JPH0682630B2 - Method for manufacturing multi-layer electrode of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to a method for manufacturing a multilayer electrode of a semiconductor element such as a diode, a transistor, or an IC.

[Problems to be Solved by Prior Art and Invention]

It is known to form a multilayer electrode composed of an Al (aluminum) layer, a Ti (titanium) layer and a Ni (nickel) layer on a silicon semiconductor element (silicon semiconductor chip) by vacuum evaporation. In this Al-Ti-Ni electrode, the adhesion of the Al layer to the silicon semiconductor element is good regardless of the conductivity type of the semiconductor region to be connected, and there is good ohmic contact with the silicon semiconductor element. It has a function as a contact metal layer to be obtained, the Ni layer has a function as a soldering metal layer with good solder adhesion, and the Ti layer is interposed between the Al layer and the Ni layer. It has the function of a glue (glue) metal layer for improving the adhesion of the layer. Therefore, the Al-Ti-Ni electrode is an ideal electrode that allows good soldering of the lead electrode and has good adhesion to the semiconductor element.

The present inventor applied the above Al-Ti-Ni electrode to an electrode of a planar type PN junction diode, and as one mode thereof, stretching the lower Al layer on the outer peripheral side of the Ni layer, and forming this Al layer into a well-known field. We tried to make an Al-Ti-Ni electrode that functioned as a plate. In this case, the Al layer is likely to be corroded due to long-term use, etc., and it may also be a cause of impairing the withstand voltage. desirable. The inventor of the present application produced the Al-Ti-Ni electrode by the following two production methods. In the first method, first, a thermal oxide film is formed on the upper surface of the semiconductor element, and then the central portion of the thermal oxide film is removed by etching. Next, the Al layer, the Ti layer, and the Ni layer are sequentially vacuum-deposited, and then the periphery of the Ni layer and the Ti layer are removed by etching to expose the Al layer functioning as a field plate. Next, a protective film (insulating film) made of a silicon oxide film or the like is formed on the exposed upper surface of the Al layer by a CVD method (vapor phase growth method) or the like. In the second method, first, a thermal oxide film is formed on the upper surface of the semiconductor element, and then the central portion of the thermal oxide film is removed by etching. Next, after vacuum-depositing the Al layer, a protective film made of a silicon oxide film or the like is formed on the upper surface of the Al layer on the element peripheral side by a CVD method or the like. Next, a Ti layer and a Ni layer are sequentially vacuum-deposited on the upper surface of the semiconductor element, and the element peripheral side of this vapor deposition layer is etched and removed. However, it has been found that the Al-Ti-Ni electrode formed by the above two manufacturing methods has the following problems. That is, in the first method, the upper surface of the Ni layer is oxidized during the formation of the protective film, and the solder adhesion is impaired. Therefore, the inventor of the present application tried to etch the upper surface of the Ni layer in order to remove the oxidation of the upper Ni layer. However, since the Ni layer is generally formed as thin as about 5000 Å, it is difficult to selectively remove only the oxide film, and if the oxide film is sufficiently removed to sufficiently improve the adhesiveness, it is difficult to remove the Ni film. The layers may be removed by etching more than necessary. Also, in the second method,
The upper surface of the Al layer is oxidized when the protective film is formed,
The adhesion with the Ti layer was reduced, and peeling between the two layers occurred. In this case, it is considered that the upper surface of the Al layer may be etched before the Ti layer is deposited. However, even with this, peeling could not be sufficiently prevented, and the yield did not increase so much.

Therefore, an object of the present invention is to provide one means for solving the above problems.

[Means for Solving the Problems]

The present invention for achieving the above object comprises a first step of preparing a semiconductor substrate having at least one main surface made of a silicon semiconductor region, and a first metal layer made of aluminum on one main surface of the semiconductor substrate. A second step of forming at least a part of the first metal layer in contact with the silicon semiconductor region, a third step of coating an outer peripheral portion of the first metal layer with an insulating film, and the first metal layer A second metal layer made of aluminum on the upper surface of the metal layer, a third metal layer having good adhesion to the aluminum layer and the nickel layer and made of a metal other than aluminum and nickel, and nickel. And a fourth step of sequentially forming a fourth metal layer by vapor deposition, which relates to a method for manufacturing a multilayer electrode of a semiconductor device.

Further, in the case of the field plate structure, the second insulating film may be provided below the outer peripheral portion of the first metal layer and the second insulating film may be provided above the outer peripheral portion of the first metal layer. desirable.

[Work]

According to the invention of claim 1, since the outer peripheral portion of the first metal layer made of aluminum is covered with the insulating film (protective film), oxidation and corrosion of the first metal layer are prevented. In addition, the withstand voltage at the outer peripheral portion of the first metal layer is improved. Further, since both the first metal layer and the second metal layer are made of aluminum, a layer called a solid solution layer (solid solution region) is formed between the first metal layer and the second metal layer and both layers are formed. The layers adhere well. Further, the second, third and fourth metal layers are made of different metal materials, but they are sequentially formed without interposing the insulating film forming step, so that the second metal layer and the third metal layer are not formed. Also, good adhesion between the third metal layer and the fourth metal layer can be obtained.

According to the second aspect of the invention, the outer peripheral portion of the first metal layer can be made to function favorably as a field plate.

[First Embodiment] A method of manufacturing a planar type PN junction diode according to the first embodiment of the present invention will be described below.

In order to form the planar type PN junction diode of this embodiment shown in FIG. 1 (E), first, the semiconductor substrate 1 made of silicon (Si) as shown in FIG. 1 (A) is prepared. This semiconductor substrate 1 has an N ⁺ region 2 of the first conductivity type, an N region 3 formed on its upper surface, and an N region 3 so that its upper surface is exposed.
The second conductivity type P ⁺ region 4 and the N ⁺ region 5 are formed in the region 3. Here, the N region 3 and the N ⁺ region 2 form the cathode region of the PN junction diode, and the P ⁺ region 4 form the anode region. The N ⁺ region 5 is spaced apart from the P ⁺ region 4 and surrounds it in an annular shape.

Next, the semiconductor substrate 1 is heat-treated in an oxidizing atmosphere,
A silicon oxide film having a thickness of about 1 μm is formed on the entire upper surface of the semiconductor substrate 1. The silicon oxide film may be a thermal oxide film formed during the diffusion of P ⁺ region 4 and N ⁺ region 2. Subsequently, the element central portion and the element peripheral portion of the silicon oxide film are etched and removed, and the first silicon oxide film 6 as the first insulating film is left in a ring shape as shown in FIG. 1 (B). Let The first silicon oxide film 6 covers the exposed surface portion of the PN junction 7 between the N region 3 and the P ⁺ region 4.

Next, an Al layer as a first metal layer is formed on the entire upper surface of the semiconductor substrate 1 by a known vacuum deposition method. Subsequently, the vapor-deposited Al layer is partially removed by etching to leave the first Al layer 8 and the EQR (equipotential ring) Al layer 9 as shown in FIG. 1 (C). Al layers 8 and 9 both have a thickness of about 5 μm
Is. The central portion of the first Al layer 8 is in ohmic contact with the upper surface of the P ⁺ region 4 exposed on the upper surface of the semiconductor substrate 1. The outer peripheral portion of the first Al layer 8 extends over the first silicon oxide film 6 and over the exposed portion of the PN junction 7 and over the N region 3. Therefore, the outer peripheral portion of the first Al layer 8 is adjacent to the N region 3 through the first silicon oxide film 6 and acts as a well-known field plate to form the PN junction 7
Contributes to the improvement of the withstand voltage of the periphery. EQR A remaining in a ring
The l layer 9 is a ring-shaped N ⁺ layer exposed on the upper surface of the semiconductor substrate 1.
It is in ohmic contact with the area 5. The Al layer 9 and the N ⁺ region 5 act as a well-known EQR (equipotential ring) and contribute to the stable breakdown voltage of the PN junction 7.

Next, after the Al layers 8 and 9 are sintered or not, a silicon oxide film with a thickness of about 1 μm is formed on the entire upper surface of the semiconductor substrate 1 by the CVD method, and then the central portion of the silicon oxide film and the periphery of the element are formed. The portion is removed by etching to form a second silicon oxide film 10 as a second insulating film as shown in FIG. 1 (D). This second silicon oxide film 10
Covers the entire upper surface of the equipotential ring Al layer 9 and the upper surface of the outer peripheral portion of the ohmic electrode first Al layer 8. An opening 11 for exposing the first Al layer 8 for ohmic electrodes is formed in the central portion of the second silicon oxide film 10. The opening 11 is arranged inside the exposed surface of the PN junction 7.

Next, prior to vacuum-depositing the second metal layer on the upper surface of the first Al layer 8, the upper surface of the first Al layer 8 is etched with an HF (hydrofluoric acid) -based etching solution, The oxide film formed when forming the second silicon oxide film 10 is removed.
The oxide film on the upper surface of the first Al layer 8 may remain if it is extremely thin.

Next, a second Al layer, a Ti layer, and a Ni layer are formed on the entire upper surface of the semiconductor substrate 1.
After the layers are sequentially vacuum-deposited, the peripheral portions of these vapor-deposited layers are removed by etching to remove the second layer as shown in FIG. 1 (E).
Al layer (second metal layer) 12 and Ti layer (third metal layer) 13 of
A Ni layer (fourth metal layer) 14 is formed. The Al layer, the Ti layer, and the Ni layer were vapor deposited materials Al, Ti, and Ti while maintaining a low-pressure atmosphere.
It is formed by a method of sequentially switching to Ni, a so-called continuous vapor deposition method. The thicknesses of the second Al layer 12, Ti layer 13 and Ni layer 14 are respectively
It is 5000Å, 1000Å, 5000Å. The second Al layer 12 is in contact with the first Al layer 8 through the opening 11 and is electrically connected to the first Al layer 8 together with the Ti layer 13 and the Ni layer 14, thereby forming the anode electrode. 15 are formed. Second Al
The outer peripheral edges of the layer 12, the Ti layer 13 and the Ni layer 14 are separated from the edge of the opening 11 of the second silicon oxide film 10. Therefore, the second Al
A part of the surface of the first Al layer 8 is exposed on the outer peripheral side of the layer 12, the Ti layer 13, and the Ni layer 14. However, since this exposed portion is small, oxidation or corrosion of this portion does not pose a problem to the characteristics or reliability of the electrode. Then 300 ℃
The first Al layer 8 and the second Al layer 12 are sintered at a temperature of 400 ° C.
Improves adhesion with. In addition, on the lower surface of the semiconductor substrate 1,
As shown in Fig. 1 (E), Ti and Ni are continuously vapor-deposited to form N ⁺
A cathode electrode 16 is formed in ohmic contact with the region 2.

According to the manufacturing method of this embodiment, the following effects can be obtained.

(1) The outer peripheral portion of the first Al layer 8 which is not covered by the second Al layer 12, Ti layer 13, and Ni layer 14 is the second silicon oxide film 10
To prevent its corrosion. Therefore, the first Al layer 8 functions well as an anode electrode and a field plate. In addition, the first Al layer 8 and A for EQR
The withstand voltage between the I-layers 9 can be sufficiently increased, and the problem of insufficient withstand voltage does not occur.

(2) Since the Ni layer 14 is formed after forming the second silicon oxide film 10 that covers the first Al layer 8, the Ni layer 14 is not oxidized. Therefore, good solder adhesion of the Ni layer 14 can be obtained.

(3) Since the second Al layer 12, the Ti layer 13 and the Ni layer 14 are continuously vapor-deposited, the adhesion between the Al layer 12 and the Ti layer 13 and the adhesion between the Ti layer 13 and the Ni layer 14 are excellently obtained. Further, although the step of forming the silicon oxide film 10 is interposed between the step of forming the first Al layer 8 and the step of forming the second Al layer 12, the first and second Al layers 8 and 12 are formed. Since they are the same metal layer, both layers adhere well. That is, even if an extremely thin oxide film remains on the first Al layer 8 when the surface of the first Al layer 8 is chemically treated before the formation of the second Al layer 12, the first and Since the second Al layers 8 and 12 are bonded by the solid solution layer formed by solid-solving the second Al layers 8 and 12, the adhesion between both layers is sufficiently high. As a result, the first Al layer 8 and the second Al layer 8
The peeling between the Al layers 12 is prevented, and the chemical treatment process of the Al layers 8 can be simplified. The second Al layer 12 is Ti
Since the layer 13 and the Ni layer 14 can be formed by continuous vapor deposition using the vapor deposition process and the thickness thereof is 5000 Å, the provision of this does not complicate the manufacturing process so much.

(4) In plan view, the outer peripheral side of the Ni layer 14 having good solder adhesion is surrounded and surrounded by the first Al layer 8 having poor solder adhesion. Therefore, when the lead electrode is soldered to the Ni layer 14, the solder spreads only on the upper surface of the Ni layer 14, and the solder does not spread on the outer peripheral portion of the first Al layer 8 serving as a field plate. As a result, the phenomenon that the peripheral part of the electrode (here, the outer peripheral part of the Al layer 8) is not peeled off due to the tensile stress caused by the solidification of the solder, etc., the mechanical strength is combined with the effect of the item (3). It is possible to form a multi-layer electrode having a large size.

[Second Embodiment] Next, a method for manufacturing a planar type PN junction diode according to a second embodiment of the present invention will be described.

In this embodiment, the PN junction diode shown in FIG. 2 is manufactured. In order to form the PN junction diode shown in FIG. 2, the semiconductor substrate 1 shown in FIG.
To prepare. Then, the semiconductor substrate 1 is subjected to the same steps as those in the first embodiment, and the semiconductor substrate 1 shown in FIG.
To prepare. Next, an Al layer, a Ti layer, and a Ni layer are continuously vapor-deposited on the entire upper surface of the semiconductor substrate 1, and then these vapor-deposited layers are selectively removed by etching. As shown in FIG. A second Al layer 12, a Ti layer 13 and a Ni layer 14 whose outer peripheral side extends to the upper surface of the silicon oxide film 10 are formed. The second
The outer peripheral edges of the Al layer 12, the Ti layer 13, and the Ni layer 14 are located inside the outer peripheral edge of the first Al layer 8. First and second Al layers 8,
12, the Ti layer 13, and the Ni layer 14 function as the anode electrode 15, and the portion of the first Al layer 8 extending to the upper surface of the N region 3 functions as a field plate. Note that Ti and Ni are continuously vapor-deposited on the lower surface of the semiconductor substrate 1 to form the cathode electrode 16, as in the first embodiment.

The second embodiment has the same effects as the items (1) to (3) of the first embodiment, and selectively and favorably the second Al layer 12, Ti layer 13 and Ni layer 14 are formed. It also has the effect of enabling etching. That is, in the first embodiment, the first Al layer 8 and the second Al layer 8
Since the Al layer 12 is continuous in the region to be etched, it is difficult to accurately etch the first Al layer 12 to the boundary with the first Al layer 8. On the other hand, according to the second embodiment, since the silicon oxide film 10 is present in a part between the first Al layer 8 and the second Al layer 12, the second Al
The layer 12 up to the interface of the oxide film 10 can be removed by etching easily with good control. Further, the peeling of the electrode at the periphery does not pose a practical problem because the adhesion between the second Al layer 12 and the second silicon oxide film 10 can be obtained relatively well.

[Modification]

The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible, for example.

(1) In the first embodiment, the opening 11 of the silicon oxide film 10
The outer peripheral edge of the second Al layer 12 may be adjacent to the edge of the.

(2) Instead of the Ti layer 13, a Cr (chrome) layer may be provided as a green metal layer.

(3) In the second embodiment, the Ti layer 13 and the Ni layer image 14 are
Second Al layer formed inside the Al layer 12 of
12 may be extended to the outer peripheral side of the Ti layer 13 and the Ni layer 14. In this case, the solder spreads only on the upper surface of the Ni layer 14 and is not formed on the upper surface of the Al layer 12, so that peeling at the interface between the Al layer 12 and the second silicon oxide film 10 can be prevented more reliably. it can. In this case, the structure is such that the periphery of the second Al layer 12 is exposed, and the exposed portion of this second Al layer 12 is the same as the Ti electrode 13 and the first electrode.
Since it is not a portion which directly functions as an electrical connection or a field plate of the Al layer 8, corrosion of this portion hardly affects the characteristics. In addition, since the upper surface of the first Al layer 8 is covered with the second silicon oxide film 10, the corrosion of the second Al layer 12 causes the corrosion of the first Al layer 8 and the semiconductor substrate 1.
Does not affect the surface.

(4) The second Al layer 12 does not have to be formed thick because it adheres well to the first Al layer 8 by the solid solution layer. Considering the shortening of the vacuum deposition process, the thickness of the second Al layer 12 is 2μ.
m or less, preferably 1 μm or less.

(5) The present invention can also be applied to the case where the first Al layer 8 is formed only inside the P ⁺ region 4 when viewed two-dimensionally (when the field plate is not provided).

〔The invention's effect〕

As described above, according to the manufacturing method of the first and second aspects, the adhesiveness between the semiconductor element and the insulating film, the adhesiveness of the solder, and the adhesiveness between the respective layers can be satisfactorily obtained, and the first adhesive made of aluminum is used. It is possible to form a highly reliable multilayer electrode in which the outer peripheral portion of the metal layer is covered with the insulating film and the oxidation and corrosion of the metal layer are reliably prevented, with a good yield, and relatively easily. According to the manufacturing method of claim 2, the field plate effect can be satisfactorily obtained.

[Brief description of drawings]

1A to 1E are cross-sectional views for explaining a method of manufacturing a semiconductor device according to a first embodiment of the present invention in the order of steps, and FIG. 2 is a semiconductor device according to a second embodiment of the present invention. FIG. 1 ... Semiconductor substrate, 6 ... First silicon oxide film, 8 ...
... first Al layer, 10 ... second silicon oxide film, 12 ... second Al layer, 13 ... Ti layer, 14 ... Ni layer.

Claims (2)

[Claims] 1. A first step of preparing a semiconductor substrate having at least one main surface made of a silicon semiconductor region, and a first metal layer made of aluminum at least a part of which is provided on one main surface of the semiconductor substrate. A second step of forming so as to be in contact with the silicon semiconductor region; a third step of covering the outer peripheral portion of the first metal layer with an insulating film; and an aluminum upper surface of the first metal layer. A second metal layer, a metal layer having good adhesion to the aluminum layer and the nickel layer, and a third metal layer made of a metal other than aluminum and nickel, and a fourth metal layer made of nickel. And a fourth step of sequentially forming by vapor deposition. 2. A first step of preparing a semiconductor substrate in which at least one main surface is a first semiconductor region of a first conductivity type made of silicon, and the first semiconductor region except the upper surface is formed in the first semiconductor region. Forming an enclosed second semiconductor region of a second conductivity type opposite to the first conductivity type, and exposing a surface of a PN junction of at least the first semiconductor region and the second semiconductor region. And a second step of forming a first insulating film that covers the vicinity thereof and has an opening that exposes the second semiconductor region; and contacting the second semiconductor region through the opening. A third step of forming a first metal layer made of aluminum at least on a surface exposed portion of the PN junction and an upper portion in the vicinity thereof through the first insulating film, and Form a second insulating film that covers the outer periphery And a second metal layer made of aluminum on the upper surface of the first metal layer, a metal layer having good adhesion to the aluminum layer and the nickel layer, and other than aluminum and nickel. And a fifth step of sequentially forming a third metal layer made of the above metal and a fourth metal layer made of nickel, the method for producing a multilayer electrode of a semiconductor device.