JPH01243546A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To effectively remove a resist by a method wherein, when a pattern is to be formed by the photoresist by using a conductor film where a passive- state film is hard to form, the photoresist is removed in a plasma atmosphere whose partial pressure of oxygen is 10Pa or lower. CONSTITUTION:A Cu film 2 is formed on the surface of a semiconductor substrate 1; a pattern of a photoresist 3 is formed on its surface. The Cu film 2 is etched selectively by an ion etching method. The resist is ashed and removed by using a parallel-plate type plasma etching apparatus. Concrete conditions are as follows; the substrate is closely contacted to a specimen- holding sheet; the inside of the etching apparatus is evacuated to produce a vacuum of 0.1Pa or lower. After that, while oxygen gas with a pressure of 10Pa or lower flows at a flow rate of 20 SCCM, RF electric power is applied and an oxygen plasma is generated. A plasma treatment is executed in an oxygen plasma atmosphere for 10 minutes. By this setup, the resist 3 can be removed effectively.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Field of Application) The present invention relates to a method for manufacturing a semiconductor device, and particularly to an improvement in a process for forming conductor wiring.

(Prior Art) In recent years, as semiconductor integrated circuits have become more highly integrated, wiring widths and thicknesses have been reduced and the number of layers has been increased. As a wiring material, an alloy film mainly composed of ANQ is often used, which exhibits a low specific resistance of 275 Ω·ram and forms a passive film to prevent corrosion. however,
The signal current is not reduced at the same rate as the wiring cross-sectional area is reduced, and as a result, the current density increases and wire breakage due to electromigration has become a serious problem.

Furthermore, due to the multilayered wiring, the wiring is subjected to a complex thermal history, and disconnection due to stress migration due to thermal stress is also becoming a problem. The main reason for these problems is that the melting point of Af is as low as f360°C, and atomic diffusion occurs at relatively low temperatures, particularly through grain boundaries, and that when tensile stress occurs, The above-mentioned atomic diffusion is further accelerated. Therefore, recently, studies have begun to consider using Cu or its alloys, which have a resistivity as low as or higher than Af and a melting point higher than /l, as wiring materials for semiconductor devices.

On the other hand, patterning of conductor wiring in integrated circuits is performed by photolithography technology using photoresist. After selectively etching the conductive film using a photoresist, the photoresist is ashed and removed by oxygen plasma irradiation. Typically, this oxygen plasma is generated by RF discharge at an oxygen partial pressure of around 130 Pa. This pressure region has a relatively high pressure and therefore a high proportion of oxygen radicals in the plasma. The mechanism of photoresist ashing is that the resist polymer is exposed to CO2 and 820
This is a reaction that decomposes into Oxygen radicals contribute to this reaction, and the resist removal rate is proportional to the oxygen radical concentration.

Therefore, in the resist removal method using oxygen plasma ashing, it is better to have a high oxygen radical concentration, and the above-mentioned oxygen partial pressure is generally selected.

By the way, when an A1 or AJL alloy film is used as the wiring, its surface is covered with a dense aluminum oxide film which is a passive film. Therefore, even if the AL film is exposed to the oxygen plasma atmosphere as described above in the photoresist removal process after wiring formation, oxidation will not progress inside the AL film.

However, in the case of Cu, a porous and brittle oxide film is formed under the above-mentioned oxygen plasma conditions, so there is a disadvantage that the Cu wiring is oxidized to the inside during the process of removing the photoresist. For example, under normal photoresist removal conditions, Cu11 with a thickness of 0.8 μm all changes to copper oxide. Due to this oxidation, the specific resistance becomes 5
This increases by more than an order of magnitude, and the wiring shape also naturally deteriorates.

(Problems to be Solved by the Invention) As described above, when a conductive film in which a passive film is difficult to form is used as a wiring material, if photoresist is removed in a plasma atmosphere under the same conditions as before, the desired wiring The problem was that it was not possible to obtain

An object of the present invention is to provide a method for manufacturing a semiconductor device that solves these problems.

[Structure of the Invention] (Means for Solving the Problems) The present invention provides a method for removing the photoresist at an oxygen partial pressure of 10 pa or less when a pattern is formed using a photoresist using a conductor film in which a passive film is difficult to form. It is characterized by being carried out in a plasma atmosphere.

(Function) CU or C in a plasma atmosphere with an oxygen partial pressure of 10 Pa or less
When the photoresist on the u-alloy film is removed, the resist removal rate is not as fast as the normal oxygen partial pressure of about 100 Pa, and the oxidation rate of Cu or CU-gold alloy can be lowered by about an order of magnitude or more. By the way, the oxygen radical concentration depends on the RF specific output oxygen flow rate, but the oxygen partial pressure is 130
In the vicinity of Pa, it is approximately 10%. Typically 7
The oxygen radical flow rate is about 0 Pa-Jl/sea.

However, when the oxygen partial pressure is less than 10 Pa, the oxygen radical concentration decreases to about 1/10. As a result, not only the oxidation rate is suppressed, but also the formed oxide film becomes denser than in the case of about 130 Pa, which effectively suppresses the progress of oxidation.

(Example) Embodiments of the present invention will be described below with reference to the drawings.

FIGS. 1A to 1C show a wiring forming process according to an embodiment of the present invention. In FIG. 1(a), 1 is a semiconductor substrate on which a desired element is formed and whose surface is covered with an insulating film, and a wiring material film is formed on the surface of the semiconductor substrate. 2 is formed, and a photoresist 3 is patterned on the surface thereof by ordinary photolithography. For example, the CLI film 2 has a thickness of 40
00 people, and the photoresist 3 has a thickness of 1.2 μm. Next, using the ion etching method, the Cul! Select and etch 2. Next, the photoresist 3 is removed by ashing using a parallel plate type plasma etching apparatus, and the wiring shown in FIG. 1(C) is formed.

The specific plasma etching conditions are as follows.

First, a substrate is placed in close contact with a sample holding plate whose back surface is water-cooled in a plasma etching apparatus, and the inside of the etching apparatus is evacuated to 0.1 Pa or less. Then, while flowing oxygen gas with a pressure of 1 Pa or less at a flow ffi of 208 ccM, RF with a frequency of 13.56 MHz and an output of 150 W was applied.
Apply electric power to generate oxygen plasma. Plasma treatment is performed for 10 minutes in this oxygen plasma atmosphere.

According to this embodiment, the photoresist is removed without substantially oxidizing the Cu film wiring.

Even if the oxygen plasma treatment was extended for 100 hours, oxidation of the Cu film wiring hardly progressed, and no change in wiring resistance or shape was observed.

FIG. 2 shows data showing the dependence of the oxidation rate of Cu wiring and the rate of resist removal on oxygen gas pressure. The processing time using oxygen plasma is twice the time required to remove the resist. Conventional example (mu.

・) is data for cylindrical type, and Example (△).

○) is data for the parallel plate type, but the difference between these devices is not essential. At the oxygen gas pressure of 130 Pa used in the conventional resist ashing process, all 4000 Cu wiring lines were oxidized. The amount of oxidation decreases as the oxygen gas pressure decreases, and at an oxygen gas pressure of 1 Pa, oxidation is suppressed to about 10 layers near the surface of the CLJ wiring. As is clear from the data in the figure, the resist removal rate does not decrease significantly even with a decrease in oxygen gas pressure. Therefore, according to this embodiment, even when patterning a Cu film interconnection that is easily oxidized, the resist can be effectively removed by plasma treatment.

In the embodiment, the case of a Cu film was explained, but the present invention is also effective in the case of a Cu alloy film. The present invention is also effective when using other conductor films in which it is difficult to form a passive film. The wiring structure is not limited to single-layer wiring, but the present invention can of course be applied to multi-layer wiring.

[Effects of the Invention] As described above, according to the present invention, when forming a conductive film in which a passive film is difficult to form by photolithography, the resist can be effectively removed without deteriorating the wiring due to oxygen plasma treatment. Removal can be performed. This makes it possible to obtain a semiconductor device with wiring that is resistant to electromigration.

[Brief explanation of the drawing]

FIGS. 1(a) to (C) show Cu1i of an embodiment of the present invention.
! FIG. 2, which is a diagram showing the line forming process, is a diagram showing the relationship between the oxidation rate of the CLJ by plasma etching and the oxygen partial pressure. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... Cu film, 3... Photoresist. Applicant's agent Patent attorney Takehiko Suzue: Figure 51

Claims (2)

[Claims] (1) A conductor film that is difficult to form a passive film is deposited on a semiconductor substrate, a photoresist is patterned on the conductor film, and the conductor film is selectively etched. A method for manufacturing a semiconductor device, characterized in that it is removed by ashing in a plasma atmosphere. (2) The method for manufacturing a semiconductor device according to claim 1, wherein the conductor film is a Cu or Cu alloy film.