The document describes fabricating two devices - a silicon device and an ITO device - in a microfabrication laboratory under supervision. It details the cleaning, oxidation, deposition, photolithography, and testing steps used. The goal was to gain experience using the facilities and characterize the resistance of thin film materials. Standard clean room procedures were followed for processes like RCA cleaning, thermal oxidation, sputtering, spin coating, and ellipsometry thickness measurement.

1. Fabricate Silicon Device and ITO Device in Micro Fabrication Laboratory
under Supervising
Author: Jiemin Zhang1
†
Affiliations:
1
Department of Electrical and Computer Engineering, Michigan Technological University, 1400
Townsend Drive, Houghton, Michigan, USA
†Corresponding author. E-mail: jieminz@mtu.edu
Abstract: Start from September 2014 until December 2014, I attended and participated in the
Micro Fabrication Laboratory in Michigan Tech, and fabricated two devices: silicon device and
ITO device. Due to I did not have enough experience in the laboratory, so I need to do it under
supervising. We started from the very beginning, we clean the wafer first, by RCA Clean
procedure, which used three steps to clean it chemically. Then we grew the oxide layer on the
wafer. After this, we would use the different path on the two different devices. When the devices
are successfully made, we would test the device we made, to see if the resistance of each device
are reasonable, which is the last step.
One Sentence Summary: Use the Micro Fabrication Facilities to fabricate two devices: silicon
device and ITO device, and test the resistance after successfully made them.
Introduction: Either silicon device or ITO device, the fabrication procedure are similar. Briefly
introduce it of the silicon device, we do the pre furnace clean, then thermal oxidation, deposit
poly-silicon on the wafer, spin photoresist on the wafer and pattern it by photolithography, etch
the wafer to make the device. Then use photoresist and photolithography to pattern the contacts
area, deposit gold and chrome as the contacts then lift off. Then we could have the overlays we
want on the wafer (Fig. 1).
The two devices we fabricated, the purpose of them are for characterization. In other word, for
example, here we have some new materials, but we don’t know the resistance of the materials
when they are just several nanometer thick on the wafer. So in this case, we could use the routine
we have been through, and finally build the small strips on the wafer, with different lengths, then
examine the resistance of each strip, to determine the resistance per length. On the other hand,
the whole routine for building the devices, most of the facilities in the laboratory could be used,
so we could getting familiar with the facilities by fabricating the device in the lab. For example,
for cleaning wafer, we use wet benches; for remove the photoresist, we use EVG Lithography
device; for determine the thickness of the layer, we use J. A. Woollam Co. VASE®Ellipsometer;
for characterize the resistance, we use Micro-Manipulator, and so on. So after fabricated the
devices, I gained the experience in the lab, which makes me more qualified to do related research
in the future.
A

2. B
Fig. 1. Overlays in the devices for characterization (A) For resistance characterization. (B) For Hall effect
characterization
Theory and Design: In the RCA Clean Procedure, the first step, organic clean and particle
clean, the solution contains a strong base, normally ammonium hydroxide, and hydrogen
peroxide. And the SC2 contains a strong acid, normally hydrochloric acid, and hydrogen
peroxide. The purpose of hydrogen peroxide in the RCA clean is to react with the exposed
silicon surface of the wafer to form a chemically grown oxide, protecting the wafer from being
etched in the strong base or acid (1). On the second step, the Hydrofluoric acid (HF) is a strong
acid which can even affect human health, so use it to remove oxide could be very effective, e.g.
SiO2 + 4HF  SiF4 + 2H2O. And hydrochloric acid could react with metallic contaminants, so
we use it in the third step, e.g. Mg + 2HCl  MgCl2 + H2 ↑.
During the photoresist (PR) spinning process SOP, we need to use Acetone Methanol and IPA
spin on the wafer one by one, the reason why we use them is they are all good solvent. And

3. about the photoresist, we have two different type of photoresist: positive and negative. The
positive one is the area exposed to the UV light would be removable, the negative one is the
exposed area is not removable. After this, we need to do soft bake, the purpose of this process
are to drive away the solvent from the resist, improve the adhesion between the resist and wafer
and anneal the shear stresses introduced during the spin-coating. (2)
When we are about to etch the wafer, there are two fundamental ways for etching: wet etching
and dry etching, we used the dry etching, with the aid of plasma. The creation of plasma is
applying a strong radio frequency (RF), the oscillating electric field ionizes the gas to create
plasma.
Fabrication Technology: Through the whole process, here are the detailed description of each
steps we operated. Some step may need to operate more than once since we need to make
different layer on the wafer. Before we start to operate, the two things we need to be clear: one is
about personal protection equipment (PPE), what the standard operating procedure for dressing
this and how could they protect us. The other is the material safety data sheet (MSDS), we need
to fully understand all the chemicals we will use by checking the book.
RCA Pre Furnace Clean. It is the standard operating procedure for cleaning a wafer before we
fabricate a device on the wafer. The facilities we need to use are the wet chemical processing
station (Fig. 2) and Spin Rinse Dryer. And the chemicals we need for this process are:
Ammonium Hydroxide (NH4OH), Hydrochloric Acid (HCl), Hydrogen Peroxide (H2O2),
Hydrofluoric Acid (HF). The properties and cautions can be found in MSDS.
Fig. 2. Wet Chemical Processing Station (3)

4. First of all, we need to start the Neutralization Station. Check all the tanks are in the low-level
mode. Then pre-clean all the tanks we will use by fill the tanks with DI water one by one and
drain them. Use aspirator for RCA heated tanks.
Next we do the RCA Clean. There are three steps: RCA Organic Bath, HF dip and RCA Ionic
Bath.
For Organic Bath, the mixture of NH4OH, H2O2 and DI water is in the ratio of 1:1:8, and the
solution is only effective in 20 minutes since there will be reaction between them after that. First
fill the tank with required DI water, turn the heater on until 85 °C, then follow the ratio, take the
amount of H2O2 in a polypropylene beaker, and pour it into the tank. Before we take NH4OH, we
need to rinse the beaker 3 times with DI water for cleaning. After this, follow the same procedure
to take the NH4OH and pour it into the tank. Then place the wafer holder with the wafers using
Teflon handle in the tank. Remove the handle and rinse in the quench tank for one minute, start
the timer, which previously set 10 minutes. While the wafer do the bath, press FILL button to fill
the rinse tank with DI water. When the timer ends, remove from the organic tank and place the
wafers in the filled rinse tank, cover and press START. When the rinse finished, we should not
take it out cause it is not supposed to be exposed in the environment.
For HF Dip, which is the second step after Organic Bath. Fill the tank with DI water. Since the
ratio of HF/DI is 1:8, so we take the amount of HF with the specific ratio to the water. Since the
HF is poison and could damage human health easily, we need to operate it with full PPE, and do
it really carefully. We do the bath for 30 seconds, after that, we place the wafer in another pre-
filled rinse tank and let it rinse 3 cycles. After this, we move to the third step: RCA Ionic Bath.
For Ionic Bath, the solution is a mixture with HCl, H2O2 and DI water in the ratio of 1:1:8, and
only effects in 20 minutes. Similar to the Organic Bath, turn on the heater, take HCl and H2O2
separately into the tank, do the bath to the wafers, and rinse the wafers in another pre-filled tank
at last.
After all the three steps on the wet station, we use the Spin Rinse Dryer. We followed the
procedures and complete the final rinse and hot nitrogen dry cycle. When the dryer finishes, take
the wafers box out and be ready to do next process.
One last thing is cleaning up. All the tanks on the wet station should be cleaned by overflow
them with DI water for 3 times. Aspirate the water from the tanks for 3 times. Rinse all the
beakers we used with DI water for 3 times.
Thermal Oxidation. In this process, we use the Mellen Oxidation Furnace (Fig. 3), which has
three zones could be monitored. First follow instructions for all three temperature controllers,
and start flowing nitrogen in the furnace. Then load wafers on the sled and place them in the
“low position”. When the temperature is between 500 °C and 600 °C, removed the cap from the
furnace tube. After that, gently put the wafer in the furnace and put the cap back on the furnace
tube.
When the temperature reaches the soak temperature, usually 1050 °C, turn off the nitrogen flow
and turn on the oxygen flow using MKS 247 channel 2, and turn the O2 control panel on. It was
really hard to reach 1050 °C, especially the last 100 °C, so to finish the task in time, we need to
turn it on hours before the oxidation process.
When the oxidation time ends, stop O2 flow and turn off the corresponding control panel, turn off
the heat of all 3 zones by programming. When the temperature reaches the unloading

5. temperature, gently pull the sled out by the glove, similar to the routine when we put them in.
Final step, let the wafers cool down before next step.
Fig. 3. MELLEN Company Split Furnaces (3)
Sputtering Deposition. In this process we need to use the sputtering system called Perkin-Elmer
Randex Sputtering System Model 2400 (Fig. 4). And this is the start of the differences for
fabricating the two devices.
Fig. 4. Perkin-Elmer Randex Sputtering System Model 2400 (3)

6. Followed the Standard Operating Procedure, we need to sign in the log book on the whiteboard
to indicate the machine is operated. Then to open the chamber and load in the wafer. Before you
open, make sure the air pressure in the chamber reaches the atmospheric pressure, around 7.2 ×
10-2
Torr. After loading the wafer, close the chamber carefully, make sure they are perfectly
matched.
Next step is pump down the chamber from atmosphere until high vacuum, to create the
environment for sputtering. Base pressure usually is smaller 5 × 10-6
Torr, which is typically
reached in 2.5 hours. Some materials’ target require pre-etching. For silicon device, we need to
make silicon sputtered on the wafer, and ITO device is sputtering ITO.
After sputtering, follow the instruction for pump down process to let the air pressure in the
chamber go back to atmospheric pressure, then finally take the sample out carefully.
Through the whole process for patterning the material on the wafer, we need to do this process
again for depositing the gold and chrome for contacts.
Ellipsometry. After sputtering, it would be better to use the ellipsometer to check the thickness
of the layer we just sputtered on. The facility we would use is J. A. Woollam Co.
VASE®Ellipsometer (Fig. 5).
Fig. 5. J. A. Woollam Co. VASE®Ellipsometer (3)
Before everything start, we need to turn on “POWER”, then “LAMP”, then “IGNITION” at last.
After ignite the lamp, we should align the sample by using standard 25nm SiO2 calibration
wafer. When putting the wafer on the holder, carefully hold the wafer on and turn on the vacuum
to fix the wafer. Then adjust the wafer by screwing the x-axis and y-axis screw, try the best to
make the cross in the center of four rectangles. After this step, screw the z-axis to maximize the
intensity of light. Then, we should calibrate system, keep using the standard calibration wafer
which is used in the previous step. After calibration, we need to align sample again, but this time

7. we use the wafer we are about to test, the routine is the same with the previous one. After all the
alignment, we will do spectroscopic scan, the parameters are defined as follows:
Wavelength: 300nm to 1000nm, step: 10nm
Angle: 65 to 75, step: 5
After the detection on the wafer, under “Model” window, choose add layer, then choose out the
substrate material and thickness of it. Then choose the layer film material, if not sure, choose
“fit”, at last generate data. Here are some data for the silicon device, measurement after
depositing poly-silicon on the wafer (Table 1, 2, Fig. 6, 7)
Table 1. 30min, 600watts deposition
Fig. 6. 30min, 600watts deposition
Table 2. 47min, 750watts deposition
Generated and Experimental
Wavelength (Å)
2000 4000 6000 8000 10000
Yindegrees
Dindegrees
0
10
20
30
40
0
50
100
150
200
Model Fit
Exp Y-E 65°
Exp Y-E 70°
Exp Y-E 75°
Model Fit
Exp D-E 65°
Exp D-E 70°
Exp D-E 75°
0 silicon 0.5 mm
1 sio2_jaw 80.000 nm
2 a-si_aspnes_cl 191.679 nm

8. Fig. 7. 47min, 750watts deposition
After the process, we still need to go through this process several times for future measurement.
For example, after etching, we want to make sure the unwanted part is gone, so we use
ellipsometer to measure. When we pattern gold and chrome, we could use it to measure. When
we done fabricate the device, we still need to use it to measure to see if everything are
reasonable.
Spin Photoresist on the wafer. This process we will make the photoresist coating on the wafer
of the mask on the material, do the preparation for patterning and make the device later. This
process we need to use the heater (Fig. 8) and spinner (Fig. 9).
Fig. 8. Heater
Generated and Experimental
Wavelength (Å)
2000 4000 6000 8000 10000
Yindegrees
Dindegrees
0
10
20
30
40
0
30
60
90
120
150
180
Model Fit
Exp Y-E 65°
Exp Y-E 70°
Exp Y-E 75°
Model Fit
Exp D-E 65°
Exp D-E 70°
Exp D-E 75°

9. Fig. 9. Spinner
Before we process, we turn on and set the temperature around 100 °C to 120 °C to the heater for
hot plate. When the temperature reaches, place the wafer on the plate for 2 minutes. This process
helps evaporating the water on the wafer then increase the adhesion between the wafer and
photoresist. After heating, we need to clean the wafer by spinning Acetone, Methanol and IPA
one by one over the wafer. We set the hot wafer on the center of the spinner, gradually adjust it
to make sure it is on the center. Then turn the vacuum on to fix the wafer. After that, we spray
Acetone, Methanol and IPA consequently on the wafer, meanwhile start the program. When the
spinner stops, the wafer should be cleaned.
Next step is spin the photoresist on the wafer, which should try to fix the wafer as before, then
use a pipette to transfer photoresist from the container to the wafer. Try the best to pour the resist
at the center of wafer and avoid air bubbles, after that, quickly close the lid and start spinning.
Deposit hexamethyldisilazane (HMDS) is required for better adhesion.
After coating the photoresist, we need to do a soft bake for driving solvent and improve
adhesion. It is the same with the preheating step.
After all the process we have been doing, clean the spinner inside and outside by wiping.
Photolithography. This process should be doing just after we coated the photoresist on the
wafer. It requires the EVG®620 Lithography and Microscope (Fig. 10) facilities. First turn on
the computer and login EVG620 software, use the appropriate configurations for pressure.
Then we need to fit in the mask first. Just follow the routine in the software, move tray out, fit in
the mask holder, put the mask in the holder, then move the tray in let the mask fixed in the stage.
After that we need to remove load frame, then insert substrate and move the tray in. This time we
need to adjust the wafer, to let the mask and substrate are precisely overlap with each other. Then
do the exposure on the substrate through the mask to pattern the photoresist on the wafer.
Before enter the next step, we could use the Microscope to see how the coating went, was that
contaminated, or if there are some mismatch for the layers.

10. Fig. 10. EVG®620 Lithography (Left) and Microscope (Right)
We will do the similar procedure when we pattern the gold and chrome on the wafer to be the
metallic contacts. Just one more attention when we do second time: we need to find the
alignment mark, or the “T” pattern, then slightly adjust the optic position and stage position, for
trying to precisely match the mask and substrate before do the exposure.
Etching. After patterning the layer we want by exposing the photoresist under mask, then we
need to do the etching (or lift off) to get rid of all the unwanted part of the layer. The facility we
need to use is Trion ICP/RIE Etch PHTII-4301 (Fig. 11). Before operating the facility, remember
to wear the latex gloves.
Make sure it is on the standby mode and chiller cooled to 20 °C before operating. Open the
chamber lid first, load in the substrate, make sure it is ate the center of the holder among three
SST washers. When it is settled, close the lid and pump down. After that we input applicable
process parameters: the gas flow, pressure settings and so on. After all parameters settled, we run
the recipe. From the small window on the side, we could see the glory plasma when the system
processing.

11. Fig. 11. Trion ICP/RIE Etch PHTII-4301 (3)
When finish etching, select standby and pump for 5 minutes for residual removal. After the
whole process finished, wait until the lid opens, load out the wafer.
When we are facing the materials which are hard to dry etch, then we need to do the lift off
procedure. Lift off procedure do the most of steps we introduced before, just the sequence will be
different. For the materials cannot be dry etched like metallic materials, we spin the photoresist
on the wafer, pattern it first, clean the area of photoresist where we want the metallic materials to
be. Then we make the metallic layer on the pattern. The last step will be lift off, clean photoresist
in the solvent, let the unwanted metallic area go away with the photoresist under them. This is
the procedure called, lift off.
Characterization. After we been through the whole processes described above, the devices have
been successfully made. The final step is the measure the properties of what we made. To do this
process, the facility we need to use is the Micro-Manipulator (Fig. 12).
First we need to turn the system on, to make sure the manipulator is functional, we should
calibrate it. We could put the probe together first, if the resistance is not 0, adjust it to 0 for
future accuracy. Then we put the probe separate with each other, then the resistance showed on
the screen should be very large or “-”, which means not measureable.
After that, we load our device to the stage, measure the resistance for every one and series. When
we use the probe to contact the metallic part on the wafer, we do not want to press the probe on
the wafer, but we really do need to see a slight move between probe and contacts in the
microscope, which could make sure the probe is contacting with the metallic part on the wafer,
so to make sure there is no mistake in contacting.
At last, we read each measurement for each one or series, analyze the data we measured.

12. Fig. 12. Micro-Manipulator (3)
Result: The final devices under microscope are shown below (Fig. 13,14).
Fig. 13. Part of the resistor chain

13. Fig. 14. Hall sensor
Table 4. Thickness of each layer in silicon device
Fig. 15. Generated and experimental data for silicon device
0 silicon 0.5 mm
1 sio2_jaw 50.000 nm
2 poly-si_comp x=0.500 200.000 nm
3 cr2o3_g 84.268 nm
Generated and Experimental
Wavelength (Å)
2000 4000 6000 8000 10000
Yindegrees
Dindegrees
0
20
40
60
80
100
0
30
60
90
120
150
180
Model Fit
Exp Y-E 65°
Exp Y-E 70°
Exp Y-E 75°
Model Fit
Exp D-E 65°
Exp D-E 70°
Exp D-E 75°

14. Table 4. The measured result for the resistors. For silicon device, the data seems not quite logic, so I will provide
my analysis in Discussion section
Discussion: At last, the device we fabricated looks pretty good (Fig.13, 14). The data we
measured for resistance (Table 4), ITO device looks reasonable, but the silicon device must have
some problem in it. We could measure the resistance of each ITO strip, which means the micro-
manipulator is functional. And illogic result for silicon device, I think one of the possible reasons
is there are some contamination or damage on the wafer.
Other possible reason is when we do the lift off, if there are some part of gold and chrome didn’t
be lifted off successfully and connected the contacts with resistance in it, then it will happens
that reading data is not we expect.
Conclusion: After the roughly 4 months study and fabrication, I have already gotten familiar
with most of the fabrication facilities. By fabricate the specific devices, we start from the
beginning: RCA clean, thermal oxidation, sputtering deposition, photolithography, etching or
lift-off, and characterization. By going through the whole process, I noticed where I need to be
cautious, and how to do to make the fabrication better. Like when we take out the photoresist out
of the container by a pipette, I will squeeze the pipette first outside of the container before going
in, to avoid contamination as much as possible. So I have gotten many experience from the
fabrication sessions.
R (kΩ) X (Ω) R (kΩ) X (MΩ) Cp (PF) D
R1 0.835259 -0.87905 6.35997 -1.01306
R1+R2 2.46635 -10.7613 8.81576 -1.01728
R1+R2+R3 6.70384 -102.997 7.26848 -1.09321
R1+R2+R3+R4 15.3717 -553.445 5.94670 -0.996659
R1+R2+R3+R4+R5 33.1670 -1537.22 7.15257 -1.30007
R2 1.64768 -7.25654 5.10076 -0.758737
R2+R3 5.87349 -94.1341 8.12779 -0.854746
R2+R3+R4 14.5540 -537.805 5.56095 -0.750902 211.937 0.007447
R2+R3+R4+R5 32.3407 -1516.17 7.25230 -1.05626 149.510 0.007598
R3 4.22767 -58.9721
R3+R4 12.9143 -464.187
R3+R4+R5 31.4403 -1412.68
R4 8.67927 -236.272
R4+R5 26.6546 -1068.15
R5 18.0265 -465.411
ITO Sample (200C annealed) Silicon Sample (200C annealed)

15. References and Notes:
1. C. Sherry, L. Fuller, Hydrogen peroxide to strong base ratio of 1:1 prevents silicon from
etching during RCA clean (Rochester Institute of Technology, 2013;
http://people.rit.edu/lffeee/RCA%20Project%20Paper%20Fuller.pdf).
2. P. Bergstrom, " Lab 4 Photolithography SOP" (Microfabrication Facility, Houghton,
Michigan, 2014).
3. P. Bergstrom, Microfabrication Facility (http://mcff.mtu.edu/mff/)
Acknowledgments:
I thank Dr. Paul Bergstrom (Micro-Fabrication Facility) for providing this course, to let us gain
experience about the microfabricaton facilities and actually participated in the fabrication
process. Thanks to the teaching assistant, Paniz Hazaveh (Michigan Technological University)
for introducing the content of the process and collecting all the data we participated. Thanks to
Nupur Bihari (Michigan Technological University) for many technical explanation through the
process.