ELEG 450/650 - Key Procedures for Field Oxidation

Cleaning (001) p-type 1-10 W -cm Resistivity Si Substrates

Use teflon tweezers

1-Organics Etch (Pyrex beaker)

-H2SO4:H2O2 (4:1): Etch 10 minutes for removal of residual organic materials. Highly reactive and exothermic etch.

-Rinse 2X in De-ionized Water (DI)

2-Metals Etch (Pyrex beaker)

-H2O:HCl:H2O2 (1:1:1): Let reaction begin, then etch 10 minutes for removal of metallic impurities. This etch also is reactive and exothermic.

-Rinse 2X in DI water

3-Final HF strip (Teflon beaker)

-Dip Si wafers in H2O:HF (20:1) for approximately 20-30s to remove the surface oxide formed during the previous two etches. The sample should be hydrophobic (i.e. repels water)

-Rinse in DI water

-Dry in pure N2

The samples are clean and are ready to be loaded

Oxidation

I will have furnace hot already (T~1100 (C). I have previously taken the temperature profile and the quartz boat has previously been cleaned in an RCA type clean (same as above etch procedure). Before class I will have steam cleaned the furnace with very diluted HCl acid, which acts to getter some harmful impurities.

-Slowly load sample into hot zone. Use correct glassware

-Dry oxidation for one hour. O2 flow is set at 4 (no bubbler).

-wet oxidation for one hour. O2 flow is set at 4. Oxygen is bubbling moderately through a 20:1 solution of H2O:HCl which is held at 90 (C.

-Dry oxidation for one hour. O2 flow is set at 4 (no bubbler)

-unload slowly

I recommend reading (at least skimming) the section on thermal oxidation of Si in Ghandi pp.451-481.

ELEG 450/650 - Key Procedures for Positive Photolithography and forming the Oxide Diffusion barrier for Source and Drain

Photolithography
  1. Spin on 5214E Photoresist. Speed=5000rpm, time = 30s.
  2. Softbake samples to drive away solvents. Place on 90 ° C hotplate. 90 seconds. Allow samples to cool.
  3. Expose through dark field mask (Mask 1) to expose resist for source/drain pattern.
  4. Develop in undiluted AZ327MIF (MIF=Metal-ion-free) for 30 seconds. Pattern development may be observed by eye.
  5. Rinse in DI water
  6. Nitrogen blow dry.
  7. Hardbake sample on 120 ° C hotplate for 90 seconds.
  8. Inspect

Etch Openings in Field Oxide for Diffusion of Source/Drain Regions
  1. Samples patterned with photoresist are to be etched in Buffered Oxide Etch for 16 minutes. This time is sufficient to remove the field oxide away from the source drain regions. This time was empirically determined by observing when the oxidized samples become hydrophobic.
  2. Rinse in DI water
  3. Nitrogen blow dry
  4. Remove photoresist mask with acetone
  5. Rinse in methanol
  6. Rinse in DI water
  7. Nitrogen blow dry
  8. Inspect

ELEG 450/650 - Key Steps in Diffusing Phosphorus to form Source and Drain

Cleaning wafers for diffusion

Use teflon tweezers

1-Organics Etch (Pyrex beaker)

-H2SO4:H2O2 (4:1): Etch 10 minutes for removal of residual organic materials. Highly reactive and exothermic etch.

-Rinse 2X in De-ionized Water (DI)

2-Metals Etch (Pyrex beaker)

-H2O:HCl:H2O2 (1:1:1): Let reaction begin, then etch 10 minutes for removal of metallic impurities. This etch also is reactive and exothermic.

-Rinse 2X in DI water

3-Final HF strip (Teflon beaker)

-Dip Si wafers in H2O:HF (20:1) for approximately 20-30s to remove the surface oxide formed during the previous two etches. The sample should be hydrophobic (i.e. repels water)

-Rinse in DI water

-Dry in pure N2

The samples are clean and are ready to be loaded into diffusion furnace.

Phosphorus Diffusion

I will have furnace hot already (T~860 (C). I have previously taken the temperature profile. Before class I will have steam cleaned the furnace with very diluted HCl acid, which acts to getter some harmful impurities.
  1. Load clean samples into Phosphorus diffusion boat. Boat is "pre-doped".
  2. Slowly push sample into hot zone under Nitrogen flow.
  3. Purge under Nitrogen for 20 minutes.
  4. 5 minute Pre-deposition: Bubble N2 (10 mm ) through POCl3. Flow N2 at 5mm and O2 at 145 mm.
  5. Drive in: 20 minutes N2 only (10 mm), no bubbler. Follow by 20 minutes O2 only, no bubbler.
  6. Slowly unload.
  7. Measure sheet resistance of dummy wafer after removing Phos-glass. Expect 35 ohms per square.
Last Updated January 11, 2001

Electrical Engineering | comments to: kolodzey@ee.udel.edu
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