JP3029681B2 - Wiring formation method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a wiring of a compound semiconductor device.

[0002]

2. Description of the Related Art For example, compound semiconductor elements such as field effect transistors and diodes, which are formed using compound semiconductors, and compound semiconductor integrated circuits in which a number of these elements are integrated (these are referred to as compound semiconductor devices). Wiring is formed between the semiconductor element and the bonding pad and between the semiconductor elements. Since a semi-insulating substrate is obtained from a compound semiconductor such as GaAs, electrical insulation can be achieved even when the wiring is directly formed on the substrate.
The wiring was formed directly on the compound semiconductor substrate.

For example, the wiring of a compound semiconductor device having a plurality of field effect transistors (FETs) on a GaAs substrate is described in the literature (Oki Electric R & D 134, Vol.
o. 2, p. 23 (1987), it was formed as described below. FIG. 3A is a plan view of a main part for explanation, and FIG. 3B is a cross-sectional view taken along a line PP of FIG. 3A.

First, a portion of the GaAs substrate 17 where the formation of the FET operating region 11, the gate electrode 13 and the ohmic electrode 15, ie, the main portion of the FET has been completed, except for the region where the wiring is to be formed is formed of a photoresist (not shown). Covered.

Next, Ti, Pt (platinum) and Au (gold) are sequentially vacuum-deposited on the sample (not shown).

Next, the sample is immersed in a suitable organic solvent to dissolve the photoresist, and a metal film such as a Ti film on the photoresist is removed (lifted off). The wiring 19 is constituted by the remaining portion of the metal film such as the Ti film.

Thereafter, in order to prevent contamination on the surface of the GaAs substrate 17, an insulating film such as a SiN film or a so-called passivation film (not shown) is formed on the sample at a temperature of about 300 to 400 ° C. by, for example, a CVD method. .

[0008]

However, the surface state of the wiring formed by the conventional method often changes during the formation of the passivation film. That is, in the conventional wiring forming method, it is difficult to obtain a wiring having a flat surface state. For this reason, there has been a problem that device characteristics are degraded due to an increase in wiring resistance, manufacturing yield is reduced, and the like.

The main reasons why it is difficult to obtain a wiring having a flat surface state are considered to be the following (a) to (d).

(A) Heat is applied to the sample during the formation of the passivation film.

(B) The compound semiconductor and Ti, Pt, Au, Al or the like used as a wiring material have a property of being easily diffused at a temperature of 300 ° C. or more.

(C) A natural oxide film (shown at 21 in FIG. 3 (B)) always exists on the surface of the compound semiconductor, or 1 to 3 due to the action of chemicals or heat before the wiring forming step. A natural oxide film having a thickness of about 2 nm is formed. However, these natural oxide films often have poor film quality and uneven thickness. This makes the interdiffusion between the wiring metal and the compound semiconductor substrate non-uniform. When the wiring metal is a metal that is easily oxidized (the above-mentioned Ti
Corresponds to this. The oxygen in the natural oxide film is reduced by the wiring metal and oxidizes a part of the wiring metal. However, since the film quality and thickness of the natural oxide film are not uniform, the partial oxidation of the wiring metal is also unevenly performed. Will be

(D) For example, when a portion of the compound semiconductor substrate exposed in an ashing process for removing a resist remaining film in a photolithography process in a manufacturing process is exposed to oxygen plasma and oxidized, the oxidation formed by the exposure is performed. Since the material is unstable, it aggregates and deteriorates the surface shape.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to form a wiring made of a metal which is easily oxidized or a multilayer wiring having the metal as the lowermost layer on a compound semiconductor base. In view of the above, an object of the present invention is to provide a method capable of forming a more stable wiring even if heat is applied to the wiring after the wiring is formed.

[0015]

Means for Solving the Problems In order to achieve this object, the inventors of the present application have made various studies. As a result, it has been considered that the object of the present invention can be achieved by positively forming a high-quality oxide film in a region where a wiring is to be formed under the compound semiconductor.

Therefore, according to the present invention, when forming a wiring made of a metal that is easily oxidized or a multilayer wiring having the metal as the lowermost layer on the compound semiconductor base, the wavelength is 185 nm.
And an ultraviolet ray including light having a wavelength of 254 nm and oxygen are uniformly brought into contact with the heated surface of the compound semiconductor base to form an oxide film on the base, and thereafter, the wiring is formed. .

Here, the compound semiconductor base is GaAs.
In the case of various compound semiconductor substrates such as a substrate, an InP substrate, a GaP substrate, an InAs substrate, etc., it refers to a broad base on which wiring can be formed, such as an intermediate in which elements are formed on these substrates.

As a method of heating the compound semiconductor base, for example, the compound semiconductor base itself is heated by, for example, a heater,
A method of heating using a lamp or the like, a method of heating by induction heating, and the like can be given.

If the heating temperature is too low, the formation rate of the oxide film is too slow to be practical, and if it is too high, abnormal phenomena such as evaporation of the constituent elements of the compound semiconductor base will occur. Good to be. For example, when a GaAs substrate is used as a compound semiconductor base,
The temperature is preferably in the range of 100 ° C to 300 ° C. This is because, if it is in this range, an oxide film can be formed at a practical speed and arsenic can be prevented from being removed from the GaAs substrate. Since the formation rate of the oxide film also depends on the oxygen gas concentration, this condition is also determined in consideration of a device to be used and the like.

On the other hand, if the thickness of the oxide film formed by the method of the present invention is too small, the oxide film has an island structure, and an oxide film having a uniform film quality and thickness is formed between the wiring metal and the compound semiconductor base. Not fit for purpose. Nor do they need to be too thick.
Accordingly, the film thickness may be set to the minimum necessary. At least 3
It is preferable that the thickness be not less than nm.

[0021]

According to the present invention, an oxide film having excellent film quality uniformity and film thickness uniformity is formed on the surface of a compound semiconductor base as compared with a natural oxide film. For this reason, the interdiffusion between the compound semiconductor base and the wiring metal uniformly occurs or is suppressed uniformly throughout the wiring.

Further, the wiring made of a metal which is easily oxidized or the multilayer wiring having the metal as the lowermost layer formed on the oxide film is in contact with the oxide film because the quality and thickness of the oxide film are uniform. Becomes uniformly oxide. In the example of the embodiment, uniform TiO _X is formed on the compound semiconductor underlayer side of the Ti film constituting the lowermost layer of the multilayer wiring composed of Ti / Pt / Au. Since this oxide is a high-quality film that is stable and has very few pinholes, this also suppresses interdiffusion between the compound semiconductor base and the wiring metal.

[0023]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a wiring forming method according to an embodiment of the present invention; In this embodiment, a plurality of field effect transistors (F
Et, Ti, Pt and Au
This is an example of forming a multi-layer wiring (Ti is the lowermost layer) composed of. Here, FIGS. 2A and 2B and FIGS.
(C) is a process drawing provided for the explanation. In particular, FIG.
2A is a plan view schematically showing a part of a compound semiconductor base having a plurality of field-effect transistors on a semi-insulating GaAs substrate as viewed from above the GaAs substrate, and FIG. 2B is a plan view of FIG. FIG. 3 is a cross-sectional view taken along line QQ of FIG. FIG.
FIGS. 3A to 3C are diagrams showing a procedure for forming wiring on the compound semiconductor base shown in FIG. 2 by a cross section corresponding to FIG.

First, as shown in FIGS. 2A and 2B, a predetermined area of a semi-insulating GaAs substrate 31 having a diameter of 3 inches (1 inch is approximately 2.54 cm; the same applies hereinafter) is provided. FE by ion implantation technology and annealing technology
An operation region 33 of T is formed, and a gate electrode 35 and ohmic electrodes 37 serving as a source / drain are formed by a known film forming method and a photolithography technique.

The gate electrode 35 is made of, for example, an alloy containing tungsten (W), such as W-Al, a compound containing W, such as WSi or WN, or a T-layer laminated in order from the substrate side.
It can be composed of a multilayer metal such as i, Pt, and Au. Further, the ohmic electrode is, for example, AuG laminated in order from the substrate side.
It can be composed of a multilayer metal composed of e, Ni and Au. Of course, other materials may be used without being limited to these.

Next, the active region 33 and the ohmic electrode 37
The GaAs substrate 31 on which is formed a low-pressure mercury lamp (300
It is installed in a container with a capacity of about 2 liters. In this embodiment, the distance between the GaAs substrate and the low-pressure mercury lamp is 5 cm. Then, this Ga
While heating the As substrate to 100 ° C. and irradiating it with light from a low-pressure mercury lamp, oxygen is flowed into the container at a rate of 10 l (liter) / min. In this manner, ultraviolet light including light having a wavelength of 185 nm and light having a wavelength of 254 nm and oxygen
The substrate is brought into contact with the aAs substrate 31 in a heated state. At this time, it was confirmed that ozone was generated in the container. The substrate installation position, the low-pressure mercury lamp installation position, and the oxygen supply method were devised so that oxygen and ultraviolet light uniformly contacted the substrate.

When the above processing was performed for 1 minute, GaAs
On the surface of the s-substrate 31 other than the portion covered with the gate electrode 35 and the portion covered with the ohmic electrode 37, the film thickness is 3n.
m of the oxide film 39 was formed. Also, it was found that the surface of the gate electrode 35 and the surface of the ohmic electrode 37 were hardly oxidized in this oxidation step (FIG. 1).
(A)). Further, the thickness of the oxide film 39 at various points in the 3-inch GaAs substrate was measured to determine the thickness distribution. The standard deviation of the distribution was found to be 0.3 nm. From these facts, it can be understood that the oxide film forming method according to the present invention can form an oxide film having a uniform thickness without damaging the element.

Next, the GaAs substrate 3 on which the oxide film 39 has been formed
A region other than the one wiring formation planned region is covered with, for example, a photoresist 41. Thereafter, the sample is placed in, for example, a vacuum evaporation apparatus (not shown). Then, in this case, Ti is formed in a thickness of 100 nm, Pt is formed in a thickness of 50 nm, and Au is formed in a thickness of 300 nm in this case. As a result, a thin film 43 for a multilayer wiring is formed on the sample with a metal (in this case, Ti) which is easily oxidized as the lowermost layer (FIG. 2).
(B)).

Next, by removing unnecessary portions of the multilayer wiring thin film 43 by a lift-off method, a multilayer wiring (Ti / Pt / Au) 43a having easily oxidizable metal as the lowermost layer can be formed (FIG. 1C). ).

The surface shape (morphology) of the multilayer wiring 43a formed in this manner is flat, and is 3D in the subsequent CVD process for forming a passivation film.
It was found that there was no change even with heat of 00 to 400 ° C.

Although the embodiment of the wiring forming method of the present invention has been described above, the present invention is not limited to the above-described embodiment, and the following modifications can be added.

For example, in the above embodiment, the oxygen flow rate is set to 10
1 (liter) / minute, but the oxygen flow rate is 1 to 50
Experiments were performed in the range of 1 (liter) / min. In each case, the same effect as in the example was obtained.

In the above embodiment, the wiring is a three-layered wiring of Ti / Pt / Au with Ti being the lowermost layer.
It is apparent that the same effect as that of the embodiment can be obtained when a two-layer wiring such as Ti / Al or Ti / Au is formed, or when the wiring is formed only of a metal which is easily oxidized.

Further, in the above-described embodiment, Ti is used as the easily oxidizable metal, but the present invention is not limited to this. For example,
It is clear that the same effects as in the embodiment can be obtained even when Ni (nickel) or Al (aluminum) is used.

Further, in the above-described embodiment, the GaAs substrate on which the FET is formed is used as the compound semiconductor base, but the present invention is not limited to this. For example, InP substrate, GaP substrate, InAs
Substrates II-VI compound semiconductor substrates and the like can also form oxide films on their surfaces by light and oxygen from a low-pressure mercury lamp, and these are also objects of the present invention.

The electrode forming method of the present invention can also be expected to be applied to the case where wiring is formed on a silicon substrate, a germanium substrate, a substrate, a SiC substrate, a boron nitride substrate, or a tantalum nitride substrate.

[0037]

As is apparent from the above description, according to the wiring forming method of the present invention, a compound semiconductor base on which a wiring made of a metal which is easily oxidized or a multilayer wiring having the metal as the lowermost layer is formed. In contrast, a high-quality oxide film was positively formed before the formation of the wiring and the wiring was formed thereafter, so that mutual diffusion between the compound semiconductor base and the wiring metal occurs uniformly in the entire wiring. Alternatively, it is uniformly suppressed.
Furthermore, since the portion of the wiring that is in contact with the oxide film is uniformly made of oxide, this also suppresses the interdiffusion between the compound semiconductor base and the wiring metal.

Therefore, even if heat is applied to the wiring after the formation of the wiring, it is possible to form a more stable wiring than before, and it is expected that the characteristics will not change even if the semiconductor device is operated at a high temperature.

[Brief description of the drawings]

FIGS. 1A to 1C are process diagrams for explaining a wiring forming method according to an embodiment;

FIGS. 2A and 2B are views for explaining a compound semiconductor base used in Examples.

FIGS. 3A and 3B are diagrams for explaining a conventional technique.

[Explanation of symbols]

31: Semi-insulating GaAs substrate 33: Operating region 35 Gate electrode 37: Ohmic electrode 39: Oxide film formed using oxygen and ultraviolet light 41: Photoresist 43: Multilayer wiring thin film 43a having easily oxidizable metal as the lowermost layer 43a ： Multilayer wiring with metal that is easily oxidized as the bottom layer

──────────────────────────────────────────────────の Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01L 21/3205-21/3213 H01L 21/768

Claims (2)

(57) [Claims] In forming a wiring made of a metal that is easily oxidized or a multilayer wiring having the metal as the lowermost layer on a compound semiconductor base, light having a wavelength of 185 nm and a wavelength of 254 nm are used.
Forming an oxide film on the underlying surface of the compound semiconductor by uniformly contacting ultraviolet light and oxygen containing the above light with the heated surface of the underlying compound semiconductor, and thereafter forming the wiring. . 2. The wiring forming method according to claim 1, wherein said easily oxidizable metal is at least one metal selected from titanium (Ti), nickel (Ni) and aluminum (Al). Wiring forming method.