2. CONTENTS
• OBJECTIVE
• MATERIAL USED
• THEORY
• FABRICATION OF POROUS SILICON
• CHARACTERIZATION
• APPLICATION IN SENSING
• CONCLUSION
• FUTURE PERSPECTIVE
3. OBJECTIVE
FABRICATION OF POROUS SILICON
EFFECT ON PORE SIZE WITH INCREASING THE CURRENT DENSITY
CHARACTERIZATION OF POROUS SILICON SAMPLES
SENSING APPLICATION OF POROUS SILICON
5. THEORY
• POROUS SILICON FIRST DEVELOPED IN 1956 BY UHLIR
• SILICON IS THE MOST DOMINANT MATERIAL USED FOR MICROELECTRONIC DEVICE.
• CRYSTALLINE SILICON IN ITS BULK APPEARANCE IS COMMONLY NOT TAKENIN TO CONSIDERATION AS OPTICAL , MECHANICAL OR BIO MEDICAL MATERIAL.
• BUT WHEN THE DIMENSIONS ARE DOWNSCALED THE PROPERTIES ARE CHANGED DRASTICALLY.
• LIGHT EMITTING PROPERTIES OCCUR DUE TO QUANTUM CONFINEMENT.
• POROUS SILICON IS INTERESTING FOR OPTICAL APPLICATIONS DUE TO ITS POROSITY.
7. We have used 5 Silicon
Wafer of
Diameter: 3” + 0.02”
Orientation: <100>
Thickness: 350-406 µm
Type: P (Boron doped)
8. PRE-CLEANING
Rinse the sample with DI
water
Boiling(56.3 C)-Silicon
wafer in acetone
Rinse with DI water and
treatment with
ethanol(5min)
Rinse with DI water
Cleaning
Heating in NH4OH: H2O2:
DI water at (1:1:5 at 70c
for 10min)
Rinse with DI water
Dipping for 10min in 3:1
H2SO4 and H202
Rinse with DI water
Dipping in 10% HF
solution
Rinse with DI water
Heating for 10min at 75c
H2O :H2O2 :HCL (6:1:1)
Dip in 10% HF solution
Rinse with DI water
Rinse with DI water
Dry
9. ETCHING
• Two electrodes are needed to maintain charge neutrality
and to complete the circuit.
• Two reactions are occurring simultaneously , the
anode(oxidation) reaction and cathode(reduction)
reaction.
• Cathode is made up of Platinum wire.
• Anode is of Aluminum Plate mount with Porous sample.
• A constant current is passed between cathode and anode
immersed in HF and DMF(1:3 ratio).
Fig. Etching set-up in our laboratory
12. SAMPLE NAME SAMPLE IMAGE AFTER ETCHING ETCHING PARAMETERS
A Current Density = 10 mA/cm2
Etching Time = 40 minutes
Electrolyte Conc. (HF:DMF) = 1:3
Current = 0.011304A
B Current Density = 20 mA/cm2
Etching Time = 40 minutes
Electrolyte Conc. (HF:DMF) = 1:3
Current = 0.022608A
C
Current Density = 30 mA/cm2
Etching Time = 40 minutes
Electrolyte Conc. (HF:DMF) = 1:3
Current = 0.033912A
D Current Density = 40 mA/cm2
Etching Time = 40 minutes
Electrolyte Conc. (HF:DMF) = 1:3
Current = 0.044216A
E Current Density = 50 mA/cm2
Etching Time = 40 minutes
Electrolyte Conc. (HF:DMF) = 1:3
Current = 0.05652A
28. CONCLUSION
• SEM IMAGES SHOWS THAT PORE SIZE INCREASE WITH INCREASE IN CURRENT DENSITY.
• PHOTOLUMINESCENCE PEAK SHIFTED TOWARDS RIGHT (BLUE SHIFT).
• RAMAN SPECTRA SHIFTED TOWARDS LEFT (RED SHIFT).
• FTIR SPECTRA SHOWS VARIOUS TYPE OF BONDS ON PS SURFACE AT DIFFERENT CURRENT DENSITY.
• POROUS SILICON SAMPLE PREPARED IS SENSITIVE TO ETHANOL VAPOR.
29. FUTURE PERSPECTIVE
• WE WILL PREPARE THE POROUSSILICON AT DIFFERENT HF CONCENTRATIONS AND ETCHING TIME.
• WE WILL DO COMPARATIVE STUDY WITH DIFFERENT ORGANIC SOLVENT SUCH AS DIMETHYLFORMAMIDE(DMF), DIMETHYLSULFOXIDE(DMSO) AND ACETONITRILE
(MECN).
• WE WILL DO COMPARATIVE STUDIES OF P-TYPE AND N-TYPE SILICON WAFER.
• WE WILL FIND THE SENSITIVITY, RESPONSE TIME, RECOVERY TIME ETC. FOR DIFFERENT SAMPLES UNDER DIFFERENT CONDITIONS AS MENTIONED ABOVE AND COMPARE
THESE PARAMETERS TO GET THE EFFICIENT SENSOR FROM THEM.
• WE WILL CHARACTERIZE THE DIFFERENT SAMPLES UNDER DIFFERENT CONDITIONS AS MENTIONED ABOVE AND COMPARE THEM ALL IN TERMS OF SURFACE
MORPHOLOGY, STRUCTURE MORPHOLOGY, RAMAN PEAKS AND PL ETC.
