JPH05144823A - High density bump forming method - Google Patents

Abstract

PURPOSE:To easily form the bump of a conductive circuit in high density by a technique in which a sleeper-like cushion part is formed using photosensitive polyimide in the vicinity of a plurality of pad parts, and a conductive circuit is formed on the region ranging from the surface of each pad part to the surface of a cushion part. CONSTITUTION:A bump height cushion part 6, having sleeper-like cross section, is formed of photosensitive polyimide in the vicinity of the outside or inside of a plurality of pad parts 3 which are arranged on the circumference of each chip 2 on a wafer 1. Then, after a conductive film has been formed on the whole surface of the wafer 1 by sputtering, a bump 11 is obtained by forming a conductive circuit 10 on the region from the surface of each pad part 3 to the surface of the cushion part 6 by conducting a photo process and an etching treatment on the conductive film. After formation of a cushion part 6 of 20mum in height and 100mum in width, for example, a conductive film is formed by sputtering Ti of 1000Angstrom , Pd of 3000Angstrom and Au of 30002r, and a conductive circuit 10 is formed by patterning the above-mentioned conductive film, and a bump 11 is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of forming bumps in a TAB or flip-chip method on a wafer at a high density for mounting a semiconductor element such as an LSI on a printed board.

[0002]

2. Description of the Related Art Conventionally, in order to form bumps on a wafer, adhesion is maintained on a pad, which is an electrical connection portion arranged around each chip on a wafer composed of completed semiconductor elements, A barrier metal layer for the purpose of preventing diffusion between metals is formed, and metal bumps of Au, Pb-Sn, Cu or the like are formed on the barrier metal layer by electrolytic plating.

Another method is to previously form metal bumps on a glass substrate or the like and copy them onto a TAB tape. Further, as a method of forming a straight bump, there is also a method of coating a thick film resist having a bump height or more on a wafer and forming a concave pattern in the exposure and development steps. If high-density bumps are to be formed by these conventional bump forming methods, the bump size will be made smaller and the pitch will be made narrower. However, in the conventional bump forming method,
In the plating resist formation process, for example, a width of 20μ
It is impossible to form a recess with a depth of 25 m and a depth of 25 μm and to form a wall with the adjacent recess to a thickness of 10 μm.
m, depth 25 μm, pitch 80 μm are the limits, and we cannot meet the demand for higher density bumps in the future.

[0004]

Therefore, the present invention is intended to provide a method for forming conductive circuit bumps at a high density on a pad portion on a wafer.

[0005]

A high density bump forming method of the present invention for solving the above problems is to expose a plurality of pads arranged around each chip on a wafer to the outside or inside of a plurality of pads. Cushion part with cross-section sleeper-shaped bump height is formed with a conductive polyimide, and then a conductive film is formed on the entire surface of the wafer by sputtering, and then this conductive film is photoprocessed and etched to form a cushion from the surface of each pad part. A bump is obtained by forming a conductive circuit up to the surface of the portion.

[0006]

As described above, in the high-density bump forming method of the present invention, since a cushion portion having a cross-section sleeper-like bump height is formed of photosensitive polyimide on the outside or inside of a large number of pad portions, this cushion portion is formed. When the conductive film is formed on the entire surface of the wafer by sputtering, it follows the underlying layer well and adheres well to the cushion portion. Further, since the conductive film is photoprocessed and etched to form a conductive circuit from the surface of each pad portion to the surface of the cushion portion, the bumps of the conductive circuit are formed by a technique using a normal thin photosensitive resist. Can be densified. Moreover, since wet plating is not performed, there is little variation in bumps, and the steps can be shortened to efficiently and inexpensively form bumps.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A high density bump forming method according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, a pad portion (an end of an LSI circuit) of Al-Si 1 wt% is provided around each chip 2 of a silicon wafer 1. A large number of electrical connection parts 3 are provided. As shown in FIG. 2, photosensitive polyimide 4 was spin-coated on this silicon wafer 1 by 40 μm, and then, as shown in FIG.
As shown in FIG. 4, the pad portion 3 around each chip 2 is masked by a mask pattern 5 in which a pattern is formed on the transparent quartz glass plate by Cr, and UV light is irradiated by an ultraviolet lamp as shown in FIG. After exposure, it was developed as shown in FIG. 5 and then baked (cured) in an N ₂ atmosphere for 1 hour and contracted to a height of 20 μm and a width of 1 as shown in FIG.
A cushion section 6 having a sleeper shape with a cross section of 00 μm was formed. Next, Ti1000Å, Pd3000Å, A on the entire surface of wafer 1.
u3000Å was sputtered to form a conductive film 7 as shown in FIG. Next, as shown in FIG. 8, a photoresist 8 is spin-coated on the conductive film 7 by 1.3 μm, and then, as shown in FIG. 9, from the respective pad portions 3 to the surface of the cushion portion 6, a transparent quartz glass plate is coated with Cr. After masking with a mask pattern 9 on which a pattern has been formed, exposing by irradiating UV light with an ultraviolet lamp, developing is performed as shown in FIG. 10, and then etching is performed to remove unnecessary portions of the conductive film 7 as shown in FIG. And then remove the resist 8 as shown in FIG.
Then, the conductive circuit 10 was formed from the surface of each pad portion 3 to the surface of the cushion portion 6 to obtain bumps 11. The arrangement and shape of the bumps 11 thus obtained on the chip 2 are as shown in FIG. A partition line 1 in FIG. 13 is a cutting line of the chip 2 on the wafer 1. The bumps 11 thus formed on the pad portion 3 around each chip on the wafer 1
With a width of 25 μm, a height of 20.7 μm and a pitch of 40 μm, it was possible to increase the density.

On the other hand, a conventional bump forming method will be described with reference to the drawings. As shown in FIG. 1, the entire surface of a silicon wafer 1 on which a plurality of chips 2 are provided with pad portions 3 of Al-Si 1 wt% respectively. As shown in Figure 14, Ti1000
Barrier metal layer 12 was formed by sputtering Å, Pd3000Å and Au3000Å. Next, as shown in FIG. 15, a photosensitive resist 13 is spin-coated on it to a thickness of 25 μm, and a photolithographic process is performed so that only the pad portion 3 is opened.
The photosensitive resist 13 was patterned as shown in 16.
Then, as shown in FIG. 17, the barrier metal layer 12 is used as a plating electrode to form an Au film having a thickness of 20 μm in the opening by a wet plating method.
The bump 14 was formed. Next, as shown in FIG. 18, the photosensitive resist 13 is peeled off, the entire surface is coated with the photosensitive resist 15 as shown in FIG. 19, and the Au bumps 14 are covered by photolithography as shown in FIG. The resist 15 was patterned. Then patterned photosensitive resist
The barrier metal layer 12 was etched using 15 as a mask as shown in FIG. After that, the photosensitive resist 15 covering the Au bumps 14 is peeled off to remove the Au bumps 14 as shown in FIG.
Formation was completed. The arrangement and shape of the Au bumps 14 on the chip 2 are as shown in FIG. The partition line 1 in FIG. 23 is a cutting line of the chip 2 on the wafer 1.

The bumps 14 thus formed on the peripheral pad portions 3 on the wafer 1 have a width of 50 μm and a height of 20.7.
The limit is μm and the pitch is 80 μm, and it is impossible to make the bump size smaller and the pitch smaller than this.

Although the cushion portion 6 is formed outside the pad portion 3 around each chip 2 in the above embodiment, it may be formed inside the pad portion 3. Further, although the cushion portion 6 is continuous on the outer peripheral side of the pad portion 3 in the above-described embodiment, it may be independent on the outer side or the inner side of each pad portion 3.

[0011]

As can be seen from the above description, according to the method for forming high density bumps of the present invention, the bumps of the conductive circuit can be easily formed in high density by the usual technique using a thin photosensitive resist. Further, since there is no wet plating process, there is little variation in bumps, and the process can be shortened to form bumps efficiently and at low cost. Furthermore, since the cushion part is formed on the lower side of the conductive circuit, elastic deformation is possible, and after mounting the chip of the wafer consisting of semiconductor elements on the glass epoxy printed circuit board, it is possible to absorb the strain due to thermal expansion and contraction. Thus, it is possible to suppress the breakage due to shearing and obtain a bump that can achieve a long life.

[Brief description of drawings]

FIG. 1 is a perspective view showing a silicon wafer in which a large number of pad portions are provided around each chip.

FIG. 2 is a diagram showing a process of an embodiment of a high density bump forming method of the present invention.

FIG. 3 is a diagram showing a process of an embodiment of the high-density bump forming method of the present invention.

FIG. 4 is a diagram showing a process of an embodiment of the high-density bump forming method of the present invention.

FIG. 5 is a diagram showing the steps of an embodiment of the high-density bump forming method of the present invention.

FIG. 6 is a diagram showing a process of an embodiment of the high-density bump forming method of the present invention.

FIG. 7 is a diagram showing steps of an embodiment of the high-density bump forming method of the present invention.

FIG. 8 is a diagram showing a process of an embodiment of the high-density bump forming method of the present invention.

FIG. 9 is a diagram showing steps of an embodiment of the high-density bump forming method of the present invention.

FIG. 10 is a diagram showing steps of an embodiment of the high-density bump forming method of the present invention.

FIG. 11 is a diagram showing a process of an embodiment of the high-density bump forming method of the present invention.

FIG. 12 is a diagram showing steps of an embodiment of the high-density bump forming method of the present invention.

FIG. 13 is a perspective view showing the arrangement and shape of bumps obtained by the high-density bump forming method of the present invention on a chip of a silicon wafer.

FIG. 14 is a diagram showing steps of a conventional bump forming method.

FIG. 15 is a diagram showing steps of a conventional bump forming method.

FIG. 16 is a diagram showing steps of a conventional bump forming method.

FIG. 17 is a diagram showing steps of a conventional bump forming method.

FIG. 18 is a diagram showing steps of a conventional bump forming method.

FIG. 19 is a diagram showing steps of a conventional bump forming method.

FIG. 20 is a diagram showing steps of a conventional bump forming method.

FIG. 21 is a diagram showing steps of a conventional bump forming method.

FIG. 22 is a diagram showing steps of a conventional bump forming method.

FIG. 23 is a perspective view showing an arrangement and shape of bumps obtained by a conventional bump forming method on a chip of a silicon wafer.

[Explanation of symbols]

 1 Wafer 2 Chip 3 Pad Part 4 Photosensitive Polyimide 5 Mask Pattern 6 Cushion Part 7 Conductive Film 8 Photoresist 9 Mask Pattern 10 Conductive Circuit 11 Bump

Claims (1)

[Claims] 1. A cushion portion having a cross-section sleeper-like bump height is formed of a photosensitive polyimide on the outside or inside of a large number of pads arranged around each chip on the wafer, and then the entire surface of the wafer is formed. A high-density bump characterized in that a conductive film is formed by sputtering on the film, and then the conductive film is photoprocessed and etched to form a conductive circuit from the surface of each pad portion to the surface of the cushion portion to obtain a bump. Forming method.