TW413946B - Semiconductor apparatus and method for manufacturing same - Google Patents

Abstract

A semiconductor device and a manufacturing method for the semiconductor device in which there is no defect such as deteriorated switching characteristics of a MOS transistor or long-term reliability of a gate oxide film, increased leakage current between a gate electrode and a silicon substrate or the deteriorated gate withstand voltage, otherwise produced due to excessive etching of a silicon oxide film in an outer trench rim neighboring to a device area to form a recess to expose the shoulder of a device area. In order to prevent this from occurring, a silicon oxide film spacer is provided on a sidewall section of an opening on a silicon substrate after an opening is formed in the silicon nitride film, in order to form a trench smaller in dismeter than the diameter of the opening in the silicon nitride film.

Description

413946 V. Description of the invention (1) Background of the invention. Field of the invention The present invention relates to a semiconductor device having a trench isolation structure for isolating and insulating active regions formed on a semiconductor substrate; and a method for manufacturing the same. _ Description of related technology In the device isolation technology of LSI, a trench separation structure is used, which is formed on the surface of a semiconductor substrate. A trench is set between the device areas and the trench is filled with an insulating film. Internal to achieve the purpose of isolation and insulation. This method of manufacturing the trench isolation structure is one of the important factors in that it does not deteriorate the performance or reliability of the device. However, the shape of the trench isolation formed by the conventional technique is to over-etch the silicon oxide film on the top of the trench near the shoulder of the device region to form a recess to expose the shoulder of the device region. In this trench isolation, there are problems related to the switching characteristics of the MOS transistor formed later or the long-term reliability of the gate oxide film, the leakage current between the gate electrode and the silicon substrate, or the breakdown voltage of the gate. . In order to deal with these problems, a method is disclosed in Japanese Patent Application Laid-Open No. 07-193083 to fill the grooves at the shoulders of the trench by subsequent steps; a device changing area is disclosed in Japanese Patent Application No. 09-321134. The method of carrier concentration in the center and shoulders is to ease the electric field concentration in the shoulders. 5a to 5d and FIGS. 6e to 6g will be described below, which are cross-sectional views showing a conventional manufacturing method of a semiconductor device step by step.

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'Firstly, as shown in FIG. 5a, a silicon oxide layer 21 is formed on the silicon substrate 21 by a thermal oxidation method to a thickness of 5 ~ 20nΠ1, and silicon nitride is formed thereon by a chemical vapor deposition method (ccvj)). The film 23 has a film thickness of 100 to 300 nm. Next, a photoresist pattern 24 is formed on a predetermined region to be a device region using a photolithography technique. Next, using a 'dry etching technique', the silicon nitride film 23 and the first silicon oxide film 22 are removed in this order by an anisotropic engraving. Next, as shown in FIG. 5b, a silicon nitride film 23 is used as a relief mask, and the silicon substrate 21 is etched anisotropically to form a trench 25. If the anisotropic dry etching is performed using a gas mixture of C F 4 and Η B r, the selection ratio of dream to silicon nitride or silicon oxide film is on the order of 10. The remainder is performed so that the trench 25 will be 150 to 500 nm deep. Next, as shown in FIG. 5c, a second silicon oxide film 26 is formed on the inner wall of the trench 25 by a thermal oxidation method. The purpose of thermal oxidation is to remove damage on the inner wall surface of the trench 25 caused by dry etching. In this way, it is appropriate that the thickness of the oxide film ranges from 10 to 30 nm. The silicon nitride film 23 is then used as an oxidation prevention film so that the device region on the surface of the substrate 21 is not oxidized. Next, as shown in Fig. 5d, a third silicon oxide film 27 is formed on the entire surface using a CVD method. The thickness of the formed film depends on the depth of the trench 25, the thickness of the first silicon oxide film 22, and the thickness of the silicon nitride film 23. The thickness of the third silicon oxide film 27 is determined such that the third silicon oxide film The film thickness of 27 is substantially equal to the sum of the depth of the trench 25, the film thickness of the first silicon oxide film 22, and the film thickness of the gasification fragment 23. The inside of the trench 25 is completely filled with a third silicon oxide film 27. Next, as shown in FIG. 6e, the third step is to use the chemical mechanical polishing (cjjp) method

413946 V. Description of the invention (3) ^ Silicon film 27 is polished. This polishing is performed until the third silicon film 27 of the silicon nitride film 23 丄 is completely removed, so that the surface of the silicon nitride film 23 is exposed. However, the polishing time needs to be adjusted so that the silicon nitride film 23 is not completely removed. In this case, the opening width χ3 in the fossil evening film 23 is larger than the opening width 2 of the trench 6. This is because the second silicon oxide film 26 is formed on the inner wall of the trench which is equal to the opening width of the vaporized silicon film 23 by a thermal oxidation method. When the silicon surface is thermally oxidized, the silicon surface is reduced by a distance equivalent to half the oxide film. If the film thickness 2 of the second silicon oxide film 26 in this structure is 30 nm, then when compared with the opening width χ3 of the silicon nitride film 23, one side of the channel width will increase by about 1511111, and the channel and groove collision degree Both sides of the silicon nitride film are increased by 30 ηπ ^. Then, as shown in FIG. 6f, the silicon nitride film 23 is selectively removed by using a phosphoric acid solution heated to about 50 °. The inside of the trench 25 is filled with the second silicon oxide film 26 and the third :: film 27 so that only the third silicon oxide film 27 protrudes on the surface of the broken substrate 21. On the surface of the broken substrate 21 / film 2 = the width of one side of the third oxygen cut film 27 on ... 21 is narrower than the width of the trench 25 by z3. Next, as shown in FIG. 6g, the first film 22 is engraved and removed using a hydrofluoric acid solution. Then, the main farm worker L T Meng ... J 2 Γ heats the device region on the surface of the broken substrate 2i by 30 nm. The film thus formed was then removed by a hydrofluoric acid solution. During the wet #etching process, the third oxide film 27 on the n plane of the ΐ i 3 λ plate was also removed by money engraving, so that the survivability of the second silicon oxide film 27 was reduced to be close to that of the silicon substrate 21 Surface of / X. ° In-depth study of the process of the present invention · 413946 V. Description of the invention (4) ~ • When to etch the third oxide of sand with this wet etching process? 7. During the middle part, the dogs are on the inner wall of the trench and the silicon film 27 with a distance of z3. Therefore, in this case, if the third oxide Mengqi 27 on the wet plate ^ with no protruding portion 21 has been engraved to the preset ', the first one protruding from the inside of the Mengji trench 2 The top of the silicon oxide film 26 is also immediately carved into the ground until the recess 28 is finally formed. As shown in FIG. 6 g, the shoulder 29 is formed in the device region formed on both sides of the trench 25. SUMMARY OF THE INVENTION In the shoulder 29 of a semiconducting device formed by a conventional method, the electric field tends to be concentrated, so that if the recess 28 is formed in the trench 25, a switch of the M0S transistor thus formed is generated Deterioration of characteristics or long-term deterioration of gate oxide film. In addition, 'the leakage current between the gate electrode and the dream substrate tends to increase' or the gate withstand voltage tends to deteriorate. In view of the above-mentioned problem, an object of the present invention is to provide a semiconductor device and a method of manufacturing the same, in which it is possible to prevent the formation of a recess on the surface of a silicon oxide film buried in a trench surface or the deterioration of the switching characteristics of a MOS transistor thus formed. Another object of the present invention is to prevent deterioration of the long-term reliability of the gate oxide film, increase of leakage current between the gate electrode and the Shixi substrate, or deterioration of the withstand voltage of the gate. Other objects of the present invention will become clearer from the contents of the entire specification. In order to accomplish the above object, the present invention provides a device in which the diameter of the trench is smaller than the opening in the first insulating film, by forming a first insulating film on a semiconductor substrate (such as a silicon nitride film 3 in FIG. 1C). ); Then on the first insulating film

Page 8 413946 V. Description of the invention (5) A second insulating film is formed on the inner wall (such as the silicon oxide film 5 in the circle lc); and then the openings provided by the first and second insulating films are used as light The trench is formed by using a mask, or the trench is formed by using only the opening of the first insulating film (such as the silicon nitride film 1 3 in FIG. 3 c) as a photomask, and then forming a trench on the inner wall of the trench. Crystal layer (such as the silicon epitaxial layer 16 in Figure 3c). More specifically, the device of the present invention has the following characteristics: In a first embodiment, the present invention provides a method for manufacturing a semiconductor device having a trench in a substrate. The method includes: forming a substrate having a preset on the substrate; A first insulating film having openings; a second insulating film disposed on an inner wall of the opening in the first insulating film; and a trench formed by using the opening provided in the second insulating film beside the first insulating film as a photomask. ΐ In a second aspect, the present invention provides a method for manufacturing a semiconductor device having a trench in a substrate, comprising: forming a first insulating film having a predetermined opening on the substrate; and using the first insulating film The openings are used as a photomask to form a trench; a worm crystal layer is formed by depositing on the inner wall of the trench; and a second insulating film is disposed on the inner wall of the epitaxial layer. The present invention also provides a method for manufacturing a semiconductor device, including the following steps: a) continuously forming a first silicon oxide film 2 and a silicon nitride film 3 on a silicon substrate; b) performing a photo-etching step on the first silicon oxide film 2 Forming openings in the silicon nitride film 3; c) disposing a silicon oxide film spacer 5 on the sidewall of the opening in the silicon nitride film 3; d) using the silicon nitride film 3 and the silicon oxide film spacer 5 as Photomask to form the trench 6; e) forming a third silicon oxide film 7 on the inner wall of the trench 6; f) burying a fourth silicon oxide film 8 into the interior of the trench 6; g) removing silicon nitride Films 3 and 1) Remove the third silicon oxide film 7 and the fourth silicon oxide protruding from the substrate

Page 9 413946 V. Description of the invention (6) Membrane .8. It is stated that the formula is β: Section ~ 1; Example of a horizontal channel forming a ditch. The first example of the Mingfa is based on the display: Step J Figure surface according to the display according to the instructions. Step by step ® for δ for Id ~ 2 horizontal? θ & 2 ^ 3 Illustration of the shape of the grooves El,-'^, -'Μ / Shi Shi Shi Shi 11 CSI second continuation of Yan Mingming's Mingfa dfa 1 * ~ Examples of this form of ditch 2 The first copy of the original version is displayed. Step by step f87 S is the cross section of the horizontal T -C? E 4 method chart into the sound I horizontal 4 ^ 5 method chart into the map is shown in the figure 3 shows the map is shown in the figure. The method of horizontally extending the method d into 3 to a shape of a ditch is shown in the figure. Continued 6g d e- 6 d Figure 5 ί a 5 Illustrated | Say one-g-3 # Fuban based silicon film oxygenated film diaphragm film sand picture broken 1 resistance ditch: the second photo-oxygen channel No. i lii one by one 2 3 4 5 6 7 8 Xihan dagger / 1/1 oxygen oxygen page 10 413946 5. Description of the invention σ) 1 1 ~ silicon substrate 1 2 ~ first silicon oxide film 1 3 ~ Silicon nitride film 1 4 to photoresist pattern 1 5 to trench 16 6 to epitaxial silicon layer 17 to 2nd insulating film. 1 8 to 3rd silicon oxide film 2 1 to silicon substrate 2 2 to 1st oxidation Silicon film ~ 2 3 ~ Silicon nitride film < 2 4 ~ Photoresist pattern 2 5-Trench 2 6 ~ Second silicon oxide film 2 7 ~ Third silicon oxide film 28 ~ Four parts 2 9 * Best implementation of shoulder DETAILED DESCRIPTION OF EXAMPLES The invention will be described below with reference to preferred embodiments. When using a silicon nitride film with a predetermined opening formed in a silicon substrate (3 in FIG. 1c) as an etching mask to form a trench, the method for manufacturing a semi-'conductor device according to the present invention is preferred. In the embodiment, a silicon oxide film separator (5 in FIG. 1 c) is disposed on the inner wall of the opening of the silicon nitride film.

Page 11 V. Description of the invention (8) In addition, a trench is formed by using a silicon nitride film (3 in FIG. 1c) with a predetermined opening formed on a silicon substrate as an etching mask (15 in FIG. 3c). Then, a silicon epitaxial layer is formed on the inner surface of the trench (16 in FIG. 3c). In order to further explain the above embodiments of the present invention, referring to FIG. 4, several examples of the present invention are shown in the order of process steps. Embodiment 1 FIGS. 1a to 1d and 2e to 2h are cross-sectional views showing a first embodiment of the present invention step by step. Meanwhile, FIG. 1 and FIG. 2 are separated for convenience of explanation. First, as shown in FIG. 1a, a first silicon oxide film 2 is formed on a silicon substrate 1 by a thermal process to a thickness of 5 to 20 nm, and nitrided by a chemical vapor deposition (CVD) method. A silicon film 3 is formed thereon to a film thickness of 100 to 300 ηπ. Next, a photoresist pattern 4 is formed in a predetermined region which will be a device region using a photolithography technique. Next, using a dry etching technique, the The silicon nitride film 3 and the first silicon oxide film 2 are anisotropically etched in this order. Then, the photoresist pattern 4 is stripped by an oxygen electrode; as shown in FIG. 1b. Then a first film is formed on the entire surface. 2 silicon oxide film. This second silicon oxide film is anisotropically etched back to leave the silicon oxide film separator 5 on the side wall of the opening of the silicon nitride film 3. It should be noted that the second oxide The film thickness of the silicon film needs to be set to a thickness that does not completely bury the openings of the silicon nitride film 3. That is, the film thickness of the silicon oxide film (the degree must be larger than the most in the range of the openings of the silicon nitride film 3). The width of the narrow part is half thin. For example, if the width of the narrowest opening is 0. 2 # m, that is 2 0 0

Page 12 413946 V. Description of the invention (9) nm. The thickness of the second silicon oxide film needs to be thinner than 1'0 0 nm, which is half of the opening width. That is, the thickness of the second silicon oxide film is preferably 30 to 80 nm. Next, as shown in FIG. 1 c, the silicon substrate 1 is anisotropically etched using the silicon nitride film 3 and the silicon oxide film spacer 5 as an etching mask to generate a trench 6. For example, if an anisotropic dry etching is performed using a mixed gas of CF4 and ㈣! &Quot;, the selection ratio of silicon to the silicon nitride film or the silicon oxide film can be obtained at about 10 degrees. The etching at this time makes the trench 6 to a depth of 150 to 500 nm. Next, as shown in FIG. 1D, a third silicon oxide film 7 is formed on the inner wall surface of the trench 6 using a thermal oxidation method. The purpose of thermal oxidation is to remove the damage caused by dry etching on the inner wall surface of the trench 6. Therefore, a thin oxide film is desirable. For example, the thickness of the oxide film is in the order of 10 to 30 nm, as required. Even if it is thick, the thickness of the oxide film needs to be thinner than twice the film thickness of the second silicon oxide film thus formed. Since the silicon nitride film 3 serves as an oxidation-resistant surface, the device region on the silicon substrate 1 is not oxidized. Next, as shown in Fig. 2e, a CVD method is used to form a fourth silicon oxide film 8 over the entire surface. The thickness of the formed film depends on the depth of the trench 6, the film thickness of the first silicon oxide film 2 and the film thickness of the silicon nitride film 3. The film thickness of the fourth silicon oxide film 8 is set to be approximately equal to the sum thereof. The inside of the trench 6 is completely filled with a fourth silicon oxide film 8. Then, the fourth silicon oxide film 8 is polished by the CMP method, as shown in FIG. This polishing is performed until the fourth silicon oxide film 8 on the silicon nitride film 3 is completely removed, so that the surface of the silicon nitride film 3 is exposed. Adjust the grinding time so that nitriding

Page 13 413946 V. Description of the Invention (Shi). Film 3 has not been completely removed. At this time, the opening width χ of the silicon nitride film 3 is wider than the width yl of the trench 6. This is because when the trench 6 is formed by the dry etching technique, the silicon oxide film spacer 5 is formed in advance on the inside of the opening in the silicon nitride film 3. Next, the phosphoric acid silicon film 3 is selectively removed using a phosphoric acid solution heated to about 150 ° C, as shown in Fig. 2g. The inside of the trench 6 is filled with the third silicon oxide film 7 and the fourth silicon oxide film 8 so that the silicon oxide film separator 5 and the fourth silicon oxide film 8 protrude out of the surface of the silicon substrate 1. 'A first silicon oxide film 2 is left on the surface of the device region. The first oxidized oxide film 2 'protruding on the silicon substrate 1 protrudes on the device region by a distance exceeding the width ζm of the trench 6. Next, as shown in FIG. 2h, the first silicon oxide film 2 is etched away using a hydrofluoric acid solution. The device region on the surface of the silicon substrate 1 is thermally oxidized 'in the thickness range of 10 nm to 30 nm to form a thermal oxide film, which is then removed by etching with a hydrofluoric acid solution. During the wet etching process, the silicon oxide film protruding from the surface of the hard substrate 1 was also removed by etching to reduce the height to about the same as the surface of the broken substrate 1. In the first embodiment, the fourth silicon oxide film 8 and the dream film spacer 5 protruding on the silicon substrate 丨 protrude on the placement area by a distance exceeding the width ζΐ of the trench 6 so that when When the wet etching process will highlight the part, there is no risk that only the third oxidized bismuth on the inner wall of the trench is exposed to the surname engraving in the comparative phase, so that it is not as accurate as the conventional technique, and a recess is formed. Henu in the shape of the top of the trench Example 2

Page 14 413946 V. Description of the invention The following steps show the convenience of opening holes in the inner wall of the first hole with a broken silicon crystal silicon substrate 1 1 well-known light 13 and oxidation to explain the second example of the present invention . S3a ~ 3d, the cross section circle 4h of the second embodiment of the invention, and divides Figs. 3 and 4 into 囷 33 ~ 3 (1 and "~ #. In order to say the month 1 embodiment, The baffle is vaporized to form a channel with a diameter smaller than that of the second channel for gasification. In the second embodiment, the growth structure of the above-mentioned diameter is formed in the interior of the channel. 12 and a silicon nitride film 13 are formed on the same as in the above-mentioned first embodiment. Next, openings are formed in the silicon nitride film silicon film 12 by using a publicly-etched technique and a dry etching technique ~. After the photoresist pattern 14 is stripped from the oxygen plasma, a silicon nitride film i 3 is used as an etching mask to etch the silicon substrate anisotropically to form a trench 5. If a gas mixture of CL and HBr is used Performing the anisotropic dry type # jjJ 'will get the selection ratio of silicon to silicon argon or silicon oxide film in the order of 〇. At this time, the etching is performed so that the depth of the trench 15 is 150 nm to 500 nm. Then "as shown in Fig. 3c", using an ultra-high vacuum CVD apparatus, silicon is grown on the inner wall of the trench 15 by selecting the vermicular crystal growth. In order to form an epitaxial silicon layer at 16 °, since the selective growth method is used in this process, the epitaxial silicon layer only grows in the area where the silicon is exposed, that is, in the interior of the trench. The thickness of the silicon film depends on the opening width of the trench 15. If the narrowest part of the opening _ is 0.2 2 m, that is, 20 nm, the thickness of the silicon film obtained by epitaxial growth is the largest. Fortunately, it is thinner than 100nm, which is half of the opening width. For example,

Page 15 413946 V. Description of the invention (12) Such as ‘30 ~ 80nm.成 于 3 于 于 ϊ: showing that the second insulating film 17 is formed on the ##, 部 的 的 ㈠ layer 16 by a thermal oxidation method. The thickness of the oxygen oxide is U = f ^ and the thickness of 疋 is the thinnest than the complete epitaxial silicon layer]. Since the dream film 13 serves as an anti-oxidation film, the device region on the f substrate 11 is not oxidized. The receiver 'uses a CMP method in which a siliconized film 18 is formed on the entire surface as in the first embodiment-a third oxygen is filled into the trench! internal. In order to completely use the third oxide film 18 to 18S, the CMP method is as described in the embodiment. At the third silicon oxide = polishing, until the surface of the hafnium nitride 13 is exposed, as shown in this figure, this is narrowed. : The growth of nitrogen causes the width of the trench 15 to be wide. The opening width X2 of the film 13 is larger than the width y2 of the trench 15. Next, as shown in FIG. 4g, the silicon nitride film 13 is selectively removed by using a film holding solution as described in the first embodiment. Fill the inside of the trench 15 with the first and second dielectrics, windows, and silicon films, and leave the second insulation on the surface of the device area. Protrude to the device area by a distance exceeding the width z 2 of the trench i 5: as shown in FIG. 4 /, using the hydrogen acid solution of the first embodiment, the silicon oxide film 12 is removed by etching. Thermally oxidize the silicon substrate with a thickness of JOrun ~ 30nra on the surface to form a thermal oxide film area

413946 V. Description of the invention (13) ^ It is removed by etching with a hydrogen I acid solution. During the wet etching process, the silicon oxide film protruding on the surface of the silicon substrate is etched equal to the height of the surface of the hair substrate 11. 2 In the second embodiment, the same as the first embodiment, the third oxidation protruding from the silicon substrate 11; ε Xiqi 18 and the second insulating film 17 is a distance exceeding the width 22 of the trench 15 , As shown in Figure 4g. Therefore, when a part of the button is removed by a wet etching process, only the part of the ϋ insulating film on the inner wall of the trench is exposed to the risk of etching in the early stage, which is not as known in the art. A recess is formed at the top of the groove. As described above, the present invention provides the following first effect of the present invention: after openings are formed in the thermally oxidized film and nitride hafnium on the substrate in a sequential shape by a photolithography process, and An oxide film barrier is formed on the side wall of the opening in the film, so the subsequent cross-section of the shape of the subsequent filling of the film filling is as shown in Figure 2f, that is, in the nitride film The width of the opening is larger than the width of the trench in the silicon nitride film, that is, the silicon oxide film protruding inside the trench is wider than the trench. Also, when the next step is to use the wet button engraving process, it will be highlighted in Shi Xi :: j κ: because of the rest of the time,… Department; ΐ: The outer edge part is excessively external.丨 is formed to prevent the shoulders of the placement area from being exposed. By this trench isolation, it is possible to prevent the formation of the mos transistor.

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Η 413946 V. Description of the invention (14) Switching characteristics deteriorate. In addition, it is possible to prevent the long-term reliability of the gate oxide film from deteriorating, prevent leakage current between the gate electrode and the silicon substrate, and prevent deterioration of the withstand voltage of the gate. 4 It should be noted that the specific embodiment mentioned in the detailed description of the preferred embodiment is only for easy explanation of the technical content of the present invention, and does not limit the present invention to the embodiment in a narrow sense. In addition, without departing from the spirit of the present invention and the scope of the following patent applications, various changes can be made without exemption.

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Claims (1)

Page 19 1999.06.28.019 Page 19, 1999. 06.28.019 413946 Amendment No. 88103918 6. Scope of patent application a) The first silicon oxide film 2 and the silicon nitride film b are continuously formed on a silicon substrate. B) Through the photo-etching step in the first An opening is formed in the silicon oxide film 2 and the silicon nitride film 3; c) a silicon oxide film spacer 5 is arranged on the sidewall of the opening in the silicon nitride film 3; d) the silicon nitride film 3 is used with The silicon oxide film separator 5 is used as a photomask to form a trench 6; e) a third silicon oxide film 7 is formed on the inner wall of the trench 6; f) a fourth silicon oxide film 8 is buried inside the trench 6 G) removing the silicon nitride film 3; and h) removing the third silicon oxide film 7 and the fourth silicon oxide film 8 protruding from the substrate @@: = 丨 The manufacturing method of the bulk device includes the following steps: a ) Forming a first silicon oxide film 12 and a silicon nitride film 13 on a silicon substrate continuously; b) forming an opening in the first silicon oxide film 12 and the silicon nitride film 13 by a photo-etching step; C) using the first silicon oxide film 12 and the silicon nitride film 13 as a photomask to form a trench 15; d) forming a roof crystal sand layer 16 by depositing on the inner wall of the trench; e) at The Lei A second insulating film i 7 is arranged on the inner wall of the crystalline silicon layer 16; f) a third silicon oxide film 18 is buried inside the trench 15; g) the silicon nitride film JJ is removed; and 1999. 06.28. 020 88103918 Year of the shirt < Month > g said correction_ VI. Patent application scope h) Remove the first silicon oxide film JJ and the first silicon oxide film JJ protruding from the substrate. 7. A semiconductor device having a trench in its substrate, wherein: the trench is provided by using a silicon nitride film and a silicon oxide film separator as a photomask, wherein the silicon nitride film is formed on the substrate On the substrate with preset openings; and the silicon oxide film separator is arranged on the inner wall of the silicon nitride film; the silicon oxide film is filled into the interior of the trench; and in it-the trench is filled The surface of the silicon oxide film of the groove is not provided with a recess. 8. A semiconductor device comprising a trench formed by using a silicon nitride film with a predetermined opening formed on a substrate as a photomask, wherein: a silicon epitaxial layer is provided on an inner wall of the trench , + A silicon oxide film is filled into the interior of the trench; and no recess is provided on the surface of the silicon oxide film filled in the trench. Page 2 1999.06, 28.021