Integration Aspects of the Implementation of Through Silicon Vias (TSV) for CMOS Image Sensors

Abstract

One of the first device types to benefit from TSV implementation is the CMOS image sensor, an image capture device designed to combine high image quality within a compact form-factor that can be mass produced at low cost. End markets include mobile phones, PDAs and gaming consoles. STMicroelectronics is pioneering their production, based on ≤65nm CMOS technology, at its 300mm facility in Crolles. These sensors employ TSVs as part of a wafer level package allowing the camera module to be directly soldered to a phone PCB thereby saving cost, space and time to manufacture. SPTS's Versalis fxP system is being used to combine multiple TSV formation processes onto one platform including hard-mask deposition, hard-mask etching, TSV etching, partial PMD etching, dielectric liner deposition and spacer etching to define the area for the metal contact. All processes are carried out on a silicon wafer bonded to a glass carrier, through which the final device is illuminated. We will present a TSV silicon etch process for 70 μm x 70 μm Vias in a thinned 300mm silicon wafer on glass carriers with an etch rate uniformity of ≤±1% and sidewall scalloping in the range 80–210 nm. We will show that this process can be conveniently mixed in production with the various oxide etches. A PECVD dielectric liner deposited at <200 °C having excellent coverage, thermal stability and adhesion combined with a breakdown voltage >8 MVcm−1 and leakage current <1E-7 Acm−2 will also be described. Process integration aspects will be discussed using high resolution SEMS to show the key material interfaces in critical areas such as feature corners and along sidewalls. Furthermore the successful implementation of TSV technology on ST's CMOS image sensors will be demonstrated through a combination of electrical characteristics, parametric device data and overall device performance/reliability.