Jeffrey C. Gelpey

Process Control for a Rapid Optical Annealing System

When high temperature processes are being carried out in a diffusion furnace, temperature control is accomplished in a straight forward manner. By using thermocouples and a proportional controller, sufficient accuracy and control are available to the process engineer. But with the current shift toward the more rapid annealing schemes, better control is a necessity. In order to achieve this accuracy, especially when the heat source is a 100 kilowatt arc lamp, more sophisticated control methods must be employed. By using an optical pyrometer tuned to operate at a wavelength where external interferences are minimized, wafer temperature may be monitored to a high degree of accuracy and with the fast response times needed. Coupling the output of the pyrometer to a microprocessor based controller allows the engineer to create and use multi stepped time/temperature profiles which are highly repeatable. This paper will describe such a system and how it is used in a production oriented rapid optical annealing system.

Uniformity characterization of an RTP system

Abstract The use of rapid thermal processing (RTP) is expanding greatly in semiconductor processing. As demands on equipment become greater, the need to characterize system performance also increases. One aspect of RTP equipment performance which has proven difficult to measure is the temperature uniformity of the wafer during processing. Several methods of direct temperature measurement are described: high speed calorimetry to measure the incident power distribution, multiple thermocouple, and scanning pyrometer measurements for directly measuring local wafer temperatures. Indirect techniques which are more applicable to end user characterization are also discussed: measurement of sheet resistance across a wafer implanted with a uniform high dose of arsenic ions and thickness uniformity of thin silicon oxides grown by rapid thermal oxidation. Finally, the use of melt uniformity and slip generation as qualitative indicators of uniformity is discussed. Examples of measurements and their use in the adjustment of a commercial system (Eaton ROA-400) are given.

Capless Rapid Thermal Annealing of Silicon Ion Implanted Gallium Arsenide

Argon arc lamp rapid thermal annealing of ion implanted gallium arsenide (GaAs) has been studied. Silicon ion was implanted into semi-insulating GaAs at 120 keV with a dose of 3×1012 cm-2. Capless annealing was performed by dc argon arc lamp at temperatures of 850-1000°C. Carrier concentration profiles are abrupt at the interface and fit well with the LSS profile. Abruptness of the profile was 0.78 at 850°C for 15 s and at 1000°C for 2 s, where the abruptness was defined as 1.0 in LSS theoretical profile and a lower value shows a gentler profile. This value is much greater than that by tungsten-halogen lamp rapid thermal annealing of 0.36 and furnace annealing of 0.34. This annealing technique is useful for the formation of a shallow channel layer with abruptcarrier concentration profile for GaAs MESFETs.

Rapid annealing using the water-wall arc lamp

Abstract Rapid annealing techniques using graphite strip heaters [1], tungsten-halogen lamps [2], and conventional arc lamps [3] have been gaining favor to provide controllable activation of ion implants while minimizing the diffusion of the implanted dopant. These conventional heat sources have given good results, but they all suffer from limitations in power output and/or the ability to change power levels rapidly. The water-wall d.c. arc lamp overcomes these limitations and allows precise control and excellent reproducability of the anneal cycle. The high power output and excellent optical coupling of the water-wall lamp allows ilumination from one side of the sample. The wafer temperature can then be directly monitored with a pyrometer and the fast response time of the lamp allows the pyrometer output to control the lamp power and, hence, provide direct feedback control of the wafer temperature. Direct control is important to overcome variations caused by different doping levels or dielectric coatings on the wafers. Annealing experiments using the water-wall lamp have shown that good activation and essentially complete removal of implant damage can be achieved while moving the junction only minimally [4,5]. The degree of dopant diffusion (generally on the order of 1000 A) is small compared to device dimensions but is somewhat more than would be expected from classical diffusion theory using published diffusion coefficients. The differences depend on the implanted species and models are being developed to explain the discrepancies. The vary rapid heating and cooling rates obtainable with the water-wall lamp offer a great deal of flexibility in the time/temperature cycles used for annealing (or other rapid thermal processes). There are indications that the ability to achieve a rapid cooling rate allows more complete activation of high dose implants and rapid heating rates may reduce the residual damage and amount of diffusion.

Comparison of the Growth Kinetics of Oxides Grown in Tungsten-Halogen and Water Cooled Arc Lamp Systems

Rapid thermal oxidation of silicon has been performed in a tungsten-halogen system (AG-410) and a water-wall arc lamp system (Eaton ROA-400). Growth kinetics of the oxides are studied with particular attention to ramp-up ambient conditions, dwell time, maximum wafer temperature and difference in activation energies. These parameters are characterized using ellipsometry in order to measure system bias with respect to growth rate and breakdown. Experiments were designed to identify the differences in the initial enhanced growth conditions, and their effect on growth kinetics during the dwell cycle.

Rapid Thermal Processing of Silicon Ion Implanted Channel Layers in GaAs

The use of Rapid Thermal Processing (RTP) for the activation of silicon ion implanted channel layers in GaAs MESFET devices has been studied. Tungsten-halogen lamp and Water-wall DC arc lamp RTP have been compared. The arc lamp gave superior abruptness of the carrier concentration profile (78% at 850°C for 15 seconds or 1000°C for 2 seconds) and dopant activation greater than 60%. These parameters are important to achieve good MESFETs fabricated using arc lamp RTP was also studied. The transconductance (g m ) of the devices usinq RTP was 78mS/mm which is much higher than achieved with similar samples using furnace annealing. Both capped and capless RTP was examined. Although capped annealing generally yields superior surface quality, the capless annealing provided good electrical properties in a process window which also yielded adequate surface quality and good devices.