JP2018088463A - Semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique for suppressing change in current sense ratio due to temperature change.SOLUTION: A semiconductor device includes: a semiconductor substrate having the area of a sense element region smaller than the area of a main element region; trenches provided in the main element region and in the sense element region on the upper surface of the semiconductor substrate; a gate insulating film; and a gate electrode. Each of the main element region and the sense element region includes a source region, a body region, and a drift region. The lower end of the source region in a range in contact with the gate insulating film in the sense element region is positioned lower than the lower end of the source region in a range in contact with the gate insulating film in the main element region. A distance between the source region and the drift region measured along an interface between the gate insulating film and the body region in the sense element region is shorter than a distance between the source region and the drift region measured along the interface between the gate insulating film and the body region in the main element region.SELECTED DRAWING: Figure 3

Description

  The present specification discloses a semiconductor device.

  A semiconductor device having a current sensing function is known. This type of semiconductor device includes a semiconductor substrate having a main element region and a sense element region. A plurality of switching elements (hereinafter referred to as main elements) are formed in the main element region, and a plurality of switching elements (hereinafter referred to as sense elements) are formed in the sense element region. The current flowing through the semiconductor device is divided into a main current flowing through the main element region and a sense current flowing through the sense element region. Since the main current value is a value corresponding to the area of the main element region and the sense current is a value corresponding to the area of the sense element region, the ratio of the main current value to the sense current value (hereinafter referred to as current sense ratio) is abbreviated. It becomes constant. Therefore, if the sense current value flowing through the sense element region is measured, the main current value can be calculated from the measured sense current value and the current sense ratio. Patent Document 1 discloses an example of a semiconductor device having such a current sensing function.

Japanese Patent No. 5417440

  In this type of semiconductor device, each of the main element region and the sense element region has a structure in which a plurality of semiconductor regions are stacked. That is, each of the main element region and the sense element region has a structure in which an n-type source region, a p-type body region, and an n-type drift region are stacked. When the semiconductor device is turned on, channels are formed in the body regions of the main element region and the sense element region, and current flows in the thickness direction of the semiconductor substrate. For this reason, the electrical resistance of the main element region and the electrical resistance of the sense element region are determined by the electrical resistance of each semiconductor region (channel and other semiconductor regions).

  When viewed from the upper surface side of the semiconductor device, the area of the sense element region is smaller than the area of the main element region. At the periphery of the main element region, current flows from outside the main element region to the channel of the main element region, and at the periphery of the sense element region, current flows from outside the sense element region to the channel of the sense element region. Since the sense element region is narrower than the main element region, the influence of the current flowing from outside the region is greater in the sense element region than in the main element region. As a result, the ratio of the electrical resistance of each semiconductor region (channel and other semiconductor regions) to the total electrical resistance of the current path differs between the sense element region and the main element region.

  When a current flows through the semiconductor device, the temperature of the semiconductor substrate changes. When the temperature of the semiconductor substrate changes, the electrical resistance of each semiconductor region (channel and other semiconductor regions) changes. For this reason, the electrical resistance of the sense element region and the electrical resistance of the main element region change. At this time, the rate of change of the electrical resistance with respect to the temperature of each semiconductor region is different from each other. Further, as described above, the ratio of the electrical resistance of each semiconductor region to the total electrical resistance of the current path is different between the sense element region and the main element region. For this reason, the electrical resistance of the sense element region (total electrical resistance of the current path) changes at a different rate of change from the electrical resistance of the main element region (total electrical resistance of the current path). Therefore, even if each semiconductor region of the main element region and the sense element region changes in temperature in the same manner, the electric resistance of the main element region and the sense element region does not change in the same way, and the current sense ratio changes. Become.

  Patent Document 1 discloses a technique for suppressing a change in the current sense ratio due to a temperature change by making the thickness of the semiconductor region different between the main element region and the sense element region. In the present specification, a technique for suppressing a change in the current sense ratio due to a temperature change by a configuration different from that of Patent Document 1 is disclosed.

  The inventors have found that the resistance ratio of the channel to the total electric resistance of the current path is larger in the sense element region than in the main element region.

  A semiconductor device disclosed in this specification includes a main element region and a sense element region, and a semiconductor substrate in which the area of the sense element region is smaller than the area of the main element region when viewed from the upper surface side; And a trench provided on the upper surface of the semiconductor substrate in the sense element region, a gate insulating film covering the inner surface of the trench in the main element region and the sense element region, and in the trench in the main element region and the sense element region And a gate electrode that is insulated from the semiconductor substrate by a gate insulating film. Each of the main element region and the sense element region includes an n-type source region in contact with the gate insulating film, a p-type body region in contact with the gate insulating film below the source region, and a lower side of the body region And an n-type drift region separated from the source region by the body region. The lower end of the source region in the range in contact with the gate insulating film in the sense element region is located below the lower end of the source region in the range in contact with the gate insulating film in the main element region. A source in which the distance between the source region measured along the interface between the gate insulating film and the body region in the sense element region and the drift region is measured along the interface between the gate insulating film in the main element region and the body region Shorter than the distance between the region and the drift region.

  In the above semiconductor device, the distance between the source region and the drift region measured along the interface between the gate insulating film and the body region in the sense element region is the interface between the gate insulating film and the body region in the main element region. Shorter than the distance between the source region and the drift region measured along. That is, when this semiconductor device is turned on, the channel length formed in the sense element region is shorter than the channel length formed in the main element region. For this reason, the difference between the resistance ratio of the channel to the total electrical resistance of the sense element region and the resistance ratio of the channel to the total electrical resistance of the main element region is reduced. As a result, when the temperature of the semiconductor substrate changes, the difference between the resistance change rate of the entire main element region and the resistance change rate of the entire sense element region can be reduced. Therefore, a change in the current sense ratio due to a temperature change of the semiconductor device can be suppressed.

1 is a diagram schematically showing a circuit diagram of a semiconductor device according to an embodiment. The top view which shows the semiconductor device of an Example typically. Sectional drawing corresponding to the III-III line of FIG.

  FIG. 1 is a schematic circuit diagram of a semiconductor device 1 according to the embodiment. The semiconductor device 1 includes a MOSFET (Metal-Oxide-Semiconductor Field-Effect Transistor) constituting the main element SW1, a MOSFET constituting the sense element SW2, a main source electrode 70, a sense source electrode 72, a drain electrode 74, and a gate pad 76. Have. The main source electrode 70 is connected to the external electrode 78. The sense source electrode 72 is connected to the external electrode 78 via the sense resistor R1.

  As shown in FIG. 2, the semiconductor device 1 has a semiconductor substrate 12. The semiconductor substrate 12 is made of, for example, SiC (silicon carbide). A plurality of main source electrodes 70, sense source electrodes 72, and gate pads 76 are formed on the upper surface of the semiconductor substrate 12. A gate wiring (not shown) that is electrically connected to the gate pad 76 is disposed around the main source electrode 70 and between the adjacent main source electrodes 70. A drain electrode 74 is formed on the back surface of the semiconductor substrate 12. A range where the main source electrode 70 is formed corresponds to the main element region 12A, and a range where the sense source electrode 72 is formed corresponds to the sense element region 12B. Thus, the main element region 12A and the sense element region 12B are formed on the same substrate, and when the semiconductor substrate 12 is viewed from the upper surface side, the area of the sense element region 12B is smaller than the area of the main element region 12A. .

  As shown in FIG. 3, the main element SW1 is formed on the semiconductor substrate 12 in the range corresponding to the main element region 12A, and the sense element SW2 is formed on the semiconductor substrate 12 in the range corresponding to the sense element region 12B. . An isolation region 12C in which no switching element is formed exists between the main element region 12A and the sense element region 12B.

  The structure of the main element SW1 and the sense element SW2 will be described. Hereinafter, components common to the main element SW1 and the sense element SW2 will be described with common reference numerals.

  A plurality of trenches 22 are provided on the upper surface 12 a of the semiconductor substrate 12. The trench 22 is provided in each of the main element region 12A and the sense element region 12B. Each trench 22 extends long in a direction perpendicular to the paper surface of FIG. The inner surface of each trench 22 is covered with a gate insulating film 24. A gate electrode 26 is disposed in each trench 22. Each gate electrode 26 is insulated from the semiconductor substrate 12 by the gate insulating film 24. The upper surface of each gate electrode 26 is covered with an interlayer insulating film 28. Each gate electrode 26 is connected to the gate pad 76 by the gate wiring (not shown) described above.

  A main source electrode 70 is formed on the upper surface 12a of the semiconductor substrate 12 in the main element region 12A. The main source electrode 70 is in contact with the upper surface 12a of the semiconductor substrate 12 at a portion where the interlayer insulating film 28 is not provided. A sense source electrode 72 is formed on the upper surface 12a of the semiconductor substrate 12 in the sense element region 12B. The sense source electrode 72 is in contact with the upper surface 12a of the semiconductor substrate 12 at a portion where the interlayer insulating film 28 is not provided.

  A drain electrode 74 is formed on the lower surface 12 b of the semiconductor substrate 12. The drain electrode 74 is connected to the lower surface 12b of the semiconductor substrate 12 in a range extending over the main element region 12A and the sense element region 12B.

  In each of the main element region 12A and the sense element region 12B, a plurality of source regions 30, a body region 32, a drift region 34, and a drain region 36 are provided inside the semiconductor substrate 12. Hereinafter, the source region 30 disposed in the main element region 12A may be referred to as a main source region 30a, and the source region 30 disposed in the sense element region 12B may be referred to as a sense source region 30b.

  Each main source region 30a is an n-type region. Each main source region 30a is disposed at a position exposed on the upper surface 12a of the semiconductor substrate 12 in the main element region 12A. Each main source region 30 a is in ohmic contact with the main source electrode 70. Each main source region 30 a is in contact with the gate insulating film 24 at the upper end portion of the trench 22.

  Each sense source region 30b is an n-type region. Each sense source region 30b is disposed at a position exposed on the upper surface 12a of the semiconductor substrate 12 in the sense element region 12B. Each sense source region 30 b is in ohmic contact with the sense source electrode 72. Each sense source region 30 b is in contact with the gate insulating film 24 at the upper end portion of the trench 22. The lower end of the source region 30 (ie, the sense source region 30b) in the range in contact with the gate insulating film 24 in the sense element region 12B is the source region 30 in the range in contact with the gate insulating film 24 in the main element region 12A (ie, main It is located below the lower end of the source region 30a).

  Body region 32 is a p-type region. Body regions 32 are provided in the main element region 12A and the sense element region 12B, respectively. The body region 32 is in contact with each source region 30. The body region 32 extends from a range between the two source regions 30 to the lower side of each source region 30. The body region 32 has a high concentration region 32a and a low concentration region 32b. The high concentration region 32a has a higher p-type impurity concentration than the low concentration region 32b. The high concentration region 32 a is disposed in a range sandwiched between the two source regions 30. The high concentration region 32 a is disposed at a position exposed on the upper surface 12 a of the semiconductor substrate 12. The high concentration region 32a of the main element region 12A is in ohmic contact with the main source electrode 70. The high concentration region 32a of the sense element region 12B is in ohmic contact with the sense source electrode 72. The low concentration region 32 b is in contact with the gate insulating film 24 below the source region 30. The lower end of the body region 32 in the range in contact with the gate insulating film 24 in the sense element region 12B is located at substantially the same depth as the lower end of the body region 32 in the range in contact with the gate insulating film 24 in the main element region 12A. .

  The drift region 34 is an n-type region. The drift region 34 is provided so as to straddle the main element region 12A and the sense element region 12B. The drift region 34 is disposed below the body region 32 in each of the main element region 12A and the sense element region 12B. The drift region 34 is separated from each main source region 30a by the body region 32 in the main element region 12A, and is separated from each sense source region 30b by the body region 32 in the sense element region 12B. The drift region 34 is in contact with the gate insulating film 24. That is, the drift region 34 is in contact with the gate insulating film 24 below the body region 32.

  The drain region 36 is an n-type region. The drain region 36 has a higher n-type impurity concentration than the drift region 34. The drain region 36 is provided so as to straddle the main element region 12A and the sense element region 12B. The drain region 36 is disposed below the drift region 34. The drain region 36 is exposed on the lower surface 12 b of the semiconductor substrate 12. The drain region 36 is in ohmic contact with the drain electrode 74.

  As shown in FIG. 3, the distance L2 between the source region 30 (that is, the sense source region 30b) and the drift region 34 measured along the interface between the gate insulating film 24 and the body region 32 in the sense element region 12B is The distance L1 between the source region 30 (that is, the main source region 30a) and the drift region 34 measured along the interface between the gate insulating film 24 and the body region 32 in the main element region 12A is shorter. The distances L1 and L2 correspond to the channel length of the MOSFET.

  Next, the operation of the semiconductor device 1 will be described. When the potential of the gate pad 76 (that is, the potential of each gate electrode 26) is raised to a potential higher than the gate threshold value, the source region 30 and the drift region 34 are formed in the body regions 32 of the main element region 12A and the sense element region 12B, respectively. A channel to be connected is formed, and the main element SW1 and the sense element SW2 are simultaneously turned on. For this reason, a current flows from the drain electrode 74 toward the external electrode 78 (see FIG. 1). Most of the current flows through the main element SW1 (that is, the main source electrode 70). A part of the current flows through the sense element SW2 (that is, the sense source electrode 72). The sense current flowing through the sense element SW2 can be measured by a potential difference between both ends of the sense resistor R1.

  Since the area of the sense element region is smaller than the area of the main element region, the channel resistance ratio of the sense element region is larger than the channel resistance ratio of the main element region when the areas of the sense element region and the main element region are equal. growing. However, in the semiconductor device 1 of this embodiment, the channel length L2 in the sense element region 12B is shorter than the channel length L1 in the main element region 12A. This reduces the difference between the channel resistance ratio in the sense element region 12B and the channel resistance ratio in the main element region 12A. For example, the channel resistance ratio in the sense element region 12B can be made substantially equal to the channel resistance ratio in the main element region 12A.

  When the semiconductor device 1 operates, the temperature of the semiconductor substrate 12 changes. Then, the electrical resistance of each semiconductor region (that is, the channel and other semiconductor regions) changes with temperature change. The rate of change in electrical resistance with respect to the temperature of the channel and the semiconductor region other than the channel is different from each other. However, in the present embodiment, the channel resistance ratios of the main element region 12A and the sense element region 12B are substantially equal. For this reason, the electrical resistance of the main element region 12A and the electrical resistance of the sense element region 12B change at substantially the same rate. Therefore, it is possible to suppress a change in the current ratio (that is, current sense ratio) between the main element region 12A and the sense element region 12B when the temperature changes.

  As described above, the semiconductor device 1 can suppress a change in the current sense ratio due to a temperature change. The current sense ratio is substantially equal to the ratio of the area of the main element region 12A and the area of the sense element region 12B. Therefore, the main current value can be accurately calculated by measuring the sense current value.

  Specific examples of the present invention have been described in detail above, but these are merely examples and do not limit the scope of the claims. The technology described in the claims includes various modifications and changes of the specific examples illustrated above.

  The technical elements described in this specification or the drawings exhibit technical usefulness alone or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technology illustrated in the present specification or the drawings achieves a plurality of objects at the same time, and has technical utility by achieving one of the objects.

1: Semiconductor device 12: Semiconductor substrate 12A: Main element region 12B: Sense element region 12C: Isolation region 12a: Upper surface 12b: Lower surface 22: Trench 24: Gate insulating film 26: Gate electrode 28: Interlayer insulating film 30: Source region 32 : Body region 34: Drift region 36: Drain region 70: Main source electrode 72: Sense source electrode 74: Drain electrode 76: Gate pad 78: External electrode R1: Sense resistor SW1: Main element SW2: Sense element

Claims (1)

A semiconductor substrate having a main element region and a sense element region, the area of the sense element region being smaller than the area of the main element region when viewed from the upper surface side;
A trench provided on an upper surface of the semiconductor substrate in the main element region and the sense element region;
A gate insulating film covering an inner surface of the trench in the main element region and the sense element region;
A gate electrode disposed in the trench in the main element region and the sense element region and insulated from the semiconductor substrate by the gate insulating film;
With
Each of the main element region and the sense element region is
An n-type source region in contact with the gate insulating film;
A p-type body region in contact with the gate insulating film under the source region;
An n-type drift region that is in contact with the gate insulating film under the body region and is separated from the source region by the body region;
With
A lower end of the source region in a range in contact with the gate insulating film in the sense element region is located below a lower end of the source region in a range in contact with the gate insulating film in the main element region;
The distance between the source region and the drift region measured along the interface between the gate insulating film and the body region in the sense element region is a distance between the gate insulating film and the body region in the main element region. A semiconductor device shorter than a distance between the source region and the drift region measured along an interface.

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