JPS5990942A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To perfectly prevent the generation of dregs after washing by leaving the protection oxide film without etching before growth of the LOCOS oxide film and washing and dehydrating the silicon substrate surface while it is covered with a hydrophilic silicon nitride and protection oxide film. CONSTITUTION:With a photo resist 4 where a protection oxide film 2 such as silicon dioxide is formed on a silicon substrate 1 and moreover a silicon nitride film 3 is formed on the protection oxide film 2 used as the mask, the silicon nitride film 3 is plasma-etched by the CF4 gas. Next, with the photo resist used as the mask, in the case of n-channel element, for example, the B<+> ion is implanted in order to form a high concentration layer 5 and the photo resist 4 is removed. After the cleaning and dehydration, a LOCOS oxide film 7 is formed, for example, through the heat treatment under the steamy ambient. After etching a very thin oxide film formed by the growth method on the silicon nitride film 3 used as the mask for oxidation while the LOCOS film 7 is formed with the aqueous solution of fluoric acid, the silicon nitride film 3 is etched by the hot phosphoric acid and thereafter a protection oxide film 2 is etched by the aqueous solution of fluoric acid.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and particularly to a selective oxidation (LOCO3) method using a silicon nitride film as an oxidation mask.

Conventional structure and problems Conventionally, the LOCO8 oxide film was formed by etching the protective oxide film (silicon oxide film) in the area on the silicon substrate where the LOCO3 oxide film was to be formed, before the LOCO8 oxide film was grown. After removal, it went through a washing, dehydration, or drying process.

First, an example thereof will be explained with reference to FIG. A protective oxide film 2 to a thickness of 500 mm, for example, is formed on a silicon substrate 1, and a silicon nitride film 3 to a thickness of 1000 mm is further formed on the protective oxide film 2 [FIG. 1(a)]. Next, the silicon nitride film 3 is plasma etched in CF4 gas using the photoresist 4 as a mask [FIG. 1(b)]. Thereafter, a heavily doped layer 6 is formed by implanting - ions into the channel by using the photoresist 4 as a mask. For example, in the case of an n-channel device, this heavily doped layer 5 is formed by implanting B+ ions.

Subsequently, the photoresist 4 is removed [FIG. 1(C)]. Next, the protective oxide film 2 is etched with a hydrofluoric acid solution using the silicon nitride film 3 as a mask, and then washed and dehydrated (FIG. 1(d)). At this time, on the silicon nitride film 3,
Cleaning residue 6 as described below is generated.

Furthermore, heat treatment is performed at 1000°C in water vapor, for example, to form a LOCO3 oxide film 7 with a film thickness of 1 μm [see Fig. 1 (e)
)]. Next, LOGO8 oxide film 7 formation 11. ! The extremely thin oxide film (not shown) grown on the silicon nitride film 3 used as a mask against oxidation was removed by etching with a hydrofluoric acid-based aqueous solution, and then the silicon nitride film 3 was etched with hot phosphoric acid. Furthermore, the protective oxide film 2 is etched with a hydrofluoric acid aqueous solution [FIG. 1(f)]. After Kono, L
A semiconductor element is formed in a region other than the region where the OCO8 oxide film 7 is formed, and then wiring is provided to complete a semiconductor integrated circuit.

However, according to this method, as shown in FIG. 1(d), cleaning residue 6 is likely to be generated on the silicon nitride film 3 during dehydration after cleaning before the growth of the LOCO8 oxide film. That is, in the case of the conventional technology, before the LOCO8 oxide film growth,
In order to remove the protective oxide film by etching, the surface of the silicon substrate is coated with a hydrophilic silicon nitride film 3 during dehydration after cleaning.
Since the silicon substrate 1 is hydrophobic (water repellent), when dehydration is performed using a normal dehydration method, for example, a spin dry method (centrifugal dehydration method), water droplets on the silicon substrate 1 are removed from the silicon nitride coating 3, which is hydrophilic. Since the hydrophobic silicon substrate 1 adhering to the wafer and surrounding the broken silicon nitride film 3 obstructs the movement of the water droplets, it is difficult for the water droplets to separate from the silicon wafer, and the water droplets evaporate during this time. At this time, a trace amount of non-shine repellent impurities dissolved in the water droplets becomes a cleaning residue 6 and remains on the silicon nitride coating 3. Then, the cleaning residue 6 is burned onto the silicon nitride film 3 by the heat treatment during the subsequent growth of the LOCO8 oxide film, so when etching the silicon nitride film 3 used as an oxidation mask after the growth of the LOCO8 oxide film 7, this cleaning is performed. The residue 6 serves as an etching mask, and the underlying silicon nitride film 3 remains without being etched, as shown in FIG. 1(f).

The region in which this silicon nitride film 3 remains is, of course, a region in which semiconductor elements will be formed later, which poses a major problem in the manufacture of integrated circuits. Note that washing before dehydration was performed for 30 minutes with ultrapure water having a specific resistance of 1 s M/, ) through a 0.211 m filter. Furthermore, although the rate of occurrence of cleaning residue 6 depends on the pattern of the photomask (the shape of the circuit), the frequency of occurrence tends to increase as the size of the pattern becomes finer.

Purpose of invention The present invention is for cleaning and dehydration before LOCO8 growth.

The present invention provides a method for manufacturing a semiconductor device that can completely prevent the generation of cleaning residue.

Structure of the Invention The present invention is a method in which, before growing a LOCO8 oxide film, the protective oxide film is left unetched, and the silicon substrate surface is cleaned and dehydrated while being covered with a silicon nitride film and a protective oxide film, both of which are hydrophilic. According to this, the hydrophobic silicon substrate surface is exposed to the cleaning liquid, and therefore no cleaning residue is generated.

DESCRIPTION OF EMBODIMENTS An embodiment of the method for manufacturing a semiconductor device according to the present invention will be described below with reference to FIG. First, a protective oxide film 2 of silicon dioxide or the like is formed to a thickness of 500 mm on a silicon substrate 1, and a silicon nitride film 3 of 100 mm thick is further formed on the protective oxide film 2 [FIG. 2(a)]. Thereafter, using the photoresist 4 as a mask, the silicon nitride film 3 is subjected to plasma etching using CF4 gas [FIG. 2 Φ]. Next, using the photoresist 4 as a mask, ions for a channel striper, for example, B''- ions in the case of an n-channel device, are implanted to form a high concentration layer 5, and then the photoresist 4
[Figure 2 (C)]. Subsequently, after a cleaning and dehydration process, a heat treatment of 1,000 tl is performed in steam, for example, to form a LOCO5 oxide film 7 with a thickness of 1 μm [Second
Figure (d)]. Next, the extremely thin oxide film grown on the silicon nitride film 3, which was used as a mask against oxidation when forming the LOCO3 oxide film 7, is etched with a hydrofluoric acid-based aqueous solution, and then the silicon nitride film 3 is etched with hot phosphoric acid. Then, the protective oxide film 2 is etched with a hydrofluoric acid aqueous solution [FIG. 2(e)]. After this 1. A semiconductor integrated circuit is completed by forming a semiconductor element in a region other than the region in which the LOCO8 oxide film 7 is formed, and then providing wiring.

Effects of the Invention According to the present invention, the silicon substrate surface is completely covered with a hydrophilic silicon nitride film and a protective oxide film in the cleaning and dehydration steps before the growth of the LOGO8 oxide film, which is different from the case of the prior art. There are no hydrophobic regions that would impede the movement of water droplets. In this case, the water droplets adhering to the silicon substrate are easily separated from the silicon substrate by the centrifugal force of the spin dryer before they evaporate, so that the generation of cleaning residue can be completely prevented. That is, LOCO8
There is no cleaning residue that is conventionally seen in the silicon nitride film etching process after oxide film growth, and the silicon nitride film can be completely removed without leaving any residue, greatly increasing the quality of product in integrated circuit manufacturing. Rise. In addition, when the present invention is used, the manufacturing process is also shortened because the protective oxide film etching step before the LOCO8 oxide film growth is eliminated.

[Brief explanation of drawings]

1(,) to (f) are preliminary process sectional views for explaining the prior art, and FIGS. 2(,) to (,) are preliminary process sectional views for explaining an embodiment of the present invention. 1...Silicon substrate, 2...Protective oxide film (silicon oxide film), 3...Silicon nitride coating, 4...Photoresist, 6... ...Cleaning residue, 7...Selective oxide film (LOCO8 oxide film). Figure 1 Figure 2 (0-2 (b) (C) (e)

Claims (1)

[Claims] A process of forming a protective oxide film on a silicon substrate. forming a silicon nitride film on the protective oxide film 2;
The method is characterized by comprising the steps of: etching the second part of the silicon nitride film to form the silicon nitride film pattern; and forming a selective oxide film in areas where the selective oxide film is exposed using the silicon nitride film as a mask. A method for manufacturing a semiconductor device.