JPH01281748A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To shorten a birds beak by forming a nitride silicon film pattern by anisotropic dry etching using a gas involving carbon, and thereafter subjecting the pattern to ashing, cold oxidization, and impregnation into an aqueous hydrofluoric acid solution to remove a carbon contaminated layer on the exposed semiconductor substrate surface. CONSTITUTION:After a layer A (silicon nitride film) is removed by ashing, a layer B (carbon contaminated layer) is completely converted to SiO2 by cold oxidization. Carbon atoms involved in the layer B are substantially entirely incorporated into the SiO2 by the cold oxidization. Accordingly, the involved carbon atoms can be removed by impregnating the SiO2 in an aqueous HF solution and removing the same. Thereafter, there are produced no defect layer due to carbon contamination and no increase of junction leakage, by selective thermal oxidization. Hereby, and birds beak can be shortened without leaving behind any defect layer which increases such junction leakage.

Description

[Detailed Description of the Invention] [Summary of the Invention] It is an object of the present invention to provide a method for manufacturing a device isolation structure with a fine width, in which a bird's beak is shortened without leaving a defective layer that increases junction leakage. to grow a silicon nitride film in direct contact with at least a portion of the surface of a semiconductor substrate,
In a method of manufacturing a semiconductor device in which the oxide film formed by forming the oxide film into a predetermined pattern and selectively oxidizing the portions of the semiconductor substrate that are not covered with the nitride film is used for element isolation, a gas containing carbon is used. After forming a pattern on the silicon nitride film by anisotropic dry etching using a method, ashing, low-temperature oxidation, and immersion in a hydrofluoric acid aqueous solution are performed in this order before the next thermal oxidation step. The structure is such that the carbon contamination layer on the surface of the semiconductor substrate exposed after the silicon nitride film is removed is removed.

[Industrial application field]

The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a device isolation structure with a fine width.

In recent years, the scale of semiconductor integrated circuits has been rapidly increasing, and there is a strong desire to improve the degree of integration.Therefore, it is absolutely necessary to miniaturize not only active elements such as transistors, but also element isolation regions. In the case of silicon LSI, the conventional element isolation method used is a dielectric isolation method using silicon dioxide (SiOz), which is formed by selective oxidation of silicon.However, with this method, so-called bird's beak occurs. There is a limit to how small the width of the isolation region can be, resulting in problems such as a decrease in the width of the active region and a decrease in the degree of integration.

The cause of the bird's beak is that the pad 5iOz layer, which is inserted between the silicon nitride (SisN4) pattern that is an oxidation-resistant mask and the silicon substrate to relieve stress and suppress crystal defects, becomes a path for oxidants.
, due to the oxidized region penetrating beneath the pattern.

Therefore, we aim to improve the degree of integration while using selective oxidation.
In other words, as a method of shortening the bird's beak, pad 5
A method is known in which field oxidation is performed by surrounding the sidewalls of the iOz layer and the Si3N4 film formed on the layer, which serves as a mask for selective oxidation, with a second 5i3Nn film formed directly on the silicon substrate without using a pad oxide film. It is being According to this method, it is possible to prevent oxidant from entering the pad SiO□, and the bird's beak can be shortened. What about this invention?
This paper relates to follow-up measures when performing fine-width element isolation.

[Conventional technology]

FIGS. 3(a) and 3(b) show the main parts of the fine width element isolation method. 1O is a silicon substrate, 11 is a pad SiO□ film formed on the substrate, and 12 is a pad 5i formed on the film 11.
3Ni film, 13 is a second S i 3 Na film surrounding the sidewalls of these films 11 and 12. Such a membrane 11.
If there is a SisNn film 13 that surrounds the sidewalls of 12 (the purpose is to close the sidewalls of SiO□1ull), it will thermally oxidize and
When forming a field oxide film (element isolation film) on 0a, 5iOzll as in the case where there is no Si3N4 film 13.
Since there is no intrusion of oxidant (indicated by the arrow) from the sidewall of 1, the field oxide film looks like the dotted line and almost no bird's beak occurs.

The nitride film 13 in FIG. 3(a) is shown in FIG. 3(e), (f), and (g).
It can be made using the process of That is, a SiO□ film 11 is formed on a silicon substrate 10 by, for example, thermal oxidation, and then a Si:+Na film 12 is grown by, for example, CVD, and then a resist is applied, exposed, developed, and patterned. Create a resist 14 with a 100% polyurethane, and use this as a mask to apply Si3N4.
Etching the film 12 and further the SiO2 film 11 (e)
state. Next, as shown in (f), after removing the resist 14, a second 5i2N film 15 is grown, and then anisotropic etching is performed to reduce the thickness of the 5iiN4 film 15 as shown by dotted lines and arrows. . Eventually (like a station,
The S i x N 4 film remains only on the side walls of the film 11.12, thus obtaining the state (g) or (a).

The second Si3N film 15 is partially composed of the first Si3N film 15.
Nm is on the film 12, but the rest is on the exposed surface 10 of the substrate 10.
It's on a. Therefore, when removing the 5i3Nn film on the exposed surface 10a by etching, the anisotropic etching (RlE: reactive ion etching) gas is directly etched on the exposed surface 10a.
There is a risk of touching a and damaging it.

Therefore, the anisotropic etching of the second nitride 11215 is performed using CF
This is carried out using a carbon-containing gas such as 4+H or CHF3+CFa.

However, even if macroscopic roughness does not occur under these etching conditions, G.

S, 0ehrlein is Proc, Symposi
um on Dry Process p59.198
6, a damaged layer as shown in FIG. 3(C) is produced. A is a C:F polymer layer, B is an amorphous Si:C layer, and C is a "H" damaged layer. D is a completely crystalline layer, and the layers other than D are altered.

Of these A-C layers, the A layer is an organic polymer containing fluorine generated from the etching gas, and can be removed by an ashing process performed to remove the photoresist after etching, but carbon ions generated in the etching plasma are implanted. The B layer and the C layer into which hydrogen ions have been implanted remain as they are. Therefore, if a device is formed by performing the steps after field oxidation using the conventional method, the same figure (
As shown in d), a defective layer (indicated by an x mark) due to the B layer remains under the field SiO□ 16, resulting in a problem that the reverse leakage current of the PN junction increases significantly.

(Problem to be solved by the invention) When performing anisotropic etching using a gas containing carbon on a silicon nitride film that is in direct contact with a silicon substrate, carbon ions are bombarded even though no macroscopic roughness occurs on the substrate surface. A layer B is formed, and defects due to carbon in the layer B are generated by subsequent heat treatment at a high temperature of, for example, 600° C. or higher.

An object of the present invention is to improve this point and provide a method for manufacturing a device isolation structure with a fine width, in which the bird's beak can be shortened without leaving a defective layer that increases junction leakage.

(Means for Solving the Problems) Fig. 1 shows the main parts of the manufacturing method of the present invention.As shown in the figure, in the present invention, Si3
N. After etching the film (2), before proceeding to the next thermal oxidation step (2), ashing (2), low-temperature oxidation (2), and dipping in an HF aqueous solution (2) are performed in this order.

The low-temperature oxidation referred to here refers to carbon (
This is an oxidation process in which C) hardly diffuses in silicon (Si) at temperatures ranging from room temperature to about 300°C. Low-temperature oxidation can be performed by immersing the silicon substrate in an oxidizing solution. Further, the ashing and low-temperature oxidation can be performed successively by exposing the silicon substrate to oxygen plasma for a predetermined period of time.

[Effect]

According to the method of the present invention, the above problem can be solved as follows.

First, after removing layer A by ashing, the entire layer B is converted to 5 iOz by low-temperature oxidation. Through this low-temperature oxidation, almost all the carbon in the 8 layers was converted into SiO□
taken inside. Therefore, by removing this SiO□ layer by immersing it in an HF aqueous solution, carbon can also be removed. If selective thermal oxidation is performed after this, a defective layer due to carbon contamination will not be generated and junction leakage will not increase.

At this time, the B layer is converted to S by high temperature thermal oxidation instead of low temperature oxidation.
When converted into iO
Even if selective oxidation is performed after the B layer is oxidized and removed, junction leakage remains.

Furthermore, it was confirmed through experiments that junction leakage can be sufficiently suppressed even if the 0 layer is not oxidized at a low temperature so thick as to convert it to Sing. This indicates that carbon contamination plays a role in the formation of defective layers that lead to junction leakage, and that hydrogen ultimately has no effect.

〔Example〕

As mentioned above, carbon contamination of the silicon substrate during anisotropic etching is the main cause of the problem, so the second Si3N,
Even in the case where the first Si, N, film 12 is anisotropically etched to expose the silicon substrate without using the film 13, the present invention can be similarly applied to obtain the same effect.

Therefore, an embodiment of the present invention will be described for a case where only the first Si3N film 12 is used. As shown in FIG. 2(a), a (100) p-type 10Ωcm silicon substrate 10
was thermally oxidized by 50 people to form an oxide film 11, and then CVD was applied on top of this.
A nitride film 12 is formed by growing 500 layers of Si3N4 by the method, and a photoresist layer 14 having a predetermined element isolation pattern is formed thereon. Next, CHF3 +CF4 (1
: 1) Parallel plate type plasma etching equipment using gas, under the conditions of 0.4 Torr + IOW/cm2,
After removing Si3N, film 12, and SiO□ film 11 by etching, B ions for channel stop are implanted into the exposed portion 10a of the substrate.

Subsequently, after removing the photoresist layer 14 and the A layer of the exposed portion 10a by ashing treatment, low-temperature oxidation was performed by immersing in sulfuric acid + hydrogen peroxide solution (100:2) at 110°C for 10 minutes, and after washing with water. , the exposed portion 10a of the B layer is removed by immersion in an HF aqueous solution (5%) for 20 seconds. After washing with water and drying, the exposed portion 10a is field oxidized,
Thereafter, a predetermined device was formed using normal steps. Figure 2 (
b) shows this state, 16 is the field oxide film, 17
18 is a PSG film for surface insulation, 18 is an electrode attached to the diffusion layer 19, 20 is a channel stop, and 21 is a conductor layer. 19 and 21 constitute, for example, a source drain and a gate electrode of a MOS PET.

FIG. 2(C) shows the results of measuring the reverse saturation current of the PN junction of the obtained devices with and without immersion in the HF aqueous solution during the above process.

The leakage current was reduced by about one order of magnitude in the HF-treated sample compared to the non-HF-treated sample, indicating that the present invention removes defective layers.

In this example, low-temperature oxidation was performed using a mixture of sulfuric acid and hydrogen peroxide, but depending on the etching conditions, the B layer may become thick and the amount of oxidation may be insufficient with this method.

In this case, good results can be obtained by adding boiled nitric acid.

Furthermore, by exposing the material to oxygen plasma generated under appropriate conditions, a sufficient amount of oxidation could be achieved at low temperatures. Therefore, good results can be obtained by ashing followed by low temperature oxidation by exposure to oxygen plasma.

Since a B layer is generated in the exposed portion of the substrate by the anisotropic etching of the nitride film 15 in FIG. 3(f), it is necessary to remove this by the method described above, and then remove the nitride film 12.15 after field oxidation. If this is removed by dry etching using a carbon-containing gas, there is a problem of the formation of a B layer. For this purpose, ashing, low-temperature oxidation, and etching with hydrofluoric acid may be performed in the same manner.

[Effects of the Invention] As described above, according to the present invention, an element isolation region with a short bird's beak and a fine width can be formed without increasing leakage of the PN junction. Therefore, by using the manufacturing method of the present invention, it is possible to improve the degree of integration of a semiconductor device without deteriorating its performance.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the manufacturing method of the present invention, FIG. 2 is an explanatory diagram of the present invention in detail, and FIG. 3 is an explanatory diagram of the conventional method. In FIGS. 2 and 3, 10 is a semiconductor substrate, 15 is a silicon nitride film, 16 is a field oxide film, and B is an amorphous 5i
This is the sC layer.

Claims (1)

[Claims] 1. A silicon nitride film (15) is grown in direct contact with at least a portion of the surface of the semiconductor substrate (10), and formed into a predetermined pattern to form a silicon nitride film (15) in direct contact with at least a portion of the surface of the semiconductor substrate (10). In a method of manufacturing a semiconductor device in which an oxide film (16) produced by selectively oxidizing a portion (10a) not covered by the film is used for element isolation, After patterning the silicon nitride film (15), ashing, low-temperature oxidation, and immersion in a hydrofluoric acid aqueous solution are performed in this order to remove the silicon nitride film before the next thermal oxidation step. Exposed semiconductor substrate surface (10a)
1. A method for manufacturing a semiconductor device, comprising removing a carbon contamination layer (B).