**4. Conclusion**

MWCNT tips are one of the best candidates to further investigate different materials in AFM imaging world, enhancing tip lifetime, eliminating the artifacts and increasing the resolution by decreasing the tip-surface forces. Many algorithms has already been proposed and implemented to scan the deep trenches, sidewall roughness and to measure other 3D parameters. However, none of them can able to 3D scan the deep via holes, which has the vertical sidewalls and real time 3D imaging protrusions features like silicon pillars. As TSVs have potential application in NAND flash memories, 3D meteorology, and 3D system integration. So, exact location of via holes, depth and internal roughness of sidewall should be measured accurately. In this work we have proposed an algorithm which has ability to scan the features above and below the surface such as TSV and silicon pillars. We have tested the algorithm on AAO in which location of holes, depth of holes as well as internal roughness of sidewalls are measured. In addition to this, real time 3D scanning has been performed by the algorithm on silicon pillars (protrusion) and it has been found that it is a best choice to measure the features having high aspect ratio. We believe that impact of this algorithm will not be limited to only the semiconductor field. In general, getting the 3D topography is a crucial issue for measuring the parameters like surface roughness, hole depth and locations etc. So far, several algorithms has been proposed which employs special type of probes, but these are specially designed to measure the structures like trenches as discussed earlier. The new method described here is a unique since it can image any kind of feature (present above or below the surface).

**Figure A1.**

**Figure A2.**

**271**

*and a tube scanner.*

*Automatic shutoff circuit for electrochemical etching of tungsten wire. Etching circuit is divided in to two resistors, i.e., 0.5 and 50 Ω (Connected to real and virtual ground, i.e., input to the current amplifier). Second stage amplifier is a voltage follower which makes the signal stable during the etching. Third stage amplifier is an inverting amplifier which inverts the signal from the first stage so that it can be compared to the set point. At the very last moment of etching, when lower part of the tip is about the drop, there might be some fluctuation in the signal and tip can be blunt or uniformity of the tip can be disturbed. To avoid this, Schmitt trigger is used at the comparator which makes the signal stable at the last moment of etching. Solid state relay is used to reduce the*

*Measuring the Blind Holes: Three-Dimensional Imaging of through Silicon via Using High…*

*DOI: http://dx.doi.org/10.5772/intechopen.92739*

*Homemade setup for 3D AFM, composed of tuning fork sensor, lock-in amplifier, PC based digital controller,*

*shut-off time. This automatic cut-off circuit has the shut-off time 0.5 μs.*

### **A. Appendix**

#### **A.1 Functionalization of MWCNT**

To functionalize the MWCNTs, 1 g of PVA was completely dissolved in 60 ml of water at room temperature. After that, 0.2 mg of MWCNTs was added into the above-mentioned solution and mixture was stirred at 70oC for 4–12 h. A centrifugal separator was used to remove the impurities or particles from the CNT-PVA solution. Centrifugation at 4000 RPM for 30 min was done several times unless the solution becomes clear and no agglomerated CNTs left in solution. To remove excess PVA from PVA-CNT solution, filter paper (Anodisc 47, Whatman) with the pore size 200 nm and diameter 47 mm was used. Filtered CNTs-PVA are then

*Measuring the Blind Holes: Three-Dimensional Imaging of through Silicon via Using High… DOI: http://dx.doi.org/10.5772/intechopen.92739*

#### **Figure A1.**

In addition to this, algorithm is applied to obtain the 3D topography of the silicon pillars. Tip start to scan the pillar in either direction. Once it encounter the sidewall of pillar, it start to follow the boundary of the silicon pillar and on completion of one rotation, scanner retracted along +Z direction to complete the next rim scan. The process continuous unless it complete scanning the pillar. Resolution of 3D image depends upon the thickness of AFM probe. We have used 20 nm tip to scan the pillar which means the last (top edge) rim scan should be approxi-

In addition to this, as the tip completes once pillar, the tip can be pushed deliberately near to the surface and moved in +X direction to find the second pillar

MWCNT tips are one of the best candidates to further investigate different materials in AFM imaging world, enhancing tip lifetime, eliminating the artifacts and increasing the resolution by decreasing the tip-surface forces. Many algorithms has already been proposed and implemented to scan the deep trenches, sidewall roughness and to measure other 3D parameters. However, none of them can able to 3D scan the deep via holes, which has the vertical sidewalls and real time 3D imaging protrusions features like silicon pillars. As TSVs have potential application in NAND flash memories, 3D meteorology, and 3D system integration. So, exact location of via holes, depth and internal roughness of sidewall should be measured accurately. In this work we have proposed an algorithm which has ability to scan the features above and below the surface such as TSV and silicon pillars. We have tested the algorithm on AAO in which location of holes, depth of holes as well as internal roughness of sidewalls are measured. In addition to this, real time 3D scanning has been performed by the algorithm on silicon pillars (protrusion) and it has been found that it is a best choice to measure the features having high aspect ratio. We believe that impact of this algorithm will not be limited to only the semiconductor field. In general, getting the 3D topography is a crucial issue for measuring the parameters like surface roughness, hole depth and locations etc. So far, several algorithms has been proposed which employs special type of probes, but these are specially designed to measure the structures like trenches as discussed earlier. The new method described here is a unique since it can image any kind of feature

To functionalize the MWCNTs, 1 g of PVA was completely dissolved in 60 ml of water at room temperature. After that, 0.2 mg of MWCNTs was added into the above-mentioned solution and mixture was stirred at 70oC for 4–12 h. A centrifugal separator was used to remove the impurities or particles from the CNT-PVA solution. Centrifugation at 4000 RPM for 30 min was done several times unless the solution becomes clear and no agglomerated CNTs left in solution. To remove excess PVA from PVA-CNT solution, filter paper (Anodisc 47, Whatman) with the pore size 200 nm and diameter 47 mm was used. Filtered CNTs-PVA are then

mately equals to the diameter of the CNT as shown in **Figure 9**.

*21st Century Surface Science - a Handbook*

and so on.

**4. Conclusion**

(present above or below the surface).

**A.1 Functionalization of MWCNT**

**A. Appendix**

**270**

*Automatic shutoff circuit for electrochemical etching of tungsten wire. Etching circuit is divided in to two resistors, i.e., 0.5 and 50 Ω (Connected to real and virtual ground, i.e., input to the current amplifier). Second stage amplifier is a voltage follower which makes the signal stable during the etching. Third stage amplifier is an inverting amplifier which inverts the signal from the first stage so that it can be compared to the set point. At the very last moment of etching, when lower part of the tip is about the drop, there might be some fluctuation in the signal and tip can be blunt or uniformity of the tip can be disturbed. To avoid this, Schmitt trigger is used at the comparator which makes the signal stable at the last moment of etching. Solid state relay is used to reduce the shut-off time. This automatic cut-off circuit has the shut-off time 0.5 μs.*

#### **Figure A2.**

*Homemade setup for 3D AFM, composed of tuning fork sensor, lock-in amplifier, PC based digital controller, and a tube scanner.*

**Figure A6.**

**Figure A7.**

**273**

*to find the location of holes.*

*DOI: http://dx.doi.org/10.5772/intechopen.92739*

*AFM image of AAO sample obtained from home built AFM using the MWCNT. Raster scan mode was applied*

*Measuring the Blind Holes: Three-Dimensional Imaging of through Silicon via Using High…*

*FD curves were measured at the different holes in AAO sample having the depth of 1 μm. Sharp decreases imply that the tip touches to the bottom of the hole, and the depths are estimated as 935 nm similar from all data.*

#### **Figure A3.**

*Experimental setup for tungsten wire etching. (a) Gold wire is used as anode and tungsten wire acts as cathode. As the etching begins, bubbles travel from anode to cathode which may deform the meniscus shape. A glass slide is placed between the electrodes to avoid this problem. (b) SEM image of tungsten wire after it has been etched using KOH solution. Once the wire has been etched, it is washed with hot D.I water to reduce the oxide layer around the etched part. We have used 2 M concentration of KOH solution. Etching takes approximately 70 s to complete the etching. After etching 5–6 tips, the solution needs to be replaced. Otherwise, etched shape may be not uniform or the surface of the tungsten becomes rough. Almost all of tips are produced uniformly and the average tip radius is found to be 80 nm.*

#### **Figure A4.**

*FTIR spectra for functionalized MWCNT. (a) FTIR spectrum depicts attachment of functional groups in CNTs: Peaks in the range of 1200–3500 confirm the presence of functional group in purified CNTs. Inset image clearly shows the peaks at 2856 and 2926. (b) Comparison between the PVA-functionalized and as grown MWCNT.*

#### **Figure A5.**

*Dielectrophoresis setup for attachment of multiwall carbon nanotube on chemically etched tungsten probe. (a) Function generator is used to apply AC voltage which generates electric field and consequently attracts the CNT towards the tungsten probe. (b) SEM image shows a single MWCNT attached to the tungsten probe via van der Waals forces. Scale bar is 500 nm.*

*Measuring the Blind Holes: Three-Dimensional Imaging of through Silicon via Using High… DOI: http://dx.doi.org/10.5772/intechopen.92739*

**Figure A6.**

**Figure A3.**

**Figure A5.**

**272**

**Figure A4.**

*Waals forces. Scale bar is 500 nm.*

*average tip radius is found to be 80 nm.*

*21st Century Surface Science - a Handbook*

*Experimental setup for tungsten wire etching. (a) Gold wire is used as anode and tungsten wire acts as cathode. As the etching begins, bubbles travel from anode to cathode which may deform the meniscus shape. A glass slide is placed between the electrodes to avoid this problem. (b) SEM image of tungsten wire after it has been etched using KOH solution. Once the wire has been etched, it is washed with hot D.I water to reduce the oxide layer around the etched part. We have used 2 M concentration of KOH solution. Etching takes approximately 70 s to complete the etching. After etching 5–6 tips, the solution needs to be replaced. Otherwise, etched shape may be not uniform or the surface of the tungsten becomes rough. Almost all of tips are produced uniformly and the*

*Dielectrophoresis setup for attachment of multiwall carbon nanotube on chemically etched tungsten probe. (a) Function generator is used to apply AC voltage which generates electric field and consequently attracts the CNT towards the tungsten probe. (b) SEM image shows a single MWCNT attached to the tungsten probe via van der*

*FTIR spectra for functionalized MWCNT. (a) FTIR spectrum depicts attachment of functional groups in CNTs: Peaks in the range of 1200–3500 confirm the presence of functional group in purified CNTs. Inset image clearly shows the peaks at 2856 and 2926. (b) Comparison between the PVA-functionalized and as grown MWCNT.*

*AFM image of AAO sample obtained from home built AFM using the MWCNT. Raster scan mode was applied to find the location of holes.*

**Figure A7.**

*FD curves were measured at the different holes in AAO sample having the depth of 1 μm. Sharp decreases imply that the tip touches to the bottom of the hole, and the depths are estimated as 935 nm similar from all data.*

#### **Figure A8**

*.*

*FD curves are measured at different holes on AAO sample having the depth of 300 nm: Measured data show that the depth is approximately 285 nm. Sharp increases indicate that the tip touches to the bottom of the hole.*

**Figure A9.**

*perfectly.*

*SW: sidewall detected, "—": not detected.*

**Table A1.**

**275**

*After the wall is encountered by the probe by tracking the difference in amplitude, motion of the scanner is determined according to Table A1. However, if the probe is unable to find the sidewall, it will move along the direction where the previous sidewall was. This gives the appropriate correction of the sidewall direction to follow the exact shape of the boundary. By this strategy, any shape of either hole or protrusion is scanned*

*Measuring the Blind Holes: Three-Dimensional Imaging of through Silicon via Using High…*

*DOI: http://dx.doi.org/10.5772/intechopen.92739*

**S.# Sidewall direction Scanner motion**

1 ———— Previous direction of sidewall

**+X +Y X Y**

 ——— SW Along +X — — SW — Along Y — — SW SW Along +X — SW — — Along X — SW — SW Along X — SW SW — Along Y — SW SW SW Along +X SW ——— Along +Y SW — — SW Along +Y SW — SW — Along Y SW — SW SW Along +Y SW SW — — Along Y SW SW — SW Along X SW SW SW — Along Y SW SW SW SW Along +Z

*Measuring the Blind Holes: Three-Dimensional Imaging of through Silicon via Using High… DOI: http://dx.doi.org/10.5772/intechopen.92739*

#### **Figure A9.**

**Figure A8***.*

*21st Century Surface Science - a Handbook*

**274**

*FD curves are measured at different holes on AAO sample having the depth of 300 nm: Measured data show that the depth is approximately 285 nm. Sharp increases indicate that the tip touches to the bottom of the hole.*

> *After the wall is encountered by the probe by tracking the difference in amplitude, motion of the scanner is determined according to Table A1. However, if the probe is unable to find the sidewall, it will move along the direction where the previous sidewall was. This gives the appropriate correction of the sidewall direction to follow the exact shape of the boundary. By this strategy, any shape of either hole or protrusion is scanned perfectly.*


#### **Table A1.**

collected and dried under vacuum. Finally, CNT-PVA was dissolved into DI water and the solution is sonicated in an ultrasonic bath for 6 h to uniformly disperse in solution. After attachment of carboxylic group, MWCNTs were investigated by Fourier transform Infrared spectroscopy (FTIR), as shown in **Figure A4**. The peaks observed at 1390 and 3425 cm<sup>1</sup> are identified with O–H bond bending and stretching, respectively [29]. The peaks observed at 1260 and 1663 cm<sup>1</sup> are due to C–O and C=O stretching of functional groups, respectively [29]. In addition, C–H stretching vibrations correspond to 2856 and 2924 cm<sup>1</sup> peaks [30].
