JPH1174307A - Electrode of semiconductor element and method of forming the same - Google Patents

Abstract

(57) [Problem] To provide an electrode in a semiconductor device and a method for forming the same, which realize both high pattern recognition and strong bondability. SOLUTION: A multi-layer bonding pad in which a second Al layer 5 made of pure Al or a material close to pure Al is formed on a pattern recognition auxiliary layer 4 made of an Al film mixed with N ₂ is formed as an electrode of a semiconductor element. It has a structure having a layer. This electrode is formed by a step of sputtering a first Al film using a sputtering gas in which an N ₂ gas is mixed with an Ar gas, and a step of sputtering the first Al film using a sputtering gas consisting only of an Ar gas. And a step of sputtering a second Al film made of pure Al or a material close to pure Al thereon.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode structure in a semiconductor device, and more particularly to an electrode of a compound semiconductor light emitting device such as a semiconductor laser and a light emitting diode and a method of forming the same.

[0002]

2. Description of the Related Art FIG. 3 shows a basic structure of a wire bonding side electrode in a general compound semiconductor. This electrode includes an ohmic layer 1 for lowering the resistance between the crystal and the electrode on the wafer 6, a barrier layer 2 for suppressing the diffusion of Ga, Zn, etc. to the bonding pad layer, and a bonding for fusing wires onto the chip during wire bonding. Pad layer 3
Are sequentially laminated.

FIG. 4 shows an example of a method of recognizing a chip pattern during wire bonding. In recognizing a chip pattern, light L1 is projected from obliquely above a chip 8 by a light projector 7, and an electrode is used at that time. This is performed by receiving the reflected light L2 reflected by the pattern by the light receiving element 9. In order to improve the pattern recognizability of the bonding pad, it is desirable that the electrode surface be in a fine rough state in order to irregularly reflect the projection light on the crystal surface which is a mirror surface.

The surface roughening treatment is performed by etching the Al surface formed by a sputtering apparatus with dilute hydrofluoric acid. The etching proceeds along the Al grain interface, and the Al surface roughened like a dendrite appears. Thus, in order to improve the pattern recognition of the bonding pad,
The surface is etched with a chemical solution to roughen the surface, irregular reflection from the electrode when light is projected onto the chip during wire bonding is increased, and binarization with the crystal surface is facilitated.

[0005] The Al film is made of Al depending on sputtering conditions.
The size of the grain boundary of the film can be varied. Generally, when Al sputtering is performed as a bonding pad, the sputtering chamber is once in a high vacuum state (1 × 1).
0 ^-7 torr), and then Ar gas (1 × 10 ^-3 torr) is sealed. The Ar gas is converted into Ar ⁺ ions by a negative voltage applied to the Al target and accelerates and collides with the Al target. Al is formed on the substrate by inelastic collision from the Al target by the colliding Ar ⁺ ions. The most effective means for changing the size of the crystal grain boundary of the Al film is to mix N ₂ gas at 3% to 4% or more with Ar gas. The dendrite-like Al grain boundary is about 10 μm to 1
It becomes smaller from μm to 2 μm.

FIG. 5 shows a model of a change in the grain boundary size of the bonding pad layer. FIG. 5A shows a case where an ohmic layer 1, a barrier layer 2 and a bonding pad layer 3 made of pure Al are sequentially stacked. (B) shows a case where an ohmic layer 1, a barrier layer 2 and a bonding pad layer 3 'made of Al mixed with N ₂ are sequentially stacked. FIG.
As shown, in the roughening process proceeds etching along the grain boundary, if the bonding pad layer due to N ₂ mixed Al, the surface state as compared with the case of pure Al has a finer dendrite shape The Al surface can be realized, and the pattern recognizability is improved.

[0007]

However, when the bonding pad layer is formed of Al mixed with N ₂ as described above, as compared with the case where the bonding pad layer is formed of pure Al.
The hardness is increased, and the Au wire does not fuse and the bondability is significantly impaired.

FIG. 6 is a structural photograph showing how the dendrite-shaped grain boundary size of the bonding pad layer changes when the N ₂ mixing ratio with respect to the Ar gas is changed.
(A) shows the case where the N ₂ mixing ratio is 0%, (b) shows the case where the N ₂ mixing ratio is 1.3%, and (c) shows the case where the N ₂ mixing ratio is 3.3%.

FIG. 7 shows the relationship between the N ₂ mixing ratio and the number of chips that could be bonded by wire bonding. Here, a large change in the Al surface shape appears when the N ₂ mixing ratio in FIG. 6C is set to 3.3% or more, but the bondability and the ball pressing strength are as shown in FIG. Already a considerable decrease is observed from the N ₂ mixing ratio of 1.3%.

[0010] As described above, the parameter for making the Al grain boundary smaller is N ₂ mixed into the sputtering gas. However, when the bonding pad layer is formed of Al mixed with N ₂ , the pattern recognizability and bondability can be improved. Is a conflicting relationship. That is, if the N ₂ mixing ratio of the bonding pad layer is increased, the Al grain boundaries become smaller, and the film becomes excellent in pattern recognition, but the bondability is reduced. Conversely, when the bonding pad layer is made of a high-purity Al film, the bonding becomes strong, but the film is not suitable for pattern recognition.

An object of the present invention is to solve such problems of the prior art, and an object of the present invention is to provide an electrode in a semiconductor device capable of realizing both high pattern recognizability and strong bondability, and a method of forming the same.

[0012]

An electrode of a semiconductor device according to the present invention comprises a _second layer made of pure Al or a material close to pure Al on a pattern recognition auxiliary layer made of an Al film mixed with N 2.
And a multi-layer bonding pad layer having an Al layer formed thereon, thereby achieving the above object.

Preferably, the thickness of the pattern recognition auxiliary layer is 900 nm, and the thickness of the second Al layer is 300 nm.
nm.

The method for forming an electrode of a semiconductor device according to the present invention comprises:
A step of sputtering the first Al film using a sputtering gas in which an N ₂ gas is mixed with an Ar gas, and a step of purely forming a pure gas on the first Al film using a sputtering gas consisting of only an Ar gas. And a step of sputtering a second Al film made of a material close to Al or pure Al, whereby the object is achieved.

The operation of the present invention will be described below.

As described above, according to the present invention, a multi-layer bonding pad layer constituting an electrode of a semiconductor element is formed by depositing pure Al on a pattern recognition auxiliary layer comprising an Al film mixed with N _2.
Alternatively, a configuration is employed in which a second Al layer made of a material close to pure Al is formed. For this reason, since the pattern recognition auxiliary layer is made of the N ₂ mixed Al film, the grain boundary size is reduced, and the second Al layer formed thereon is deposited while inheriting the grain boundary size reduced by the pattern recognition auxiliary layer. Is done. as a result,
Although the second Al layer is made of pure Al or a material close to pure Al, it has a surface state having a fine dendrite shape after the surface roughening treatment, and the pattern recognizability is improved. Moreover,
Since the second Al layer is made of pure Al or a material close to pure Al, the Au wire is easily fused and the bondability is improved.

In particular, the thickness of the pattern recognition auxiliary layer is set to 9
When the thickness is set to 00 nm and the thickness of the second Al layer is set to 300 nm, the electrode is excellent in bondability and pattern recognition.

Further, according to the above-described method for forming an electrode of a semiconductor element, it is possible to reliably manufacture an electrode having the above advantages.

[0019]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below with reference to the drawings.

FIG. 1 shows an electrode structure of a semiconductor device according to the present invention.

The electrodes are formed on the wafer 6 from an ohmic layer 1 for lowering the resistance between the crystal and the electrode, a barrier layer 2 for suppressing the diffusion of Ga, Zn and the like to the bonding pad layer, and an Al film mixed with N _2. Pattern recognition auxiliary layer 4 and pure A
1 or a multilayer structure in which bonding pad layers 5 made of a material close to pure Al are stacked in this order.

Next, a method for forming an electrode having the above-mentioned multilayer structure will be described.

A GaAs wafer 6 on which AgZn is deposited is introduced as an ohmic layer 1 into a film forming chamber of a multi-chamber type sputtering apparatus, and Ti / Al sputtering is performed. The barrier layer 2 is formed on the ohmic layer 1 of the wafer 6 by a Ti sputtering process.

In the subsequent Al sputtering process, a sputtering gas in which N ₂ gas is mixed at 5% with respect to Ar gas is used to deposit N ₂ mixed Al on the barrier layer 2.
A pattern recognition auxiliary layer 4 made of a film is formed. Next, A
A bonding pad layer 5 made of pure Al is formed on the pattern recognition auxiliary layer 4 using a sputtering gas consisting of only r gas.

Table 1 below shows the conditions of the above Al sputtering.

[0026]

[Table 1]

Through the above steps, the electrode of the semiconductor device of the present invention is manufactured.

Next, the N ₂ mixing ratio with respect to the Ar gas is set to 5%.
Of the surface of the pure Al layer as the bonding pad layer when the film thickness of the N ₂ mixed Al layer as the pattern recognition auxiliary layer was changed from 600 nm to 1350 nm by performing sputtering using the sputtering gas set as above. I do. Figure 2 shows the manner of change of the grain boundary size of the pure Al layer when the organization photograph, (a) represents N ₂
600 nm thickness of mixed Al layer, 300 n thickness of pure Al layer
(b) is a film thickness of 900 n of the Al layer mixed with N _2.
m, in the case of thickness 300nm of pure Al layer, (c) is N ₂
The thickness of the mixed Al layer is 1200 nm and the thickness of the pure Al layer is 30
In the case of 0 nm, (d) shows the thickness 135 of the N ₂ mixed Al layer.
0 nm and a case where the thickness of the pure Al layer is 300 nm are shown.

As a result, as shown in FIG. 2, it can be seen that the dendrite shape on the Al surface observed after the surface roughening treatment becomes smaller as the film thickness of the N ₂ -containing Al layer increases. This is, as shown by the model in FIG.
When forming a pure Al layer on the ₂ mixed Al film, a pure Al layer is for reduced intergranular size of N ₂ mixed Al layer yet pure Al is deposited taken over. Therefore, the pure Al layer becomes a surface state having a fine dendrite shape after the surface roughening treatment, and the pattern recognizability is improved. Moreover,
Since it is made of pure Al, the Au wire is easily fused and the bondability is improved.

In particular, when the thickness of the N ₂ -containing Al layer is 900 nm and the thickness of the pure Al layer is 300 nm in FIG. 2B, a bonding pad layer excellent in pattern recognition and bondability can be realized. Was. It has been confirmed by experiments that bondability is ensured when the thickness of the pure Al layer is 300 nm or more.

In the above embodiment, a multi-chamber type sputtering apparatus is used, but a compact chamber type sputtering apparatus may be used.

[0032]

According to the present invention, the multi-layer bonding pad layer is formed by forming the _second Al layer made of pure Al or a material close to pure Al on the pattern recognition auxiliary layer made of the Al film mixed with N _2. , The second A
The l layer is deposited while inheriting the grain boundary size reduced by the pattern recognition auxiliary layer. As a result, although the second Al layer is made of pure Al or a material close to pure Al, the second Al layer has a surface state having a fine dendrite shape after the surface roughening treatment, so that the pattern recognizability can be improved. Moreover,
Since the second Al layer is made of pure Al or a material close to pure Al, bondability can be improved.

According to the second aspect of the present invention, the pattern recognition auxiliary layer has a thickness of 900 nm.
Since the thickness of the second Al layer is 300 nm, an electrode having excellent bondability and pattern recognizability can be obtained.

Further, according to the method for forming an electrode of a semiconductor device according to the third aspect, an electrode having the above advantages can be reliably manufactured.

[Brief description of the drawings]

FIG. 1 is a diagram showing an electrode structure of a semiconductor device of the present invention.

FIG. 2 shows N in a multilayer bonding pad layer of the present invention.
₂ is a structural photograph showing a change in the grain boundary size of the pure Al layer when the thickness of the mixed Al layer is changed, and FIG.
₍₂₎ 600 nm thickness of mixed Al layer, 300 thickness of pure Al layer
(b) is a 900 nm film thickness of the N ₂ mixed Al layer.
m, in the case of thickness 300nm of pure Al layer, (c) is N ₂
The thickness of the mixed Al layer is 1200 nm, and the thickness of the pure Al layer is 300
(d) is a film thickness of 1350 of the N ₂ mixed Al layer.
nm, and a case where the thickness of the pure Al layer is 300 nm.

FIG. 3 is a diagram showing an electrode structure on a wire bonding side in a general compound semiconductor.

FIG. 4 is a diagram illustrating an example of a chip pattern recognition method during wire bonding.

FIG. 5 is a model showing how a grain boundary size of a pure Al layer and an N ₂ mixed Al layer in a conventional bonding pad layer changes.

FIG. 6 is a structural photograph showing a state of a change in the grain boundary size of the dendrite shape when the N ₂ mixing ratio in the conventional bonding pad layer is changed, and (a) shows a case where the N ₂ mixing ratio is 0%. , (B) shows the case where the N ₂ mixing ratio is 1.3%,
(C) shows the case where the N ₂ mixing ratio is 3.3%.

FIG. 7 is a diagram showing the relationship between the N ₂ mixing ratio and the number of chips that can be bonded;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Ohmic layer 2 Barrier layer 3, 3 ', 5 Bonding pad layer 4 Pattern recognition auxiliary layer 6 Wafer

Claims (3)

[Claims] 1. An electrode of a semiconductor element having a multilayer bonding pad layer in which a second Al layer made of pure Al or a material close to pure Al is formed on a pattern recognition auxiliary layer made of an Al film mixed with N _2. . 2. The method according to claim 1, wherein the thickness of the pattern recognition auxiliary layer is 900.
2. The electrode according to claim 1, wherein the thickness of the second Al layer is 300 nm. 3. 3. A step of sputtering a first Al film using a sputtering gas in which an N ₂ gas is mixed with an Ar gas, and a step of sputtering the first Al film using a sputtering gas comprising only an Ar gas. Sputtering a second Al film made of pure Al or a material close to pure Al on the film.