JPH0653222A - Formation method of bump electrode - Google Patents

Abstract

PURPOSE:To achieve that a bump electrode can be formed at a prescribed height without reducing the maximum width of the bump electrode by a method wherein a protrusion-shaped metal layer is covered with a photoresist, the photoresist at the upper part is removed and the head part of the protrusion- shaped metal layer which has been exposed is removed by etching by a definite thickness. CONSTITUTION:A protrusion-shaped metal layer 9 is formed in such a way that it is provider with a support part 9a which is fixed and bonded directly to a semiconductor substrate 1 or fixed and bonded indirectly via conductive layers 2, 5, 6 and that it is provided with a head part 9b formed at the upper part of the support part 9a so as to protrude to the outside from the side part of the support part 9a. Then, the protrusion-shaped metal layer 9 is covered with positive-type photoresists 10, 11, and the photoresists 10, 11 with which the upper part of the head part 9b of the protrusion-shaped metal layer 9 is covered are removed selectively by etching. Then, the head part 9b of the protrusion-shaped metal layer 9 which is exposed from the photoresists 10, 11 is removed by etching by a prescribed thickness. For example, a protrusion- shaped metal layer 9 is formed as a plated layer composed of copper.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bump electrode forming method.

[0002]

2. Description of the Related Art A protruding electrode of a semiconductor element called a bump electrode has a base metal layer connected to a semiconductor substrate through an opening formed in an insulating film and a mushroom-shaped cross section formed 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.

[0003]

By the way, in the case of forming this kind of bump electrode at a low height, the upper portion thereof may be removed by etching, but if etching is simply performed, the diameter of the bump electrode becomes small. is there.

Therefore, the present invention provides a method of forming bump electrodes which can form bump electrodes at a desired height without reducing the maximum lateral width of the bump electrodes.

[0005]

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. A step of forming a protruding metal layer having a head formed on the top of the support, a step of coating the protruding metal layer with a positive photoresist, and an upper part of the head of the protruding metal layer. The method includes a step of selectively removing the photoresist to be coated by etching, and a step of removing the head portion of the protruding electrode layer exposed from the photoresist by a certain thickness by etching. This bump electrode forming method may further include a step of selectively forming a metal film on the upper surface of the head. In the step of coating the photoresist, a first positive photoresist having a relatively high fluidity and a second positive photoresist having a relatively low fluidity are formed on the surface of the first photoresist. And a process may be included.

[0006]

Function: The photoresist covering the upper part of the head of the protruding metal layer is selectively removed by etching, and the remaining part of the photoresist is used as a mask to remove the head of a certain thickness by etching. The head thickness can be reduced without substantially reducing the maximum lateral width.

[0007]

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 of this 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 whose exposed areas are soluble in a developing solution. Copper plating layer (9)
The facing interval between the head portion (9a) and the insulating film (3) is 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 applied. By coating, a large resist film thickness can be secured and the narrow region A can be filled with the photoresist well.

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

Next, the photoresists (10) and (11) are irradiated with ultraviolet rays for a certain period of time in the direction of arrow B in FIG. 6 which is orthogonal to the surface of the semiconductor substrate (1). The photoresist (10) (11) filled in the narrow region A is protected from ultraviolet rays by the head portion (9b) of the copper plating layer (9) serving as a light shielding mask.
Therefore, when developed later, photoresist (10)
Although (11) is exposed to light and removed by etching, the photoresists (10) and (11) in the narrow region remain. Further, since the photoresist is formed relatively thick on the outer peripheral side of the head (9b), if an appropriate exposure amount and development time are selected, the outer peripheral side of the head (9b) will be changed as shown in FIG. Photoresist (10) (1) also on the peripheral side of the bump electrode so as to cover it.
1) remains partially.

Next, the remaining photoresist (10) (1
Using 1) as a mask, the bump electrode is etched. Since the photoresists (10) and (11) remain on the side surface of the bump electrode and the outer peripheral side of the head portion (9b), the head portion (9b) of the bump electrode is etched only in the vertical direction as shown in FIG. ,
The diameter (maximum width) of the head (9b) does not become substantially smaller.

Next, nickel (Ni) plating is applied to the semiconductor substrate (1) of FIG. 8 to form a 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). The insulating film (3) made of silicon dioxide is completely separated from the nickel plating layer (12) by the photoresists (10a) (11a), and the nickel plating does not adhere.

Finally, as shown in FIG. 10, solder is selectively adhered to the upper surface of the copper plating layer (9) through the nickel plating layer (12) by plating or the like to obtain lead (Pb) and tin (Pb). Forming a hemispherical solder layer (13) containing Sn) as a component,
Complete the bump electrodes. The thickness of the nickel plating layer (12) is preferably 1 μm or less in order to reduce mechanical stress, but in order to sufficiently suppress mutual diffusion of metal components between the copper plating layer (9) and the solder layer (13), 0.3 μm or more is preferable.

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

(1) The photoresists (10) and (11) can suppress the etching of the bump electrode in the radial direction, and can form the bump electrode at a low height without reducing the diameter.

(2) 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.

(3) Since the nickel plating layer (12) is formed only on the upper surface of the copper plating layer (9), the influence of mechanical stress caused by the difference in the expansion coefficient of the nickel plating layer (12) and the like is prevented from occurring in the insulating film. Do not apply to (3) and 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 a power Schottky barrier diode 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 is shown, a plating layer of another metal such as aluminum may be used.

[0024]

As described above, according to the present invention, the height of the bump electrode can be lowered without reducing the maximum lateral width of the bump electrode.

[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 cross-sectional view showing a state in which the upper surface of the protruding metal head is removed by etching.

FIG. 9 is a cross-sectional view showing a state where a nickel plating layer is formed on the upper surface of the protruding metal removed by etching.

FIG. 10 is a sectional view showing a state in which a solder layer is formed on a nickel plating layer.

[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 (3)

[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, a step of coating the protruding metal layer with a positive photoresist, and selectively etching the photoresist covering the top of the head of the protruding metal layer by etching. A method of forming a bump electrode, comprising: a step of removing; and a step of removing a head portion of the protruding electrode layer exposed from the photoresist by a predetermined thickness by etching. 2. The bump electrode forming method according to claim 1, further comprising the step of selectively forming a metal film on the upper surface of the head. 3. The step of coating the photoresist comprises applying a first positive photoresist having a relatively high fluidity and a second positive photoresist having a relatively low fluidity to the first photoresist. The method of forming a bump electrode according to claim 1, further comprising the step of forming the bump electrode on the surface of the bump electrode.