electron beam lithography sop - 4d labs · 2 simon fraser university 8888 university drive,...

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Simon Fraser University 8888 University Drive, Burnaby, B.C. V5A 1S6

E [email protected] T 778.782.8158 F 778.782.3765 www.4dlabs.ca

Raith e_LiNE Electron Beam Lithography

Standard Operating Procedure 2 (For a patterned sample)

Revision: 6.0 — Last Updated: March.9/2015, Revised by Mohamad Rezaei

Overview

This document will provide a detailed operation procedure of the Electron Beam Lithography sys-

tem. Formal Training is required for all users prior to using the system.

Revision History

# Revised by: Date Modification

1 Grace Li 03/20/07 Document initial release

2 Grace Li 01/22/08 Format Updating

3 Grace Li 11/14/08 Format Updating to include Version 5.0, TOC and Doc No.

4 Nathanael Sieb 02/04/09 Updated format, modified contact info, and added more pro-

cedure details including coordinate positions

5 Nathanael Sieb 01/18/10 Update for 2010

6 Mohamad Rezaei 04/09/2015 Updated with loadlock and new software info.

Document No. 4DSOP000X

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Table of Contents

General Information ................................................................................................................................. 4

1. Clean Room Supplies ....................................................................................................................... 4

2. Prerequisites .................................................................................................................................... 4

3. Designing the Patterns ..................................................................................................................... 5

4. Spin Coating PMMA ......................................................................................................................... 5

Operation Procedure ................................................................................................................................ 6

1. Start the system ............................................................................................................................... 8

2. Copy GDS File to Raith Lithography Monitor ..................................................................................... 8

3. Load the Sample .............................................................................................................................. 8

4. Start the Column ............................................................................................................................ 15

5. Optimize the Column Settings ........................................................................................................ 16

6. Set-up the Coordinate System ........................................................................................................ 18

6.1 Origin Correction ..................................................................................................................... 18

6.2 Angle Correction ...................................................................................................................... 19

6.3 Three-point focus alignment ..................................................................................................... 19

7. Write Field Alignment..................................................................................................................... 21

7.1 Locating a Mark or Particle ...................................................................................................... 21

7.2 Alignment Procedure ............................................................................................................... 21

8. Exposure Parameters ...................................................................................................................... 23

8.1 Measuring Beam Current ......................................................................................................... 23

8.2 Setting Patterning Parameters .................................................................................................. 23

9. Height Control (optional) ................................................................................................................ 25

9.1 Adjusting focus and working distance (Adjust W) ..................................................................... 25

9.2 Setting up Height Control datasets ........................................................................................... 26

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9.3 Monitoring CCD peak detection ............................................................................................... 26

9.4 Controlling and correcting the sample height using Process Mode............................................. 28

9.4.1 Using Focus correction during Positionlist scan ...................................................................... 28

10. Exposure ...................................................................................................................................... 30

11. Unload the Sample ....................................................................................................................... 30

12. Exit the System ............................................................................................................................ 33

Reference and Files ................................................................................................................................ 33

Contact Information ............................................................................................................................... 33

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General Information

Raith e_LiNE (Version 6.0) is an ultra-high resolution electron beam lithography tool. The system

is designed with thermal field emission (TFE) Schottky source, a crossover-free beam path that provides

extremely high beam current density. The column voltage varies from 100 eV – 30 keV.

The stage is laser interferometer-controlled with travel range of 100 x 100 mm. The stage move-

ment has a precision of 2 nm XY position at any working distance, writefield size and SEM magnification.

Users can define the write field from 0.5 µm to 2.0 mm with automated calibration and selection.

There are six apertures on the system: 7.5, 10, 20, 30, 60, and 120 µm. The electron beam cur-

rent is controllable by choosing the appropriate aperture.

1. Clean Room Supplies

1. Electron beam resist: 950K PMMA 5%, 3%, and 2% (in Anisole); ma-N 2403

2. Developer: MIBK:IPA = 1:3, AZ Developer Diluted 1:1

3. Laurence Spin coater: Spin speed up to 4000 rpm

4. Digital Hot Plate: 180 °C (for PMMA)

2. Prerequisites

We ask users to be experienced in use of SEM before using the e_LiNE system. If you never used

SEM before, you should receive the SEM training and be completely able to use it before you plan to use

the e_LiNE system.

Formal training is required to use the system. Before you receive training, you need to contact the

acting clean room manager or a staff member to complete an application form.

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3. Designing the Patterns

Raith uses GDS files in the exposure system. If you don’t have GDS software in your computer, you

can use Design CAD or other drafting software to draw your own patterns. But later on, you need to con-

vert it into a GDS file by the following steps:

• From Design CAD, export your design as a DXF file

• Using Link CAD (installed on the design computer) convert to GDS file

• Save the GDS file on a USB flash drive for transfer to the Raith computer.

4. Spin Coating PMMA

Prior to lithographically writing your sample, you must spin coat a layer of PMMA on your sample

(or substrate). The layer thickness depends on what patterns you want to make. For instance, patterns

made via lift-off will require thicker layers of PMMA than chemically etched patterns. Some spin speed

curves for PMMA are shown in the figure below. The negative resist ma-N 2403 has different spin curves.

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Operation Procedure

The Raith Lithography monitor is on the Right and the Column monitor is on the Left. The joystick on the

far left is used to move the stage.

The following operation steps are for overlaying a design on a patterned sample. For writing a pattern on

an un-patterned sample, please use Raith e_LiNE Standard Operation Procedure 1

We will use the Raith Demo pattern Chip (see figures below) as an example to describe the overlay expo-

sure steps. We will also assume that the basic pattern (layers 1-6, 8, 10-12) already exists on the sub-

strate. The arrow in the first figure indicates the position of the HEMT structures. The lower-left figure is a

magnifications HEMT structure where the gap between the source/drain is 200nm. The operation steps in

this SOP describe how to obtain an overlay pattern to place the gate in this gap as seen in the lower-right

figure.

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Raith Demo pattern “Chip”. The arrow is

pointing to the HEMT structures.

HEMT before overlay exposure (layers 6,8). HEMT after overlay exposure (add layer 9).

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1. Start the system

Start the column software by double clicking “Raith EO” (on the Column Monitor) and log in as user

“4dlabs” and password “4duser”. Also, ensure that the control program RemCom32 is running.

Start the Raith lithography software by double clicking “e_LiNE” (on the Lithography Monitor) and

log in with your own account (after training, you will get your account).

2. Copy GDS File to Raith Lithography Monitor

Insert the USB flash drive with your GDS file into the Lithography monitor (the USB cable is on the

computer desk, located between 2 monitors).

You may copy the pattern into the folder C:\e_LiNE\User\*username*\GDSII if you wish.

3. Load the Sample

• Carefully remove the sample holder from the desiccator.

Sample holderSample holder

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• Use soft plastic tweezers around the sample holder. Metal tweezers are not allowed since they may

damage the sample holder. Put your sample on the sample holder, and then fasten the clip.

• If your sample has no marks to identify the U, V coordinate system, make a scratch in the left corner of

the sample as indicated.

• Use nitrogen to blow off the front and back side of the sample holder, in order to remove any dust.

• Open the load lock door and set the sample holder on the mounting rods of the load lock door and

carefully close it, sealing the door shut using the thumb screw.

Clips

Faraday Cup

Sample Left Corner

Clips

Faraday Cup

Sample Left Corner

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• In order to begin the loading process, enable the Raith window. Click on the Load Lock icon followed

by the Load Sample button in the right hand vertical panel.

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• By default, the following prompt message will be displayed on the PC monitor:

• Press OK

• The Load procedure will be carried out step-by-step and the progress bar will indicate the Activation

Progress.

• The button indicates the currently active step, the button indicates a completed step.

You can stop the Load procedure at any time by pressing the STOP button.

• The software asks the following question:

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• Press Yes to proceed

• The following window message will be displayed

• Make sure the load lock door is closed then press OK

• After a while the following message will be displayed on the PC monitor:

• Open the load lock valve:

o Lift the load lock valve locking pin

o Turn the locking lever from “Locked” to “Open” and pull out to open the loadlock valve

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• Insert the transfer rod into the stage chamber. WARNING: Make sure the load lock valve is

open otherwise the transfer rod would be bent by pressure!

• Press OK then the stage will lift sample holder off the transfer rod

• After a few minutes the following message will be displayed on the PC monitor:

• Remove the transfer rod from the chamber

• Close the load lock valve:


o Push in the locking lever, turn it clock-wise until it has snapped into place

• Press OK

• During the loading process, a number of pop-ups will prompt the user for action. Press Yes, enter a

sample name of your choice, press OK, press NO, and press OK

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• At this stage, the sample holder will be visible in the SEM window

• If high-resolution patterns (<100 nm) are required, then turn off the mini-environment fan.

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4. Start the Column

• After your sample is loaded, click Stage Control on the right side menu bar (using Lithography

monitor).

• In the Stage Control window, select the Drive tab and select . Enter 26 mm into the Z coor-

dinate and press Start to drive the stage to the required height.

• In order to apply the acceleration voltage (EHT), select Column Control on the right side menu

bar.

• Select the aperture size and EHT by clicking the in front of the desired data set. (Raith has already

saved several different sets of apertures and accelerating voltages for you to choose)

• Then press to activate the selected mode.

NOTES: (1) The acceleration Voltage (EHT) is selectable: 0.2- 30 KV. For greater than 20 KV, you need to

select the SE2 detector. Otherwise use the InLens detector.

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(2) To select the detectors, click Detector on the SEM Control panel (Column monitor), and then choose the

one want to use.

(3) There are 6 apertures that can be chosen in this system: 7.5, 10, 20, 30, 60, 120 µm. If you are not

happy with the apertures available on the Column Control window, you can choose a different size of ap-

erture. To do so, click Aperture on the SEM Control panel (Column monitor), and then select the one you

want from the Aperture Size list.

(4) The EHT can be changed by double clicking on the EHT value on the bottom information bar in the

Raith EO software (Column monitor). Enter your desired accelerating voltage in the EHT Target window.

5. Optimize the Column Settings

• If you already know the clip position which your sample is in, then on the Stage Control window go

to the Positions tab. Select the clip which your sample is in and then click Go. The system will au-

tomatically drive to your sample position.

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If you do not know the position of the clips or of your sample, then use the joystick to find your sample and

save the position for your future use.

• Turn on the beam by clicking Beam On/Off on the Lithography monitor.

• Find the left corner of the sample where you previously made a scratch.

• In the Raith EO software, use the following buttons on the top menu bar to obtain good focus and

stigmation on the sample surface: magnification/focus , stigmation , and bright-

ness/contrast . The primary function (e.g., magnification) is activated with the left mouse

button and the secondary function (e.g., focus) is activated with the right mouse button. The pa-

rameters are changed by holding the mouse button down and moving the mouse.

• Find a small particle on the surface and obtain good focus and stigmation at a higher magnification

(~100 kx).

• In the SEM Control window, click on Aperture Align, and mark the Focus Wobble. Move the

mouse in the X and Y directions to minimize the image shift during the wobble sequence.

• Turn off the focus wobble and recheck focus and stigmation

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• Move to an unexposed region of your sample using the Step tab in the Stage Control window.

• To create a contamination dot, select Spot Short in the Raith EO software. This function will create

a 5 s long exposure. You must quickly turn the beam on by selecting Beam On/Off in the

e_LiNE software. Alternatively, a longer exposure can be achieved by selecting Spot Long (middle

mouse button). This function will expose the sample until Long Spot is selected again. A good dot

should be circular with a diameter of less than 20 nm at 10 kV, 30 µm apertures. An example is

shown in the image below.

6. Set-up the Coordinate System

These steps create a UV coordinate system for the sample.

6.1 Origin Correction

• Use joystick move to the left corner of the sample, and zoom to ~100 x.

• Select Adjustments on the right side menu bar.

• In the Adjust UVW (Global) window, click on the tab Origin Correction. Ensure, that it is on

Global; if it is on Local, click on the button once to change it to Global (left bottom corner of Adjust

UVW window).

• Select Adjust. The lower left corner is now defined as the origin of this UV coordinate.

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6.2 Angle Correction

• In the same Adjust UVW (Global) window, click on the tab Angle Correction, and then click on

Read (Label 1) for Label 1. The actual XY coordinates are displayed.

• Switch back to low magnification and move to the lower right corner of the sample.

• Zoom to 600 x and click on Read at for Label 2.

• Select Adjust to calculate the transformation angle between XY and UV coordinate systems. (NOTE:

the computer assumes the +U direction is along the vector from point 1 to point 2.)

6.3 Three-point focus alignment

Since already a pattern exists on the sample, we need link the UV coordinates displayed in the Coordinates

window to the uv coordinates of GDSII design.

In the Adjust UVW (Global) window, go to the menu and Options… and select “Enable automat-

ic focus correction” and Correct Focus by “working distance”. Click Ok.

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In the Adjust UVW (Global) window, click on the tab Adjust W, then click on Read , make sure

sample is focused, and click Ok. Click Adjust. W will now be updated to the actual working dis-

tance.

In the Adjust UVW (Global) window, click on the tab 3-Points.

In the lower-left corner of the sample, focus on a particle. Click on Read , beside P1. Type in the

exact current UV coordinates. Activate the checkbox next to P1.

In the lower-right corner of the sample, focus on a particle. Click on Read , beside P2. Type in

the exact current UV coordinates. Activate the checkbox next to P2.

In the upper-right corner of the sample, focus on a particle. Click on Read , beside P3. Type in

the exact current UV coordinates. Activate the checkbox next to P3.

Select Adjust to calculate the focus plane.

Test the alignment by using the lightning icon next to UV in P1, P2, and P3 to drive to those loca-

tions. Check that the focus is preserved.

You can also create a ‘stage position’ entry in the position list to test. Note, use the UV template, NOT

the UVW template.

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7. Write Field Alignment

Now the beam needs to be aligned to the UV coordinate system. For a patterned sample, this will align

the write field (WF) to marks that are on the sample.

7.1 Locating a Mark or Particle

• Move the stage back to the lower left corner of the sample. You can click the lightning icon beside

Label 1 in the Adjust UVW (Global) to quickly do this.

• Locate a small reference particle with the aid of the crosshairs on the Column PC display at ~1000x.

• Select Microscope Control on the Lithography monitor.

• In the Microscope Control window select the appropriate magnification and write field size (e.g.,

1000 x, 100 µm) and then press to activate.

• Open the File menu and select New positionlist.

7.2 Alignment Procedure

• Open GDSII file, drag and drop Raith demo pattern “Chip” into the positionlist.

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• Right-click on the Positionlist item “Chip”, and then select Properties to open the Patterning

Properties window.

• Click on Layer icon and select layer 63 (for performing manual WF alignment), then click OK.

• Click Working Area and select “Write Field Calibration”, then press OK.

• Enter the location where the GDSII structure should be aligned. The coordinates are sample-UV-

coordinates. Within the design-UV-coordinates this position corresponds to the center of the first write

field. For example:

• If the sample coordinates are identical to the GDSII-coordinates, it is possible to use the button to cal-

culate the UV-position on the basis of the stored working area and current write field size. In this

case, click Position and then OK. This step will set the position to the middle of the first

writefield (likely 0.05, 0.05).

• Select the Positionlist item “Chip”, and then press Scan .

• While holding the Ctrl key down, use the left mouse button to select and move the cross to the center

of the alignment mark. Once you have reached the new position, release the Ctrl button and a blue

cross will be displayed at the selected position.

• Click on “Continue”, and the stage will move into the next corner for you to perform the same mark

alignment.

• Click “Continue” when the two more scans are presented. Align the cross in each one.

• Then the software will ask you if you want to accept the changes, click Accept.

• Open the Patterning Properties window for “Chip” again.

• Click on Layer icon and select layer 61 (for performing automatic WF alignment), then click OK.

• Select the Positionlist item “Chip”, and then press Scan .

• Repeat the last steps (if necessary) until the “Factor zoom” correction values are between 0.999 to

1.000. Check this by clicking on the Internet Explorer icon at the bottom of the lithography computer’s

screen and clicking on the “Write Field Alignments” button.

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NOTES: (1) Expert users can examine the automatic alignment results by opening the positionlist

“Align.pls”. Individual scans can be analyzed by double-clicking on the list item.

(2) As you perform more automatic WF alignments, it will be more difficult for the software to accu-

rately determine the edges of the structures. This effect is due to overexposure of the resist.

8. Exposure Parameters

8.1 Measuring Beam Current

• Before you start setting the exposure parameters, you need measure the beam current first.

• In the Positions tab, select Faraday Cup and click on Go.

• Turn on the beam by clicking Beam On/Off on the Lithography monitor.

• Use the crosshairs to center the Faraday cup on the Column monitor. Be careful to not disturb the

beam focus, alignment or stigmation settings. Zoom in until the entire screen is black (within the cup).

• Click on Exposure on the Lithography monitor. In the Beam Current window ensure <cur-

rent position> is selected and press Measure. The beam will switch to a small spot completely con-

fined within the Faraday cup and the picoammeter will measure the current. Perform this step a cou-

ple of times to ensure that the current is fairly stable.

8.2 Setting Patterning Parameters

• Right-mouse-click the “Chip” position and select Properties from the context menu

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• Click on the Layer icon and select the layers to be exposed (layers 7, 9, and 61).

• Click Working Area and select Complete Pattern.

• Open the Patterning Parameter and then press the Calculator button to set up step sizes and

dwell times according to the beam current and the required clearing dose.

• Enter the location where the GDSII structure should be exposed. The coordinates are sample-UV-

coordinates. Within the design-UV-coordinates this position corresponds to the center of the first write

field.

• If the sample coordinates are identical to the GDSII-coordinates, it is possible to use the button to cal-

culate the UV-position on the basis of the stored working area and current write field size. In this

case, click Position and then Ok. This step will set the position to the middle of the first

writefield (likely 0.05, 0.05).

• Calculate the Dwell Time for each index tab displayed (Area, Curved Elements, Line, and Dot).

For reasonable results, the beam speed should not exceed 10 mm per second. If it does, increase the

Step Size and recalculate.

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NOTE: If a different dose is required (e.g., for non-PMMA resists or other accelerating voltages), then re-

member to enter those values first.

9. Height Control (optional)

This section describes how to control the height of a sample surface via the Height Sensing soft-

ware module in combination with a Laser Height Sensing tool (LHS) in order to keep the electron beam

in focus. The Height Sensing software module consists of the following main dialogs:

o Height Control to choose and activate a proper height control method for your sample or appli-

cation.

o CCD Control for monitoring and adjusting the CCD peak detection as well as for calibrating the

CCD camera.

9.1 Adjusting focus and working distance (Adjust W)

As a precondition for the reliable use of the height control functions of the LHS, the working dis-

tance measured by the electron and the working distance calculated by the software must be synchronized

(Adjust W procedure).

• Focus to any point on the sample.

• In the Adjust UVW (Global) window, click on the tab Adjust W, then click on Read , make sure

sample is focused, and click Ok. Click Adjust. W will now be updated to the actual working dis-

tance.

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9.2 Setting up Height Control datasets

A height control dataset serves to store and recall all height control settings for a sample or special appli-

cation.

• Click on Height Control icon

• Click on to set up a new height control dataset for the current sample or application.

• The New Sample dialog will be opened.

• Type in a name for the dataset by using a significant name for your sample or application.

• The height control dataset is stored with the current settings of the Height Control dialog. For use and editing,

it can be selected of the Sample: combo box. Any change of the settings can be added to the dataset by click-

ing on .

9.3 Monitoring CCD peak detection

For the use of the LHS it is presumed that the CCD peak detection works reliable. Therefore, it is

possible to monitor the peak detection. To monitor the peak detection, the laser light distribution can be

read out periodically and will be displayed in the CCD Control dialog graphically. By default, the CCD

Control dialog will be displayed as minimized window in the desktop area of the “eLINE” software in

lithography monitor.

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Proceed as follows to monitor and evaluate the CCD peak detection:

• Maximize the CCD Control dialog.

• Click on to activate the continuous CCD polling.

The polling will be performed at pre-defined intervals – e.g. every 3.0 s. You can define the polling interval via

Height Control dialog Height Control tab Polling rate.

• The CCD peak detection will be displayed as a frequency function of the laser light distribution:

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• The CCD peak is a calculated value and represents the current position of the sample on the X-axis. The fre-

quency distribution of the laser light distribution indicates all reflected light signals of the laser beam. It should

be as thin as possible.

9.4 Controlling and correcting the sample height using Process Mode

In the Focus Correction mode, the working distance will be corrected during a patterning process or Posi-

tionlist scan after the stage was moved from one position or one stitch field to another one. At a single-field pat-

terning this correction will be executed after driving to the destination directly before starting the pattern-

ing. At a multi-field patterning this correction will be executed in front of every stitch field.

When using the Focus Correction mode the working distance has to be in the range of W = 9 mm to

W = 11 mm.

You can one of the below (9.4.1 or 9.4.2) methods to control and correct the sample height

9.4.1 Using Focus correction during Positionlist scan

• Enable the height control function via Extras Settings Drive Scan Enable Height Control.

• Generate a new Positionlist or open an existing one via the main menu bar File New positionlist/Open

positionlist...

• Change to the Height Control dialog Height Control tab.

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• In the Upper threshold input field, enter an upper threshold for the working distance. Up to this value, the

correction of the focus will be performed.

• Select by working distance: The system will adjust the working distance of the electron or ion optics.

• Click on Process Mode. The process Mode mode is activated.

• Focus the electron beam at the desired height. Take care not to expose any position where a patterning will be

placed later on.

• Click on New Scan to take a reference scan of the current position. The corresponding LED illuminates green to

indicate an active reference scan.

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• Start the Positionlist scan. The focus will be corrected during the positionlist scan.

10. Exposure

• Add “Beam Shutdown” if desired from the Automation section to the end of the positionlist.

• Now, it is time to write your pattern! To do so, select the positions on the positionlist to be scanned

and click Scan to start the exposure.

11. Unload the Sample

• Click EHT in the lower-right corner of the Column monitor screen, and click on EHT off.

• Turn on the mini-environment fan if it was previously turned off.

• On the lithography menu (lithography monitor) Click on LoadLock dialog

• On the sample exchange window click on the Unload sample


• Press OK

• The Unload procedure will be carried out step-by-step and the progress bar will indicate the Activation

Progress:

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• The button indicates the currently active step, the button indicates a completed step.

You can stop the Unload procedure at any time by pressing the STOP button.


• Make sure that the load lock door is closed then press OK


.

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• Open the load lock valve:


o Turn the locking lever from “Locked” to “Open” and pull out to open the loadlock valve

• Insert the transfer rod into the stage chamber. WARNING: Make sure the load lock valve is

open otherwise the transfer rod would be bent by pressure!

• Press OK

• After a few minutes the following prompt message will be displayed on the PC monitor:

• Remove the transfer rod from the chamber

• Close the load lock valve:


o Push in the locking lever, turn it clock-wise until it has snapped into place

• Make sure the load lock valve is closed then press OK


• Press OK

• The Unload procedure is completed and you can remove the sample holder from the load lock.

• Return the sample holder into the desiccator.

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• The system vacuum can be degraded by dust or dirt from the load lock chamber. Remember to close

the door to the load lock chamber after you have removed the sample holder.

12. Exit the System

• Press File and then Exit to close the e_LiNE control program (Lithography monitor).

• The Raith EO software is generally left running.

• In the end, do not forget to fill in the Log Book.

Reference and Files

Raith e_LiNE Manual and training notes.

Contact Information

Questions or comments in regard to this document should be directed towards Mohamad Rezaei (re-

[email protected]) in 4D LABS at Simon Fraser University, Burnaby, BC, Canada.

electron beam lithography sop - 4d labs · 2 simon fraser university 8888 university drive,...

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