allwin21 corp-accuthermo aw610 - engineering research

1 12/2015 Rijuta Ravichandran, Devan Boyce

Allwin21 Corp-AccuThermo AW610

The following document is intended to describe the safe operating procedures of the

AccuThermo AW610 for CNM2 members. This manual is meant to used as a reference

and does not replace formal training. In order to gain access to the tool, formal

qualification by staff is required.

System Overview

The AccuThermo AW610 is a rapid thermal processing (RTP) system. It uses high

intensity visible radiation to heat single wafers for short process periods of time at

precisely controlled temperatures.

The system itself consists of an oven unit and a computer running the AW-610 controller

software. The oven unit consists of a quartz tray that slides into an isolation tube

between two sets of lamps that provide the source of heat. The lamp intensity and heat

is adjusted by recipes created on the controller software.

2 12/2015 R. Ravichandran, D. Boyce

System Configuration

Water-cooled, aluminum chamber with gold plating for temperature uniformity

Isolated quartz tube

Quartz tray for 4 to 6 in wafer (contact staff if using pieces)

Thermocouple (100-550C)

Pyrometer for non-contact temperature sensing (400-1250C)

0-300 seconds for “steady” processing time (Fig 1.)

4’’ Thermocouple wafer for pyrometer calibration

Nitrogen and Argon gas flow

Advantages (over conventional furnace)

Fast heating and cooling rates in short amounts of time

Superior heating uniformity to minimize thermal stress

Allows for multiple processes without cross contamination

Disadvantages

Single wafer only

Limited in duration of heating and processing

Not easily integrated with other heating processing steps (i.e. oxidation)

Figure 1. Time vs. Temp chart for selecting appropriate anneal times (min) for “steady” step

processing time


Principle of Operation

The AccuThermo Allwin610 system is a rapid thermal processing (RTP) unit, which uses high intensity

visible radiation to heat single wafers for short process periods of time at precisely controlled temperatures.

Figure 2 describes the general temperature profile for any given recipe. First the system is purged of ambient air

in the delay stage, and then wafer is pre-heated in the intensity stage, if the

pyrometer sensor is selected. Next, the system ramps to the desired set point, there can be subsequent ramps in a

recipe. The transition stage is when the temperature control changes from ramp to steady- state, to stabilize the

temperature in the system. During steady state control, the process is set to keep the temperature constant for a

given time programmed (0-300s) in the recipe. After this step, the lamps turn off and the wafer goes through a

cool-down stage. This process provides a short thermal annealing process for either Silicon or III-V materials.

The key component throughout this process is accurately measuring and modulating the temperature of

the system. There are two sensors available to measure temperature in the system: thermocouple and

pyrometer. The thermocouple is generally used for processes below 550C and will degrade above those

temperatures. The pyrometer is used for processes between 400 and 1250C, and

has a much faster response time than the thermocouple. Once the correct temperature sensor of the

system has been identified, it is important to apply the appropriate compensation and correction factors for the

sensor.

The correct material type, emissivity values, and other temperature correction variables must be

selected in order to ensure accurate temperature readings. If you are working with III-V compounds or other IR-

transparent materials you must use a wafer susceptor. Because the thermal capacitance of the susceptor is very

different from the standard silicon wafer, it is important to indicate when you are using a Si wafer or a susceptor. If

you are using non-standard silicon wafers it is important to find the correct emissivity value for your material. The

emissivity value is used as a correction factor for the pyrometer, and acts an offset for the temperature readings.

Lastly, there are four variables: Gain, Sensitivity, Delay, and Steady Intn factor that are all used to fine tune

temperature performance. It is possible to permanently damage the tool without properly checking these settings.

Therefore, it is critical to choose the correct sensor, select the correct emissivity values, and fine-tune the

temperature profile for your process. More information on selecting the correct settings and variables for your

process will be discussed in the attached supporting documentation.


Figure 2. Temperature profile of RTP process. Not shown: The DELAY stage is used to purge the

chamber of ambient air. The INTENSITY stage preheats the wafer to a temperature that is

sufficient for the pyrometer to be usabl


OPERATING INSTRUCTIONS Open the required facilities gas lines

Turn all required gases to the “valve open” position shown here. Without opening these

valves there will be no gas flow into the chamber. The Clean Dry Air (CDA) line must always

be open when running the RTP.

Valve open

Valve closed

CDA: Clean dry air

Valve MUST be open

(shown: open)

Turn on lamp power

Temperature display ( kC)

Currently displayed: 69C

Lamp power switch (on)

Lamp power indicator


Loading samples into chamber

Shown: Chamber door in LOCK position.


Push handle downwards to move the chamber door to UNLOCK position

CAREFULLY pull chamber door out to place your wafer on the quartz tray. Make sure the wafer

is in contact with the thermocouple or the sample will overheat and damage the chamber.

Shown: 6’’ wafer that melted inside the chamber because the sample was overheated.

CAREFULLY slide the chamber door closed. Pull chamber handle upwards to lock the door.


Running a recipe

4. Click to select a Recipe from the list of Recipes in the column “Recipe File”. You can

scroll through the list of filenames by using the slider to the right of the list, or using the up and

down arrow keys on the keyboard. A selected filename is highlighted in red. You can also select

a filename by manually typing in the filename into the field above the list.

From the main menu, select "Process for Production


WARNING: Selecting a filename and pressing DEL on the keyboard will

permanently delete the file 5. Select the folder with your username (created during the training session) under “DirID”.

Select or create a “Lot ID” from the list of Lot IDs. This specifies where the process data is stored

upon completion

6. To run the selected Recipe, click on the Start Process button. This will display the

Process Monitor screen while the process is running. The Process Monitor screen shows a

completed process curve. In figure 3, the x-axis indicates the process time and the y-axis

indicates the measured process temperature.

The curves display aspects of the monitored process:


Figure 3: Process window as the RTP runs your recipe. X-axis displays time and then y-axis

displays process temperature. The process temperature is also determined based on the

temperature sensor used and the other settings selected are displayed on the right hand side of

the screen.

Green: recipe temperature as defined by the Recipe.

Black: Model (ideal) temperature curve.

Blue: real, measured temperature during the wafer process.

Red: The lamp intensity (power percentage) during the wafer process. The range is

from 0 to 100.

Light Blue: temperature feedback from the thermocouple.

Pink: temperature feedback f r o m t h e p y r o m e t e r . The t e m p e r a t u r e from

this pyrometer is not reliable below 450 °C.

Broad Lines: Various gas flows


7. A process may be interrupted and stopped at any time by pressing the ESC key on the

keyboard. This will turn off the lamps. If the “Turn Off Gases After Process” in the recipe is set

to NO, then the gases that are on will stay on and flow at the current flow rate. If it is set to YES,

then the gases will be shut off.

At the end of the process, “Process Over” will be displayed on the Process Monitor screen and

be blinking in different colors. Press any key to save the process data. This will also exit back to

the Process for Production screen.

To view the last run process data graphically, click on the Display Last Data button. This will

display the process data on a screen very similar to the Process Monitor screen. To view

process data from previous runs, select the process data to be viewed from the “Data ID”

column, and then click on the Display Process Data button.


Creating and editing a recipe

Use the recipe

menu to select

file to edit

Open the recipe menu from the main menu to see a list of pre-programmed recipes that are

available to be viewed or to be edited for your own process.

Use the arrow keys to scroll through the recipe files. Select a recipe file and click on “Recipe

edit” to view the set points of the process.

WARNING: Selecting a file and then pressing "delete" will

permanently delete the file.


(1a) Recipe Name: Limited to 8 characters

(2e) Steady Intensity (Intn) Factor. Used to fine tune the temperature profile.

(2d) Wafer Type: Wafer or Suceptor

(2c) Gain, Sensitivity, and Delay values for fine-tuning the temperature profile

(2b) Emissivity Values for Si substrate

(2a) Sensor Type: Pyrometer of thermocouple

(1e) Recipe Validate before exiting and saving

(1d) Gas Type (N2 or Ar) and flow rate (SLPM)

(1c) Processing time for each step

(1b) Processing Steps: Delay, Intensity, Ramp, Steady,(...) Delay


1a. After you have selected an existing recipe and change its name before modifying the

parameters and saving it. Recipes must comply with the following format or they may

be deleted by staff at any time:

Leave the EXT field as RCP.

Pyrometer recipe names must begin with “p_” and TC recipe names must begin

with “t_”.

Recipes must also include the temperature, gas, and time of the process at the

final temp (ex. P600AR30, T200N20, etc).

All recipes have an 8 char max, please try to be as descriptive as possible given the

limitations.


1b. In the lower half of the screen, the recipe contains steps that describe the process cycle.

Step Temp Func is the Process Function, which describes the type of process function for that

step. It can be RAMP, INTN, STEADY, DELAY, or FINISH.

Ramp: The Ramp step instructs the controller to increase the temperature at a

constant rate until the specified temperature has been reached. The rate is

calculated by dividing the difference between the temperature specified in the step

and the temperature specified in the previous step by the time specified in the step.

The process controller cannot do two consecutive RAMP steps.

Intn: The controller keeps the lamp power at a constant intensity during an Intensity

step. The Intn step is used to heat the wafer to a temperature where the wafer is

seen by the pyrometer. The minimum reliable temperature for use of the

pyrometer is 500ºC.

Steady: During the Steady step, the lamp intensity is controlled to maintain the

specified anneal temperature. It then maintains that value until the specified time

spent in the step has elapsed.

Delay: The Delay step instructs the controller to turn the lamps off while setting and

maintaining the set point of the other controlled parameters (i.e. Gases), until the

specified time spent in the step has elapsed.

Finish: This ends the recipe.


1c. Time: This is the amount of time, in seconds, to act on the current step. Please refer to the

time-temperature guide below for the maximum steady-state time for each temperature:

(REFERENCE: Stanford SNF)

Temp/Intn: This is the target temperature or intensity system strives for.

Step Function Field-entry description

Steady Set-point temperature to be maintained

Ramp Ending temperature of the ramp

INTN The percentage of the lamp power intensity

Delay No effect. Lamps are turned off during this step

1d. Gas Flow rates: The various gas columns specify the flow rate of each gas for each step. The

system is configured for max 10SLPM flow rate of both N2 and Ar. If the “turn off gas after

process” button is selected to say “yes” it will turn off the gases after the process. Click on this

button to toggle between yes/no.


1e. When entering data values into the data entry area, the recipe editor checks for out-of-

range entries. If a value is out-of-range, the editor will alert you and will advise you of the

proper range. The recipe can be validated by clicking on the Recipe Validate (F10) button. All

errors need to be corrected before the recipe can be used for processing. Click Save and Exit

the Recipe Editor.

WARNING: Recipe Validate does not

consider the time constraints for

various temperatures. Please refer to

the time vs. temperature chart to

choose the appropriate time settings

for the “steady” step.


Shown: Recipe after successful validation. Press save and exit this menu.

2a. Sensor type must be set to either thermocouple or pyrometer depending on the

temperatures used in your process. Use the thermocouple for processes up to 550°C. The

pyrometer is unreliable for temperatures under 500°C, but can read temperatures up 1100°C.

2b. Emissivity is a correction factor for the pyrometer. A standard silicon wafer has an

emissivity of 77.04. The software treats emissivity as a factor that offsets the pyrometer

temperature reading.

2c. The variables - Gain, Sensitivity, Delay, Steady Intn Factor - are for fine tuning the

temperature control performance. It is best to start with the default values in the recipe and

fine tune them as needed. More information about adjusting these parameters are included in

the supporting documentation.

A. Gain: The value for the gain of the temperature PID control for the process steps

RAMP and STEADY.

B. Sensitivity: The value for the coefficient of the gain in the STEADY period of the

recipe. This makes the gain for a STEADY step different from a RAMP step. The

gain value for STEADY is GAIN x SENSITIVITY. If the SENSITIVITY value is 1.0, there

is no difference between the gain for a RAMP and a STEADY.

C. Delay: This is the value for the transient period from RAMP to STEADY. Normally

the default value is 1.0.

D. Steady Intn Factor: This is a coefficient used only during RAMP and STEADY

steps. It is used at the beginning of the steps to correct the initial lamp power

intensity. This feature is used to trouble-shoot temperature profiles and

explained in more detail in supporting documentation.


Overview-Hardware

Supporting Documentation

LED Dis play

(wafer temp)

Chamber door handle

(shown: lock position)

Emergency Off

EMO

Lamp power

Indicat or

Lamp power

switch (on/off)

Oven overheat

indicator

Chamber door


Recipe Menu for

editing processes

To run process,

and view data

STAFF ONLY

STAFF ONLY

Exit System

Login here

Eqpt manual

Overview-Software


(1a) Recipe Name: Limited to 8 characters

(2d) Wafer Type: Wafer or Suceptor (2a) Sensor Type: Pyrometer or

thermocouple (2b) Emissivity Values for Si substrate

(2c) Gain, Sensitivity, and Delay values for fine-tuning the temperature profile

(1e) Recipe Validate before exiting and saving

(1d) Gas Type (N2 or Ar) and flow rate (SLPM)

(2e) Steady Intensity (Intn) Factor. Used to fine tune the temperature profile

(1c) Processing time for each step

1b) Processing Steps: Delay, Intensity, Ramp, Steady,(...) Delay


TEMPERATURE MONITORING

The AccuThermo RTP system can be equipped with two types of temperature monitoring devices: a thermocouple and an optical pyrometer. The thermocouple is used for controlling processes at temperatures below 550°C and starts to degrade and fuse to samples around 800°C. The optical pyrometer is the extended range pyrometer (ERP). Unlike earlier pyrometers used that were restricted to use at process temperatures above 800°C, the ERP can be used throughout the recommended process temperature range of 400°C to 1200°C.

Thermocouple

The AccuThermo RTP system only uses the K-type (NiCr/NiAl) thermocouple. When in

use, the thermocouple wires should not be touching each other, and the thermocouple bead is

the only point in which the thermocouple should be in contact with the wafer (Fig 4). If the two

different metal alloy wires are touching each other at any other point other than the wafer, it

will read an inaccurate temperature. This could lead to the temperature overshooting, wafers

melting, and damaged quartzware. Thermocouple voltages are fed to a temperature

compensation circuit. The thermocouple compensation circuit contains an analog linearizing

circuit with an output calibrated to 1 mv/°C. The signal is digitized and sent to the computer for

use by the temperature control system.

Figure 4. Top and side views of thermocouple and wafer placement in quartzware inside chamber


CAUTION

Thermocouple may fuse into th e wafer at temp er atur es above 8 0 0 °C. As a result, the thermocouple should be removed and the pyrometer should be used for temperature measurement when the oven is to be operated at temperatures higher than 700°C.

Pyrometer

The Extended Range Pyrometer (ERP) is a dual infrared detector that provides accurate and consistent temperature measurement during rapid thermal processing of semiconductor wafers at higher temperatures (Fig 5). The ERP measures wafer temperature by detecting infrared light radiation emitted from the wafer within a specified wavelength range. The resulting signal is adjusted to compensate for the effects of non-wafer radiation sources.

Optical pyrometer readings are emissivity-dependent (see “Compensating for Emissivity”). This means that these readings are affected by changes in wafer backside surface color and roughness, deposited backside layers, or variations in substrate materials.

Chamber

Figure 5. Side view of RTP to show placement of pyrometers and wafers within the chamber. The extended range pyrometer can measure temperatures between 400°C to 1200°C using infrared light radiation.


Compensating for Emissivity

When adjusting the emissivity values, make sure that the “Use Emissivity Local” button is active. If the “Use Emissivity System” is selected, it will use the default factory value. This means you will end up with the same pyrometer offset readings regardless of how you change the emissivity value on your recipe page.

When the pyrometer is used as the temperature sensor for temperature control, the

EMISSIVITY compensation must be set to suit the emissivity of the type of wafer being processed. This value compensates for the reflective properties that are different from the “standard” wafer. The standard wafer is usually pure silicon and it has an emissivity of 77.

To determine the correct EMISSIVITY setting, you will need the TC wafer thermocouple

assembly. The thermocouple wafer is used to indicate the true temperature in the oven while the oven is run under pyrometer control. The wafer is heated to the processing temperature that will be used. The output of the thermocouple is read by the control software.

When the steady-state temperature is reached, read the TC temperature, as this

indicates the “real temperature”. Compare this reading with the pyrometer-indicated temperature. If the readings differ, the EMISSIVITY must be adjusted, such that the pyrometer temperature matches the “real temperature” as read by the TC wafer. The heating cycle and adjustment are repeated until the pyrometer shows the same temperature as indicated by the TC wafer.

If the Pyrometer is less than the Real Temperature, then decrease the emissivity If the Pyrometer is greater than the Real Temperature, then increase the emissivity


TROUBLESHOOTING THE TEMPERATURE CONTROL

This section will describe the common problems with temperature control and how to correct them. These problems are temperature oscillation, overshoot and undershoot. When diagnosing temperature control problems, refer to the process data graph and use the pink vertical line to help understand the situation. The pink vertical line can be moved with the left and right keyboard arrow keys and moving the mouse pointer to a position on the graph and clicking the left mouse button.

Oscillation Oscillation occurs when the wafer temperature does not stabilize within the steady state or ramp, as shown in figure 6. This problem is cause by the temperature control over compensating the intensity to try to get the wafer temperature to the set point.

During the Ramp step,

Figure 6. Oscillations

o short time oscillations are eliminated by decreasing GAIN. o long time oscillations are eliminated by increasing GAIN.

During the Steady step,

o short time oscillations are eliminated by decreasing SENSITIVITY. o long time oscillations are eliminated by increasing SENSITIVITY.

Remember, SENSITIVITY is dependent on the GAIN. Therefore, if the GAIN has been changed, SENSITIVITY may also have to be changed.

Be careful. The oscillation of the intensity needs to be controlled. If it spikes too much, the gain needs to be reduced.


Overshoot An overshoot is when the wafer temperature exceeds the steady state temperature during a transition and then drops back down to the steady state set point, as shown in figure 7.

Figure 7. Overshoot

The following variables can be changed to compensate for an overshoot. Change only one variable at a time and run a few cycles. If the overshoot still occurs, change another variable.

If the temperature is oscillating during the Ramp Up, there would be a good chance an overshoot would occur. Decrease the GAIN until the oscillation is eliminated (refer to the oscillation section above).

If the overshoot is caused by the intensity being too high during the transition, decrease Steady-Intn-Factor for the RAMP step. The temperature at the end of the transition should be exactly the same as the setpoint for the Steady step.

If the overshoot is caused by the intensity being too high at the end of the transition, decrease Steady-Intn-Factor for the STEADY step.

If the overshoot cannot be controlled during the transition by decreasing the Steady- Intn-Factor for the RAMP step, the transition may be too short. Increase DELAY.


Undershoot An undershoot occurs when the transition from Ramp to Steady-State is too gradual and the temperature takes too long to get to the Steady-State set point, as shown in figure 8.

Figure 8. Undershoot

The following variables can be changed to compensate for an undershoot. Change only one variable at a time and run a few cycles. If the undershoot still occurs, change another variable.

If the real-temperature is oscillating during the Ramp Up, there would be a good chance

an undershoot would occur. Decrease the GAIN until the oscillation is eliminated (refer to the oscillation section above).

If the real-temperature is sluggish during the Ramp Up and not reaching the model- temperature, increase the GAIN until the real-temperature follows the model- temperature.

If the undershoot is caused by the intensity being too low during the transition, increase Steady-Intn-Factor for the RAMP step. The temperature at the end of the transition should be exactly the same as the set point for the Steady step.

If the end of the transition reaches the set point temperature, but there is a dip at the beginning of the Steady step, the intensity is too low at the end of the transition. Increase Steady-Intn-Factor for the STEADY step.

If the Steady-Intn-Factor for the Ramp and Steady steps are large, then the DELAY may be too large. Decrease DELAY.


THERMOCOUPLE REPLACEMENT

At temperatures above 800C the thermocouple will melt and can fuse to silicon wafers. Additionally, the thermocouple life can be shortened when used with oxygen gas flows. Therefore, it may be necessary to remove the thermocouple and only use the pyrometer at times, and replace the thermocouple back into the chamber once you have finished your process. Additionally, if there is overheating or the thermocouple becomes damaged, we have extra pieces on-hand. Please follow the procedure described to remove or install a thermocouple wire into the system.

Removal of thermocouple

1. Remove all samples from the process chamber. Shown: Empty quartzware with thermocouple and bead placed in the chamber.

Thermocouple bead that comes into

contact with sample in chamber

Quartz holder for

thermocouple wires

Thermocouple sensor screws


2. Use the screwdriver to loosen screws highlighted in red below (~3 turns), until the wires can be removed from under the screw heads.

3. Remove Thermocouple from the processing chamber and set aside in a safe location for installation later. If the thermocouple is damaged please discard.

4. Tighten down screws highlighted in red. Make sure not to overtighten the sensor screws or you may crack the quartzware.

Installation of thermocouple

1. Open process chamber and remove all samples from quartzware. 2. Using magnetic tool distinguish the two wires.

a. Place the magnetic lead (NiAl) on the left screw head and the non- magnetic wire (NiCr) on the right screw head.

3. Loosen the screws just enough that the wires can be slipped between the screws and the leads for the machine. Bend the thermocouple wire around the screw. You don’t need to loop the wire around the screw in order to get accurate readings.

Magnetic (NiAl) wire

on left sensor lead

Non-magnetic (NiCr)

wire on the right lead


4. Tighten screws and trim the excess wiring so as to not produce false reading 5. Ensure that you have installed the thermocouple correctly, run a simple recipe with a

dummy wafer in the chamber. a. If the temperature goes up then you may resume processing as normal. b. If the temperature goes down and even into the negative, stop the

process immediately and reverse the wiring of the thermocouple as soon as the chamber returns to room temperature.

Correct Wiring Signal

Incorrect Wiring Signal


DATA EXTRACTION 1. Insert your flash drive into the computer. Note: The software will not recognize a flash drive that is larger than 2GB.

2. Reboot the computer using ctrl + alt + del This will allow the computer to read the flash drive and take you to the main menu

3. Press the green exit icon to leave the main menu


4. Locate the letter assignment of your flash drive by inputting: dir D: a. If you can’t find your flash drive in dir D:, then use dir E: b. When you find the correct letter for your drive, press enter. Then reactivate the

system by typing rtapro into the command line after the “>”.


5. Log back onto the software using the log-on key

6. Open process for production and select the data file or recipe that you wish to extract.


7. Select the Transfer to Text File button

8. Appropriately name the new text file so that you may find it later


9. Exit the program through the main screen. 10. Back up the drive onto the flash drive. Input the following commands as described with the

exception of name which will be determined by the user. a. Input the code: d: to select the flash drive b. Input: mkdir name with “name” being your user ID to create a new folder on that flash

drive i. If this is not your first time extracting

data you will need to delete the files in that directory using the command: del name. You will not lose any of your previous data as this will still be copied over during the back up.

c. Input: xcopy \rtapro\*.* d: \name\*.* “name” is the title of the new folder that you created in the drive

d. Wait for the program to completely finish copying the files over. You will receive a message similar to the screen below. This should not take more than 5 mins to complete


11. Remove flash drive and restart the computer using ctrl+alt+del 12. Check for file on flash drive which can then be converted into an excel spreadsheet. 13. Converting .txt to .xlsx

a) Open excel and start the open dialog box b) From the drop down menu of file types select text file (.txt) c) You should see a conversion dialog box

d) Click delimited and then click next e) On the next screen choose that the data is comma separated


f) Finally click finish when the data is sorted into the desired column

allwin21 corp-accuthermo aw610 - engineering research

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