JPH0637093A - Forming method for bump electrode - Google Patents

Abstract

PURPOSE:To prevent peeling of an intermediate metal layer and a solder layer of a bump electrode and to prevent damage of an insulating film and a semiconductor substrate by covering a protrusionlike metal layer with a positive type photoresist, irradiating it with light, allowing the photoresist to remain on an intermediate region between a head part and the substrate, and selectively forming a metal film on an upper surface of the head part. CONSTITUTION:A copper-plated layer 9 having a support part 9a fixed directly to or through conductive layers 5, 6 to a semiconductor substrate 1 and a head part 9b protruding outside from a side of the part 9a and formed on the upper part of the part 9a is formed. The layer 9 is coated with positive type photoresists 10, 11, irradiated with light, allowed the photoresists 10, 11 to remain on an intermediate region between the part 9b and the substrate 1, and a metal film is selectively formed on the part 9b. Peeling of the metal layer and the solder layer is prevented by the metal film, and generation of a damage of the insulating film and the substrate can be also suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate of a semiconductor device, and more particularly to a method of forming a bump electrode capable of preventing metal from diffusing inside.

[0002]

2. Description of the Related Art A protruding electrode of a semiconductor element, called a bump electrode, is formed on a base metal layer connected to a semiconductor substrate through an opening formed in an insulating film and a mushroom-shaped cross section on the upper surface of the base metal layer. It is composed of an intermediate metal layer and a solder layer formed in a hemispherical shape on the upper surface of the intermediate metal layer.

An intermediate metal layer having a mushroom-shaped cross section is made of copper (C
u) It is often formed by a plating layer, and in this case, the copper of the intermediate metal layer reacts with the tin (Sn) component in the solder layer to easily form a tin-copper alloy layer at the interface between the two layers. Has been confirmed. This alloy layer may reduce the bond strength of both layers with the passage of time, and eventually lead to peeling of the solder layer. Therefore, a technique has been proposed in which the surface of the copper plating layer is plated with nickel (Ni) to suppress the growth of the alloy layer.
In this technique, the nickel plating layer can suppress mutual diffusion of metal components between the solder layer and the intermediate metal layer. Further, compared to the alloy layer formed by the reaction of tin and copper, the growth rate of the nickel-copper alloy layer is sufficiently slow,
It is possible to solve the above-mentioned problem of peeling accompanying the growth of the alloy layer.

[0004]

However, the intermediate metal layer can be plated with nickel to prevent the peeling of the solder layer, but cracks are likely to occur in the laminated portion of the insulating film and the semiconductor substrate near the peripheral portion of the bump electrode. It has been found. The reason for this is not clear, but it is presumed that the nickel plating layer formed on the portion other than the intermediate metal layer causes unexpected mechanical stress during the heat treatment.

Therefore, it is an object of the present invention to provide a bump electrode forming method capable of surely preventing separation of an intermediate metal layer and a solder layer and suppressing damage to an insulating film and a semiconductor substrate.

[0006]

SUMMARY OF THE INVENTION A bump electrode forming method according to the present invention comprises a support portion fixed directly to a semiconductor substrate or indirectly fixed via a conductive layer and protruding outward from a side portion of the support portion. Forming a protruding metal layer having a head formed on the top of the support, coating the protruding metal layer with a positive photoresist, and irradiating the photoresist with light And removing the photoresist on the upper surface of the head, but leaving the photoresist in the intermediate region between the head and the semiconductor substrate, and a step of selectively forming a metal film on the upper surface of the head. including.

[0007]

In the exposure, the head of the protruding metal layer is used as a light-shielding mask to selectively leave a positive photoresist below the head, and the remaining photoresist is further used as a mask for plating or vapor deposition. The metal layer can be selectively formed on the upper surface of the head.

When a solder layer is formed on the upper surface of this metal layer,
This metal layer has an effect of suppressing mutual diffusion of metal components between the protruding metal layer and the solder layer. Further, since the metal layer is formed only on the upper surface of the head, the mechanical stress caused by the difference in the expansion coefficient of the metal layer can be reduced.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of a bump electrode forming method according to the present invention will be described below with reference to FIGS.

First, aluminum (Al) is formed on the entire upper surface of a semiconductor substrate (wafer) (1) made of silicon (Si) or the like.
Is vacuum-deposited, and then selectively etched to form an aluminum layer (2) having a thickness of about 2 μm (micrometer) shown in FIG.

Next, the well-known CVD (Chemical Vapor Dep
After forming a silicon dioxide (SiO2) film on the entire upper surface of the semiconductor substrate (1) by an osition method or the like, it is selectively etched to have an opening (4) in a bump electrode formation planned region as shown in FIG. An insulating film (3) is formed. The center side of the aluminum layer (2) is exposed from the opening (4) and the peripheral side is covered with the insulating film (3).

Then, as shown in FIG. 3, the semiconductor substrate (1)
Of chromium (Cr) and copper (Cu) are continuously vacuum-deposited on the entire upper surface of the substrate to form a chromium layer (5) having a thickness of about 4,500 Å and a copper layer (6) having a thickness of about 3 μm. . The aluminum layer (2), the chromium layer (5) and the copper layer (6) form a conductive layer, and the chromium layer (5) and the copper layer (6) form an intermediate metal layer.

Further, a photoresist is formed on the entire upper surface of the copper layer (6) and a part thereof is selectively removed by etching.
As shown in FIG. 4, a photoresist film (8) having an opening (7) is formed. A part of the copper layer (6) is exposed from the opening (7) provided in the bump electrode formation planned region. Then, the photoresist film (8) in and around the opening (7)
A copper plating layer (9) having a thickness of 30 to 40 μm is formed thereon as a protruding electrode layer. The cross-sectional shape of the copper plating layer (9) has a supporting portion (9a) that directly contacts the copper layer (6) through the opening (7).
And a head portion (9b) extending on the upper surface of the photoresist film (8) near the opening (7). Therefore, the support portion (9a) of the copper plating layer (9) is embedded in the opening (7), and the head portion (9b) extends outward from the side portion of the support portion (9a) and the peripheral edge of the opening (7). There is.

Next, after removing the photoresist film (8) of FIG. 4, the semiconductor substrate (1) is immersed in a predetermined etching solution to support the copper plating layer (9) as shown in FIG. The chromium layer (5) and the copper layer (6) extending outside the portion (9a) are partially removed. Since the copper plating layer (9) serves as a mask during etching, the chromium layer (5a) and the copper layer (6a) remain below the supporting portion (9a) and in the vicinity thereof.
In this embodiment, the respective peripheral portions of the chromium layer (5) and the copper layer (6) forming the intermediate metal layer are located inside the head portion (9b). In the etching treatment, the surface portion of the copper plating layer (9) is also slightly melted, but since the diameter and thickness of the copper plating layer (9) are sufficiently larger than those of the chromium layer (5) and the copper layer (6),
The effect of etching the copper plating layer (9) is negligible.

Next, as shown in FIG. 6, a first positive photoresist (10) is formed on the entire upper surface of the semiconductor substrate (1).
And a second positive photoresist (11) are sequentially applied.
Both the first positive photoresist (10) and the second positive photoresist (11) are photoresists that become soluble in a developing solution such as an alkaline aqueous solution when exposed. Here, the head (9b) of the copper plating layer (9)
And the insulating film (3) face each other in a narrow region A of several tens of μm. In this embodiment, after filling the narrow region A with the first positive photoresist (10) having relatively high fluidity, the second positive photoresist (11) having relatively low fluidity is provided. By applying (1), it is possible to secure a large resist film thickness and satisfactorily fill the narrow region A with photoresist.

As shown in FIG. 6, the photoresist has a head (9
It is formed relatively thin on the outer peripheral side of b). Also, the head (9
The thickness of the photoresist becomes thinner as it is separated from the outer peripheral side of b).

Next, the photoresists (10) and (11) are irradiated with ultraviolet rays in the direction of arrow B in FIG. 6 which is orthogonal to the surface of the semiconductor substrate (1), whereby the copper plating layer (9) serving as a light-shielding mask is formed. The head portion (9b) blocks irradiation of the photoresist (10) (11) filled in the narrow region A with ultraviolet rays. When the semiconductor substrate (1) is dipped in a developing solution such as an alkaline aqueous solution after being irradiated with ultraviolet rays, as shown in FIG. 7, the photoresists (10a) and (11a) in the narrow region A remain and the photo resists in other regions are left. The resists (10) (11) are removed by etching.

Next, the semiconductor substrate (1) of FIG. 7 is plated with nickel (Ni), and the head portion (9b) of the copper plating layer (9).
Nickel plating layer (12) with a thickness of about 0.5 μm on the top surface
Is formed as a metal film. Photoresist (10a) (11
The underside of the head (9b) covered by a), the support (9
a), the nickel plating layer (12) is not formed on the side surfaces of the chromium layer (5a) and the copper layer (6a). In particular, the photoresists (10a) (11a) effectively prevent the nickel plating layer (12) from adhering to the chromium layer (5a) and the copper layer (6a). Since the insulating film (3) made of silicon dioxide is completely separated from the nickel plating layer (12) by the photoresists (10a) (11a), the nickel plating does not adhere to it.

Finally, as shown in FIG. 9, lead (P) is formed on the upper surface of the copper plating layer (9) through the nickel plating layer (12).
Solder containing b) and tin (Sn) as components is selectively adhered by plating or the like to form a hemispherical solder layer (13) to complete the bump electrode. The thickness of the nickel plating layer (12) is
The thickness is preferably 1 μm or less in order to reduce the mechanical stress, but is preferably 0.3 μm or more in order to sufficiently suppress the mutual diffusion of metal components between the copper plating layer (9) and the solder layer (13).

According to the bump electrode formed in this embodiment, the following effects can be obtained.

(1) Since the nickel plating layer (12) is interposed between the copper plating layer (9) and the solder layer (13), copper of the copper plating layer (9) and lead of the solder layer (13) or Mutual diffusion of tin is suppressed, and delamination of the bump electrodes due to alloy layer growth can be prevented.

(2) Since the nickel plating layer (12) is formed only on the upper surface of the copper plating layer (9), the mechanical stress due to the difference in the expansion coefficient of the nickel plating layer (12) is caused by the insulating film ( 3) and does not affect the semiconductor substrate (1).

The embodiment of the present invention is not limited to the above embodiment, and can be modified. For example, the present invention can be applied to power Schottky barrier diodes and other semiconductor devices. Further, although the conductive layer is composed of the aluminum layer (2), the chromium layer (5) and the copper layer (6), the conductive layer may be omitted and the copper plating layer (9) may be directly fixed to the semiconductor substrate (1). The copper plating layer (9) can be fixed to the semiconductor substrate (1) through a desired number of layers. Furthermore, although the example in which the copper plating layer (9) is formed as the protruding electrode layer has been shown, other metals such as aluminum may be used. Photosensitization and development of the photoresists (10) and (11) may be performed twice. First, as shown in FIG. 10, by utilizing the difference in the thickness of the resist, the resist is left on the outer peripheral side of the head portion (9b), and the photoresist is developed again to form the resist as shown in FIG. Good.

[0024]

As described above, according to the present invention, the metal layer formed only on the upper surface of the head prevents the intermediate metal layer and the solder layer from being separated from each other, and the insulating film and the semiconductor substrate. A bump electrode forming method capable of suppressing the occurrence of damage to the bump electrode is obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a state in which an aluminum layer is formed on a semiconductor substrate used in the method for forming bump electrodes according to the present invention.

FIG. 2 is a sectional view showing a state in which an insulating layer is formed in FIG.

FIG. 3 is a cross-sectional view showing a state in which an intermediate metal layer is formed in FIG.

FIG. 4 is a cross-sectional view showing a state in which a copper plating layer is formed as a protruding electrode layer in FIG.

FIG. 5 is a cross-sectional view showing a state in which the peripheral edge portion of the intermediate metal layer is removed by etching in FIG.

FIG. 6 is a cross-sectional view showing a state in which a photoresist is applied in FIG.

FIG. 7 is a cross-sectional view showing a state in which the photoresist around the protruding electrode layer has been removed after irradiation with ultraviolet rays in FIG.

FIG. 8 is a sectional view showing a state in which a nickel plating layer is formed on the upper surface of the protruding metal.

FIG. 9 is a sectional view showing a state in which a solder layer is formed on a nickel plating layer.

FIG. 10 is a sectional view showing another embodiment of the present invention.

[Explanation of symbols]

(1). ． ． Semiconductor substrate, (2). ． ． An aluminum layer, (3). ． ． Insulating layer, (4). ． ． Opening,
(Five). ． ． Chrome layer (conductive layer), (6). ． ． Copper layer (conductive layer), (7). ． ． Opening, (8). ． ． Photoresist film, (9). ． ． Copper plating layer, (9a). ． ． Support, (9
b). ． ． Head, (10), (11). ． ． Photoresist, (12). ． ． Nickel plating layer (metal film), (1
3). ． ． Solder layer,

Claims (1)

[Claims] 1. A support portion directly fixed to a semiconductor substrate or indirectly fixed via a conductive layer, and a head portion protruding outward from a side portion of the support portion and formed on an upper portion of the support portion. A step of forming a protruding metal layer provided with, a step of coating the protruding metal layer with a positive photoresist, irradiating the photoresist with light to expose it to light, Although the photoresist is removed, the method includes the steps of leaving the photoresist in an intermediate region between the head and the semiconductor substrate, and selectively forming a metal film on the upper surface of the head. Forming method of bump electrode.