Aluminium passivation for TMAH based anisotropicetching for MEMS applications

Study on anisotropic silicon etching characteristics in various surfactant-added tetramethyl ammonium hydroxide water solutions

“…Accordingly, the SDSS-added TMAHW solution exhibits the poorest wetting ability, yielding the greatest roughness but the highest etching rate as etching temperatures are varied from 90 to 100 • C. Moreover, adding cationic ASPEG yields a reasonable etching rate of 0.7 µm min −1 and the lowest surface roughness of 4 nm in TMAHW solutions at an etching temperature of 100 • C. Another important finding is that adding surfactants to TMAHW solution will restrain the etching of aluminum. Many additives, such as silicon powder [26,33], acids (silicic acid (SiAc) [2,25], (NH 4 ) 2 CO 3 and (NH 4 )HPO 4 [33]), ammonium persulfate (APS) [25][26][27] and water glass (WG) [27] have been put into TMAHW solutions to improve the aluminum passivation and reduce the etching rate of the aluminum. Sarro et al [2] reports that the non-ionic surfactant, NCW-601A, does not affect the aluminum passivation in a 25 wt% TMAHW solution to which SiAc had been added.…”

“…Appropriate forced convection by external agitation and the modification of the essential properties of etchants can improve the etching rate and the roughness quality of the etched surface. For example, ultrasonic agitation has been presented to evaluate the silicon wet etching properties [11,17,18]; moreover, different additives, including isopropyl alcohol (IPA) [8,[19][20][21], IPA-pyrazine system [22,23], potassium ion addition (K 2 CO 3 ) [24], strong oxidizer (ammonium persulfate (APS)) [25][26][27], water glass (WG) [27], non-ionic surfactant (NCW-601A) [2,28], catalyst [29] and others, had been added to TMAHW solutions to modify the essential properties of the etchants and thus improve the anisotropy of the etching, to reduce the undercut or improve the roughness and the etching rate. IPA is the most popular alcohol additive for reducing the roughness of the etched (1 0 0) silicon plane and the undercutting of convex corners; however, it also reduces the etching rate [19], especially some crystal planes with indices that are higher than (1 0 0) [30].…”

SOI CMOS Compatible Low-Power Microheater Optimization for the Fabrication of Smart Gas Sensors

“…In order to keep aluminum as the first metallic layer under gold electrodes, effective passivation of aluminum has to be achieved, since pure TMAH attacks aluminum interconnections. Excellent results were obtained using optimized chemical passivation through additives in the etching solution [4], [5], as will be described in Section V.…”

<title>Fully CMOS-compatible low-power microheater</title>

“…Excellent results were obtained using optimized chemical passivation through additives in the etching solution[16]-[17]. SPIE Vol.…”