Heidelberg µpg 101 Laser Writer

Heidelberg µpg 101 Laser Writer Standard Operating Procedure Revision: 3.0 Last Updated: Aug.1/2012, Revised by Nathanael Sieb Overview This document will provide a detailed operation procedure of the Heidelberg µpg 101 laser writer. Formal Training is required for all users prior to using the system. Revision History # Revised by: Date Modification 1 Nathanael Sieb September 16, 2009 Initial Release 2 Nathanael Sieb May 20, 2010 Added sections on alignment 3 Nathanael Sieb Aug 1, 2012 Added section on fixed autofocus with air off 4 5 Document No. 4DSOP000X

Table of Contents General Information... 3 1. Safety Considerations... 3 1.1 Electrical... 3 1.2 Laser Radiation... 3 1.3 Safety Interlocks... 4 1.4 Servicing... 4 2. Write Lenses and Parameters... 5 3. Materials and Processing... 5 Operation Procedure... 6 1. Simple Exposure... 6 2. Manual Alignment... 10 3. Automatic Alignment... 11 4. Determining Energy... 14 5. Fixed Autofocus with Air Off... 16 Reference and Files... 20 Contact... 20 2

General Information The Heidelberg µpg 101 Laser Writer is a laser pattern generator with a 375 nm, 18 mw diode source laser. 1. Safety Considerations 1.1 Electrical The µpg 101 is fused for 10A. Electrical voltages of up to 230VAC and 120V DC are present within the system when it is connected and turned on. Except when loading media, never push objects of any kind through openings in the equipment. Dangerous voltage levels may be present. Conductive foreign objects could produce a short circuit resulting in a fire, electric shock, or permanent damage to the equipment. 1.2 Laser Radiation The µpg 101 Mask Writer employs a UV Diode laser (~375 nm) with a laser output power of 18 mw. Laser light exhibits many characteristics that are different from those found in conventional light 3

sources. Safe use depends on awareness of these characteristics and proper treatment of the laser instrument. If a beam passes directly into the eye, serious damage may occur, including vision loss. In addition, a beam remains coherent even when reflected, and it may cause eye damage even when contacted indirectly from reflective surfaces. 1.3 Safety Interlocks The µpg 101 protects operators from exposure to moving parts and laser energy while operating the equipment. All moving parts, lasers and their associated optics are enclosed within the lithography system. During operation, opening the cover lid will automatically stop an exposure. Users should never attempt to access the internal optics, electronics, or try to bypass the safety interlocks. 1.4 Servicing The following does not apply to users. When conditions require internal access to the lithography system (such as for servicing or troubleshooting by trained service personnel), the accessible energy of the laser is of the class 3B category. In such a case, personnel should observe all normal electrical and mechanical safety precautions as well as those applicable to lasers of this class. Both the laser head and power supplies contain electrical circuits operating at high voltages. If access to the laser interior or any power supply is necessary, exercise extreme caution to avoid contact with lethal high voltages. 4

2. Write Lenses and Parameters The system is equipped with one 4mm lens that can write 1 μm features. Table 1: Nominal parameters for the μpg laser writing system. Minimum structure size [μm] 1 Address Grid [nm] 40 Write speed [mm 2 /min] 3 Edge roughness [nm] 200 Line width uniformity [3,nm] 400 Alignment accuracy [3,nm] 500 Maximum Write Area [mm x mm] 30 x 30 3. Materials and Processing Many substrates and photoresists can be used with this system. AZ MIR 300 photoresist on a silicon wafer is commonly used. The process is summarized as follows: 1. Clean wafer. 2. Spin AZ MIR 703 photoresist at 4000 rpm for 60 sec. 3. Bake at 90 C for 90 sec. 4. Expose with upg at 15 mw and 40 %. 5. Bake at 110 C for 60 sec. 6. Develop in AZ MIF 300 developer for 90 sec. 5

Operation Procedure For easy use, the µpg 101 provides an Exposure Wizard that guides the operator through most steps of an exposure. 1. Simple Exposure This procedure is used when no alignment is necessary and the energy values are already known. 1. Prepare the design in cif, dxf, or bmp format. 2. Copy the design into the Designs folder on the PC. Use a USB stick to bring the pattern into the Clean Room. 3. Start the μpg 101 Exposure Wizard using the icon on the desktop. The startup screen will open showing the progress of the connection and initialization sequence. This takes approximately two minutes. Once the startup sequence is finished, click on Next. 4. Click on Load Design. 5. Select the design and click OK. Note that.bmp files will rotate 90. 6

6. A dialog window requests the size that was defined for one drawing unit during design creation. Enter the number and click OK. (often this number is 1) 7. Some design parameters are now listed, and a preview appears in the preview window. Clicking on the preview window will open the preview image in a larger window. Click on Next to continue. 8. Make sure the cover lid is closed (interlock lamp off). Click on the button Load Substrate. The stage will move to the loading position at the front of the machine. Wait until all movement has finished and the PC prompts you to load the substrate. 9. Open the cover lid. On the chuck, mount the alignment pins in appropriate locations. Make sure the resist coated side of the substrate is turned up, and position it against the alignment pins. Note that the coordinate system of the stage is oriented such that the x-axis corresponds to a backward-forward movement, while the y-axis corresponds to a left-right movement when standing in front of the machine. 10. Switch on the vacuum with the vacuum turn knob. Check whether the plate is really held tight by trying to move it slightly sideways. If a vacuum region bigger than 2" is required, activate the required vacuum region extension using the vacuum field adjustment screws. If the substrate is thin- 7

ner than, or of equal thickness as, the alignment pins, remove the alignment pins. CAUTION: If the alignment pins are left on the stage during an exposure of a thin substrate, the system can take serious damage! 11. Close the cover lid and make sure the interlock lamp is off. 12. Click OK. The stage will move to the center position, and the write head will move down until the focal point is on the substrate top. 13. Select No Alignment. (alignment procedures will be covered in another section) 8

14. Set the laser power and the power percentage for the resist being used. (e.g., 15 mw, 40% for 1.1-µm thick AZ 703) 15. Select whether you want the design to be inverted (usually not). 16. After all parameters and options have been set, click on Next to proceed to the Expose Design window. Here, all options and parameters are displayed for double-checking. 17. Choose whether or not to automatically unload the sample after exposure, whether to expose with fixed autofocus (used for small samples), and whether to write in unidirectional mode or not (unidirectional will produce better results but take double the time). 18. Click on Expose to start the exposure. During an exposure, the exposure status is shown online in the window. To interrupt an exposure, click on the red "BREAK" label in the Expose Design window. 19. After exposure is finished, press Yes to unload the sample. The write lens is retracted to the upper position, and the stage moves automatically to the unloading position. 20. Wait until all movement has stopped. Open the lid, switch off the vacuum with the vacuum turn knob and carefully lift the substrate off the chuck. 9

21. Develop, etch and strip the substrate according to the directions of the resist manufacturer and the manufacturers of the chemicals used. 2. Manual Alignment A manual alignment procedure can be used to input an intentional offset. 1. Load the sample and pattern as described in section 1, step 1 12. 2. Select Manual Alignment. 3. Set the laser power and the power percentage for the resist being used. (e.g., 15 mw, 40% for 1.1-µm thick AZ 703) 4. Select whether you want the design to be inverted (usually not). 5. Select the approximate wafer size. 6. The manual alignment window displays a graphic of the mask (i.e., the substrate) with the pattern in the center. 7. If known, you may immediately enter the x and y offset in μm and press Offset. 10

8. If you need to center your pattern on a specific structure, open the Camera window. The arrow buttons and step size may be used to move around the substrate. Clicking on a location in the live view will move that spot to the center. When the desired structure is centered, click Accept Offset followed by Offset in the next window. 9. If you wish to center your pattern on the substrate, select Find Plate Center and Start. When the procedure is complete, select Accept Exit Offset. This procedure uses the air autofocus system to find the edges of the substrate. 10. After all parameters and the manual alignment have been set, click on Next to proceed to the Expose Design window. Here, all parameters and the manual offset are displayed for confirmation. 11. Complete the exposure as described in section 1, step 17-21. 3. Automatic Alignment The automatic alignment procedure can be used to align a new pattern to an existing pattern on the substrate. The procedure can be used to input an offset (one-point) or a rotational (two-point) alignment. 1. Load the sample and pattern as described in section 1, step 1 12. 2. Select Auto Alignment. 11

3. Set the laser power and the power percentage for the resist being used. (e.g., 15 mw, 40% for 1.1-µm thick AZ 703) 4. Select whether you want the design to be inverted (usually not). 5. Click New to design a new alignment procedure. If you have an existing alignment procedure, you may load it and skip to step 15. 6. To create a new alignment mark, select Create Mark to open the camera window. If you already have created your marks, you may skip to step 11. 7. Find the alignment mark on the substrate. 8. Click Make. Center the box over your mark. Click Learn. 9. Run a Test Search to ensure that the software can find your alignment mark. 10. Save the mark and give it a unique name. 11. Click Add Mark to add an existing alignment mark. 12. Select the image of your mark. Enter the x and y coordinates that the mark correspond to in your pattern. 12

13. Up to 2 marks can be added for offset and rotational alignment. 14. Save the alignment procedure. 15. Click Next to proceed to the expose window. 13

16. Perform the Test Alignment procedure to ensure that your alignment process works. You may need to use the camera window to locate the general vicinity of the alignment mark. The mark needs to be in the camera window in order for the alignment procedure to work. 17. The alignment results will be displayed and the exposure can be completed as described in section 1, step 17-21. 4. Determining Energy The photoresist, thickness of resist, and reflectivity of the substrate, will all affect the energy required for exposure. In order to determine the correct energy, a series of standard patterns must be written at different energies (both laser power and percentage). In general, it is better to aim for a higher laser power with a lower percentage (similar to pixel dwell time). A very low laser power (<3 mw) will result in a low signal-to-noise ratio. An energy series is written as follows: 1. Select the Expose Energy Series function in the Tools menu. 2. Enter the laser power, which corresponds to the 100% pixel strength, and click OK. 3. Choose whether to expose a wide range energy series or a small one. The coarse series exposes 10 fields from 10% until 100% pixel strength, with steps of 10%. 14

4. For the fine series, define the starting percentage (1%-91%). With increments of 1%, 11 exposures will cover a smaller but finer area of exposure energy. 5. Click Load to load sample. Load the stage with a test sample, on which the energy series should be exposed. Load a test sample in the center position of the stage. The size of the test sample should be at least 25 mm x 25 mm. 6. The chosen energy series parameters are displayed again for confirmation, and the exposure procedure can be started with Execute. 7. After the series has been finished, unload the test sample, develop, and examine the exposures to determine the best energy. 8. Press Exit to return to the previous screen. The dimensions of the performance pattern are displayed below: 15

5. Fixed Autofocus with Air Off With large area grayscale structures written in AZ 9260 resist, it has been observed that the air from the autofocus mechanism will locally change the properties of the resist near the writehead. To avoid the inconsistency this problem causes, the autofocus must be disabled. NOTE: This procedure is dangerous to the tool and can ONLY be performed after additional training. 1. Load the sample and pattern as described in section 1, step 1 12. 2. Select Manual Alignment. 3. Set the laser power and the power percentage for the resist being used. (e.g., 15 mw, 40% for 1.1-µm thick AZ 703) 4. Select whether you want the design to be inverted (usually not). 5. Select the approximate wafer size. 6. The manual alignment window displays a graphic of the mask (i.e., the substrate) with the pattern in the center. 16

7. Open the Camera window. Move to the area of the sample you wish to write. The arrow buttons and step size may be used to move around the substrate. Clicking on a location in the live view will move that spot to the center. When the area is located, click Focus. The writehead is now focused at this location. Click Accept Offset followed by Offset in the next window. 8. Open the TeraTerm terminal program and press Ok for New Connection. 17

9. Login with the username and password upg101. 10. Enter the command: hw afix+ 11. The autofocus mechanism is now fixed. Turn off the valve for the incoming air (picture below shows on position). 18

12. After all parameters and the manual alignment have been set, click on Next to proceed to the Expose Design window. Here, all parameters and the manual offset are displayed for confirmation. 13. Activate the options to automatically unload and expose with fixed autofocus. 14. Choose whether to write in unidirectional mode or not (unidirectional will produce better results but take double the time). 15. Click on Expose to start the exposure. The system will give an error stating Writehead not in Focus! Press OK to continue anyway. 16. During an exposure, the exposure status is shown online in the window. To interrupt an exposure, click on the red "BREAK" label in the Expose Design window. 17. After exposure is finished, the write lens is retracted to the upper position, and the stage moves automatically to the unloading position. 18. Wait until all movement has stopped. Open the lid, switch off the vacuum knob and carefully lift the substrate off the chuck. 19

19. Turn on the air supply to the system before any further steps. 20. Develop, etch and strip the substrate according to the directions of the resist manufacturer and the manufacturers of the chemicals used. Reference and Files Heidelberg µpg 101 Manual and training notes. Contact Questions or comments in regard to this document should be directed towards Nathanael Sieb (sieb@4dlabs.ca) in 4D LABS at Simon Fraser University, Burnaby, BC, Canada. 20