**3.3 Finding the first sidewall of hole**

As tip find the real bottom of the hole, it will start moving in either direction (along +X axis) to find the first sidewall. Starting from the center (bottom) of the hole, tip start piercing the direction of sidewall by moving forward and backward along all the axis individually as shown in **Figure 6**. At each step, either the sidewall is present or not, its location is stored in variable. This is important because at some point the tip might not found the sidewall, then the direction of motion of probe will be decided by 'location of previous sidewall' and it can only be done storing the direction of sidewall at each step. In addition to this, if the tip has lost the sidewall (due to drift), then tip will move to the nearest sidewall present by tracking the history of motion that probe has moved.

#### **Figure 6.**

*Algorithm to find the direction of sidewall. As the tip reaches at the bottom of the hole, it starts to find the sidewall in all direction by moving forward-backward motion and tracking the amplitude. Any encounter with the sidewall causes to decrease in amplitude. Direction of the sidewall is stored in the variable1 to make the movement accordingly.*

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

For example, tip move one step in +X direction and move back by tracking the amplitude. If the amplitude remains the same, it means there is no sidewall along +X direction. Similarly, the same phenomena is repeated by scanner for other axes (+Y, X, Y). The direction of sidewall is checked at every step. If the sidewall is detected in any direction, the corresponding motion will be performed by the scanner (Appendix).

#### **3.4 Making the motion corresponding to the sidewall detected**

As the tip is scanning to find the sidewall along all the direction, at some point, the sidewall will be detected along +X axis and according the algorithm the tip will move along +Y direction. After that, the direction of sidewall will be checked again. If the sidewall is along +Y direction, then the motion will be along -X axis. Similarly, following the counterclockwise scheme, motion will be along +X direction if the sidewall will be in -X direction. If at next step, tip found no sidewall then the scanner will move in the direction where the last sidewall was. This technique helps the tip to strictly follow the boundary of the hole and with the motion decided by the algorithm, the perfect boundary of the feature can be determined sophisticatedly. The situation is more interesting when the tip experience two or three sidewalls and motion of the scanner will be followed as described in **Table A1** (Appendix). However, if all sidewall direction is found then tip is assumed to be trapped and should be retracted along +Z direction for its safety. **Figure 6** shows the working strategy to find the side wall of algorithm to track the boundary of the hole and tracking the amplitude as shown in **Figure 7**. To know the exact shape of the boundary, X and Y step size can be varied. However, there are two types of steps, i.e., jump step and motion step. The first one is jump step along any axis to check the direction of sidewall, which is usually greater than the motion step size. This is necessary to make the tip at a safe distance so that the tip not wear or to minimize the van der Waals forces between the tip and the sidewall. The motion step can be decreased to few nanometers for high resolution and to measure the exact shape of feature. After that, arithmetic is done by the algorithm, by considering the jump step, to calculate the diameter of each complete rim scan by adding the jump step to diameter obtained from 3D scanning.

#### **Figure 7.**

depth was only 10 nm. However, the Van der Waals forces may vary

protrusion.

**Figure 6.**

**266**

*movement accordingly.*

**3.3 Finding the first sidewall of hole**

*21st Century Surface Science - a Handbook*

history of motion that probe has moved.

measurement-to-measurement as the tip goes deep inside the hole. Moreover, there was no significant damage to the apex of the tip. In **Figure 5(c)**, 120 nm shows the best result in stability as well as depth measurement and 3D scanning of deep holes. On the contrary side, 20 nm is suitable for 3D scanning of shallow holes as well as

As tip find the real bottom of the hole, it will start moving in either direction (along +X axis) to find the first sidewall. Starting from the center (bottom) of the hole, tip start piercing the direction of sidewall by moving forward and backward along all the axis individually as shown in **Figure 6**. At each step, either the sidewall is present or not, its location is stored in variable. This is important because at some point the tip might not found the sidewall, then the direction of motion of probe will be decided by 'location of previous sidewall' and it can only be done storing the direction of sidewall at each step. In addition to this, if the tip has lost the sidewall (due to drift), then tip will move to the nearest sidewall present by tracking the

*Algorithm to find the direction of sidewall. As the tip reaches at the bottom of the hole, it starts to find the sidewall in all direction by moving forward-backward motion and tracking the amplitude. Any encounter with the sidewall causes to decrease in amplitude. Direction of the sidewall is stored in the variable1 to make the*

*Working strategy of Algorithm to find the sidewall and scan the via holes. (a) Algorithm record the amplitude before and after moving towards the position of sidewall. If there is sidewall, rapid decrease in amplitude is detected as can be seen in (b). (c) Motion of the tip to follow the boundary of the via hole. The step size can be varied for high resolution. Tip start from the centre of the hole and start moving along +X direction to find sidewall. As it finds the sidewall, it starts following the boundary of hole in xy plane in counter clockwise.*

#### **3.5 3D scanning of hole AAO**

To test the feasibility of the proposed three-dimensional imaging algorithm of via holes as well as protrusion, we first done the simulation in the LABVIEW software (Appendix). The versatility of the software can be seen in such a way that any irregular shape of hole as well as protrusion can imaged using this algorithm.

once the 3D scan of first hole is completed and tip is escaped from the hole (in line profile straight line shows that the tip is escaped from the hole), using the coordinates of next hole, tip moves along –Z direction and reaches at the bottom of the hole. Once it touches to the bottom, 3D scanning is done in the same fashion as of

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

*Image of silicon pillars. (a) SEM image of silicon pillars. (b) Lines showing the scan direction of tip. As the tip comes near the surface it is retracted (offset) few hundreds of nm to avoid any interface of surface with the tip. As the tip is moving in +X direction to find the sidewall, at some point it find the sidewall of silicon pillar and according to algorithm, it start to find the boundary of the pillar. As once rotation completed, tip retracted along +Z direction to scan next rim. If the straight line is found in the scan, as shown in figure, it means that the tip has completed scanning the pillar and similarly next pillar can be scanned using the same scheme. (c) FIB treated 20 nm MWCNT (without capping) used to obtain the 3D profile of silicon pillar (d) 3D image of silicon pillar obtained from the 3D scanning algorithm with the step size 19 nm along X, Y direction and 20 nm along +Z direction. However, the step size along all axis can be even smaller for high resolution. The scale bar is 500 nm. The edge of the tip is limited to the radius of the probe. In our case, tip radius of arc grown CNT is 20 nm. (e) 3D image of silicon pillars: After completing one pillar, tip is brought near to the surface again (moved along –Z*

*direction) to scan the next pillar. Motion of the probe is shown by the red arrow in figure.*

first hole.

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

**Figure 9.**

**269**

The above-mentioned algorithm is implemented in LabVIEW software and tested on Anodic Aluminum Oxide (AAO) sample bought from Vida Biotechnology CO. LTD. We have three samples with 300 nm, 500 nm and 1 μm depth. Diameter of the holes were 350 nm. For protrusion, silicon pillars bought from NT-MDT having the approx. Height of 500 nm and 3 μm periodicity along lateral and 2.1 μm along diagonal direction. Dimension of the sample was as: 2.5 � 2.5.

**Figure 8(b)** shows the 3D image of AAO hole having the depth of 650 nm when the algorithm is applied to scan the internal topography of hole. Z step is set to 34 nm, however for higher resolution it can be decreased. Moreover, **Figure 8(c)** is the AFM image obtained using conventional AFM which cannot go deep more than 530 nm due to low aspect ratio. This shows our 3D AFM algorithm has strong potential to scan the features having high aspect ratio. As the tip goes deep inside the hole more than a micron, Van der Waals forces between the tip and sidewall also increases which may lead to the instability of the CNT. However, this problem can be overcome by using increasing number of layers of CNT so that it will be rigid, less flexible and stable for 3D scanning.

As the location of the holes (coordinates) is evident from the FD mapping (Z scanning) as shown in **Figure 4(c)**, next holes can be easily scanned. For example,

#### **Figure 8***.*

*AAO image with the depth 1um and pore diameter 350 nm. (a) SEM image of AAO. (b) 3D image of inside of hole which shows that the tip scanned 650 nm depth. Tip goes deep inside of hole and find the bottom where it has to start the 3D scanning as marked by the dot in figure. Then it moves in either direction (+X) to find the sidewall. Once the sidewall is found, tip start to follow the boundary. After completing the one rotation* 360o ð Þ*, scanner retracted along +Z direction to start new rim scan. When the straight line is found during scanning, it means that the tip is escaped from the hole or tip finished scanning the hole (straight line not shown in figure). (c) Raster image obtained from conventional AFM used to find the location of hole. Due to the low aspect ratio of the conventional AFM, it cannot go deep and limited to 532 nm, however, the original sample depth is 1* μm*. 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*

once the 3D scan of first hole is completed and tip is escaped from the hole (in line profile straight line shows that the tip is escaped from the hole), using the coordinates of next hole, tip moves along –Z direction and reaches at the bottom of the hole. Once it touches to the bottom, 3D scanning is done in the same fashion as of first hole.

#### **Figure 9.**

**3.5 3D scanning of hole AAO**

*21st Century Surface Science - a Handbook*

less flexible and stable for 3D scanning.

**Figure 8***.*

**268**

*Scale bar is 500 nm.*

To test the feasibility of the proposed three-dimensional imaging algorithm of

**Figure 8(b)** shows the 3D image of AAO hole having the depth of 650 nm when

As the location of the holes (coordinates) is evident from the FD mapping (Z scanning) as shown in **Figure 4(c)**, next holes can be easily scanned. For example,

*AAO image with the depth 1um and pore diameter 350 nm. (a) SEM image of AAO. (b) 3D image of inside of hole which shows that the tip scanned 650 nm depth. Tip goes deep inside of hole and find the bottom where it has to start the 3D scanning as marked by the dot in figure. Then it moves in either direction (+X) to find the sidewall. Once the sidewall is found, tip start to follow the boundary. After completing the one rotation* 360o ð Þ*, scanner retracted along +Z direction to start new rim scan. When the straight line is found during scanning, it means that the tip is escaped from the hole or tip finished scanning the hole (straight line not shown in figure). (c) Raster image obtained from conventional AFM used to find the location of hole. Due to the low aspect ratio of the conventional AFM, it cannot go deep and limited to 532 nm, however, the original sample depth is 1* μm*.*

the algorithm is applied to scan the internal topography of hole. Z step is set to 34 nm, however for higher resolution it can be decreased. Moreover, **Figure 8(c)** is the AFM image obtained using conventional AFM which cannot go deep more than 530 nm due to low aspect ratio. This shows our 3D AFM algorithm has strong potential to scan the features having high aspect ratio. As the tip goes deep inside the hole more than a micron, Van der Waals forces between the tip and sidewall also increases which may lead to the instability of the CNT. However, this problem can be overcome by using increasing number of layers of CNT so that it will be rigid,

via holes as well as protrusion, we first done the simulation in the LABVIEW software (Appendix). The versatility of the software can be seen in such a way that any irregular shape of hole as well as protrusion can imaged using this algorithm. The above-mentioned algorithm is implemented in LabVIEW software and tested on Anodic Aluminum Oxide (AAO) sample bought from Vida Biotechnology CO. LTD. We have three samples with 300 nm, 500 nm and 1 μm depth. Diameter of the holes were 350 nm. For protrusion, silicon pillars bought from NT-MDT having the approx. Height of 500 nm and 3 μm periodicity along lateral and 2.1 μm

along diagonal direction. Dimension of the sample was as: 2.5 � 2.5.

*Image of silicon pillars. (a) SEM image of silicon pillars. (b) Lines showing the scan direction of tip. As the tip comes near the surface it is retracted (offset) few hundreds of nm to avoid any interface of surface with the tip. As the tip is moving in +X direction to find the sidewall, at some point it find the sidewall of silicon pillar and according to algorithm, it start to find the boundary of the pillar. As once rotation completed, tip retracted along +Z direction to scan next rim. If the straight line is found in the scan, as shown in figure, it means that the tip has completed scanning the pillar and similarly next pillar can be scanned using the same scheme. (c) FIB treated 20 nm MWCNT (without capping) used to obtain the 3D profile of silicon pillar (d) 3D image of silicon pillar obtained from the 3D scanning algorithm with the step size 19 nm along X, Y direction and 20 nm along +Z direction. However, the step size along all axis can be even smaller for high resolution. The scale bar is 500 nm. The edge of the tip is limited to the radius of the probe. In our case, tip radius of arc grown CNT is 20 nm. (e) 3D image of silicon pillars: After completing one pillar, tip is brought near to the surface again (moved along –Z direction) to scan the next pillar. Motion of the probe is shown by the red arrow in figure.*

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

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 and so on.
