Advanced epitaxial growth techniques permit the use of pseudomorphic Si/sub 1-x/Ge/sub x/ alloys in silicon technology. The smaller bandgap of these alloys allows for a variety of novel band-engineered structures that promise to enhance silicon-based technology significantly. The authors discuss the growth and properties of pseudomorphic Si/sub 1-x/Ge/sub x/ structures and then focus on their applications, especially the Si/sub 1-x/Ge/sub x/-base heterojunction bipolar transistor (HBT). They show that HBTs in the Si/sub 1-x/Ge/sub x/ system allow for the decoupling of current gain and intrinsic base resistance. Such devices can be made by using a variety of techniques, including molecular-beam epitaxy and chemical vapor deposition. The authors describe the evolution of fabrication schemes for such HBTs and describe the DC and AC results obtained. They show that optimally designed HBTs coupled with advanced bipolar structures can provide performance leverage. >

Heterojunction bipolar transistors using Si-Ge alloys

The physics and technology of a relatively new, short‐time, thermal processing technique, namely rapid isothermal processing (RIP), based on incoherent sources of light for the fabrication of semiconductor devices and circuits, are reviewed in this paper. Low‐cost, minimum overall thermal budget, low‐power consumption, and high throughput are some of the attractive features of RIP. The discussion of RIP, in the context of other thermal processes, history, operating principles, different types of RIP systems, various applications of RIP using single processing steps, and novel applications of RIP, including in situ processing and multistep processing, is described in detail. Current trends are in the direction of RIP‐dominated silicon integrated circuit fabrication technology that can lead to the development of the most advanced three‐dimensional integrated circuits suitable for applications such as parallel processing and radiation hardening. RIP is not only a superior alternative to furnace processing, but it is also the only way to perform certain crucial steps in the processing of compound semiconductor devices such as high‐mobility transistors, resonant tunneling devices, and high‐efficiency solar cells. Development of more accurate temperature measurement techniques and theoretical studies of heat transfer and other fundamental processes are needed. Dedicated equipment designed for a specific task coupled with in situ processing capabilities will dominate the future direction of RIP.

Rapid isothermal processing

In accordance with the method, an integrating kaleidoscope and lamps combine to cause heating of a semiconductor wafer to achieve desired effects such as annealing, etc. In one form of the method, the heating of the wafer is such as to achieve rapid annealing by isothermal heating alone. In another form of the method the heating is such as to effect isothermal heating immediately followed by thermal flux heating.

Apparatus for heating semiconductor wafers in order to achieve annealing, silicide formation, reflow of glass passivation layers, etc.

RTA studies of B, BF 2 and As implantations in silicon are reviewed. The optical coupling properties of the wafer are considered as a motive for obtaining accurate temperature assessment. Optical pyrometer techniques with feedback control are now commonly used. Enhanced diffusion of boron is widely reported for the channel tail in the several second time frame at ∼1050°C. Boron diffusion in preamorphized and crystalline silicon are compared, and dopant interactions (gettering) with residual disorder located just beyond the amorphous/crystalline (α/c) interface are discussed. The removal of residual α/c disorder from a 5 × 10 15 As/cm 2, 100 keV implant is shown to occur with ∼5.0 eV energy, while a “normal” concentration enhanced diffusion with ∼4.0 eV activation energy is obtained including data in the several second (RTA) time frames. Shallower defect free arsenic junctions are made using high temperature-short time cycles, rather than longer times at lower temperatures. The arsenic diffusion issues are discussed.

A review of rapid thermal annealing (RTA) of B, BF 2 and As ions implanted into silicon

This study was directed toward exploring the relationship between the implant conditions and the depth and nature of the amorphous layers generated in silicon. Interest in amorphous layer morphology stems from its role in affecting crystal defects remaining after amorphous‐to‐crystalline transformation. High‐dose implants of As, P, and B were used to generate buried and surface amorphous layers at slightly higher than room temperature. The amorphous layer depths were measured and the depth‐fluence and depth‐energy relationships were compared with Brice’s analysis. It was found that good fits were obtained for a threshold damage density of 2.5×1020 keV cm−3 for As and 1.0×1021 keV cm−3 for P. For B, the results could be described by a threshold damage density of 5.0×1021 keV cm−3 or greater. Lower weight ion implantations exhibit a greater tendency to generate buried amorphous layers as well as to generate amorphous layers which include a smaller fraction of the total implanted fluence than is found for he...

Formation of amorphous layers by ion implantation

Short time annealing has recently become of interest in silicon processing as a technique to activate ion implanted dopants, remove defects, and regrow amorphized silicon, with minimal diffusion of the dopant atoms. Short time annealing is carried out using a variety of energy sources ranging from arc lamps and resistance heaters with heating times of a few tens of seconds, to laser, electron, and ion sources with heating times of a few milliseconds down to nanoseconds. The annealing processes are grouped according to the time durations of the anneal and with reference to the thermal response time of the silicon. These are designated as adiabatic for 10−2 sec. Processes in the adiabatic regime result in surface melting, regrowth of silicon free of extended defects, and complete dopant activation. However, the dopant diffuses throughout the melt zone. In the thermal flux and isothermal annealing regimes the dopant can be activated, and amorphous silicon regrown epitaxially with little dopant diffusion. In the limited results reported to date, the complete removal of extended defects has not been achieved. Further investigation may yield new results in extended defect removal.

T. O. Sedgwick

Papers

Short time annealing