Rapid thermal processing

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Rapid Thermal Processing (or RTP) refers to a semiconductor manufacturing process which heats silicon wafers to high temperatures (up to 1,200 °C or greater) on a timescale of several seconds or less. During cooling, however, wafer temperatures must be brought down slowly so they do not break due to thermal shock. Such rapid heating rates are often attained by high intensity lamps or lasers. These processes are used for a wide variety of applications in semiconductor manufacturing including dopant activation, thermal oxidation, metal reflow and chemical vapor deposition.

Temperature Control

One of the key challenges in rapid thermal processing is accurate measurement and control of the wafer temperature. Monitoring the ambient with a thermocouple has only recently become feasible, in that the high temperature ramp rates prevent the wafer from coming to thermal equilibrium with the process chamber. One temperature control strategy involves in situ pyrometry to effect real time control.Used for melting iron for welding purposes.

Rapid thermal anneal

Rapid thermal anneal (RTA) is a subset of Rapid Thermal Processing. It is a process used in semiconductor device fabrication which consists of heating a single wafer at a time in order to affect its electrical properties. Unique heat treatments are designed for different effects. Wafers can be heated in order to activate dopants, change film-to-film or film-to-wafer substrate interfaces, densify deposited films, change states of grown films, repair damage from ion implantation, move dopants or drive dopants from one film into another or from a film into the wafer substrate.

Rapid thermal anneals are performed by equipment that heats a single wafer at a time using either lamp based heating, a hot chuck, or a hot plate that a wafer is brought near. Unlike furnace anneals they are short in duration, processing each wafer in several minutes.

To achieve short time annealing time trade off is made in temperature and process uniformity, temperature measurement and control and wafer stress as well as throughput.

Recently, RTP-like processing has found applications in another rapidly growing field — solar cell fabrication. RTP-like processing, in which an increase in the temperature of the semiconductor sample is produced by the absorption of the optical flux, is now used for a host of solar cell fabrication steps, including phosphorus diffusion for N/P junction formation and impurity gettering, hydrogen diffusion for impurity and defect passivation, and formation of screen-printed contacts using Ag-ink for the front and Al-ink for back contacts, respectively.

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