JPH01297837A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To restrict the short channel effect of a semiconductor device that has a channel stopper below a field oxide film by forming the channel stopper by effecting ion implantation before and after the formation of the field oxide film. CONSTITUTION:A pad SiO2 film 12 and a polycrystalline Si film 13 are laminated on the surface of a Si substrate 11, and a non-oxidizing Si3N4 film 14 is formed on the film 13. A BF2 ion 15 is implanted using the film 14 as a mask. In succession, a field oxide film 16 is formed in an element isolation region to separate the films 14, 13, 12, and a gate SiO2 film 17 is formed at that part. Thereafter, there are implanted B ions 21 by the use of the film 16 as a mask, the ions serving as channel stopping and punch-through-prevention. For this, an amount of the ions implanted before formation of the film 16 is reduced compared with a case where the ions are implanted at a time before the formation of the film 16. Therefore, the degree of ion diffusion from the film 16 into the element formation region is reduced, and hence a desired semiconductor device with restricted short channel effect is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method of manufacturing a semiconductor device in which a channel stopper is formed under a field oxide film of a semiconductor substrate.

[Summary of the invention]

The present invention provides a method for manufacturing a semiconductor device as described above.
By performing the ion implantation for forming the channel stopper before and after the formation of the field oxide film, the narrow channel effect can be suppressed.

[Conventional technology]

As semiconductor integrated circuits become more highly integrated, miniaturization of MOS transistors is also required. On the other hand, a channel stopper for preventing inversion is formed under a field oxide film formed by the LOCO3 method, which is a typical element isolation technique.

Conventionally, impurities for forming a channel stopper have been temporarily ion-implanted using an oxidation-resistant film for forming a field oxide film as a mask before forming a field oxide film.

[Problem to be solved by the invention]

However, when the gate width is narrowed in order to miniaturize a MOS transistor, a narrow channel effect occurs.

In order to suppress the narrow channel effect, a method of implanting impurity ions under the field oxide film after forming the field oxide film is also considered.

However, in this method, impurities are also implanted into the element formation region, so if the amount of impurities required to prevent inversion is implanted,
The substrate concentration in the element formation region becomes higher than necessary. As a result, another problem arises in that the junction capacitance and substrate effect increase.

[Means to solve the problem]

In the method for manufacturing a semiconductor device according to the present invention, a semiconductor substrate 11
a step of selectively forming an oxidation-resistant film 14 thereon; a step of performing a first ion implantation into the semiconductor substrate 11 using the oxidation-resistant film 14 as a mask; and a step of implanting the oxidation-resistant film 14 after the first ion implantation. A step of selectively forming a field oxide film 16 on the surface of the semiconductor substrate 11 using a film 14, and performing a second ion implantation at least under the field oxide film 16, and combining the second ion implantation and the second ion implantation. 1 ion implantation, a channel stopper 23 is formed under the field oxide film 16.
and a step of forming.

[Effect]

In the method for manufacturing a semiconductor device according to the present invention, the ion implantation for forming the channel stopper 23 is carried out separately before and after the formation of the field oxide film 16. The amount of ions 15 implanted into the semiconductor substrate 11 before the formation of the field oxide film 16 is smaller than when the field oxide film 16 is formed at the same time.

Therefore, when forming the field oxide film 16, ions 15 diffuse from below the field oxide film 16 to the element formation region.
The amount of is small.

〔Example〕

Hereinafter, an embodiment of the present invention applied to the manufacture of a MOS transistor will be described with reference to FIG.

In this embodiment, as shown in FIG. 1A, a pad SiO□ film 12 with a thickness of about 50 layers, a polycrystalline Si film 13 with a thickness of about 500 layers, and an i3N film 13 with a thickness of about 1000 layers are formed on a Si substrate 11, as shown in FIG. 1A.
4 films 14 are formed sequentially, and then 5iJ4 films 1
4 and a predetermined thickness of the polycrystalline St film 13, a portion corresponding to the element isolation region is selectively removed.

Next, as shown in Figure 1B, BF for channel stop
215 is ion-implanted at a dose of about 2 to 3×10 13 cm −” and an energy of about 60 keV.

After annealing the ion-implanted BF215, thermal oxidation is performed to obtain a thickness of 3000 mm as shown in FIG. 1C.
An iO□ film 16 with a field strength of about 4,000 is formed in the element isolation region.

Next, as shown in FIG. 1D, the 5iJ4 film 14 and the polycrystalline S
The i film 13 and the pad SiO□ film 12 are peeled off, and then
The thickness is approximately 120 mm), and the SiO□ film is 17 layers in shape.

Next, as shown in FIG.
Ion implantation is performed at a dose of about 11-'' and an energy of about 100 keV.

After annealing the ion-implanted B21, a gate electrode 22 is formed as shown in FIG. 1F. By annealing B21, Bpt is formed directly under the field 5i02 film 16.
15 and B21 form a P- region 23 for channel stop, and a P- region 24 for punch-through prevention is formed below the gate SiO□ film 17.

In this embodiment as described above, in order to form the P- region 23 for channel stop, the field SiO□ film 16 is ion-implanted after the formation of the field SiO Before forming the 5i02 film 16, ions of BP 15 may be implanted.

That is, conventionally, before forming the field 5iO7 film 16, 5×
10' 3 marks - 2 or more BF215 ions were implanted, but in this example, as described above, 2 to 3 x 1013 cm
” ” is sufficient.

Therefore, during thermal oxidation for forming the field SiO□ film 16, the amount of BF 215 that diffuses from below the field t'' SiO□ film 16 into the element formation region is small, and the narrow channel effect is suppressed to that extent.

The B21 ion-implanted after the formation of the field SiO□ film 16 is not segregated in the field 5iO7 film 16 during thermal oxidation to form the field 5i02 film 16, so it is in a trace amount compared to BF215. However, the effect of preventing reversal is very large.

In order to form the field 5i02 film 16, in this example, the pad SiO□ film 12, the polycrystalline Si film 13, the Si3N film 14 were formed on the Si substrate 11. Pad SiO□ film 12 and Si3
Only the N4 film 14 may be formed on the Si substrate 11.

〔Effect of the invention〕

In the method for manufacturing a semiconductor device according to the present invention, when forming the field oxide film, the amount of ions that diffuse from under the field oxide film to the element formation region is small, so that the narrow channel effect is suppressed.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view sequentially showing one embodiment of the present invention. In addition, in the symbols used in the drawings, 11---11111---5i substrate 14-
m------------3iJ4 membrane 15
−−−−−−−−−−−−BF. 16----------Field SiO□
Film 23---------------- P- region.

Claims (1)

[Scope of Claims] A step of selectively forming an oxidation-resistant film on a semiconductor substrate, a step of performing a first ion implantation into the semiconductor substrate using the oxidation-resistant film as a mask, and the first ion implantation. After that, a step of selectively forming a field oxide film on the surface of the semiconductor substrate using the oxidation-resistant film; performing a second ion implantation at least under the field oxide film; and forming a channel stopper under the field oxide film by first ion implantation.