Preparing for EBeam Write

Transcription

1 Preparing for EBeam Write Electron beam lithography is a time-intensive process that takes many steps to properly prepare for writing. In order to make the process as efficient and simple as possible, we have divided the work into stages that you should taken into consideration before reserving time on JEOL via Badger. Use the instrument with care, and keep in mind that the JEOL is a valuable and heavily booked instrument. When in doubt, consult with a JEOL staff member or an experienced user. Pattern Preparation (see previous section) Pattern feasibility Sample compatibility Setup time constants Setting the Electron Optics Coat sample with resist Loading & pumping down sample CAD and pattern file conversion (JDF & SDF files) Setup Time Constants It is NECESSARY to arrive EARLY to your reservation time to prepare your samples. 1. Setting the Electron Optics (EOSSET) Verify that the JEOL is currently set to the EOS that you intend to use (i.e. EOS3_2000pA_60uM), otherwise you will have to set it yourself. If someone is using the tool before you, speak with them and ask them to set (EOSSET) to the EOS you want when they are done with their job. It takes minutes when switching from EOS3 to EOS6 to stabilize. For critical, demanding writes, it s actually advisable to do it as soon as possible, to give the lenses a few minutes to settle down. 1. Open the CALIB control (Clb.) 2. Click EOSSET and then "Edit Parameter" a. Choose the calibration table you will use by clicking "Equipment calibration condition file selection..." and then finding the desired table from the choices listed. i. There are separate listings for EOS 3 and EOS 6, so make sure you choose appropriately for your exposure ii. If there is no appropriate existing calibration table or you would like to create a new one, please talk with Rich T. about creating a new table. iii. There are common calibration tables (usually named by the current) and there are some user-specific calibration tables. DO NOT USE OR CHANGE ANY USER SPECIFIC TABLES WITHOUT PERMISSION. 3. Select boxes next to "RESTOR execution" and "DEMAG execution" if they are not already selected. 4. Click "Execute" 5. The system will now restore the values from this table. You can now click "CANCEL" to close the window. 21

2 Note: In Badger, you can write a note to state what EOS you are using-- it is a courtesy to set the next user s EOS once you are done with your write. 2. Coat Resist Most resists use 180 ºC for baking. Verify one hotplate is set to the temperature you need to use-- it takes a little while to ramp up to a temperature and a long time to ramp down. Leave a note if you need a special temperature and won t be near the hotplates. Clean, spin, and bake your chip with your resist in advance of your reservation. 3. Loading & Pumping Down Sample 3.1 Mounting the Sample to the Holder 1. There several sample holders are available; choose one which matches the size of your chip. It should be slightly wider so it won t fall through and so your alignment marks are visible on the other side. Use the Diagram 1 to determine the location of your chip slot. For the example below, it will be 2E. 2. Carefully flip the holder to the back side and put your sample resist side down. Select the appropriate fitting and insert it into the sample holder. Push down the leaf springs, rotate the fixation piece clockwise ( Figure 6 ). Diagram 1. Mounting the sample to the holder 3. Firmly holding your sample holder, flush the top and sides of the holder with the nitrogen gun. The N 2 can come out strongly. Figure 6. Mounting the sample to the holder 22

3 3.2 Loading the Sample into JEOL 1. Make sure you have logged into Badger. In order to use the left screen, you will need to be logged into Badger. 2. Make sure no sample is in the JEOL. Ways to see that are: The holder transfer arm should be fully retracted and the rod at the end of it should point to the end of the room away from the door ( Figure 7 ). On the panel at the door, the stage position should be home (100,100) and 4 green LEDs should be flashing Figure 7. Two ways to show there is no sample in the JEOL. Left image shows stage is about (100,100) and 4 green LEDs are flashing; right image shows the rod is pointing to stage empty. 3. Vent the load lock system. Turn the handle clockwise all the way and then press the VENT button. Venting will take a few minutes. Do not overturn; it should be horizontal when venting. Note: Venting will only work if the valve between load lock and main chamber is closed and the holder transfer arm is fully retracted ( Figure 8 ). 4. Remove the cassette. Carefully remove the cassette and do not bump the walls. Make sure your gloves are clean when handling the cassettes. Flush the cassette with the nitrogen gun. Note: If it is going to take you a few minutes to load your sample into the cassette or you need to do some pre-alignment, you should pump the autoloader back down to avoid absorbed moisture and increasing pump down times for the autoloader. Figure 8. Venting the load lock system 23

4 5. Load your sample. Sample loading should be done in designated area. Please keep this area neat & clean for all users. Load sample into the cassette, taking care to not bump the teflon walls or let the sample slide out. The red text on the cassette indicates which side is open-- your sample surface is pointing up in the cassette. Put your fingers under the handle and carry the cassette tilted as in the photos ( Figure 9 ). If you tilt it the other way, the holder might slide out. Insert the cassette into the load lock ( Figure 10 ). Make sure that the hook of the loading arm catches the handle on the holder ( Figure 11 ). If this is not the case, it might be impossible to retrieve the holder later, and the machine will have to be shut down. Figure 9. Proper way to hold the cassette and sample holder Figure 10. Cassette inside load lock Figure 11. Proper way to hold cassette 6. Pump down. Close latch, turn the lever clockwise to close, and press VENT button again to evacuate the autoloader. The Vent and IV open button (or one of them) will be flashing until the vacuum is ready. Pumping will take a few minutes - you can convert CAD design files in the meantime. You can check the pressure by activating the touch screen at the side of the JEOL. Take care to wake it up by touching it where the green arrow points ( Figure 12 ). Orange Yellow You can check the pressure while it is pumping by Figure 12. Touch screen at the side of the JEOL, where you can opening the Ldr. interface on the JEOL workstation. check the vacuum system.. When the vacuum is ready, everything From the menu, click Equipment-Status > ALD Unit turns from yellow to orange. Detailed Status. You can hit "Update" to get the most recent vacuum reading. 24

5 7. Insert the cassette. Once the system is pumped down to 4.0 x 10-3, the system is ready. Vacuum indicator lights will stop flashing. Press IV open button to open the gate valve between load lock and main chamber (you ll hear it opening). Push the arm in using only your finger (it doesn t need a lot of force). There should be a bit of friction, especially when you reach the end. Once inserted, turn the rod at the end of it towards the door to open the transfer arm and sample holder. Retract the arm again all the way; close the break. Close the valve between load lock and vacuum chamber by pressing IV open and keep pumping the sample down. Check on the display next to the door. The stage coordinates should be still (100,100), but only two LEDs should be flashing, since a holder is now loaded. 4. CAD and pattern file conversion. 1. Prepare you layout and convert to GDSII format file prior to arriving at the JEOL. 2. Convert GDSII pattern information to J52 v3.0 (.v30 file) with LayoutBEAMER software (available in the the Stanford Nanopatterning Cleanroom) a. Start LayoutBEAMER by typing "LayoutBEAMER" in a terminal window b. Click and drag functional elements from the menu into the workspace c. Standard conversion of GDSII files requires only IMPORT of the GDSII file and EXPORT of the v30 file. i. Drag IMPORT from functional elements into the workspace ii. A dialogue window will open prompting for the desired CAD file. Select the file from your directory iii. Drag EXPORT from functional elements into the workspace overlapping it with the IMPORT box. They will automatically be connected 25

6 iv. A dialogue window will open prompting you to select the destination and name for the output file v. Double check that the output file is JEOLV30 format vi. A dialogue window will open asking for export parameters: 1. Field Size 2. Shot Spacing vii. Press "Run" at the top of the BEAMER window. A green check mark indicates that the conversion is complete. viii. Double check your conversion with "View Layout" on the EXPORT function. d. Transfer your file to the JEOL computer. Use the network for file transfer to the patterns directory: /home/eb0/jeoleb/patterns/user/j52v30/ e. Optional. Copy premade SDF/JDF files to JEOL job directory: /home/eb0/jeoleb/job/user/username HELPFUL TIP: At any point in BEAMER, you can display the output of a step by right clicking on the function and selecting "View Layout"or by clicking the boxes in the element after the element has been run. 26

7 Preparing SDF & JDF Files The JEOL gets the details for a write from two files: the jobdeck (JDF) and schedule file (SDF) file. Both need to be adapted for each write and then compiled. This section contains information regarding some important parameters of these files. It s always easier to start from an existing SDF/JDF file. Jobdeck file (JDF) - specifies the shape and size of the substrate, arrangement of pattern data and character strings on the substrate, and the method and sequence for writing them. You can create the jobdeck file by using the text editor that you use for modifying and editing programs and text on the computer. Schedule file (SDF) - specifies the substrate number, jobdeck file name, calibration condition name, and various conditions for writing. The schedule file specifies the overall flow of the writing, whereas the jobdeck file specifies the details of the writing for each substrate. The example shown here has a very basic set of commands, but there are many more options to choose from. Contact a lab member for assistance. JDF File Specifying the type and size of the substrate, arrangement of chip patterns and characters on the substrate, and the method and sequence for writing them. Below is an example of a JDF file. 27

8 JDF Line JOB/W Note 1 PATH Note 1 ARRAY (X,#X,DeltaX) Note 2 ASSIGN Note 3 Layer Note 4 & 5 Function JDF files always begins with a line like this. The 3,3 means it is a 3 inch wafer with a 3 inch writing area, sets the center point. Everything goes inside a PATH command. Choose PATHs in your JDF file to define calibration routines before and during exposure. Do not change any existing items. You may add items. The array command sets up the array. Even if you are doing only one pattern, it is still an array. The command has two sets of numbers separated by a "/" The first are for the x-elements of the array, the second are for the y-elements The command works as follows: (offset x, # of elements in x, pitch x) / (offset y, # of elements in y, pitch y) The array always starts in the top left so enter the appropriate offsets The pitch is always a positive number Once the array is set up, this is where you assign something to each array point. NOTE: you can nest arrays by assigning arrays to array points. A generic assignment statement has the form: ASSIGN P(n) -> ((x,y),shot_table)) where: P(n) is a pattern which will be assigned later in the LAYER block. (x,y) is an array position (for example (2,1) shot_table is a table where you can assign the doses to different shot ranks when applicable. This is also done in the LAYER block This is the LAYER block. The example shown here has a very basic set of commands, but there are many more options to choose from. See the manual for a complete listing. Layer - This assigns a layer number. You can have multiple layers in your JDF file each with different patterns, currents, shot spacings, etc. P(n) - Here you assign the pattern name(s) that you've listed above. Type in the exact file name (cap-sensitive) for the pattern(s) you wish to expose. The file name is listed in single quotes as shown in the example version EOS (Electron Optics System) - The first number is the EOS mode. Typically it is either 3 (100 kv 4th lens) or 6 (100 kv 5th lens). The second number is the calibration table name Typically the names have the beam current in them The table name is listed in single quotes as shown in the example file and is also cap-sensitive. SHOT - Here we provide the shot spacing for this layer, in nm. Different layers can have different spacings. The command is typically written as A,# where A means that the shot time is automatically calculated (this is used almost all of the time) The # is the number of steps per pixel In Mode 3, there is 2 nm/step so the # = pixel spacing in 2 nm units (e.g., A,2 means 4 nm shot spacing) 28

9 In Mode 6, there is nm/step so the # = pixel spacing in nm units. RESIST X,Y,Z - This command sets the base dose for the exposure and can be modulated below if desired. The RESIST command takes in 2 numbers: The first is the area dose in mc/cm 2 The second is the line dose in nc/cm. Note: If you are not using the line dose, the second number is not important. It is recommended you use the same number in this case for safety. STDCUR - This is the current you intend on using for the exposure in na units. Remember that the machine will calculate the dwell times based on the actual current reading, not what you tell it in the JDF. The value here is for calculation purposes only and is not absolutely necessary, but recommended. MODULAT - You can set up shot modulation tables if necessary. Here you can assign a table to each name listed above. Follow the syntax from the example: TABLE_NAME: MODULAT ((SR#1, %_MOD),(SR#2,%_MOD),...) For each shot rank in your pattern file, you can assign a different modulation. Modulations are in % to be added to the base dose. Negative % values are permitted. SDF File Specifying Jobdecks to write, cassette numbers, entire chip pattern/character string arrangement on the substrate, various writing conditions, sequences, and writing control instructions. An SDF file can multiple blocks in it or just one. Below is an example of a SDF file. SDF Line MAGAZIN Function Every SDF file begins with the MAGAZIN command. You can enter a name for the job here if you wish. 29

10 #n An SDF file can multiple blocks in it or just one-- each block starts with a #n command. The n refers to the number of the shelf of the cassette you are using. The cassettes and their shelf-assignments are as follows: #1-3 inch wafer #2-4 inch wafer #3-4 inch mask #4-65 mm imprint template #5 - piece holder JDF The JDF command calls the JDF file you would like to write. The number after the comma refers XX. You can use multiple blocks to write different layers, different JDF files, or similar exposures in different spots, on different substrates or on different cassettes. OFFSET END If desired, you may use the OFFSET command to place the write in a specific spot, otherwise it will write in the center of the cassette. The END command can be followed by a number that tells the tool to leave the cassette from that shelf number on the stage after exposure. It is recommended to leave the cassette you are exposing on the stage. 30