Coating apparatus – Gas or vapor deposition – Crucible or evaporator structure
Patent
1998-07-08
1999-11-02
Bueker, Richard
Coating apparatus
Gas or vapor deposition
Crucible or evaporator structure
C23C 1400
Patent
active
059762632
DESCRIPTION:
BRIEF SUMMARY
The invention relates to apparatus for depositing layers of semiconductor material upon a substrate under vacuum conditions. More specifically, the invention relates to Molecular Beam Epitaxy apparatus, particularly to an improved source design for use in such apparatus.
There are many deposition techniques which may be used in the manufacture of semiconductor devices. One such technique is Molecular Beam Epitaxy (MBE), in which epitaxial (i.e. single-crystal) layers of materials are deposited upon a substrate wafer. The technique involves placing the material which is to be deposited inside the crucible of an MBE source within an ultra-high vacuum (UHV) system (<10.sup.-10 Torr), and heating the crucible. The material is thus vaporized and a beam of the material is formed, the characteristics of which depend on the source design. In MBE, the beam is a so-called "molecular beam", which can be defined as a collimated beam of atoms or molecules at low pressure, in which all the particles are travelling in the same direction and few collisions occur between them. This molecular beam travels from the source to impinge upon a substrate wafer where the material is deposited. Layers of different materials are formed by providing a plurality of sources containing, for example, Gallium, Indium, Aluminium, Arsenic, etc. In this way, semiconductor devices may be manufactured.
The deposited layers must fulfill stringent criteria in order to be useful for device manufacture. One requirement to be satisfied is that the layers must be uniform. Commonly, the substrate is rotated in order to improve the uniformity of deposition. Other requirements are freedom from impurities and surface defects. As mentioned, the source design greatly affects the nature of the layers, and much research has been performed on the properties and behavior of various different source designs.
FIGS. 1a-1e are diagrammatic representations of various known source configurations, and FIGS. 2a-2e show the profile of the layer deposited using each configuration. The figures are not to scale.
FIG. 1a shows a simple cylindrical crucible (1) with an open neck, known conventionally as a K-cell. This makes good use of the heated volume, and a high vapour flux may be obtained. As can be seen from FIG. 2a the layer uniformity over the central portion of the wafer (2) is fairly good, but the uniformity falls off towards the edges of the wafer. If a smaller wafer is used, spanning only the central portion, layer uniformity is improved but a large amount of material misses the wafer and goes to waste. Another drawback of the open-necked cylindrical crucible is that as the level of material in the crucible decreases, the length of crucible through which the vaporized material leaving the surface of the material must pass before exiting the crucible mouth is increased, which results in increased collimation of the "beam", of vapour. Thus, since the degree of collimation changes as the level of material becomes lower, the beam profile alters over time, reducing the reproducibility of substrate deposition, and the stability of deposition over time. Another problem is that recondensed droplets of material at the neck of the crucible result in oval defect formation on the substrate. A common solution to this problem is to provide the source with additional heating means around its open end, thus forming a two-zone source.
FIG. 1b shows a conical crucible (3), which addresses some of the problems of the cylindrical crucible. This is also a type of conventional K-cell. Because of the shape, the "beam collimation" problem is less relevant. As can be seen from FIG. 2b, layer uniformity is also good, although material wastage is high. The design of the conical crucible does not, however, avoid the problem of oval defects, although as before, additional heating means may be provided so as to form a two-zone source. Furthermore, heat loss is higher due to the wide mouth, and the use of the heated volume is inefficient. Another problem is that as the level of material in
REFERENCES:
patent: 4550411 (1985-10-01), Stonestreet et al.
patent: 4856457 (1989-08-01), Knauer
patent: 5026454 (1991-06-01), Parmenter et al.
"Multiholed-Plug Cell for Molecular Beam Source", by Takashi Nomura et al., Bulletin Research Institute for Electron, vol. 19, pp. 37-42, 1984.
"Multiholed Plug Effusion Cell", by Takashi Nomura et al., Journal Vacuum Society of Japan, vol. 29, pp. 309-314, 1986.
"Angular Distribution of Molecular Beams From Modified Knudsen Cells for Molecular-Beam Epitaxy", by L.Y.L. Shen, Journal of Vacuum Science and Technology, vol. 15, pp. 10-12, 1977.
Bueker Richard
Thermo Instrument Systems Inc.
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