Emitter Etching and Endpoint Detection of Heterojunction Bipolar Transistors

S. W. Pang, S. Thomas III, D. J. Kahaian, H. H. Chen, and E. W. Berg

University of Michigan, Ann Arbor, Michigan 48109-2122, USA

Endpoint detection for the emitter etch of an AlInAs/GaInAs heterojunction bipolar transistor with a graded nine period AlInAs/GaInAs superlattice was investigated. Ga optical emission at 417.2 nm was detected after ~10 nm of the superlattice had been etched. (Figure 1) Once this occurred, an additional overetch of 30 nm is required to completely remove the superlattice and the lightly doped p-type GaInAs spacer layer. The etch-induced damage was characterized by measuring the contact resistivity (¦Ñc) of the base layer and comparing this to a wet etched sample. Two step etching was studied to minimize surface roughness and reduce damage. This requires etching at high rf power initially to maintain smooth surface morphology and then etching at reduced rf power to remove damage created in the first part of the etch. By etching the first 50% of n-type GaInAs at 160 W rf power and the rest at 30 W rf power, a nearly damage free smooth surface can be achieved. Etching with just 30 W rf power can completely eliminate the damage. Damage to both n-type and p+-GaInAs has been studied. For n-type material, damage decreases rc and for p+-type material damage increases rc when compared to the wet etched samples. The effect of annealing on the transmission line measurements was also studied. For the p+-GaInAs, an annealed contact on the sample etched with low rf power had a contact resistivity of 8.1X10-6 ¦¸ cm2. This is lower than the wet etched sample, where rc was 1.6X10-5 ¦¸ cm2. (Figure 2) This could be related to the smoother surface that was obtained from dry etching when compared to wet etching.

Optical emission spectroscopy was used to monitor the Ga emission intensity at 417.2 nm for endpoint detection in order to overcome nonselective etching between AlInAs and GaInAs as well as run-to-run variations in etch rate. The etching of the AlInAs emitter layer was stopped at different overetch times after the increase in the Ga intensity was detected. (Figure 3) Ex situ surface analysis was used to characterize the surface after etching. X-ray photoelectron spectroscopy showed that both Al and Ga were present on the surface when overetching 3 s. No Al was detected for the 6 s overetch time, indicating that the AlInAs layer was completely removed. The specific contact resistivity (¦Ñc) at the etched surface was evaluated using transmission line measurements. As the overetch time increased from 3 to 6 s, rc decreased from 7.3x10-4 to 4.1x10-4 -cm2. This also indicates complete removal of the AlInAs emitter layer. Overetching of the GaInAs base layer should be limited for low base resistance to achieve better device performance. Therefore, reflectometry was used to measure the remaining thickness of GaInAs. For a 6 s overetch, less than 5 nm of the GaInAs base layer was removed and the AlInAs layer was completely etched. The surface morphology was also studied using atomic force microscopy. (Figure 4) The root mean square surface roughness of 2.5 nm was obtained for the optimum overetch time. This was significantly lower than the value of 4.4 nm obtained after wet etching.

Figure 1. Ga optical emission obtained from etching abrupt AlInAs/GaInAs heterojunction and from etching HBT emitter stack. The etch conditions were 50 W of microwave power, 100 W of rf power, Cl2/Ar gas flow at 3/27 sccm, 2 mTorr chamber pressure, and 13 cm source to sample distance.

Figure 2. The use of low rf power allows low rc to be obtained for dry etched p+-GaInAs. Also shown is rc measured for a two step etch. The contact resistivities before and after annealing are shown.

Figure 3. Ga optical emission intensity at 417.2 nm as a function of etch time for three different runs. The etches were stopped at 3, 6, and 12 s after the increase in the Ga signal was detected.

Figure 4. Comparison of dry etched (left) and wet etched (right) AlInAs/GaInAs emitter base structure. The RMS roughness was 2.5 nm for the dry etched sample and 4.4 nm for the wet etched sample.

References

  1. W. D. Zhou, J. Sabarinathan, B. Kochman, E. W. Berg, O. Qasaimeh, S. W. Pang, and P. Bhattacharya, "Electrically Injected Single-Defect Photonic Bandgap Surface-Emitting Laser at Room Temperature", Electronics Lett. 36, 1541 (2000).
  2. E. W. Berg and S. W. Pang, "Low Pressure Etching of Nanostructures and Via Holes Using an Inductively Coupled Plasma Source", J. Electrochem. Soc. 146, 775-779 (1999).
  3. E. W. Berg and S. W. Pang, "Optical and Electrical Characteristics of InGaAs and GaAs Quantum Wires after Plasma Passivation in an Inductively Coupled Plasma Source", J. Vac. Sci. Technol. B 17, 2745-2749 (1999).
  4. S. W. Pang, T. Tamamura, M. Nakao, A. Ozawa, and H. Masuda, "Direct Nano-Printing on Al Substrate using SiC Mold", J. Vac. Sci. Technol. B 16, 1145-1149 (1998).
  5. S. Thomas III, H. H. Chen, and S. W. Pang, "Precise Etch Stop for Emitter Etching of Self-Aligned Heterojunction Bipolar Transistors", Appl. Surf. Science, 117-118, 758-764 (1997).
  6. S. Thomas III, H. H. Chen, and S. W. Pang, "Effects of Graded Superlattice on Endpoint Detection For Low Damage Heterojunction Bipolar Transistor Etching", J. Vac. Sci. Technol. B 15, 681-686 (1997).
  7. C. K. Hanish, J. W. Grizzle, H. H. Chen, L. I. Kamlet, S. Thomas III, F. L. Terry, and S. W. Pang, "Modeling and Algorithm Development for Automated Optical Endpoint of an HBT Emitter Etch", J. Electron. Mat. 26, 1401-1408 (1997).
  8. F. Ying, W. H. Juan, and S. W. Pang, "Etching of High Aspect Ratio Microcavity Structures in InP", J. Vac. Sci. Technol. B 15, 665-669 (1997).
  9. S. Thomas III , E. Berg, and S. W. Pang, "In-situ Fiber Optic Thermometry Measurements of Wafer Temperature during Plasma Etching", J. Vac. Sci. Technol. B 14, 1807-1811 (1996).
  10. K. K. Ko, S. W. Pang, and M. Dahimene, "Relating Electric Field Distribution of an Electron Cyclotron Resonance Cavity to Dry Etching Characteristics ", J. Vac. Sci. Technol. A 14, 2020-2025 (1996).
  11. S. Thomas III and S. W. Pang, "Dry Etching of Horizontal Distributed Bragg Reflector Mirrors for Waveguide Lasers", J. Vac. Sci. Technol. B 14, 4119-4123 (1996).
  12. S. Thomas III, H. H. Chen, C. K. Hanish, J. W. Grizzle, and S. W. Pang, "Minimized Response Time of Optical Emission and Mass Spectrometric Signals for Optimized Endpoint Detection", J. Vac. Sci. Technol. B 14, 2531-2536 (1996).
  13. K. K. Ko, E. Berg, and S. W. Pang, "Effects of Etch-Induced Damage on the Electrical Characteristics of In-Plane Gated Quantum Wire Transistors", J. Vac. Sci. Technol. B 14, 3663-3667 (1996).
  14. E. S. Snow, W. H. Juan, S. W. Pang, and P. M. Campbell, "Si Nanostructures Fabricated by Anodic Oxidation with an Atomic Force Microscope and Etching with an Electron Cyclotron Resonance Source", Appl. Phys. Lett. 66, 1729-1731 (1995).
  15. W. H. Juan and S. W. Pang, "High Aspect Ratio Si Etching For Microsensor Fabrication", J. Vac. Sci. Technol. A 13, 834-838 (1995).
  16. K. K. Ko and S. W. Pang, "Deep Via Hole Etching of InP", J. Electrochem. Soc. 142, 3945-3949 (1995).
  17. K. K. Ko, K. Kamath, O. Zia, E. Berg, S. W. Pang, and P. Bhattacharya, "Fabrication of Dry Etched Mirrors for In0.2Ga0.8As/GaAs Multiple Quantum Well Waveguides Using an Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 13, 2709-2713 (1995).
  18. D. J. Kahaian, S. Thomas, and S. W. Pang, "In-Situ Monitoring of GaAs Etched with a Cl2/Ar Discharge in an Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 13, 253-257 (1995).
  19. S. Thomas III, K. K. Ko, and S. W. Pang, "Monitoring GaAs and InP Etched in Cl2/Ar Plasma Generated by Electron Cyclotron Resonance Source Using Optical Emission Spectroscopy", J. Vac. Sci. Technol. A 13, 894-899 (1995).
  20. S. Thomas III and S. W. Pang, "Atomic Force Microscopy Study of III-V Materials Etched Using and Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 13, 2350-2354 (1995).
  21. K. T. Sung, W. H. Juan, S. W. Pang, and M. Dahimene, "Dependence of Etch Characteristics on Charge Particles as Measured by Langmuir Probe in a Multipolar Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. A 12, 69-74 (1994).
  22. W. H. Juan and S. W. Pang, "High Aspect Ratio Polyimide Etching Using an Oxygen Plasma Generated by Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 12, 422-426 (1994).
  23. K. T. Sung and S. W. Pang, "Mass Spectrometry and Atomic Force Microscopy Studies of Si Etch Characteristics in Cl2 Plasma Generated by Electron Cyclotron Resonance Source", Jpn. J. Appl. Phys. 33, 7112-7116 (1994).
  24. S. Thomas and S. W. Pang, "Dependence of Contact Resistivity and Schottky Diode Characteristics on Dry Etching Induced Damage of GaInAs", J. Vac. Sci. Technol. B 12, 2941-2946 (1994).
  25. K. T. Sung, W-Q. Li, S. H. Li, S. W. Pang, and P. K. Bhattacharya, "Application of High-Quality SiO2 Grown By Multipolar ECR Source to Si/SiGe MISFET", Electronics Lett. 29, 277-278 (1993).
  26. L. Davis, K. K. Ko, W-Q. Li, H. C. Sun, Y. Lam, T. Brock, S. W. Pang, P. K. Bhattacharya, and M. J. Rooks, "Photoluminescence and Electro-Optic Properties of Small (25-35 nm) Quantum Boxes", Appl. Phys. Lett. 62, 2766-2768 (1993).
  27. K. T. Sung and S. W. Pang, "Etching of Si with Cl2 using an Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. A 11, 1206-1210 (1993).
  28. C. Thirstrup, S. W. Pang, O. Albrektsen, and J. Hanberg, "Effects of Reactive Ion Etching on Optical and Electro-Optical Properties of GaInAs/InP Based Strip-Loaded Waveguides", J. Vac. Sci. Technol. B 11, 1214-1221 (1993).
  29. K. K. Ko and S. W. Pang, "Controllable Layer by Layer Etching of GaAs with an Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 11, 2275-2279 (1993).
  30. K. T. Sung, W. H. Juan, S. W. Pang, and M. W. Horn, "Low Temperature Etching of Silylated Resist in an Oxygen Plasma Generated by an Electron Cyclotron Resonance Source", J. Electrochem. Soc. 140, 3620-3623 (1993).
  31. J. A. Bride, S. Baskaran, N. Taylor, J. W. Halloran, W. H. Juan, S. W. Pang, and M. O'Donnell, "Photolithographic Micromolding of Ceramics Using Plasma Etched Polyimide Patterns", Appl. Phys. Lett. 63, 3379-3381 (1993).
  32. S. W. Pang, K. T. Sung, and K. K. Ko, "Etching of Photoresist Using Oxygen Plasma Generated by a Multipolar Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 10, 1118-1123 (1992).
  33. K. T. Sung and S. W. Pang, "Low Temperature Silicon Oxidation with Oxygen Plasma Generated by an Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 10, 2211-2216 (1992).
  34. K. T. Sung and S. W. Pang, "Selective Etching of Bilayer Photoresist using Multipolar Electron Cyclotron Resonance Source", J. Electrochem. Soc. 139, 3599-3602 (1992).
  35. S. W. Pang and K. K. Ko, "Comparison Between Etching in Cl2 and BCl3 for Compound Semiconductors using Multipolar Electron Cyclotron Resonance Source", J. Vac. Sci. Technol. B 10, 2703-2707 (1992).
  36. S. W. Pang, Y. Liu, and K. T. Sung, "Etching of GaAs and InP Using a Hybrid Microwave and rf System", J. Vac. Sci. Technol. B 9, 3530-3534 (1991).
  37. D. J. Ehrlich, P.A. Maki, S. W. Pang, M. Rothschild, R. R. Kunz, M. W. Horn, and M. A. Hartney, "Excimer Laser Patterning Technologies for Microfabrication", Tr. J. of Physics 14, 1-11 (1990).
  38. S. W. Pang and M. W. Horn, "Amorphous Carbon Films As Planarization Layers Deposited By Plasma Enhanced Chemical Vapor Deposition", IEEE Electron Device Lett. 11, 391-393 (1990).
  39. S. W. Pang and M. W. Horn, "Plasma Deposited Amorphous Carbon Films As Planarization Layers", J. Vac. Sci. Technol. B 8, 1980-1984 (1990).
  40. M. W. Horn, S. W. Pang, and M. Rothschild, "Plasma Deposited Organosilicon Thin Films As Dry Resists For Deep UV Lithography", J. Vac. Sci. Technol. B 8, 1493-1496 (1990).
  41. S. W. Pang, R. R. Kunz, M. Rothschild, R. B. Goodman, M. W. Horn, and D. J. Ehrlich, "Aluminum Oxides As Imaging Materials For 193-nm Excimer Laser Lithography", J. Vac. Sci. Technol. B 7, 1624-1628 (1989).
  42. S. W. Pang, M. W. Geis, W. D. Goodhue, N. N. Efremow, D. J. Ehrlich, and J. N. Randall, "Pattern Transfer by Dry Etching Through Stencil Masks", J. Vac. Sci. Technol. B 6, 249-252 (1988).
  43. S. W. Pang, "Submicrometer Structure Fabricated by Dry Etching and Masked Ion Beam Lithography", J. Electrochem. Soc. 135, 1526-1529 (1988).
  44. D. J. Ehrlich, J. G. Black, M. Rothschild, and S. W. Pang, "Emerging Technology for in situ processing: Patterning Alternatives", J. Vac. Sci. Technol. B 6, 895 (1988).
  45. S. W. Pang, T. M. Lyszczarz, C. L. Chen, J. P. Donnelly, and J. N. Randall, "Masked ion beam lithography for submicrometer-gate-length transistors", J. Vac. Sci. Technol. B 5, 215-218 (1987).
  46. J. Melngailis, D. J. Ehrlich, S. W. Pang, and J. N. Randall, "Cermet as an Inorganic Resist for Ion Lithography", J. Vac. Sci. Technol. B 5, 379 (1987).
  47. M. W. Geis, N. N. Efremow, S. W. Pang, and A. C. Anderson, "Hot Jet Etching of Pb, GaAs, and Si", J. Vac. Sci. Technol. B 5, 363 (1987).
  48. W. D. Goodhue, S. W. Pang, G. D. Johnson, D. K. Astolfi, and D. J. Ehrlich, "Nanometer Scale Columns In GaAs Fabricated by Angled Ion Beam Assisted Etching", Appl. Phys. Lett. 51, 1726-1728 (1987).
  49. S. W. Pang, J. N. Randall, and M. W. Geis, "Sub-100nm-wide, deep trenches defined by reactive-ion etching", J. Vac. Sci. Technol. B 4, 341-344 (1986).

Last Updated: November 19, 2007

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