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METHOD OF IMPROVING STEP COVERAGE OF ELECTROPLATED PATTERNED MATERIALS

IP.com Disclosure Number: IPCOM000025674D
Original Publication Date: 1987-Apr-30
Included in the Prior Art Database: 2004-Apr-04
Document File: 4 page(s) / 186K

Publishing Venue

Xerox Disclosure Journal

Abstract

Devices such as integrated circuits, printed circuit boards, and thermal printheads require electrical conductors. These conductors require some form of passivation to prevent shorting or to protect the leads and devices from the immediate operating environment or ambient conditions in general.

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Page 1 of 4

XEROX DISCLOSURE JOURNAL

METHOD OF IMPROVING STEP COVERAGE OF ELECTROPLATED PATTERNED MATERIALS
James F. O'Neill

Proposed Classification

US. C1.291625 Int. C1. H05k 3/12

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Fig. 1

NORMAL PROCESS REVERSE PROCESS WITH MODIFIED

NOVALAK - BASED PHOTORESIST

DEVELOP

PLATE

STRIP RESIST AND BASE

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30

20 I I //I I

22

32

Fig. 2

Volume 12 Number 2 March/April 1987 61

[This page contains 1 picture or other non-text object]

Page 2 of 4

METHOD OF IMPROVING STEP COVERAGE OF ELECTRO- PLATED PATTERNED MATERIALS (Cont'd)

Devices such as integrated circuits, printed circuit boards, and thermal printheads require electrical conductors. These conductors require some form of passivation to prevent shorting or to protect the leads and devices from the immediate operating environment or ambient conditions in general.

Three methods of forming conductors are presently prominent in the industry. In one method, a thin film is blanket deposited on a substrate. The substrate is patterned with resist and then etched to form the desired electrical conductor pattern. This process yields properly tapered walls, although the walls have rather rough edges. Problems are encountered with this method as linewidths shrink more rapidly than film thicknesses. A selective etchant must be used, so as not to etch underlying films.

In another method, a conductor material is deposited onto a substrate on which a photoresist pattern has previously been defined. The resist pattern must have an overhang profile for success. Such overhang profile may be achieved by either a method of reverse imaging of the positive resist, or the three-layer method of applying resist 12, an unreactive film 14, and a thin resist. In Figure 1, the resist 12 and the unreactive film 14 on substrate 10 are patterned, so that the unreactive film is used for a mask to expose the initial resist. The resist 12 is overetched to form an overhang by the unreactive film
14. The conductor material (not shown) is then deposited, contacting the substrate only where desired, i.e, where the resist has been removed. Because of the overhang, deposited material is discontinuous between the substrate and that on the overhang material. The resist is stripped, removing the unwanted material with it and leaving the desired pattern. This process yields tapered side walls.

A third method is electroplating, in which a substrate is initially blanket deposited with a conductive film, followed by patterning of a resist. The substrate is electroplated and the resist removed. Electroplating is prominent where precious metals or expensive materials are used or where large thickness to linewidth ratios are required. A typical resist profile, however, causes a negative slope to be formed during the plating operation. This negative slope leads to voids and poor step coverage of ensuing vapor deposited insulators. Refer to the normal process in Figure 2. This poor step coverage can lead to shorts between layers of conductors or l...