JPH0430179B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a method for manufacturing a semiconductor device, and in particular to a method for electrically isolating a plurality of circuit elements formed on a common semiconductor substrate, for example, involving a selective thermal oxidation process for a silicon substrate. The present invention relates to a method for manufacturing a semiconductor device, which is applied when obtaining a semiconductor integrated circuit device, etc., which involves a step of selectively forming an oxide insulating layer.

BACKGROUND TECHNOLOGY AND PROBLEMS For example, in semiconductor integrated circuits, in order to electrically isolate multiple circuit elements formed on a common silicon substrate, the silicon substrate is selectively thermally oxidized between these elements to provide thick oxide insulation. There is a method of forming layers and performing electrical isolation.

When performing selective thermal oxidation on a silicon substrate to form an oxide insulating layer in this way, silicon nitride is deposited on the surface of the semiconductor substrate as a mask for oxidation.
Generally, a Si ₃ N ₄ film is formed and selective thermal oxidation of the semiconductor substrate is performed through an opening formed in the Si 3 N 4 film. In this case, if a Si ₃ N ₄ oxide mask layer is formed directly on the silicon semiconductor substrate,
This intrinsic stress in the Si ₃ N ₄ film causes strain at the Si-Si ₃ N ₄ interface, which causes instability such as generation of crystal defects during subsequent heat treatment.

Therefore, when using such an oxidation mask made of a Si ₃ N ₄ film, a pad layer 2 made of a thin SiO ₂ film of several hundred angstroms is formed on the surface of a silicon substrate 1, as shown in FIG. A nitride Si ₃ N ₄ layer 3 is deposited as an oxidation mask on the substrate, and openings 4 are formed in this layer 3 by photo-etching or the like at the portions where thermal oxidation is to be performed. Thereafter, the surface of the silicon substrate 1 is thermally oxidized through the opening 4 to selectively form an oxide layer 5 on the silicon substrate 1 as shown in FIG.
We are trying to form a However, when the SiO ₂ pad layer 2, which has no oxidation masking effect, is interposed between the substrate 1 under the oxidation mask Si ₃ N ₄ layer 3, this SiO ₂ layer 2 substantially Due to the gap, a so-called bird's beak 6 is formed around the obtained oxide layer 5 and extends below the edge of the opening 4 of the mask layer 3, thereby preventing the oxide layer 5 from being sufficiently covered. Since the width cannot be formed narrowly, it is difficult to improve the degree of integration of circuit elements in an integrated circuit, for example.

OBJECTS OF THE INVENTION The present invention is directed to improving the degree of integration in, for example, semiconductor integrated circuits by effectively avoiding the occurrence of bird's beaks at the periphery of an oxide layer due to the selective oxidation in the method of manufacturing a semiconductor device that involves selective oxidation. Plan.

Further, the present invention aims to improve and stabilize the characteristics of circuit elements formed on the surface of a silicon substrate, such as insulated gate field effect transistors (MOS transistors).

Summary of the Invention In the present invention, a silicon nitride layer such as Si ₃ N ₄ is formed as a mask for selective thermal oxidation on a silicon substrate. It is formed by ion-implanting nitrogen atoms into the surface of a silicon substrate through an amorphous layer containing silicon. The nitride layer obtained in this way is then thermally oxidized as an oxidation mask, and this mask layer is then removed. Furthermore, the nitrogen atoms remaining on the silicon substrate surface are removed by forming a silicon oxide layer SiO ₂ on the silicon substrate.
By forming a layer, it is adsorbed onto this layer and eliminated.

That is, in the present invention, first, an amorphous layer containing silicon is deposited on one main surface of a silicon substrate, and nitrogen ions are selectively implanted into the silicon substrate in a predetermined pattern through this amorphous layer. to form a silicon nitride layer. Then, using this nitride layer as a mask, a thermal oxidation treatment is performed on the silicon substrate to form a silicon oxide layer in a predetermined pattern, and then an amorphous layer that has been similarly oxidized by this thermal oxidation and a nitride layer are formed. After removing the nitride layer, an oxide layer is again formed on the surface of the substrate from which the nitride layer has been removed, for example, by thermal oxidation, and in this oxide layer, the nitrogen atoms remaining on the silicon substrate surface, that is, donor impurities, are removed. Adsorbs nitrogen atoms, which act as Thereafter, by removing this oxide layer, nitrogen, that is, a donor impurity, is removed from the silicon substrate, and the electrical conductivity of the silicon surface is reduced due to the remaining donor impurity in, for example, a MOS transistor that is subsequently formed on the surface of the silicon substrate. This eliminates the difficulty of control.

Embodiment An example of a method for manufacturing a semiconductor device according to the present invention will be described in detail with reference to FIG. 3 and subsequent figures. First, as shown in FIG.
A silicon-containing amorphous layer 12, for example, a SiO ₂ thermal oxide film, is formed on one main surface 11a of the silicon substrate 11 of the mold.
The film is deposited to a thickness of about 100 Å. Then, on this amorphous layer 12, an ion implantation mask layer 13 such as a photoresist layer is selectively formed in a portion where selective oxidation is to be performed, such as a portion where insulation separation between circuit elements in a semiconductor integrated circuit is to be performed. . This selective formation can be achieved by well-known photographic techniques.

Next, as shown in FIG. 4, the surface 11a of the base 11 is
From the side, using the photoresist mask layer 13 as a mask for ion implantation, N ₂ ions are implanted at a dose of 1.5×10 ¹⁷ cm ^-2 at an implantation energy of 20 keV, for example, from a direction tilted approximately 7° in any direction from the 100 axis. A nitride layer 14 is formed on the main surface 11a of the substrate 11 in a predetermined pattern, that is, on the portions where the mask layer 13 is not deposited. In this case, amorphous layer 1
2 is also doped with nitrogen atoms to form silicon oxynitride, and a nitride layer 14 of approximately 400 Å thick, ie, a silicon nitride layer of, for example, Si ₃ N ₄ , is formed below this.

After this ion implantation, annealing is performed at 900°C for 30 minutes in a nitrogen atmosphere, followed by high-pressure oxidation at 900°C for about 60 minutes at a high pressure of about 5 kg/ ^cm2 , as shown in Figure 5. oxide of about 6000Å
A SiO ₂ layer 15 is formed. In this case, the annealing treatment and the selective oxidation treatment for forming the oxide layer 15 are performed at 800°C to 1100°C for at least 60 minutes, including both, to form the silicon substrate 1.
Many of the nitrogen atoms introduced into the nitride layer 14
For the formation of , the number of nitrogen atoms remaining in the silicon substrate 11 is reduced by migrating into this layer 14, ie to the substrate surface. By the oxidation treatment to form this oxide layer 15, the amorphous layer 1
2 and a part of the nitride layer 14 are oxidized and changed into a silicon oxide film, resulting in a two-layer structure consisting of a silicon oxide film of about 200 Å and a silicon nitride film of about 300 Å.

These are removed by etching using a suitable etching solution or etching gas as shown in FIG.

Thereafter, as shown in ^FIG .
An oxide layer 16 is formed by thermal oxidation of .ANG.

Thereafter, as shown in FIG.
Remove by etching. It was confirmed that no N-type carriers, which are generated when nitrogen atoms become donors, remain on the surface of the semiconductor silicon substrate 11 from which the thermal oxide layer 16 has been removed in this way. This was confirmed by forming a MOS capacitor on the surface of this silicon substrate and finding that its threshold voltage V _th was the same as that without implanting nitrogen ions. This removal of nitrogen atoms is due to nitrogen atoms being introduced into the oxide layer 16 and removed by subsequent removal of the oxide layer 16.

When ion-implanting nitrogen atoms, the ions are implanted without passing through the amorphous layer formed by the thermal oxide film, and annealing treatment is performed at 900°C to 1200°C for about 30 minutes to form the nitride layer 1.
4, a concentration of about 5×10 ¹⁷ cm ^-3 of N
Mold carriers exist to a depth of 0.2 μm.

Also, before the nitrogen ion implantation, that is, the nitride layer 14
The thermal oxide film as the amorphous layer 12 formed before the formation of the substrate 11 is deposited for the purpose of preventing the channeling effect at the initial stage of ion implantation caused by the fact that the substrate 11 is a single crystal. 12 is 30 when performing the 20keV N ₂ ion implantation described above.
Thicknesses in the range ~200 Å can be chosen. Also,
This amorphous layer 12 is not limited to a thermally oxidized SiO ₂ film, but may also be formed of, for example, a polycrystalline silicon layer or a silicon nitride film. The thickness of this amorphous layer 12 is selected to be smaller than the projected range of the N ₂ ions, so that the N ₂ ions are implanted sufficiently deeply into the silicon substrate 11 to form a silicon nitride or nitride layer 14. The material and thickness are selected so that it can be used.

Effects of the Invention According to the manufacturing method of the present invention described above, the formation of the nitride layer 14 as an oxidation-resistant mask layer for performing selective oxidation is performed by ion implantation of nitrogen atoms into the silicon substrate. Therefore, since the nitrogen concentration decreases with a desired distribution between the nitride layer 14 and the basic region containing no nitrogen, the occurrence of strain is small even without the interposition of a pad layer. Furthermore, since this implantation method is used, for example, when a nitride layer is formed by chemical vapor deposition or thermal nitriding, there is The formation of a silicon oxide layer can be avoided. By avoiding the presence of such a SiO ₂ film, the production method of the present invention avoids the occurrence of the bird's beak mentioned at the beginning.

Furthermore, since the nitride layer is formed by this ion implantation method, no oxygen is contained in the nitride layer 14, which has excellent oxidation resistance and is an excellent mask for selective oxidation. layers can be formed. Furthermore, by using a mask layer 13 such as a photoresist layer, the nitride layer 14 can be
This has the advantage that the oxide layer 15 can be formed in any desired pattern. On the other hand, even though the nitride layer is formed in the silicon substrate in this way, the nitrogen atoms that diffuse into the substrate are eliminated by being adsorbed into the oxide layer 16. Base body 11
Donors caused by nitrogen atoms can be reliably removed from the surface of the silicon substrate, thereby stabilizing the electrical characteristics of the silicon substrate surface and stabilizing the characteristics of circuit elements such as MOS transistors formed thereon. can be measured.

[Brief explanation of drawings]

1 and 2 are schematic cross-sectional views of each process for explaining the conventional method for manufacturing a semiconductor device, and FIGS. 3 to 8 are schematic cross-sectional views of each process of an example of the method for manufacturing a semiconductor device according to the present invention. FIG. 11 is a silicon substrate, 12 is an amorphous layer, 14 is a nitride layer, 15 is an oxide layer, and 16 is an oxide layer.

Claims (1)

[Claims] 1 a step of forming an amorphous layer containing silicon on one main surface of a silicon substrate; a step of ion-implanting nitrogen into the silicon substrate to form a nitride layer in a predetermined pattern under the amorphous layer; A step of thermally oxidizing the main surface of the silicon substrate, a step of removing the oxidized amorphous layer and a nitride layer, and a step of forming an oxide layer on the surface of the substrate from which the nitride layer has been removed. and a step of removing the oxide layer.