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--- electron_beam_lithography [2008/04/16 15:31] – verstoep
+++ electron_beam_lithography [2008/06/03 10:54] (current) – verstoep
@@ Line 1: / Line 1: @@
-**FIXME: this is a late night hack and needs a lot of improvement!**
 ====== Introduction =======
 E-beam lithography is not something you will learn in a day. You will have to know about SEM use, structure design, resist chemistry and processes, etching processes, proximity effect, alignment, EBPG use etc. etc.
-The first step is to get experienced with SEM operation. **READ the SEM manual [[JEOL 820 SEM|here.]]**
+The first step is to get experienced with SEM operation. **PRINT AND READ the SEM manual [[JEOL 820 SEM|here.]]**
-The SEM becomes an EBPG with the Elphy Quantum system, beam blanker and motor control. The Elphy Quantum program has been set up to divide each writing stepdivides the process in 4 phases (desktops):
+The SEM becomes an Electron Beam Pattern Generator (EBPG) with the Elphy Quantum system, beam blanker and motor control. The Elphy Quantum program has been set up to divide each writing step divides the process in 4 phases (desktops):
    - Design
    - UV coordinate system calibration
@@ Line 16: / Line 13: @@
 Take into account the proximity effect caused by forwardscattering of electrons in the resist and backscattering in the substrate. Ask help if you need to place features very close together.
-====GDSII====
+=====GDSII=====
 Create a new gdsii database or open an existing one (desktop 1). gdsii is a hierarchical format where you can design elements that can be used in elements... and so forth.
-====Structures====
+=====Structures=====
 Create a new structure in the gdsii database. Structures are elementary pieces of design that can be reused, put in a matrix etc. Alignment markers are typically things that you would put in a structure. Referenced structures are displayed as red rectangles, if you push ''<alt-i>'' you see the contents (increase hierarchy level, reverse with ''<alt-d>''.
-===Layers and working areas===
+====Layers and working areas====
-Layers and working areas form the unit of exposure. What gets exposed in a single step is exactly the set-intersection of design elements in a layer and a working area. Layers are part of the gdsii database and all structures in the database will inherit the layers. Layers are a logical/functional way of grouping design elements. Working area's are a different way of grouping elements, those that fall completely in a rectangle. Typical layer definitions would be your one for each processing stage of your geometry, large contacts and markers (they require different writing parameters / procedures). The //working area// ---the logical writing area--- must be smaller than or equal to the //writing field// (the physical beam deflection field). The placement of the working area in the writing field is set in the ''pos'' settings in a position list. The center of a writing field is the UV coordinate at the sample set by the stage, but not that to reproduce this between lithographic steps the electronic beam shift must be the same, so if in your sample ana alignment is going to be done, always set the beam shift to zero!
+Layers and working areas form the unit of exposure. What gets exposed in a single step is exactly the set-intersection of design elements in a layer and a working area. Layers are part of the gdsii database and all structures in the database will inherit the layers. Layers are a logical/functional way of grouping design elements. Working area's are a different way of grouping elements, those that fall completely in a rectangle. Typical layer definitions would be your one for each processing stage of your geometry, large contacts and markers (they require different writing parameters / procedures). The //working area// ---the logical writing area--- must be smaller than or equal to the //writing field// (the physical beam deflection field). The placement of the working area in the writing field is set in the ''pos'' settings in a position list. The center of a writing field is the UV coordinate at the sample set by the stage, but not that to reproduce this between lithographic steps the electronic beam shift must be the same, so if in your sample any alignment is going to be done, always set the beam shift to zero!
-===Markers===
+====Markers====
 If a layer needs to be aligned to an already present pattern (a previous layer) alignment markers have to be present in this previous layer. To get an accurate placement relation between parts of the design and these markers, write critical, small (=fast) elements first to avoid drift of the machine to cause placement errors. Order the exposure sequence by pushing ''<o>''.
 The layer that has to be aligned needs to contain mark scans at the places of the markers of the previous layer. These mark scans must be large enough to be certain to 'hit' the marker and far enough away from critical parts of the design such that the starting error will not cause an e-beam scan over the critical region. Take into account an initial error of at least 2 um (the stage error plus the rotation error) and write large markers at 1,1 and 14,1 (for a 15x15 mm substrate) for UV calibration.
-In a lithographic step, try to avoid changes of the write field size that require a change in the working distance, because then recalibration of writing field and UV system are needed.
+**In a lithographic step, try to avoid changes of the write field size that require a change in the working distance, because then recalibration of writing field and UV system are needed.**
-====Beam current====
+==== Design tricks ====
+To rotate a group of structures:
+  - select the group of structures that you want to rotate by pressing ''<ctrl-right click>''
+  - go to menu modify
+  - select rotate free
+  - press a number on the keyboard and you get a pop up window where to write the center of rotation (0,0).
+  - press again a number, to select the angle of rotation. The angle is measured from the xy reference system and the line that connects the 2 points that you have just defined. For instance if you want to rotate of 45 deg, you can select the two points (0,0) and (1,1); for a 180 deg rotation (0,0) and (-1,0).
+=====Beam current=====
 When the layers and working areas of your sample have been designed, it is time to think about the beam current. See the calibration plot at the machine for spot sizes. Use 20-100 pA for small features and 5 nA for large ones as a start, make adjustments if this leads to excessive writing times (the higher the current the larger the spot, the smaller the spot the smaller the current and therefore the larger the exposure time fore a given pattern).
-====Position lists====
-Position lists are Elphy's abstraction for any scanning job, whether writing a single pattern, a matrix, doing an alignment to an existing structure or calibrating the writing field size. Here, all information about your design comes together: what layer and working area to write of what pattern in what gdsii database at what place at what beam current with what resist sensitivity, beam step size, dwell time etc. The ''matrix copy'' function is handy for matrix exposures and dose tests/scans. ** Due to a bug in the software it is critical to select the right writefield size in ''microscope control'' and click ''set'' before dragging items into a position list (or doing anything eles for that matter).**
+=====Position lists=====
+Position lists are Elphy's abstraction for any scanning job, whether writing a single pattern, a matrix, doing an alignment to an existing structure or calibrating the writing field size. Here, all information about your design comes together: what layer and working area to write of what pattern in what gdsii database at what place at what beam current with what resist sensitivity, beam step size, dwell time etc. The ''matrix copy'' function is handy for matrix exposures and dose tests/scans.
-====== Exposure =======
+You can make a position list (and design) in advance, since this may take quite some time (~1 hour). Making a position list takes the following steps
-If your positionlist is ready, it's time for the hands-on part: the exposure. Mount the sample aligned with the edge of the sample holder to minimize rotation with respect to the sample holder and while taking into account everything written in [[JEOL 820 SEM]] usage click the sample holder onto the stage. Be careful not to accidentally expose the resist by moving the stage!
+  - file->new position list
+  - Drag a structure from your database to your position list. ** Due to a bug in the software it is critical to select the right writefield size in ''microscope control'' and click ''set'' before dragging items into a position list (or doing anything else for that matter).**
+  - right click on the newly created entry and select properties.
+  - press the icon with three layers. Here select the layer you want to configure and write (for example "layer 0")
+  - Go back to the previous screen.
+  - Enter where on your sample this structure should be put by specifying the UV-position (in mm)
+  - Press [Exposure parameters]; the window will expand.
+    - Disable all defaults.
+    - Disable lines and dots.
+    - Press Calculator
+      - Take a look at the Beam Current VS Spot Size graph, which is on the cover of the manual of the SEM which you will find on the console.
+      - If you want to have a 100 nm resolution (Step Size = 0.1 um) (80 nm is about the best of this system), you will need  10<sup>-10</sup> A.
+      - Set your Area Dose to the value required by your process. (For hardening resist, you typically require between 40 and 160 uAs/cm<sup>2</sup>)
+      - Use the calculate Icon to calculate the missing parameter(s) [Dwell Time].
+   - the button [Times] shows you how long the etching will take.
-===== Chessy operations=====
-  - Set the working distance to the desired value (10 mm, 8 for exceptional situations, 3x3 or 4x4 marker for large fields)
-  - Select the required aperture
-  - Drive the stage to the chessy and switch on the machine.
-  - Switch on the SEM at 20 kV, increase HV slowly to 30 kV
-  - Set the current to about 1 nA
-  - Let the machine warm up for half an hour
-  - Adjust filament saturation
-==== Focussing and astigmatism correction ====
+====== Start-Up =======
-  - Focus on the chessy
-  - Zoom in
-  - Correct astigmatism
-  - You should see 50 nm details easily at 1 nA
-==== Write field calibration ====
+===== Loading the sample =====
-Alignment is similar to writefield calibration but done on the sample markers. It is usually a good idea to still calibrate the write field (and set ''shift'' to zero!) to get an accurate starting position for alignment.
+  - If your positionlist is ready, it's time for the hands-on part: the exposure. Mount the sample aligned with the edge of the sample holder to minimize rotation with respect to the sample holder and while taking into account everything written in [[JEOL 820 SEM]] usage.
+  - Load the sample into the SEM by using the loadlock which is controlled by the red button. With this single button you can vent and pump down the loadlock. The button lights up if the loadlock is venting or pumping down. Read the [[JEOL 820 SEM#Startup|Start-Up Section of the JEOL 820 SEM Wiki]] for a step-by-step description of the load-process.
+  - Slide the sample holder inside the vacuum chamber onto the stage.
-  - Go to desktop 3
-  - Select your writing field in microscope control and click ''set''
-  - Open a new image and scan it
-  - The image should have the right size and not be rotated
-=== Course ===
-If this is not the case a write field alignment has to be performed (normally not necessary unless something weird happens like the JEOL service people recalibrating the scan field of the SEM itself :-) )
-  - Drive the stage to the center of a chessy block (point at it and click ''<crtl+mouse-right>''. repeat if necessary
+===== System Start-Up =====
-  - Open a writefieldcalibration positionlist called ''Align<size>'' or ''align<size>''
+  - Turn on the display of the computer. Log in to Elphy Quantum.
-  - Markers appear in the image
+  - Set the working distance of the SEM to 10 mm (8 in exceptional situations) for small structures, 3x3 for a 3x3 mm working field or 4x4 marker for a 4x4 mm working field
-  - Drag all 4 markers to the right place. They have to be moved!
+  - check that aperture (Diafragma) '3' is selected (At the extruding part at the top of the SEM).
-  - Click ''calculate'' and ''send''
+  - Drive the stage to the chessy position with the ''stage control'' window. This is done so that you will not accidentally expose the resist when moving the stage later on. In general: **don't image your sample, because it will expose your resist!**.
+  - Check that PCD is on.
+  - Check that the voltage is set to 20 kV and that the filament current is 0 A.
+  - Turn on the main power (red square button). It will light up.
+  - Increase the voltage in steps to 30 kV.
+  - Switch EBPG -> SEM
+  - Blanking Switch to center position (off).
+  - Setting filament power
+    - Switch current meter to 1 nA full scale
+    - Slowly turn filament heating current to the indicated value (at the ‘shoulder’, see plot. do not exceed 2.6A. Ask if unsure)
+    - You should now measure a current on the sample
+    - Actually you should let the machine warm up for half an hour to let it stabilize for thermal drift.
+    - Adjust filament saturation
+{{images:emission.png}}
+  - Getting an initial image
+    - Check that Hardware is set to: EBPG -> SEM/ green button ''TV'' is selected / Blanking switch should be set to center position (off) / PCD off
+    - Set the Contrast and brightness (Bottom left of top console) to maximum (OR 3 O'clock).
+    - Set the current to about 1 nA (With bottom right knobs)
+  - Improving the image
+    - Use the knobs on the bottom console to change brightness and contrast.
+    - Use magnification and the position joystick to change the position you look at.
+    - Focus the image (you should be able to have a 100 nm resolution). The option coarse allows you to toggle between making large or small adjustments.
+    - Change the current with the bottom right knobs ''course'' and ''fine''. You should see the measured current on the sample change.
+    - iterate the above steps.
+  - astigmatism correction
+    - Zoom in (until you see about 4 of the smallest squares)
+    - Correct astigmatism
+    - You should see 50 nm details easily at 1 nA
+====== Calibration ======
+===== Calibrate the Write field on the chessy =====
+In order to define the dimensions of your sample and your coordinate system well, the system first needs to be calibrated. This can be done by informing the system of the position of a square of the chessy so that it can calculate any transformations.
+It is usually a good idea to still calibrate the write field (and set ''shift'' to zero!) to get an accurate starting position for alignment. It can be done in two steps. One rough step (coarse) and a fine step. Sometimes the coarse step may be omitted if the alignment is already good enough.
+  - Go to desktop 3
-=== Fine ===
+  - Set the hardware to: slow 2 / EBPG / Beam Blanking external
-  - Click ''scan all'' in the writefield calibration position list
+  - Select your writing field in microscope control and click ''set''. A magnification of 20X gives you a writing field of 3000 um; 100X = 800 um; 170X = 400 um; etc. For magnifications 100X and higher the best lens is used.
-  - A macro will execute and ask you to click the marker centers. The marker has to be moved!
+  - Set Magnification with the knob to the corresponding value you have entered for the writing field.
-  - When the macro finishes and all positionlist entries have a blue marker click ''calculate'' and ''send''
+  - Open a new image (file->new image) and scan it (Press the icon with (a microscope-ray?) and a small 1 in the bottom-left corner).
-  - Set ''shift'' to zero
+  - The image should have the right size and not be rotated (it doesn't have to be centered); If not: follow the steps below (normally not necessary unless something weird happens like the JEOL service people recalibrating the scan field of the SEM itself :-) ).
+  - **Course:**
+    - Drive the stage to the center of a chessy block (point at it and click ''<crtl+rightmouse>''. repeat if necessary
+    - Open a writefield calibration positionlist (file->open positionlist) called ''Align<size>'' or ''align<size>''
+    - Scan the image. Maximize the window of the image.
+    - Markers appear in the image
+    - Drag (ctrl-leftclick) all 4 markers to the right place. They have to be moved!
+    - To apply the alignment press ''calculate'' and ''send'' in the ''align write field''-window.
+  - **Fine:**
+    - Optionally scan the image again.
+    - Select your position list (Now you will have the right menu commands).
+    - Click ''scan all'' in the writefield calibration position list (OR: Menu->Scan all).
+    - A macro will execute and ask you to click the marker centers. The marker has to be moved! Press Continue in the dialog that has popped up each time you want to continue to the next marker.
+    - When the macro finishes and all positionlist entries have a blue marker click ''calculate'' and ''send'' in the ''align write field''-window.
+    - Iterate the above steps if necessary.
+    - Close the image window (Don't save), Close the postionlist (Don't save)
+    - Set ''shift'' to zero by subtracting the current values.
+    - Press send in the ''align write field''-window.
-===== UV coordinatesystem calibration =====
+===== UV coordinate system calibration =====
 The UV coordinate system is the sample coordinate system. Do not perform a 3-point correction unless necessary (motor step size and stage orthogonality), I do this when I set up your account; 3-point correction requires a trick.
-  - Drive the stage to the lower left corner and perform an origin correction (0,0) or drive the stage to the lower left marker and perform an origin alignment (1,1)
+  - Set Hardware to: SEM / TV / Blanking off / PCD off
+  - Drive the stage (with the joystick) to the lower left corner of your sample and perform an origin correction (0,0) or drive the stage to the lower left marker and perform an origin alignment (1,1)
   - Wait 3 seconds
   - Use this point as the first point for the ''angle correction''
@@ Line 97: / Line 159: @@
-===== focussing =====
+===== focusing =====
+Because the sample has another thickness than the chessy you need to refocus. You can burn spots on your sample to focus on OR you can use a spot of dirt on your sample to focus on. Below is the method to burn spots and focus on them:
   - Go to the middle of the sample (beam off!) or to the middle of the x-axis
   - focus on a particle
@@ Line 104: / Line 168: @@
   - repeat
-===== Alignment =====
+===== Calibrate the Write Field on your sample =====
-For now, see //write field calibration//. I will normally teach you this procedure because it is situation dependent.
+You cannot perform this step if you don't have markers on your sample.
+You must (can) recalibrate the transformations of your writing field, because the system may have deformed due to thermal drift or the deformations may be non linear (with respect to stage displacements).
+Alignment is similar to "[[#Calibrate the Write field on the chessy]]", but done on the sample markers.
+I will normally teach you this procedure because it is situation dependent.
+====== Writing ======
+===== Preparing your program =====
+The positionlist is the list of commands that will be executed when writing. There are many options to configure. Below are some important things to keep in mind:
+  - Load the positionlist you want to write: file->open position list
+  - Make sure your Area Dose corresponds to your process (For hardening resist, you typically require between 40 and 160 uAs/cm<sup>2</sup>). You can check this by [right-clicking] on an entry in your position list; select [properties]. Expand dialog by pressing [exposure parameters]. Press [calculator].
+  - Make sure you have selected the right layer for exposure. This is indicated with an integer in the layer field of your list.
+  - In the positionlist your Pos1 & Pos2 should be half the size of your writing field.
+There are two ways to do the etching: with beam stabilizer OR without beam stabilizer.
-===== writing =====
+===== Writing without beam stabilizer =====
-  - PCD in
+  - Set Hardware to: TV / PCD on
-  - TV scan
+  - Select magnification (Manually with knob in bottom console) entered in ''microscope control'' (you //did// click set i hope :-) )
-  - Select magnification entered in ''microscope control'' (you //did// click set i hope :-) )
+  - Set Hardware to: Slow 2 (If you forget this, the SEM will write interlaced) / Blanker to external (blanking is now controlled by the icons in the software)
-  - Slow 2
   - Beam on (click 'un'blank icon)
-  - Set beam current electrometer to desired scale
+  - Set beam current (that hits the Sample or PCD) electrometer to desired scale
-  - Set beam current to desired value (current knobs: left=up, right=down)
+  - Set beam current to desired value (bottom-right current knobs: left=up, right=down)
-  - Blank (click 'blank' icon)
+  - Blank (click 'blank' icon) (the current indicator will show 0)
-  - Switch to ''EBPG''
+  - Set Hardware to: ''EBPG''/ blanker to ''External'' / PCD off.
-  - Switch blanker to ''External''
+  - Select your position list (And the first entry that should be written).
-  - PCD out
+  - Click ''menu->scan'' or scan all **THIS INITIATES THE WRITING**
-  - Click scan or scan all
   - The current you read is lower than the set value because of backscattering
-===== writing with beam stabilizer =====
+===== Writing with beam stabilizer =====
 NEW!! (March 2006)
 This takes over the fine adjustment control of the beam current using a PI controller. The dial on the controller is set such that 0-10 represents the full scale 0-1 range on the TOP beam current meter, (e.g. for 10nA on a 30nA range you choose something near to 3.20 to get the correct setting on the lower scale). The controller will actively control ~30 seconds after the beam is unblanked, and continue to do so until the beam is blanked for more than a few seconds. If this happens then the controller remembers the last value, and will use that for the first 30 seconds after the beam is unblanked again, (after which it will again start to stabilize).
@@ Line 142: / Line 223: @@
 Other Note: In the description above, the current you set using the stabilizer is the current you get during exposure, which is less than the current you measure with the PCD on. If you prefer setting the desired current with the PCD on, you have to slightly change the above procedure. Set the correct current with PCD on at a harmless spot, PCD off to see the effect of backscattering, and then use the stabilizer to stabilize this current.
-====== Finally =======
+====== Shutting Down =======
-Switch off the machine and remove the sample holder as described in [[JEOL 820 SEM]] operation.
+  - Switch off the machine and remove the sample holder as described in [[JEOL 820 SEM]] operation  <= PRINT THIS.
+====== Advanced functions =======
+**Top Console:**
+  - [RDC] When in slow scan you can choose to only scan a slow area.
+  - [Wobler] This changes the focus with a sine function so you can check for astigmatism (The image should not rotate when wobbling). This might also be compensated by adjusting the apertures.
+  - [BEIH] Backscatter: You could use this to do spectroscopy. It detects electrons that had such an high energy that they reflected instead of going into your sample.
+  - [AEM] Current on your sample. The range knob selects the scale.
+  - [PCD] Blocks your bundle. You can read the true current on the AEM-scale. (When the current goes trough your sample you loose some signal due to resistance).
+  - [SEM - EBPG switch] In SEM mode the bundle is driven by a sawtooth voltage. When in EBPG the bundle is controlled by the computer (Requires slow 2 / Beam blanking external)
+  - [Beam Blanking] Deflect the electron beam.
+  - [mode switch] Control current by custom PID.
+**Software:**
+  - [menu->option->Hierarchy->Increase/Decrease] Make substructures of a design visible/invisible.
+**Determining process parameters:**
+  - [Doses Test] If you don't know what the area dose of your structures should be you can perform a doses test. You need to design structures with a varying Area Dose (typically between ~60 to ~160 uAs/cm<sup>2</sup>. After writing you develop your sample and look at it under an optical microscope to see if the remaining layer has the right thickness. (A red colour indicates a thin layer, a green colour a thick layer).