JPS59152648A - Multilayer interconnection method - Google Patents

Abstract

PURPOSE:To improve the yield and the reliability of an air bridge by protecting the lower layer wirings of a crossover by an insulating film, thereby eliminating a shortcircuit of upper and lower wirings and eliminating a stepwise disconnection or a restriction in the stage of works. CONSTITUTION:Upper layer wirings 22 cross lower layer wirings 21 through an insulating film 23 having a smooth section and an insulating film 24 under the film 23. The film 23 is etched by gas plasma which does not affect the influence to a substrate, wiring metal and the film 24, thereby forming an air bridge in noncontact. After lower layer wiring metal 31 is formed by normal photolithographic and lift-off methods, a nitrided silicon film 34 is formed, and a photoresist (OFPR-800) is formed on the entire substrate. A resist film 22 is allowed to remain only on the crossover of the upper and lower layer wirings for forming the air bridge by lithography. A lower insulating film pattern 34 is formed by plasma etching with CF4 gas. When it is baked at 200 deg.C for 20min, the resist is flowed to form a semispherical shape by the surface tension. Then, upper layer wirings 32 are formed. The film 33 of air bridge structure is removed by plasma etching with oxygen gas.

Description

[Detailed Description of the Invention] Technical Field The present invention provides transistors, resistors, coils, etc. on a semiconductor substrate.
The present invention relates to structural manufacturing technology for so-called integrated circuits in which electronic components such as capacitors are formed and interconnected.

BACKGROUND ART In order to increase the operating speed of integrated circuits and reduce power consumption, it is essential to miniaturize elements and increase the degree of integration of circuits.

As a result, each component and the wires for connecting them to each other are brought closer to each other, and the number of intersections between the wires increases.

As a result, the wiring capacitance in particular increases, leading to a reduction in operating speed. To prevent this, an effective method of insulating the wiring is required. Particularly in the high frequency range of microwaves or higher, reducing the wiring capacitance is an essential issue for improving characteristics.

The air bridge method is an effective means for achieving this purpose. This is a one-layer wiring technology in which, as shown in FIG. 1, when lower metal wiring and upper metal wiring intersect in an integrated circuit, the upper metal wiring intersects three-dimensionally without intervening an insulating film between the two. The feature of this method is that since the two types of wiring are insulated by air having the lowest dielectric constant, the capacitance between the two wirings is the smallest compared to the case where any other insulating film is used. The wiring capacitance within this diagonal circuit is reduced and the operating speed of the integrated circuit is improved.・However, due to the structure of the air bridge, the upper layer wiring is suspended in the air, and after the air bridge is formed, it is no longer possible to contact the surface. For this reason, various technical problems and restrictions as described below arise in subsequent steps.

In other words, ①) When thinning the substrate from the back side in order to improve high frequency characteristics, it is necessary to form a protective film necessary for chemical etching. On the other hand, when thinning a substrate by mechanical polishing, it is necessary to contact the substrate surface.

2) Semiconductor device 1- repeatedly formed on a substrate in large numbers
In the scribing and separating processes that produce chips by tilling, processing is often performed from the back side to prevent debris or dirt from adhering to the surface or causing scratches, and the process inevitably comes into contact with the front surface.

3) In the bonding process in which chipped semiconductor devices are attached to a package one by one, the surface side of the chip is attracted using a collet or vacuum tweezers.

4) When a protective film is finally formed on the integrated circuit, an opening is provided in the protective film in order to take out electrical connections to the outside.

If photolithography using normal contact exposure is applied here, the substrate surface will be tightly adhered to the photomask.

The above process cannot be carried out from the viewpoint of protecting the air bridge, and in order to carry out the same process as the above, a complicated process will be added.

In this case, a problem arises in that the productivity and yield of semiconductor devices are significantly deteriorated.

On the other hand, the air bridge itself has a weak structure, and there is a problem in that the upper layer wiring is often broken or comes into contact with the lower layer wiring due to external force, resulting in a low yield. Also,
In order to prevent contact between wires, the upper layer wires are often formed as high as possible, creating a risk of step breakage.

DISCLOSURE OF THE INVENTION The present invention provides a new multilayer wiring method that solves the problems of the prior art described above.

The following will explain the implementation/implementation.

FIG. 2' is for showing an example of an embodiment of the present invention, and shows an insulating film 23 with a smooth cross section and an insulating film 2 below it.
4, the upper layer wire 22 intersects with the lower layer wiring 21. The insulating film 23 is connected to a substrate, wiring metal, or insulating film 2.
An air bridge can be formed without contact by etching with a gas plasma that does not affect etching. An example of the air bridge manufacturing process will be described below with reference to FIG. 3.

After forming the lower wiring metal 31 by ordinary photolithography and lift-off method, a silicon nitride film 34f with a thickness of 0.3 μm is formed by plasma CVD method, and photoresist (OFPR) is formed on the entire surface of the substrate by spin coating method. -8o
o) is formed to a thickness of 2.5 μm.

A resist film 33 is applied only to the intersection of upper and lower layer interconnections and the surrounding area where air bridges are formed by lithography.
leave. (FIG. 3-(5)) A lower insulating film pattern 34.2 is formed using the upper insulating film 33 as a mask by plasma etching using CF4 gas. (Figure 3-(B
)) This was followed by baking at a temperature of 200°C for 20 minutes.

The temperature at this time is sufficiently higher than the temperature at which the resist softens, and the muddy resist flows into a hemispherical shape due to surface tension. (Figure 3-(C1) Next, the same as the lower layer wiring'
The entire upper layer wiring 32 is formed by the method described in (a). (Figure 3-(Dl
) Since the cross section of the insulating film 33 is softened and almost circular, it is possible to eliminate so-called step breakage in which the upper layer wiring is broken at the step part of the insulating film.

Subsequently, the photoresist film 33'f! having an air bridge structure is formed by plasma etching using oxygen gas. :Removed to obtain an air bridge in which the lower wiring at the intersection is protected by an insulating film as shown in Figure 3-@. Thereafter, a semiconductor device can be realized by applying conventional techniques to the assembly processes such as back polishing, scribing, seven-barrelation, bonding, etc., and the protective film forming process.

Here, the step of removing the photoresist film 33 of the air bridge structure is gas plasma etching, and the insulating film 33 can be left until it is no longer necessary to contact the substrate surface during the assembly process. This solves the problem that the air bridge is damaged and the yield is reduced. In the embodiment, photoresist was used for the insulating film 33, but any material that softens at temperatures as low as 500°C or lower and can be selectively removed from the insulating film 34 using gas plasma can meet the requirements of the present invention. and is not limited to photoresist in any way.

Further, the object of the present invention is satisfied if the insulating film 34 can be processed independently from the insulating film 33 in the process of forming or removing it, and the material is not limited to silicon nitride, but may be made of, for example, an organic resin. Inorganic compound films such as films, polyimide resins, silicon oxides, and alumina oxides can also be used.

Effects of the Invention The present invention forms an air bridge in which the lower layer wiring at the intersection is protected by an insulating film, and it is possible to eliminate short circuits between the upper and lower wirings that occur due to insufficient mechanical strength of the upper layer wiring. Furthermore, by softening the upper insulating film and performing non-contact gas plasma etching, it is possible to eliminate step cuts and process constraints, and it is possible to improve the yield and reliability of the air bridge.

[Brief explanation of drawings]

FIG. 1 is an example of an air bridge structure, FIG. 2 is an example of an embodiment of the present invention, and FIGS. 3(5), (B), (C), and D(5) are diagrams for explaining the manufacturing process thereof. 11, 21.81... Lower wiring 12, 22.
32... Upper wiring 23, 33...
......L side insulating film 24.34...
・・・・・・Lower insulation film diagram N Figure 2 Figure 3

Claims (1)

[Scope of Claims] (1) Among multilayer wiring technologies for integrated circuits, in the air bridge method in which the upper and lower wiring metals cross three-dimensionally without intervening an insulating film, the intersection of the upper and lower wirings is A multilayer wiring method characterized in that the lower layer wiring is covered with an insulating film.・(2) Cover the lower layer wiring and the intersection with an insulating material consisting of two types of films that can be selectively removed from each other, then form the upper layer wiring, and then remove only the upper layer insulation film material □ to form an air bridge. A multilayer wiring method according to claim 1, characterized in that: (3) The temperature of the upper layer of the two types of insulation films is 500°C.
3. The multilayer interconnection method according to claim 2, wherein the material is softened at a temperature below and can be removed by gas plasma.