JP2005347565A - Semiconductor device and method for manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve a breakdown strength characteristics by relaxing the electric field strength near the surface of an element. <P>SOLUTION: In a semiconductor device, using an insulating area buried in the surface area of a semiconductor substrate 31 as an element breakdown strength part, a plurality of trenches are formed on the semiconductor substrate 31, a thermal oxidation film 37 is formed on the side faces and bottom of each trench by thermal oxidation, in a state that a gap to be a slit 38 is left on the center of the trench, and a semiconductor between adjacent trenches is completely oxidized. At least the apertures of the gaps left on the center of respective trenches are covered with an HTO film 39. The thermal oxidation film 37 is buried in a space between a source electrode 61 and a drain electrode 62 which are separately formed on the surface of the substrate 31 by using the substrate 31; and one or more slits 38 having a dielectric constant smaller than that of the thermal oxidation film 37 are formed in the thermal oxidation film 37 to manufacture the semiconductor device. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor device using an insulating region embedded in a surface region of a semiconductor substrate as an element breakdown voltage portion and a method for manufacturing the same.

  In recent years, devices using a trench itself formed in a semiconductor substrate as a functional element, such as a trench gate MOSFET (insulated gate field effect transistor) and a trench lateral device, have attracted attention. As one of such devices, a three-dimensional insulating region is formed by embedding a trench having a depth of about 20 μm formed in a silicon semiconductor substrate with an oxide, and the outer periphery of the insulating region is used as an extended drain region. Is known (for example, see Patent Document 1).

  In the device described above, the element is not formed on the surface of the semiconductor substrate as in the conventional lateral MOSFET, but the element is formed around the trench, so that the element size can be reduced and the on-resistance can be reduced. There is an advantage that can be achieved. Further, since the power element portion is manufactured on one side of the semiconductor substrate, there is an advantage that a high-functional device in which the power element and the control IC are integrated can be manufactured. In a power element such as a normal IGBT (insulated gate bipolar transistor) or MOSFET, electrodes are formed on both the front surface and the back surface of the semiconductor substrate, so that integration with a control IC is difficult.

  Next, a conventional method for manufacturing the above-described device will be described. 20 to 23 are longitudinal sectional views showing structures in the process of manufacturing a semiconductor device using a conventional trench itself as a functional element. These drawings show the structure of the semiconductor device in a cross section corresponding to the line A-A ′ in FIG. 7 showing a mask pattern of a resist mask for trench etching, for example. However, only two trenches are shown in order to avoid the figure becoming complicated.

  First, as shown in FIG. 20, a thermal oxide film having a thickness of 800 nm is formed by thermal oxidation on the surface of a p-type silicon semiconductor substrate 1 having a sheet resistance of about 100 Ωcm. And after apply | coating a photoresist on this thermal oxide film, exposure and image development are performed using the mask which is not shown in figure, and the resist mask 3 is formed.

This resist mask 3 has a pattern in which a plurality of island regions having a length of 1.4 μm in a direction parallel to the drawing in FIG. 20 (hereinafter referred to as Y direction) are arranged at intervals of 1.4 μm. Using this resist mask 3 as a mask, anisotropic dry etching is performed using a mixed gas of CHF ₃ , CF ₄ and Ar, and a part of the thermal oxide film is removed to form a hard mask 4.

Next, as shown in FIG. 21, anisotropic dry etching is performed using the hard mask 4 as a mask and a mixed gas of Cl ₂ and O ₂ , and in FIG. 21, a direction perpendicular to the drawing (hereinafter referred to as the X direction). ) Is 20 μm, and a plurality of trenches 6 having a depth direction (hereinafter referred to as Z direction) length of 20 μm are formed. Subsequently, isotropic etching is performed using a mixed gas of CF ₄ and O ₂ to remove the protective film on the trench side wall generated during the trench etching and round the corners of the trench.

  At this time, the width of the upper end of a semiconductor portion (hereinafter referred to as a silicon pillar) 5 remaining between adjacent trenches 6 is adjusted to be approximately 1.4 μm. Further, it is desirable that the angle of the trench side wall is inclined at about 89 ° with respect to the substrate surface so that the width of the trench 6 becomes narrower from the opening end of the trench toward the bottom.

Subsequently, in FIG. 21, phosphorus ions are implanted in an oblique direction from the upper front side to the lower rear side of the drawing. Further, in FIG. 21, phosphorus ions are implanted in an oblique direction from the upper rear side to the lower front side of the drawing. The angle formed by the two ion implantation directions and the normal direction of the substrate surface (that is, the side surface of the trench 6) is approximately + 44 ° and −44 °. The ion implantation amount is, for example, 1 × 10 ¹² cm ⁻² .

Subsequently, phosphorus ions are implanted from a direction perpendicular to the substrate surface, that is, a direction of 90 ° with respect to the bottom surface of the trench 6. In this ion implantation, phosphorus ions are implanted only at the bottom of the trench 6. If the ion implantation amount at this time, for example, ^{7 × 10 11 cm -2, n} - can be made uniform surface concentration of phosphorus ions in the surrounding of the offset drain region. Subsequently, driving is performed so that the diffusion depth xj of phosphorus ions is about 5 μm, for example, to form an n ⁻ offset drain region.

  Next, as shown in FIG. 22, the silicon substrate 5 is completely oxidized by exposing the semiconductor substrate 1 to a water vapor atmosphere at 1100 ° C. for about 10 hours. By this oxidation treatment, all the silicon pillars 5 become silicon oxides (hereinafter referred to as silicon oxide pillars). At that time, due to expansion when silicon becomes silicon oxide, adjacent silicon oxide pillars completely fill and integrate the trenches 6 between them. Moreover, the silicon oxide pillars at both ends completely fill the trench 6 between them due to their own expansion and expansion due to the oxidation of the semiconductor substrate 1 on the outside.

  Finally, as shown in FIG. 23, the silicon oxide on the silicon surface is removed by CMP (chemical mechanical polishing). Thus, the oxide bulk 7 that is long in the Y direction is embedded in the semiconductor substrate 1. Next, various semiconductor regions, electrodes, and the like are formed on the semiconductor substrate 1 by a known method.

FIG. 24 is a longitudinal sectional view showing the structure of a lateral type high withstand voltage trench power MOSFET manufactured by applying the manufacturing method described above. In FIG. 24, reference numeral 11 denotes a p semiconductor layer, which corresponds to the semiconductor substrate 1 in the description of the conventional manufacturing method described above. Reference numeral 12 denotes a p-well layer. Reference numeral 13 denotes an n-well layer. Reference numeral 14 denotes an n ⁻ offset drain region.

Reference numeral 15 denotes a uniform insulating region, which corresponds to the oxide bulk 7 in the description of the conventional manufacturing method described above. Reference numeral 16 denotes a p-channel region. Reference numeral 17 denotes an n ⁺ semiconductor region serving as a source region. Reference numeral 18 denotes an n ⁺ semiconductor region serving as a drain region. Reference numeral 19 denotes a gate insulating film. Reference numeral 20 denotes a gate electrode. Reference numeral 21 denotes a source electrode. Reference numeral 22 denotes a drain electrode. The withstand voltage value of the trench lateral MOSFET actually manufactured according to the manufacturing method described above was 510V.

JP-A-8-97411

However, in the conventional semiconductor device manufactured as described above, the electric field strength near the surface tends to increase as shown in FIG. 25 with its potential distribution and breakdown point (portion surrounded by a circle). In many cases, the breakdown voltage is regulated by the gate or drain provided near the surface. In order to increase the breakdown voltage, it is necessary to improve the potential distribution by introducing electric lines of force to the extended offset drain region (n ⁻ offset drain region) 14 at the bottom of the insulating region 15 and to relax the electric field strength near the surface. .

  In order to eliminate the above-described problems caused by the prior art, the present invention reduces the electric field strength near the surface of the element in the semiconductor device using the insulating region embedded in the surface region of the semiconductor substrate as the element withstand voltage portion. It is an object of the present invention to provide a semiconductor device having high breakdown voltage characteristics and a method for manufacturing the same.

  In order to solve the above-described problems and achieve the object, a semiconductor device according to a first aspect of the present invention includes a first electrode and a second electrode which are provided apart from each other on a surface of a semiconductor substrate, and the semiconductor substrate. An insulating region embedded in a surface region between the first electrode and the second electrode, and one or more slits provided in the insulating region, wherein the slit comprises the insulating material. It has a smaller dielectric constant than the material constituting the region.

  A semiconductor device according to a second aspect of the present invention is the semiconductor device according to the first aspect, wherein the slit has a width of 1 μm or less.

  A semiconductor device according to a third aspect of the present invention is the semiconductor device according to the second aspect, wherein the slit has a width of 0.1 μm or more.

  A semiconductor device according to a fourth aspect of the present invention is the semiconductor device according to any one of the first to third aspects, wherein the slit is in a high vacuum state.

  A semiconductor device according to a fifth aspect of the present invention is the semiconductor device according to any one of the first to third aspects, wherein the slit is filled with a material having a dielectric constant smaller than a material constituting the insulating region. It is characterized by.

  A semiconductor device according to a sixth aspect of the present invention is the semiconductor device according to any one of the first to fifth aspects, wherein the insulating region is in contact with the semiconductor substrate in a cross section including the slit and parallel to the slit. The thickness of the portion is 1 μm or more.

  A semiconductor device according to a seventh aspect of the present invention is the semiconductor device according to any one of the first to fifth aspects, wherein the insulating region is in contact with the semiconductor substrate in a cross section including the slit and parallel to the slit. The thickness of the portion is 1.5 μm or more.

  A semiconductor device according to an invention of claim 8 is the semiconductor device according to claim 6 or 7, wherein a thickness of a portion of the insulating region in contact with the semiconductor substrate in the cross section including the slit and parallel to the slit is 5 μm or less.

  According to a ninth aspect of the present invention, in the semiconductor device according to the fifth aspect, the material forming the insulating region is a nitride, and the material filling the slit is a silicon oxide. And

  According to the first to ninth aspects of the present invention, in the insulating region embedded in the surface region between the first electrode and the second electrode of the semiconductor substrate, the dielectric constant is higher than the material constituting the insulating region. Since one or more small slits are provided, electric lines of force are concentrated in the slits, and the electric field is increased at the bottom of the insulating region. Therefore, the electric field strength near the surface of the element is relaxed and the withstand voltage is increased. According to the invention of claim 4 or 5, when the electric field is concentrated in the slit, there is a risk that reliability may be lowered due to fixed charges at the interface portion or polarization in the residual gas, but this can be avoided. it can.

  In order to solve the above-described problems and achieve the object, a semiconductor device manufacturing method according to a tenth aspect of the present invention includes a first electrode and a second electrode which are provided apart from each other on the surface of a semiconductor substrate. When manufacturing a semiconductor device in which one or more slits having a dielectric constant smaller than the material constituting the insulating region are provided in the insulating region, a plurality of trenches are formed in the semiconductor substrate. The side surface and the bottom surface of the trench are thermally oxidized with the first step to be formed and a gap serving as a slit remaining in the central portion of the trench, and the semiconductor portion between the adjacent trenches is completely thermally oxidized. A second step and a third step of closing at least the opening of the gap remaining in the central portion of the trench.

  According to an eleventh aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to the tenth aspect of the present invention, wherein, in the first step, the gap remains with a width of 1 μm or less when the second step is completed. In addition, a plurality of trenches are formed.

  According to a twelfth aspect of the present invention, in the semiconductor device manufacturing method according to the eleventh aspect of the present invention, in the first step, the gap has a width of 0.1 μm or more when the second step is completed. A plurality of trenches are formed so as to remain.

  A method of manufacturing a semiconductor device according to a thirteenth aspect of the invention is characterized in that, in the invention according to any one of the tenth to twelfth aspects, the inside of the slit is in a high vacuum state.

  According to a fourteenth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to any one of the tenth to twelfth aspects of the present invention. It is characterized by filling with a small material.

  A method of manufacturing a semiconductor device according to a fifteenth aspect of the present invention is the method according to any one of the tenth to fourteenth aspects, wherein in the second step, the cross section includes the gap and is parallel to the gap. Thermal oxidation is performed so that a thickness of a portion of the thermal oxide film in contact with the semiconductor substrate becomes 1 μm or more.

  According to a sixteenth aspect of the present invention, there is provided a method for manufacturing a semiconductor device according to any one of the tenth to fourteenth aspects, wherein, in the second step, the cross section includes the gap and is parallel to the gap. Thermal oxidation is performed so that a thickness of a portion of the thermal oxide film in contact with the semiconductor substrate becomes 1.5 μm or more.

  According to a seventeenth aspect of the present invention, in the semiconductor device manufacturing method according to the fifteenth or sixteenth aspect, in the second step, the thermal oxide film in a cross section including the gap and parallel to the gap is provided. The thermal oxidation is performed so that the thickness of the portion in contact with the semiconductor substrate is 5 μm or less.

  A method for manufacturing a semiconductor device according to an invention of claim 18 is the invention according to any one of claims 10 to 17, wherein the side surface of the trench and the side of the trench are provided after the first step and before the second step. The method further includes a fourth step of implanting impurity ions into the bottom surface.

  According to invention of Claims 10-18, it is more dielectric than a thermal oxide film in the insulation area | region which consists of a thermal oxide film embedded in the surface area | region between the 1st electrode and 2nd electrode of a semiconductor substrate. A semiconductor device having one or more slits with a low rate is obtained. In this semiconductor device, the electric field lines concentrate in the slit and the electric field is increased at the bottom of the insulating region, so that the electric field strength near the surface of the element is relaxed and the withstand voltage is increased. According to the invention of claim 13 or 14, when the electric field is concentrated in the slit, there is a risk that reliability may be reduced due to fixed charges at the interface portion or polarization in the residual gas, but this can be avoided. it can. According to the invention of claim 18, the offset drain region is formed around the insulating region.

  According to a nineteenth aspect of the present invention, there is provided a method of manufacturing a semiconductor device, wherein an insulating region is embedded between a first electrode and a second electrode which are provided apart from each other on a surface of a semiconductor substrate, and constitutes the insulating region. In manufacturing a semiconductor device in which one or more slits having a dielectric constant smaller than that of the material are provided in the insulating region, a first step of forming a plurality of trenches in the semiconductor substrate and a gap in the central portion of the trenches A second step of thermally oxidizing the side and bottom surfaces of the trench while leaving a gap, and completely thermally oxidizing a semiconductor portion that becomes a slit between adjacent trenches, and the gap remaining in the central portion of the trench. And a third step of filling with a material having a dielectric constant larger than that of the thermal oxide film generated by the second step.

  According to a twentieth aspect of the present invention, in the semiconductor device manufacturing method according to the nineteenth aspect, impurity ions are implanted into the side surface and the bottom surface of the trench after the first step and before the second step. The method further includes a fourth step.

  According to the invention of claim 19, an insulating region made of a material having a dielectric constant greater than that of the thermal oxide film is embedded in a surface region between the first electrode and the second electrode of the semiconductor substrate, In addition, a semiconductor device having one or more slits made of a thermal oxide film in the insulating region can be obtained. In this semiconductor device, the electric field lines concentrate in the slit and the electric field is increased at the bottom of the insulating region, so that the electric field strength near the surface of the element is relaxed and the withstand voltage is increased. According to the invention of claim 20, the offset drain region is formed around the insulating region.

  According to a semiconductor device and a manufacturing method thereof according to the present invention, in a semiconductor device using an insulating region embedded in a surface region of a semiconductor substrate as an element withstand voltage portion, a high withstand voltage can be obtained by relaxing electric field strength near the surface of the element. There is an effect that characteristics can be obtained.

  Exemplary embodiments of a semiconductor device and a method for manufacturing the same according to the present invention will be explained below in detail with reference to the accompanying drawings.

Embodiment 1 FIG.
1 to 6 are longitudinal sectional views showing structures in the process of manufacturing a semiconductor device manufactured by the manufacturing method according to the first embodiment of the present invention, and FIG. 7 is for trench etching used in this manufacturing method. It is a top view which shows an example of the mask pattern of a resist mask. 1 to 6 show the structure of the semiconductor device in a cross section corresponding to the line AA ′ in FIG. However, only two trenches are shown in order to avoid the figure becoming complicated.

  First, as shown in FIG. 1, a p-type silicon semiconductor substrate 31 having a sheet resistance of, for example, about 100 Ωcm is thermally oxidized to form a thermal oxide film 32 having a thickness of, for example, 800 nm on the substrate surface. Next, as shown in FIG. 2, after applying a photoresist on the thermal oxide film 32, exposure and development are performed using a mask (not shown) to form a resist mask 33.

If the direction parallel to the drawing in FIG. 2 is the Y direction, as shown in FIG. 7, the resist mask 33 has a plurality of island regions 33a each having a length in the Y direction of 1.4 μm, for example, at intervals of 1.6 μm, for example. With the pattern arranged in The opening 33b having a width of 1.6 μm corresponds to a trench 36 described later. Then, using the resist mask 33 as a mask, anisotropic dry etching is performed using, for example, a mixed gas of CHF ₃ , CF _4, and Ar, and a portion of the thermal oxide film 32 corresponding to the trench 36 is removed to remove the hard mask 34. Form.

Then, as shown in FIG. 3, the hard mask 34 as a mask, for example, by anisotropic dry etching using a mixed gas of Cl ₂ and O _2, a direction perpendicular to the drawing in FIG. 3 (hereinafter, the X-direction A plurality of trenches 36 having a length in the depth direction (hereinafter referred to as Z direction) of, for example, 20 μm. Subsequently, for example, isotropic etching is performed using a mixed gas of CF ₄ and O ₂ to remove the protective film on the trench side wall generated during the trench etching and round the corners of the trench.

  At this time, the width of the upper end of the semiconductor portion remaining as the silicon pillar 35 between the adjacent trenches 36 is adjusted to be approximately 1.4 μm, for example. Further, since it is desirable that the trench side wall is inclined so that the width of the trench 36 becomes narrower from the opening end of the trench toward the bottom, the angle of the trench side wall is inclined at, for example, about 89 ° with respect to the substrate surface. To do.

Subsequently, in FIG. 3, for example, phosphorus ions are implanted in an oblique direction from the upper front side to the lower rear side of the drawing. Further, in FIG. 3, for example, phosphorus ions are implanted in an oblique direction from the upper rear side to the lower front side of the drawing. The angle formed between the direction of the two ion implantations and the normal direction of the substrate surface (that is, the side surface of the trench 36) is approximately + 44 ° and −44 °, for example. The ion implantation amount is, for example, 9.3 × 10 ¹¹ cm ⁻² .

Subsequently, phosphorus ions are implanted from a direction perpendicular to the substrate surface, that is, a direction of approximately 0 ° with respect to the side surface of the trench 36. In this ion implantation, phosphorus ions are implanted only into the bottom of the trench 36. The ion implantation amount at this time is, for example, 6.6 × 10 ¹¹ cm ⁻² . The reason is that the surface concentration of phosphorus ions around the n ⁻ offset drain region becomes uniform. Subsequently, driving is performed for about 6 hours in a nitrogen atmosphere at 1150 ° C., for example, to form an n ⁻ offset drain region having a phosphorus ion diffusion depth xj of about 4 μm, for example. In FIG. 3, the n ⁻ offset drain region is omitted.

  Next, as shown in FIG. 4, the silicon substrate 35 is completely oxidized by exposing the semiconductor substrate 31 to a water vapor atmosphere at 1100 ° C. for about 10 hours, for example. By this oxidation treatment, the silicon pillar 35 becomes a silicon oxide pillar made of silicon oxide. At that time, due to expansion when silicon becomes silicon oxide, a slit 38 having a width of, for example, about 0.1 μm remains between adjacent silicon oxide pillars. At this time, the thickness of the formed thermal oxide film 37 is, for example, 3.1 μm.

  Next, as shown in FIG. 5, an HTO film (high temperature thermal CVD oxide film) 39 is deposited on the thermal oxide film 37 by, for example, a low pressure CVD method to close the opening at the upper end of the slit 38. At that time, since the fluidity of HTO is small, the slit 38 cannot be completely filled with HTO. Therefore, a slit 38 remains between the thermal oxide film 37 and the HTO film 39.

  Finally, as shown in FIG. 6, the HTO film 39 and the thermal oxide film 37 on the silicon surface are removed by, for example, CMP, wet etching, dry etching, or the like. In this way, a trench insulating structure is obtained in which the thermal oxide film 37 and the HTO film 39 are integrated and the insulating region 40 including the slit 38 is included. Next, various semiconductor regions, electrodes, and the like are formed on the semiconductor substrate 31 by a known method. The breakdown voltage value of the trench lateral MOSFET actually manufactured according to the manufacturing method described above was 760V.

FIG. 8 is a vertical cross-sectional view showing a cross-sectional structure including slits of a horizontal type high breakdown voltage trench power MOSFET which is an example of a semiconductor device manufactured by applying the manufacturing method described above. As shown in FIG. 8, the lateral trench MOSFET includes a p semiconductor layer 51, a p well layer 52, an n well layer 53, an n ⁻ offset drain region 54, an insulating region 55, a p channel region 56, which correspond to the semiconductor substrate 31. n ⁺ semiconductor region 57 becomes a source region, n ⁺ semiconductor region 58 as a drain region, a gate insulating film 59, gate electrode 60, a drain electrode corresponding to the source electrode 61, and the second electrode corresponding to the first electrode 62.

The insulating region 55 is embedded in the surface region of the semiconductor substrate and is composed of the thermal oxide film 37 and the HTO film 39. The slit 38 is included in the insulating region 55. The n ⁻ offset drain region 54 is formed so as to surround the side surface and the bottom surface of the insulating region 55. The p well layer 52 is formed adjacent to the outside of the n ⁻ offset drain region 54 in the surface portion of the p semiconductor layer 51 on the source side with respect to the insulating region 55.

The p channel region 56 is formed on the surface portion of the p well layer 52. The n ⁺ semiconductor region 57 is formed away from the n ⁻ offset drain region 54 in the surface portion of the p channel region 56. The n well layer 53 is formed so as to be connected to the n ⁻ offset drain region 54 in the surface portion of the p semiconductor layer 51 on the drain side (opposite the source side) with respect to the insulating region 55.

N ⁺ semiconductor region 58 is formed on the surface portion of n well layer 53. Gate insulating film 59 is formed on the surface of p channel region 56 between n ⁺ semiconductor region 57 and n ⁻ offset drain region 54. The gate electrode 60 is formed on the gate insulating film 59. Source electrode 61 is in contact with p channel region 56 and n ⁺ semiconductor region 57. The drain electrode 62 is in contact with the n ⁺ semiconductor region 58.

  Although not shown, the gate electrode 60 is insulated from the source electrode 61 and the drain electrode 62 by an interlayer insulating film. The entire apparatus is covered with a passivation film.

Next, analysis results performed by the present inventors using simulation will be described. In the structure shown in FIG. 8, a thermal oxide film 37 having a dielectric constant of 3.9 is embedded in the trench, and a slit 38 having a dielectric constant of 1 is provided therein, and a two-dimensional breakdown voltage simulation is performed. The impurity concentration of the p semiconductor layer 51 was 1.0 × 10 ¹⁴ cm ^−3, and the surface concentration of the n ⁻ offset drain region 54 was 8.0 × 10 ¹⁵ cm ⁻³ . In an actual element structure, a rectangular parallelepiped-shaped insulator serving as a slit 38 is embedded in a rectangular parallelepiped thermal oxide film 37.

  The relationship between the thickness of the insulator in the slit 38 and the withstand voltage was examined by two-dimensional simulation. The result is shown in FIG. When the dimension of one side of the trench 36 is 20 μm, the withstand voltage becomes maximum when the thickness of the insulator is 3 μm, and the value is 705V. When the thickness of the insulator was 5 μm, the withstand voltage value was 639V. Further, the withstand voltage value when the trench 36 was filled only with the thermal oxide film 37 without providing the slit 38 in the trench 36 was 480V.

  The potential distribution and breakdown point (portion surrounded by a circle) when the thickness of the thermal oxide film 37 was changed were examined. The results are shown in FIGS. In FIGS. 10, 11 and 12, the thickness of the thermal oxide film 37 is 1.5 μm, 3 μm and 5 μm, respectively. Comparing these figures with FIG. 25 showing the potential distribution and breakdown point of the conventional semiconductor device without the slit 38, it can be seen that the breakdown voltage characteristics are improved by providing the slit 38. FIG.

  That is, due to the presence of the slit 38 having a dielectric constant smaller than that of the surrounding insulator (the thermal oxide film 37 having a dielectric constant of 3.9), the lines of electric force are concentrated in the slit 38, and an electric field is generated at the bottom of the trench. The distribution becomes higher. As a result, the electric field strength near the surface of the element, which is a conventional rule point, is alleviated, so that the withstand voltage increases.

  However, due to the concentration of the electric field in the slit 38, there is a concern that reliability may be lowered due to fixed charges at the interface portion or polarization in the gas remaining in the slit 38. In order to avoid such a problem, the inside of the slit 38 is preferably made into a high vacuum or filled with an insulating material having a low dielectric constant.

  The relationship between the aspect ratio of the trench 36, the so-called aspect ratio, and the breakdown voltage was examined. As a result, when the dimensions of the trench 36 in both the X direction and the Z direction are 20 μm (the aspect ratio is 1), the breakdown voltage is 693 V when the slit 38 is present, and 489 V when the slit 38 is not present. It was. Further, when the dimensions of the trench 36 in the X direction and the Z direction are 15 μm and 25 μm, respectively (the aspect ratio is 1.66), the withstand voltage is 725 V when the slit 38 is present, but without the slit 38. It was 568V.

  Further, when the dimensions of the trench 36 in the X direction and the Z direction are 10 μm and 25 μm, respectively (the aspect ratio is 2.5), the withstand voltage is 470 V when the slit 38 is present, but without the slit 38. 360V. From this result, it was found that when the aspect ratio is 1 to 2.5, there is a pressure resistance improving effect, and in particular, the aspect ratio close to 1 is more effective.

  Next, a thermal oxide film 37 having a dielectric constant of 3.9 is filled in the trench 36, slits 38 having a dielectric constant of 1 are provided therein, and the relationship between the number and arrangement of the slits 38 and the device breakdown voltage is examined. The three-dimensional simulation will be described. FIG. 13 is a layout diagram showing the three-dimensional simulation model.

In this simulation, the size of the trench 36 is 20 μm × 20 μm (the aspect ratio is 1), the thickness of the thermal oxide film 37 is 2 μm, the number of slits 38 is 1 to 5, the width of the slits 38 is 0.1 μm, The thickness was 0.5 μm and 1 μm. Further, the impurity concentration of the p semiconductor layer 51 was set to 1.0 × 10 ¹⁴ cm ^−3, and the concentration of the n ⁻ offset drain region 54 (not shown) was fixed to 6.0 × 10 ¹⁴ cm ⁻³ .

  The result of the three-dimensional simulation is shown in FIG. In the case where the width of the slit 38 is 0.1 μm, if the number of the slits 38 is three or more, a remarkable pressure resistance improvement effect is obtained. In the case where the width of the slit 38 is 0.5 μm, if the number of the slits 38 is four or more, a remarkable pressure resistance improvement effect is obtained. In the case where the width of the slit 38 is 1 μm, by providing the five slits 38, a remarkable pressure resistance improvement effect was obtained.

  As described above, even in the three-dimensional model, the presence of the slit 38 having a dielectric constant smaller than that of the surrounding insulator (the thermal oxide film 37 having a dielectric constant of 3.9) makes it possible to concentrate the electric field on the element surface. It was found that the withstand voltage can be improved by changing the electric field distribution. The effect of improving the breakdown voltage varies depending on the positional relationship between the slit 38 and the trench 36, the shape of the slit 38, and the aspect ratio of the trench 36, but the optimum range was obtained by simulation and experiment.

  According to the first embodiment, one or more slits 38 having a dielectric constant smaller than that of the thermal oxide film 37 constituting the insulating region 55 in the insulating region 55 buried between the source electrode 61 and the drain electrode 62. Therefore, the electric lines of force concentrate in the slit 38 and the electric field is increased at the bottom of the insulating region 55. Therefore, the electric field strength near the surface of the element is relaxed and the withstand voltage is increased.

Embodiment 2. FIG.
In the second embodiment, a silicon oxide column formed by thermally oxidizing a silicon column between adjacent trenches is used as a slit having a low dielectric constant. 15 to 19 are longitudinal sectional views showing structures in the process of manufacturing a semiconductor device manufactured by the manufacturing method according to the second embodiment of the present invention. The mask pattern of the resist mask for trench etching used in this manufacturing method is the same as the pattern shown in FIG. 15 to 19 show the structure of the semiconductor device in a cross section corresponding to the line AA ′ in FIG. However, only two trenches are shown in order to avoid the figure becoming complicated.

  First, as shown in FIG. 15, a hard mask 74 and a resist mask 73 are provided on the semiconductor substrate 31 as in the first embodiment. The resist mask 73 has a pattern in which a plurality of island-like regions whose length in the Y direction parallel to the drawing in FIG. 15 is 0.2 μm, for example, are arranged at an interval of 1.6 μm, for example. Therefore, the hard mask 74 also has the same pattern as the resist mask 73.

Next, as shown in FIG. 16, after forming the silicon pillar 75 and the trench 76, the protective film on the trench side wall is removed and the corners of the trench are rounded as in the first embodiment. In the same manner as in the first embodiment, for example, phosphorus ions are implanted from two oblique directions, and, for example, phosphorus ions are implanted into the bottom of the trench 76. Thereafter, driving is performed to form an n ⁻ offset drain region (not shown).

  Next, as shown in FIG. 17, for example, the semiconductor substrate 31 is exposed to a water vapor atmosphere at 1100 ° C. for about 1 hour to completely oxidize the silicon pillars 75 to form silicon oxide pillars made entirely of silicon oxide. At this time, the width of the silicon oxide pillar is, for example, about 0.4 μm. Thermal oxide films 77 (including silicon oxide pillars) are generated on the side surfaces and the bottom surface of the trench 76. The dielectric constant of the thermal oxide film 77 is 3.9.

  Next, as shown in FIG. 18, a nitride film 79 is deposited on the thermal oxide film 77 by, eg, plasma CVD, and the trench 76 is filled with the nitride film 79. The dielectric constant of the nitride film 79 is about 8. Finally, as shown in FIG. 19, the nitride film 79 and the thermal oxide film 77 on the silicon surface are removed by, for example, CMP. In this way, a trench insulating structure is obtained in which the thermal oxide film 77 and the nitride film 79 are integrated, and the insulating region 80 includes the silicon oxide pillar that is a part of the thermal oxide film 77 as the slit 78. Next, various semiconductor regions, electrodes, and the like are formed on the semiconductor substrate 31 by a known method.

  The breakdown voltage value of the trench lateral MOSFET actually manufactured according to the manufacturing method described above was 489V. Note that the breakdown voltage value when the trench 76 was filled with only the nitride film 79 without providing the thermal oxide film 77 in the trench 76 was 416V. In the second embodiment, the nitride film 79 having a dielectric constant of about 8 is provided with a slit 78 made of a thermal oxide film 77 having a dielectric constant of 3.9. Since the electric field on the surface is relaxed, the breakdown voltage is improved.

  In the second embodiment, instead of the nitride film 79, a high dielectric constant material such as tantalum or hafnium may be used as a material having a higher dielectric constant than the material constituting the slit 78. In addition, in embedding a high dielectric constant material such as the nitride film 79, a coating method or a sputtering method may be used in addition to the plasma CVD method.

  As described above, the present invention is not limited to the above-described embodiments, and various modifications can be made. For example, the size and concentration of each part, the ion implantation amount, various processing conditions, and the like shown in each embodiment are examples, and the present invention is not limited to these values. Further, the present invention can be similarly realized even when the p-type and the n-type are inverted. Furthermore, the present invention is not limited to silicon semiconductors, and the same holds true when other semiconductor materials are used.

  As described above, the semiconductor device and the manufacturing method thereof according to the present invention are useful for a semiconductor device using an insulating region embedded in a surface region of a semiconductor substrate as an element withstand voltage portion, and in particular, a power device such as a trench lateral device. Suitable for

It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 1 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 1 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 1 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 1 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 1 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 1 of this invention. It is a top view which shows an example of the mask pattern of the resist mask for trench etching used in the manufacturing method concerning Embodiment 1 of this invention. It is a longitudinal cross-sectional view which shows the structure of the trench power MOSFET manufactured by the manufacturing method concerning Embodiment 1 of this invention. It is a characteristic view which shows the relationship between the thickness of the insulator in a slit of the semiconductor device concerning Embodiment 1 of this invention, and a proof pressure. FIG. 3 is a potential distribution diagram showing a potential distribution and a breakdown point of the semiconductor device according to the first embodiment of the present invention. FIG. 3 is a potential distribution diagram showing a potential distribution and a breakdown point of the semiconductor device according to the first embodiment of the present invention; FIG. 3 is a potential distribution diagram showing a potential distribution and a breakdown point of the semiconductor device according to the first embodiment of the present invention; 1 is a layout diagram illustrating a three-dimensional simulation model of a semiconductor device according to a first embodiment of the present invention; It is a characteristic view which shows the relationship between the slit number of the semiconductor device concerning Embodiment 1 of this invention, and a proof pressure. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 2 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 2 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 2 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 2 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the semiconductor device manufactured by the manufacturing method concerning Embodiment 2 of this invention. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the conventional semiconductor device. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the conventional semiconductor device. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the conventional semiconductor device. It is a longitudinal cross-sectional view which shows the structure in the middle of manufacture of the conventional semiconductor device. It is a longitudinal cross-sectional view which shows the structure of the conventional trench power MOSFET. It is a potential distribution diagram showing a potential distribution and a breakdown point of a conventional semiconductor device.

Explanation of symbols

31 Semiconductor substrate 35, 75 Semiconductor portion between trenches (silicon pillar)
36, 76 Trench 37, 77 Thermal oxide film 38, 78 Slit 40, 55, 80 Insulating region 61 First electrode (source electrode)
62 Second electrode (drain electrode)
79 Nitride film

Claims (20)

A first electrode and a second electrode provided apart from each other on the surface of the semiconductor substrate;
An insulating region embedded in a surface region of the semiconductor substrate between the first electrode and the second electrode;
One or more slits provided in the insulating region,
The semiconductor device according to claim 1, wherein the slit has a dielectric constant smaller than a material constituting the insulating region.   The semiconductor device according to claim 1, wherein a width of the slit is 1 μm or less.   The semiconductor device according to claim 2, wherein a width of the slit is 0.1 μm or more.   The semiconductor device according to claim 1, wherein the inside of the slit is in a high vacuum state.   The semiconductor device according to claim 1, wherein the slit is filled with a material having a dielectric constant smaller than that of the material constituting the insulating region.   6. The thickness of a portion that includes the slit and is in contact with the semiconductor substrate in the insulating region in a cross section parallel to the slit is 1 μm or more. Semiconductor device.   6. The thickness of a portion that includes the slit and is in contact with the semiconductor substrate in the insulating region in a cross section parallel to the slit is 1.5 μm or more. A semiconductor device according to 1.   8. The semiconductor device according to claim 6, wherein a thickness of a portion of the insulating region in contact with the semiconductor substrate in a cross section including the slit and parallel to the slit is 5 μm or less.   6. The semiconductor device according to claim 5, wherein the material constituting the insulating region is nitride, and the material filling the slit is silicon oxide. An insulating region is embedded between the first electrode and the second electrode that are provided apart from each other on the surface of the semiconductor substrate, and the one or more slits having a dielectric constant smaller than the material constituting the insulating region are In manufacturing a semiconductor device provided in an insulating region,
A first step of forming a plurality of trenches in a semiconductor substrate;
A second step of thermally oxidizing the side surface and the bottom surface of the trench while leaving a gap serving as a slit in the central portion of the trench, and completely thermally oxidizing the semiconductor portion between the adjacent trenches;
A third step of closing at least the opening of the gap remaining in the trench central portion;
A method for manufacturing a semiconductor device, comprising:   11. The manufacturing method of a semiconductor device according to claim 10, wherein in the first step, a plurality of trenches are formed so that the gap remains with a width of 1 [mu] m or less when the second step is completed. Method.   12. The semiconductor device according to claim 11, wherein in the first step, a plurality of trenches are formed so that the gap remains with a width of 0.1 [mu] m or more when the second step is completed. Manufacturing method.   The method for manufacturing a semiconductor device according to claim 10, wherein the inside of the slit is in a high vacuum state.   13. The method of manufacturing a semiconductor device according to claim 10, wherein the slit is filled with a material having a dielectric constant smaller than that of the thermal oxide film generated by the second step.   In the second step, thermal oxidation is performed so that a thickness of a portion in contact with the semiconductor substrate of the thermal oxide film in a cross section including the gap and parallel to the gap is 1 μm or more. The method for manufacturing a semiconductor device according to claim 10.   In the second step, thermal oxidation is performed so that a thickness of a portion of the thermal oxide film in contact with the semiconductor substrate in a cross section including the gap and parallel to the gap is 1.5 μm or more. The method for manufacturing a semiconductor device according to claim 10, wherein:   In the second step, thermal oxidation is performed so that a thickness of a portion in contact with the semiconductor substrate of the thermal oxide film in a cross section including the gap and parallel to the gap is 5 μm or less. A method for manufacturing a semiconductor device according to claim 15 or 16.   18. The method according to claim 10, further comprising a fourth step of implanting impurity ions into a side surface and a bottom surface of the trench after the first step and before the second step. The manufacturing method of the semiconductor device of description. An insulating region is embedded between the first electrode and the second electrode that are provided apart from each other on the surface of the semiconductor substrate, and the one or more slits having a dielectric constant smaller than the material constituting the insulating region are In manufacturing a semiconductor device provided in an insulating region,
A first step of forming a plurality of trenches in a semiconductor substrate;
A second step of thermally oxidizing the side and bottom surfaces of the trench with a gap left in the central portion of the trench, and completely thermally oxidizing a semiconductor portion that becomes a slit between the adjacent trenches;
A third step of filling the gap remaining in the central portion of the trench with a material having a dielectric constant larger than that of the thermal oxide film generated by the second step;
A method for manufacturing a semiconductor device, comprising: 20. The method of manufacturing a semiconductor device according to claim 19, further comprising a fourth step of implanting impurity ions into a side surface and a bottom surface of the trench after the first step and before the second step. .

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