JPH0358471A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To prevent impurity from being injected into a well forming region and to improve an element formed in a well in characteristics by a method wherein an active region is covered with a multilayered film which includes an acid-resistant oxide film and a photoresist when a reverse conductivity type channel stopper region is formed. CONSTITUTION:An oxide film 2 is formed on the whole face of a silicon substrate 1, and a P-well 4 is formed using a photoresist 3 as a mask. Then, a nitride film 5 is formed on the whole face, which is etched using a photoresist 6 as a mask to selectively leave the nitride film 5 unremoved as prescribed, and the unremoved nitride film 5 and the photoresist 6 are used as a mask to form an N-type channel stopper region 7 on a field region. Furthermore, a P-type channel stopper 9 is formed in the field region on the P-type well 4 side using a photoresist 8 as a mask. Then, the photoresists 6 and 8 are removed, a field oxide film 10 is formed using the nitride film 5 as a mask, the nitride film 5 is removed, and an N-well 12 is formed using a photoresist 11 as a mask. By this setup, impurity is prevented from being injected into a well forming region and an element formed in a well can be improved in characteristics.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a manufacturing method suitable for manufacturing a semiconductor device using a MOS transistor. [Prior Art] Conventionally, in a semiconductor device including a MOS transistor, a structure is used in which an active region is surrounded by a field region formed by a thick oxide film in order to electrically isolate adjacent elements from each other. ．． In this structure, elements can be easily isolated by simply increasing the thickness of the oxide film in the field region, making it easy to achieve high integration of this type of semiconductor device.

FIGS. 3(a) to 3(d) are diagrams illustrating a conventional manufacturing method of this type of field region in the order of steps.

First, as shown in FIG. 3(a), an oxide film 2 is formed on a semiconductor substrate l.
Then, using the photoresist 3 as a mask material, boron ions are implanted and diffused to form a P-well 4. Next, as shown in FIG. 3(b), after removing the photoresist 3, a nitride film 5 is formed on the entire surface, and selective etching is performed using another photoresist 6 to form a nitride film on the part where a transistor will be formed later. Membrane 5 is left. Further, another photoresist 8 is selectively applied, and using this as a mask, boron ions are implanted into the P-well 4 side of the element isolation region to form a P-type channel stopper region 9.

Next, as shown in FIG. 3(C), photoresists 6 and 8 are applied.
After removing phosphorus, phosphorus ions are implanted into a portion of the element isolation region other than the P well 4 using the photoresist 14 as a mask to form an N-type channel stopper region 7.

Thereafter, as shown in FIG. 3(d), the photoresist 14 is removed, thermal oxidation is performed using the nitride film 5 as a mask, and a thickness of 6
000 film F oxide film 10 is formed. Thereafter, phosphorus ions are implanted using the photoresist 11 as a mask to form an N well 12.

[Problem to be solved by the invention]

In the conventional manufacturing method described above, when ion-implanting phosphorus into the N-type channel stopper region 7 in the step shown in FIG. . The thickness of the nitride film 5 cannot be too thick because it is necessary to suppress stress at the bird's beak during formation of the field oxide film and to suppress leakage in the diffusion layer. Therefore, when ion-implanting phosphorus into the N-type channel stopper region 7, phosphorus is implanted into the N-well formation region as an active region, and the subthreshold of elements such as MOS transistors to be formed later in the N-well 12 is reduced. There are problems in that voltage controllability is deteriorated and drain breakdown voltage is reduced.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for manufacturing a semiconductor device that prevents impurity injection into a well-forming region and improves the characteristics of an element formed in the well.

[Means to solve the problem]

The manufacturing method of the present invention includes a step of forming a well of one conductivity type in a semiconductor substrate, a step of covering an active region of the semiconductor substrate with a multilayer film including at least an oxidation-resistant film and a photoresist, and a boundary of the active region. forming a channel stopper region of opposite conductivity type by implanting impurities of opposite conductivity type into the region;
After covering this opposite conductivity type channel stopper region with a film such as a photoresist, impurities of one conductivity type are implanted into the boundary of the one conductivity type well to form a one conductivity type channel stopper region. a step of forming a field oxide film by a selective oxidation method using the oxidation-resistant film as a mask; and a step of implanting an impurity of the opposite conductivity type into a region bounded by the channel striker region of the opposite conductivity type. and forming a conductive type well.

[Function] This manufacturing method uses a multilayer film containing at least an oxidation-resistant film and a photoresist when forming a channel region of the opposite conductivity type by implanting impurities of the opposite conductivity type into the boundary of the active region. Since the active region is covered, the impurity of the opposite conductivity type is prevented from being implanted into the active region, and it becomes possible to suitably control the impurity concentration of the well formed in the active region. [Example] Next, the present invention will be described with reference to the drawings.

FIGS. 1(a) to 1(d) are cross-sectional views showing the first embodiment of the present invention in the order of steps. First, as shown in FIG. 1(a), an oxide film 2 is formed on the entire surface of a silicon substrate 1, and boron or the like is ion-implanted using a photoresist 3 as a mask to form a P-well 4. Next, as shown in FIG. 1(b), a nitride film 5 is formed over the entire surface and etched using a photoresist 6, leaving the nitride film 5 in the area where a transistor will be formed later.
Then, using the nitride film 5 and the photoresist 6 as a mask, phosphorus ions are implanted into the entire field region to form an N-type channel stopper region 7.

Furthermore, as shown in FIG. 1C, boron ions are implanted into the P well 4 side of the field region using the photoresist 8 as a mask to form a P type channel stopper 9.

After that, as shown in FIG. 1(d), photoresist 6.8
After removing the nitride film 5, thermal oxidation is performed using the nitride film 5 as a mask to form a field oxide film 10 having a thickness of about 6000λ. Then, the nitride film 5 is removed and the photoresist 11
Using this as a mask, phosphorus ions are implanted to form an N well 12.

According to this manufacturing method, when ion-implanting phosphorus when forming the N-type channel stopper 7, the shape of the N-well 12 is
Ii. Since the two-layer structure film of the nitride film 5 and the photoresist 6 is used as a mask in the 'pM region, it is possible to prevent phosphorus from being implanted into the formation region of the N-well 12. }Improves controllability of subthreshold voltage of elements such as transistors.

FIGS. 2(a) and 2(b) are sectional views showing a part of the process of a second embodiment of the present invention.

First, the P well 4 is formed by the same process as in the first embodiment. Then, as shown in Fig. 2(a), nitriding flow 5 is applied to the entire surface.
and the oxide film 13 are shaped and photo-etched to leave the nitride film 5 and the oxide film 13 in the area where a transistor will be formed later. Thereafter, phosphorus ions are implanted into the entire field region to form N-type channels 1 and brim region 7.

Next, as shown in FIG. 2(b), the photoresist 6 is removed, and using the photoresist 8 as a mask, boron ions are implanted into the P-well 4 side of the field region to form a P-type channel stopper 9. do.

Thereafter, after removing the photoresist 8 and the oxide film 13, the steps after forming the field oxide film are performed in the same manner as in the first embodiment.

Also in this manufacturing method, when forming the N-type channel stopper 7, the formation region of the N-well 12 is covered with the nitride film 5, the oxide film 13, and the photoresist 8, so that phosphorus is not implanted.

Note that the present invention can be similarly applied to cases where the conductivity type of the impurity is opposite to that of each of the above embodiments.

[Effects of the Invention] As explained above, the present invention covers the active region with a multilayer film including an oxidation-resistant film and a photoresist when forming a channel stopper region of the opposite conductivity type. It is possible to prevent impurities from being implanted into the active region, to appropriately control the impurity concentration of the oxide formed in the active region, and to improve the drain breakdown voltage of elements such as MOS transistors formed in the active region. This has the effect of making it possible to manufacture a semiconductor device that prevents a decrease in voltage and improves the controllability of the threshold voltage.

[Brief explanation of drawings]

Figures 1 (a) to (d) are cross-sectional views showing the first embodiment of the present invention in the order of manufacturing steps, and Figures 2 (a) and (b) show a part of the process of the second embodiment of the present invention. 3(a) to 3(d) are cross-sectional views showing a conventional manufacturing method in the order of steps. DESCRIPTION OF SYMBOLS 1... Semiconductor substrate, 2... Oxide film, 3... Photoresist, 4... P well, 5... Nitride film, 6...
- Photoresist, 7... N-type channel stopper region, 8... Photoresist, 9... P-type channel stopper region, 10... Field oxide film, 11... Photoresist, l2...・N well, 13... Oxide film, 14... Photoresist. Figure 1

Claims (1)

[Claims] 1. Forming a well of one conductivity type in a semiconductor substrate;
covering the active region of the semiconductor substrate with a multilayer film including at least an oxidation-resistant film and a photoresist; and forming a channel stopper region of the opposite conductivity type by implanting impurities of the opposite conductivity type into the boundary of the active region. After covering this opposite conductivity type channel stopper region with a film such as photoresist, impurities of one conductivity type are implanted into the boundary of the one conductivity type well to form a one conductivity type channel stopper region. forming a field oxide film by selective oxidation using the oxidation-resistant film as a mask; and implanting impurities of opposite conductivity type into a region bounded by the channel stopper region of reverse conductivity type to form a field oxide film of opposite conductivity type. 1. A method of manufacturing a semiconductor device, comprising the step of forming a mold well.