JPH0284725A - Semiconductor device and manufacture thereof - Google Patents

Abstract

PURPOSE:To prevent a passivation film from exfoliating from a wiring surface by the effect of electrodes coated with a noble metal layer, and improve the reliability and the yield of a semiconductor device by interposing a layer composed of metal easy to be oxidized, between the noble metal layer and the passivation film. CONSTITUTION:A passivation film 14 is formed on electrodes 3-5 or wiring on which a noble metal layer is formed. In this semiconductor device, a layer 13 composed of metal easy to be oxidized is interposed between the above noble metal layer and passivation film 14. For example, after an N-type GaAs semiconductor layer 2 is formed on a GaAs semiinsulative substrate 1, and an ohmic metal layer 11 of AuGe is patterned, a gate metal layer 12 like Ti/Pt/ Au turning to a Shottky barrier layer is formed. Next, after a metal layer 13 like Ti easy to be oxidized is formed, the gate metal layer 12 and the metal layer 13 are simultaneously patterned, and a source electrode 3, a drain electrode 4 and a gate electrode 5 are formed. After that, the passivation film 14 is formed, and the metal layer 13 on the upper surface of electrodes is eliminated.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to semiconductor device technology and also to a technology for forming a passivation film on an electrode made of a noble metal layer, and is particularly applicable to the formation of a passivation film for a high frequency GaAs FET. Regarding effective techniques.

[Prior Art] Generally, semiconductor devices such as FETs (field effect transistors) formed on semiconductor substrates are made using SiO, such as SiO, to protect the active layer and electrodes on the surface and insulate between the electrodes. covered with a passivation film.

For example, in a high-frequency GaAs FET, the gate length of the gate electrode is as narrow as 1 μm or less, and the gate width is very long compared to the gate length, so it is easily cut.
The gate electrode, source electrode, and drain electrode are very close to each other and leakage easily occurs. Therefore, in addition to increasing the insulation between the electrodes, the active layer of the semiconductor substrate exposed between the gate electrode and the drain and source electrodes is A passivation film was formed to protect the surface.

[Problems to be Solved by the Invention] By the way, in GaAs FETs, it is necessary to reduce the resistance of the gate electrode with a small cross-sectional area, and to apply bonding to the pad portion of the gate electrode to which the bonding wire is connected, and the surfaces of the source and drain electrodes. A noble metal layer such as Au is formed to improve the adhesion of the wire.

However, the noble metals are 5ixty and 5ixNyOz, which are used as passivation films.

It has been found that the passivation film is not easily compatible with insulating films such as Si x Ny, and therefore has the disadvantage that the passivation film peels off easily, reducing the reliability and yield of semiconductor devices.

Particularly in high-frequency FETs, a large parasitic capacitance between the gate and drain deteriorates the high-frequency characteristics, so it is desirable that the padding film be as thin as possible. However, experiments have also confirmed that the thinner the passivation film is, the more likely it is that the noble metal layer will peel off from the electrode on which it is formed.

An object of the present invention is to provide a semiconductor technology that can prevent a passivation film from peeling off from the surface of an electrode or wiring coated with a noble metal layer in a semiconductor device, thereby improving the reliability and yield of the semiconductor device. - [Means for Solving the Problems] In order to achieve the above object, the present invention provides a coating of Ti, AQ, , a metal layer that is easily oxidized, such as Cr, is formed.

In addition, the metal layer that is easily oxidized at the portion that will become the wire bonding portion of the electrode on which the noble metal layer is formed is removed to expose the noble metal layer.

[Function] According to the above-mentioned means, metals that are easily oxidized generally have good adhesion to noble metals, and metals that are easily oxidized also have good adhesion to insulating films such as SiO, so that the passivation film formed on the electrode peeling can be prevented.

In addition, for areas where the noble metal layer should be exposed, such as wire bonding parts, any mask is added by removing the easily oxidized metal layer on the surface of the noble metal layer using a passivation film or a mask for forming a passivation film as an etching mask. Peeling of the passivation film can be prevented without causing any damage.

[Example] FIG. 1 shows an example in which the present invention is applied to a high-frequency GaAs FET in the order of manufacturing steps.

In this embodiment, first, an n-type GaAs semiconductor layer 2 which will become an active layer is deposited on a GaAs semi-insulating substrate 1 by a vapor phase growth method or the like.
form.

Next, unnecessary active J12 is removed by mesa etching, the AuGe ohmic metal layer 11 is patterned, and then a gate metal [12] which becomes a Schottky barrier such as Ti/Pt/Au is formed. .

In this embodiment, a metal layer 13 that is relatively easily oxidized, such as Ti (titanium), is formed on the gate metal layer 12 to a thickness of about 200 layers, and then a layer 13 that is easily oxidized with the gate metal layer 12 is formed. The metal layer 13 is simultaneously patterned to form a source electrode 3, a drain electrode 4, and a gate electrode 5 (FIG. 1(A)).

Next, a photoresist film is deposited on the entire surface of the substrate 1, and after removing the photoresist in the portion where the passivation film is to be left, 5ixty or 5iNyOz, Six
After depositing an Ml film such as Ny on the entire surface, unnecessary parts of the insulating film are removed by lift-off method, and the result is shown in Figure 1 (B).
), a passivation film 14 is formed from above the gate electrode 5 to part of the source and drain electrodes 3.4.

Thereafter, using this passivation film 14 as an etching mask, reactive ion etching is performed to remove the metal layer (Ti) 13 on the upper surface of the electrode and expose the noble metal layer (FIG. 1(C)).

Specifically, in a high-frequency FET, the high-frequency characteristics will be better if the parasitic capacitance between the gate and drain is minimized, so the final film thickness of the passivation film 14 is 80 mm.
It is desirable to have around 0 people.

Therefore, in this embodiment, the passivation film 14 is formed in advance to a thickness of 1,400 to 1,500 layers. As a result, the passivation film 14 can be formed to a desired thickness even if the entire surface is etched without using a mask when removing unnecessary portions of Ti.

FIG. 2 shows another method of forming a metal film 13 that is easily oxidized between the noble metal layer on the surface of each electrode 3 to 5 and the passivation film 14.

The first half of the steps in this embodiment, that is, the steps up to the formation of the gate electrode 5 having the easily oxidized metal M13 on the surface, and the source and drain electrodes 3 and 4, are the same as those in the first embodiment.

In this second embodiment, electrodes 3 to 3 having a Ti layer on the surface are used.
5, a passivation film 1 such as SiO is formed.
4 on the entire surface. Then, a photoresist film 15 is deposited thereon.

The photoresist corresponding to the portion that will become the wire bonding portion is removed (FIG. 2(A)). Thereafter, using the photoresist film 15 as an etching mask, an opening 14a for bonding is first formed in the passivation film 14. Then, the easily oxidized metal M13 on the surfaces of the source electrode 3 and drain electrode 4 is removed to expose the noble metal layer on the electrode surfaces (FIG. 2(B)).

In both of the first and second embodiments described above, after the back side of the substrate 1 is shaved by lapping after the steps shown in FIG. 1(C) and FIG. is formed, and the whole process is completed.

In conventional devices, the passivation film peels off at a rate of about 30%, and the rate of peeling varies greatly, but by applying the above example, the passivation film peels off at a rate of about 30%. 1
It has become possible to prevent almost 00% of this.

In the above embodiment, Ti was used as the metal layer formed on the noble metal layer on the surface of the electrode and wiring, but any other metal that is easily oxidized, such as All or Or, may be used. be able to.

Further, the present invention includes At as a noble metal layer on the surface.

It can be widely used when it is desired to form an insulating film on the surface of an electrode or wiring on which Ag or other highly stable and low-resistance metal is formed.

Furthermore, as an insulating film, other than 5ixty and SixNy, S
It can also be applied to cases where organic compounds other than ixNy are used.

[Effects of the Invention] As explained above, the present invention provides a layer of a relatively easily oxidized metal such as Ti on the surface of the uppermost noble metal layer of the electrode (including wiring) on which the passivation film is deposited. Since a metal layer with good adhesion to both the noble metal and the passivation film is interposed between the electrode and the passivation film, even if the noble metal layer is formed on the surface of the electrode, Peeling of the passivation film can be prevented.

As a result, the reliability and yield of semiconductor devices are improved.

In addition, in the manufacturing method of the first embodiment, the passivation film is used as a mask, and in the manufacturing method of the second embodiment, the mask for forming the passivation film (photoresist film) is used as the mask to oxidize the surface of each electrode. Since the metal layer that is easily etched is etched, a structure that prevents the passivation film from peeling off can be realized without adding any new mask. In other words, the manufacturing method for preventing peeling is simple and increases in cost can be suppressed.

[Brief explanation of drawings]

FIGS. 1(A) to (C) show that the present invention is made of GaAs for high frequency.
FIGS. 2A and 2B are cross-sectional views showing the main parts of the second embodiment in the order of steps. FIGS. 1... Semi-insulating substrate, 2... Active layer, 3...
- Source electrode, 4...Drain electrode, 5...Gate electrode, 11...Ohmic metal layer, 12...
...gate metal layer, 13...metal layer that is easily oxidized,
14... Passivation film, 15... Resist film. Figure 1 ■ Amendment to figure procedure January 19, 1989 Director General of the Patent Office Yoshi 1) Takeshi Moon 1, Indication of the case Patent Application No. 10233 of 1988 2, Name of the invention Semiconductor device and its manufacturing method 3, Relationship with the case of the person making the amendment Patent applicant name Nippon Mining Co., Ltd. 4, agent 105 Phone number 505-8730 Address 2-1-1-3 Toranomon, Minato-ku, Tokyo Details of the invention in the specification subject to amendment Explanation column 7, amendment details page 9, lines 4-5 “At, Ag as noble metal layer”
"Others" is corrected to "Au, Pt, Ag, and other noble metal layers."that's all

Claims (2)

[Claims] (1) In a semiconductor device in which a passivation film is formed on an electrode or wiring formed with a noble metal layer, a layer made of a metal that is easily oxidized is interposed between at least the noble metal layer and the passivation film. A semiconductor device characterized by: (2) After forming a conductive layer having a noble metal layer to serve as an electrode or wiring on a semiconductor substrate, forming a layer made of a metal that is easily oxidized on the noble metal layer, and then applying a passivation film to desired areas. A method for manufacturing a semiconductor device, characterized in that unnecessary portions of the metal layer that is easily oxidized are removed after forming the metal layer.