MEMORANDUM

To:            BSAC Faculty Directors

                Bill Flounders, Microlab Technology Manager

From:        Matthew Wasilik, BSAC, Senior Development Engineer

Subject:     2006 Year-End Report

Date:         19 January 2006

Cc:            Katalin Voros, Microlab Manager

                Professor Tsu-Jae King, Microlab Faculty Director

 

 

I have worked as a development engineer for the Berkeley Sensor & Actuator Center for nearly 7 years now. The following summarizes what I have accomplished during the past 12 months. 

I.        ENGINEERING, DESIGN, & DEVELOPMENT OF NEW EQUIPMENT IN MICROLAB

I worked to engineer and design a custom 172nm wavelength emission “stovetop,” low profile lamp assembly for integration into AMST equipment. The dielectric barrier discharge VUV (Vacuum Ultra Violet) lamp assembly was designed to enable investigation of novel photochemical processing and surface modification at AMST. The assembly design included a Suprasil port inclusion for the MVD AMST vacuum chamber lid, AMST lid modification, UHMW polyethylene insulator housings and electrodes, feedthroughs for the lamp, N2 purge and cooling ports, and exhaust lines for ozone deterrence. The design was modeled using Solidworks, AutoCAD, and MathCAD software. All assembly components were fabricated at the Cory Hall Machine Shop. Once the parts were completed I worked to test the design. Initially problems were encountered with proper lamp plasma discharge. After much troubleshooting, it was determined that the lamp power supply was faulty, and it was returned to Ivanhoe for repair. Another problem was found with the N2 cooling/purging. Upon introducing N2 into the system the lamp failed to discharge. Further review revealed that a naturally occurring N2 corona discharge was shorting out the high voltage electrodes. With power to the high voltage supply ON, air near the electrodes became ionized (partially conductive). But, with no forced flow input, ionization did not extend beyond a localized region. Thus no interference with the lamp discharge was observed in the absence of N2 flow. However, with N2 flowing an ionized region continued to grow instead of stopping at certain radius, and such opened a conductive path between the electrodes. The solution: A self adhesive silicone foam rubber (polysiloxane) strip was set between the top and bottom electrode inside the assembly and around perimeter of the lamp. The closed cell polysiloxane seal prevented the corona from migrating. After this adjustment had been made, a proper lamp discharge was observed. Ivanhoe Technologies’ claim of a 25mW/cm2 or higher lamp intensity at 172nm was supported by measuring the amount of ozone generated at AMST. The lamp design demonstrated its merit with the success of a photochemical deposition of thin layer oxide at room temperature. First a chemical vapor deposition of TEOS was performed on a silicon substrate at 35C. The substrate was then irradiated with the lamp for 20 minutes. Measurements at Sopra revealed that a 5 angstrom thick layer of oxide had formed, ostensibly due to volatilization and further siloxane linkage during the irradiation. Reports detailing all tests and experiments were written and submitted to supervisor. Results and further applications were also presented in detail at the Fall BSAC IAB.

I studied to become a superuser on the AMST equipment. This involved learning all operations procedures with the system; source change, plumbing configuration, etc. Such was clearly necessary in designing the new VUV system described above. I worked to troubleshoot recipe/equipment and software issues with this machine. I developed a successful standard APTS (Aminopropyltriethoxysilane) process for BSAC researchers, and likewise was further able to  implement a new process application for AMST: molecular vapor deposition of APTS for polyimide adhesion. The liquid “spin-on” variety of APTS has historically been problematic as an adhesion promoter for polyimide, especially when high resolution lithography is involved. I was able to demonstrate that by depositing a thin surface layer of APTS on silicon using molecular vapor deposition at AMST, much better results could be achieved: superior adhesion, lithographic resolution, and a much simplified process flow.

Due to clamping issues with the electrostatic chuck at Idonus’ hfvapor tool, I set about to design a new mechanical clamping mechanism. Because this new design holds wafers and dies with simple mechanical force, it is less susceptible to malfunction. The design is slated to be fabricated and integrated into the hfvapor equipment in early 2007.

II.       SUSTAINING OF EXISTING TOOLSET & SUPPLEMENTARY PROCESS DEVELOPMENT IN MICROLAB

Applied Material’s Centura DPS DT etch chamber continues to serve as a versatile etch system and research tool in the UCB Microlab. I continued to operate as an equipment and process engineer for this important system. In the spring of 2006, I worked to solve what became a particularly thorny issue with the DPS DT chamber. After performing a routine mechanical chamber clean due to an observed drop in etch rate, a poor rate-of-rise was encountered. Systematic troubleshooting of the chamber ensued. Processing tests, followed by strict monitoring of base pressure and rate of rise were catalogued. Strange chamber behavior was consistently observed and recorded. The tests seemed to reveal that DPS DT’s capacity to hold base pressure was linked to process gas introduction. Meticulous Helium leak detection tests ensued. The possibility of an atmospheric leak from the system’s o-ring seals was ruled out as a result of the He testing. Next all of the incoming gas lines were capped for ROR testing. And, the possibility of an internal or “virtual” leak due to process gas seals was precluded at that time. This was clearly not an easy problem to solve due to the amorphous symptoms that the machine continuously exhibited. Eventually though the evidence seemed to point to a leak in the cathode bellows, and a special He leak detection port test substantiated this. I proceeded to work to convince AMAT personnel that this was the source of the leak, and that the bellows needed replacement. The ordeal culminated when AMAT service personnel replaced the bellows in a laborious, 4-day undertaking. Through perseverance, the DPS issues were finally fixed. The ability to retain base pressure was verified, and a process recharacterization followed. The DPS DT chamber currently performs at its former, distinguished level.

I advised the Cory Hall Machine Shop concerning the definition and design of a hoist for the DPS DTCU (dome temperature control unit). Because the DPS chamber components weigh at least 45 lbs., a hoist mechanism greatly simplifies access to system internals as necessary. The completed hoist not only saves time with the dismantling of the chamber components, but it also obviates any risk of harm to personnel performing the breakdown procedure. Access to the inside of the DPS chamber is now straight forward.

The Suss MicroTec FC-150 flipchip bonder  is one of the more sophisticated, high performance equipments currently in the Microlab. It is capable of performing thermocompression substrate bonding of dies at 450C with a post-bond alignment accuracy of 1 micron. I continued to serve as engineering and process support on this equipment in 2006. Due to several former mishaps with the silicon carbide tooling FC150 uses (due to Labmember error), I worked to revise the training and qualification procedures with this special equipment. Dual training sessions, provided solely by me, are now required prior to qualification. The operations manual and written test were also further improved. Notwithstanding, the training sessions enable Labmembers to fully understand and make the best use of such a versatile and powerful machine. Examples of further engineering and process support that I’ve provided for flipchip include troubleshooting and fixing mechanical issues. After the bonding arm failed to “home” to its origin after use, I investigated and determined the cause to be a failure with a shaft coupling component. I specified, ordered, and further “machined-to-fit” a new coupling component. After reinstallation of the coupler the bonding arm performed to expectations again. There was also a small vacuum leak in the system that prevented tooling from being held with sufficient force. I worked to determine where the origin of the leak lay, and eventually brought in third party service personnel to help install new vacuum fittings. During the same service personnel visit, I had a 6 inch chuck installed onto the system. Flipchip is now capable of TC bonding dies to dies, 4 inch, and 6 inch wafers.

I worked to bring a standard parylene deposition process back online after issues with the cold trap were met. In my experience working in the University lab environment, I have found that equipment can never be left as stand-alone working items. There is always the requirement of consistent process sustaining and maintenance if good results are expected to be achieved. Some confusion had arisen among Labmembers over the years concerning process and operations with respect to parylene. I served to step in and (a) revise the operations manual for proper LN2 cold trap procedure, and (b) inform researchers of a lesser known process anomaly that was contributing to poor deposition results. A follow-up controlled recharacterization henceforth brought the parylene process back within expectations. The operations manual was updated likewise. Parylene currently working well for researchers.

I evaluated a near field holography (NFH) device when I learned of a “bolt-on” system that Suss offers for use with the MA6 (Ksaligner) equipment. The NFH system allows a contact printing  resolution of 200nm using a special mask. Although the system qualified as worthwhile, the acquisition of such a tool was ultimately put on hold. In an altogether entirely different investigation, I evaluated and composed a presentation table comparing Suss’ and other vendors’ probe stations. Included were manual, semi-automated, vacuum, and cryo probe stations. Recommendations were provided to supervisor.   

KSbonder is a wafer-level bonding tool, capable of performing both anodic and thermocompression bonds. I provided process evaluation, recipes, troubleshooting, analysis, and solutions in solving what have become frequent mechanical problems with this system. In one incident, a faulty encoder was found to have sabotaged the system’s z-axis motor. Although the encoder was promptly replaced with a new unit, it took some time before determining that the original encoder was proprietarily wired. Further problems with SB6 proprietary circuit boards were also sustained with this tool. Ksbonder is currently up and running, but plans are prudently in place to replace this problematic equipment.

I continued to provide extended technical support concerning maintenance and lithographic processing for Ksaligner. Aside from routine qualifications and solving process issues, I compiled a set of data concerning Mercury bulb life vs. intensity. The goal of this study was to determine if more lamp life at the equipment could be harnessed. It was concluded that the experienced bulb life was adequate. Further studies to potentially improve the cost-to-life ratio of lamp are in the works.

STS continues to be a deep reactive ion etch workhorse in the Microlab. Aside from routine training and qualifications I also provided process support for MEMS Exchange’s resident process engineer in an attempt to repair an SOI wafer set. In this particular case, MX had formerly, and improperly, processed the SOI wafers. The device layer had not properly been etched through to the buried oxide. This repair was challenging because MX continued the process flow after disregarding the aforementioned problem. Only at end of process was the problem discovered. The wafer set was sent to UCB Microlab for repair. I’m happy to report that wafer-recovery plan worked. The etches were successful, and the SOI wafers were salvaged. I furthermore worked to support Microlab engineering test requests with respect to STS processing.

I performed several engineering test requests using flipchip equipment for Prof. Richard Lander of UC Davis Physics Dept. The diamond substrate sensor chips that were bonded are slated to ultimately be installed at the Large Hadron Collider (LHC) at CERN. LHC is the largest particle collider built to date with planned collisions of up to 14 TeV.

III.      PROJECTS

The Oxford2 PECVD equipment experienced a failure with its wafer pedestal heater in October 2007. This pedestal essentially served to hold the substrate at the correct height under a plasma while heating the wafer in a vacuum. A vacuum sealing weldement on the pedestal was found to have had failed. This disallowed any further processing. After agreeing to become involved in the redesign of the pedestal, I first worked to understand the original cause of failure. Surprisingly, I found that under normal operating conditions the original pedestal design was doomed to fail.  With this in mind I worked to engineer and design a completely new pedestal, operating under a list of functional requirements. I used Solidworks, AutoCAD, and MathCAD to design the new system. The assembly is currently being fabricated in the Cory Hall Machine Shop, and I have continually interfaced with the machinists there in this undertaking. The new pedestal heater assembly is scheduled to be completed in early 2007.  

I developed a gas vapor pressure interactive spreadsheet. Common etch gas vapor pressures vs. variable temperatures are tabulated in the document. Applications of the spreadsheet are universal, but its original need stemmed out of setting the proper mass flow controller pressure regulation at Centura and other equipment. Anticipation and prevention of gas condensation in a delivery line is key.

I proposed an improved set-up for examining bond alignment integrity for flipchip, KSBA6, and KSBONDER bonding. The proposed system included a near-IR camera with a special video card for superimposing visible and infrared images. Soon thereafter Microlab dedicated a trans-illumination microscope for this purpose. Although I worked to further specify necessary components for completing the system, the project culminated with the donation of a integrated NIR camera system from MicroAssembly Technologies. The system will be formally characterized in early 2007.

I performed a comprehensive dry etch study and enumerated the information in a quick reference chart. This study assisted me in determining some lesser known aspects of dry etch mechanisms. Pertaining to the Centura cathode bellows replacement ordeal detailed above, I performed a C4F8 + O2 etch test in Centura DPS. My etch chart predicted that under the right conditions, C4F8 would actually etch silicon. The results of the test substantiated this theory. Due to the previous O2 leak in the bellows, former strange DPS etch behavior could now be explained. This evidence demonstrated how an atmospheric leak could have skewed previous DOE results. There was also the case of a residue from HBr/Cl2 based recipes appearing inside Centura DPS. It was determined from literature that some HBr or Cl2 based processes were likely to leave behind SiBrxOy or SiClxOy type residue. I used the etch chart to estimate a good starting point for a residue removal recipe. A new cleaning recipe was determined satisfactory after several experiments. Researchers using HBr were notified to use the newly developed cleaning recipe at DPS, the end goal being to alleviate residue buildup and increase equipment uptime.

IV.     OTHER  RESPONSIBILITIES

I served as default host for the weekly BSAC lunch seminar. And, although the list is not all inclusive, I provided Microlab tours for the following companies/organizations: Canon, Kodak, New EECS Faculty Candidates, Nortel, Raytheon, Samsung, Sony, and Toyota.

V.   FUTURE GOALS

Testing of  the electrostatic displacement microactuator that had formerly been fabricated in the Microlab’s CMOS baseline process will resume. A working device will have the capacity to test the mechanical properties of different materials, including modulus of elasticity, stress, and strain. New designs will also be submitted for future runs.

I will work to develop a standard liftoff process in the Microlab. The composition of this characterization has already been completed.

I will work to transfer BSAC’s Zyvex equipment, currently installed at Microlab’s JEOL, into The LBL Molecular Foundry’s LEO SEM. Such should allow for easier use of the Zyvex tool. MF has expressed a willingness to accept the system. A formal proposal will likely be needed to complete the transfer.