JPS6292452A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To improve the integration by converting a recess surface formed on a semiconductor substrate to an amorphous state, and forming a thick oxide film on the recess by selectively oxidizing, thereby obtaining an insulator separating region of the prescribed thickness while holding the substrate substantially flat. CONSTITUTION:An N-type epitaxial layer 2 is formed on a P-type silicon substrate 1, a silicon oxide film 3 is formed thereon, a silicon nitride film 4 is formed thereon, and the films 3, 4 of desired regions are removed by etching. Then, a thick oxide film 5 is formed, only this is removed by etching, and an amorphous layer 6 is formed on the exposed layer 2. This amorphous layer is formed by implanting molecular ions such as BF<+>2 ions in high density. Further, a low density P-type impurity layer 7 is formed directly under the layer 6 and the side wall region by an ion implanting method. Thereafter, the layer 2 is oxidized by a selectively oxidizing method to complete an insulator separating region 8 having flat surface and oxidized downward.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a method of manufacturing a semiconductor device, and more particularly to a method of manufacturing a semiconductor device having an insulating isolation region made of a thick oxide film for insulating and isolating elements.

[Conventional technology]

In general, semiconductor integrated circuit bags that use bipolar transistors as elements! In this case, a PN junction is used to insulate and separate each element. However, in this PN junction, it is necessary to diffuse the P-type impurity from the surface of the N-type epitaxial layer to the P-type substrate in order to form the junction, which requires heat treatment at high temperature and for a long time. For this reason, this heat treatment causes diffusion of impurities from the buried layer, which is a high-concentration impurity layer already formed in the substrate, into the epitaxial layer (1), which causes a problem of a decrease in breakdown voltage in semiconductor integrated circuit devices with thin epitaxial layers. . Further, due to the isotropic diffusion of the P-type impurity, the diffusion in the planar direction also progresses, and the exclusive area of the isolation region increases, resulting in a decrease in the degree of integration of the semiconductor integrated circuit device.

For this reason, recent semiconductor integrated circuit devices use a method of selectively and thickly oxidizing the surface of a semiconductor substrate, the so-called LOCO.
There is a tendency for the insulation isolation region to be formed by a thick oxide film formed by the three methods.

[Problem that the invention seeks to solve]

The method for forming a thick oxide film using the conventional LOCO3 method described above is a method in which the surface of the semiconductor substrate is selectively masked and then the exposed surface of the semiconductor substrate is oxidized. As oxidation progresses toward the inside of the semiconductor substrate, for example, an epitaxial layer,
At the same time, oxidation progresses upward as well. Normally, the thickness ratio between the upper part and the lower part is 6:4. As a result, parts of the thick oxide film protrude significantly beyond the surface of the semiconductor substrate, impairing the flatness of the surface of the semiconductor substrate, which is particularly important for various types of highly integrated semiconductor integrated circuit devices that are formed on semiconductor substrates in fine patterns. There is a risk that reliability may be reduced due to disconnection of electrodes or wiring. Further, in the insulation isolation region of this thick oxide film, there is also a problem that the bird's beak generated at the edge of the oxide film increases the area occupied in the plane of the region, impairing its miniaturization.

[Failure to solve the problem]

The manufacturing method of the present invention forms an insulating isolation region made of a thick oxide film without increasing the occupied area while maintaining the flattening of the surface of the semiconductor substrate. This manufacturing method includes the steps of making the four surfaces amorphous and selectively oxidizing them to form a thick oxide film at the four locations. Furthermore, a molecular ion implantation method is used for this amorphization.

〔Example〕

Next, the present invention will be explained with reference to the drawings.

FIG. 1 is a cross-sectional view of a semiconductor device manufactured by the method of the present invention. In this example, an N-type epitaxial layer 2 is formed on a P-type silicon substrate 1, and a P-type impurity layer 9 as a channel stopper is formed here. Then, an insulating isolation region 8 made of a thick insulating film is formed thereon. This insulating film A11
In I region 8, oxidation progresses inward from the surface side of silicon substrate 1, thereby flattening the surface of silicon substrate 1.

FIGS. 2(a) to 2(d) are cross-sectional views for explaining the manufacturing method of the present invention step by step, and in particular only the insulating film HfiJW region is shown.

First, as shown in the figure <a>, an N-type epitaxial layer 2 is formed on a P-type silicon substrate l, for example, as a collector region of an element to be formed, and a silicon oxide film 3 is formed thereon by a thermal oxidation method. . Furthermore, a silicon nitride film 4 is formed thereon by the LPCVD method. Then, the silicon oxide film 3 and silicon nitride film 4 in desired areas are etched away using a known photo-etching technique.

Next, as shown in FIG. 4B, the surface of the epitaxial layer 2 is oxidized using the silicon nitride film 4 as a mask to form a thick oxide film 5.

Then, as shown in FIG. 2C, only this thick oxide film 5 is removed by etching, and an amorphous layer 6 is formed on the exposed surface of the epitaxial layer 2.

For this amorphization, a method is used in which molecular ions, such as BF2', are implanted at a high concentration with an energy range that does not exceed the thickness of the silicon nitride film 4 during ion implantation. Here, the molecular ion implantation method means that when plasma is generated using a gas such as IIFa as the ion source of a normal ion implantation device, l1lB+, l
Single ions such as IB+, 19B+, BF'', B
Molecular ions such as F2'' and BF''+ are generated, and this is a method in which only these molecular ions are selectively implanted. Furthermore, a low concentration P-type impurity layer 7 is formed directly under the amorphous layer 6 and in the sidewall region by ion implantation.

In addition, as shown in FIG. 2(d), by oxidizing the surface of the epitaxial layer 2 by selective oxidation, the oxidation rate of the amorphous layer 6 is higher than that of other parts, so that it is difficult to form the amorphous layer 6 by oxidation. The thick oxide film 8 is oxidized at a high rate both upwardly and downwardly of the epitaxial layer 2. As a result, an insulating film 11111 region 8 is completed which is flat lFt on the upper surface and oxidized downward.

During this selective oxidation, an impurity layer 9 serving as a channel stopper is formed below the insulating isolation region 8 by expanding the low concentration P-type impurity layer 7.

Thereafter, a predetermined element, for example a bipolar transistor, is formed according to normal steps, and a semiconductor device such as a semiconductor integrated circuit is completed.

Therefore, according to this manufacturing method, when forming a thick oxide film as an insulating isolation region, a desired part of the substrate 1 is recessed, and molecular ions are implanted into the four surfaces of the recess to make the core part amorphous. Since the layer 6 is formed, the inward oxidation rate of the substrate 1 can be made much higher than the upward oxidation rate in the subsequent selective oxidation, which prevents unevenness from occurring on the surface of the substrate 1. The thick oxide film 8 can be formed to the required depth without any problems. In addition, this manufacturing method includes an oxide film etching step and an 8-molecular ion implantation step in addition to the step of forming an insulating isolation region using the conventional selective oxidation method.

Since it is only necessary to add another selective oxidation step and no special film formation step is required, the insulation isolation region can be easily formed.

In addition, in this method, the progress of oxidation on the surface side is relatively suppressed during selective oxidation of the insulation isolation region 8, so the progress of so-called bird's beak is also suppressed, and the planar area occupied by the insulation isolation region is reduced. It is also effective in achieving miniaturization and improving the degree of integration of semiconductor devices.

〔Effect of the invention〕

As explained above, the manufacturing method of the present invention involves forming a recess on the surface of a semiconductor substrate, making the four surfaces amorphous, and performing oxidation to form a thick oxide film in the recess. Since the oxidation rate of this thick oxide film can be increased inwardly than above the semiconductor substrate,
Thereby, an insulating isolation region having a desired thickness can be manufactured while keeping the surface of the semiconductor substrate substantially flat. Furthermore, it is possible to reduce the planar area occupied by the insulating isolation region to achieve miniaturization, thereby improving the degree of integration of the semiconductor device.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a part of a semiconductor device manufactured by the method of the present invention, and FIGS. 2(a) to 2(d) are cross-sectional views for explaining the method of the present invention in the order of steps. 1... Silicon substrate, 2... Epitaxial layer, 3
... silicon oxide film, 4... silicon nitride film, 5.
... Thick oxide film, 6... Amorphous layer, 7... Low concentration P-type impurity layer, 8... Thick oxide film (insulating isolation region),
9...Channel stopper. Figure 2 (a) Figure 2 (b)' 51, ・Tanushikuma

Claims (1)

[Claims] 1. A method for manufacturing a semiconductor device in which a thick insulating film is formed on a semiconductor substrate by a selective oxidation method, and this is configured as an insulating isolation region between elements, in which the insulating isolation region is formed. A process of recessing the surface of the semiconductor substrate at the desired location to the required depth, a process of amorphizing the recessed surface to form an amorphous layer, and performing selective oxidation to recess the recessed area. 1. A method of manufacturing a semiconductor device, comprising: forming a thick oxide film. 2. A method of manufacturing a semiconductor device according to claim 1, wherein a molecular ion implantation method is used to form the amorphous layer.