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Plasma Etching of Polyimide Through an Aluminum Mask

IP.com Disclosure Number: IPCOM000041412D
Original Publication Date: 1984-Jan-01
Included in the Prior Art Database: 2005-Feb-02
Document File: 2 page(s) / 57K

Publishing Venue

IBM

Related People

Chapman, SG: AUTHOR [+2]

Abstract

Plasma etching of polyimide through an aluminum mask in an oxidizing atmosphere enables the entire mask to be converted to oxide and removed by a back door etch process. Alternatively, the thickness of aluminum can be increased so that some metal remains to protect the polyimide during subsequent RF sputter cleaning and to enable direct deposition of second level aluminum metallization. As shown in Fig. 1, an aluminum mask 10 of around 250-400 A thickness is used to define via holes 11 through a polyimide insulation layer 12 to enable contact with a first level aluminum metallization level 13 on the surface of wafer 9. Both aluminum layers are covered with thin layers 14 and 15 of native oxide.

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Plasma Etching of Polyimide Through an Aluminum Mask

Plasma etching of polyimide through an aluminum mask in an oxidizing atmosphere enables the entire mask to be converted to oxide and removed by a back door etch process. Alternatively, the thickness of aluminum can be increased so that some metal remains to protect the polyimide during subsequent RF sputter cleaning and to enable direct deposition of second level aluminum metallization. As shown in Fig. 1, an aluminum mask 10 of around 250-400 A thickness is used to define via holes 11 through a polyimide insulation layer 12 to enable contact with a first level aluminum metallization level 13 on the surface of wafer 9. Both aluminum layers are covered with thin layers 14 and 15 of native oxide. During plasma etching in an oxidizing atmosphere the oxide thickness in layer 10 is increased until all or most of the mask is converted to oxide. Both the mask and the native oxide can now be removed together by a so-called "back door etch" process in an aqueous solution of ammonium phosphate. As an alternative, where a second level of metallization is required, the thickness of layer 10 can be increased to 400-700 A . In this case, as shown in Fig. 2, not all the mask is converted to oxide and aluminum remains on the surface after the back door etch. This aluminum is used to protect the polyimide from surface damage during RF sputter clean prior to second level metallization. The aluminum also maintains the front surfa...