Transient and Spatial Radiative Properties of Patterned Wafers during Rapid Thermal Processing
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Author to whom all correspondence should be addressed 287 Mat. Res. Soc. Symp. Proc. Vol. 389 01995 Materials Research Society
Consequently, monitoring and correcting only the center region of the wafer may lead to damage or uneven growth at the edges. This uneven cooling or heating at the edges is due to the physical geometry of the wafer, the chamber design, and the multilayer structures on the wafer. Efforts to map the temperature distribution over the wafer transiently have been investigated [8]. Patterning Emissivity, absorptivity, reflectivity and transmissivity of the wafer are dependent on several microscale radiation effects: partial transparency of silicon at low temperatures, surface roughness, thin film structures already present in the wafer, thin films being grown on the wafer, and the spectral characteristics of the heat source. These variations alter pyrometry readings and the radiative exchange with the wafer. The deposition uniformity, which affects the radiative properties, in RTCVD has been found to be coupled to the temperature uniformities [9,10]. Patterning the wafer affects the radiative properties of the wafer during processing. Patterns of many different dimensions are used in the microelectronic industry. The dimensions of patterns range from sub-micron to millimeter length scales. The materials used in the patterns includes semiconductors, dielectrics, metals, and silicides. The radiative characteristics of these patterns affect pyrometer readings as well as heat transfer dynamics during processing. In fact, calibrating RTP systems with unpatterned wafers may lead to errors during the processing of patterned wafers. Patterning effects on macroscale patterning could lead to temperature non-uniformities that could reach -90'C [11]. Local temperature non-uniformities on a smaller scale were on the order of -5'C [12]. Additionally, the patterning affects the radiative properties, heat transfer dynamics, wafer warpage, and localized stress effects. Silicidation and other microstructural processes RTP has found application in changing the microstructure of thin films as well as for alloying processes. Aluminum alloying (below 600'C) was investigated for temperature and processing uniformities [16]. Results indicated a variation in grain sizes over the wafer due to temperature non-uniformities. Other researchers have examined the effect of metallization (over Si and GaAs wafers) on radiative properties and temperature non-uniformities [17]. RTP has also found use in crystallization of ferroelectric films for nonvolatile memory devices [18]. The static and dynamic radiative properties must be considered in analyses and temperature measurements. This is especially true with RTP silicidation. The application of RTP to silicidation has been successful because of the reduced contamination levels and the limited junction diffusion [4]. One promising process is the thermal reaction of Co with silicon for self-aligned silicidation (salicide). The Co does not react with the oxide, but does react with
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