High temperature diffusion, wafer

The model is based on the schematic representation of the commercial reactor shown in Figure le. The wafers are supported concentrically and perpendicular to the flow direction within the tube. The heats of reaction associated with the deposition reactions are small because of the low growth rates obtained with LPCVD ( 2 A/s). Furthermore, at high temperatures (1000 K) and low pressures (100 Pa), radiation is the dominant heat-transfer mechanism. Therefore, temperature differences between wafers and the furnace wall will be small. This small temperature difference eliminates the need for an energy balance. Moreover, buoyancy-driven secondary flows are unlikely. In fact, because of the rapid diffusion, the details of the flow field... 

Secondly, the wafer must be very "clean." Even a clean substrate will have 20 to 50 A layer of native oxide on it, and/or some carbon, and this will be enough to impede nucleation and give rise to many defects.1S After wafers are cleaned and inserted into the reactor, there is still the oxide layer to be removed as well as possibly some carbon on the surface. The traditional way of dealing with this phenomena is to operate a high-temperature HCI (1200°C) etch before attempting depositions. This etches away the native oxide, and any carbon on the surface diffuses into the bulk at this temperature. 

The deposition processes discussed so far typically operate such that all the material required for the growing film comes from the overlying gas or liquid phase. Other deposition reactions involve reaction (and therefore consumption) of the underlying substrate itself. Examples of such deposition processes include thermal oxidation, nitridation, or silicidation of silicon, which can be accomplished by exposing a silicon wafer at high temperature to oxygen, ammonia, or titanium tetrachloride, respectively, to form silicon dioxide, silicon nitride, or titanium disilicide. Solid-phase diffusion and reaction processes are involved in each case. 

Thermal oxidation or deposition. The silicon polished wafers are heated in the diffusion furnaces at high temperature ranging between 700 and 1300°C and exposed to a reactive atmosphere of water and ultrapure oxygen under carefully controlled conditions forming an... 

The diffusion mechanisms of dilute Fe atoms in semiconductors are currently one of the most important topics in solid-state physics and related applications. Dilute impurity Fe atoms aregenerallythoughtto occupy only interstitial sites in Si, resulting in rapid diffusion. Fe atoms usually contaminate Si via diffusion annealing and quenching from high temperatures during fabrication of Si wafers. The nature of Fe impurities has been evaluated at low temperatures in such samples. The nature of Fe impurities were then evaluated at low temperature in such samples that must contain differently distributed and/or clustered Fe atoms. 

Diffusion and ion implantation are the two processes used to introduce dopant elements into the wafer. In diffusion, the wafer is heated to high temperatures (800-1300°C) in a quartz tube with the parent chemical and the element diffuses into the wafer. With ion implantation, a newer technology, ions derived from the parent chemical are accelerated down a beam-path and precisely implanted into the wafer. 

---