Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01F—MEASURING VOLUME, VOLUME FLOW, MASS FLOW OR LIQUID LEVEL; METERING BY VOLUME
  • G01F1/00—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow
  • G01F1/68—Measuring the volume flow or mass flow of fluid or fluent solid material wherein the fluid passes through a meter in a continuous flow by using thermal effects
  • G01F1/684—Structural arrangements; Mounting of elements, e.g. in relation to fluid flow
  • G01F1/6845—Micromachined devices
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01K—MEASURING TEMPERATURE; MEASURING QUANTITY OF HEAT; THERMALLY-SENSITIVE ELEMENTS NOT OTHERWISE PROVIDED FOR
  • G01K7/00—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements
  • G01K7/02—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples
  • G01K7/028—Measuring temperature based on the use of electric or magnetic elements directly sensitive to heat ; Power supply therefor, e.g. using thermoelectric elements using thermoelectric elements, e.g. thermocouples using microstructures, e.g. made of silicon

Definitions

• the invention relates to a method for producing a thermal membrane sensor over a silicon substrate according to the preamble of claim 1 and to membrane sensors produced by this method.
• a method for producing a thermal membrane sensor over a silicon substrate according to the preamble of claim 1 and to membrane sensors produced by this method.
• Such a method and such sensor sensors are known from "ITG Technical Report 126: Sensor Technology and Application", pp. 285-289.
• Thin layers deposited over a silicon substrate, in particular silicon layers, under which there is a spacing free space and which thus function as a membrane, are used in technology for various purposes.
• An area of application for such membrane components is sensors and here in particular thermal membrane sensors with which physical quantities, e.g. a mass flow, can be detected by detecting a change in temperature in the thin membrane layer.
• the thin membrane layer is thermally decoupled from the substrate as well as possible.
• a thin membrane is used as the sensor carrier by anisotropic backside etching of a silicon wafer generated.
• a double-sided lithography is used for masking, which is only possible through increased equipment complexity.
• the deep etching pits form a mechanical weak point through the entire wafer, which forces it to be very careful when it is processed further in order not to break the wafer plate. Since the etch stop planes run obliquely in the crystal, the opening on the back is larger than on the front. This increases the required wafer area per sensor considerably.
• the use of complicated layer packages made of metal and insulators on the silicon membrane can cause great problems with regard to drift of the layers and long-term stability, for example by detachment of the layers from one another.
• I forming an etching mask leaving a region on the silicon substrate in which the membrane is to be formed on a main surface of the substrate; II electrochemically etching the exposed substrate area to a certain depth to form porous silicon within the exposed area; III removing the mask; IV depositing a thin membrane layer of silicon carbide or nitride; V opening predetermined areas in the membrane layer of silicon carbide or nitride from its upper surface; VI Selective formation of circuit structures on the upper surface of the membrane layer, and VII Removing the porous silicon layer (2) under the membrane layer by sacrificial layer etching.
• circuit structures in the known thermal membrane sensor have been deposited by sputtering metal atoms on the upper surface of the membrane and are therefore sensitive to external mechanical and chemical influences.
• step VI such a method is characterized in that in step VI the circuit structures are implanted in the upper surface of the membrane layer.
• porous silicon thus offers the possibility of producing a silicon carbide or silicon nitride membrane inexpensively and quickly over the silicon substrate, and then, according to the invention, a masked or thermoresistive doping Manufacture thermoelectric sensor so that its circuit structures are largely protected against external mechanical and chemical influences.
• the process according to the invention is not only suitable for the production of a thermal membrane sensor, but also for any type of thin elements using membranes exposed over a silicon substrate, e.g. also for the production of actuators that contain a membrane deflected by pressure or vacuum.
• the membrane thickness achievable with the method is in a range from a few 10 to a few 100 n.
• the porous silicon layer is preferably formed in the silicon substrate by an electrochemical anodizing process in hydrofluoric acid electrolyte.
• the layer of silicon carbide or silicon nitride deposited above is preferably formed by a low-temperature LPCVD or PECVD process. Alternatively, such a thin layer can also be deposited by a reactive sputtering process. It should be emphasized here that a silicon carbide layer should be preferred with regard to its greater mechanical and chemical strength or resistance.
• the openings in the silicon carbide or nitride layer are preferably made by a dry etching process, e.g. formed in a plasma etcher.
• the desired conductor tracks for the thermo-resistive elements are now defined by a further lithography step and generated in at least one implantation step. The conductor tracks are formed, for example, from aluminum.
• thermoresistive unit can be placed directly in the upper surface of the membrane with the help of a surface Design the micro-electronics so that the thermal sensor is CMOS-compatible and insensitive to external chemical and mechanical influences.
• the inventive method can also be used to produce a thermal membrane sensor which uses the thermoelectric effect by using a thermopile made of two different substances with a large Seebeck effect, e.g. Antimony / Wi ⁇ muth or silicon / aluminum, is implanted in the upper surface of the membrane. An additional implantation is carried out after a further lithography.
• a thermopile made of two different substances with a large Seebeck effect e.g. Antimony / Wi ⁇ muth or silicon / aluminum
• a thin protective coating made of silicon carbide or silicon nitride can be applied over the entire surface.
• the production method according to the invention can also be used to produce a thermal membrane sensor used as a radiation sensor (bolometer).
• a radiation sensor bolometer
• an additional absorber layer is applied, which consists, for example, of black gold or black silicon.
• Black gold shows a broadband strong absorption of approximately 98% and is generated by thermal evaporation of gold in a low-pressure nitrogen atmosphere.
• black silicon is generated, for example, in a plasma etcher by suitable process control.
• porous silicon is used as
• Support material and support for the thin membrane layer has served in a suitable solvent, such as.
• porous silicon has an extremely enlarged surface area compared to the educt.
• the ratio of the surface of nanoporous silicon to the surface of bulk silicon is approximately 10 6 .
• the above-described method according to the invention makes it possible for the first time to manufacture a thermal sensor in surface micromechanics CMOS-compatible, the active surface of which has a very large substrate spacing due to the technology used for the porous silicon, and thus a substantial thermal decoupling from the substrate.
• the support material of the membrane in particular silicon carbide, is chemically and mechanically very resistant.
• thermal membrane sensor Due to the particularly simple process step sequence and the low wafer area consumption in comparison to conventional structuring steps (e.g. with KOH), the production of a thermal membrane sensor can be carried out very inexpensively. All process steps are available in semiconductor manufacturing.
• the drawing figures 1A-1E show individual process steps of a preferred exemplary embodiment in the form of a schematic cross section through a wafer area in which a thermal membrane sensor is formed.
• FIG. 1A shows process steps I and II, by means of which an etching mask 3 in the form of a photoresist is first applied to an upper surface of a correspondingly pretreated substrate block 1, which then exposed and then removed (step I).
• the masked substrate 1 is then locally porously etched to a defined depth by electrochemical anodization in a hydrofluoric acid electrolyte, as a result of which a layer 2 of porous silicon is formed (step II).
• Fig. 1B shows that over the layer 2 made of porous silicon after removing the mask 3, a thin membrane layer 4 made of silicon carbide or nitride, particularly preferably made of silicon carbide, either by a low-temperature LPCVD process or a low-temperature PECVD process or by reactive sputtering is separated (steps III and IV).
• FIG. IC shows, the upper surface of the thin membrane layer 4 is lithographically structured and the membrane layer 4 by a dry etching process, e.g. in a plasma etcher, which creates openings 5, 7 which extend through the membrane layer 4 to the porous silicon layer 2 (step V).
• a dry etching process e.g. in a plasma etcher
• openings 5, 7 which extend through the membrane layer 4 to the porous silicon layer 2 (step V).
• the membrane, the central region of layer 4 that can be seen in FIG. IC is connected to the peripheral region 4 'of the membrane layer by bridges.
• thermoresistive elements in particular heater and sensor, are now defined by a further lithography step and implanted in an implantation step in the upper surface of the membrane layer 4 (step IV).
• Aluminum is particularly suitable for implanting conductor tracks.
• thermoresistive elements in the form of a thermopile can also be formed by implanting two different substances with a large Seebeck effect in the upper surface of the membrane 4. Such substances are, for example, antimony / bismuth and silicon / aluminum. there an additional implantation is carried out after a further lithography step.
• an additional thin, all-over protective layer 9 made of silicon carbide or silicon nitride can be applied to protect against soiling, which can impair the function of the sensor.
• the thermal membrane sensor is used as a radiation meter (bolometer), an additional absorber layer (not shown in the figure), e.g. made of black gold.
• an additional absorber layer e.g. made of black gold.
• the sacrificial layer 2 made of porous silicon is removed by means of a suitable solvent, such as e.g. Ammonia, removed.
• a suitable solvent such as e.g. Ammonia

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• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Fluid Mechanics (AREA)
• Chemical & Material Sciences (AREA)
• Crystallography & Structural Chemistry (AREA)
• Photometry And Measurement Of Optical Pulse Characteristics (AREA)
• Micromachines (AREA)
• Pressure Sensors (AREA)
• Measuring Fluid Pressure (AREA)
• Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)

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• 1997
  • 1997-11-25 DE DE19752208A patent/DE19752208A1/de not_active Ceased
• 1998
  • 1998-11-23 EP EP98963367A patent/EP0961921A2/de not_active Ceased
  • 1998-11-23 WO PCT/DE1998/003444 patent/WO1999027325A2/de not_active Application Discontinuation
  • 1998-11-23 US US09/355,373 patent/US6825057B1/en not_active Expired - Fee Related
  • 1998-11-23 JP JP52738199A patent/JP2001510641A/ja active Pending

Non-Patent Citations (1)

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