In order to address new technology requirements, Spray Photoresist Dispense Processing has been developed to aid in the manufacturing of High Aspect Ratio devices. The choice of process pump to affect the Spray Process is critical to the results, as the dispense uniformity is greatly influenced by the type of pump used to supply fluid to the Ultra Sonic dispense nozzle. Previous methods used had insufficient ramp rate of the dispense output. The pressure on demand dispense unit has excellent ramp rate to required flow rate, and the Patented Control Technology provides stability within tolerance to improve overall uniformity. The implementation of this method will improve cycle time and reduce the processing cost of wafers.
Defectivity requirements are constantly put to new standards, even in older
factories where new toolsets aren't a feasible alternative. To prolong the life of this
equipment, Integrated Designs has created the digital dispense valve system. Tracks with
older pump systems are plagued with repeatability and suckback issues that are key
factors in eliminating or reducing defectivity. The digital dispense system not only
increases the pump's capability to hold suckback across significant amounts of idle time
regardless of viscosity, but also allows for lower dispense volumes due to more
repeatable dispenses. Combining these factors results in a significant decrease in
defectivity with only minor equipment additions, that previously would have required
costly pump and track upgrades.
Resist minimization techniques have been around since the mid-1990s. As the volume decreases, the accuracy of the systems must increase. These inaccuracies can negate any savings that could potentially be acquired due to rework or even scrap. This has become a problem for older factories with pumps that are not accurate below 2.0ml. In order to help with these issues, Integrated Designs has created the digital dispense valve. This mechanical addition can prolong the life of a pump and saving the costly pump replacement scenario. The digital dispense valve increases the accuracy at lower dispense volumes and give more repeatable suckback control than was previously available for this generation of pump systems.
The via-first process is unique by the fact that a material is needed to fill the vias to some arbitrary value, with little or no isolated-dense via bias so that the underlying layer underneath the via is protected from the trench etch step. Secondly, this material may have to coat over the surface of the wafer with some chosen thickness again with minimum or no bias to maximize the trench photolithography process window. Finally, the material must be easily removed from the via after the trench etch with no residue, crowning, or fencing. The ideal via fill material would be able to perform all the above listed parameters, but no perfect solution exists yet. The etchback process that is discussed herein, called the solvent etchback (SOLVE) process bypasses these lengthy modules, will fit within today’s manufacturing processes and will have little impact on throughput of the photobay coating tools. The process utilizes industry standard photoresists solvents such as PGMEA, Ethyl Lactate, PGME and existing solvent prewet dispense nozzles in the BARC coater module. Also, this process only requires one material that can both fill the via and act as a BARC during the trench photo step with a user defined thickness on top the wafer that will minimize light reflections coming from the substrate. The process flow for the SOLVE process is: 1. Coat a wafer with a thick BARC to planarize the wafer and minimize isolated-dense bias. 2. Bake the BARC so that it is partially crosslinked.
3. Apply a solvent to the wafer and etchback the BARC to a thickness that suits the trench photo step. 4. Bake the BARC to fully crosslink the BARC. Process variables that can have an affect on the SOLVE process are the softbake temperature and time to modify the BARC thickness on the wafer. Dispense parameters that will modify the post-etch uniformity of the wafer include the dispense time, dispense spin speed and the IDI M450 dispense pressure. The repeatability of the process can be modified by changing the solvent spin off speed and acceleration.
A design of experiment (DOE) was implemented to show the effects of various point of use filters on the coat process. The DOE takes into account the filter media, pore size, and pumping means, such as dispense pressure, time, and spin speed. The coating was executed on a TEL Mark 8 coat track, with an IDI M450 pump, and PALL 16 stack Falcon filters. A KLA 2112 set at 0.69 μm pixel size was used to scan the wafers to detect and identify the defects. The process found for DUV42P to maintain a low defect coating irrespective of the filter or pore size is a high start pressure, low end pressure, low dispense time, and high dispense speed. The IDI M450 pump has the capability to compensate for bubble type defects by venting the defects out of the filter before the defects are in the dispense line and the variable dispense rate allows the material in the dispense line to slow down at the end of dispense and not create microbubbles in the dispense line or tip. Also the differential pressure sensor will alarm if the pressure differential across the filter increases over a user-determined setpoint. The pleat design allows more surface area in the same footprint to reduce the differential pressure across the filter and transport defects to the vent tube. The correct low defect coating process will maximize the advantage of reducing filter pore size or changing the filter media.