Raith e_LiNE USER GUIDE
November 2009
Contacts:
 G. Patrick Watson - gwatson@Princeton.EDU ; 8-4626
 Mike Gaevski- gaevskim@princeton.edu; 8-8234
0.Overview
Raith eLiNE lithography system can be used for writing features with critical dimension of about 20
nm over wafers up to 100 mm in diameter. Thickness of the sample for writing has to be less than 3
mm. First, user has to create the design using AutoCAD, L-Edit or Raith software and transfer it to
eLiNe machine. Second, coat the sample with e- beam resist and bake it. Third, load the sample into
eLiNE chamber; do all necessary alignments; expose the sample with sharply focused electron beam
according to the design pattern. Fourth, develop the pattern and postbake. Later, pattern obtained in
resist layer can be transferred into the sample using lift-off procedure or etching.
Remember, this instruction is written to ONLY provide some key operational procedures in a stepby-step manner. The vendor’s manual provides information with much greater details and users are
encouraged to master the main procedures.
 Raith e_LiNE SEM is designated for electron beam lithography. It is not an imaging tool.
Users who need to do imaging should utilize the SEM located at PMI.
1. Design
Three PCs, equipped with Raith software in D002
One can use any of design software that
saves the results in DXF or GDSII files.
Computer in E-Quad Atrium (students
office area) dedicated for design, has
AutoCAD, L-Edit and LinkCAD
software. We also have two computers
with Raith software for editing GDSII
files in D002. Once you have the access
to the room, you can start using these
machines for designing. The login to
the user account of the PCs is “training”
and there is no password required.
However, in order to access the Raith
software, you will need an account
which must be set up by the administrator.
Using LinkCAD (installed on the design computer in Atrium), convert DXF to a GDS file. Save the GDS
file on a memory stick for transfer to the Raith computer. You can also convert DXF using Raith
software, Edit→Load→DXF.
All designs have to be checked and corrected using Raith software before actual writing. Log-in to one of
the Raith computers, open your GDS file using Edit button in GDSII window. Select appropriate layer.
Click View→Fill. All exposed area within the layer will appear uniformly filled with layer color. Use
“+” and “-” buttons to zoom in/out and arrows to mover over the pattern. Following parameters are
particularly important to check:
 Dose factor. The default dose factor is set as 1. Smaller and staying alone features could require

higher dose factor because of proximity effect. Open Edit Parameters window by double clicking
on the feature (or Modify→Atributes/Dose) and correct dose factor.
Order. Stage and beam drifts should be taken into account to specify the optimal writing sequence
of the different parts of the design. To specify order one can use command Modify→Order.

Stitching field position. You should take care about stitching if your working area is larger than
write- field. The working area is the portion of your design that you would like to write. Writefield is the area exposed without stage movement which closely related to the SEM field of view
at certain magnification. Default write-field for Raith is 100x100 m2 at 1000 magnification. It is
recommended to specify the working area in enough integer multiples of write-fields to contain
the pattern. For example, if your pattern is 2.2 mm by 1 mm, specify a working area of U: -1150
μm to 1150 μm; V: -550 μm to 550 μm. The result is a working area that is large enough to
contain the entire pattern, built out of integer multiples of 100 μm. It is also good to avoid
dividing the most critical areas between different write-fields, so you don’t have to worry about
the Raith stitching your device incorrectly. To do that you can adjust your 1) working area size
using command Edit/Working areas and/or 2) write-field size using Microscope Setting window.
Apart of regular shapes like box and circle one can copy-paste features from preexisted designs. Raith
demo pattern is a good source of building blocks for pattern design. You can build new structure from
these blocks using Modify→Multiply, Hierarchy, Boolean functions.
Do not forget to save new version of GDSII file. Saved files are located in c:\eLiNE\user\Your User
Name\GDSII folder. Here you can see four files with the same name and different extensions. To transfer
your design between Raith computers you only need CSF file.
Mark Design for Overlay Alignment
Raith writing system deals with three (or more) coordinates system: stage (X,Y,Z), wafer (U,V,W), beam
(u,v,w) (see alignment section). There could be several more local coordinate systems on one wafer. For
the first layer writing over bare sample surface you can use corners of you sample or edges of wafer cut
on rounded semiconductor wafer for alignment between stage and wafer coordinate systems. Then you
can use precise stage movement to align beam coordinate to stage coordinate system. Thus you do not
need alignment marks at all.
E-beam lithography layer can be also written over a substrate that already has a pattern layer(s) formed
using e-beam or photo-lithography. Those layer(s) should have alignment marks for overlay purpose. We
have to align both sample stage and electron beam. It means, structure should have at least two sets of
alignment marks. Marks for stage should be close to wafer edge, so you can easily find them without
exposing large area. One can see example of stage alignment mark- light green crosses in the corners of
Raith demo pattern. Note that they also placed far enough from critical area. Each of this big crosses
surrounded by four small crosses for electron beam alignment. For complete alignment including zoom,
shift and rotation adjustment separately for both U and V axes, you only have to scan three of them. You
also may put small alignment crosses into write-field where you have the most sensitive to the alignment
elements of your design. Thus Demo pattern has extra beam alignment marks in the fields with Vernier
pattern and HEMTs. To read preexisted alignment marks you have to insert into new lithography layer
(one that you are going to write now) special elements: MarkScan (layer 63 and 61). Click on
Add→MarkScan, select between auto (layer 61) and manual (layer 63) alignment procedure, edit
scanning field position and size as well as noise reduction parameters by clicking on selected MarkScan
feature in your design (or using Modify→Atributes). Alternative way to set alignment marks: copy all
this parts from Demo pattern. Note that three marks for full alignment should not stay in one line. If your
pattern in its critical area is very dense and you do not have enough space for three alignment marks, you
can do full alignment somewhere else, for example, around stage alignment mark at the corner of your
sample, and insert only one beam alignment mark with relatively small MarkScan field for shift
correction. Scanning of only one mark also safes system time when you are writing pattern over very
large area with huge number of write-fields.
2. Sample preparation
Similar to the photolithography, e-beam lithography utilize resist layer for design transferring. The ebeam resist is sensitive to electron beam irradiation. Before you start processing, you have to determine
what resist will serve for you better. Good source of information regarding resists is Cornell NanoScale
Science & Technology Facility webpage: http://www.cnf.cornell.edu/cnf_process_ebl_resists.html. The
resists that cleanroom provides are 950k PMMA with different level of dilution in Anizole,
P(MMA/MAA) copolymer 9% and ZEP520A. To achieve desirable film thickness, users by themselves
can dilute resist more. PMMA 950k 4% and ZEP520A can be diluted in ZEP-A thinner (Anizole).
Thin layers of PMMA recommended for writing fine features. Combination of two layers: PMMA on top
and copolymer at the bottom can be used to improve lift-off procedure for relatively thick metals.
ZEP520 has higher contrast, lower dose and stays several times better than PMMA under dry etching
conditions.
Precleaning
Before coating you have to preclean sample surface. Especially it is important for sample after
photolithography. All remains of photoresist have to be removed otherwise during e-beam resist baking
step at high temperature they will burn into sample surface forever. You can use all kind of strippers,
oxygen plasma or deep UV-ozone cleaning to remove photoresist.
For fresh surface 3-solvent clean (TCE→Acetone→Methanol) is recommended, 5 min each solvent in
ultrasound bath followed by prebake for 2 min at 180°C (to drive off solvents).
Spin coating PMMA
First determine the desired thickness of the resist.
 If you intend to do metallization after the exposure, the total resist thickness should be about 2 to
3 times thicker than the metal film. Bilayer of resist helps to create undercut which makes the
liftoff easy.
 If you plan to use resist as a wet etch mask, thin resist layer (100nm) is good for the purpose.
 The thickness of the resist is associated with the concentration of the resist, the spin speed, and
the sample size (if the chip is very small). For a 1cm x 1cm Si chip, 4% PMMA spun with 6000
rpm produces a thickness around 200nm.
Use a disposable pipette to place a few droplets of resist on the sample just before spinning or during the
spin-up. Note that solvent evaporates fast from thin layer so act quickly to achieve uniform thickness.
Example of spin coating recipe from Harvard University to achieve the same 200 nm thickness of
PMMA: Spin on PMMA 950K 3% in Chlorobenzene. Set up spinner with a 5s spin-up at 500 RPM
followed by a 40 s spin at 4000 RPM. Use a ramp rate of 2000 RPM.
Resist Baking
There are two ways to go with baking: in oven or on hotplate. The baking temperature has to be 170°C180°C. The baking time on a hotplate is much shorter (10-15 min depends on thickness) than oven baking
which takes at least several hours. The advantage of oven bake is the better uniformity of the resist. Use
oven for electron beam lithography with temperature set 170°C. If you use several resist layers, bake each
layer properly to avoid intermixing.
3. Writing procedure
 Book Raith e-LiNE system using PRISM reservation webservice.
 Each time you use the eLiNE, you MUST fill out all items in the log-book. Please also
record any problems that occur. Below is a sample of the information to fill out in the logbook.
Name: ABC
Date: 03/25/07
Sample No.: a-1
Substrate: Si
Resist: 950k PMMA
EBL___X___
Thickness: 100 nm
Other_______
Time start_9:30_______ Time end__14:20____
WorkDistance: 10 mm
Aperture: 30 µm
Acc. Volt: 10kV
Beam Current: 0.2032nA
Dose: Area:100 uC/cm2 Line 300pC Dot: 0.1pC
Problems? Describe:
i.e. Load-lock pumping error: mechanical pump fail
EHT off ____X___
Log off ____X_____
 If, during the operation, you have encountered an unknown problem, please contact Mike
Gaevski or Pat Watson immediately, instead of trying to fix the problem yourself.
Raith e_LiNE has two major parts: first part includes electron gun, electron optics and vacuum
control system designed by Zeiss Inc. and controlled using Column PC. One can use the Column PC
to define magnification, astigmatism correction, aperture (beam current), acceleration voltage, etc.
Second part consists from laser stage, electrostatic beam blanker, pattern generator and loading unit
controlled by Raith PC.
USB hub for
design
transfer
Raith PC
Column PC
USB port
for image
transfer
The Raith PC is used to carry out stage and beam alignment, exposure control, loading-unloading
procedure etc. The Raith PC is located in the control stack. Users can transfer design files to their
folders on Raith PC using USB hub located on the table on the left from Raith PC monitor.
Raith
terminal
Column
terminal
Stage
joystick
Start the system
Under normal operation conditions both PCs as well as all other hardware parts of eLiNE should be on.
In the case of software malfunction restart computer (computers) using login “User” and password
“eLiNE”. Run the Raith and Column software using username and password provided during the
training.
e-LiNE software layout
Beam blank
Toggle control
between PCs
Navigators
Local/global
Section Selector
Load/Unload Sample
Carefully remove the sample holder from the box. Do not drop the sample holder (as some people have
previously done). If there is any silver paint on the front of the sample holder, carefully clean it off with
acetone and a cleanroom wipe or a cleanroom Q-tip. Use only soft tweezers around sample holder. Note
the numerous scratches caused by inconsiderate people who have used metal tweezers. Liberally blowoff the front and back of the sample holder using compressed nitrogen. Be sure to remove all dust and cat
hair from the two holes and glass roads on the back of the holder; anything sitting in these holes will lead
to drift.
Faraday cup
Sample clips
Blow these
places with N2
Clip 1
Topside of the sample holder
Bottom side of the sample holder
Note that the sample height must be LESS THAN 3mm to avoid damaging the column.
There are two options of loading the sample: through the load-lock (for most uses); and through the front
door (only if you have a large substrate, i.e. squared 4” mask plate). Contact Mike or Helena before
loading your sample through the front door. The loading procedure will take about 8 min for load lock
and about an hour for chamber.
Load sample through the load-lock: In the Raith software, use the Navigator#1
by clicking on the
middle traffic lights icon on toolbar. Choose via load-lock. The program will guide you through the
loading/unloading procedure. Check the status of the stage/ transfer arm/sample holder using CCD
camera image before every step of loading/unloading procedure. At the end of the loading procedure, the
program will prompt you to set acceleration voltage and aperture. Immediately after that The EHT will be
turned on automatically.
It is important before turning on the EHT to check that:
(a) The gate valve completely closed and locked
(b) The system pressure is below 2 x 10 -6 Torr , gun pressure below 2 x 10 -9 Torr
At the end of loading procedure, the program will prompt you to turn on EHT from the Raith PC. The
available acceleration voltage ranges from 1 to 30 kV and aperture size from 7.5 µm to 120 µm. User
should select values suitable for desired e-beam writing resolution and efficiency. The typical
parameters, 10 kV and 30 µm aperture size, enable writing of sub-100nm features in a 100 μm work field
while maintaining high image contrast suitable for alignment mark recognition. The values of both
acceleration voltage and aperture size can be changed later during the operation. If the sample is already
inside and, EHT has to be changed/turned on use Navigator #2- Set Stigmator/Aperture option
.
This will also reset dynamic correction parameters of eLiNE according to EHT.
 Note the time when EHT was switched on in your lab book, it is nice to know how long the beam
has been warming up before you begin writing.
When beam is ON you can start from finding your sample. When Column PC works in CCD camera
mode, drive stage in Z coordinate to appropriate height (1-30 mm). The typical height is Z=26 mm which
corresponds to an approximate working distance of 10mm (depends on sample thickness). In the “Stage
control” window, under the “command” tab, select “Faraday cup on USH” and click go. This drives the
stage to the Faraday cup. Toggle Column PC from CCD to SE mode by clicking the button with small
blue screen. Turn on the beam by clicking the beam blank/unblank button on the Raith computer
command bar. To set the magnification, first click on the zoom/focus button on the Column control bar
hold the left mouse button of the SEM mouse, and move the mouse left or right (to zoom out or in).
Zoom all the way out. Look for the Faraday Cup. Faraday cup is a good starting position for your sample
hunting. If you every time use same position for you sample you can safe it in position list under
“command” tab. For example, if you use lowest clip (see image of the sample holder), you can click on
“Clip1”, and stage will drive to this clip. Disable scan rotation clicking on Scanning→Rotate/Tilt. All
boxes in Rotate/Tilt window should be unchecked. Now sample holder (how you can see it on image
above) will move exactly in the way how you tilt joystick handle. You tilt it to the right stage will move
to the right and your field of view will shift from Faraday Cup to the center of sample holder. You tilt it
up (forward) and eventually you will see Clip 1. Open Service
Motor Control window and select
Joystick. Adjust the motor speed to 9 for fast mode and 2 or 3 for slow mode. When driving the stage
switch between fast and slow using left button on joystick box. Use the Joystick to drive the stage (at
high speed) to an area close to the corner of the substrate.
SEM software layout
Beam freezes in the
center of the screen
CCD
Camera/SE
Crosshair
Aperture
alignment
Stigmation XY/
Focus
Reduced raster
Scan rate selector
Brightness/
Contrast
Detectors
Data zone.
Double click on a parameter
from data zone to edit it
Stigmation
Magnification/ Focus
Status of mouse button control
green is the left, yellow is the
wheel/side mouse buttons
Focusing, Adjusting Stigmation, and Aperture Align
The goal of this step is to obtain high quality beam and image (like in the image below). Toggle between
CCD camera mode and SEM mode to help with moving the stage. Zoom in and find small features on the
surface of the substrate. Adjust focus and stigmation to obtain a good image so that you can burn a
contamination dot.
 Adjust brightness and contrast from the Column PC and make sure automatic brightness and
contrast (ABCC) functions are turned OFF.
To focus, hold the wheel or side mouse button on the Column mouse and drag left or right.
On the Column computer, turn on the “SEM control” window by clicking on the red-and-green-circulardial-looking button on the command bar. Click the “Apertures” tab on the SEM control panel. Zoom to
about 50 kX Click the “Focus Wobble” box, then the “Aperture Align” button. After clicking the
“Aperture Align” button, the current values for the aperture alignment appear in a green box at the
bottom of the SEM screen. Double click this box to enter the alignment values from your previous Raith
session as a starting point. Fine tune the aperture alignment by either dragging the red dot in the SEM
control panel, or by moving the slider bars, or by (after clicking the Ap. Align button) left-click-dragging
up/down or left-right on the SEM image. The alignment is correct when the image does not move due to
focus wobble, but instead only changes focus. Click on the magnifying glass button on the control bar to
return to zoom/focus mode. (Otherwise when you try to zoom/focus, you will accidentally adjust the
aperture align). Refocus, zoom in, repeat. Click the “Stigmation” button. Enter the previous good
stigmation values in the green box. Unless somebody turns the filament off or otherwise crashes the
system, the stigmation values are fairly stable from day-to-day, so write your values down to use next
time. Zoom to about 100 kX or higher. Fine tune the stigmation. The idea is to first focus somehow, then
to improve the focus and eliminate directionally-preferential focusing by adjusting the stigmation. Again
refocus, zoom in, repeat.
 Good focus is critical not just to achieve small size features, but also to get robust, reproducible
results in terms of exposure. In other words, if the spot-size of the beam changes from one writing
session to the other, you will not be able to control the dose correctly.
Final stage of the focus correction is burning contamination dots. Side-click the “Short/Spot” button
(rectangular with a small green cross) to stop the beam from rastering and to build up a contamination
bump into the PMMA at the location of the crosshairs. Wait for 30 seconds, then Side-click the button
again to return to normal SEM mode. Because the working distance is probably off by up to 0.1 mm, the
beam will not be very concentrated on the spot and it takes a long time (30 s) to burn a visible spot. After
returning to normal SEM mode, it may or may not be possible to see a faint, ghostly blob. You may need
to zoom out to about 100-200 kX if the spot is quite large. Focus on the ghostly blob. When the focus is
correct, the ghostly blob looks more like a ghostly doughnut; that is, brighter around the edges and darker
in the middle. After focusing, tap the joystick to move away from your 30 second spot, and burn another
spot for about 10 seconds. This spot should have a much smaller diameter because the beam is much
better focused (which is also why a shorter burn time can be used). Focus on the 10 second spot, move
away from it, and burn a 5 second spot. When the spot size is 20-30 nm, the working distance is correct
for this (U,V) location. If the spot is not circular, you will need to adjust the aperture and stigmation until
it is circular. You can click the marker button to put two measurement markers on the SEM image to
check the diameter in the two “45 degree” directions, otherwise the optimistic eye can be fooled into
believing that an oval is a circle.
 Note that the size of the contamination dots, 20-30nm, is not an absolute value. It is affected by
the type of resist used, thickness of the resist, the condition of the resist, aperture size, and even
the choice of the acceleration voltage and substrate material.
Obtained beam parameters for each acceleration voltage, aperture and working distance can be stored by
clicking on first traffic light icon (gun configuration).
Adjust UVW window
This is a key step since the stitching depends critically on the coordinates. The purpose of defining the
Global (UVW) coordinates is to create a sample/wafer-based coordinates, directly correlated with (XYZ)
the stage coordinate, that make the on-wafer mapping straightforward and convenient. In this coordinate
system W corresponds to the working distance, assuming that sample in focus, this will be the distance
between sample surface and objective lens.
Set Zoom ~1000X that is default magnification for magnification range # 2. The idea is to use the same
magnification range for alignment as you will use for writing.
 Make sure to choose Global coordinates by clicking on the Global/Local button. If the button at
Design
Microscope control
Adjustments
Global/local button in global status
Exposure
Stage control
Automation
Administration
Height control
Service
the lower left reads “-> Global”, click it so that it reads “-> Local.” You will see glob sign
indicating the system set in the Global UVW.
The adjustment of UVW can be done in two different ways:
I.
Origin definition and angle correction
Select Origin:
Find lower left corner of sample using stage joystick control.
Center the corner of the sample with the help of image crosshairs
Select the Origin Correction index tab
Assign this (XY) stage location the (UV) coordinate (0,0) by pressing the Adjust button.
Angle Correction
Select the Angle Correction index tab.
Read this XY location (origin) as point 1. Note the microscope MAG setting.
Drive stage to lower right corner of the sample.
Read this XY location as point 2 using the same MAG as used at point 1.
Press Adjust button to calculate transformation angle between XY and UV coordinates systems.
(NOTE: the computer assumes +U direction along the vector from point 1 to point 2.)
NOW, the origin and angle of the UV coordinates are set, so it should be possible to move around your
sample by entering absolute or relative coordinates in the “Stage Control” window.
W correction
Focus very well (see instruction above).
Open the Adjust UVW window and choose Adjust W. Make sure the CCD camera mode is unchecked.
Read from the stage control the value of W and click Adjust. This action will precisely assign W for this
particular point. During writing you can correct W manually burning dots and focusing nearby critical
regions of your design. The other option is to use laser height correction option. In this case you have to
focus very well at least 1 mm away from the wafer edge (laser spot is relatively large). Then open laser
height correction window, switch on laser correction at exposure, collect reference spectrum, check it
using CCD window. The spectrum should have one strong sharp peak. Changing in position of this
spectral peak will be used for height correction during exposure. Unfortunately, not every sample is
suitable for laser correction. The performance of this unit depends on surface roughness, reflectivity and
so on. Great advantage of this option – you can correct height during exposure of curved sample and
samples with complicate surface relief.
 Depth of focus can be increased by using smaller aperture and higher accelerating voltage. Means
that when you are writing over small flat sample using 7.5 um aperture and 30 kV you probably
do not have to worry about height correction at all.
 Remember. Height correction does not work in fixed beam moving stage (FBMS) mode.
II.
Three point alignment
You will define three point (Ui,Vi,Wi) using (Xi,Yi,Zi) (i=1-3). These three points should not be on one
line. In this way you will define entire plane (UVW), and system will be able to recalculate U, V, and
also W coordinates for any point on this plane. It is recommended to use for overlay exposure when you
want to align new lithographic layer to already existed one that probably, was done using different
machine (photolithography aligner and so on). This time you teach the stage how and where to move,
means that you force perfectly calibrated stage to move less precise to make perfect match with previous
layer. Thus you have to be extremely careful because stage will follow exactly your instructions. You
also can choose during writing between mechanical height correction using stage and electronic W
correction using magnetic lenses (working distance adjusting). Mechanical correction can cause of small
shift, while working distance correction can result in slight rotation. Both effects can be corrected by
extra beam alignment (write-field alignment) included into critical region (see next section). To activate
height correction you have to select 3-point alignment window, click on Edit -> Options, check box for
one of the options: stage Z or working distance correction. After that the red message “Focus correction”
will appear at the bottom of 3-point alignment window, indicating that focus correction is enabled. If you
prefer to keep this function disabled, your still can use laser height correction or adjust focus manually as
described above.
 Never use both laser height correction and 3-point focus correction at the same time.
Next you have to assign three points. For overlay exposure these will be three alignment marks from
previous layer. In this case you already know from your design what distance between marks and how
they placed on your sample in respect of each other. Enter the (U,V) values for these three points into the
U and V columns of the “3-point Adjust UVW (Global)” window. As quickly as possible, use the
joystick to navigate along the edge of your chip to a place where you expect to find alignment marks.
Focus on anything you can find (i.e., the edge of the chip). Find your alignment marks, trying to stay near
the edges of the chip to avoid exposing active areas of the chip. If you need to stop and think, blank the
beam. Focus on the alignment cross as well as possible. Center the crosshairs on the cross, zooming in to
minimize error. Focus on the cross as well as possible as described above. Once the working distance the
value need to be fed to the Raith computer. In the “Adjust UVW (Global)” window, click the “Read”
button on line 1 to get the (x,y) coordinates and the working distance of the current location. Click the
checkbox on line 1 to tell the Raith that everything is set (lines 2 and 3 remains unchecked). Press Adjust
button. Find second point and repeat the procedure. Click the check box on line two (line 3 unchecked).
After you done with two points you roughly define coordinate system. Then you can blank the beam,
click the UV lightning bolt on line 3 to move to your next focus location, and again repeat the entire
focus procedure. Check it and press the adjust button. Recheck all three points you most probably will
have to repeat focus correction once again at each point due to memory effect in magnetic lenses. But
this time you will use UV lightning bolt to move from point to point.
Stage now drives in the coordinate space defined by the alignment marks created by previous lithography
step.
 It is convenient, first, to do Origin-Angle alignment in Global coordinate system and, second, use
new – local (uvw) coordinates that corresponds to the existed pattern. Thus you can more or less
precisely jump from point to point during 3-point alignment without exposing large area. Do not
forget to toggle global-local coordinate system.
Write field alignment
This step calibrates the electron beam deflection so that the beam movement accurately corresponds to
the length defined by the coordinates of the patterns on the substrate.
Open the Microscope Control window and set Magnification -Write Field Size. 1000X - 100 µm is a
common choice. This means the Write Field has a size of 100 by 100 µm2 with beam scan step =100
µm/216 (16-bit DAC).
 Choosing higher magnification will increase the beam resolution with the trade off of a reduced
Write Field size. Thus you probably will have to do stitching.
Adjust Brightness and Contrast on Column PC to give good image. Select File >> New Positionlist
from menu.
CASE A — for unpatterned (i.e., bare) sample: This will calibrate the beam deflection using the
Set
button
Magnification/write field
selection
Write field alignment
Current Zoom/Shift/And
rotation parameters and
alignment corrections
Correction parameters
movement of the stage.
During alignment the stage will move the sample in the way that central portion of the write-field will
be precisely shifted toward to one of the corners. Electron beam will first scan small area (scan field)
in center of the write field, then stage moves, and beam will scan the very same scan field but shifted
into the corner. In the case of perfect beam alignment you have to see exactly the same image every
time.






Choose suitable reference particle or burned dot and move it to the center of column PC
display with aid of crosshairs.
From the Scan Manager window, Select Align Write Field Procedures -> Manual.
Right-click on desired alignment template and select Properties. It is recommended to use
a larger scan field first (i.e. 25 µm). Adjust parameters using “calculate” buttons and press
OK.
Drag-and-drop defined Align WF procedure into the Positionlist.
Perform the write field alignment by clicking right mouse button and selecting Scan. Press
and hold [Ctrl], then press and hold left-mouse-button and drug the movable cross-mark to
the center of selected particle each time it is scanned. So the system will know that actual
center of scan field should be there. Release left-mouse-button, release [Ctrl].
Repeat last 3 steps with sequentially smaller scan sizes increasing precision of alignment.
For optimal stitching, final scan size should be = 1% of Write field size. (1 µ for 100 µ
WF.) The zoom correction factors both for U and V coordinates should be close to one
(1.0000..., or 0.9999…)
CASE B — for patterned sample (i.e., for overlay or mix-and-match exposure):
This will align the WF to marks that are already defined on the sample. In this case stage will not move,
but beam will scan different areas within write field where you have alignment marks. If beam is aligned
to existed pattern all you alignment marks should be exactly at the center of the image.





Drag-and-drop your GDSII pattern into the Positionlist.
Perform manual (coarse) WF alignment. Expose GDSII pattern with only layer 63 and
appropriate Working Area (as described below in 8 Exposure step.) with reducing
scanning field sizes down to 5-10µm. The centers of scanning windows in the layer 63 of
your drawing for the current exposure level have to exactly coincide with the centers of
alignment marks in the drawing for the existed pattern.
During alignment the images of each scanning field will appiar one by one. Perform
alignment for each scanning field: press and hold [Ctrl], press and hold left mouse button,
align center of movable cross with center of alignment mark, release left-mouse-button,
release [Ctrl].
Perform automatic WF alignment using mark detection. Expose GDSII with only layer 61.
Open the last Line scan (File-Open Linescan) sorting them by Date modified. Press
“Apply active filter” button (blue square) to verify linescans and threshold algorithm for
proper mark recognition.
Check Protocol file for convergence of parameters. Repeat last step as many times as
required increasing accuracy. For auto alignment you need high contrast mark (like
relatively thick gold cross on silicon wafer). It has to be an L-shaped or a cross-shaped
mark. Arms of the cross should be long enough matching specified in layer 61 width of
scan field plus small misalignment error.
Unload the sample
 Turn off the EHT
 Unload sample using Navigator Exchange on the lithography PC
. Select “Via loadlock”“Unload”, and follow the instruction on the screen, before each step check the current status of
the stage/sample holder/transfer arm using the CCD image.
 Exit control program Raith e_LiNE on the lithography PC.
 Turn off both PC monitors.
 Finish filling out the log-book
4. Postwriting procedures
Developing
The resist developer for the PMMA resist: Methyl Isobutyl Kethone (MIBK) is also provided. Users
should mix it with isopropyl alcohol (IPA) before using. The recommended ratio is MIBK: IPA = 1:3.
 Prepare two beakers: MIBK:3IPA and IPA. The developing time is about 1 minute in MIBK
:3IPA for a 200nm thick resist. Rinse in IPA for at least 30sec.
 The developing time has to be adjusted according to resist thickness: for thicker resist one has to
use longer developing time.
 Blow dry using nitrogen gun
Develop ZEP520A resist in ZD-50N developer for 2 min, rinse in pure MIBK for 30 sec. and then in IPA
for 30 sec. Thus in this case you will need three beakers.
Double layers PMMA/MMA, PMMA/PMGI, ZEP/PMGI
Bake
Bake on 110 C hotplate for 5 min ( or use vacuum YES oven recipe #6) to remove remaining solvents.
Discum
Sample ready for further etching or metal deposition.