J.H. Comfort

75-GHz f/sub T/ SiGe-base heterojunction bipolar transistors

The fabrication of silicon heterojunction bipolar transistors which have a record unity-current-gain cutoff frequency (f/sub T/) of 75 GHz for a collector-base bias of 1 V, an intrinsic base sheet resistance (R/sub bi/) of 17 k Omega / Square Operator , and an emitter width of 0.9 mu m is discussed. This performance level, which represents an increase by almost a factor of 2 in the speed of a Si bipolar transistor, was achieved in a poly-emitter bipolar process by using SiGe for the base material. The germanium was graded in the 45-nm base to create a drift field of approximately 20 kV/cm, resulting in an intrinsic transit time of only 1.9 ps.<<ETX>>

Si/SiGe epitaxial-base transistors. I. Materials, physics, and circuits

A detailed review of SiGe epitaxial base technology is presented, which chronicles the progression of research from materials deposition through device and integration demonstrations, culminating in the first SiGe integrated circuit application. In part I of this paper, the requirements and processes for high-quality SiGe film preparation are discussed, with emphasis on fundamental principles. A detailed overview of SiGe HBT device design and implications for circuit applications is then presented. >

Si/SiGe epitaxial-base transistors. II. Process integration and analog applications

For pt. I, see ibid., vol. 3, p. 455-68 (1995). This part focuses on process integration concerns, first described in general terms and then detailed through an extensive review of both simple non-self-aligned device structures and more complex self-aligned device structures. The extension of SiGe device technology to high levels of integration is then discussed through a detailed review of a full SiGe HBT BiCMOS process. Finally, analog circuit design is discussed and concluded, with a description of a 12-bit Digital-to-Analog Converter presented to highlight the current status of SiGe technology. >

On the profile design and optimization of epitaxial Si- and SiGe-base bipolar technology for 77 K applications. I. Transistor DC design considerations

The DC design considerations associated with optimizing epitaxial Si- and SiGe-base bipolar transistors for the 77-K environment are examined in detail. Transistors and circuits were fabricated using four different vertical profiles, three with a graded-bandgap SiGe base, and one with a Si base for comparison. All four epitaxial-base profiles yield transistors with DC properties suitable for high-speed logic applications in the 77-K environment. The differences between the low-temperature DC characteristics of Si and SiGe transistors are highlighted both theoretically and experimentally. A performance tradeoff associated with the use of an intrinsic spacer layer to reduce parasitic leakage at low temperatures and the consequent base resistance degradation due to enhanced carrier freeze-out is identified. Evidence that a collector-base heterojunction barrier effect severely degrades the current drive and transconductance of SiGe-base transistors operating at low temperatures is provided. >

A room temperature 0.1 /spl mu/m CMOS on SOI

An advanced 0.1 /spl mu/m CMOS technology on SOI is presented. In order to minimize short channel effects, relatively thick nondepleted (0.15 /spl mu/m) SOI film, highly nonuniform channel doping and source-drain extension-halo were used. Excellent short channel effects (SCE) down to channel lengths below 0.1 /spl mu/m were obtained. It is shown that undepleted SOI results in better short channel effect when compared to ultrathin depleted SOI. Devices with little short channel effect all the way to below 500 /spl Aring/ effective channel length were obtained. Furthermore, utilization of source-drain extension-halo minimizes the bipolar effect inherent in the floating body. These devices were applied to a variety of circuits: Very high speeds were obtained: Unloaded delay was 20 ps, unloaded NAND (FI=FO=3) was 64 ps, and loaded NAND (FI=FO=3, C/sub L/=0.3 pF) delay was 130 ps at supply of 1.8 V. This technology was applied to a self-resetting 512 K SRAM. Access times of 2.5 ns at 1.5 V and 3.5 ns at 1.0 V were obtained. >

73-GHz self-aligned SiGe-base bipolar transistors with phosphorus-doped polysilicon emitters

The authors report a thermal-cycle emitter process using phosphorus for the fabrication of self-aligned SiGe-base heterojunction bipolar transistors. The low thermal cycle results in extremely, narrow basewidths and preservation of lightly doped spacers in both the emitter-base and base-collector junctions for improved breakdown. Transistors with 35-nm basewidths were obtained with low emitter-base reverse leakage and a peak cutoff frequency of 73 GHz for an intrinsic base sheet resistance of 16 k Omega / Square Operator . Minimum NTL (nonthreshold logic) and ECL (emitter-coupled logic) gate delays of 28 and 34 ps, respectively were obtained with these devices.<<ETX>>

Profile leverage in self-aligned epitaxial Si or SiGe base bipolar technology

The authors have developed a planar, self-aligned, epitaxial Si or SiGe-base bipolar technology and explored intrinsic profile design leverage for high-performance devices in three distinct areas: transit time reduction, collector-base (CB) junction engineering, and emitter-base (EB) junction engineering. High f/sub T/ Si (30-50 GHz) and SiGe (50-70 GHz) epi-base devices were integrated with trench isolation and polysilicon load resistors to evaluate ECL (emitter coupled logic) circuit performance. A 15% enhancement in ECL circuit performance was observed for SiGe relative to Si devices with similar base doping profiles in a given device layout. Minimum SiGe-base ECL gate delays of 24.6 ps (8 mW) were obtained. Lightly doped spacers were positioned in both the EB and CB junctions to tailor junction characteristics (leakage, tunneling, and avalanche breakdown), reduce junction capacitances, and thereby obtain an overall performance improvement.<<ETX>>

SiGe-base heterojunction bipolar transistors: physics and design issues

It has been shown that SiGe technology has the capability to extend the performance of Si bipolar transistors at both high and low current levels. The ability to tailor the bandgap, independently of the doping profile design, provides considerable flexibility for optimizing cutoff frequency, intrinsic base resistance, and junction capacitances for a given application. It is concluded that, when combined with a self-aligned process, SiGe can significantly improve the speed of Si bipolar circuits.<<ETX>>

The thermal stability of SiGe films deposited by ultrahigh‐vacuum chemical vapor deposition

The thermal stability of SiGe films deposited by ultrahigh‐vacuum chemical vapor deposition was studied. Various Ge compositional profiles, including boxes, trapezoids, and triangles were examined. Planar‐view transmission electron microscopy was performed following growth and after furnace annealing at 950 °C for 30 min to determine the presence and density of misfit dislocations. All profiles showed very similar stability behavior when expressed in terms of the total thickness of the film, heff, and the effective strain present in the layer, eeff. Following the anneal, misfit dislocations were observed when heff exceeded the critical thickness, as defined by Matthews and Blakeslee [J. Cryst. Growth 27, 118 (1974)], by a factor of ∼2.

63-75 GHz f T SiGe-base heterojunction bipolar technology

Experimental results for maximum cut-off frequency (fT) values of 75 and 52 GHz were achieved for SiGe-base and Si-base bipolar transistors with intrinsic base sheet resistances in the 10-17 k&Omega;/square range. These results extend the speed of silicon bipolar devices into a regime previously reserved to GaAs and other compound semiconductor technologies. Excellent junction characteristics were also obtained for devices as large as 100000 &mu;m2 and for current densities as high as 106 A/cm2. The performance levels obtained for the SiGe transistors, which contain less than 10% germanium in the base, represent almost a factor of two increase in the speed of a Si bipolar transistor. These results demonstrate the significant performance advantage offered by SiGe heterojunction technology