Gallium arsenide wafer

A technician handling a gallium arsenide wafer in a clean-room facility in the semiconductor industry. 

Galliiun phosphide and gallimn arsenide deposition on gallium arsenide wafers require heavy concentrations of dopant gases (eg., arsine and phosphine). Prescrubbers for these CVD reactors contain high concentrations of arsine and phosphine, and exposure far above acceptable limits can occur if these prescrubbers are indiscriminately opened, t l... 

FIGURE 14 Cathodoluminescence image of defects in a gallium arsenide wafer. 

Monolayers can be transferred onto many different substrates. Most LB depositions have been perfonned onto hydrophilic substrates, where monolayers are transferred when pulling tire substrate out from tire subphase. Transparent hydrophilic substrates such as glass [18,19] or quartz [20] allow spectra to be recorded in transmission mode. Examples of otlier hydrophilic substrates are aluminium [21, 22, 23 and 24], cliromium [9, 25] or tin [26], all in their oxidized state. The substrate most often used today is silicon wafer. Gold does not establish an oxide layer and is tlierefore used chiefly for reflection studies. Also used are silver [27], gallium arsenide [27, 28] or cadmium telluride wafer [28] following special treatment. 

For all its advantages, gallium arsenide has yet to be used on any large scale, at least outside optoelectronic applications. The reasons are cost (over ten times that of silicon), small wafer size, low thermal conductivity (1/3 that of silicon), and low strength. 

Gallium arsenide ingots are wax mounted to a graphite beam and sawed into individual wafers through the use of automatically operated inner diameter (ID) diamond blade saws. This operation is done wet with the use of lubricants and generates a gallium arsenide slurry. 

To appreciate the rapid development of process technology, the progression of the IC industry must be considered first. (For summaries of the historical development of this field, see references 1 and 2.) A central theme in the IC industry is the simultaneous fabrication of hundreds of monolithic ICs (or chips) on a wafer (or slice) of silicon (or other material such as gallium arsenide), which is typically 100-150 mm in diameter and 0.75 mm thick. In silicon technology, chip areas generally range from a few square millimeters to over 100 mm2. A large number (often more than 100) of individual process steps, which are precisely controlled and carefully sequenced, are required for the fabrication. 

There are enough suppliers of this type of silicon, including, for instance, Dow-Coming, Dynamit Nobel, Shin-Etsu, Tokuyama Soda, Motorola, and Texas Instruments. A possible substitute for the silicon used to produce wafers is gallium arsenide, in which Rhone-Poulenc, ICI, and Shinetsu are already involved. 

On high-power-density chips, such as gallium arsenide, it is a common practice to reduce the thermal resistance by thinning the wafer via chemical and mechanical means from 0.015 in. to as thin as 0.002 in. If a chip thickness... 

The most common substrates used in the semiconductor industry are Si and other compound semiconductor wafers such as gallium arsenide (GaAs). These wafers are produced in various sizes and cut along different crystalline planes. They are also doped with many types and concentrations of impurities that determine whether they are n- or p-type semiconductors. 

Chemical Vapor Deposition. Chemical vapor deposition (CVD) is a process where by the heat-induced decomposition of gases form different semiconductor layers such as silicon dioxide, silicon nitride, polysilicon, and gallium arsenide on the surface of the wafer. When the layer formed is a continuation of the crystalline structure of the substrate, the process used is epitaxial growth. Other, non-epitaxial forms of CVD involve the deposition of layers that are a different structure than the substrate. Table 5 outlines typical chemistries associated with CVD. 

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