- Email: [email protected]
Structure of lapped germanium
Wear, 107
(1986)
183
183
- 188
Technical
Note
Structure
of lapped germanium
H. FURUICHI Department of Mechanical Kofu 400 (Japan) (Received
October
16, 1985;
Engineering, accepted
Faculty November
of Engineering,
Yamanashi
University,
8, 1985)
Indium-doped germanium was lapped parallel to the (111) plane in the slip direction as a preliminary step to determine the structural changes which occur in lapped semiconductors. It was found that, when lapped with coarse abrasive grains, subgrains appeared in the affected layer. The difference in the orientation of the subgrains in comparison with the original crystal and inter-grain orientation was of the order of 1 mrad. In the case of fine abrasive grains, only the lines of etch pits parallel to the lapping direction were observed.
1. Introduction Semiconductors are, in general, lapped when shaped into components, thus forming the so-called “affected layer”. Because of the lack of knowledge of this layer, unnecessary mechanical and chemical polishing is performed which wastes not only precious resources but also manpower. As a preliminary step to obtain knowledge of this layer, the structure of the affected layer of lapped germanium was studied, although the study of germanium is no longer very popular. It is considered that the phenomena observed in the affected layer of germanium are applicable also to studies of the affected layer of the other semiconductors. 2. Experimental details The material used was an ingot of indium-doped germanium manufactured by Hoboken Company. The resistivity parallel to the (111) direction was 1.0 - 1.2 S2 cm and the dislocation density was about 3500 cm-*. The ingot was cut parallel to the (111) plane, into slices 2 mm thick, in running water to avoid an increase in temperature. After this, the slices were lapped with rough and then fine abrasives. When lapped with coarse abrasive grains (BM 180, BM 302 and BM 304, British American Optical Company), flat glass was used as the lap and for fine abrasive grains (BM 309, British American Optical Company) felt was used. In all cases the lapping speed was 25 - 30 cm s-l and the pressure was about 980 MPa. After lapping, the speci0043s1648/86/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
18.1
mens were finished by chemical polishing (HNO,, 40 cm-‘; CHsCOOH. 30 cm3; bromine, 0.6 cm3; stirring at room temperature). The affected layer formed during lapping was removed completely by the chemical polishing described above, as far as could be determined by observation through an optical microscope; in this case the specimens were etched with a mixture of KOH (6 g), K,Fe(CN), (4 g) and Hz0 (50 cm3) (stirring at room temperature). The etchant mentioned above is not frequently used (ref. 1, Appendix). However, it gives a good enough result to reveal the structure for observation through an optical microscope. 3. Results and discussion The structure before lapping is shown in Fig. 1. No detail can be seen. Figure 2 shows the structure after lapping with the coarse abrasive grains in the (110) direction (slip direction). Structures such as subgrains are revealed. These are oriented in a direction independent of the lapping direction, except for the sample lapped with BM 180 abrasive (Fig. 2(a)) in which many of the grams have oriented themselves in the lapping direction. In all cases, there is no difference in the gram size (about 35 pm). The degree of etching increases with the coarseness of the abrasive grains (Appendix A). Here and there, structures resembling the piling up of defects such as dislocations are observed (Fig. 3).
Fig.
1. Optical
micrograph
showing
the structure
before
lapping.
Figure 4 shows the profile of one of the spots in the back-reflection X-ray diffraction pattern before and after lapping. It is clearly seen that the spot divides itself into two. The same phenomenon was observed with the other spots revealed in the diffraction pattern. The facts mentioned above lead us to the conclusion that lapping produces subgrains with orientations slightly different (of the order of 1 mrad) from the original grain and intergrain orientation. The mechanism of formation of the subgrains is not clear. The rapid increase in dislocations [ 21 during lapping, however, can be considered to be the cause.
(a)
(b)
(cl Fig. 2. Optical micrographs showing the structure abrasives: (a) BM 180; (b) BM 302; (c) BM 304.
after
lapping
with
various
coarse
Figure 5 shows the etched affected layer after lapping with fine abrasive grains. Instead of subgrains, only etch pits oriented in the lapping direction were observed. It may be said, therefore, that the state of the affected layer after lapping varies with the size of abrasive grains used.
Fig. 3. Optical micrograph showing locations against sub-boundaries
(a)
the
etch
pits
which
resemble
the
piling
up of dis-
(b)
Fig. 4. Typical change in the state of the spots in the back-reflection X-ray diffraction pattern (a) before and (b) after lapping. (The darkness of one of the spots was measured photometrically.)
187
Fig. 5. The etched affected surface after lapping with fine abrasive grains.
4. Conclusions Lapping slip direction
of indium-doped was carried
germanium
parallel
to the {ill}
plane
in the
out.
After lapping with coarse abrasive grains subgrains were observed, whose size is independent of that of the abrasive grains (about 35 pm); in contrast, only etch pits parallel to the lapping direction were observed when lapping with fine abrasive grains. The subgrains oriented themselves at random except when lapping with the coarsest abrasive grains; in this case most of the subgrains oriented themselves parallel to the lapping direction. It may be said that the state of the affected layer changes not continuously but abruptly with the size of the abrasive grains used (see Appendix A). 1 P. R. Camp, A study of the etching rate of single-crystal germanium, J. Electrochem. Sot., 102 (10) (1955) 586 - 593. 2 J. Friedel, Dislocations, Pergamon, Oxford, 1964, pp. 104 - 108.
Appendix
k
The abrasive grains are not always regular in shape and size (Fig. Al). Therefore, their grain size was not given in the text. The spectrochemical analysis revealed that BM 180 contains a large amount of magnesium together with some silicon and aluminium; this suggests that BM 180 is a blend of MgO, Sic and A1203, of which MgO is the major constituent. For BM 302 and BM 304, Al*Os is thought to be the major constituent. BM 309 contains a large amount of titanium and some zinc; this suggests that BM 309 is a blend of TiOz and ZnO, of which TiOs is the major constituent.
_. c
‘. 1
.
(a)
(b)
(d) Fig. Al. The abrasive
grains:
(a) BM 180; (b) BM 302; (c) BM 304; (d) BM 309
(1986)
183
183
- 188
Technical
Note
Structure
of lapped germanium
H. FURUICHI Department of Mechanical Kofu 400 (Japan) (Received
October
16, 1985;
Engineering, accepted
Faculty November
of Engineering,
Yamanashi
University,
8, 1985)
Indium-doped germanium was lapped parallel to the (111) plane in the slip direction as a preliminary step to determine the structural changes which occur in lapped semiconductors. It was found that, when lapped with coarse abrasive grains, subgrains appeared in the affected layer. The difference in the orientation of the subgrains in comparison with the original crystal and inter-grain orientation was of the order of 1 mrad. In the case of fine abrasive grains, only the lines of etch pits parallel to the lapping direction were observed.
1. Introduction Semiconductors are, in general, lapped when shaped into components, thus forming the so-called “affected layer”. Because of the lack of knowledge of this layer, unnecessary mechanical and chemical polishing is performed which wastes not only precious resources but also manpower. As a preliminary step to obtain knowledge of this layer, the structure of the affected layer of lapped germanium was studied, although the study of germanium is no longer very popular. It is considered that the phenomena observed in the affected layer of germanium are applicable also to studies of the affected layer of the other semiconductors. 2. Experimental details The material used was an ingot of indium-doped germanium manufactured by Hoboken Company. The resistivity parallel to the (111) direction was 1.0 - 1.2 S2 cm and the dislocation density was about 3500 cm-*. The ingot was cut parallel to the (111) plane, into slices 2 mm thick, in running water to avoid an increase in temperature. After this, the slices were lapped with rough and then fine abrasives. When lapped with coarse abrasive grains (BM 180, BM 302 and BM 304, British American Optical Company), flat glass was used as the lap and for fine abrasive grains (BM 309, British American Optical Company) felt was used. In all cases the lapping speed was 25 - 30 cm s-l and the pressure was about 980 MPa. After lapping, the speci0043s1648/86/$3.50
0 Elsevier
Sequoia/Printed
in The Netherlands
18.1
mens were finished by chemical polishing (HNO,, 40 cm-‘; CHsCOOH. 30 cm3; bromine, 0.6 cm3; stirring at room temperature). The affected layer formed during lapping was removed completely by the chemical polishing described above, as far as could be determined by observation through an optical microscope; in this case the specimens were etched with a mixture of KOH (6 g), K,Fe(CN), (4 g) and Hz0 (50 cm3) (stirring at room temperature). The etchant mentioned above is not frequently used (ref. 1, Appendix). However, it gives a good enough result to reveal the structure for observation through an optical microscope. 3. Results and discussion The structure before lapping is shown in Fig. 1. No detail can be seen. Figure 2 shows the structure after lapping with the coarse abrasive grains in the (110) direction (slip direction). Structures such as subgrains are revealed. These are oriented in a direction independent of the lapping direction, except for the sample lapped with BM 180 abrasive (Fig. 2(a)) in which many of the grams have oriented themselves in the lapping direction. In all cases, there is no difference in the gram size (about 35 pm). The degree of etching increases with the coarseness of the abrasive grains (Appendix A). Here and there, structures resembling the piling up of defects such as dislocations are observed (Fig. 3).
Fig.
1. Optical
micrograph
showing
the structure
before
lapping.
Figure 4 shows the profile of one of the spots in the back-reflection X-ray diffraction pattern before and after lapping. It is clearly seen that the spot divides itself into two. The same phenomenon was observed with the other spots revealed in the diffraction pattern. The facts mentioned above lead us to the conclusion that lapping produces subgrains with orientations slightly different (of the order of 1 mrad) from the original grain and intergrain orientation. The mechanism of formation of the subgrains is not clear. The rapid increase in dislocations [ 21 during lapping, however, can be considered to be the cause.
(a)
(b)
(cl Fig. 2. Optical micrographs showing the structure abrasives: (a) BM 180; (b) BM 302; (c) BM 304.
after
lapping
with
various
coarse
Figure 5 shows the etched affected layer after lapping with fine abrasive grains. Instead of subgrains, only etch pits oriented in the lapping direction were observed. It may be said, therefore, that the state of the affected layer after lapping varies with the size of abrasive grains used.
Fig. 3. Optical micrograph showing locations against sub-boundaries
(a)
the
etch
pits
which
resemble
the
piling
up of dis-
(b)
Fig. 4. Typical change in the state of the spots in the back-reflection X-ray diffraction pattern (a) before and (b) after lapping. (The darkness of one of the spots was measured photometrically.)
187
Fig. 5. The etched affected surface after lapping with fine abrasive grains.
4. Conclusions Lapping slip direction
of indium-doped was carried
germanium
parallel
to the {ill}
plane
in the
out.
After lapping with coarse abrasive grains subgrains were observed, whose size is independent of that of the abrasive grains (about 35 pm); in contrast, only etch pits parallel to the lapping direction were observed when lapping with fine abrasive grains. The subgrains oriented themselves at random except when lapping with the coarsest abrasive grains; in this case most of the subgrains oriented themselves parallel to the lapping direction. It may be said that the state of the affected layer changes not continuously but abruptly with the size of the abrasive grains used (see Appendix A). 1 P. R. Camp, A study of the etching rate of single-crystal germanium, J. Electrochem. Sot., 102 (10) (1955) 586 - 593. 2 J. Friedel, Dislocations, Pergamon, Oxford, 1964, pp. 104 - 108.
Appendix
k
The abrasive grains are not always regular in shape and size (Fig. Al). Therefore, their grain size was not given in the text. The spectrochemical analysis revealed that BM 180 contains a large amount of magnesium together with some silicon and aluminium; this suggests that BM 180 is a blend of MgO, Sic and A1203, of which MgO is the major constituent. For BM 302 and BM 304, Al*Os is thought to be the major constituent. BM 309 contains a large amount of titanium and some zinc; this suggests that BM 309 is a blend of TiOz and ZnO, of which TiOs is the major constituent.
_. c
‘. 1
.
(a)
(b)
(d) Fig. Al. The abrasive
grains:
(a) BM 180; (b) BM 302; (c) BM 304; (d) BM 309