JPH04307937A - Manufacture of semiconductor element - Google Patents

Abstract

PURPOSE:To obtain high bond strength without changing the conditions of wire bonding even when a polyimide resin, etc., are used as a protective film by providing a process, in which an organic group substance reattached onto a wafer is removed through etching during heat treatment for curing the polyimide resin, etc. CONSTITUTION:The upper section of a semiconductor wafer, to which an element is formed, is coated with a polyimide resin or polyimide-isoindolo- quinazolidiode (PII) 6, and patterned. Heat treatment for curing said polyimide resin of PII 6 is executed, and an organic substance 8 reattached onto a wafer by the heat treatment is removed through etching. The organic substance 8 for example, reattached onto the whole surface of the wafer including a wiring pad 2 through an annealing process for film-curing the polyimide resin 6 is taken off through plasma ashing, etc., in a reaction system containing oxygen gas or wet etching by the etchant, etc., of a hydrazine group.

Description

[Detailed description of the invention]

0001

[Industrial Field of Application] This invention relates to a protective film for semiconductor elements,
In particular, it relates to a surface protective film that prevents malfunctions of integrated circuits due to heat, humidity, or incidence of alpha rays.

0002

2. Description of the Related Art Semiconductor devices are generally sealed in ceramic packages or plastic packages. These materials contain several ppm of radioactive impurities such as uranium and thorium.

It is known that alpha rays emitted from these impurities can invert stored charge data in memory devices such as DRAMs (dynamic random access memories), causing malfunctions (generally referred to as soft errors). It is being For this reason, the reliability of the device may be significantly reduced.

[0004] In order to reduce this soft error, it is possible to use highly pure materials (low uranium, low thorium) for ceramic packages or plastic packages, but this is not suitable for practical use because it causes a significant increase in cost.

For this reason, as a means to attenuate and absorb alpha rays coming from impurities and the like, it is widely used to cover and protect semiconductor elements with polyimide resin or polyimide isoindolo quinazolidione resin (hereinafter referred to as PII). These resins can be applied using the potting method, in which the semiconductor elements are dripped onto the electrode pads for connecting external electrodes after the wiring (wire bonding), such as gold wire, is completed, and the potting method, in which the semiconductor elements are not individually cut out (before scribing). ) There is a wafer coating method in which spin coating is performed at the wafer stage. The former process is performed on each cut out semiconductor element, which increases the number of man-hours and costs. Furthermore, in the case of large-area semiconductor chips or rectangular semiconductor chips with a large side-to-side ratio, there are problems such as difficulty in uniformly coating the semiconductor chip with resin, so the latter wafer coating method is becoming widely used. An example thereof will be explained using FIGS. 3 and 4. Note that the same parts are given the same reference numerals.

First, in FIG. 3, various elements such as resistors and transistors are formed in or on a semiconductor substrate, and then wiring pads 2 for external connection terminals are formed on the insulating film 1 by a photolithography/etching process (not shown). . This wiring pad is usually made of aluminum alone or an aluminum alloy containing impurities such as Si and Cu. This material is used not only for wiring but also for forming elements such as transistors. Next, an oxide film 3 containing impurities such as phosphorus and a silicon nitride film 4 are sequentially formed. The wiring pad 2 is removed by a photolithography/etching process (not shown).
A portion of the upper oxide film 3 and silicon nitride film 4 is selectively removed to form an opening 5 to obtain a structure as shown in FIG. 1(a).

Next, polyimide resin 6 is applied to the entire surface,
Prebaking is performed, for example, at 100° C. for 1 minute.

Next, a resist (not shown) is applied and patterned, and using this as a mask, the polyimide resin 6 is selectively etched by wet etching with a hydrazine etchant or dry etching, and the resist is removed to form the openings 7. The structure shown in FIG. 1(b) is obtained.

Thereafter, annealing is performed at 200° C. and 300° C. for 1 hour each in a nitrogen or inert gas atmosphere to cure the polyimide resin film 6.

FIG. 4 shows another method. Similar to the method described above, an oxide film 3 containing phosphorus or the like and a silicon nitride film 4 are formed on the wiring pad 2 formed on the insulating film 1, and then a polyimide resin 6 is formed. Prebaking is performed as necessary, and then a resist (not shown) is applied and patterned. Using this as a mask, polyimide resin 6, silicon nitride film 4, and oxide film 3 are etched away continuously or sequentially to form openings 5. Figure 4 by forming and removing the resist.
A structure as shown in (a) is obtained.

Thereafter, annealing is performed at 200° C. and 300° C. for 1 hour each in a nitrogen or inert gas atmosphere to cure the polyimide resin film 6.

0012

[Problems to be Solved by the Invention] However, in any of the above methods, during the heat treatment for annealing and curing the polyimide resin that has been patterned to form openings, A phenomenon may occur in which organic substances such as solvents and low-molecular polyimide precursors are desorbed from the resin film, and these substances (mostly carbon) re-deposit on the wiring pads and wafers. It's been found. This is shown in Figures 3(c) and 4.
The black circle (number 8) shown in (b) means an organic substance.

FIG. 5 shows an example in which bonding is performed using the gold wire 10 with the organic material re-attached to the wiring pad, and the organic material remains interposed between the aluminum wiring pad and the gold wire 10. It has become. When the shear strength of the gold wire 10 was measured in this state, it was 100 g or less. On the other hand, wiring pad 2 that does not use polyimide resin (for example, FIG. 3(a))
The shear strength of the gold wire bonded under the same bonding conditions as the bonding with the organic substance redeposited exceeds 130 g.

The decrease in shear strength is caused by the deterioration of the reliability of the semiconductor device because when the semiconductor device is sealed in a package, the contact pressure with the molten mold material and the stress caused by the temperature cause peeling of the bonding wiring at the wiring pad part. There was a problem. Furthermore, in order to increase the bonding strength, it is possible to increase the temperature, time, and pressure during bonding, but there is a problem in that the stress caused by heat and pressure causes cracks to occur at or near the wiring pad.

[0015]

[Means for Solving the Problems] The present invention etches the surface layer and removes organic substances on wiring pads after the polyimide resin, which is a protective film for semiconductor elements, is cured by thermal annealing. be.

[0016]

[Operation] According to the method of manufacturing a semiconductor device of the present invention, the organic substance on the wiring pad is removed by etching, which improves the adhesion between the gold wire and the wiring pad during wire bonding, thereby solving the above-mentioned problem. It can be removed.

[0017]

Embodiment FIGS. 1(a) to 1(d) and FIGS. 2(a) to 2(c) are process sectional views showing an embodiment of the present invention. Note that the same parts are given the same reference numerals.

1(a) to (c) and FIG. 2(a) to (b) are the same as the manufacturing method of the conventional example, so the explanation will be omitted.

First, the polyimide resin is annealed and a film curing process is performed, and then the wafer is placed in a reaction system containing oxygen gas, and the organic substances that have been redeposited over the entire surface of the wafer, including the wiring pad portion, are treated, for example, in a reaction system containing oxygen gas. Ashing (ashing) processing is performed using plasma ashing or optical ashing to remove a portion of the wafer surface layer by etching. (9 in FIG. 1(d) and 9 in FIG. 2(c)) By adding this step, the organic material on the wiring pad is removed. Further, this step may be wet etching using a hydrazine-based etchant.

[0020] Since the polyimide resin on the wafer has already been thermally hardened, even if the etching process is added, the film thickness will not decrease much. For example, if the etching is about 1000 Å, the film may be made thicker at first.

After adding this step and bonding under the same conditions, the shear strength of the gold wire was measured, and it was found that the shear strength of the gold wire, which was less than 100 g in the conventional example, recovered to 130 g, the same as when no polyimide was used. was.

[0022]

As explained in detail above, according to the present invention, after patterning and annealing thermosetting of polyimide resin or PII, the entire wafer surface is ashed (
By adding a step of ashing or wet etching, it is possible to remove the organic material on the wiring pad that will become the lead electrode portion.

[0023] Therefore, bonding conditions (temperature, pressure,
Sufficient bonding strength can be obtained without increasing the time (time), device deterioration such as cracks in the passivation protective film and peeling of the wire bonding gold wire can be prevented, and a highly reliable device can be obtained.

[Brief explanation of drawings]

[Fig. 1] Process cross-sectional diagram showing a first embodiment of this invention

[Fig. 2] Process sectional view showing a second embodiment of this invention

[Figure 3]
Process cross-sectional diagram showing the first example of the conventional technology

[Fig. 4] Process sectional view showing a second embodiment of the conventional technology

[Figure 5] Cross-sectional view of gold wire bonded onto wiring pads using conventional technology

[Explanation of symbols]

1 Semiconductor substrate 2 Wiring pad 3 Oxide film containing impurities such as phosphorus 4 Silicon nitride film 5, 7 Opening 6 Polyimide resin 8 Organic substance 9 Etching 10 Gold wire

Claims (1)

[Claims] 1. A step of applying and patterning a polyimide resin or polyimide isoindolo quinazolidione (PII) on a semiconductor wafer on which elements have been formed, and a step of applying heat treatment to harden the polyimide resin or PII. . A method of manufacturing a semiconductor device, comprising sequentially performing the steps of: etching away organic substances re-attached to the wafer due to the heat treatment.