Thermal Physical Vapor Deposition

Introduction

In physical vapor deposition system, material is deposited on to the desired substrate. There are many ways by which one can do this, most used one are thermal vapor deposition or sputtering. Here I am going to discuss thermal vapor deposition.

At certain temperature every material changes into vapor state. These vapor can then be deposited into any substrate of choice. For example aluminum (Al) melts at 933K and evaporates at ~2800K. These vapors can then be deposited into substrate which is kept at  much lower temperature. For heating the metal usually Tungsten heaters are used. When very high current is allowed to pass through Tungsten it heats up. Tungsten is used because of its low electrical resistance (52nohm.m), high melting point (~3700K). These Tungsten heaters are in the form of boats to hold the melted metals. In my system, I use a 5V power supply capable of providing very high current. My system is described below

Statement of Operation of the my tool is at the end of this document and can be useful to understand how these systems work.

Depositing Metals 

1) Lead (Pb)
Its fairly easy to deposit lead as it melts at 600K and evaporates at 2022K. Tungsten (W) boat can be used for evaporating lead as it does not form ally with Pb

For measuring thickness, the system use a quartz crystal who's resonant frequency changes as metal deposit on it. This change in resonance frequency is used to calculate the thickness of deposited metal. Since each metal has different frequency, one need to specify this into the thickness meter to correctly calculate the thickness of corresponding metal. The parameters for all the metals can be found out in the "Thickness monitor manual". For Pb these parameters are -

Density - 11.3
z - factor (acoustic impedance) - 7.81
Tooling factor - 1.0
(this should be determined by first actually calculating deposited thickness and then back calculating tooling factor. For now, I am just using 1.0)

In thickness monitor system, I have set layer 8 for lead, were all this parameters are already entered.

2) Aluminum (Al)

Aluminum wets the tungsten and make alloy so usually alumina coated tungsten boast is used for Al deposition. However, because alumina causes thermal resistance usually 20%-50% more power is required to melt Al than using only tungsten boat.

First, I tried alumina coated tungsten boat and only when I use the boat for the first time I could manage to get 0.1nm/sec deposition rate at 13A, however increasing the current to 14A will cause the circuit break then power supply will shut off. Using the second boat for second time did not even gave 0.1nm deposition rate at 13A and it used to get circuit break if I try to increase the current to 14A. So I concluded that my system simply can not provide enough power to deposit aluminum using alumina coated boat.

Next, I tried tungsten boat. At around 10A the aluminum melted. The moment aluminum melts it wets the boat decreases the resistance of the boat and which cause sudden decrease in the boat temperature (I could see the glow stops when aluminum melts and the recover in 2-3sec). The melted aluminum keep on flowing over the boat covering entire boat. The deposition rate was first 0.5nm/sec which decreased to 0.2nm/sec possibly because all the alumina wetted the boat and there was nothing to evaporate.I further increased the current to 12A and could see increase in the deposition rate. I used 2 pellets and was able to deposit 88nm thick aluminum. I hoping since my boat is already wet with aluminum now, next time when I will use the same boat I will be able to deposit more aluminum.


Shadow Mask

I am making shadow mask for myself so that I can make many devices per lot without manyally sticking all  sample substrate with the sample holder. For this I am using 0.050" thick stainless steel sheets. I will water jet cut windows in this laser cut sheet for mask. I am buying the sheet from McMaster product number - 1773T15. For mask I will order a laser cut or etch mask which will be sandwiched between these to stainless steel sheets. Sample size is (12.3,13.16).

Size of center hole - 6.5mm
Side hole size -4.0mm
Thickness of mask sheet - 0.006" stainless steel

Metal Evaporator Operation Manual

Last update: March 19, 2013 by Prashant Patil

You should be trained before you use this machine. Please email prashant.patil@cba.mit.edu for training information

Machine Overview

This machine can evaporate metal under high vacuum while measuring the thickness by quartz crystal microbalance. Up to four different materials can be loaded in one batch. Since its thermal nature, metals with relatively low melting temperatures are more reliable. Following is verified list.

Reliable deposition: gold, silver, aluminum, copper
Marginal deposition: chrome
Very tough control: titanium
Unsuccessful: platinum

All the metals are stored in the nitrogen box beside the refrigerator.

Procedure

Let’s assume the machine is in vacuum status.

 

1. Check nitrogen cylinder open. Check source control ‘off’. Check current dial ‘zero’. Then, press ‘vent’ button in the control panel.
You can hear hissing sound. Venting takes less than 2~3 minutes.

2. Open the chamber door using handle. If venting is completed, the door opens without any resistance.
After open, press ‘seal’ button in the control panel. This stops nitrogen supply.

3. Relocate the venting port plug.

During venting, port plug pops out as shown in the picture. If contaminant goes into the venting hole, that may interfere the valve operation. Therefore, relocate the port plug right after the chamber opening.

4. Attach your sample to the sample holding disk.

Kapton or carbon tape is convenient to use. However, if it is exposed to the high temperature source for a long time, the sticky adhesives remain residue. In such a case, use screws and clips instead.

5. Plug the rod of sample holding disk into the slot. Then, the sample is facing down toward the source as shown in the picture.
6. Install the boat and put metal pellets.

                    Loosen the knuckles and install the boat. Put 1~2 pellets.
                    Using source selector, adjust the boat position.
                    Adjust electrode arm position. It must make a intimate contact to the knuckle body.

7. Close the chamber, and press ‘cycle’ to vacuum the chamber.

                    Typical operation vacuum is <2 1="" about="" e-6="" hour.="" it="" mbar.="" span="" takes="">

8. Pressing ‘data’ button changes the indication mode from rate to layer, density…… Go to ‘layer’.
9. Choose the layer(preset of material properties) according to your metal source using arrow buttons.

Currently, 1-Au, 2-Ti, 3-Cr, 4-Al, 5-Pt, 6-Cu, 7-Ag.

10. After choosing layer, press ‘run’ button twice.

                    Whenever pressing ‘run’ button, the status changes between ‘close’ and ‘open’. By pressing twice, it will switch ‘close’à’open’à’close’. This resets the thickness monitor to zero.
                    The ‘open’ and ‘close’ only mean the thickness monitor(QCM) operation. It is not synchronized with physical shutter.

11. Once pressure reaches operation condition, put source control ‘on’ (Man - manual)
12. Gradually increase the current using current dial while seeing the source boat through the window.

                    The number in dial is fake. Only read the current meter.
                    Typically, you can see the boat glowing at around 8 in the current meter. Up until this point, you can increase the current quite fast.( in about 10~20 seconds)
                    From 8 point, be patient to watch out the status of the metal. Low melting point metal start to melt around this point. If properly melted, the liquid swirls in the boat. If it does not melt, increase the current slightly(about 1~2 each time) and watch.
                    It is good to memorize typical operation point of the metal. In my observation, gold and aluminum melt around 10~12.

13. After seeing stable swirling of the metal source, open the shutter by shutter handle and press ‘run’ button in the thickness monitor simultaneously.
14. See the deposition rate in the thickness monitor. Adjust current dial to desired deposition rate.
15. When desired thickness reaches, close the physical shutter first, then press ‘run’ button to close the QCM.
16. Decrease the current using dial.

                    Decrease into half, wait about 30 seconds. Repeat these cycle 2~3, then put the current zero.

17. Turn the source control ‘off’.
18. Cool the substrate at least 15 minutes.

                    If opened immediately, metal film may delaminate.

19. Vent the chamber and remove your sample and metal source.
20. Vacuum the chamber.

Metal Pellets stock

Al, Sn, Au, Ni, Cr, In, Ti, Ag, Zn,Pb

Boat Stock-

In

Notes

1. Aluminum foil cover

                    All inside wall of the chamber and shutter is covered by aluminum foil. Regularly, replace this aluminum foil. Otherwise, detached metal flakes may contaminate the chamber.

2. Cleaning

                    Regularly, clean the chamber with cleanroom vacuum cleaner. Especially, remove metal flakes thoroughly. They frequently stick to valves/sealing degrading vacuum quality.

3. Windows shield

Window is shielded by a couple sheets of slide glass. Regularly replace these slide glasses. Otherwise, it is very hard to see the inside through the window.

4. Door rubber sealing

                    Regularly clean the rubber sealing of the chamber door. First, swipe the sealing with IPA soaked wiper. Clean and dry thoroughly. Then, spread a small amount of high vacuum grease(Dow Corning).

5. QCM replacement

                    Using ‘data’ button in the thickness monitor, go to ‘usage’. This indicates the usage of QCM. When new QCM is installed, this value is around 20. Do not exceed 100.

                    If QCM needs replacement, pop out the holder.(Then, thickness monitor automatically turns off.) Remove old QCM and install new one as shown in the picture.(electrode on top) Plug in, then you can see the thickness monitor on again.

                    QCM is sold in many venders including Fil-Tech and Maxtek.(ex. Maxtek P/N 103200-2)

6. Metal boat

                    Typically, tungsten boat is used. Order them to Kurt J. Lesker.
Tungsten Boat - P/N-EVS2B015W

http://www.lesker.com/newweb/Evaporation_Sources/thermal_boat_Dimple.cfm?pgid=4

Alumina Coated Tungsten Boat - P/N-EVS2BAOW

http://www.lesker.com/newweb/Evaporation_Sources/thermal_Al_boat.cfm?pgid=8

For the following materials, use alumina coated tungsten boat instead.
Aluminum: It easily wets tungsten boat.
Chrome: It forms alloy with tungsten.

7. Circuit breaker

                    Circuit breaker locates just above the turbo pump control unit. The breaker trips when too large current is drawn, or the circuit is shortened. In such a case, press the white button. It is unclear the roles of other two buttons.

8. Pump maintenance

                    In case of roughing pump, change the oil regularly. Typically once a year.
Turbo pump needs cooling. Regularly check the coolant/chiller. However, even if the chiller fails, turbo can be operational under proper air cooling. Install a fan and leave the cabinet door open.

9. Manual control

                    The machine parameters can be manually controlled by hidden menu. Press ‘no’ button in control panel. Then, you can see several submenus by arrow button. Pressing ‘yes’ selects current indication.

                    -Sequence run => default screen
                    -Set point
                    -Manual mode
                    -Adjust mode
                    -System ID

                    Using Manual mode, each valves/relays can be operated.

Chiller maintenance

Note:

The maintenance consists of two parts.
        - Circulation water refill
        - Recovery from dried-out status
        - Emergency operation during chiller broken-down

1) Circulation water refill

Interval: every week

Purpose:

Metal evaporator chiller is not well sealed. Therefore, the water loss is fast, which means weekly checkup required. The compressor is air-cooled. No need of external coolant.

Procedure:

1. Open the lid of the reservoir.
2. If water level is low, refill potable mineral water.

2) Recovery from dried-out status

Interval:

Purpose:

If the water reservoir remained below minimum level for a long time, the chiller is automatically turned off and put into standby. It must be recovered by resetting.

Procedure:

1. Refill the water first.
2. Push the red reset button on the right side of the unit.

3) Emergency operation during chiller broken-down

Interval:

Purpose:

This chiller frequently experiences compressor failure. During fixture, there is no circulating water. However, fortunately, turbomolecular pump of metal evaporator had run without chilling water making no problems. But, as a precaution, set up an air-cooling platform.

Procedure:

1. Open metal evaporator cabinet door.
2. Place a fan, and blow the air continuously until chilling water is recovered.

Fundametal of Network Analyzer

%%%%% draft %%%%%

Introduction

When getting signal from one point to other, we are most conserend about 

A Vector network analyzer measures both magnitude and phase.



S - Parameter Measurement Using Network Analyzer

Given a circuit or network with certain ports. A simplest circuit is the one with two port.

Fabrication of Inelastic Electron Tunneling Spectroscopy Devices

Introduction 

The device structure is Al-A2O3-Pb.

Substrate -

I am using glass as substrate for fabrication of IETS devices.

Cleaning of the substrate

First Lot of Fabricated Devices

Pb 500nm


Second lot of Fabricated Devices -
Date - 03/19/13

Fabrication Steps

Step -1 : Deposited 100nm Al on pre-cleaned glass substrate using thermal physical vapor deposition at 5x10^-6mbar pressure.
Step -2: The devices was in deposition vacuum chamber for around 12 hours. The devices was than exposed to air for 6 hours for growing Al2O3 which will act as tunneling barrier. For doping tunneling junction, Acetophenone was spin coated on grown Al2O3 at 6000rpm.
Step -3: 100nm of Pb was deposited on cross electrode geometry using thermal physical vapor deposition system. The devices were kept in vacuum chamber for around 1 day.

The resistance between two terminal of one of the electrode was infinity making these devices useless. Possible reason of this could be that the thickness of the electrode were too thin (~100nm). I am not sure which electrode was showing infinite resistance but I suspect its mostly Pb electrode.

Calculation for resistance of the electrodes

Lead Pb:
L = 6mm, b = 1mm, t = 100nm  and p = 208nohm.m so calculated R = 12ohm

Aluminum Al
L = 6mm, b = 1mm, t = 100nm  and p = 28nohm.m so calculated R = 1.6ohm

Cause of failure - I am assuming its because of the thickness of the Pb electrode. At the junction, there could be discontinuity because of the step at the junction area (the thickness of the Al/Al2O3 at device area is 100nm+ ). Since the height difference is more ~100nm+oxide thickness and Pb deposited height is around 100nm, there could be discontinuity at the junction in Pb electrode. Another reason could be that because of small thickness of the electrode, indium in not making good contact.

I am gonna fabricated another set of devices with this time electrode thickness of ~200nm for Al and 500nm for Pb. I am also gonna check the resistance of the Al electrode to make sure which metal electrode is showing infinite resistance.

Third LOt of Fabricated Devices -
 03/21/13

This time, I deposited 80nm of Aluminum using Tungsten boat (as alumina coated Tungsten boat was giving me hard time). After ~1hour, I opened the chamber and removed the devices and checked its device resistance. The resistance of the aluminum lead was 67ohms. I immediately changed the orientation of the device and kept it inside the chamber for Pb deposition. The time should be around ~10min so I just gave this much time for the oxidation of aluminum. After that I deposited 500nm of Pb. This time there was no infinite resistance of any lead so I concluded that previously the infinite resistance was shown by Pb leads and it was because of the discontinuity in the Pb electrod at the junction. The resistance of the Pb electrode was 21ohm. The resistance of the Pb electrode seems to increase with time. The device impedance could be of the order of 1ohm because when I applied 1mA current and used four probe method to measure the voltage, it was about 1.1mV.

Getting Driving License in Massachusetts

As an international student in MA, I am required to get a MA driving license in order to drive in Massachusetts. Most students apply for Class D driving license. In order to get your driving license, first you need to apply for "Class D Learners Permit". Once you have permit, you can drive provided you are accompanied by someone who is at least 21 years old and hold a valid Class D driving license.

Here are the steps to get your driving license -

Step-1: Go to http://www.massrmv.com/ and familiarize yourself with the rules and regulations. Its a good idea to go through the "Drivers manual" (link - http://www.massrmv.com/rmv/dmanual/Drivers_Manual.pdf). Be aware, there are many privately own website with similar domain names.

Have a look at massrmv online services -

http://www.massrmv.com/OnlineServices.aspx

You can apply for permit, schedule your road test etc in above page.

Step-2: Apply for Class D learners permit online here

https://secure.rmv.state.ma.us/prestageas/PST_IntroAndTermsAndConditions.aspx?Transaction=NewPermit

You will be asked for documents verifying your date of birth, signature and residency. Not that you can not use same document to verify two things. For example, you can not use passport to verify both date of birth and signature.

I selected following documents when asked

1) Date of Birth - Non US passport

You will be asked if you have I-94 and class of Visa. You will also need I-20 when you will visit the MASSRMV office.

2) Document providing signature - Social Security card

3) Proof of residency - Bank statements etc (no older that 60 days)

 You can also book an appointment before saving the document.

Step-3: Visit the office at your appointment time with following documents

1) Passport
2) I20
3) SSN Card
4) Bank Statement (no older than 60 days)
5) Completed Application Form

Remember to bring or wear your corrective vision lenses for vision test. You will need to give following tests

a) Class D Learner's Permit Exam
b) Vision Test

Step-4: Prepare for Class D Learner's Permit Exam

The exam consist of 20 objective type questions. You must score 70% (i.e. 14 correct answer) to pass the exam. The duration of the exam is 20 minute. The questions are asked from "Drivers Manual". You can download the copy of drivers manual from here.

http://www.massrmv.com/rmv/dmanual/Drivers_Manual.pdf

Its very helpful if you give some online test before appearing for actual exam. Some of the online test can be found out here

http://driving-tests.org/massachusetts/massachusetts-dmv-practice-test-3/


Step-4: Road test.

Fill the "Road Test Application" form which can be found here - http://www.massrmv.com/rmv/forms/21844.pdf

Or you can also apply online 

Some Useful commands in Ubuntu

- Deleting a file

$ sudo rm filename

- Deleting a non-empty directory

sudo rm -rf  dirname

- Deleting empty directory

sudo rmdir dirname

- Creating a directory

$ mkdir dirname

- Creating sub-directory

$mkdir -p dirname/subdirname

AVR Programming with AVRDUDE

Computer Interface Connection

1. Connect the FTDI cable to PC and run the following command in terminal
   
   ls /devIn the list if you see something like "ttyUSB0" than the FTDI cable is correctly installed.
2. Connect AVR ISP mkII to PC
3. Connect the AVR ISP mkII 6 pin programming header to Board
4. Connection for AVR ISP mkII Programmer

Programming in Ubuntu

 Setting up Ubuntu for AVR development

 You need following package for setting up your ubuntu of AVR programing

1. gcc-avr The GNU c compiler for AVR

Libusb may be in a "universal" repository so you probably want to modify your repository list to include the "universal" repositories. libusb-dev is required if you want to use usb programmer such as avrisp2 or usbtiny

5. AVRDUDE - program to writes data on the microcontroll

sudo apt-get install flex byacc bison gcc libusb-dev avrdude

sudo apt-get install gcc-avr  

2. avr-libc C library for AVR

sudo apt-get install avr-libc

sudo apt-get install libc6-dev  

3. binutils-avr - Essential utility of C compiler (it stands for "Binary Utilities").

 

6. avr-gdb The GNU debugger for AVR. This program runs from the
terminal avr-gdb, avr-gdbtui, avr-run

Open the terminal and  navigate to the folder where you have filename.c and filename.make file and run follwing commads

1) Make Hex file

make -f  filename.make

2) Program fuses using avrispmk2 programmer (or other programmer, see makefile)

sudo make -f .make program-avrisp2-fuses

3) Program flash

sudo make -f .make program-avrisp2

To run term.py

python term.py /dev/tttyUSB0 115200

Eagle and PCB Milling