional CVD systems relates to system throughput. During CVD processing, gases are distributed from the showerhead inlet, through the dispersion plate and across the substrate with a low-conductance uniform flow. After deposition of the desired film, gas flow through the inlet is ceased by a shutoff valve, and residual gases are removed from reaction chamber through an exhaust located at the bottom of the reaction chamber. This results in process gas flowing over the entire length of the reaction chamber. Once the residual gas is removed from the reaction chamber, the substrate can be removed from the reaction chamber for further processing. For instance, the hub system sold by CVC, Inc. can move the substrate between several reaction chambers through a central hub, thus minimizing contamination of the substrate between the deposition of different material layers in separate reaction chambers.
To minimize contamination of the hub and associated reaction chambers during substrate handling, a thorough evacuation of residual gases upon completion of a deposition process is generally accomplished before transfer of the substrate through the hub. The low conductance of the reaction chamber and show
Messner William J.
Moslehi Mehrdad M.
Nagy Edward J.
Omstead Thomas R.
Starks William
Baker & Botts L.L.P.
Beck Shrive
Chen Bret
CVC Products Inc.
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