JPH05102143A - Method for forming wiring of semiconductor device - Google Patents

Abstract

PURPOSE:To resolve the problem of mask matching at the time of additionally piling up a metal for wiring by forming SiO2 which thicker than a first wiring layer by liquid phase growth after the first wiring is formed and growing a metal by plating on the first wiring by using the SiO2 as a mask. CONSTITUTION:At the time of forming the wiring of a semiconductor device, a metallic layer 5 is formed on a first wiring layer 3 after the wiring layer 3 is formed. In such wiring, SiO2 4 is formed on the layer 3 so that the SiO2 4 can become thicker than the layer 3 by liquid phase growth after the layer 3 is formed and the metallic layer 5 is grown by plating on the layer 3 by using the SiO2 4 as a mask. For example, after an SiO2 film 2 is for on a GaAs substrate 1, Ti/Pt/Au wiring 3 is formed on the film 2 by using a spacer lifting- off method. Then, after forming a thick SiO2 film 4 by liquid-phase growth, electroless plating 5 of Au is performed by using the film 4 as a mask.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the formation of wiring for semiconductor devices, and more particularly to the formation of thick wiring when low resistance of the wiring is required.

[0002]

2. Description of the Related Art A conventional method for thickening a wiring is shown in FIG.

First, a first wiring layer is formed on a semiconductor by using a known technique, such as a spacer lift-off method, as shown in FIG. 2A. In order to thicken this wiring, first, a pattern of the first wiring is formed. A photoresist is formed by the photolithography technique so as to be the same as the first wiring or have an opening inside the pattern. This is to prevent adjacent first wirings to be insulated from existing in the same opening.

However, since the wiring in recent years is extremely finely processed, the alignment accuracy at the time of mask formation cannot keep up, and the photoresist must be formed in consideration of this misalignment. In practice, therefore, it is necessary to form it inside the first wiring. Also, on extremely fine wiring,
It was difficult to open the resist. Then, a metal layer is formed in the resist opening by the plating method using the above photoresist as a mask to thicken it.

In this method, the formation of the resist pattern described above is very important and it is necessary to open a pattern which is the same as or smaller than the first wiring, but the first wiring is limited by photolithography. When the dimensions are set, it becomes impossible to form such a resist pattern. or,
Even if it can be formed, the final shape can have a very large step, so that it is obvious that various obstacles occur in the formation of the wiring in the upper layer.

[0006]

As described above, according to the conventional wiring forming method, it is difficult to form and align a resist that serves as a mask for the additional wiring, and it is impossible to build up on a fine wiring. There was the problem of being very large.

The present invention provides an effective solution to this problem and, for the first problem, provides a method of self-aligning the build-up. At the same time, a method capable of solving the second problem is provided.

[0008]

[Means for Solving the Problems] A means for solving the above-mentioned problems is to form a liquid phase growth SiO after forming a first wiring.
₂ (LPD-SiO ₂ ) is grown in a self-aligned manner using the first wiring as a mask. At this time, an important point is to grow LPD-SiO ₂ to a thickness obtained by adding the plating growth thickness to the thickness of the first wiring so as to serve as a mask for the subsequent plating process. As a result, the mask can be formed on the first wiring without performing any mask alignment. That is, first, the first wiring is formed on the hydrophilic insulating film. Then, SiO ₂ is grown on the hydrophilic insulating film in a self-aligned manner by a liquid phase growth method using the first wiring layer as a mask. At this time, the thickness of the liquid phase growth is made to be the thickness of the first wiring plus the thickness to be accumulated. At this time, liquid phase grown SiO
₂ has an opening on the wiring in a self-aligned manner, so this S
Plating is performed using iO ₂ as a mask. Also, the plating is Si
Perform to the same thickness as the surface of O ₂ . This enables thick and flat wiring in a self-aligning manner.

[0009]

Since the LPD-SiO ₂ serves as an ideal mask in which only the first wiring is opened, the resistance can be reduced by increasing the wiring even if the wiring is fine, especially when the space between adjacent wirings is extremely small. It will be possible. In addition, when plating is performed using LPD-SiO ₂ as a mask, there is an effect that the plating solution is less contaminated by carbon, which is a problem in general resists.

[0010]

EXAMPLE As an example of the present invention, the case of application to wiring of a GaAs semiconductor will be shown. This will be described with reference to FIGS.

First, an insulating film (2) is formed on a GaAs substrate. At this time, this insulating film is formed of SiO ₂ which will be used in a later step.
A hydrophilic insulating film that enables liquid phase growth (LPD), such as SiO ₂ , is used. After that, Ti is formed on the insulating film by using a conventionally known spacer lift-off method.
/ Pt / Au wiring (Ti500nm / Pt500nm
/ Au 10000 nm). Next, this substrate is dipped in a supersaturated solution of hydrogen fluoride to form a SiO ₂ film by the well-known LPD method. Since it is usually used for flattening or the like, the growth film thickness is the same as that of the previous wiring, which is 11000 nm when applied to this embodiment. However, in the present invention, since this is used as a self-aligning mask, 11000n
Since m is a thick film formed by the addition, which is the original purpose, the thickness is expected to grow thicker. In the case of this example, 2 μm was further added to grow a total of 3.1 μm.

As a result, a mask was formed in which only the upper portion of the wiring was opened in a self-aligned manner. By performing electroless plating of Au using this SiO2 as a mask, it succeeded in stacking thickly without performing mask alignment. Also at this time Au
If the plating is grown to the same height as the upper surface of the mask, planarization is secondarily performed at the same time.

This embodiment is only one example of the present invention. Considering, for example, the case where the first wiring is formed by milling instead of lift-off, the SiO deposited over the entire surface of the GaAs substrate is considered.
_Then , Ti / Au is deposited on the entire surface, and Ti / Au is processed into a desired pattern using the resist as a mask. After that, LPD growth is performed without removing the resist, the resist is removed thereafter, and plating is similarly performed. At this time, the milling mask works effectively also as a LPD mask, and it has been found that it is better to take it after LPD.

[0014]

According to the present invention, a mask is formed in a self-aligning manner with respect to a mask alignment error, which is a problem in increasing wiring metal for reducing the resistance of a wiring required for a GaAs IC or the like. It can be solved by

[Brief description of drawings]

FIG. 1 is a diagram of an embodiment of the present invention.

FIG. 2 is a diagram of a conventional example.

Claims (1)

[Claims] 1. In the wiring formation of a semiconductor device, in a wiring in which a metal layer is further formed on the first wiring after forming the first wiring, SiO is formed after the first wiring is formed.
_A method for forming a wiring of a semiconductor device, comprising at least a step of forming ₂ thicker than a first wiring layer by a liquid phase epitaxy method and a step of growing a metal on the first wiring by a metal transfer using the SiO ₂ as a mask.