Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L21/00—Processes or apparatus adapted for the manufacture or treatment of semiconductor or solid state devices or of parts thereof
  • H01L21/02—Manufacture or treatment of semiconductor devices or of parts thereof
  • H01L21/02041—Cleaning
  • H01L21/02043—Cleaning before device manufacture, i.e. Begin-Of-Line process
  • H01L21/02052—Wet cleaning only

Definitions

• This invention relates to a method for the low temperature cleaning of group III-V semiconductor substrates, in particular substrates containing indium or antimony.
• group III-V semiconductor substrates in particular substrates containing indium or antimony.
• the preparation of clean, atomically flat substrate surfaces, and the removal of native oxides prior to epitaxial growth, is of major importance in the manufacture of electronic and photonic devices based on group III-V semiconductors.
• the most important surface plane in device fabrication is the (001) plane and the technique most widely used to clean the substrate surface is thermal desorption ofthe native oxide, often using a group V overpressure to maintain the surface stoichiometry.
• this process is known to result in a roughening ofthe surface on an atomic scale [G.W. Smith et al. 1991, Appl. Phys. Lett. 59(25)3282] which has to be smoothed out by the growth of buffer layers before epitaxial growth is possible.
• Indium antimonide is an important group III-V semiconductor and has electronic properties which are well known for their applications to mid-infrared emitters and detectors, and ultra high speed electronic devices.
• the conventional thermal desorption technique is not practical for cleaning InSb substrates.
• the oxide desorption temperature of InSb is very close to the bulk melting temperature of 525°C, and well above the non-congruent evaporation temperature of 325°C, and consequently the thermal desorption process takes several hours [J.F. Klem et al. 1991 J. Vac. Sci. Technol. A 9 (6) 2996] .
• the process also results in a very rough surface, characterized by large In droplets, which is not suitable for epitaxial growth.
• argon ion bombardment Another technique employed to remove the native oxide from InSb substrates is argon ion bombardment. This technique uses argon ions of several hundred eV to sputter the oxide from the surface, followed by low temperature annealing to reduce any structural damage induced by the ion beam. Like the thermal desorption technique, this process is time consuming and argon ion cleaned surfaces are usually indium rich, due to the preferential removal ofthe group V species. The cleaned surface also has an n-type layer as a consequence of damage by the ion beam.
• the present invention relates to a method for the low temperature preparation of oxide-free, atomically flat substrates using a chemical cleaning agent.
• the resulting surface is suitable for epitaxial growth.
• the method has important advantages for the preparation of thermally unstable substrates, particularly InSb, since it may be carried out at temperatures significantly below those required for thermal desorption techniques.
• the present method can be much less time- consuming than the thermal desorption process and also offers the advantage of a single gas source compared to a much more expensive plasma source.
• a method for removing oxide from a substrate containing indium or antimony comprises the steps of;
• the method includes the further steps of
• annealing said substrate for a period of time up to 30 minutes, and typically for 10 minutes, during which time the temperature ofthe substrate is maintained and the substrate remains exposed to the chemical.
• the element X is one of arsenic (As), antimony (Sb) or phosphorus (P).
• the chemical of the form (Me 2 N) 3 -X and the substrate are comprised of the same group V element.
• the chemical is tris(dimethylamino)antimony, (Me 2 N) 3 Sb
• the substrate is indium antimonide (InSb).
• the chemical is tris(dimethylamino)arsine, (Me 2 N) 3 As
• the substrate is indium arsenide (InAs).
• the chemical is tris(dimethylamino)phosphine, (Me 2 N) 3 P, and the substrate is indium phosphide (InP).
• the chemical is tris(dimethylamino)antimony, (Me 2 N) 3 Sb
• the substrate is gallium antimonide (GaSb).
• Figure 1 shows a schematic diagram of a system which may be used to remove the oxide from a group III-V semiconductor substrate, in particular a substrate containing indium or antimony, by exposure to a chemical acting as a cleaning agent and
• Figure 2 shows the structure of a chemical ofthe form (Me 2 N) 3 -X, where X is a group V element, e.g. arsenic (As), antimony (Sb) or phosphorus (P).
• X is a group V element, e.g. arsenic (As), antimony (Sb) or phosphorus (P).
• the substrate 1 has an oxide layer 2 which must be removed, leaving a smooth group V terminated surface suitable for epitaxial growth.
• the reactor 4 is a standard CBE-style (Chemical Beam Epitaxy) reactor and the pressure inside the reactor 4 is maintained at a pressure of between 10 " and 10 " torr by means of a vacuum pump 5.
• Chemical 7 is ofthe form (Me 2 N) 3 -X.
• X is a group V element, for example, As, Sb or P.
• the chemical 7 is introduced from a source 8 into the reactor 4. This is enabled by means of a main valve 9, which turns the chemical supply on and off, and a variable leak valve 10 which regulates the rate of flow ofthe chemical 7 into the reactor 4.
• the chemical 7 is passed into the reactor 4 along heated gas lines 11 to prevent condensation. Removal ofthe oxide layer is initiated by a chemical reaction between the compound (Me 2 N) 3 - X and the surface oxide species, whereas the presence ofthe arsenic, antimony or phosphorus in the chemical leaves a smooth surface morphology if used on a substrate which contains the same group V element. Therefore, preferably, the substrate 1 is exposed to a chemical 7 comprising of the group V element present in the substrate.
• the chemical 7 contains antimony e.g. TDMASb
• the chemical 7 contains arsenic, e.g. TDMAAs
• the substrate 1 to be cleaned is InP
• the chemical 7 contains phosphorus, e.g. TDMAP.
• oxide removal can still be initiated by using any other chemical ofthe form (Me 2 N) 3 -X, where X is a group V element.
• a substrate temperature in excess of 300°C is required. As the reaction proceeds at a higher rate for higher substrate temperatures, it was found to be more convenient to heat the substrate to a temperature in excess ofthe minimum temperature required to cause the oxide removal.
• the oxide was removed from InSb by holding the temperature ofthe substrate at 400°C and exposing to TDMASb.
• the oxide was removed by holding the temperature ofthe substrate at 380°C and exposing to TDMAAs. These temperatures are considerably lower than those required for conventional thermal desorption processes.
• the system shown in Figure 1 was monitored by using RHEED (Reflection High Energy Electron Diffraction) which requires a RHEED gun 12 on one side ofthe reactor and a RHEED screen 13 on the opposite side ofthe reactor.
• RHEED Reflect High Energy Electron Diffraction
• the use of a RHEED technique in this way would be conventional to one skilled in the art.
• the substrate 1 is annealed for a period of time up to 30 minutes, and typically for 10 minutes. During this time, the substrate 1 continues to be exposed to the chemical 7 and the temperature ofthe substrate 1 is maintained throughout this time.
• the substrate is maintained at a temperature of approximately 400°C
• the substrate temperature is maintained at approximately 380°C.
• the temperature ofthe substrate was monitored by means of a thermocouple calibrated using a technique conventional to one skilled in the art.
• the substrate is cooled at a rate of approximately 30°C per minute.
• the temperature decreases to approximately 300°C the exposure to the chemical 6 is ceased and the substrate is ready for subsequent processing steps, such as epitaxial growth of the device layers.
• the substrate 1 may be removed from the reactor 4 and Atomic Force Microscopy (AFM) images may be used to indicate the state ofthe surface morphology.
• AFM Atomic Force Microscopy
• the process may also be carried out in a standard MOVPE-style (Metal-Organic Vapour Phase Epitaxy) reactor.
• fhe diagram shows the structure of a chemical ofthe form (Me 2 N) 3 -X, where 14 is a group V element.
• the chemical is tris(dimethylamino)arsine [TDMAAs]
• the chemical is tris(dimethylamino)antimony [TDMASb]
• the chemical is tris(dimethylamino)phosphine [TDMAP].

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• 1995
  • 1995-08-03 GB GBGB9515902.6A patent/GB9515902D0/en active Pending
• 1996
  • 1996-08-01 WO PCT/GB1996/001864 patent/WO1997006555A1/en not_active Application Discontinuation
  • 1996-08-01 EP EP96925907A patent/EP0842531A1/de not_active Withdrawn

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