Method of manufacturing semiconductor integrated circuit device

Abstract

A method of manufacturing a semiconductor integrated circuit device according to this invention, comprises a step of forming in a semiconductor substrate a deep groove for trench isolation with an aspect ratio of greater than 1, a step of burying a first insulating film in the deep groove in such a way that a shallow groove with an aspect ratio of not greater than 1 remains, and a step of depositing a second insulating film over the semiconductor substrate and then removing the upper portion of the second insulating film to planarize the upper surface of the second insulating film buried in the shallow groove in such a way that the upper surface of the second insulating film is almost flush with the surface surrounding the shallow groove.

Description

BACKGROUND OF THE INVENTION

The present invention relates to a method of manufacturing a semiconductor integrated circuit device and more specifically to a semiconductor integrated circuit device manufacturing method having a process of forming a trench isolation.

The trench isolation is an element isolating part in a semiconductor substrate, which electrically isolates adjoining semiconductor integrated circuit elements by filling a groove formed between adjacent semiconductor integrated circuit elements with a specified burying material.

An example method of forming trench isolation examined by the inventor of this invention will be described below. After a groove is formed in a semiconductor substrate, an insulating film is formed on the inner surface of the groove. Then, a polycrystalline silicon film is deposited on the semiconductor substrate, after which the polysilicon film is etched back to fill only the groove with the polysilicon. After this, the semiconductor substrate is oxidized to oxidize the upper part of the polysilicon film in the groove, thus transforming the upper part into an insulating film.

An example method of burying an insulating film in the groove is disclosed in Japanese Patent Laid-Open No.143548/1983. The outline of this method is as follows. First, a side wall of an insulating film is formed on the inner wall surface of the groove to form a tapered surface on the inner wall surface of the groove, after which a burying insulating film is deposited over the semiconductor substrate. Next, the burying insulating film is etched back to bury the insulating film only in the groove.

SUMMARY OF THE INVENTION

The inventor of this invention, however, has found that the conventional art involves the following problems.

In the conventional art, by which a groove is filled with a polysilicon film and the upper part of the film is oxidized to ensure the insulating properties of the upper part of the polysilicon film in the groove, because there is a difference in the oxidation rate of the polysilicon film in the groove between the periphery of the groove and the center, the thickness of the insulating film formed at the top of the polysilicon film is thinner at the groove periphery than at the central portion. As a result a recess in formed in the groove periphery, and in the subsequent process of forming conductor patterns, conductor film residue tends to remain in a recessed central part of the groove, leading to a short circuit between patterned conductors.

A conventional technique to solve this problem is proposed in Japanese Patent Laid-Open No. 149849/1991, which discloses a method of forming an insulating film to ensure the flatness of the top part of the polysilicon film before and after oxidizing the top part of the polysilicon film in the groove. This method, however, requires an additional process for forming an insulating film for ensuring the flatness.

The conventional technique of burying an insulating film in the groove is effective for the grooves with an aspect ratio of less than 1. As the aspect ratio becomes larger than 1, a problem arises that a cavity may form in the groove. This cavity is formed because the insulating film in the groove is coarse, the coverage of the groove is bad, and the film is not completely buried in the groove. This cavity appears on the top part of the groove causing a conductor film to remain during the subsequent process for forming a conductor pattern, with the result that the residual conductor film may short-circuit the patterned conductors.

An object of this invention is to provide a technique which allows a deep groove for a trench isolation to be filled completely without forming a dent or recess at the top of the filled groove.

Another object of this invention is to provide a technique which allows a deep groove for a trench isolation to be filled completely without forming a dent or recess at the top of the filled groove and without incurring a significant increase in the number of manufacturing steps.

A further object of this invention is to provide a technique which allows a deep groove for a trench isolation to be filled completely without exposing cavities from the top surface.

A further object of this invention is to provide a method of manufacturing a semiconductor integrated circuit device and more specifically to provide a technique which allows a deep groove for a trench isolation to be filled preferably without exposing cavities from the top surface and incurring a significant increase in the number of manufacturing steps.

These and other objects and novel features of this invention will become apparent from the following description in this specification and the accompanying drawings.

Representatives of the invention disclosed in this specification will be briefly summarized below.

A method of manufacturing a semiconductor integrated circuit device according to this invention comprises a step of forming in a semiconductor substrate a deep groove for a trench isolation with an aspect ratio larger than 1, a step of burying a first insulating film in the deep groove so that a shallow groove with an aspect ratio of not greater than 1 remains in the deep groove, and a step of depositing a second insulating film over the semiconductor substrate and removing an upper part of the second insulating film to planarize the upper part of the a second insulating film buried in the shallow groove.

Further, a method of manufacturing a semiconductor integrated circuit device according to this invention forms a recess at the central part of the top surface of the first insulating film buried in the deep groove.

Further, a method of manufacturing a semiconductor integrated circuit device according to this invention comprises a step of forming in a semiconductor substrate a deep groove for a trench isolation with an aspect ratio larger than 1, a step of forming an insulating film on an inner wall surface of the deep groove and burying a semiconductor in the deep groove so that a shallow groove with an aspect ratio of not greater than 1 remains in the deep groove, and a step of depositing a second insulating film over the semiconductor substrate and removing the upper part of the second insulating film to planarize the upper part of the second insulating film buried in the shallow groove.

Further, the method of manufacturing a semiconductor integrated circuit device according to this invention forms a tapered portion in the opening portion of the deep groove.

According to the above-mentioned method of manufacturing a semiconductor integrated circuit device of this invention, the step of filling a deep groove for a trench isolation with a high aspect ratio is divided into two steps. In the first filling step, the deep groove is turned into a shallow groove by filling the deep groove to a specified extent to lower the aspect ratio. In the second filling step, the shallow groove is filled and the upper part of the filling material in the shallow groove is planarized. These steps makes it possible to fill a deep groove preferably without causing cavities to appear on the upper part of the deep groove, without forming a recess in the outer periphery of the upper part of the deep groove, and without incurring a significant increase in the number of manufacturing steps.

Further, according to the above-mentioned method of manufacturing a semiconductor integrated circuit device of this invention, by forming a recess in the central portion of the upper surface of the first insulating film buried in the deep groove, a certain thickness of the second insulating film buried in the shallow groove can be ensured at the central upper part of the first insulating film, so that even if a cavity is formed in the center of the first insulating film, it is possible to prevent a large recess or a groove communicating with the cavity in the center of the first insulating film from being formed at the center of the second insulating film.

Further, according to the above-mentioned method of manufacturing a semiconductor integrated circuit device of this invention, a tapered portion is formed in the opening part of the deep groove. This makes it possible to bury a second insulating film in the shallow groove without forming any cavities.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an overall plan view of a semiconductor chip that makes up a semiconductor integrated circuit device of a first embodiment of this invention;

FIG. 2 is a plan view of an essential portion of the semiconductor chip of FIG. 1 ;

FIG. 3 is a circuit of a memory cell making up the semiconductor integrated circuit device of Figure FIG. 4 is a cross section of an essential portion of the semiconductor integrated circuit device of FIG. 1 ;

FIG. 5 is a cross section of an essential portion of the semiconductor substrate in a step of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 6 is a cross section of an essential portion of the semiconductor substrate in a step, following the step FIG. 5 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 7 is a cross section of an essential portion of the semiconductor substrate in the step, following the step of FIG. 6 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 8 is a cross section an essential portion of the semiconductor substrate in a step, following the step of FIG. 7 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 9 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 8 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 10 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 9 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 11 is a graph showing the ratio of the rate of depositing an insulating film in a groove having a tapered portion to that on a planar portion.

FIG. 12 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 10 , of making the semiconductor integrated circuit device as a first embodiment of this invention;

FIG. 13 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 12 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 14 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 13 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 15 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 14 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 16 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 15 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 17 is a perspective view of an essential portion of the semiconductor substrate in a step of FIG. 16 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 18 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 16 , of making the semiconductor integrated circuit device of the first embodiment of this invention;

FIG. 19 is a cross section of an essential portion of the semiconductor substrate in a step of making the semiconductor integrated circuit device of a second embodiment of this invention;

FIG. 20 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 19 , of making the semiconductor integrated circuit device of the second embodiment of this invention;

FIG. 21 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 20 , of making the semiconductor integrated circuit device of the second embodiment of this invention;

FIG. 22 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 21 , of making the semiconductor integrated circuit device of the second embodiment of this invention;

FIG. 23 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 22 , of making the semiconductor integrated circuit device of the second embodiment of this invention;

FIG. 24 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 23 , of making the semiconductor integrated circuit device of the second embodiment of this invention;

FIG. 25 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 24 , of making the semiconductor integrated circuit device of the second embodiment of this invention;

FIG. 26 is a cross section of an essential portion of the semiconductor substrate in a step, following the step FIG. 25 , of making the semiconductor integrated circuit device of the second embodiment of this invention;

FIG. 27 is a cross section of an essential portion of the semiconductor substrate in a step, following the step of FIG. 26 , of making the semiconductor integrated circuit device of the second embodiment of this invention; and

FIG. 28 is an enlarged view of a part of the semiconductor integrated circuit device of FIG. 9 .

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described in detail referring to the accompanying drawings.

Embodiment 1

FIG. 1 is an overall plan view showing a semiconductor chip making up a semiconductor integrated circuit device of a first embodiment of this invention. FIG. 2 is a plan view of an essential portion of the semiconductor chip of FIG. 1 . FIG. 3 is a circuit of a memory cell forming the semiconductor integrated circuit device of FIG. 1 . FIG. 4 is a cross section of an essential portion of the semiconductor integrated circuit device of FIG. 1 . FIGS. 5 to 10 are cross sections of an essential portion of the semiconductor substrate in the steps of making the semiconductor integrated circuit device of the first embodiment of this invention. FIG. 11 is a graph showing the ratio of the rate of depositing an insulating film in a groove having tapered portion to that on a planar portion. FIGS. 12 to 16 are cross sections of an essential portion of the semiconductor substrate in the manufacturing steps, following the step of FIG. 10 . FIG. 17 is a perspective view of an essential portion of the semiconductor substrate in the manufacturing step of FIG. 16 . FIG. 18 is a cross section of an essential portion of the semiconductor substrate in a manufacturing step following the step of FIG. 16 .

The semiconductor integrated circuit device of the embodiment 1 is a composite gate array comprising a logic circuit region and a memory circuit region, both formed on a single semiconductor chip. A plan view of the semiconductor chip of the embodiment 1 is shown in FIG. 1 .

On the periphery of a semiconductor chip 7 is arranged an input/output circuit region 2 , in which is formed input/output circuit including, e.g., an input buffer circuit and an output buffer circuit.

This input/output circuit is the one for transforming input signals from external devices into signals that can be used by internal circuits formed in the semiconductor chip 1 and for amplifying signals from the internal circuits so that they can be transmitted to external devices through long transmission lines. The input/output circuit is electrically connected to external devices through a plurality of CCB (Controlled Collapse Bump) electrodes 2 a arranged in the input/output circuit region 2 .

At the center of the semiconductor chip 1 is arranged a logic circuit region 3 , in which is arranged an input/output circuit region 3 a that extends laterally of FIG. 1 , dividing the logic circuit region 3 into the upper and lower parts. Further in this logic circuit region 3 , input/output circuit regions 3 b extending vertically in FIG. 1 are arranged at specified intervals. These input/output circuit regions 3 a , 3 b divide the logic circuit region 3 into 10 sections.

In the logic circuit region 3 divided by the input/output circuit regions 3 a , 3 b , there are provided a plurality of logic circuit blocks 3 c , in each of which are arranged, for example, an ECL (Emitter Coupled Logic) circuit drivable at high speed and a CMOS (Complementary MOS) circuit drivable with low power consumption.

In FIG. 1 , memory circuit regions 4 are arranged above and below the logic circuit region 3 . In each of the memory circuit regions 4 , there is provided a periphery circuit region and input/output circuit region 4 a that extend laterally in FIG. 1 , dividing the memory circuit regions 4 into upper and lower parts. Each of the memory circuit regions 4 also has periphery circuit regions and input/output circuit regions 4 b arranged at specified intervals. These input/output circuit regions 4 a , 4 b divide each memory circuit region 4 into, for instance, eight memory mats 4 c.

Though not shown, CCB electrodes 2 a are also formed in the input/output circuit regions 3 a , 3 b , 4 a , 4 b , and the input/output circuits formed on the inner side of the semiconductor chip 1 are connected to external devices through the CCB electrodes 2 a.

Further, CCB electrodes 2 a are also arranged on the logic circuit blocks 3 c and the memory mats 4 c and used for power supply and as dummy electrodes. That is, the CCB electrodes 2 a are arranged in array on the semiconductor chip 1 .

Each of the memory mats 4 c includes a plurality of memory cells (not shown in FIG. 1 ). The plan view and circuit diagram of this memory cell are shown in FIG. 2 and 3 , respectively.

A memory cell 4 d is an SRAM (Static RAM) cell formed basically of a flip-flop circuit and comprises, for example, two p-channel MOSFETs (simply referred to as pMOSs) 4 dp and four n-channel MOSFETs (simply referred to as nMOSs) 4 dna , 4 dnb.

The PMOS 4 dp is a MOSFET forming a flip-flop circuit and has a pair of semiconductor regions 4 dp L, 4 dp L making up source and drain regions and a gate electrode 4 dg 1 arranged over the area between these semiconductor regions 4 dp L, 4 dp L.

The paired semiconductor regions 4 dp L of the pMOS 4 dp are doped, for example, with boron of p-type impurity. One of the semiconductor regions 4 dp L of the pMOS 4 dp is electrically connected to a power supply potential Vcc through a power supply line.

The nMOS 4 dna is a MOSFET forming a flip-flop circuit and has a pair of semiconductor regions 4 dna L, 4 dna L making up source and drain regions and a gate electrode 4 dg 1 arranged over the area between these semiconductor regions 4 dna L, 4 dna L. The gate electrode 4 dg 1 is commonly used with the above-mentioned gate electrode for the pMOS 4 dp.

The paired semiconductor regions 4 dna L of the nMOS 4 dna are doped, for example, with phosphorus or arsenic of n-type impurity. One of the semiconductor regions 4 dna L of the nMOS 4 dna is electrically connected to a ground potential Vss through a power supply line.

In an element isolation region between the pMOS 4 dp and the nMOS 4 dna is arranged a trench isolation 5 described later. In embodiment 1, by using the trench isolation 5 for the element isolation, it is possible to reduce the interval between the pMOS and nMOS, which is conventionally some 2.5 μm to ensure the latchup resistance, down to about 1.2 μm.

The nMOS 4 dnb is a MOSFET for switching and has a pair of semiconductor regions 4 dnb L, 4 dnb L making up source and drain regions and a gate electrode 4 dg 2 arranged over the area between these semiconductor regions 4 dnb L, 4 dnb L. This gate electrode 4 dg 2 is a part of a word line 4 W and is commonly used for two nMOSs 4 dna , 4 dnb.

The paired semiconductor regions 4 dnb L of the nMOS 4 dnb are doped, for example, with phosphorus or arsenic of n-type impurity. One of the semiconductor regions 4 dnb L of the nMOS 4 dnb is electrically connected to a bit line 4 B. The other semiconductor region 4 dnb L of the nMOS 4 dnb is electrically connected to the semiconductor regions 4 dp L, 4 dna L of the pMOS 4 dp and the nMOS 4 dna.

A cross section of an essential portion of the semiconductor integrated circuit device of embodiment 1 is shown in FIG. 4. A semiconductor substrate la forming the semiconductor chip 1 has, for example, an SOI (silicon-on-insulator)structure consisting, for example, of a support substrate 1 a 1 , an insulating layer 1 a 2 formed on the support substrate 1 a 1 , and a semiconductor layer 1 a 3 formed on the insulating layer 1 a 2 .

The support substrate 1 a 1 is formed, for instance, of monocrystalline silicon. The insulating layer 1 a 2 is made of, say, silicon dioxide (SiO 2 ) and has a thickness of, e.g. about 0.5 μm to 1 μm thick. The semiconductor layer 1 a 3 is made of an n-type monocrystalline silicon and its upper portion is an epitaxial layer. The thickness of the semiconductor layer 1 a 3 is, for instance, about 2 μm and the thickness of the epitaxial layer is, for example, about 1 μm.

In the semiconductor layer 1 a 3 , in the pMOS forming region P the pMOS 4 dp is formed. In the semiconductor layer 1 a 3 in the pMOS forming region P, a buried region 6 a , a channel stopper region 7 a and an element region 8 a , in the order from the bottom.

In to the buried region 6 a , for example, antimony of n-type impurity is introduced. The channel stopper region 7 a and the element region 8 a are doped, for instance, with phosphorus or arsenic of n-type impurity.

The paired semiconductor regions 4 dp L of the pMOS 4 dp are formed in the device region Ba. The gate electrode 4 dg 1 is formed over the area between the paired semiconductor regions 4 dp L through a gate insulating film 4 dox . The paired semiconductor regions 4 dp L are electrically connected to electrodes 11 a through connecting holes 10 a made in an insulating film 9 a . The gate insulating film 4 dox and the insulating film 9 a are formed, for example, of silicon dioxide. The electrodes 11 a are made from an alloy based on aluminum, such as Al—Si—Cu alloy (Al:98.5−97.5 wt %, Si: 1-2 wt %, Cu: 0.5 wt %).

In an nMOS forming region N of the semiconductor layer 1 a 3 , the nMOS 4 dna is formed. In the semiconductor layer 1 a 3 of the nMOS forming region N, a channel stopper region 7 b and a device region 8 b in order from the bottom. The channel stopper region 7 b and the device region 9 b are doped with boron of p-type impurity, for example.

The paired semiconductor regions 4 dna L of the NMOS 4 dna are formed in the device region 8 b . The gate electrode 4 dg 1 is formed over the area between the paired semiconductor regions 4 dna L through the gate insulating film 4 dox . The paired semiconductor regions 4 dna L are electrically connected to electrodes 11 b through connecting holes 10 b made in the insulating film 9 a . The electrodes 11 b are made, for example, of an Al—Si—Cu alloy.

In the semiconductor layer 1 a 3 , in a bipolar transistor forming region Bi an npn-type bipolar transistor 12 that, for instance, makes up the above-mentioned ECL circuit is provided.

In the semiconductor layer 1 a 3 in the bipolar transistor forming region Bi, a collector buried region 12 c 1 , a collector region 12 c 2 and a collector leadout region 12 c 3 are formed.

The collector buried region 12 c 1 is doped with antimony of n-type impurity, for example. The collector region 12 c 2 and the collector leadout region 12 c 3 are doped with phosphorus or arsenic of n-type impurity. The collector leadout region 12 c 3 is electrically connected to collector electrodes 11 c through connecting holes 10 c in the insulating film 9 a . The collector electrodes 11 c are made, for example, of an Al—Si—Cu alloy.

On the collector region 12 c 2 is formed a base region 12 b , which consists of an intrinsic base region 12 b 1 at the center of the collector region and a base leadout region 12 b 2 at the periphery. The base region 12 b is doped with boron of p-type impurity.

The base leadout region 12 b 2 is electrically connected to a base leadout electrode 13 b , which is made of a p-type polycrystalline silicon and electrically connected to a base electrode lid through a connecting hole 7 d made in the insulating films 9 a , 9 b . The base electrode lid is made of an Al—Si—Cu alloy, for instance.

On the intrinsic base region 12 b 1 is formed an emitter region 12 e , which is doped with phosphorus or arsenic of an n-type impurity. The emitter region 12 e is electrically connected to an emitter readout electrode lie through a connecting hole 10 e formed in the insulating film 9 b.

The emitter leadout electrode 13 e is formed of an n-type polycrystalline silicon, for example, and is electrically connected to an emitter electrode 11 e through a connecting hole 10 f formed in the insulating film 9 a . The emitter electrode lie is made, for instance, of an Al—Si—Cu alloy. The insulating film 9 a is formed of a BPSG (Boron Doped Phospho-Silicate Glass). The insulating film 91 is formed of SiO 2 .

A field insulating film 14 and a trench isolation 5 are formed between the pMOS 4 dp and the nMOS 4 dna and between the nMOS 4 dna and the bipolar transistor 12 .

The field insulating film 14 is made of SiO 2 , for instance. The trench isolation 5 is formed by burying, from the bottom, a buried insulating film (first insulating film) 5 b 1 and a buried insulating film (second insulating film) 5 b 2 , both formed of SiO 2 , in a deep groove 5 a formed at a position of the field insulating film 14 .

The upper surface of the upper buried insulating film 5 b 2 in the deep groove 5 a is almost flush with the upper surface of the field insulating film surrounding the groove 14 . The deep groove 5 a has an aspect ratio larger than 1 and is deep enough to reach the insulating layer 1 a 2 of the semiconductor substrate 1 a.

Next, referring to FIGS. 5 to 18 , the method of manufacturing the semiconductor integrated circuit device of embodiment 1 will be described. In embodiment 1, a BiCMOS (Bipolar Complementary MOS) process is taken as an example.

FIG. 5 is a cross section of an essential portion of the semiconductor substrate 1 a in a step of making the semiconductor integrated circuit device of embodiment 1. The semiconductor substrate 1 a of embodiment 1 has an SOI (silicon-on-insulator) structure comprising a support substrate 1 a 1 , an insulating layer 1 a 2 formed on the support substrate 1 a 1 , and a semiconductor layer 1 a 3 formed on the insulating layer 1 a 2 .

The support substrate 1 a 1 is made of for instance, a monocrystalline silicon. The insulating layer 1 a 2 is formed of silicon dioxide and for example, is 0.5-1 μm thick.

The semiconductor layer 1 a 3 is formed of an n-type monocrystalline silicon and its upper portion (above the dashed line) is an epitaxial layer. The semiconductor layer 1 a 3 is about 2 μm thick and the epitaxial layer about 1 μm thick.

In the semiconductor layer 1 a 3 , in the pMOS forming region P and the bipolar transistor forming region Bi, a buried region 6 a and a collector buried region 12 c 1 are formed, respectively.

The buried region 6 a and the collector buried region 12 c 1 are doped, for instance, with antimony (Sb) of n-type impurity, whose concentration is about 1×10 19 cm −3 . The buried region 6 a and the collector buried region 12 c 1 are formed simultaneously by thermal diffusion, for example.

Over the epitaxial layer in the element isolation region or in the intra-element isolation region, the field insulating film 14 is formed by a LOCOS method. The field insulating film 14 is made of SiO 2 , for example, and its thickness is about 4,000 Å. In the element forming region is formed an insulating film 15 a which is made, for instance, of SiO 2 .

Over the field insulating film 14 and the insulating film 15 a are deposited an insulating film 15 b of, say, silicon nitride (Si 3 N 4 ) by a CVD (Chemical Vapor Deposition) method. The insulating-film 15 b is a film that functions as an etching stopper as described later and its thickness is about 1,000 Å.

Over the insulating film 15 b is deposited an insulating film 15 c of PSG (Phospho Silicate Glass) by a CVD method. The thickness of the insulating film 15 c is about 2,000 Å.

Over the insulating film 15 c is so formed a photoresist pattern 16 a that a part of the top portion of the element isolation field insulating film 14 is exposed. The photoresist pattern 16 a is formed by an ordinary photolithography. That is, the photoresist pattern 16 a is formed by applying a photoresist film and then exposing and developing the photoresist film.

By performing an anisotropic etch, such as reactive ion etching using a reactive fluorine-based gas, of the semiconductor substrate 1 a with the photoresist pattern 16 a as an etching mask, the insulating films 15 b , 15 c and the field insulating film 14 , exposed from the photoresist pattern 16 a , are etched away. The cross section of an essential portion of the semiconductor substrate 1 a after being etched is shown in FIG. 6 .

Next, the photoresist pattern 16 a is ashed away, after which the semiconductor substrate 1 a is subjected to an anisotropic etching such as a reactive ion etching using a reactive chlorine-based gas with the insulating films 15 b , 15 c as an etching mask.

Because the etch rate of the semiconductor layer 1 a 3 is about 30 times as high that of the insulating film 15 c , the portion of the semiconductor layer 1 a 3 that is exposed from the insulating films 15 b , 15 c are etched away. Then, as shown in FIG. 7 , in the semiconductor layer 1 a 3 are formed the deep grooves 5 a that reach the insulating layer 1 b 2 . The deep groove 5 a has a depth of about 3 μm and a width of about 0.5 μm.

Then, as shown in FIG. 8 , a buried insulating film (first insulating film) 5 b 1 of non-doped SiO 2 is deposited over the semiconductor substrate 1 a by a CVD to fill the deep groove 5 a with the buried insulating film 5 b 1 . The thickness of the buried insulating film 5 b 1 is about 5,000 Å.

Because the coverage of the buried insulating film 5 b 1 is low at about 0.8, the central part of the deep groove 5 a is not completely filled, leaving a cavity 5 c . The cavity 5 c extends from near the bottom of the deep groove 5 a to around the upper surface of the field insulating film 14 .

Next, the semiconductor substrate 1 a is subjected to a reactive ion etching to etch away the buried insulating film 5 b 1 and the underlying insulating film 15 c deposited over the semiconductor substrate 1 a.

In this step, the insulating film 15 b under the insulating film 15 c functions as an etching stopper, which stops the etching of the semiconductor substrate 1 a at the surface of the insulating film 15 b.

In the region where the deep groove 5 a is formed, however, because the insulating film 15 b is partly removed, the etching progresses into the deep groove 5 a . Thus, the upper part of the buried insulating film 5 b 1 in the deep groove 5 a is etched away. Hence, as shown in FIG. 9 , a shallow groove 5 a 1 with a depth d of about 1,500 Å is formed in the deep groove 5 a.

The bottom portion of the shallow groove 5 a 1 is located within the thickness of the field insulating film 14 . As shown in FIG. 28 , a recess 5 d is formed in an upper central portion of the buried insulating film 5 b 1 in the deep groove 5 a . The recess formed at the upper central portion of the buried insulating film 5 b 1 in the deep groove 5 a is intended to maintain at the central portion of the shallow groove 5 a 1 a certain thickness of the buried insulating film described later, which fills the shallow groove 5 a 1 .

In the cases where a cavity 5 c is formed in the central part of the buried insulating film 5 b 1 , if the insulating film buried in the shallow groove 5 a 1 is not made sufficiently thick at the center of the shallow groove, a large recess may be formed at the center of the insulating film buried in the shallow groove 5 a 1 or a groove may be formed there which communicates with the cavity 5 c , making it impossible to completely fill the deep groove 5 a.

The inner wall surface of the shallow groove 5 a 1 is tapered by the buried insulating film 5 b 1 , without any special technique during the etching process. The tapered portion. of the inner wall surface of the shallow groove 5 a 1 has an angle θ of about 70 degrees (see FIG. 28 ).

Then, as shown in FIG. 10 , a buried insulating film (second insulating film) 5 b 2 of non-doped SiO 2 is deposited by CVD over the semiconductor substrate 1 a to fill the shallow groove 5 a 1 with the buried insulating film 5 b 2 . The thickness of the buried insulating film 5 b 2 is about 1,000 Å.

In this case, the buried insulating film 5 b 2 , like the above-mentioned buried insulating film 5 b 1 , has a low coverage but can be filled in the shallow groove 5 a 1 without forming a cavity for the following reasons.

First, because the shallow groove 5 a 1 has a low aspect ratio, and the buried insulating film 5 b 2 can be deposited from the bottom of the groove upward.

Second, because the tapered portion is provided to the inner wall surface of the shallow groove 5 a 1 , and hence the buried insulating film 5 b 2 can be deposited properly also in the central portion of the shallow groove 5 a 1 . When the angle θ of the tapered portion on the inner wall surface of the shallow groove 5 a 1 is set at around 70 degrees, the deposit condition is significantly improved.

FIG. 11 shows the dependency on the groove geometry of the ratio of an insulating film deposition rate at the bottom central portion of the shallow groove 5 a 1 to that of the peripheral portion. The closer the angle of the inner wall surface of the groove is to a vertical, the faster the insulating film deposition rate at the bottom central portion of the groove becomes and the coarser the film becomes. Particularly when the angle θ is greater than 85 degrees, the rate of insulating film deposition rate becomes infinite, virtually indicating the presence of a cavity in the groove.

In embodiment 1, the angle θ of the tapered portion of the inner wall surface of the shallow groove 5 a 1 is set to about 70 degrees. This allows the buried insulating film 5 b 2 to completely fill the shallow groove 5 a 1 without forming a cavity in the shallow groove 5 a 1 .

The buried insulating film 5 b 2 is then etched back by, for example, a reactive ion etching. At this time, the underlying insulating film 15 b acts as an etching stopper. As shown in FIG. 12 , the etching of the-semiconductor substrate 1 a can be stopped at the upper surface of the insulating film 15 b .

Further, in embodiment 1, by monitoring the intensity of light emitted by reaction products formed in the etching atmosphere, it is possible to stop the etching when the buried insulating film 5 b 2 on the insulating film 15 b is completely removed.

This makes it possible to prevent overetching in the shallow groove 5 a 1 . As a result, the upper surface of the buried insulating film 5 b 2 in the shallow groove 5 a 1 can be almost flush with the upper surface of the field insulating film 14 surrounding the shallow groove 5 a 1 .

After the deep groove 5 a is filled with the buried insulating films 5 b 1 , 5 b 2 to form the trench isolation 5 in the above steps, the insulating film 15 b which functions as an etching stopper is removed. The cross section of an essential portion of the semiconductor substrate 1 a after being subjected to this processing is shown in FIG. 13 .

In embodiment 1, as shown in FIG. 13 , the deep groove 5 a can be filled with the buried insulating films 5 b 1 , 5 b 2 without exposing a cavity from the top of the deep groove 5 a and without forming a recess in the top. The upper surface of the buried insulating film 5 b 2 can be made flat and almost flush with the upper surface of the surrounding field insulating film 14 .

In embodiment 1. therefore, because the conductive films deposited in the subsequent steps do not remain an the surface of the trench isolation 5 , short-circuit between adjacent conductor patterns caused by the residual conductive film remaining an the trench isolation 5 can be prevented.

Next, the step of fabricating the pMOS 4 dp , nMOS 4 dna and bipolar transistor 12 in the element forming region enclosed by the trench isolation 5 will be described referring to FIGS. 14 to 18 .

FIG. 14 shows a cross section of an essential portion of the semiconductor substrate 1 a after the trench isolation 5 is formed. In the semiconductor layer 1 a 3 of the pMOS forming region P, a channel stopper region 7 a is formed over the buried region 6 a.

The channel stopper region 7 a is doped with phosphorus or arsenic of n-type impurity by ion implantation. The implanting energy is about 150 KeV and the surface impurity concentration is about 5×10 12 cm −2 .

Over the channel stopper region 7 a is formed an n-type element region 8 a , whose impurity concentration is so set that a specified threshold voltage can be obtained.

In the semiconductor layer 1 a 3 of the NMOS forming region N is formed a channel stopper region 7 b , which is doped with boron of p-type impurity by ion implantation. The implanting energy is about 40 KeV and the surface impurity concentration is about 1×10 2 cm −2 .

Over the channel stopper region 7 b is formed a p-type element region 8 b , whose impurity concentration is so set that a specified threshold voltage can be obtained.

In the semiconductor layer 1 a 3 of the bipolar transistor forming region Bi, a collector leadout region 12 c 3 is formed over the collector buried region 12 c 1 .

The collector leadout region 12 c 3 is formed by ion implantation, and the ion implanting energy is about 80 KeV. The surface impurity concentration of the region is about 1×10 6 cm −2 .

The upper surface of the semiconductor substrate 1 a is subjected to thermal oxidation to form a gate insulating film 4 dox and an insulating film 15 d , both formed of SiO 2 , over the semiconductor layer 1 a 3 enclosed by the field insulating film 14 . Then, as shown in FIG. 15 , over the semiconductor substrate 1 a is deposited by CVD a semiconductor film 17 a of polycrystalline silicon, whose thickness is about 2,000 Å.

Thereafter a photoresist pattern 16 b is formed over the semiconductor film 17 a by photolithography. Then, with the photoresist pattern 16 b as a mask the semiconductor film 17 a is patterned to form a gate electrode 4 dg 1 , as shown in FIG. 16 .

Then, the photoresist pattern 16 b is ashed away. A perspective view of an essential portion of the semiconductor substrate 1 a after the gate electrode 4 dg 1 is formed is shown in FIG. 17 . In embodiment 1, because the upper surface of the deep groove 5 a is planar, the semiconductor film 17 a for forming the gate electrode does not remain over the deep groove 5 a . It is therefore possible to prevent short-circuit between adjacent gate electrodes 4 dg 1 which would be caused by residual matters of the semiconductor film 17 a.

Next, according to the normal MOSFET forming process, the semiconductor regions 4 dp L, 4 dna L for source and drain are formed in a self-alignment manner on both sides of each gate electrode 4 dg 1 of the MOSFET to form the pMOS 4 dp and nMOS 4 dna , as shown in FIG. 18 .

Then, according to the bipolar transistor forming process, a base region 12 b , a base leadout electrode 13 b , an emitter region 12 e , an insulating film 9 b and an emitter leadout electrode 13 e are formed to fabricate the bipolar transistor 12 .

The base region 12 b comprises an intrinsic base region 12 b 1 and a base leadout region 12 b 2 , both doped with, e.g. boron of p-type impurity. The base leadout electrode 13 b is made of, for instance, a p-type polycrystalline silicon. The emitter leadout electrode 13 e is formed of an n-type polycrystalline silicon. The insulating film 9 b is made of SiO 2 , for instance, to electrically isolate the emitter leadout electrode 13 e and the base leadout electrode 13 b from each other.

Then, as shown in FIG. 4 , the insulating film 9 a of, say, BPSG is deposited on the semiconductor substrate 1 a , which is then subjected to a heat treatment at, say, around 900° C. to planarize the upper surface of the insulating film 9 a . The thickness of the insulating film 9 a is about 1 μm.

Next, in the insulating film 9 a , connecting holes 10 a - 10 f that reach the semiconductor regions 4 dp L, 4 dna L, the collector leadout region 12 c 3 , the emitter leadout electrode 13 e and the base leadout electrode 13 b are made. After this, a metal film of, say, an Al—Si—Cu alloy is deposited over the insulating film 9 a by sputtering.

This is followed by the patterning of the metal film by, e.g. dry etching to form the electrodes 11 a , 11 b , emitter electrode 11 e , collector electrode 1 c and base electrode 11 d simultaneously.

Then, the pMOS 4 dp and the nMOS 4 dna are electrically connected through interconnecters to form the memory cell. The bipolar transistor 12 is used to form a peripheral circuit and an ECL circuit of the memory circuit region. In such a way, the semiconductor integrated circuit device is fabricated.

Embodiment 1 has the following advantages. (1) When the deep groove 5 a for a trench isolation having a high aspect ratio is filled, the filling step is divided into two steps. In the first step the deep groove 5 a is filled to a specified extent to lower the aspect ratio of the deep groove 5 a and thereby transform the deep groove 5 a into a shallow groove 5 a 1 . In the second step the shallow groove 5 a 1 is filled and the top portion of the buried material in the shallow groove 5 a 1 is planarized. Consequently, it is possible to satisfactorily fill the deep groove 5 a of a high aspect ratio without exposing a cavity from the top of the deep groove 5 a , without forming a recess at the top periphery of the deep groove 5 a , and without incurring a significant increase in the number of manufacturing steps.

(2) By forming a recess in the top central portion of the buried insulating film 5 b 1 in the deep groove 5 a , it is possible to ensure a sufficient thickness of the buried insulating film 5 b 2 filled between the central portion of the top surface of the buried insulating film 5 b 1 and the top surface of the shallow groove 5 a 1 . Hence, if a cavity is formed in the center of the buried insulating film 5 b 1 , it is possible to prevent a large recess due to the cavity or a groove communicating with the cavity from being formed in the center of the overlying buried insulating film 5 b 2 .

(3) By forming a tapered portion in the opening of the deep groove 5 a , the buried insulating film 5 b 2 can be buried into the shallow groove 5 a 1 without forming a cavity.

(4) Because of the above items (1) to (3), no recess nor cavity is formed in the top of the trench isolation 5 , making it possible to prevent short-circuit between the gate electrodes 4 dg 1 , which would be caused by a gate electrode forming polycrystalline silicon film remaining in the recess and the cavity. It is therefore possible to improve the yield and reliability of the semiconductor integrated circuit device.

Embodiment 2

FIGS. 19 through 27 are cross sections of an essential portion of the semiconductor substrate in a step of fabricating the semiconductor integrated circuit device of a second embodiment of this invention.

In embodiment 1, description was made of a case where the buried material for filling the deep groove in the semiconductor substrate is SiO 2 . However, the buried material is not limited to this material and may be selected from a variety of materials.

In embodiment 2, description will be made of a case where a polycrystalline silicon is used as the deep groove filling material with reference to FIGS. 19 to 27 .

First, as shown in FIG. 19 , a photoresist pattern 16 a is formed over the semiconductor substrate 1 a by photolithography. At the opening of the photoresist pattern 16 a a part of the top surface of the insulating film 15 c above the element isolation field insulating film 14 is exposed. The width of the opening in the photoresist pattern 16 a is about 0.5 μm.

Next, with the photoresist pattern 16 a as an etching mask, the insulating films 15 b , 15 c and the field insulating film 14 that are exposed from the photoresist pattern 16 a are etched away, as shown in FIG. 20 , by anisotropic etching using a gas mixture of CH 2 F 2 and CF 4 .

In this step, a tapered portion is formed on the inner wall surface of the opening in the field insulating film 14 . In forming this tapered portion the proportion of CH 2 F 4 in the gas mixture used in the etching is increased.

Increasing the proportion of CH 2 F 4 results in an increase in the proportion of carbon in a plasma, making it easier for reaction products including carbon to adhere to the inner wall surface of the opening in the field insulating film 14 , thereby forming the tapered portion on the inner wall surface. The angle θ of the tapered portion is set at, say, around 70 degrees as in embodiment 1.

Then, the photoresist pattern 16 a is ashed away, and the semiconductor substrate 1 a is subjected to anisotropic etching, such as reactive ion etching using a reactive chlorine gas, with the insulating film 15 c as an etching mask.

Because the etching rate of the semiconductor layer 1 a 3 is about 30 times as high as that of the insulating film 15 c , the semiconductor layer 1 a 3 that are exposed from the insulating film 15 c are etched away. Then, as shown in FIG. 21 , in the semiconductor layer 1 a 3 deep grooves 5 a that reach the insulating layer 1 b 2 are formed. The deep groove 5 a has a depth of, for example, about 3 μm.

Next, as shown in FIG. 22 , a buried insulating film 5 b 3 of, say, SiO 2 is deposited over the semiconductor substrate 1 a by CVD. Then, a buried semiconductor film 5 b 4 of, say, polycrystalline silicon is deposited over the buried insulating film 5 b 3 by CVD to fill the deep groove 5 a . The thickness of the buried insulating film 5 b 3 is about 2,000 Å and that of the buried semiconductor film 5 b 4 is about 4,000 Å.

Then, the buried semiconductor film 5 b 4 is etched back. At this time, allowing the buried insulating film 5 b 3 below the buried semiconductor film 5 b 4 to function as an etch stopper, the etching of the semiconductor substrate 1 a can be stopped at the upper surface of the buried insulating film 5 b 3 .

In the region where the deep groove 5 a is formed, however, the etching progresses, the upper portion of the buried semiconductor film 5 b 4 in the deep groove 5 a is etched away. Hence, as shown in FIG. 23 , a shallow groove 5 a 1 about 1,000 Å deep can be formed in the deep groove 5 a.

Then, as shown in FIG. 24 , a buried insulating film (second insulating film) 5 b 2 of, say, non-doped SiO 2 is deposited by CVD over the semiconductor substrate 1 a to bury the buried insulating film 5 b 2 in the shallow groove 5 a 1 . The thickness of the buried insulating film 5 b 2 is about 5,000 Å.

At this time, the buried insulating film 5 b 2 , too, has a low coverage, but can satisfactorily fill the shallow groove 5 a L for the following reasons.

First, because the shallow groove 5 a 1 has a low aspect ratio, and the buried insulating film 5 b 2 can be deposited from the bottom of the groove. Second, because the tapered portion is provided to the inner wall surface of the shallow groove 5 a 1 , and the buried insulating film 5 b 2 can be satisfactorily deposited also in the central portion of the shallow groove 5 a 1 . Particularly cavity 5 c formed in the buried insulating film 5 b 2 is located higher than the upper surface of the field insulating film 14 , and accordingly does not affect the subsequent processes.

Further, in embodiment 2, because the buried insulating film 512 is deposited over the buried semiconductor film 5 b 4 , there is no need to oxidize the upper part of the buried semiconductor film 5 b 4 in the deep groove 5 a.

Then, the buried insulating film 5 b 2 is etched backed by, e. g. reactive ion etching.

At this time, the insulating film 15 b underlying the buried insulating film 5 b 2 functions as an etching stopper. Thus, as shown in FIG. 25 , the etching of the semiconductor substrate 1 a can be stopped at the upper surface of the insulating film 15 b.

Further, in embodiment 2, by monitoring the intensity of light emitted by reaction products formed in the etching atmosphere during this process, it is possible to stop the etching when all the buried insulating film 5 b 2 on the insulating film 15 b is removed.

This makes it possible to prevent overetch in the shallow groove 5 a 1 . As a result, the upper surface of the buried insulating film 5 b 2 in the shallow groove 5 a 1 can be almost flush with the upper surface of the field insulating film 14 surrounding the shallow groove 5 a 1 .

After the deep groove 5 a is filled with the buried semiconductor film 5 b 4 and the buried insulating films 5 b 2 , 5 b 3 to form the trench isolation 5 in the above processes, the insulating film 15 b , which functions as an etching stopper, is removed. The cross section of an essential portion of the semiconductor substrate 1 a after this processing is shown in FIG. 26 .

In such a way, in embodiment 2, too, the deep groove 5 a can be filled with the buried semiconductor film 5 b 4 and the buried insulating films 5 b 2 , 5 b 3 , as shown in FIG. 26 , without forming a cavity in the upper part of the deep groove 5 a . It is also possible to ensure a planar surface at the top of the buried insulating film 5 b 2 and to make the upper surface of the buried insulating film 5 b 2 almost flush with the upper surface of the field insulating film 14 .

Hence, also in embodiment 2, because no undesired conductive films remain on the surface of the trench isolation 5 , in the subsequent processes short-circuit between adjacent conductive patterns due to the remaining conductive films can be prevented.

Then, as in embodiment 1, according to a normal MOSFET forming process, the pMOS 4 dp is formed on the semiconductor layer, as shown in FIG. 27 .

In such a way, embodiment 2 has the similar advantages to those of embodiment 1.

The present invention has been described in connection with the preferred embodiments. It should be noted, however, that this invention is not limited to these embodiments and that various modifications may be made without departing the gist of the invention.

While in the embodiments the etching stopper film is made of silicon nitride, other materials may be used. For example, polycrystalline silicon may be used. In this case the thickness of the polycrystalline silicon is about 1,000 Å.

In embodiment 2, when the tapered portion is formed in the opening of the deep groove, the proportion of the reactive gas CH 2 F 4 used during the etching process for forming the deep groove is increased. The method of forming the tapered portion is not limited to this method and may be any other method. For instance, isotropic etching may be used for forming the deep groove. It is also possible to lower the etching selectivity of the field insulating film to the photoresist for forming the deep groove.

By this techinique, the field insulating film portion under the photoresist pattern, too, can be etched away during the etching for forming the deep groove, thus forming a tapered portion in the opening in the field insulating film.

Although the above description was made of a case where the present invention is applied to a composite gate array, the field of application which is the background of this invention, there are a variety of possible applications. This invention can be applied to, for example, an ordinary gate array having only logic circuits, and to other types of semiconductor integrated circuit devices such as logic circuits and semiconductor memories fabricated by an ordinary fabrication method.

Representatives of this invention disclosed by this patent application will be briefly summarized as follows.

(1) By a method of manufacturing a semiconductor integrated circuit device according to this invention, when the deep groove for a trench isolation having a high aspect ratio is filled, the filling process is divided into two steps. In the first step the deep groove is filled to a specified extent to lower the aspect ratio of the deep groove and thereby transform the deep groove into a shallow groove. In the second step, the shallow groove is filled and the top portion of the buried material in the shallow groove is planarized. By this filling techinique, it is possible to satisfactorily fill the deep groove of a high aspect ratio without exposing a cavity from the top of the deep groove, without forming a recess at the top periphery of the deep groove, and without incurring a significant increase in the number of manufacturing steps.

Because short-circuit defect between conductive patterns, which would be caused by presence of residual conductor film in a recess or cavity formed in the upper part of the trench isolation, can be prevented during a step of forming conductor patterns after the trench isolation is formed, it is possible to improve the yield and reliability of the semiconductor integrated circuit device.

(2) By a method of manufacturing a semiconductor integrated circuit device according to this invention, by forming a recess at the top central portion of a first insulating film buried in the deep groove, it is possible to ensure a sufficient thickness of a second insulating film filled between the central portion of the top surface of the first insulating film and the top surface of the shallow groove. Hence, if a cavity is formed in the center of the first insulating film, it is possible to prevent a large recess due to the cavity or a groove communicating with the cavity from being formed in the center of the second insulating film.

(3) By a method of manufacturing a semiconductor integrated circuit device according to this invention, by forming a tapered portion in the opening of the deep groove, the second insulating film can be buried in the shallow groove without forming a cavity.

Claims

1. A method of manufacturing a semiconductor integrated circuit device, comprising steps of:forming in a semiconductor substrate a first groove, for trench isolation, with an aspect ratio of greater than 1; depositing a first insulating film in the first groove; removing a part of the first insulating film to form a second groove, in a remaining part of the first insulating film, having an aspect ratio of not greater than 1, and having a taper angle of an inner side surface of the second groove, with respect to the semiconductor substrate, which is less than a taper angle of an inner side surface of the first groove with respect to the semiconductor substrate; and burying a second insulating film in the second groove so as to fill the second groove.

2. A method of manufacturing a semiconductor integrated circuit device according to claim 1, wherein said first insulating film is comprised of a silicon oxide film, and said second insulating film is comprised of a silicon oxide film.

3. A method of manufacturing a semiconductor integrated circuit device according to claim 2, wherein in said depositing step said first insulating film is formed such that a cavity is left in said first insulating film.

4. A method of manufacturing a semiconductor integrated circuit device according to claim 1, wherein in said depositing step said first insulating film is formed such that a cavity is left in said first insulating film.

5. A method of manufacturing a semiconductor integrated circuit device according to claim 1, wherein said second insulating film is buried in said second groove such that a thickness of said second insulating film at a central portion of said second groove is greater than a thickness of said second insulating film at a peripheral portion of said second groove.

6. A method of manufacturing a semiconductor integrated circuit device according to claim 1, wherein said second groove is provided within the first groove.

7. A method of manufacturing a semiconductor integrated circuit device, comprising steps of:forming in a semiconductor substrate a first groove, for trench isolation, with an aspect ratio of greater than 1; depositing a first insulating film in said first groove; removing a part of said first insulating film to form a second groove, in a remaining part of said first insulating film, having an aspect ratio of not greater than 1, and having a taper angle of an inner side surface of said second groove, with respect to said semiconductor substrate, which is less than a taper angle of an inner side surface of said first groove with respect to said semiconductor substrate; depositing a second insulating film in said second groove; and removing a part of said second insulating film to bury said second insulating film in said second groove so as to fill said second groove.

8. A method of manufacturing a semiconductor integrated circuit device according to claim 7, wherein said first insulating film is comprised of a silicon oxide film, and wherein second insulating film is comprised of a silicon oxide film.