etching of semiconductor

Group 101 Lab Report: M104

Table of Contents

1. Introduction……………………………………... 02

2. Experimental Work…………………………….. 03

2.1. Equipment and Auxiliaries

2.2. Experimental Procedure

3. Observations…………………………………….. 04

4. Results………………………………………………. 05

5. Discussion……………………………………….. 09

6. Conclusion………………………………………. 10

7. References………………………………………. 11


Etching of Semiconductors

1. Introduction

Silicon is the basic material used in the electronic world. The main

purpose of this experiment is to understand silicon substrate by

taking its chemical reactions with different etching solutions and

using their effect for different applications.

Theory:

Experimental manual M104, provided by the supervisor

2. Experimental Work

2.1. Equipment and Auxiliaries

Main equipment, which is used in this process, is:

Silicon Wafer

Teflon Bath

Heating Plate with Stirrer (IKA C-MAG HS7)

Air Drier

Sample Holder

Optical Microscope

Chemical Solutions:

1. Agent For Polishing:

60 ml HF (48 % aq. solution)

100 ml HNO3 (65 % aq. solution)

60 ml CH3COOH (96 % aq. solution)

2. Defect Etching:

K2Cr2O7 = 1.452 g

H2O = 33 ml

HF (48%) = 67 ml

3. Pyramid structuring/ Anisotropic Etching:

70 g KOH pellets


190 ml deionized water

Mix on warm surface (max. 80 °C) until KOH has

completely dissolved

40 ml Isopropanol.

2.2. Experimental Procedure

The first step in the etching of semiconductor was the cutting of P-type single

crystal silicon wafer into pieces for the polishing, defect and anisotropic

etching under optical microscope.

Solutions were already prepared by the supervisor. Four samples were prepared

by cutting silicon wafer and placed in a holder to put into the chemical

polisher. Temperature of polisher (Teflon Bath) measured before polishing by

Digital Thermometer and then samples were placed into Teflon bath and then

covered with lid. As samples were placed in the polishing solution, temperature

of polishing bath starts increasing (as a result of exothermic reaction). As the

lid of the Teflon bath is opened, a gas is evolved (Nitrogen dioxide evolved)

which gives the proof of chemical reaction. Polishing time is noted. Samples

were taken out of the bath and rinsed in the de-ionized water.

Total four samples were polished from which one sample was air dried and

examined under the microscope. Second polished sample is again hold in the

holder and placed in the bath of defect etchant for five minutes at room

temperature. To reveal pyramid structuring sample three and four were hold in

the holder and placed in the KOH bath for 30 minutes at room temperature

20°C and 80°C respectively. To heat KOH etching solution bath heating plate

is used with magnetic stirrer.

These all samples were then viewed under the microscope and characterized.

Samples were views at 20x, 50x, 100x, 200x and 1000x magnifications.

Temperature before polishing: 18.5°C

Temperature after polishing: 33.2°C

Total time of polishing: 4 minutes and 4 seconds

Time provide for defect etching = 5 minutes

Time provide for anisotropic etching = 30 minutes


3. Observations

Nitrogen Dioxide (Yellowish color) gas evolved during the

polishing which assured that the chemical process taking

place. Also we observed that the temperature raise during the

polishing process which was the indication that it should be

exothermic.

Also we didn’t provide sufficient time for complete polishing

because if it completely polished we didn’t see any image in

the microscope because of complete reflection. Moreover, we

get mirror like surface after polishing.

It was seen that after Anisotropic etching sample which kept

at 20°C has still the polished surface while the sample at

80°C lost its shine and become dull and rough.


4. Results Figure 1 correspond to silicon wafer shown at 50X magnification, has a

contrast of black and white. Figure 2 is the same material seen at 1000X

magnification.

Figure 1: Unpolished Silicon at 50X

Figure 2: Unpolished Silicon at 1000X


Figure 3 and 4 were the results of electrochemical polishing of silicon in

Polishing solution (composed of HF, HNO3, CH3COOH) wafer at 50X

and 1000X magnification respectively

Figure 3: Polished Silicon at 50X

Figure 4: Polished Silicon at 1000X


Figure 5 corresponds to defect etching of Silicon Substrate at 1000X in

which defect show appearance. Figure 6 shows that the effects of KOH

etching (Pyramid Structuring) at room temperature at 100X.

Figure 5: Defect Etched Silicon at 1000X

Figure 6: KOH Etched Silicon at 20°C at 100X

Series of

Dislocation


Figure 7 and 8 correspond to KOH etching at 80°C at 200X and 1000X. It

shows that many part of structure composed of pyramid.

Figure 7: KOH etched silicon at 80°C at 200X

Figure 8: KOH Etched Silicon at 80°C at 1000X

Pyramid

Structure form

from resistance

of (111) plane.


5. Discussion

Figure 1 indicates that it is unpolished and roughed surface.

From Figure 2 it could observe the up and down which

correspond to the non-flat surface and the black surface

conformed to unpolished surface.

Small black spot see in figure 3 is due to the lack of complete

polishing. Polishing is an exothermic process therefore

temperature is rising during the polishing process and

evolution of Nitrogen dioxide (Yellowish Color) gas also

observed after polishing. We can see pronounce effect of

Sample flatness from figure 4 in comparison to the figure 2

(as received sample), it also conform about incomplete

polishing of surface because if our sample is completely

polished we can’t see any image in Optical Microscope.

From figure 5 i.e. defect etching, defects in the sample etched

more preferentially than other part therefore we can see the

series of dislocation and point defect (like vacancies) if any

will etch at high rates as compare to other part.

From figure 6 it indicates that no change occur due to the low

kinetics of the etching reaction at room temperature. Figure 7

Corresponds to Anisotropic etching at 80°C, at small

magnification large part of the microstructure composed new

pyramid type structure. At high magnification (figure 8) it is

more pronounce and clear about new pyramid shape structure.

This pyramid type structure is result of the resistance of

certain plain which show this pyramid type structure. By

observing both the figure (7 and 8), it is concluded that the

process of etching at 80°C is very fast.


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6. Conclusion

Wrought single crystal P-type Silicon is polished by solution

(60ml HF, 60ml CH3COOH and 100ml HNO3) which give

you Flat, Scratch less and completely polished surface which

act like a mirror.

P-type Silicon etching in SECCO solution result the defect in

material etched more preferentially than other part.

Anisotropic Etching of Silicon showed Pyramid Type

structure which is the result of (111) plane, which shows more

resistance in comparison to other plane.

7. References

Experimental manual M104, provided by supervisor.

etching of semiconductor

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