Browsing by Subject "Semiconductor fabrication"

Now showing 1 - 3 of 3

A novel fabrication process for CMUTs in air
(2017-12) Hord, Samuel Kay; Hall, Neal A.; Wilson, Preston S
A novel fabrication method for producing capacitive micromachined ultrasonic transducers (CMUTs) is presented. The process uses conductive silicon on insulator (SOI) substrates to produce an unstressed transducer diaphragm. By etching release holes through the device layer and selectively removing the underlying buffered oxide (BOX) layer, an ultrasonic transducer can be made using only two photolithography steps. The process is described in detail, including models predicting the modal behavior and the collapse voltage of the device. The acoustical behavior of a perforated plate over a sealed cavity is modeled using mechano-acoustical circuit analysis. The device is found to produce sound despite the perforations so long as the holes are sufficiently small and the frequency of operation is sufficiently high. A pitch-catch measurement verifies the transduction of the device. To the author’s knowledge, this is the simplest method for CMUT fabrication to date.
Design of particle mitigating wafer chucks for yield enhancement
(2014-08) Westfahl, Andrew Ian; Sreenivasan, S. V.; Crawford, Richard H.
As the semiconductor industry drives down the minimum feature size on wafers to increase performance and device density, the necessary site flatness of a standard 26 x 33 mm field becomes much more stringent. A significant unresolved cause for non-planarity is particle contamination at the interface of the wafer substrate and the wafer chuck. The result is an out of plane distortion that can affect a significant portion of the wafer resulting in device yield loss. This research looks at two methods for mitigating the effects of particle contamination. The first method investigates using an in-situ cleaning approach in a wafer chuck to eliminate particles. This concept is called a Particle Eliminating Pin (PEP) chuck. The second method proposes enhancements to a wafer chuck design based on compliant mechanisms resulting in a chuck that is tolerant of particle contamination, referred to here as the enhanced compliant pin chuck (E-CPC). The PEP chuck was explored relative to well-established methods for removing back-side particles and demonstrated it could eliminate an additional 18.5% of particles that could not be removed via the well-established methods. Additional potential effectiveness of a PEP chuck is also discussed based on future improvements. A scaled prototype of the proposed new design of the E-CPC was fabricated and tested as well. The prototype validated most of the proposed improvements but failed to maintain the mechanism’s rotational requirement. With the understanding gained from this design and experimental research a future design of the E-CPC has been proposed in the future research section such that this new design can achieve all the proposed goals while still maintaining the required mechanism rotation.
Modeling and model based fault diagnosis of dry vacuum pumps in the semiconductor industry
(2013-12) Choi, Jae-Won, active 2013; Bryant, Michael David
Vacuum technology is ubiquitous in the high tech industries and scientific endeavors. Since vacuum pumps are critical to operation, semiconductor manufacturers desire reliable operations, ability to schedule downtime, and less costly maintenance services. To better cope with difficult maintenance issues, interests in novel fault diagnosis techniques are growing. This study concerns model based fault diagnosis and isolation (MB-FDI) of dry vacuum pumps in the semiconductor industry. Faults alter normal operation of a vacuum pump resulting in performance deviations, discovered by measurements. Simulations using an appropriate mathematical model with suitably chosen parameters can mimic faulty behavior. This research focuses on the construction of a detailed multi-stage dry vacuum pump model for MB-FDI, and the development of a simple and efficient FDI method to analyze common incipient faults such as particulate deposition and gas leak inside the pump. The pump model features 0-D thermo-fluid dynamics, scalable geometric representations of Roots blower, claw pumps and inter-stage port interfaces, a unified pipe model seamlessly connecting from free molecular to turbulent regimes, sophisticated internal leakage model considering true pump geometry and tribological aspects, and systematic assembly of a multi-stage configuration using single stage pump models. Design of a simple FDI technique for the dry vacuum pump includes staged fault simulations using faulty pump models, parametric study of faulty pump behaviors, and design of a health indicator based on classification. The main research contributions include the developments of an accurate multi-stage dry pump model with many features not found in existing pump models, and the design of a simple MB-FDI technique to detect and isolate the common faults found in dry vacuum pumps. The proposed dry pump model can pave the way for the future development of advanced MB-FDI methods, also performance improvement of existing dry vacuum pumps. The proposed fault classification charts can serve as a quick guideline for vacuum pump manufactures to isolate roots causes from faulty symptoms.