IE51854B1

IE51854B1 - Method of fabricating a metallic pattern on a substrate

Info

Publication number: IE51854B1
Application number: IE269181A
Authority: IE
Original assignee: Memorex Corp
Priority date: 1980-12-03
Filing date: 1981-11-17
Publication date: 1987-04-15
Also published as: DE3147401C2; FR2495192A1; IE812691L; FR2495192B1; JPS57120675A; JPH037756B2; DE3147401A1; GB2088412A; GB2088412B

Abstract

A method for fabricating a metallic pattern (6) eg of Ni-Fe alloy on a substrate (1) eg of SiO2 or glass consists of depositing an adhesive metal layer (2) and/or, plateable metal layer (3) which become(s) cathodic during etching, on a substrate. A narrow self-supporting border of photoresist (15, 16) is then applied. An anodic layer (4, 5 and 6) is then deposited and the photoresist removed. The adhesive and plateable metal material is etched in those areas (11, 12) previously covered by the photoresist and fresh photoresist (8) applied to encapsulate those areas (6) of the anodic layer which form the final pattern of interest. The unwanted anodic material (4 and 5) is then etched and the photoresist removed. The adhesive metal (2) may be Cr, Ti, Ta, W, Nb, V or Zr; and the plateable metal (3) may be Au, Pt, Pd, Cu, Ni or Ni-Fe. The invention overcomes the problem of severe undercutting of the cathodic layers (2 and 3).

Description

This invention relates to a method of fabricating a metallic pattern on a substrate.

When fabricating metallic patterns to form, for example the pole pieces of thin film magnetic recording heads or other high tolerance elements, new techniques have developed in electroplating and etching sheet materials whose composition and structure must be accurately controlled in order to achieve uniformity of performance. As taught in U.S. Patent No. 3,853,715 conventional masking techniques are quite ineffective in producing these elements.

What has been done in the prior art, in dealing with the plating of an alloy, such as Permalloy, a mixture of nickel and iron, was to plate the alloy in sheet form and then etch the sheet into desired patterns. However, when de15 posting films by electroplating, it is necessary to employ an adhesive layer between the alloy and the substrate that will support the alloy pattern. Since on certain adhesive layers it is not possible to electroplate, it is at times necessary to deposit a thin layer of fairly noble metal, such as Au, Pt, Pd, Cu, Ni, etc. on the adhesion layer.

Unfortunately, many adhesive and plating base layers that are compatible with the magnetic alloy in the substrate become cathodic to the alloy during etching, producing severe undercutting. For example, nickel-iron alloy is made adhesive to glass or silicon by interposing a thin layer of chromium or titanium between the nickel iron alloy and its associated substrate. As taught in U.S. Patent No. 61884 - 3 3,853,715, when such plural layers are etched, a severe undercut is observed in the etched material. Such undercutting is due to several separate effects taking place during etching and is neither reproducible nor controllable. The undercutting is due to the fact that the chemical etching is an accelerated form of corrosion. The corrosion is isotropic in principle? it should take place at equal rates both normal to the thickness of the etched metal and parallel to the thickness. This results in uniform undercutting of the metal. But due to the extremely small film thicknesses and pattern dimensions, the dimensions of the metal crystallites and grains cannot be ignored. The grain boundaries and grains etch at different rates, resulting in ragged edges.

During the terminal stages of etching, when the adhesive and/or the plating base metal layers are exposed, the dissimilar metals form a galvanic cell which results in extremely rapid etching of the anodic metal. In case of titanium and chromium, each of these metals passivate extremely quickly and becomes cathodic to nickel, nickeliron and to the metals of the iron group. When the metals such as platinum, palladium, gold or copper are present in the sandwich with the iron group metals, they act cathodically and the etching of the nickel, nickel-iron alloy, etc. is impossible to control.

Such undercutting is detrimental to the making of batch-fabricated arrays, such as the pole pieces of thin film magnetic heads.

U.S. Patent No. 3,853,715 recognizes the abovedescribed difficulties and teaches a solution. In order to achieve uniform etching of multi-layered electroplated metals without undercutting, the patent teaches placement of a very S18B4 - 4 narrow border of photoresist on top of the cathodic adhesive metal layer prior to electroplating the anodic metal.

The narrow border closes upon itself to serve as a frame, while a second photoresist layer is deposited and developed so as to be present only over the anodic material to be retained after etching. The second photoresist overlays the first photoresist to completely encapsulate the anodic layer. It is taught that subsequent etching of the surplus anodic material not needed in the ultimate pattern leaves the desi10 red portions of the pattern free from attack, avoiding the undercutting that occurs when two or more dissimilar metals are subject to a common etchant.

It has now been found that the prior art solution to the problem of undercutting is not entirely adequate. More specifically, it has been determined that after the electroplated anodic material, such as Ni-Fe alloy, has been etched away, the etchant then has access to the cathodic metal/adhesive layers and lateral etching occurs below the border photoresist. Once this begins to occur, the adhesive main20 taining the photoresiet in place loses its structural integrity and the photoresist begins to remove from the substrate further compounding the undercutting problem.

In order to substantially eliminate the problem of undercutting, the present invention places a border of photoresist to define the later formed eleotrodeposited anodic material, such as Permalloy. Although the prior art, namely, U.S. Patent No. 3,853,715, also uses a border of photoresist, the present invention differs therefrom in completely encapsulating the anodic material by photoresist which extends all the way to the inert substrate. Like the prior art, the present invention places the border of photoresist on the cathodic metal/adhesive layer so as to define the final metal - 5 product being produced. After the photoresist is formed, the anodic material is deposited on the cathodic metal/ adhesive underlayer and the photoresist then removed to expose said cathodic metal/adhesive underlayer only in those regions previously covered by the self-supporting border of photoresist. The cathodic meta1/adhesive underlayer is then removed in these exposed regions and photoresist is then reapplied extending all the way to the inert support and covering and thus encapsulating the anodic material intended as the final product.

By practicing the present invention, the photoresist acts as a substantially impermeable barrier to lateral etching, thus substantially eliminating the problem of undercutting. The corrosive etching is allowed to travel along the cathodic metal/adhesive underlayer, but when the etchant confronts the photoresist, a barrier is encountered terminating the etching process.

In the accompanying drawings :FIG. 1 and 2 show prior art processing steps as taught in U.S. Patent No. 3,853,715.

FIGS 3-7 show the sequential processing steps for the elimination of undercutting during the fabrication of a metallic pattern on a substrate by chemical etching according to the present invention.

FIG. 1 shows an electroplated sheet being processed whereby substrate 1 of silicon dioxide, glass or other similar self-supporting insulating material is caused to support a thin layer of adhesion metal 2, such as chromium, titanium, tantalum, tungsten, niobium, vanadium or zirconium. Such adhesive metal 2 is used primarily to make the main metal of interest such as Ni-Fe alloy, referred to as the - 6 anodic metal, adherant to the substrate. Since one cannot readily electroplate or electrolessly plate on such adhesion layer, it is desirable to sequentially metallize the adhesion layer 2 with readily plateable metal 3, such as Au, Pt, Pd, Cu, Ni, Ni-Fe or with a metal alloy. Such adhesion layer 2 and conductive layer 3 can be applied by sputtering, evaporating, or in any other manner.

According to the prior art, at this stage of the processing sequence, photoresist-7 and 17 is deposited by conventional lithographic techniques and the anodic material 6 such as Permalloy is deposited.

After the plating of the Permalloy layer 6, another photoresist layer 8 is applied by conventional photolithographic techniques to the top of anodic metal 6. The excess anodic material shown as areas 4 and 5 of FIG. 1 is then etched away, FeCl3 being a suitable etchant for Ni-Fe, the photoresist borders 7, 17 and 8 encapsulting the anodic material.

The prior art teaches that the photoresist prevents the active metal such as Ni-Fe from being etched, while in the presence of cathodic metal, such as chromium, titanium, gold, etc. After the more active metal 6 was etched with FeCl3, it is taught that the plating base metal 3 and adhesion layer 2 are etched with suitable chemical etchants. As stated previously, however, it has been discovered that etchants used to remove non-wanted anodic areas 4 and 5 together with plating base metal 3 and adhesion layer 2 laterally etch layers 2 and 3 below photoresist boundary areas 7 and 17 causing serious undercutting and loss of sharp edge etch30 ing as shown in FIG. 2 at 9 and 10. Once lateral etching begins, photoresist areas 7 and 17 lose their adhesion to supporting layers 2 and 3, which further aggrevates the - 7 problem. Furthermore, because of the difference in electrochemical potentials between the adhesion metal layer 2, such as titanium, and the anodic metal, such as Ni-Fe, a battery is formed as soon as the adhesive metal layer is exposed to the etchant, and the etch rate of the Ni-Fe is increased to such an extent that it makes control of the etching process very difficult if not impossible.

In order to overcome these difficulties, reference is made to FIGS. 3-7. FIG. 3 shows the processing which would be substantially equivalent to the prior art at an equivalent point in its processing cycle. More specifically, upon adhesive metal layer 2 and plateable metal layer 3 has been applied a very narrow border of photoresist shown as elements 15, 16. The anodic layer is then deposited upon metal layer 3 as a uniform coating shown as regions 4, 5 and 6. It is region 6 which is intended to be the pattern of interest as the final product and its configuration is defined by the very narrow self-supporting border of photoresist 15. 16.

Unlike the prior art, the border of photoresist 15, is now removed by any well known technique, thus exposing adhesive metal layer 2 and plateable metal layer 3 selectively in those areas which were defined by the very narrow self-supporting border of photoresist. As shown in FIG. 4, adhesive metal layer 2 and plateable metal layer 3 are selectively removed by any well known technique, such as by sputter etching or ion milling, resulting in voids 11 and 12 extending all the way to base 1 at 13, 14. These voids, preferably approximately 0.1 to 0.2 mils (2.5 to 5 microns) wide, define the final pattern or patterns of anodic material, which will become, for example, the pole pieces of thin film magnetic heads.

The voids 11, 12 are filled with photoresist 8 which is caused to completely encapsulate anodic material 6 on three sides with the fourth side of this region being encapsu lated by inert base 1.

As shown in FIG. 5, photoresist 8 can extend slightly beyond filled voids 11, 12. The excess anodic material 4, 5, such as electrodeposited Permalloy, is then etched away, FeCl3 being a suitable etchant for Fe-Ni alloy. Plating base metal 3 and adhesive layer 2 can be etched with suitable chemical etchants. Because photoresist 8 is in physical contact with support base 1, the etching of areas 4 and 5, as well as layers 2 and 3, does not in any way adversely effect the sharp edge integrity of the anodic metal or support layers 2 and 3 located within the boundaries defined by photoresist 8 (FIG. 6). The photoresist material 8 is lastly removed by any well known technique resulting in the final sharp-edged pattern, unattainable in the prior art (FIG. 7).

The teachings of U.S. Patent No. 3,853,715 including preferred photoresist materials as well as etchants are hereby incorporated by reference herein.

Claims

1. A method for fabricating a metallic pattern on a substrate comprising the steps of: a. depositing a first thin metallic layer on an inert substrate; b. depositing a self-supporting border of a given height of photoresist material on such metallic layer, said border outlining the configuration of a pattern of interest of a subsequent second metal to be deposited on said thin metallic layer, said subsequent second metal becoming anodic with said first metallic layer during its etching? c. depositing said second metal on said first metal? d. removing said self-supporting border of photoresist exposing said first thin metallic layer; e. removing said first thin metallic layer in those areas exposed in step d; f. depositing photoresist to substantially cover the pattern of interest and to substantially fill the regions previously occupied by the self-supporting border of photoresist to thus substantially encapsulate the second metal within the pattern of interest? and g. etching away all the anodic material not encapsulated.

2. A method for fabricating a metallic pattern on a substrate comprising the steps of: a. depositing an adhesive and/or plating base material which becomes cathodic during a subsequent etching process on an inert substrate? b. placing a self-supporting border of a given height of photoresist material on such cathodic material, said - 10 border outlining the configuration of a pattern of interest of subsequent anodic material to be deposited on said cathodic material; c. depositing anodic material on said cathodic 5 material; d. removing said self-supporting border of photoresist exposing said cathodic material; e. removing the cathodic material in those areas exposed in step d; 10 f. depositing photoresist to substantially cover the pattern of interest and to substantially fill the regions previously occupied by the self-supporting border of photoresist to thus substantially encapsulate the anodic material within the pattern of interest; and 15 g. etching away all the anodic material not encapsulated.

3. The method of Claims 1 or 2 wherein the anodic material not encapsulated is removed by chemical etching.

4. The method of Claim 1 wherein the first thin metallic 20 layer is removed by sputter etching in those areas exposed by removal of the self-supporting border of photoresist.

5. The method of Claim 1 wherein the first thin metallic layer is removed by ion milling in those areas exposed by removal of the self-supporting border of photoresist. 25 5. The method of Claim 2 wherein substantially all adhesive and plating base material is removed by sputter etching in those areas exposed by removal of the self-supporting border of photoresist.

6. 7. The method of Claim 2 wherein substantially all adhe30 sive and plating base material is removed by ion milling in - 11 those areas exposed by removal of the self-supporting border of photoresist.

7. 8. The methods of Claims 1 or 2 wherein the anodic material comprises an alloy of nickel and iron.

8. 9. A pole piece for a thin film head made by the method of Claims 1 or 2.

9. 10. The method of Claim 1 wherein said second metal is electroplated on said first metal.

10. 11. The method of claim 2 wherein said anodic material is electroplated on said adhesive and/or plating base material.

11. 12. The method of Claim 1 wherein said second metal is deposited upon said first metal to a height that is substantially no greater than the height of the self-supporting border of photoresist.

12. 13. The method of Claim 2 wherein said anodic material is deposited upon said cathodic material to a height that is substantially no greater than the height of the self-supporting border of photoresist.

13. 14. The method of Claims 1 or 2 wherein said narrow area is approximately 0.1 to 0.2 mils (2.5 to 5 microns) wide.

14. 15. A metallic pattern formed on a substrate produced according to any one of the preceding claims.

15.

16. A method of fabricating a metallic pattern on a substrate substantially as described with reference to Figures 3 to 7 of the accompanying drawings.