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--- electron_beam_lithography [2008/04/17 12:40] – Lay-out & coherence update verstoep
+++ electron_beam_lithography [2008/06/03 10:54] (current) – verstoep
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 The first step is to get experienced with SEM operation. **PRINT AND READ the SEM manual [[JEOL 820 SEM|here.]]**
-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 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 22: / Line 22: @@
 ====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 any alignment is going to be done, always set the beam shift to zero!
@@ Line 31: / Line 32: @@
 **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.**
+==== 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).
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 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.
-You can make a position list (and design) in advance, since this may take quite some time (~1 hour). Making a postion list takes the following steps
+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
   - 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).**
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     - 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 (80 nm is about the best of this system), you will need  10<sup>-10</sup> A.
+      - 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 prosess. (For hardening resist, you typically require between 40 and 160 uAs/cm<sup>2</sup>)
+      - 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).
+      - Use the calculate Icon to calculate the missing parameter(s) [Dwell Time].
+   - the button [Times] shows you how long the etching will take.
 ====== Start-Up =======
 ===== Loading the sample =====
   - 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 lits 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-proces.
+  - 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.
 ===== System Start-Up =====
   - Turn on the display of the computer. Log in to Elphy Quantum.
-  - Set the working distance of the SEM to 10 mm. (OR: 8 for exceptional situations, 3x3 or 4x4 marker for large fields)
+  - 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
   - check that aperture (Diafragma) '3' is selected (At the extruding part at the top of the SEM).
   - 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.
@@ Line 80: / Line 98: @@
 {{images:emission.png}}
   - Getting an initial image
-    - Check that switch EBPG -> SEM
+    - Check that Hardware is set to: EBPG -> SEM/ green button ''TV'' is selected / Blanking switch should be set to center position (off) / PCD off
-    - check that 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. The option coarse allows you to toggle between making large or small adjustments.
+    - 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)
+    - 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 (untill you see about 4 of the smallest squares)
+    - 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 =====
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   - Go to desktop 3
-  - Set Magnification to desired value (for example 100X)
-  - Drive the stage to the center of a chessy block (point at it and click ''<crtl+mouse-right>''. repeat if necessary
   - Set the hardware to: slow 2 / EBPG / Beam Blanking external
-  - Select your writing field (you can use 400 (@ 50X ?) um OR 800 um (@ 100X)) in microscope control and click ''set''
+  - 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.
+  - Set Magnification with the knob to the corresponding value you have entered for the writing field.
   - 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).
   - 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+mouse-right>''. repeat if necessary
+    - Drive the stage to the center of a chessy block (point at it and click ''<crtl+rightmouse>''. repeat if necessary
-    - Open a writefieldcalibration positionlist (file->open position list) called ''Align<size>'' or ''align<size>''
+    - 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''
+    - To apply the alignment press ''calculate'' and ''send'' in the ''align write field''-window.
   - **Fine:**
     - Optionally scan the image again.
@@ Line 127: / Line 143: @@
     - Iterate the above steps if necessary.
     - Close the image window (Don't save), Close the postionlist (Don't save)
-    - Set ''shift'' to zero
+    - Set ''shift'' to zero by subtracting the current values.
-    - Press send (Where?)
+    - 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.
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-===== 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:
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 ====== Writing ======
 ===== Preparing your program =====
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   - 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. Check by?
+  - 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 without beam stabilizer =====
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   - Set Hardware to: ''EBPG''/ blanker to ''External'' / PCD off.
   - Select your position list (And the first entry that should be written).
-  - Click ''menu->scan'' or scan all **THIS INITIATES THE ETCHING**
+  - Click ''menu->scan'' or scan all **THIS INITIATES THE WRITING**
   - The current you read is lower than the set value because of backscattering
@@ Line 220: / Line 238: @@
   - [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 tickness. (A red colour indicates a thin layer, a green colour a thick layer).
+  - [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).