JPS607432A - Improved formation of fine metal wire - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates generally to an improved method of forming ultrafine metal wires. More generally, the present invention provides submicron (s.
ub-micron) Expert in how to make metal wire.

Background of the invention Is the width of the invention thinner than 1 micron? <'s culm or trace ff: It is economical and can be grown with just one ounce of trust (<
-4- It is often necessary or desirable to do so. For example, the production of high frequency SAW devices having transducer fingers four wavelengths wide requires lines on the order of microns or less in width when using a typical piezoelectric substrate.

It is theoretically possible to use electron beam (E-beam) writing to expose photoresist with resolution fine enough to create lines of 1 micron or less. However, as a result of practical problems such as charge accumulation in the photoresist layer, it has become difficult to etch several organic photoresist layers in combination with several different ion etching steps to create reliable submicron metal wires. A complex process was developed. These complicated methods add considerable extra cost to the manufacturing process.

For example, at the "Ultrasonic Symposium" in 1980, "Low loss 0.9-t9GHz with submicron era electrodes"
The process described by Urabe et al. under the title "SAW filter" uses PMMA and AZ-1350 photoresists and both oxygen ion and argon ion beam etching steps. , l,) requires a precisely controlled etching rate.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an improved method of making fine metal wires.

Another object of the present invention is to provide an improved method of making fine metal wires using E-beam exposure.

A specific embodiment of the present invention provides a PMM with E-beam writing.
A (polymethyl methacrylate) photoresist method involving thermal light. The stress on the photoresist layer that results in poor resolution is accounted for by the aluminum layer underlying the photoresist.

The stripped photoresist is removed 5 and a titanium layer is deposited over the ♀ surface. Next, the remaining C photoresist and the titanium film on the lrO are removed, leaving the aluminum layer and one titanium line on it. Next, a chemical etching solution is applied to the surface of the etching solution 3, which removes the aluminum but does not remove the tan. Therefore, the parts of the aluminum layer not covered by titanium are removed. In a preferred embodiment, a SAW transducer? The remaining metal lines comprise an underlying aluminum layer approximately 500-1000 angstroms thick and approximately 200-3. , I
an overlying titanium layer of 0 angstroms.

The 2 Ji metal wires produced by this process can be fabricated locally with a width of microns or less and a high thickness of 48 mm. Furthermore, the fact that the metal wire contains two layers of metal improves the electrical properties of the wire.

These and other advantages of the present invention will be apparent to those skilled in the art from the drawings and detailed description below.

FIG. 1 is a 'LAJ'r view of a device undergoing processing in accordance with the principles of the present invention. In one particular embodiment of the present invention, this process is used to create transusers for SAW devices on LiNb0j substrates.

Specific cut of the 1LiNbox used (128°Y
The surface acoustic velocity on the - should be approximately 0.5 microns wide.

The substrate is provided in a conventional sigma method for this particular application with an annealing step which is not appropriate for this particular application. As with all process steps that use high temperatures, the annealing step is sufficient, especially for the 128° Y-X cut of LiNbO5.
[3] Sufficient cooling time must be provided for stress relaxation. A layer 11 of the first metal is deposited to a thickness of approximately 1 angstrom by vapor deposition or by a process such as sputtering or taring. The first consideration is to ensure that layer 11 has almost no pinpoles. In the particular embodiment of the invention disclosed herein, layer 11 comprises approximately 700 angstroms of aluminum.

A photoresist layer 12 is then deposited on metal layer 11 -1. A preferred photoresist is a solution of PMMA (polymethyl methacrylate) dropped onto the center of the wafer while it is being rotated. First, the wafer 6 is rotated at about 500 rpm. The rotational speed is gradually increased to 54[) Orpm during 60 seconds. PM
In the case of MA photoresist, the wafer must be baked before ring formation with photoresist. After this is completed, the electrode pattern is exposed using the electron beam 14. An E-beam current of 2 nanoamps per square centimeter and a Charge of 110 microcoulombs was found to be satisfactory. Charge accumulation on the PMMA during E-beam exposure is controlled by a grounding layer 11. Although some control can be achieved without grounding, grounding is preferred.

Referring now to FIG. 2, the wafer of FIG. 1 is shown at a subsequent processing stage. Metal layer 11 is still on substrate 10. Is the exposed portion of the photoresist layer 12?
Developed to remove. PMMA photoresists can be developed by dipping the film in methyl isobutylkene (MIBK) for 70 seconds at a temperature of 60°C. Immediately rinse off the water by immersing it in a solution of 3 parts isobutyl alcohol and 1 part MI solution for 5 seconds, then dipping into Inglovir alcohol.

The tube is then rotated and dried with hot nitrogen while being washed with methanol. Once the wafer has dried, expose the wafer to an oxygen pragma for 15 seconds to remove any remaining PMMA from the developed area.
It has been found that removing tV is useful.

Referring to FIG. 6A, the first
The diagrams in Figure 2 and Figure 2 are clearly illustrated. Board 1
0. Metal layer 11 and development [7 photoresin] 121
;t, the previous one remains ℃. Furthermore, @4J2 metal layer 1
6 is deposited over the entire wafer.

The second metal, which is preferably titanium, is selected so that the chemical etch that removes the second metal has little effect on the second metal. Therefore,)gq1
6 is used as a mask in the chemical etching step of layer 11. In a preferred embodiment, layer 16 is deposited to a thickness of about 200 angstroms at a rate of 15 angstroms per second in an E-beam evaporation chamber. The second metal must be placed in close proximity at an angle of incidence of 90°.This requires a maximum practical spacing between the wire and the crucible.

Referring to FIG. 3B, an enlarged view of the wafer shown in FIG. 3A is shown. Photoresist layer 12 adjacent to the portion of photoresist layer 120 that was removed during the development process
The wall 20 is somewhat concave. This is coupled by ensuring that the development process runs completely 11L. Insufficient development of the photoresist layer σ does not result in the desired side Ai geometry and hinders subsequent process steps. As seen in FIG. 6B, the width W of the portion of the metal+gate is overlying the metal layer 11σ)1 is determined by the upper edge of the photoresist layer 12. This υ
The fact is that the metal layer 16 is truncated at the edge of the developed area to facilitate the subsequent lift-off process. The desired sidewall geometry may require some modification of the process structure.

Figure 4 shows the subsequent process of starting the process. 7'i21 Underdeveloped area of 5th layer and photoresist σ)-
1 - The river (3) of the 16th layer is lit off the first.
Ill). This is the first +! .

It's one person to receive one blessing from Wet Keaseton-C'
4'j i)reZ). If the lift-off process is not completed well even after soaking in acetone, add aluminum etchant to the aluminum etching solution. +: i'+"t L super t1θ V vibration HijII fire addition ・2 is 101 ability. And force 7.7101
/ Cyst and Leopard 1 Funeral 2 Gold N+ layer complete 1jfu 1
Mefke(r(if actually the most effective method II)
31,1. It is important to carefully mark the end point of the chair at i1(.

Insufficient development and excessive release of oxygen plasma are desired at 1°, (1'4 artificial ridge formation on the side wall geometry =
SS ability car. Once the lift-off process is complete, it will not be damaged\σ) by the portion of the second gold 1i4%I?/i16σ9・-JL'' that was not removed in the F (! The substrate 10 remains with the defined electrode pattern.

Referring to FIG. 5, the completed device is shown. First metal layer 11 is etched using second metal layer 16 as a mask, leaving isolated metal lines on the surface of substrate 1o. In the case of the aluminum-titanium system mentioned above, the aluminum etching solution was 1 part nitric acid and 4 parts deionized water.

It is preferable to use 18 parts of phosphoric acid. This etching process is carried out for about 60 seconds at room temperature or until the F-side substrate 10 is exposed. Care should be taken not to use too much etching solution. The wafer should be immediately rinsed in deionized water and isopropyl alcohol.

It has been found that it is possible to commercially and reliably and economically produce SAW devices having transducer fingers that are 'A microns wide using the disclosed process. Not only does the present invention eliminate the multiple photoresist layers and ion beam etching steps involved in prior art processes, but the metal lines produced have improved electrical properties due to the fact that the final metal line consists of two metal layers. have characteristics. This means that pinholes in any one full layer can have a significant effect on the electrical performance of the device9.
Give less skill.

Although the invention has been particularly shown and described with reference to preferred embodiments thereof, it is contemplated that other modifications and changes may be made thereto without departing from the spirit and scope of the invention. will be understood by those skilled in the art.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view of a portion of a device processed in accordance with the principles of the present invention. FIG. 2 is a diagram 914 corresponding to FIG. 1 of the device at a subsequent stage of processing in accordance with the principles of the present invention. FIG. 3A is a top view corresponding to FIG. 2 of the device during a subsequent stage of processing in accordance with the principles of the present invention. FIG. 3B is an enlarged cross-sectional view of a portion of the device shown in FIG. 6A. FIG. 4 is a cross-sectional view corresponding to FIG. 6A of the device at a subsequent stage of processing in accordance with the principles of the present invention. FIG. 5 is a cross-sectional view corresponding to FIG. 4 of the device after processing according to the principles of the present invention has been completed. In FIG. 3A, 10 is a substrate 11 is a metal layer 12 is a developed photoresist layer 16 is a second metal layer (titanium) Patent applicant Motorola Inc. Patent attorney Patent attorney Kugo Tamamushi 1 F'lG, 1 77″G, 2 F'lG, 3△ F', IC, 3:9 P'IC, 5'

Claims (1)

Claims: 1. Depositing a first metal on a substrate surface; depositing an E-beam photoresist on the first metal layer; E-beam? The photoresist in a predetermined pattern using? exposing the photoresist to light; developing the photoresist; depositing a selected second metal layer on the photoresist layer and the first metal layer; removing the remaining portions of the photoresist and portions of the second metal layer overlying the photoresist; and removing the remaining portions of the second metal layer that are not captured by the second metal layer. removing a portion of one metal layer with said agent. 2. The feature further comprises the step of grounding the first metal layer during the period of the E beam yK light.Claim 1
Metal wire forming method according to section. The step of developing the photoresist' further comprises:
The photoresist requires exposure to a developer for a sufficient time to form a concave structure? The metal wire forming method according to claim 1, which lacks the ability to make a metal wire.