Coating apparatus – Program – cyclic – or time control – Having prerecorded program medium
Reexamination Certificate
2000-07-11
2002-03-05
Lund, Jeffrie R. (Department: 1763)
Coating apparatus
Program, cyclic, or time control
Having prerecorded program medium
C118S715000, C118S725000, C700S095000, C700S108000, C700S121000, C700S266000, C700S275000, C700S282000
Reexamination Certificate
active
06352591
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to semiconductor processing. More specifically, the invention relates to a method and apparatus for forming dielectric films over high aspect ratio features at temperatures greater than about 500° C., with the dielectric films having low moisture content and low shrinkage. Embodiments of the present invention are particularly useful to deposit doped dielectric films, such as borophosphosilicate glass (BPSG) films, borosilicate glass (BSG) films, or phosphosilicate glass (PSG) films, and to form ultra-shallow doped regions used, for example, as source/drain junctions or as channel stop diffusions in shallow trench isolation. In addition, embodiments of the present invention may also be used to deposit doped dielectric films used as premetal dielectric (PMD) layers, intermetal dielectric (IMD) layers, or other dielectric layers. Further embodiments of the present invention may further be used to deposit undoped dielectric films, such as undoped silicate glass (USG) films used as shallow trench isolation filling oxides, insulating layers, capping layers, or other layers.
One of the primary steps in fabricating modern semiconductor devices is forming a dielectric layer on a semiconductor substrate. As is well known, such a dielectric layer can be deposited by chemical vapor deposition (CVD). In a conventional thermal CVD process, reactive gases are supplied to the substrate surface where heat-induced chemical reactions (homogeneous or heterogeneous) take place to produce a desired film. In a conventional plasma process, a controlled plasma is formed to decompose and/or energize reactive species to produce the desired film. In general, reaction rates in thermal and plasma processes may be controlled by controlling one or more of the following: temperature, pressure, and reactant gas flow rate.
Semiconductor device geometries have dramatically decreased in size since such devices were first introduced several decades ago. Since then, integrated circuits have generally followed the two-year/half-size rule (often called “Moore's Law”) which means that the number of devices which will fit on a chip doubles every two years. Today's wafer fabrication plants are routinely producing 0.5 &mgr;m and even 0.35 &mgr;m feature size devices, and tomorrow's plants soon will be producing devices having even smaller feature sizes. As device feature sizes become smaller and integration density increases, issues not previously considered crucial by the industry are becoming of greater concern. In particular, devices with increasingly high integration density have features with high (for example, greater than about 3:1 or 4:1) aspect ratios. (Aspect ratio is defined as the height-to-spacing ratio of two adjacent steps.)
Increasingly stringent requirements for processes in fabricating these high integration devices are needed in order to produce high quality devices, and conventional substrate processing systems are becoming inadequate to meeting these requirements. One requirement is that the dielectric films formed in the process of fabricating such devices need to be uniformly deposited over these high aspect ratio features without leaving substantial gaps or voids. Another requirement is that these films need to exhibit low shrinkage so that subsequent heating and/or wet etching steps do not cause voids to open up in the deposited film. However, conventional substrate processing systems that typically deposit dielectric films at temperatures less than about 450° C. are unable to produce low moisture films having good gap-filling capabilities without opening substantial voids in subsequent heating and/or wet etching steps. As is well known, these gaps or voids may contribute to device performance unreliability and other problems. Dielectric films used, for example, as PMD or IMD layers in such devices need good high aspect ratio gap-fill capability to avoid problems caused by these gaps or voids. A further requirement is that metal contamination into the wafer during the processing steps be minimized to avoid short circuits and other problems in the devices. As is well known, conventional substrate processing systems using in situ plasma during processing experience physical sputtering of ions which attack chamber surfaces, such as aluminum walls, resulting in metal contamination of the substrate. Use of in situ plasma is therefore undesirable. An improved substrate processing system, which does not use in situ plasma, is needed to provide dielectric films with the desired characteristics of low moisture, high density, low shrinkage, good high aspect ratio gap-filling capability.
In addition to meeting these stringent requirements, substrate processing systems must be able to meet the higher demands for forming ultra-shallow doped regions, which are necessary for high integration devices with shrinking device geometries. With the advent of smaller device geometries, ultra-shallow doped regions in semiconductors are needed for various applications including, for example, source/drain junctions, channel stop diffusions for shallow trench isolation, etc. For example, MOS devices with channel lengths of less than 0.8 &mgr;m often require source/drain junctions having depths less than about 250 nanometers (nm) for adequate device performance. For transistors separated by trench isolation structures of about 0.35 &mgr;m depth, ultra-shallow channel stop regions having a depth on the order of hundreds of nm are usually required. For applications requiring ultra-shallow doped regions, it is important to provide uniform dopant distribution in the doped regions and good control of junction depth.
Current approaches to forming ultra-shallow doped regions, such as ion implantation and gaseous diffusion, are inadequate in some applications. With these current approaches, the ability to control dopant distribution and junction depth is limited, especially as the doped regions become shallower. With an approach like ion implantation, controlling dopant distribution is made difficult due to the built-up concentration of ions at the surface of the semiconductor material. Also, ion implantation causes damage to the semiconductor surface, and methods for repairing this substrate damage often make it more difficult to control dopant distribution and junction depth for ultra-shallow doped regions. For example, ions bombarded at relatively high energy levels have a tendency to tunnel or channel through the semiconductor material and cause damage such as point defects. These point defects, which may lead to irregular and nonuniform junction depths, may be fixed by annealing the implanted semiconductor material at high temperatures (greater than about 900° C.). Annealing the implanted semiconductor material, however, may further increase the junction depth beyond that desired. With an approach like gaseous diffusion, controlling dopant distribution and junction depth is difficult to control in forming ultra-shallow doped regions. As technology progresses to even smaller geometry devices, an alternative approach that is able to control the dopant uniformity and junction depth in ultra-shallow doped regions is needed.
In forming ultra-shallow doped regions, one alternative approach to the current approaches of ion implantation and gaseous diffusion is the use of a doped dielectric film as a dopant diffusion source. In this alternative approach, a doped dielectric film is deposited onto a substrate and used as a source of dopants which are diffused into the substrate to form ultra-shallow doped regions. For example, doped dielectric films are deposited at temperatures less than 500° C. in a deposition chamber, and subsequently heated at temperatures greater than 500° C. in a different chamber, such as an annealing furnace, to perform the dopant diffusion to form the doped region. Controlling thickness, uniformity, and moisture content of the doped dielectric film is important in efficiently forming ultra-shallow doped junctions in the semiconductor mate
Nemani Srinivas
Xia Li-Qun
Yieh Ellie
Applied Materials Inc.
Lund Jeffrie R.
Townsend & Townsend & Crew
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