JP3598564B2 - Bump forming method - Google Patents

Description

[0001]
[Industrial applications]
The present invention relates to a method for forming a bump for connecting a substrate and a semiconductor chip, and more particularly to a method for forming a bump which is effective when the arrangement of bumps is dense.
[0002]
The connection of semiconductor chips using bumps was primarily a form of mounting an IC package or bare chip on a printed board or mounting a chip on a package, and the arrangement of bumps was relatively sparse. In recent years, the arrangement of bumps has become denser with the miniaturization of bare chips. In particular, when connecting a two-dimensional infrared sensor formed on a HgCdTe chip to a Si substrate, the bumps are also two-dimensional as shown in FIG. Extremely dense situation such as arrangement in
[0003]
[Prior Art and Problems to be Solved by the Invention]
In the early bump formation technology, in addition to a method in which fine solder balls were placed on a pad and heated and reflowed to form a bump welded to the pad, the substrate surface was covered with an insulating film such as an oxide film, A method has been adopted in which after opening a window in a portion, a solder layer is left on the pad and in the vicinity thereof by vapor deposition and patterning of the entire surface of the solder layer, and reflow is performed to form a bump.
[0004]
Since then, improvements have been made in response to situations such as miniaturization of bumps and close proximity of formation positions, but basically the above method is followed.
In the prior art, a so-called dam is formed by surrounding a pad with a material having poor wettability to solder so that solder balls before melting do not roll or melt does not spill during reflow. It is well known. At that time, since the opening area of the pad was relatively large, it was not so difficult to sufficiently improve the wettability to the solder melt by using a surface treatment or a flux.
[0005]
However, in the hybrid chip in which the Si chip and the HgCdTe chip are combined, the pad opening area is very small, and there is also a restriction that processing that adversely affects the formed element must be avoided. It is difficult to make the formation surface sufficiently clean. As a result, the bump formation position may be incorrect.
[0006]
This will be described with reference to FIG. When bumps (8) are to be formed on pad electrodes (2) provided on a substrate (1) made of Si or the like, the solder melt during reflow tends to shrink spherically due to surface tension. If the pad metal is not sufficiently wet, it may roll on the pad and move, and the position of the completed bump will be off center. In the figure, the position indicated by the broken line is the original position, and the position indicated by the solid line is the bump formed off the center.
[0007]
Usually, the pad is surrounded by an insulating film or the like, so the moving range is limited to the pad.However, if the bumps are reduced in size and the arrangement pitch is finer, slight misalignment that was not a problem in the past Will greatly affect the yield.
[0008]
An object of the present invention is to provide a method for accurately forming a bump at the center of a pad even when wettability is not sufficient as compared with the surface tension of a solder melt. Even so, it is an object of the present invention to provide a method of forming a precise position.
[0009]
[Means for Solving the Problems]
In order to solve the above-mentioned problem , the present invention forms a wall surrounding a pad on a peripheral portion of a pad on which a bump is to be formed , and applies a soft solder material on the pad surrounded by the wall. , a bump forming method for melt processing, the height of the wall is approximately equal to the height of the maximum horizontal cross-sectional position of general spherical body caused by deformation is more soft brazing material該熔melt processing or than To be set to large.
[0010]
The region surrounded by the wall includes a polygon, and the ratio (H / D) of the height (H) of the wall to the diameter (D) of a circle having the same area as the region surrounded by the wall is be such that from 1/2 to atmospheric, the pad, the smaller opening than the maximum horizontal cross section of the schematic spherical body is so covered with the insulating film provided on the pad, further, form the walls The object of the present invention can be achieved more accurately by using a polyimide as the material to be formed or an indium alloy as the material to form the bumps .
[0011]
[Action]
The operation and effect of the present invention are shown in the principle diagram of FIG. One point of the present invention is that the height (H) of the surrounding wall provided at the bump formation position is set to a value close to the opening diameter (D).
[0012]
When the columnar space surrounded by the wall is filled with a solder material by a method such as vapor deposition and then reflowed, the density after resolidification of the solder becomes larger than that at the time of deposition. Are substantially spherically aggregated in the columnar space.
[0013]
In the present invention, the wall surrounding the solder melt sphere is sufficiently high so that the melt sphere is supported by this wall and is located substantially at the center of the columnar space. That is, the object of the present invention of accurately forming a bump at the center of a pad is achieved.
[0014]
Furthermore, when the bumps are arranged in a matrix, the surrounding wall of the present invention is formed in a mesh shape. However, when the pitch of the bump arrangement becomes finer and becomes closer to the opening diameter, the upper surface of the wall is formed. Even if the melting process is performed with the solder placed on the solder balls, this portion is absorbed by the solder balls, so that it is unnecessary to remove them in advance.
[0015]
【Example】
2, 3 (a) to 3 (h) show the steps of the embodiment of the present invention. Hereinafter, description will be made with reference to FIG.
[0016]
FIG. 2A shows a pad electrode (2) formed on the surface of a Si substrate (1). The pad electrode is formed, for example, by patterning a titanium film. However, the present invention can also be applied to a case in which a titanium film is coated as a barrier metal on another type of wiring metal layer. In addition, although an IC is usually formed on the Si substrate (1), it may be one having only a wiring pattern, and the material may be a ceramic plate or the like.
[0017]
A CVD oxide film (3) is deposited on the entire surface of the Si substrate in this state, a through hole (4) having a diameter of 5 to 10 μm is opened, and the barrier metal at the bump formation position is partially exposed. This state is shown in FIG.
[0018]
Next, a non-thermoplastic polyimide resin is deposited to a thickness of about 20 μm to form a cylindrical space having a diameter of 30 μm on the pad. The shape of the columnar space may be a prism and is not a necessary condition, but its horizontal cross section is desirably a regular polygon. This state is shown in FIG. Further, if the polyimide resin is photosensitive, patterning by photolithography can be performed without additionally applying a resist.
[0019]
In this embodiment, the resin layer other than the pad area is also removed to leave only the polyimide wall (5) . However, when the pads are arranged in a dense matrix as shown in FIG. Since the same type of space is formed, the shape becomes close to the shape of FIG. 2C without intentionally forming a wall shape. When patterning is performed using an ordinary polyimide resin etchant, the etching of the upper portion of the resin layer proceeds more strongly than the lower portion, so that the cross-sectional shape of the wall becomes an inverted V-shape, which is desirable in the present invention.
[0020]
When the formation of the surrounding wall is completed, an indium layer (6), which is a solder, is deposited to a thickness of 16 μm as shown in FIG. When the size of the columnar space defined by the wall has the above value, the indium layer is deposited to fill the inside of the wall even when formed by vapor deposition. Subsequently, a flux (7) is spin-coated on the indium layer. This state is shown in FIG.
[0021]
When heat treatment is performed at 170 ° C. for 30 minutes, the indium once melted becomes spherical due to surface tension, and a bump (8) is formed as shown in FIG. 3 (f). The height of the bump is about 18 μm, and it is almost spherical and smaller than the diameter of the cavity in the surrounding wall. However, the bump does not move much because of the wall nearby and stays at a position close to the center.
[0022]
The flux changes into a shell-like hardened flux (7a), which is removed by ultrasonic treatment with a petroleum-based solvent. Also, some of the indium adhering to the substrate surface other than the pad area falls off the substrate during melting and the other solidifies again, but the wettability with the underlying insulating film is extremely poor. When peeled off easily. This state is shown in FIG.
[0023]
Further, when the surrounding wall of the polyimide is removed with an etching solution, the bump is completed as shown in FIG. When the polyimide is photosensitive, the portion remaining as a wall is hardly soluble in an ordinary developer, but can be removed using a solvent such as a mixed solution of hydrazine and ethylenediamine.
[0024]
【The invention's effect】
As described above, according to the present invention, bumps having a uniform height can be accurately formed at the center of the pad by a relatively simple process, and furthermore, the bumps are densely arranged in two dimensions, and the pitch is small. The present invention can be applied to fine cases.
[Brief description of the drawings]
FIG. 1 is a diagram showing the principle of the present invention. FIG. 2 is a view showing steps of an embodiment of the present invention (part 1).
FIG. 3 is a view showing a step of the embodiment of the present invention (part 2).
FIG. 4 is a diagram illustrating a two-dimensional arrangement of bumps. FIG. 5 is a diagram illustrating a problem of the conventional technique.
Reference Signs List 1 Si substrate 2 Pad electrode 3 Insulating film 4 Through hole 5 Wall (polyimide)
6 Indium layer 7 Flux 7a Cured flux 8 Bump

Claims (2)

A method of forming a substantially spherical bump on a pad,
(a) forming an insulating film having an opening partially exposing the metal film pattern on a metal film pattern which is a pad on which a bump is to be formed;
(b) forming a wall made of a heat-resistant resin surrounding the pad on the insulating film on a peripheral portion of the pad;
soft brazing material in a region surrounded by (c) wall and a step of melt processed mixture was allowed to deposit,
The opening is smaller than the maximum horizontal cross section of the schematic spheroids, also the height of the wall is approximately equal to the height of the maximum horizontal cross-sectional position of general spherical body caused by deformation soft brazing material by該熔fusion treatment or bump forming method, characterized in that it than is large. The ratio (H / D) of the height (H) of the wall to the diameter (D) of a circle having the same area as the area surrounded by the wall is greater than 1/2. Bump formation method.

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