Semiconductor device

Abstract

To enable stabilization of the forward output voltage of a temperature sensing diode in a semiconductor device having a gate-insulating transistor and a temperature sensing diode without adding a significant number of processes.SOLUTION: On the bottom side of a temperature sensing diode 120, trenches 131 are periodically formed in a semiconductor substrate 101. A source field plate 133 is placed inside the trench 131 via an insulating film. A P-type diffusion layer 134 is formed between adjacent trenches 131. The source field plate 133 and P-type diffusion layer 134 are connected to the source potential.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present disclosure relates to a semiconductor device, for example, a semiconductor device including a diode for temperature measurement.

Background Art

[0002] As related art, Patent Document 1 discloses a semiconductor device. The semiconductor device described in Patent Document 1 includes a semiconductor substrate and a polysilicon diode (hereinafter also referred to as a temperature detection diode) for detecting the temperature of the semiconductor substrate. The semiconductor substrate has a cell region in the central part of the chip where an insulated gate type power transistor such as a power MOS (Metal Oxide Semiconductor) FET (Field Effect Transistor) is disposed. The space between the edge of the semiconductor substrate and the cell region is filled with an annular P-well region. The polysilicon diode is disposed in the annular P-well region.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the semiconductor device described in Patent Document 1, a P-well region is formed under the polysilicon diode which is the temperature detection diode. In this case, by applying a source potential to the P-well region, it is possible to suppress the output of the temperature detection diode from becoming unstable due to the influence of drain voltage or substrate voltage fluctuations. However, the process of forming the insulated gate type power transistor does not necessarily include the process of forming the P-well region. When the process of forming the insulated gate type power transistor does not include the process of forming the P-well, it is necessary to add a process of forming the P-well only for the purpose of stabilizing the output of the temperature detection diode.

[0005] Other problems and novel features will become apparent from the description of this specification and the accompanying drawings.

Means for Solving the Problems

[0006] According to one embodiment, a semiconductor device is provided. The semiconductor device includes a gate-insulated transistor, a temperature detection diode, and a lower structure of the temperature detection diode. The lower structure of the temperature detection diode includes a source field plate disposed in a trench formed periodically and a diffusion layer formed between adjacent trenches. The source field plate and the diffusion layer are connected to a source potential.

Advantages of the Invention

[0007] According to the above embodiment, in a semiconductor device having a gate-insulated transistor and a temperature detection diode, the forward output voltage of the temperature detection diode can be stabilized without significant additional processes.

Brief Description of the Drawings

[0008]

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Embodiments for Carrying Out the Invention

[0009] Hereinafter, embodiments to which means for solving the above problems are applied will be described in detail with reference to the drawings. For clarification of the description, the following description and drawings are appropriately omitted and simplified. In each drawing, the same elements are denoted by the same reference numerals, and redundant descriptions are omitted as necessary.

[0010] In the following embodiments, when necessary for convenience, they will be described by being divided into a plurality of sections or embodiments. However, unless otherwise specifically stated, they are not unrelated to each other, and one is related to a part or all of the other as a modification example, application example, detailed description, supplementary explanation, etc. Further, in the following embodiments, when referring to the number of elements, etc. (including the number, numerical value, quantity, and range, etc.), unless otherwise specifically stated and unless it is clearly limited to a specific number in principle, it is not limited to that specific number, and it may be more than or less than the specific number.

[0011] Furthermore, in the following embodiments, the constituent elements (including operation steps, etc.) are not necessarily essential unless otherwise specifically stated and unless it is clearly considered essential in principle. Similarly, in the following embodiments, when referring to the shape, positional relationship, etc. of the constituent elements, etc., unless otherwise specifically stated and unless it is clearly considered otherwise in principle, it includes those that are substantially approximate or similar to the shape, etc. This also applies to the above numbers, etc. (including the number, numerical value, quantity, and range).

[0012] In the following embodiments, the MOSFET includes not only FETs in which the gate insulating film is an oxide film but also FETs that use an insulating film other than the oxide film as the gate insulating film. Also, the MOSFET includes not only FETs in which the gate electrode is formed of metal but also FETs in which a conductor other than metal is used as the gate electrode. In the following embodiments, an example of an insulated gate transistor with a split gate structure being a MOSFET will be described. However, the insulated gate transistor is not limited to MOSFETs. The insulated gate transistor may be an IGBT (Insulated Gate Bipolar Transistor).

[0013] [Embodiment 1] FIG. 1 shows an example of a cross-sectional structure of a semiconductor device according to Embodiment 1 of the present disclosure. The semiconductor device 100 includes a semiconductor substrate 101, a MOSFET 110 which is an insulated-gate transistor, and a temperature detection diode 120. The semiconductor substrate 101 is an N-type semiconductor substrate. In the present embodiment, the MOSFET 110 is a vertical MOSFET in which one surface of the semiconductor substrate 101 serves as a source and the other surface serves as a drain. The semiconductor device 100 is, for example, a 100V-class power discrete semiconductor.

[0014] In the region of the MOSFET 110, a plurality of trenches 111 are periodically formed in the semiconductor substrate 101. The MOSFET 110 has a source field plate 113 and a gate electrode 114 embedded in the trench 111 via an insulating film 112. A source potential is applied to the source field plate 113. The MOSFET 110 has a channel P diffusion layer 115 and a source N+ diffusion layer 116 between two adjacent gate electrodes 114. The gate electrode 114 and the source N+ diffusion layer 116 are covered by insulating films 135 and 136. The MOSFET 110 is a transistor having a split-gate structure in which the gate electrode 114 and the source field plate 133 to which a source potential is applied are embedded in the trench 111.

[0015] The temperature detection diode 120 has a P-type region 121 and an N-type region 122. The temperature detection diode 120 is formed of, for example, polysilicon. The P-type region 121 and the N-type region 122 are formed, for example, by introducing impurities into polysilicon, respectively. The MOSFET 110 generates heat when current flows through it. The temperature detection diode 120 is a diode for temperature measurement used to measure the temperature of the semiconductor device 100.

[0016] In the region on the lower layer side of the temperature detection diode 120 in the semiconductor substrate 101, a plurality of trenches 131 are formed. Assume that the width and depth of the trench 131 are equal to the width and depth of the trench 111 in the MOSFET 110. Also, assume that the distance between two adjacent trenches 131, that is, the pitch a, is equal to the pitch b of the trench 111. In the trench 131, a source field plate 133 is disposed via an insulating film 132. The insulating film 132 is also called a field plate insulating film. A P-type diffusion layer 134 is formed between two adjacent trenches 131. The position of the bottom of the P-type diffusion layer 134 in the substrate depth direction is shallower than the bottom of the gate electrode 114 in the MOSFET 110. A source potential is applied to the source field plate 133 and the P-type diffusion layer 134.

[0017] In the region on the lower layer side of the temperature detection diode 120, an insulating film 135 is formed on the upper layer side of the source field plate 133 and the P-type diffusion layer 134. The insulating film 135 covers the source field plate 133 and the P-type diffusion layer 134. The temperature detection diode 120 is formed on the upper layer of the insulating film 135. The insulating film 135 is also called a diode lower insulating film. An insulating film 136 is formed on the upper layer side of the temperature detection diode 120 and the insulating film 135. For the insulating films 135 and 136, a silicon oxide film formed by, for example, chemical vapor deposition (CVD) method is used. The insulating films 135 and 136 have a film thickness of about 150 nm, for example.

[0018] FIG. 2 shows an example of the planar structure of the temperature detection diode 120. In the temperature detection diode 120, the P-type region 121 is formed, for example, in a rectangular shape as shown in FIG. 2. The N-type region 122 is formed so as to surround the rectangular P-type region 121. In the semiconductor substrate 101, a plurality of trenches 131 extending in a predetermined direction are formed at a predetermined pitch below the temperature detection diode 120. Also, a plurality of P-type diffusion layers 134 extending in a predetermined direction are formed at a predetermined pitch below the temperature detection diode 120. As shown in FIG. 1, a source field plate 133 is disposed in the trench 131.

[0019] In the present embodiment, the semiconductor device 100 has a source field plate 133 and a P-type diffusion layer 134 to which a source potential is applied as a lower structure of the temperature detection diode 120. In the semiconductor device 100, by setting the lower structure of the temperature detection diode 120 as the source potential, it is possible to suppress the influence of the fluctuation of the drain potential of the MOSFET 110, that is, the substrate potential, on the forward output voltage of the temperature detection diode 120.

[0020] Also, in the present embodiment, the lower structure of the temperature detection diode 120 has a structure similar to the structure of the MOSFET 110 which is the main body cell. The trench 131 below the temperature detection diode 120 can be formed simultaneously with the trench 111 in the MOSFET 110. Also, the source field plate 133 below the temperature detection diode 120 can be formed simultaneously with the source field plate 113 in the MOSFET 110. Further, the P-type diffusion layer 134 below the temperature detection diode 120 can be formed simultaneously with the channel P diffusion layer 115 in the MOSFET 110.

[0021] Next, the manufacturing process of the semiconductor device 100 will be described. FIGS. 3 to 15 show cross-sections in the manufacturing process of the semiconductor device 100. As shown in FIG. 3, in the process of forming trenches, a plurality of trenches 111 are formed in the region of the N-type semiconductor substrate 101 where the MOSFETs are formed. Also, a plurality of trenches 131 are formed in the region of the semiconductor substrate 101 where the lower structure of the temperature detection diode is formed. Next, as shown in FIG. 4, in the process of forming the feed plate insulating film, an insulating film 141 is formed on the surface of the semiconductor substrate 101. The insulating film 141 corresponds to the insulating film 112 (see FIG. 1) in the MOSFET 110. Also, the insulating film 141 corresponds to the insulating film 132 in the lower structure of the temperature detection diode.

[0022] As shown in FIG. 5, in the process of forming electrodes, polysilicon 142 is deposited on the insulating film 141. The deposited polysilicon is planarized by chemical mechanical polishing (CMP). As shown in FIG. 6, in the etching process, the polysilicon 142 is etched entirely, and the polysilicon 142 protruding from the trenches 111 and 131 is removed.

[0023] Thereafter, as shown in FIG. 7, the region of the lower structure of the temperature detection diode is covered with a photoresist 151, and by etching the polysilicon 142 using the photoresist 151 as a mask, a part of the polysilicon 142 in the trench 111 is removed. The remaining polysilicon 142 in the trench 111 corresponds to the source field plate 113 in the MOSFET 110. Also, the polysilicon 142 in the trench 131 corresponds to the source field plate 133 in the lower structure of the temperature detection diode.

[0024] Subsequently, as shown in FIG. 8, in the step of forming the gate oxide film, a part of the insulating film 141 is removed by etching. As shown in FIG. 9, in the step of forming the gate electrode, polysilicon is deposited in the trench 111, and the gate electrode 114 is formed. As shown in FIG. 10, in the step of forming the channel P diffusion layer, the channel P diffusion layer 115 is formed between two adjacent trenches 111. Also, the P-type diffusion layer 134 is formed between two adjacent trenches 131. As shown in FIG. 11, in the step of forming the source N+ diffusion layer, the source N+ diffusion layer 116 is formed in a part of the channel P diffusion layer 115.

[0025] As shown in FIG. 12, in the step of forming the diode lower insulating film, the surface of the semiconductor substrate 101 is covered with the insulating film 135. Thereafter, as shown in FIG. 13, in the step of forming polysilicon, polysilicon 143 is formed in the portion where the temperature detection diode 120 is formed on the insulating film 135. As shown in FIG. 14, in the step of forming the temperature detection diode, by introducing impurities into the polysilicon 143, the P-type region 121 and the N-type region 122 are formed. Thereafter, as shown in FIG. 15, an insulating film 136 is formed on the surface of the semiconductor substrate 101 so as to cover the temperature detection diode 120.

[0026] [Effect] The semiconductor device 100 according to the present embodiment has a trench 131 in which the source field plate 133 is embedded and a P-type diffusion layer 134 in the lower structure of the temperature detection diode 120. The source field plate 133 and the P-type diffusion layer 134 are each connected to the source potential. With such a configuration, even when the substrate potential, that is, the drain potential of the MOSFET 110 fluctuates, the lower structure of the temperature detection diode 120 can be fixed to the source potential. As a result, even when the substrate potential fluctuates, it is possible to suppress the output of the temperature detection diode 120 from becoming unstable. Also, in the present embodiment, the source field plate 133 embedded in the trench 131 also functions as an internal RC snubber. Therefore, in the semiconductor device 100, a recovery surge reduction effect can be expected.

[0027] In comparison with Patent Document 1, in Patent Document 1, since a P-well is formed under the temperature detection diode, a process for forming the P-well is required. However, the manufacturing process of the MOSFET 110 which is the main body cell does not include the process of forming the P-well. Therefore, when forming a P-well under the temperature detection diode, it is necessary to add processes of photolithography, ion implantation, and high-temperature diffusion to the manufacturing process of the MOSFET 110. This increases the process cost.

[0028] In the present embodiment, the lower structure of the temperature detection diode 120 has the same structure as that of the MOSFET 110. Therefore, the trench 131, the source field plate 133, and the P-type diffusion layer 134 in the lower structure of the temperature detection diode 120 can be formed simultaneously with the trench 111, the source field plate 133, and the channel P-diffusion layer 115 in the MOSFET 110, respectively. Accordingly, the present embodiment can suppress the influence of the substrate potential fluctuation on the forward output voltage of the temperature detection diode 120 without increasing the process cost.

[0029] Note that in the semiconductor device 100, the pitch a of the trench 131 in the lower structure of the temperature detection diode may be wider than the pitch b of the trench 111 in the MOSFET 110. By widening the pitch a of the trench 131 in the lower structure of the temperature detection diode, the breakdown voltage of the lower structure of the temperature detection diode can be made higher than the breakdown voltage in the main body cell. However, if the pitch a of the trench 131 is extremely widened, the breakdown voltage will decrease. In particular, in order to prevent the breakdown voltage from decreasing significantly in a low-temperature environment, the pitch a of the trench 131 is preferably set, for example, to be wider than 1 times and not more than 1.1 times the pitch b of the trench 111.

[0030] When the pitch a of the trench 131 is set to be wider than 1 times and equal to or less than 1.1 times the pitch b of the trench 111, the breakdown voltage of the lower structure of the temperature detection diode 120 can be made higher than the breakdown voltage of the main body cell in which the MOSFET 110 is formed. In this case, even when a voltage equal to or higher than BVDSS is applied between the drain and source of the MOSFET 110 and avalanche breakdown occurs, no current flows to the P-type diffusion layer 134 in the lower structure of the temperature detection diode 120, and potential fluctuations in the lower structure of the temperature detection diode 120 can be suppressed. Therefore, the output stability of the temperature detection diode can be enhanced.

[0031] [Embodiment 2] FIG. 16 shows an example of a cross-sectional structure of a semiconductor device according to Embodiment 2 of the present disclosure. The configuration of the semiconductor device 100a shown in FIG. 16 is different from the configuration of the semiconductor device 100 shown in FIG. 1 in that boron 137 is implanted at the bottom of the trench 131 in the lower structure of the temperature detection diode. In the present embodiment, the pitch of the trench 131 in the lower structure of the temperature detection diode may be equal to the pitch of the trench 111 in the MOSFET 110, or may be wider than the pitch of the trench 111.

[0032] FIG. 17 shows a cross-section in the manufacturing process of the semiconductor device 100a. In the process shown in FIG. 3, after a plurality of trenches 111 are formed in the semiconductor substrate 101, as shown in FIG. 17, boron 137 is implanted at the bottom of the trench 111 in the process of implanting boron. The subsequent processes may be the same as the processes shown in FIGS. 4 to 15.

[0033] [Effect] In this embodiment, in the lower structure of the temperature detection diode 120, boron 137 is implanted at the bottom of the trench 131. By implanting boron 137 at the bottom of the trench 131 in which the source field plate 133 is embedded, the breakdown voltage of the lower structure of the temperature detection diode 120 can be increased compared to the case where boron is not implanted. With such a configuration, in the semiconductor device 100, the breakdown voltage of the lower structure of the temperature detection diode 120 can be made higher than the breakdown voltage of the MOSFET 110. In this case, even when a voltage equal to or higher than BVDSS is applied between the drain and source of the MOSFET 110 and avalanche breakdown occurs, the potential fluctuation of the lower structure of the temperature detection diode 120 can be suppressed. Therefore, the output stability of the temperature detection diode can be enhanced. Other effects are the same as those described in Embodiment 1.

[0034] [Embodiment 3] FIG. 18 shows an example of a cross-sectional structure of a semiconductor device according to Embodiment 3 of the present disclosure. FIG. 19 shows an example of a planar structure of a temperature detection diode. In the present embodiment, the source field plate disposed in the lower structure of the temperature detection diode 120 includes a source field plate 133a embedded in the trench 131 and a flat source field plate 133b. The source field plate 133b is also called a diode lower plate. The source field plate 133a is also called the first portion of the source field plate. The source field plate 133b is also called the second portion of the source field plate.

[0035] In this embodiment, the source field plate 133b covers the entire lower part of the temperature detection diode 120 via the insulating film 135. A source potential is applied to the source field plates 133a and 133b. In the semiconductor device 100b according to this embodiment, unlike the semiconductor device 100 according to Embodiment 1 shown in FIG. 1, a P-type diffusion layer 134 is not formed between two adjacent trenches 131. The semiconductor device 100b may be configured such that boron 137 is implanted into the bottom of the trench 131, similar to the semiconductor device 100a shown in FIG. 16. In this embodiment, the source field plate 133a embedded in the trench 131 and the source field plate 133b which is a diode lower plate also function as an internal RC snubber.

[0036] FIGS. 20 and 21 show cross-sections in the manufacturing process of the semiconductor device 100b. By the processes shown in FIGS. 3 to 5, a plurality of trenches 111 are formed in the semiconductor substrate 101, an insulating film 141 is formed on the surface of the semiconductor substrate 101, and polysilicon 142 is deposited on the insulating film 141. Then, as shown in FIG. 20, in the step of forming the diode lower plate, the region of the lower structure of the temperature detection diode is covered with a photoresist 152, and the polysilicon 142 is etched using the photoresist 152 as a mask. By this step, the polysilicon 142 protruding from the trench 111 is removed in the region of the MOSFET 110. In the region corresponding to the lower structure of the temperature detection diode 120, as shown in FIG. 20, the polysilicon 142 on the surface of the semiconductor substrate 101 is not removed.

[0037] Next, as shown in FIG. 21, the region of the lower structure of the temperature detection diode is covered with a photoresist 153, and by etching the polysilicon 142 using the photoresist 153 as a mask, a part of the polysilicon 142 in the trench 111 is removed. The polysilicon 142 in the trench 111 corresponds to the source field plate 113. The subsequent processes may be the same as the processes shown in FIGS. 8 to 15, except that a P-type diffusion layer 134 is not formed in the region of the lower structure of the temperature detection diode in the process shown in FIG. 10.

[0038] In this embodiment, in the lower structure of the temperature detection diode 120, the entire temperature detection diode 120 is covered by the source field plate 133b. In this case, compared with the configuration of Embodiment 1 shown in FIG. 1, the breakdown voltage of the lower structure of the temperature detection diode 120 can be increased. In this embodiment, in the semiconductor device 100b, the breakdown voltage of the lower structure of the temperature detection diode 120 can be made higher than the breakdown voltage of the MOSFET 110. In this case, similar to Embodiment 2, even when a voltage equal to or higher than BVDSS is applied between the drain and source of the MOSFET 110 and avalanche breakdown occurs, potential fluctuations in the lower structure of the temperature detection diode 120 can be suppressed.

[0039] In this embodiment, in order to form the diode lower plate, photolithography is added to the manufacturing process of the MOSFET 110. However, the addition of photolithography is simpler than the process of forming the P-well. Therefore, in this embodiment, no significant additional processes are required in forming the lower structure of the temperature detection diode. Accordingly, this embodiment can stabilize the forward output voltage of the temperature detection diode 120 even when the substrate potential fluctuates without increasing the process cost.

[0040] Note that in the semiconductor device according to the above embodiment, the conductivity type (P-type or N-type) of the semiconductor substrate, semiconductor layer, diffusion layer, diffusion region, etc. may be inverted. For example, one of the N-type and P-type conductivity types is defined as the first conductivity type, and the other conductivity type is defined as the second conductivity type. In that case, the first conductivity type can be P-type and the second conductivity type can be N-type, or conversely, the first conductivity type can be N-type and the second conductivity type can be P-type.

[0041] As described above, the invention made by the present inventor has been specifically described based on the embodiments. However, it goes without saying that the present invention is not limited to the embodiments already described, and various modifications can be made without departing from the gist thereof.

Description of Reference Numerals

[0042] 100: Semiconductor device 110: MOSFET 111: Trench 112: Insulating film 113: Source field plate 114: Gate electrode 115: Channel P diffusion layer 116: Source N+ diffusion layer 120: Temperature detection diode 121: P-type region 122: N-type region 131: Trench 132: Insulating film 133: Source field plate 134: P-type diffusion layer 135, 136: Insulating film 137: Boron 141: Insulating film 142, 143: Polysilicon 151 - 153: Photoresist

Claims

1. A semiconductor substrate of a first conductivity type, A gate-insulated transistor having a split gate structure formed on the semiconductor substrate, A diode for temperature measurement, And a lower structure of the diode formed on the semiconductor substrate, The lower structure of the diode, A source field plate disposed via an insulating film inside a trench periodically formed in the semiconductor substrate and supplied with a source potential, A diffusion layer of a second conductivity type, which is formed between adjacent trenches and has a conductivity type opposite to that of the first conductivity type and is supplied with the source potential, A semiconductor device having a diode lower insulating film that covers the source field plate and the diffusion layer and has the diode formed thereon.

2. The transistor, A source field plate and a gate electrode disposed via an insulating film inside a trench periodically formed in the semiconductor substrate, The semiconductor device according to claim 1, further comprising a diffusion layer of a first conductivity type and a diffusion layer of the second conductivity type, which are formed between adjacent trenches and laminated in the depth direction of the semiconductor substrate.

3. The trench of the lower structure of the diode is formed in the semiconductor substrate in the step of forming the trench of the transistor, The source field plate of the lower structure of the diode is formed in the step of forming the source field plate of the transistor, The semiconductor device according to claim 2, wherein the diffusion layer of the second conductivity type of the lower structure of the diode is formed in the step of forming the diffusion layer of the second conductivity type of the transistor.

4. The semiconductor device according to claim 2, wherein the pitch of the trench of the lower structure of the diode is wider than the pitch of the trench of the transistor.

5. The semiconductor device according to claim 1, further comprising boron implanted at the bottom of the trench of the lower structure of the diode.

6. A semiconductor substrate of a first conductivity type, A gate-insulated transistor having a split gate structure formed on the semiconductor substrate, A diode for temperature measurement, And a lower structure of the diode formed on the semiconductor substrate, The lower structure of the diode, A source field plate to which a source potential is applied, the source field plate having a first portion disposed via an insulating film inside a trench periodically formed in the semiconductor substrate and a flat plate-shaped second portion disposed via an insulating film on the surface of the semiconductor substrate. A semiconductor device having a diode lower insulating film that covers the surface of the semiconductor substrate and the source field plate and has the diode formed on the upper portion.

7. The transistor is A source field plate and a gate electrode disposed via an insulating film inside a trench periodically formed in the semiconductor substrate. The semiconductor device according to claim 6, further comprising a diffusion layer of a first conductivity type formed between adjacent trenches and laminated in the depth direction of the semiconductor substrate, and a diffusion layer of the second conductivity type.

8. The trench of the lower structure of the diode is formed in the semiconductor substrate in the step of forming the trench of the transistor. The semiconductor device according to claim 7, wherein the source field plate of the lower structure of the diode is formed in the step of forming the source field plate of the transistor.

9. The semiconductor device according to claim 6, further comprising boron implanted at the bottom of the trench of the lower structure of the diode.

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