Kasper Mask Aligner Manual 1. Introduction The Kasper Wafer Alignment System is an integrated optical-mechanical, pneumatic-electrical system which allows accurate alignment of sensitized semiconductor wafers with a mask and exposes them to ultraviolet radiation. It is a high precision piece of equipment and should be treated with care. It is imperative that you understand the machine completely before proceeding. Keep in mind that a great threat to long life for the Kasper Aligner is dirt. The exposure source is a 200 watt high pressure mercury arc lamp. It is left on at all times. Do NOT turn it off. If the lamp is off, do not turn it on as there is a special procedure for relighting. The N2 purge switch, labeled purge under the right hand cowling of the machine, has to be on when the machine is in use. Turning it off will cause the aligner to malfunction. 2. Operating Procedure 1. Preliminary Set-Up 1. You will find the machine in standby mode. 2. POWER, PRESS CONT, MASK CLAMP, and MASK LOAD buttons should be lit. 3. TURN ON THE VACUUM by operating the toggle valve mounted on the table to the right of the machine. A hissing sound indicates that the vacuum is on. 2. Alignment System and Turret Positions The alignment system consists of a precise X-Y stage which moves the wafer and mask together (scan) and a second X-Y stage which adjusts the wafer position with respect to the mask (align). Incorporated with the "align" stage is a rotating knob for angular alignment. Each stage is controlled by a hand disc. There are two degrees of alignment for the "align" stage. Shifting from 150:1 ratio to 3:1 ratio is done by pressing the button on the right-hand disc control. Rotational alignment is accomplished with either coarse linear actuated motion or a 700:1 rotational fine adjustment. There are three positions for the optical turret. A "Row and Column" position allows coarse alignment with a lower power, single field microscope. A "Split Field" position allows fine alignment at a high power by simultaneous viewing of two separate areas of the wafer. The "Expose" position provides a reflector to direct the UV light down to the wafer.3. Centering the Wafer with Respect to the Mask Holder Opening 1. Press the VISUAL ALIGN switch. The top portion of the mask aligner will automatically rise. 2. Slide the wafer chuck assembly out all the way towards you. With tweezers, center a test dummy wafer on the chuck (the dummy wafer should be found next to the Kasper). Align flat against the white plastic flat-finder. 3. Raise the plastic flat-finder out of the way. Slide the chuck assembly all the way back. Lift off the mask support plate. 4. Press the WAFER LOAD switch. Adjust the position of the wafer, using the second X-Y stage hand disc controller (on the right side of the Kasper), so that it is centered with respect to the opening in the mask holder. 4. Centering the Illumination Over the Mask and Wafer 1. Press the VISUAL ALIGN switch to lower the optical head. 2. Rotate the optical turret to the EXPOSURE position. Press the CONTACT switch. 3. Press the MANUAL EXPOSE button. Check that the illumination is centered over the mask holder opening. If it is not centered, adjust this with the first X-Y stage hand disc controller (on the right side of the Kasper), which moves the mask and the wafer together. 5. Loading the Mask 1. Press the VISUAL ALIGN switch to raise the top portion of the mask aligner. 2. Lift off the mask support plate and place your mask in the vacuum chuck opening with the emulsion or chrome side facing down (and load the masks always with the letters to the left). The mask should rest against the pins in the upper left corner. Center the mask support plate over the mask and press the MASK CLAMP button to fix mask plate to mask. Center mask and mask plate over the opening and press MASK LOAD to fix assembly to the mask vacuum chuck. 6. Gross Alignment of the Mask 1. Press the VISUAL ALIGN switch to lower the optical head. Turn up the power for the microscope illuminator. Turn the optical turret to the "Split Field" position. The alignment marks should be visible on each half of the split field image (adjust the focus, if necessary, with the knob on the back left of the optical head). If you don't see both of the alignment marks, or if the marks are not centered in the image field, align the mask as follows: 1. Press the MASK LOAD switch to release the mask from the vacuum chuck. 2. Move the mask plate (with the mask) very slowly and carefully until you find and center the alignment marks in the image field. 3. Press the MASK LOAD switch again to fix the assembly to the vacuum chuck. 7. Loading and Aligning the Wafer 1. Slide the wafer vacuum chuck assembly out all the way towards you. With tweezers, center your wafer on the chuck. Align flat against the white plastic flat-finder. Push the wafer chuck 1 or 2 inches and listen to the click, this is the vacuum coming on. Raise the plastic flat-finder out and fully push the assembly back under the mask. 2. Press WAFER LOAD switch and the wafer will be raised under the mask and held in place. The SEP button should light, indicating that there is a separation between the wafer and the mask. The instrument goes into separation mode automatically.3. Turn the optical turret to the "Row and Column" position and check that the instrument is in the SEP mode. 4. Roughly align the wafer pattern to the mask pattern in the desired position by first making the rotation adjustment and then the X-Y adjustment. 5. Turn the optical turret to the "Split Field" position to perform fine alignment of the wafer to the mask. Perform fine rotational and X-Y alignment with the rotation knob and X-Y alignment disc until the alignment marks on the wafer are perfectly centered within the mask alignment marks. 6. When alignment is complete, press the CONTACT button which brings the wafer into contact with the mask and actuates the positive pressure. Check to make sure the alignment is correct. If an adjustment is necessary, press the SEP button and realign. 8. Exposing the Wafer 1. Rotate the optical turret to EXPOSURE position, check the timer for correct setting, and press the MANUAL EXPOSE button. You can enter 3 digits on the timer for exposure. Be aware that the last number is in units of .1 seconds (e.g. a setting of 100 is 10.0 seconds!). The maximum timer setting is 99.9 seconds. Exposure cannot occur
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