Junction Depth Measurement

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Junction Depth Measurement

• For Epi films and diffusion

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Junction Depth Measurement

• Groove and Stain
• Bevel and Stain
• The wafer is subjected to a mechanical abrasion
  to expose the junction for viewing. The
  junction is delineated by utilizing the
  electrical differences between N-type and P-type
  materials

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Groove and Stain

• A grooving machine ( Philtec ) is used to create
  a groove in the wafer
•  
• A wafer or section of wafer is loaded into the
  holder.
• A micro-abrasive paste is applied to the roller
  of the machine
• The sample holder is placed into the machine
• The roller is turned on (specific settings for
  diameter of wafer)
• The sample holder is held against the drum and a
  groove is ground into the wafer. The groove size
  is dependant on diameter of the roller

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• Philtec groove and stain

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Wafer holder
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Groove drum
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Bevel and stain

• A bevel is ground onto the edge of a sample
•  
• A small piece of the wafer is epoxied to the
  specimen holder overlapping the center of the
  bevel on the holder
• The specimen holder is attached to the body of
  the holder
• A small amount of micro-abrasive is placed on a
  specially prepared glass plate

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Bevel and Stain

• The specimen holder is placed into the chuck
  and the entire assembly is carefully placed on
  the glass plate into the micro-abrasive
• The holder is moved on the glass plate in a
  figure 8 pattern to polish or grind a bevel onto
  the edge of the specimen
• The specimen is carefully washed in preparation
  for staining

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• Lapping chuck

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• Lapping chuck and specimen holder

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• Lapping plate prepared by rubbing 2 pieces of
  glass together with a 25 micron slurry
• Larger plate will be used for the lapping process

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• Specimen epoxied to specimen holder
• Note angle of holder

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• Micro abrasives for the lapping process

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• Lap specimen by a figure 8 motion
• No pressure is applied to holder, weight of
  holder is enough for process

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Etching Technique

• Place drop of HF and water mixture over exposed
  junction
• Heat lamp is directed onto the exposed junction
• Heat and light cause holes or electrons to flow
  in each region
• As a result of the current flow, the etch rate of
  the HF-H2O mix is higher for the N-type region
  making it appear darker

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Staining Technique

• mixture containing copper is dropped onto
  exposed junction
• heat lamp is directed onto junction
• a battery is formed by the poles of the
  junctions, with the copper solution being the
  electrolytic solution
• the current flow causes the copper in the
  solution to plate onto the N-type side of the
  junction

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• Once specimen is lapped and washed, surface is
  stained to delineate junction

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Delineation observations

• After delineation optical interference fringes
  are created by shining a monochromatic light
  source onto a glass slide over the delineation
•  
• Each optical interference fringe represents a
  specific depth, adding them up gives you the
  junction depth.
•  
• In our lab we will use the microscope as a
  reference to calculate the junction depth
• It is simple geometry to determine the actual
  junction depth.

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• Stained section from project W2002
• Note drain and source diffusions as dark areas on
  right side of image --- the brown area being the
  lapped part of wafer

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Spreading Resistance Probe

• Another method to determine junction depth is to
  use the Spreading Resistance probe
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• a taper is ground onto the edge of a sample (same
  method as above)
• very fine probes are used to measure the
  resistance value along the taper
• the measurements are fed into a computer to
  calculate the doping profile
• the measurements are graphed and the junction
  depth is determined

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ENDJunction Depth Measurement

• For Epi films and diffusion