Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H01L29/70—Bipolar devices
  • H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
  • H01L29/73—Bipolar junction transistors
  • H01L29/737—Hetero-junction transistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/66007—Multistep manufacturing processes
  • H01L29/66075—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials
  • H01L29/66227—Multistep manufacturing processes of devices having semiconductor bodies comprising group 14 or group 13/15 materials the devices being controllable only by the electric current supplied or the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched, e.g. three-terminal devices
  • H01L29/66234—Bipolar junction transistors [BJT]
  • H01L29/66242—Heterojunction transistors [HBT]
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/02—Semiconductor bodies ; Multistep manufacturing processes therefor
  • H01L29/06—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions
  • H01L29/10—Semiconductor bodies ; Multistep manufacturing processes therefor characterised by their shape; characterised by the shapes, relative sizes, or dispositions of the semiconductor regions ; characterised by the concentration or distribution of impurities within semiconductor regions with semiconductor regions connected to an electrode not carrying current to be rectified, amplified or switched and such electrode being part of a semiconductor device which comprises three or more electrodes
  • H01L29/1004—Base region of bipolar transistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H01L29/70—Bipolar devices
  • H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
  • H01L29/73—Bipolar junction transistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L29/00—Semiconductor devices specially adapted for rectifying, amplifying, oscillating or switching and having potential barriers; Capacitors or resistors having potential barriers, e.g. a PN-junction depletion layer or carrier concentration layer; Details of semiconductor bodies or of electrodes thereof ; Multistep manufacturing processes therefor
  • H01L29/66—Types of semiconductor device ; Multistep manufacturing processes therefor
  • H01L29/68—Types of semiconductor device ; Multistep manufacturing processes therefor controllable by only the electric current supplied, or only the electric potential applied, to an electrode which does not carry the current to be rectified, amplified or switched
  • H01L29/70—Bipolar devices
  • H01L29/72—Transistor-type devices, i.e. able to continuously respond to applied control signals
  • H01L29/73—Bipolar junction transistors
  • H01L29/737—Hetero-junction transistors
  • H01L29/7371—Vertical transistors
  • H01L29/7378—Vertical transistors comprising lattice mismatched active layers, e.g. SiGe strained layer transistors
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
  • H01L31/0248—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies
  • H01L31/0256—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof characterised by their semiconductor bodies characterised by the material
  • H01L31/0264—Inorganic materials
  • H01L31/0328—Inorganic materials including, apart from doping materials or other impurities, semiconductor materials provided for in two or more of groups H01L31/0272 - H01L31/032

Definitions

• the invention relates to silicon germanium (SiGe) heterojunction bipolar transistors
• This bandgap offset provides the unique advantages of the SiGe HBT by creating a grading field in the base to enhance carrier diffusion across the base and thus improve transistor speed.
• SiGe HBTs have been used as transistors for small signal amplifiers (i.e. switching approximately 5 volts or less) to provide the switching speeds (above 1GHz) necessary for current wireless communications devices.
• One of the difficulties encountered by the inventors in utilizing SiGe HBTs for small signal amplifiers is that the common emitter output characteristics (i.e. the collector current versus the collector-emitter voltage) for such amplifiers generally exhibit poor Early voltage.
• Fig. la (Prior Art) illustrates the Early voltage for SiGe HBTs without use of the invention. The individual curves indicate the output characteristics for different applied base voltages; the higher the curve, the higher the applied base voltage. Note that as applied base current increases, the slope of the curves become more vertical.
• N A is a key indicator of the current gain cutoff frequency (f ⁇ ) for a SiGe HBT.
• f ⁇ current gain cutoff frequency
• the invention is a SiGe HBT comprising a SiGe layer having a thickness and Ge concentration greater than the SiGe stability limit, and a plurality of misfit dislocations therein that do not create appreciable charge trapping sites.
• the invention is a SiGe HBT with an SiGe layer that has a thickness of at least approximately 70nm and a Ge concentration of at least 10% on a plurality of isolation structures, a base/collector junction above the isolation structures, and a plurality of misfit dislocations that do not appreciably extend above the base/collector junction.
• the invention is a bipolar transistor for a small signal amplifier that has a cutoff frequency of at least approximately 19 GHz, a SiGe layer having a thickness and a Ge content that is greater than the SiGe stability limit, a plurality of isolation regions abutting said collector region, and a base region formed on said collector region, said SiGe layer having a plurality of misfit dislocations therein adjacent said plurality of isolation regions and extending into said collector region without substantially extending into said base region.
• the invention is a method of forming a bipolar transistor, comprising the steps of forming a plurality of isolation regions in a silicon substrate; forming a SiGe layer on said substrate and said isolation regions, said SiGe layer having a thickness and a Ge content that is greater than the SiGe stability limit; and doping said SiGe layer and the substrate with a first dopant to form a collector region, wherein said collector region comprises a plurality of misfit dislocations that do not substantially extend beyond said collector region into other portions of the bipolar transistor.
• Fig. la is plot of IC versus NCE for an experimental SiGe HBT
• Fig. lb is plot of IC versus VCE for an SiGe HBT of the present invention
• Figure 2 shows a plot of collector current density versus cutoff frequency for ⁇ P ⁇ s shown with the Early voltages shown in Figs, la and lb, respectively;
• Fig. 3 is a plot of SiGe concentration versus thickness, showing various experimental data points that include those of the invention, superimposed on the SiGe stability curves reported by prior art articles;
• Fig. 4 is a cross-sectional view of a SiGe HBT constructed in accordance with the teachings of a first embodiment of the invention;
• Fig. 5 shows the Gummel plots (IC, IB vs NCE) of the ⁇ P ⁇ s shown with the Early voltages shown in Figs, la and lb, respectively;
• Fig. 6 is a plot of normalized yield data for SiGe HBTs of the thicknesses shown by the data points in Fig. 3;
• Fig. 7 is a graph illustrating three embodiments of Ge concentration versus layer thickness for the SiGe layer of the invention. Best Mode For Carrying Out The Invention The present inventors found that Early voltage (and hence cutoff frequency) can be substantially enhanced by increasing the thickness of the SiGe layer. While in the prior art it is known to increase SiGe thickness for other purposes, thicker SiGe layers are generally avoided for fear of creating misfit dislocations. As will be explained in more detail below, the present inventors have found that when managed properly, misfit dislocations do not adversely affect the performance or yield of the resulting SiGe HBTs.
• SiGe enhances charge mobility by introducing mechanical strain due to the lattice mismatches inherent in the Si-Ge compound.
• the accepted wisdom in the art is that the resulting crystal dislocations will reduce both performance and yield.
• the performance penalty would be due to dislocations relieving the mechanical stresses that create the bandgap offsets that SiGe provides.
• the yield penalty would be due to the defects disturbing the crystallography of the substrate.
• SiGe stability limits The different SiGe stability limits reported by Matthews-Blakesley and Stiffler are plotted in Fig. 3, which shows the reported optimal relationships between SiGe thickness and Ge concentration.
• Fig. 3 illustrates the SiGe thicknesses and concentrations that were used to provide the data reported herein. For the sake of comparison Ge concentration was fixed at 10%, and thickness was increased. Note that the first two data points are at or below the SiGe stability curves; these devices provided the Early voltage results shown in Fig. la .
• the SiGe thicknesses of the invention start at approximately 70nm. As shown in Fig.
• the SiGe HBT of the invention is formed on a monocrystalline silicon substrate 10 having shallow trench isolation regions (STI) 12 therein.
• An SiGe layer 14 is epitaxially grown using conventional techniques on the substrate 10, to a thickness t of at least 40nm and a Ge concentration of at least approximately 10%.
• the SiGe layer is insitu doped during growth with boron to form a base region 14B (not shown to scale laterally). Note that as a practical matter boron from the base region can diffuse deeper into the SiGe layer during various processing thermal cycles, from a depth X to a depth Y into the SiGe layer 14. As such, the resulting base/collector junction can be at JA or JB.
• Fig. lb illustrates the collector current versus the collector-emitter voltage for the SiGe HBT of the invention. Note the substantial improvement in Early voltage (the plots are far more horizontal for all applied base voltages, meaning collector current is constant for increased collector- emitter voltages).
• Figure 2 shows a plot of collector current density versus cutoff frequency for (a) an NPN with Early voltages as shown in Fig. la (indicated by the dashed line); and (b) the NPN with the Early voltages shown in Fig. lb (indicated by the solid line).
• An aspect of the invention is that these gains in Early voltage and cutoff frequency do not come at the expense of dislocations that decrease performance (by charge trapping) or yield (by crystal dislocations).
• Fig. 5 shows the Gummel plots (IC, IB vs VCE) of the NPNs shown with the Early ⁇ voltages shown in Figs, la and lb, respectively. Note that the IB and IC curves in the Gummel plots have ideal slopes (n ⁇ l (n is a measure of ideality) or 60 mV/decade at room temperature) which indicates that there was no substantial charge trapping induced by the misfit dislocations formed as part of the thicker SiGe layer.
• Fig. 6 shows a plot of normalized yields for SiGe HBTs of the invention, for different SiGe thicknesses.
• the first region shown thickness of 300 angstroms, Ge concentration of 10%
• Fig. 2 shows the upper limit of the SiGe stability curves (see Fig. 2).
• Fig. 7 is a plot of Ge concentration percentage versus depth of a 70nm thick SiGe layer, for three embodiments of the present invention.
• the Ge concentration in the SiGe layer of the invention is approximately 10% throughout the thickness of the 40nm-thick SiGe film.
• This embodiment produced the collector current versus the collector-emitter voltage plot of the invention as shown by the solid lines of Fig. 3.
• the Ge concentration in the SiGe layer of the invention is approximately 10% throughout the thickness of the 70nm-thick film.
• the first and second embodiments produced the yield data shown in Fig. 6.
• the Ge concentration in the SiGe layer of the invention is approximately 25% at the upper surface of the SiGe layer and for the first third of its thickness (approximately 23nm for a 70nm-thick SiGe film), then the Ge percentage is dropped in a substantially linear manner from 25% to 10% over the second third of the thickness of the SiGe film, then the concentration is at 10% for the remaining thickness of the film.
• the SiGe layer is 150nm thick, and has a Ge concentration of approximately 10% throughout this thickness.
• the inventors found that even at this thickness and Ge content the misfit dislocations had the general properties reported herein. Based on these results, the inventors believe the SiGe layer could be even thicker than 150nm and still provide the reported properties.
• the ideal Gummel plots indicate that the resulting dislocations did not establish appreciable charge trapping sites.
• the inventors have found that SiGe layers that have misfit dislocations can improve performance without degrading yield.
• the inventors have found that the large numbers of misfit dislocations, in and of themselves, are not determinative of performance or yield. Rather, the key is that the dislocations do not create appreciable charge trapping, and do not extend in large numbers past the base/collector junction.
• the invention has applicability to electrical circuits and devices, especially those used in communication systems.

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• 2002
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