Abstract:
This invention provides a method of forming a buried element isolation region in a semiconductor substrate. The method comprises steps of forming a gate electrode material pattern on a gate insulating film formed on a semiconductive substrate, forming a gate electrode by selectively forming a groove in said gate electrode material pattern to thereby isolate said pattern and burying insulating material in the groove.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of manufacturing a semiconductor device and, more particularly, to an improvement in isolating elements of a MOSLSI (Metal Oxide Semiconductor Large Scale Integrated Circuit). 
     Heretofore, a selective oxidation method has been in general employed as an interelement isolating method in the step of manufacturing a semiconductor device and particularly an MOSLSI. This method will be described in more detail using an n-channel MOSLSI as an example. 
     As shown in FIG. 1(A), an SiO 2  film 2 is first grown by thermal oxidation on a p-type Si substrate 1 having a crystal plane (100), and an Si 3  N 4  film 3 is accumulated on the film 2. Subsequently, a resist film 4 is formed by a photoetching method on an element forming portion. With the film 4 as a mask, the film 3 except the element forming portion is etched and removed, and an Si 3  N 4  pattern 3&#39; is formed. Then, a boron ion implantation is, for example, performed, thereby forming a p +  type region 5 as a channel stopper region in the field region (FIG. 1(B)). After the film 4 is removed, a wet oxidation is carried out with the pattern 3&#39; being employed as a mask, and a thick field oxidized film (field region) 6 is selectively grown (FIG. 1 (C)). Subsequently, the pattern 3&#39; and the film 2 are etched and removed, thereby forming an element forming region 7 isolated between field regions 6 (FIG. 1(D)). Thereafter, as shown in FIG. 1(E), a gate electrode 9 formed of a polycrystalline silicon is formed through a gate oxidized film 8 on the region 7, and arsenic is, for example, diffused in the region 7 to form n +  regions 10 and 11 as a source and a drain. A CVD-SiO 2  film 12 are eventually accumulated as an interlayer insulating film on the overall surface. Contacting holes 13 are opened at the portions corresponding to the regions 10 and 11, and the gate electrode 9 over the film 8, and aluminum wires 14 are formed in film 12, thereby manufacturing an n-channel MOSLSI (FIG. 1(F)). 
     The above-described conventional selective oxidation method of manufacturing the MOSLSI, however, has various drawbacks as described below. 
     FIG. 2 shows in detail a sectional structure of the MOSLSI in which the field region 6 is formed with the pattern 3&#39; shown in FIG. 1(C) as a mask. It is in general known that the region 6 intrudes into the region under the pattern 3&#39; when growing by the selective oxidation method (a region F in FIG. 2). In this case, the region F consists of a portion D or a so-called &#34;bird&#39;s beak&#34; where an oxidizer is diffused through the thin film 2 under the pattern 3&#39; during the field oxidation, and a portion E where the thick part of the region 6 is laterally intruded. When the region 6 is 1 μm in thickness for example, and is grown under the conditions that the thickness of the pattern 3&#39; is 1,000 Å and the film 2 under the pattern 3&#39; is 1,000 Å thick, the length of the portion F reaches approximately 1 μm. It is assumed that a distance A between the patterns 3&#39; is 2 μm. Then, the width C of the field region cannot be reduced to less than 4 μm, since the width of the portion F is 1 μm, resulting in a large obstruction in the integration of an LSI. Thus, a method of suppressing a bird&#39;s beak (the portion D in FIG. 2) by reducing the thickness of the film 2 under the pattern 3&#39; use of a thick pattern 3&#39; and a method of suppressing the intruded portion F of the field by reducing the thickness of the grown film of the field 6 have been recently proposed. However, the former causes a large stress at the end of the field, resulting in the ready production of defects, and the latter has a problem of a decrease in the inverted voltage of the field. In this manner, there is a limit to the integration of an LSI by the conventional selective oxidation method. 
     When a channel stopper is provided, boron ions implanted as the channel stopper diffuses laterally during a field oxidation. As shown in FIG. 3(A), part of the region 7 becomes the region 5, and the effective element region is narrowed from the width G to the width H. As a result, a narrow channel effect such as a reduction in the current of a transistor or an increase in the threshold voltage occurs when microminiaturization of an element is carried out. Since the region 5 extends further laterally, a junction between the region 11 (or 10) and the region (5) in the region 7 becomes wide as shown in FIG. 3(B), resulting in an increase in the floating capacitance between the regions 10, 11 and the substrate 1. This capacitance cannot be ignored as the element is reduced. 
     Further, the conventional element isolating method has the following drawbacks. 
     As shown in FIG. 4(A), since the region 6 and the electrode 9 are not self-aligned, it is necessary to provide an alignment margin portion 15 in the region 6 to enable the electrode 9 to extend into the region 6. This structure obstructs the integration of the LSI. More particularly, as shown in FIG. 4(B), it is necessary to form a spacing I (which depends upon the minimum size of a photoetching method) between gate electrodes 9 1  and 9 2 , in addition to margins J and K of the portions 15 1  and 15 2 , so that different electrodes 9 1  and 9 2  face each other on the region 6. It is assumed that the relationship of the lengths of the margins J and K and the spacing I is J=K=I=1 μm. Then, the minimum width M of the region 6 in this portion should become 3 μm. Thus, it is impossible to form the field region having a width less than this length. 
     SUMMARY OF THE INVENTION 
     The present invention has been made to eliminate the above-described drawbacks and disadvantages and has for its object to provide a method of manufacturing a semiconductor device which is capable of high integration and high performance by using a novel element isolating system. 
     According to an aspect of the present invention, there is provided a method of manufacturing a semiconductor device which comprises the steps of forming a gate electrode material pattern on a gate insulating film deposited on a conductive type semiconductor substrate, forming a gate electrode by selectively forming a groove on the gate electrode material pattern and isolating the pattern, and burying an insulating material in the groove. 
     In the step of forming the gate electrode material pattern, the same gate electrode as the conventional electrode may be simultaneously and partially formed directly on the semiconductor substrate. 
     The gate insulating film employed in this method includes, for example, an SiO 2  film, a two-layer film of the SiO 2  film and an Si 3  N 4  film, and a two-layer film of the SiO 2  film and an Al 2  O 3  film. The gate electrode material includes, for example, a polycrystalline silicon, an impurity-doped polycrystalline silicon, metal such as aluminum, molybdenum, tungsten or tantalum, or metal silicide such as molybdenum silicide, tungsten silicide or tantalum silicide. 
     Then, with the gate electrode material pattern (and the gate electrode) as a mask, an impurity having reverse or opposite conductive type to the semiconductor substrate is doped with the substrate, thereby forming impurity regions as a source region and a drain region, as required. 
     Subsequently, a mask material, from which a portion is removed when a groove is to be formed, such as a resist pattern is formed on the semiconductor substrate thus formed with the gate electrode material pattern, the electrode material pattern exposed from the mask material is then partially and selectively etched, thereby forming a groove, the pattern is isolated, and a gate electrode is formed. The formation of this groove is not limited to when the thickness of the pattern is etched. For example, the groove may be formed by etching the gate insulating film under the pattern, or by further etching the surface of the semiconductor substrate under the insulating film. The groove may not only be formed on the pattern, but may be simultaneously formed on the exposed substrate part. When a reactive ion etching method is employed as etching means in this step, a groove having substantially vertical side surfaces may be formed. However, a groove having a tapered or inverted tapered side may be formed by other etching means. The number of the grooves may be one or more, and the depths of the grooves may be variously formed. 
     Then, with a masking material as a mask, an impurity having the same conductive type as the semiconductor substrate is doped with the substrate under the groove, thereby forming an impurity region. When the groove is formed only by etching of the gate electrode material pattern, an ion implantation method is employed as the doping means. When the groove is formed over the gate electrode material pattern and the gate insulating film or further over the surface layer of the semiconductor substrate, an ion implantation method or a thermal diffusion method may be employed as doping means. When the groove is formed over the surface layer of the semiconductor substrate so that the depth in the substrate is deeper than the depth of the impurity region used as source and drain regions, an impurity region capable of being utilized as a wiring layer or a resistor may be formed by doping a reverse conductive type impurity on the substrate under the groove. 
     Subsequently, after the removal of the masking material, an insulating material is accumulated on the overall surface of the semiconductor substrate including the gate electrode and the groove in such a manner that the width of the opening of the specific groove is represented by &#34;a&#34; and the inclining angle of the side surface is θ, and the material accumulated in a thickness being larger than (a·[cot (θ/2)]/2, so that the material is buried to the opening of at least one groove. The material includes, for example, SiO 2 , Si 3  N 4  or Al 2  O 3 , and may include, as required, low melting point insulating materials such as phosphorus silicate glass, boron silicate glass. The insulating material may be buried by dividing the material into a plurality of steps, as will be described later. In this case, it is not necessary to form a thickness to fill completely the groove in the first burying as described above. 
     The accumulating means of the insulating material includes, for example; a CVD (Chemical Vapor Deposition) method or a PVD method such as a sputtering method. When the grooves are formed also through the gate insulating film and further through the surface layer of the semiconductor substrate prior to the accumulation of the insulating material, the grooves may be at least partly oxidized or nitrided to grow an oxidized film or nitrided film which does not block the groove. The doping of the impurity at this time may be before or after the oxidizing or nitriding. When such methods are employed together, the field region thus obtained has an oxidized or nitrided film which has excellent density in contact with the substrate and the insulating material formed by accumulation, and remarkably improves the element isolating performance as compared with a method which employs only an insulating material. In this case, it is possible to bury a conductive material such as a polycrystalline silicon, metallic silicide or tungsten. After the accumulation of the insulating material, a low melting point substance such as boron, phosphorus or arsenic is doped entirely or partly on the surface layer of the insulating film. The film is then heat-treated to melt the doped layer of the insulating film. Alternatively, a low melting point insulating material, such as boron silicate glass (BSG), phosphorus silicate glass (PSG) or arsenic silicate glass (AsSG), or an organic substance such as polyimide or resist material is accumulated entirely or partly on the insulating film, and then the low melting point insulating film may be melted. By employing such means, when the part corresponding to the groove becomes recessed according to the accumulation of the insulating material, the recess will be buried by the material, thereby flattening the recess. As a result of this, when the entire surface is etched, the insulating material remaining in the groove can be prevented from becoming lower than the level of the opening of the groove. 
     Subsequently, the insulating film thus accumulated on the substrate is etched and removed without the masking material until the gate electrode, except for the groove (or the surface of the substrate), is exposed, thereby forming a field region in which the insulating material remains in the groove. The etching step in this process includes, for example, an entire surface etching method which employs an etchant or a plasma etchant or a reactive ion etching method. In this etching step, a partial region of the insulating film is covered with a masking material, and the other film is etched, so that the insulating film remains on all the portion except the groove. Since the insulating material is accumulated after the gate electrode, source and drain regions are formed, the insulating film is not etched, but remains and may be used as an interlayer insulating film. 
     Then, an interlayer insulating film is accumulated (in some cases, the remainder of the interlayer insulating film is unnecessary without etching the insulating material), contacting holes are opened at the interlayer insulating film on the source and drain regions, and the gate electrode and the metal wires are formed, thereby manufacturing a semiconductor device such as MOSLSI. 
     However, according to the present invention, at least the gate electrode material pattern is formed through the gate insulating film on the semiconductor substrate. A groove is selectively formed at least through the material pattern to isolate the pattern, thereby forming the gate electrode. The insulating material is then buried in the groove, thereby making possible both the formation of the gate electrode and the field region. Therefore, a semiconductor device which has the various advantages as described below can be obtained. 
     (1) Since the gate electrode and the field region are self aligned, it is not necessary to provide an alignment margin to allow the gate electrode to extend on the field region, as in the conventional method. Consequently, when the gate electrodes face each other with the field region as the center, it is unnecessary to widen the field region by the amount of the portion of the length corresponding to the alignment margin, and the microminiaturization of the field region, and hence the integration of the semiconductor device, can be performed. 
     (2) Since the area of the field region is determined by the area of the groove formed in advance on the gate electrode material pattern, the area of the groove is reduced, thereby readily forming the ultrafine field region of the object of the present invention and obtaining a semiconductor device having a high integration. 
     (3) Since the effective vertical length of the field region is determined by the depth of the groove formed on the substrate, irrespective of the area, the depth is arbitrarily selected, thereby effectively preventing current leakage between elements in the field region, thereby obtaining a semiconductor device having high performance. 
     (4) After a groove is formed and selectively doped, the high-temperature, long-time thermal oxidation step, such as the conventional selective oxidation, is not employed, so the impurity region rediffuses to the surface of the element formation region, preventing the contraction of the effective field region. Further, it can prevent the impurity from out-diffusing onto the surface of the substrate. In this case, when the doping of the impurity is performed by ion implantation, the impurity ion implantation layer can be formed on the bottom of the groove. Thus, since the ion implantation layer does not extend to the surface layer (the part to be formed with elements) of the region even if the ion implantation layer is rediffused, the contraction of the effective field region can be prevented. 
     When there is the possibility of a leakage current at the side surface of the field region, p +  type doping may be, for example, performed at the side surfaces of the groove. In this case, when the section of the groove is formed in a V-shaped taper, p +  type doping may be, for example, performed simply at the side surface of the groove by ordinary ion implantation. 
     Further, an insulating layer such as an SiO 2  film connected to the field region remains on the gate electrode at the time of etching the insulating film accumulated on the substrate, and may be used as an interlayer insulating film for multilayer wires. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention can best be understood by reference to the accompanying drawings of which: 
     FIGS. 1(A) to 1(F) sre sectional views showing the steps of manufacturing an n-channel MOSLSI employing the conventional selective oxidation method; 
     FIG. 2 is an enlarged sectional view showing the state of the semiconductor substrate after the selective oxidizing step; 
     FIGS. 3(A) and 3(B) are sectional views for explaining the problems of the conventional selective oxidation method; 
     FIGS. 4(A) and 4(B) are plan views for explaining the problems in the conventional selective oxidation method after forming the field region and forming the gate electrode by the selective oxidation method; 
     FIGS. 5(A) to 5(F) are sectional views showing the steps of manufacturing an MOSLSI in an embodiment of the present invention; 
     FIG. 6 is a plan view of FIG. 5(B); 
     FIG. 7 is a plan view of FIG. 5(F); 
     FIGS. 8(A) and 8(B) are sectional views showing the steps up to the formation of a field region, illustrating a modified embodiment of the present invention; 
     FIG. 9 is a sectional view of the step up to the formation of the field region shown in the modified embodiment of the present invention; 
     FIGS. 10(A) to 10(C) are sectional views showing the steps up to the formation of the field region in the second embodiment of the present invention; 
     FIG. 11 is a plan view of FIG. 10(C); 
     FIGS. 12(A) to 12(D) are sectional views showing the steps up to the formation of the field region in the third embodiment of the present invention; 
     FIGS. 13(A) to 13(D) are sectional views showing the steps up to the formation of the field region in the fourth embodiment of the present invention; 
     FIGS. 14(A) to 14(D) are sectional views showing the steps up to the formation of the field region in the fifth embodiment of the present invention; 
     FIGS. 15(A) to 15(E) are sectional views showing the steps up to the formation of the field region in the sixth embodiment of the present invention; 
     FIGS. 16(A) to 16(E) are sectional views showing the steps up to the formation of the field region in the seventh embodiment of the present invention; 
     FIGS. 17(A) to 17(D) are sectional views showing the steps up to the formation of the field region in the modified embodiment of the present invention; 
     FIG. 18 is a sectional view showing other means for forming a field inversion preventing region in the groove; 
     FIGS. 19(A) and 19(B), 20 and 21 are sectional views showing the modified examples of the groove; and 
     FIG. 22 is a sectional view for the explanatory purpose of the modified embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Example 1 
     This example will describe a method of manufacturing an n-channel MOSLSI according to the present invention. 
     (i) A silicon oxidized film 102 was grown by thermal oxidation on a p-type silicon substrate 101 which had a crystalline plane of (100), and an arsenic-doped polycrystalline silicon film 103 was then accumulated on the overall surface (FIG. 5(A)). Subsequently, the film 103 was patterned by a photoetching technique, thereby forming gate electrodes 104 1 , 104 2  and a polycrystalline silicon pattern 105 as a gate electrode material pattern. With the electrodes 104 1 , 104 2  and the pattern 105 as masks the film 102 was etched, thereby forming a gate oxidized film 106. Then, with the electrodes 104 1 , 104 2  as masks an n-type impurity, such as arsenic ions, was implanted, thereby forming n +  type impurity regions 107 to become source and drain regions (FIG. 5(B) and FIG. 5). FIG. 6 is a plan view of FIG. 5(B). 
     (ii) Then, a resist pattern 108, from which portions to be formed with grooves are removed, was formed on the overall surface. Subsequently, with the pattern 108 as a mask the substrate 101 formed of the regions 107, the pattern 105, the film 106 and the surface layer of the substrate 101 was etched by a reactive ion etching. At this time, as shown in FIG. 5(C), strip grooves 109 each having side surfaces substantially vertical to the substrate 101, and grooves 109&#39; each connected to the grooves 109 were formed over the polycrystalline silicon patterns, gate oxidized films and the surface layer of the substrate 101. The patterns were isolated by the formation of the grooves 109&#39; at the polycrystalline silicon pattern, thereby forming gate electrodes 104 1  &#39; to 104 4  &#39;. Simultaneously, the regions 107 were isolated, thereby forming n +  type source and drain regions 110. Subsequently, with the patterns 108 as masks, p-type impurity ions and hence boron ions were, for example, implanted in the substrate 101 under the grooves 109 and 109&#39;, which were then heat treated, thereby forming p +  type field inversion preventing region 111 on the bottoms (FIG. 5(C)). 
     (iii) Subsequently, after the pattern 108 was removed, an SiO 2  was accumulated by a CVD method in the grooves 109, 109&#39; to a thickness larger than (a·[cot (θ/2)]/2) (e.g., 0.6 μm), where the width of the openings of the grooves 109, 109&#39; is represented by &#34;a&#34; and the inclining angle of the side surface is represented by θ. The SiO 2  was gradually accumulated on the substrate 101, the electrodes 104 1 , 104 2 , 104 1  &#39; to 104 4  &#39; and the inner surfaces of the grooves 109, 109&#39; at this time. As shown in FIG. 5(D), a CVD-SiO 2  film 112 which filled each of the grooves 109, 109&#39; was formed. Since a thermal oxidation at high temperature for a long time was not performed like the conventional selective oxidation method, the rediffusion of the source and drain regions 110, and the region 111 did not substantially occur. 
     (iv) Subsequently, the film 112 was entirely etched with an ammonium fluoride until the substrate 101 except the grooves 109, 109&#39; and the electrodes 104 1 , 104 2 , 104 1  &#39; to 104 4  &#39; were exposed. At this time, as shown in FIG. 5(E), the film 112 remaining in the grooves 109, 109&#39;, was buried in the substrate 101 and the portions of the surface of the substrate 101 between the electrodes 104 1  &#39; to 104 4  &#39;, thereby forming strip field regions 113 which were connected to each other. Thereafter, an interlayer insulating film 114 was accumulated on the overall surface. After contacting holes 115 were opened at the film 114, an aluminum film was deposited on the overall surface. The electrodes were isolated to form aluminum wires 116 for connecting predetermined source and drain regions 110 to the electrodes 104 1 , 104 2 , 104 1  &#39; to 104 4  &#39; through the contacting holes 115, and thereby manufacturing an MOSLSI (FIG. 5(F) and FIG. 7) FIG. 7 is a plan view of FIG. 5(F). 
     Since the electrodes (particularly 104 1  &#39; to 104 4  &#39;) and the region 113 can be formed self aligned in the MOSLSI thus obtained, in this Example 1, as shown in FIG. 5(F) and FIG. 7, it is not necessary to provide an alignment margin to allow the gate electrode to extend to the field region in the conventional structure as shown in FIG. 4. As a result, when the gate electrodes face each other with the field region as the center (e.g., the electrodes 104 1  &#39; and 104 2  &#39;), it becomes unnecessary to widen the field region by an amount corresponding to the alignment margin, the microminiaturization of the region 113 can be performed, and an MOSLSI having high density and high integration can be obtained. 
     Since the width of the region 113 can be determined by the width of the groove 109, the width can be reduced to as little as 1 μm in an ultrafine area, and the area of the region 113 which is in the LSI can be thus contracted. 
     Since the region 113 is further formed at the same level as the surface of the substrate 101 or at the same level as the surface of the gate electrode without stepwise difference, the stepwise disconnection between the region 113 and the element region can be prevented when forming the wires 116. 
     Further, since no field oxidizing step, such as in the conventional selective oxidation method, is employed, a defect of the silicon substrate upon production of a stress at the time of growing the oxidized film can be prevented. In addition, the rediffusion of the region 111 can be also prevented. 
     In etching the film 112 in the above Example 1, after a resist pattern 117 is formed on the predetermined part on the film 112 as shown in FIG. 8(A), a CVD-SiO 2  film 112&#39; which is connected to the film 112 forming the region 113 may remain by etching the substrate 101 or the electrode 104 2  &#39; as shown in FIG. 8(B). This film 112&#39; may be utilized as an interlayer insulating film for forming an aluminum wiring layer thereon. 
     The region 113 is formed and a CVD-SiO 2  film 112&#34; may remain on the side surfaces of the electrodes 104 2 , 104 1  &#39; as shown in FIG. 9 by etching the entire surface of the CVD-SiO 2  film by reactive ion etching instead of employing an ammonium fluoride in etching the film 112 as in the above Example 1. The films 112&#34; are formed, for example, to form n -  type layers 110a on both sides of the electrodes 104 2 . An electric field in the vicinity of the gate electrode may be reduced by reducing the density of the n -  type layer in the vicinity of the electrode 104 2 , thereby suppressing a hot electron effect. The method of forming the layer 110a may include the steps of thinly doping an n-type impurity with the source and drain regions with the electrode 104 2  as a mask before accumulating the film 112 (FIG. 8(A)), forming the films 112&#34; on both side surfaces of the electrodes 104 2 , and further doping an n-type impurity with the films 112&#34; and the electrode 104 2  as masks. The groove for burying the insulating film may be partly and shallowly formed so as to pass only the gate electrode material, as shown at the right side of FIG. 9, and the insulating film may be formed thereon. 
     Example 2 
     The grooves 109&#39; were first formed in the substrate 101, and CVD-SiO 2  was then buried in the grooves 109&#39; in the same method as that in Example 1, thereby forming a first field region 113 1  (FIG. 10(A)). Subsequently, a thermal oxidation was then performed to grow a silicon oxidized film on the substrate 101. Further, an arsenic-doped polycrystalline silicon film was accumulated, and the polycrystalline silicon film was then patterned by a photoetching technique, thereby forming a polycrystalline silicon pattern 105 as a gate electrode material pattern. Thereafter, with the pattern 105 as a mask the silicon oxidized film was then etched, thereby forming the gate oxidized film 106. Successively, with the pattern 105 as a mask arsenic ions were implanted, thereby forming an n +  type impurity region (FIG. 10(B)). 
     Subsequently, with a resist pattern (not shown) as a mask, grooves 109 were formed by selectively etching the pattern 105, the film 105 and the surface layer of the substrate 101. Then, the patterns 105 were isolated, thereby forming a gate electrode 104 5  &#39; and gate electrodes 104 1  &#39;, 104 2  &#39; crossing the first film region 113. Thereafter, the grooves 109 were buried with the CVD-SiO 2  in the same manner as that in Example 1, thereby forming a second field region 113 2  (FIG. 10(C) and FIG. 11). FIG. 11 is a plan view of FIG. 10(C). 
     According to the method in Example 2, an MOSLSI which has gate electrodes 104 5  &#39; commonly crossing the flat substrate 101 with a plurality of MOS transistors can be provided. 
     Example 3 
     (i) A p-type silicon substrate 201 having a crystalline plane of (100) was first thermally oxidized, thereby growing a silicon oxidized film (not shown). Then, an arsenic-doped polycrystalline silicon film (not shown) was accumulated thereon. Subsequently, the polycrystalline silicon film was patterned by a photo-etching technique, thereby forming a crystalline silicon pattern 202 as a gate electrode material pattern. With the pattern 202 as a mask the silicon oxidized film was etched, thereby forming a gate oxidized film 203. Thereafter, with the pattern 202 as a mask, arsenic ions were implanted in the substrate 201, thereby activating the substrate, and an n +  -type impurity region (not shown) was formed (FIG. 12(A)). 
     (ii) Subsequently, with the resist pattern (not shown) as a mask, the polycrystalline silicon pattern, the gate oxidized film and the surface layer of the substrate were etched and removed by a reactive ion etching. Thus, a plurality of first grooves 204 1  to 204 4  each having side surfaces formed substantially vertically were formed, thereby isolating the polycrystalline silicon patterns and forming gate electrodes 205 1  to 205 3 . Simultaneously, the n +  type impurity regions were isolated, thereby forming n +  type source and drain regions (not shown). The grooves 204 2 , 204 3 , 204 4  of the first grooves 204 1  to 204 4  were formed near each other. Subsequently, p +  type field inversion preventing regions 206 were formed in the substrate 201 under the firsts grooves 204 1  to 204 4  and the grooves 204 1  to 204 4  were filled with CVD-SiO 2  207, in the same manner as that in Example 1 (FIG. 12(B)). 
     (iii) Then, a photoresist film 208 was positioned to cover the portions except the region between the grooves 204 2  to 204 4 . Film 208 also covered part of the exposed surface of film 207 at both ends of the first grooves 204 2  and 204 4 . The portion between grooves 204 2  and 204 4  was etched by a reactive ion etching. At this time, as shown in FIG. 12(C), the polycrystalline silicon, the gate oxidized film 203 and the substrate 201 were selectively removed between the grooves 204 2  and 204 4  exposed by the film 208, thereby forming two second grooves, 209 1 , 209 2 . Subsequently, with the film 208 as a mask boron ions were implanted in the substrate 201 into the second grooves 209 1 , 209 2 , thereby activating them and forming p +  type field inversion preventing regions 206&#39; (FIG. 12(C)). 
     (iv) Subsequently, the film 208 was removed. Then, the second grooves 209 1 , 209 2  were buried with CVD-SiO 2  207&#39; in the same manner as that in Example 1. Thus, the film 207 remaining in the first grooves 204 2  to 204 4  were integrated with the film 207&#39; buried in the second grooves 209 1 , 209 2 , thereby forming a wide field region 210 between the electrodes 205 2  and 205 3 . The regions 206&#39; under the second grooves 209 1 , 209 2  were integrated with the regions 206 under the first grooves 204 2  to 204 4  by the thermal treatment in the step of burying the film 207&#39;, thereby forming a wide p +  type field inversion preventing region 206&#34;. Further, the film 207 buried in the groove 204 1  was utilized as a field region 210&#39; (FIG. 12(D)). 
     According to the method in Example 3, the electrodes 205 1  to 205 3  and the regions 210, 210&#39; can be formed by self-alignment, and the narrow field region 210&#39; and the wide field region 210 can be formed between the gate electrodes. 
     Example 4 
     (i) The gate electrode 205 made of an arsenic-doped polycrystalline silicon and the polycrystalline silicon pattern 202 as a gate electrode material pattern were formed on the gate oxidized film 203 on the p-type silicon substrate 201. Then, with the electrode 204 and the pattern 202 as masks, n-type impurity ions such as arsenic ions were implanted, thereby forming n +  type impurity regions 211 which become source and drain regions (FIG. 13(A)). 
     (ii) Subsequently, with a resist pattern (not shown) as a mask the silicon substrate 201 formed with the regions 211, the pattern 202, the film 203 and the surface layer of the substrate 201 were removed by a reactive ion etching. At this time, a plurality of first grooves 204 1  to 204 5  each having side surfaces formed substantially vertical to the substrate 201 were formed. The pattern 202 was isolated by the formation of the groove 204 5 , the gate electrode 205&#39; was formed, and the regions 211, were isolated, thereby forming n +  type source and drain regions 212. The grooves 204 1  to 204 3  of the first grooves 204 1  to 204 5  were formed near each other. Subsequently, the regions 206, were formed in the substrate 201 under the grooves 204 1  to 204 5  in the same manner as Example 1, and the grooves 204 1  to 204 5  were buried with the film 207 (FIG. 13(B)). 
     (iii) Then, the photo-resist film 208 was positioned to cover the exposed portions except the region between the 240 1  and 204 3 . Film 208 also covered part of the exposed surface of film 207 at both ends of the grooves 204 1  and 204 3 . The portion between grooves 204 1  and 204 3  was then etched by a reactive ion etching. The part of the substrate 210 between the grooves 204 1  and 204 3  exposed by the film 208 was selectively removed as shown in FIG. 13(C), thereby forming two second grooves 209 1 , 209 2 . Subsequently, with the film 208 as a mask boron ions were implanted in the substrate 201 in the grooves 209 1 , 209 2 , thereby activating it and forming a p +  type field inversion preventing region 206&#39; (FIG. 13(C)). 
     (iv) Subsequently, the film 208 was removed, and the grooves 209 1 , 209 2  were filled with the film 207&#39; in the same manner as that in Example 1. Thus, the film 207 remaining in the grooves 204 1  to 204 3  was integrated with the film 207&#39; buried in the grooves 209 1 , 209 2 , thereby forming a wide field region 210 in the substrate 210. The regions 206 under the grooves 204 1  to 204 3  were integrated with the regions 206&#39; under the grooves 209 1 , 209 2  by the heat treatment in the step of burying the film 207&#39;, thereby forming a wide p +  type field inversion preventing region 206&#34;. The films 207 buried in the grooves 204 4 , 204 5  were utilized as the field regions 210&#39;, 210&#39; (FIG. 13(D)). 
     According to the method in Example 4, the electrodes 205&#39; and the region 210&#39; can be self-aligned, and wide and narrow field regions 210 and 210&#39; can be formed at the substrate 201 and between the electrodes. 
     Example 5 
     (i) A gate electrode formed of an arsenic-doped polycrystalline silicon and a polycrystalline silicon pattern 304 as a gate electrode material pattern were formed through a gate oxidized film 303 on a p-type silicon substrate 301. Then, with the electrode 303 and the pattern 304 as masks, n-type impurity ions such as arsenic ions were implanted, thereby forming n +  type impurity regions 305 which become source and drain regions (FIG. 14(A)). 
     (ii) Then, with a resist pattern (not shown) as a mask, the portions over the pattern 304, the film 302 and the surface layer of the substrate 301 as well as the substrate 301 were etched by reactive ion etching. At this time, grooves 306 each having side surfaces formed substantially vertical and which were connected to each other were formed in the polycrystalline silicon pattern, the gate oxidized film and the surface layer of the substrate. One of the grooves 306 was formed in the substrate 301 in a portion of region 305 as shown in FIG. 14(B). Thus, the patterns 304 were isolated, thereby forming gate electrodes 303 1  to 303 4 . Simultaneously, the n +  type impurity regions were isolated, thereby forming n +  type source and drain regions 307. Subsequently, boron ions were implanted in the substrate 301 in the bottoms of the grooves 306, thereby activating them and forming a p +  type field inversion preventing region 308. Then, the grooves 306 were filled with CVD-SiO 2  309 in the same manner as Example 1, thereby forming the field region 310 (FIG. 14(B)). 
     (iii) Subsequently, a silicon nitride film 311 was accumulated on the overall surface. A resist pattern 312, from which the portion corresponding to the electrode 303 4  was removed, was formed on the film 311. With the pattern 312 as a mask, the film 311 was selectively etched. Then, the electrode 303 and the film 302 under the film 311 were further removed by etching. Subsequently, with the pattern 312 as a mask, boron ions were implanted in the substrate 301, thereby activating it and forming a p +  type field inversion preventing region 308&#39; (FIG. 14(C)). 
     (iv) Then, the pattern 312 was removed, and the film 311 was treated as an oxidation resistant mask in a high temperature oxygen atmosphere, thereby forming a wide field region 310&#39; which was connected to the film 309 of the region 310 (FIG. 14(D)). 
     According to the method in Example 5, the electrodes 303 1  to 303 3  and the field region 310 can be formed by self-alignment, and the wide field region 310&#39; which was connected to the region 310 can be formed on the surface of the substrate 301. 
     Example 6 
     (i) The gate electrode 303 formed of an arsenic-doped polycrystalline silicon and the pattern 304 as a gate electrode material pattern were formed on the film 302 on the substrate 301. Then, with the electrode 303 and the pattern 304 as masks, n-type impurity ions such as arsenic ions were implanted, thereby forming n +  type impurity regions 305 which become source and drain regions (FIG. 15(A)). 
     (ii) Subsequently, with the resist pattern (not shown) as the mask, the portions of the pattern 304, the film 302 and the surface layer of the substrate 301 were etched and removed by reactive ion etching. At this time, the grooves 306 each having side surfaces formed substantially vertical and connected to each other were formed, thereby isolating the patterns 304, and forming the electrodes 303 1  to 303 3 . Simultaneously, the regions 305 were isolated, thereby forming n +  type source and drain regions 307. Subsequently, boron ions were implanted to the substrate 301 in the bottom of the grooves 306, thereby activating it and forming the p +  type field inversion preventing regions 308. Then, the film 309 was buried in the groove 306 in the same manner as that in Example 1, thereby forming the region 310 (FIG. 15(B)). 
     (iii) Then, the film 311 was accumulated on the overall surface, and a resist pattern 312&#39;, was formed on the film 311. With the pattern 312&#39; as a mask, the film 311 was selectively etched, and the substrate 301 formed with the source regions (or drain regions) 307 under the film 311 was etched to a predetermined depth (FIG. 15(C)). Subsequently, with the pattern 312&#39; as a mask, boron ions were implanted in the part of the etched substrate 301, thereby forming a p +  type field inversion preventing region 308&#39; (FIG. 15(D)). 
     (iv) Subsequently, the pattern 312&#39; was removed. Then, with the film 311 as an oxidation resistant mask, the film was treated in a high-temperature oxygen atmosphere, thereby forming a wide field region 310&#34; connected to the film 309 of the region 310 in the substrate 301 (FIG. 15(E)). 
     According to Example 6, the electrodes 303 1  to 303 3  and the region 310 can be self-aligned. The wide field region 310&#34; which is connected to the region 310, and which is substantially the same level as the surface of the substrate 301, can be formed on the substrate 301. 
     Example 7 
     (i) Grooves 402 1 , 402 2  each having a narrow width were first formed in a p-type silicon substrate 401 so that the extending directions of the grooves become perpendicular to each other (FIG. 16(A)). Subsequently, an oxidized film was grown by thermal oxidation on the surface of the substrate 401 which had grooves 402 1 , 402 2 . Further, an arsenic-doped polycrystalline silicon film was accumulated to sufficiently fill the grooves 402 1 , 402 2 . Subsequently, the polycrystalline silicon film was etched until the oxidized film on the surface of the substrate 401 was exposed, thereby leaving the polycrystalline silicon in the grooves 402 1 , 402 2 . Thus, a gate electrode 403 and a polycrystalline silicon pattern 404 were formed as the gate electrode material pattern in the grooves 402 1 , 402 2 . With the electrode 403 and the pattern 404 as masks, the oxidized film on the substrate 401 was removed, and a gate oxide film 405 was then formed. Thereafter, with the electrode 403 and the pattern 404 as masks n-type impurity ions such as arsenic ions were implanted in the substrate 401, thereby activating it and forming n +  type impurity regions 406 which become source and drain regions (FIG. 16(B)). 
     The regions 406 may also be formed by the steps of forming in advance an n +  type layer 406 2  on the overall surface of the substrate 401, as shown in FIG. 16(C), then forming the grooves 402 1 , 402 2  by etching. Then, growing the oxidized film, accumulating the polycrystalline silicon film and forming the electrode 403 and the pattern 404 by etching as described above. 
     (ii) Subsequently, with a resist pattern (not shown) as a mask, the portions over the substrate 401 formed with the regions 406, the pattern 404, the film 405 and the surface layer of the substrate 401 were selectively etched by a reactive ion etching, and removed. At this time the grooves 407 each have side surfaces formed substantially vertical and connected to each other were formed as shown in FIG. 16(D), thereby isolating the buried polycrystalline silicon pattern 404. Thus, the electrodes 403 1 , 403 2  were formed, and then n +  type impurity regions were also isolated, thereby form n 30  type source and drain regions 408. Subsequently, boron ions were implanted in the substrate 401 in the bottom of the grooves 407, the substrate 401 was thus activated, thereby forming p +  type field inversion preventing region 409. Then, the film 410 was accumulated on the overall surface to sufficiently fill the grooves 407 (FIG. 16(D)). 
     (iii) The film 410 was entirely etched with ammonium fluoride until the substrate 401, except the grooves 407 and the electrodes 403, 403 1 , 403 2 , were exposed. At this time, as shown in FIG. 16(E), CVD-SiO 2  remained only in the groove 407, thereby forming strip field regions 411 connected to each other. 
     According to the method in Example 7, the electrodes 403 1 , 403 2  and the region 411 can be formed by self-alignment. Further, the electrodes 403, 403 1 , 403 2  were buried in the substrate 401, and the region 411 was formed at the same level as the surfaces of the electrodes 403, 403 1 , 403 2 . Accordingly, after the formation of the region 411 the surface of the substrate 401 becomes flat. Consequently, when the wires of the source, drain and gates were formed after the accumulation of the interlayer insulating film and the opening of the contacting holes, the stepwise disconnection of the wire caused by the stepwise difference among the electrodes, substrate, field region and the substrate can be prevented. 
     In the Examples described above, the grooves were formed with the resist pattern as a mask. However, with an insulating film as a mask, the grooves may be formed as follows. In other words, as shown in FIG. 17(A), a polycrystalline silicon pattern as a gate electrode material pattern is formed on a gate insulating film 502 on a p-type silicon substrate 501, and an insulating film 503 is opened at portions where grooves are to be formed on the pattern. Then, with the film 503 as a mask, the polycrystalline silicon pattern, the gate insulating film and the surface layer of the substrate 501 were selectively etched, thereby forming grooves 504. Thus, the polycrystalline silicon patterns were isolated, thereby forming gate electrodes 505 1 , 505 2 . Subsequently, a p +  type field inversion preventing region 506 was formed on the part of the substrate 501 under the grooves 504. Then, a CVD-SiO 2  film 507 was accumulated on the overall surface of the film 503 so as to sufficiently fill the grooves 504 (FIG. 17(B)). Subsequently, the film 507 was etched with ammonium fluoride until the surface of the film 503 was exposed, thereby leaving CVD-SiO 2  in the grooves 504, so thereby form the field region 508 (FIG. 17(C)). 
     Further, only the film 503 was selectively etched and removed, and the height of the field insulating film 508 may remain higher than the surface of the electrodes 505 1 , 505 2  or the substrate 501, as shown in FIG. 17(D). The projections of the field insulating film 508 may be advantageous to compensate for the reduction in the thickness of the film in the later step and to complete the insulating effect of the film. 
     In the embodiments described above, the doping of the same conductive type impurity as the substrate was performed by implanting ions substantially vertical to the substrate. However, as shown in FIG. 18, p +  type field inversion preventing region 603&#39; may be formed not only on the p +  type field inversion preventing region 603 in the bottoms of the grooves 602 of the substrate 601, but also on the side surfaces of the grooves by obliquely implanting the ions, as well. 
     In the embodiments described above, the grooves were formed vertically or almost vertically to the substrate. However, the grooves need not always be formed like this, but may be formed as follows. 
     (a) As shown in FIG. 19(a), V-shaped grooves 602&#39; having an oblique angle θ at the side surfaces may be formed in the substrate 601. At this time, the thickness of the insulating film 604 to be accumulated is determined to be more than (a·[cot (θ/2)]/2), where the width of the opening of the groove 602&#39; is represented by a (FIG. 19(B)). 
     (b) As shown in FIG. 20, the groove 602&#34; having a flat bottom is formed in the substrate 601. At this time, the thickness of the insulating film to be accumulated is determined to (a·[cot (θ/2)]/2) in the same manner as the V-shaped groove as described above. 
     (c) As shown in FIG. 21, the groove 602&#39;&#34; having side surfaces formed of inclined curved surfaces is formed in the substrate 601. At this time, the thickness of the insulating film to be accumulated is determined to (a·[cot (θ/2)]/2) in the same manner as described above. 
     When the tapered grooves are thus formed, not only the bottom of the groove 602&#39; but the side surfaces of the groove may be simultaneously formed, for example, with a p +  type field inversion preventing region 603&#39; by implanting ions vertically from above, as shown in FIG. 22. In FIG. 22, reference numeral 601 designates a semiconductor substrate. 
     According to the present invention, the production of a defect in the substrate due to the microminiaturization of the field region and the elimination of the thermal oxidation of the semiconductor substrate for a long period of time can be prevented, and a method of manufacturing a semiconductor device which has high integration and high performance can be provided.