JPH03280428A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To avoid the occurrence of a bird's beak for enhancing the integration by a method wherein, during the formation process of an element isolation region by selective oxidation, a mask is formed not to make a silicon oxide film 2 lie between the end of a thermal resistant mask film and a silicon substrate. CONSTITUTION:A thermal oxide film 2 is formed on a silicon substrate 1 and then a photoresist mask 3a having opening parts along the edge of an element isolating region is pattern-formed to form nitrogen ion implanted regions 4 which are heat treated, after removing the silicon thermal oxide film 2, to be converted into local silicon nitride films 5a. Next, after burying the thin oxide film 2 at the peripheral part of the silicon nitride films 5a on the silicon substrate 1, the silicon nitride film 5 is thermal-oxidized and then deposited. Later, a silicon nitride film mask 5b pattern-formed by the conventional process using a photo resist mask 3b is pressure-oxidized, an element isolating region 6 is formed and then the silicon nitride film 5b and the thin oxide film 2 are removed to expose an element formation region 7.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming an element isolation region using a selective thermal oxidation method. [Prior Art 1] FIG. 3 fat to fdl are process diagrams for forming element isolation regions in a conventional semiconductor device. That is, after a thermal oxide film 2 with a thickness of about 50nIl is formed on a silicon substrate l, a silicon nitride film 5 (Sx3N41) is deposited with a thickness of about 1100n by a vapor phase growth method [see Fig. 3 (at)]. Next, a silicon nitride film mask 5b is patterned through a photoresist mask 3b [see FIG. 3 fb)]
Next, the element isolation region 6 is formed by performing pressure thermal oxidation utilizing the heat resistance of the silicon nitride film.
See figure [C]]. Here, by removing the silicon nitride film mask 5b which is no longer needed, the element formation region 7 can be obtained.
[See Figure 3 (dl)] [Problems to be Solved by the Invention] However, in the conventional method for forming an element isolation region described above, prior to depositing the silicon nitride film 5, crystal defects in the substrate are removed. Since it is necessary to form a thermal oxide film 2 for the purpose of preventing this, there is a drawback that a thick oxide film gets under the edge of the silicon nitride film mask during the pressure oxidation process, creating a bird's beak 10.The area of this bird's beak 10 is , it is only a wasted area for reducing the element isolation region 7, which reduces the degree of integration of the element.In view of the above circumstances, an object of the present invention is to provide a selective thermal oxidation method that can reduce the formation of bird's peaks. An object of the present invention is to provide a method for manufacturing a semiconductor device including a step of forming an isolation region. [Means for Solving the Problems] According to the present invention, a method for manufacturing a semiconductor device includes forming an isolation region by selective oxidation. The formation step includes forming a mask so that no silicon oxide film is interposed between the end of the heat-resistant mask film used in the selective oxidation and the silicon substrate. [Function] According to the present invention For example, when forming an element isolation region by pressure oxidation,
Since there is no thermal oxide film intervening at the end of the heat-resistant mask film, which penetrates underneath, it is possible to reduce the generation of buzz beaks that cause wasted area at the end of the element isolation region. [Example] Next, the present invention will be explained with reference to the drawings. FIGS. 1(a) to 1(h) are process diagrams for forming element isolation regions showing one embodiment of the present invention. According to this embodiment, the first
As shown in FIG. fa), a thermal oxide film 2 having a thickness of 50 nm is first formed on a silicon substrate I as in the conventional method. Next, the first
As shown in Figure fbl, a photoresist mask 3 with band-shaped openings along the edge of the element isolation region to be formed
A is patterned [see Figure 1 + BL], and nitrogen (N2) is applied in the substrate 1 to a depth of 50 r + m, 6 degrees 1O18~1
Nitrogen ion implantation region 4 is formed by ion implantation to form 019CIn-3 [see Figure 1 (Cl)].Next, after removing silicon thermal oxidation 11!2 used as a mask, the silicon ion implantation region 4 is heated at a temperature of 900 to 1100°C. The nitrogen ion implantation region 4 is covered with a local silicon nitride film (313
N4) 5 Convert to a [Figure 1 tdl Prayer 1
゜Next, after performing thermal oxidation and filling the periphery of the silicon nitride film 5a on the silicon substrate 1 with a thin oxide film 2 with a thickness of 50 nm, silicon nitride 1]fffS is further formed by vapor phase growth.
zJ4) Deposit 5 [see Fig. 1(e) 1゜The following steps are the same as the conventional method; as shown in Fig. Perform pressure oxidation to form element isolation regions 6 (FIG. 1fg)? 'Shine]. After that, the silicon nitride M5b and thin oxide film 2 of the mask which are no longer needed are removed to expose the element formation region 7 [see FIG. 1 fh]. As is clear from this embodiment, according to the present invention, the silicon thermal oxide film that causes the formation of bird's beaks is removed from the peripheral edge of the silicon nitride film mask, so the formation of bird's beaks is reduced. FIG. 2 (a) to (fl are process diagrams for forming element isolation regions showing other embodiments of the present invention. According to this embodiment, silicon nitride oxide is formed on the surface of the silicon substrate l by plasma CVD. A film (SiONl 8) is directly deposited to a thickness of 150 nm without intervening a silicon thermal oxide film 2 as in the conventional method. At this time, a plasma damaged layer 9 is formed on the surface of the silicon substrate l [see Fig. 2 ia). 1. This silicon nitride oxide film (SiONl 8) was patterned using a photoresist mask 3b to form a heat-resistant mask 8b [see Fig. The element insulating region 6 is formed by a pressure oxidation method [see FIG.
Figure (see dl j) Further, this surface layer is oxidized to a thickness of about 50 nm to remove the plasma damage layer 9 [Figure 2 f
) Kenaki]. After that, the entire process is completed by removing the thin oxide film 2 from above the element forming region 7. In this embodiment, since the silicon thermal oxide film iii, which is a factor in the formation of bird's beak, is not formed from the beginning under a thermal mask, the formation of bird's beak can be effectively prevented. In addition, low-temperature growth (approximately 30%
Silicon nitride oxidation by plasma CVD method at 0°C) 11
Q fsiON) was used to reduce stress due to the difference in thermal expansion coefficient with the silicon substrate. That is, silicon nitride 11Q (S
Even when compared to +3N+1, the stress generated is about as small as that, so it has the effect of improving work reliability. [Effects of the Invention 1] As explained in detail above, according to the present invention, there is a gap between the edge of a heat-resistant mask such as a silicon nitride film that is selectively oxidized under pressure and the silicon substrate during oxidation under pressure. Since the oxide film that enters the crotch of the mask is removed and the mask film is deposited so as not to exist, it is possible to suppress the occurrence of bird's beak and improve the degree of integration.

[Brief explanation of drawings]

Fig. 1 (a) to (h) are process diagrams for forming an element isolation region showing one embodiment of the present invention, and Fig. 2 (a) to ffl are forming process diagrams of an element isolation region showing another embodiment of the present invention. Process diagram, 3rd
Figures (al to fd) are process diagrams for forming element isolation regions in conventional semiconductor devices. 1- Silicon substrate, 2 Silicon thermal oxide film, 3.3a, 3b- Photoresist mask, 4...
Nitrogen ion implantation region, 5.5a--Silicon nitride film, 5b--Silicon nitride film mask, 6--Element isolation region, 7--Element formation region, 8--Silicon nitride film (SiONl) , 8b...
Silicon nitride oxide film mask, 9... plasma damage layer, 10-...bird's beak. Patent applicant NEC Corporation

Claims (1)

[Claims] A semiconductor device characterized in that, in the step of forming an element isolation region by selective oxidation, the mask is formed so that no silicon oxide film is interposed between the end of the heat-resistant mask film used in the selective oxidation and the silicon substrate. Production method.