Integration of benzocyclobutene polymers and silicon micromachined structures using anisotropic wet etching
(Color online) (a) Cross section schematic of desired structure. CYCLOTENE and Cr/Au are deposited first. Metal is patterned, CYCLOTENE and SiN are etched in plasma etcher, and Si is etched in KOH. CYCLOTENE layer is masked by Cr/Au during Si etch process. (b) Schematic top view of test structures. The dimensions are not to scale.
(Color online) Optical micrograph of a die with /CYCLOTENE/ Cr/ Au films etched in a 20 wt%, 80 °C KOH solution. (a) The metal layers were peeled off after 10 min exposure to KOH and underlying CYCLOTENE layer was attacked by KOH. Sample was prepared by metal deposition on hard cured CYCLOTENE. (b) Shows negligible metal peel-off after 8 h of etching. The CYCLOTENE film was soft cured and covered with AP3000 prior to metallization, and hard cured afterwards.
(Color online) Scanning electron micrograph (SEM) of the cross section of the etched silicon structure in presence of CYCLOTENE and metal mask. CYCLOTENE was protected by metal mask during 8 h KOH etching.
(Color online) ToF-SIMS depth profiles of samples I and II. (a) Shows insignificant Cr concentration at the Au surface of sample I. (b) Shows three orders of magnitude Cr signal intensity increase after curing at 250 °C for 1 h for sample II. Curing has caused the Cr diffusion into Au.
(Color online) AES depth profile of sample I (a) and II (b) is performed to quantify the Cr concentration at Au surface. Cr concentration was found to be 1 at. % at the Au surface.
(Color online) High resolution ToF-SIMS images show lateral distribution of Cr and Au ions of sample II. From left to right: (a) Cr (116: ), (b) Au (229: ), (c) superposition of the first two ( in red, in cyan), (d) ratio, and (e) ratio. The field of view is and lateral resolution is about 0.2.
(Color online) Molecular structure of (a) CYCLOTENE monomer, (b) AP3000 (Vinyl-triacetoxy-silane) adhesion promoter.
(Color online) Positive SIMS profile of (a) sample III, (b) sample IV. The profile of Cr, Si, CrSiO, CrO, and SiH are shown. Adhesion promoter track marks are detected.
(Color online) Positive ToF-SIMS depth profiles with sputtering together with flooding of (a) samples III (unfilled graph) and IV (filled graph), (b) samples V (unfilled graph) and VI (filled graph). Diffusion of Si into Cr layer after hard curing is enhanced by using AP3000.
(Color online) Negative ToF-SIMS depth profiles with sputtering of (a) samples III (unfilled graph) and IV (filled graph), (b) samples V (unfilled graph) and VI (filled graph). Cr is oxidized at the interface and diffusion of C into Cr layer after hard curing is enhanced by using AP3000.
(Color online) Coefficient of thermal expansion (CTE) of materials used in the test structure.
(Color online) Interface study samples.
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