Browse Prior Art Database

TIN ETCHANT

IP.com Disclosure Number: IPCOM000005694D
Original Publication Date: 1988-Oct-01
Included in the Prior Art Database: 2001-Oct-26
Document File: 1 page(s) / 46K

Publishing Venue

Motorola

Related People

William H. Lytle: AUTHOR [+2]

Abstract

A chemical etchant is described for etching tin which does not attack the photoresist or underlying metal. In addition, this etchant does not passivate the underlying metal. This process uses readily available materials; generates no new wastes; and the reaction product is soluble in water.

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M-ROLA Technical Developments Volume 8 October 1988

TIN ETCHANT

by William H. Lytle and Earl D. Fuchs

   A chemical etchant is described for etching tin which does not attack the photoresist or underlying metal. In addition, this etchant does not passivate the underlying metal. This process uses readily available materials; generates no new wastes; and the reaction product is soluble in water.

   The objective is to provide a tin etchant which does not etch the passivation or undercut the underlying metal layers. The solution consists of ammonium persulfate [(NH&%OB], hydrofluoric Acid [HF], and water[H>O]. The ammonium persulfate oxidizes the tin forming a resultant tin oxide [Sn(OH),]. The tin oxide is then dis- solved by the hydrofluoric acid forming tin fluoride (SnF.1 which is soluble in water. The reaction equation is:

(NH+S20a + Sn + 3H20 + Sn(OH)d + (NH+SO, + H&GO3

Sn(OH), + 4HF ---) SnFa + 4H10

   This process was tested using metallized 1OOmm silicon wafers processed through the normal mesadiode steps through the top metal. The wafers were then evaporated or plated with tin over the entire surface and patterned with photoresist. Using the etchant, the wafers were etched with the following etch rates for different thicknesses.

Sn Thickness

20 kA evaporated 40 kA plated 100 kA plated 200 kA plated

Etch Rate

138 Alsec 133 A/set 175 A/set 300 Alsec

In the figure, the final product is illustrated. The top metal layer consists of: 1 kA titanium (Ti), 500 A nickel (Ni)...