JP5573527B2 - Semiconductor device - Google Patents

Description

  The present invention relates to a semiconductor device having a main cell portion and a sense cell portion in which an insulated gate bipolar transistor (hereinafter simply referred to as IGBT) is formed, and having a current detection resistor in an emitter electrode of the sense cell portion.

Conventionally, in order to detect a main current flowing in a main cell portion in which an IGBT is formed, a sense current smaller than the main current is supplied and connected to a current detection resistor and the sense cell portion in which the IGBT is formed is connected to the main cell portion. A semiconductor device formed therewith is known. Specifically, such a semiconductor device is configured as follows. That is, in each of the main cell portion and the sense cell portion, an n ⁺ type buffer layer is formed on the main surface of a p ⁺ type substrate as a collector layer, and an n ⁻ type drift layer is formed on the buffer layer. A p-type base region is formed in the surface layer portion of the layer. An n ⁺ -type emitter region is formed on the surface layer portion of the base region so as to be separated from the drift layer by a predetermined distance, and a portion of the surface of the base region disposed between the emitter region and the drift layer is formed. A channel region is configured. A gate electrode is formed on the surface of the base region serving as the channel region via a gate insulating film, and an emitter electrode is formed via an interlayer insulating film formed so as to cover the gate electrode. The emitter electrode is electrically connected to the emitter region and the base region through a contact hole formed in the interlayer insulating film, and is also electrically connected to a current detection resistor. Further, a back electrode common to the main cell portion and the sense cell portion is provided on the back surface of the p ⁺ type substrate.

  In such a semiconductor device, a sense current proportional to the main current flowing in the main cell portion flows in the sense cell portion and the current detection resistor. Therefore, the current value of the main current is detected by detecting the voltage across the current detection resistor. .

However, such a semiconductor device includes a heavy metal that cannot be avoided when manufacturing the semiconductor device, for example, a heavy metal that diffuses from the back electrode to the p ⁺ type substrate. There is a problem that the characteristics of the semiconductor device change over time due to diffusion.

In order to solve this problem, a gettering layer containing a large number of crystal defects is formed in a p ⁺ type substrate, and the heavy metal is captured by the gettering layer to prevent the heavy metal from diffusing. It is known to suppress changes with time (for example, see Patent Document 1).

JP 2008-41836 A

  However, even in a semiconductor device having such a gettering layer, diffusion of heavy metal cannot be completely prevented, and the semiconductor device changes over time. When heavy metal diffuses, the main current flowing through the main cell section and the sense current flowing through the sense cell section change with time, so the main current detected from the voltage across the current detection resistor and the main cell section actually There is a problem that an error occurs between the flowing main current and detection accuracy is lowered.

  FIG. 3 is a diagram showing a circuit configuration of a semiconductor device having a main cell portion and a sense cell portion and having a current detection resistor in the emitter electrode of the sense cell portion. As shown in FIG. 3, in such a semiconductor device, since the current detection resistor 9 is provided in the emitter electrode of the sense cell unit 10b, the sense cell unit is compared with the gate-emitter bias of the main cell unit 10a. The gate-emitter bias of 10b is reduced, and the electron current is less likely to flow in the sense cell unit 10b than in the main cell unit 10a. In other words, in the sense cell unit 10b, the ratio of the hole current to the entire current value is higher than that in the main cell unit 10a.

  In addition, when heavy metal diffuses, it is the hole current that is easily affected by the heavy metal. Therefore, the sense current having a high hole current ratio is more likely to change with time than the main current. That is, in such a semiconductor device, when heavy metal diffuses, the main current and the sense current change with time. For this reason, an error occurs between the main current detected from the voltage across the current detection resistor 9 and the main current that actually flows through the main cell portion 10a, and the detection accuracy decreases.

  An object of this invention is to provide the semiconductor device which can suppress that detection accuracy falls in view of the said point.

  In order to solve the above problems, the present inventors have provided a semiconductor device having a main cell portion and a sense cell portion in which an IGBT having a gettering layer is formed, and a current detection resistor connected to the emitter electrode of the sense cell portion. First, investigation was conducted focusing on the resistivity of the drift layer, and the following knowledge was obtained.

  That is, when the resistivity of the drift layer in the main cell portion and the sense cell portion is lowered, an electron current is easily injected from the emitter region into the drift layer, so that the ratio of the electron current to the entire current value can be increased. In other words, the ratio of the hole current to the entire current value can be reduced. As described above, it is the hole current that is easily affected by the heavy metal when the heavy metal diffuses.

  For this reason, the inventors can reduce the main current and the sense current over time by decreasing the resistivity of the drift layer and reducing the ratio of the Hall current to the entire current value, respectively, It has been found that the difference in the rate of change with time of the current and the main current can be reduced, and that the detection accuracy of the semiconductor device can be suppressed from decreasing.

  However, in such a semiconductor device, by reducing the resistivity of the drift layer, the difference in the rate of change with time of the main current and the sense current can be reduced, but the new withstand voltage as a semiconductor device is lowered. A problem will occur.

  For this reason, the inventors next focused on the fact that the sense current has a higher Hall current ratio with respect to the entire current value, and the sense current is more likely to change with time than the main current, as described above. In other words, this characteristic is that the rate of change with time of the operating resistance of the main cell unit is different from the rate of change with time of the combined resistance of the operating resistance of the sense cell unit and the current detection resistor.

  That is, in such a semiconductor device, as shown in FIG. 3, the main current and the sense current have a ratio of the operating resistance of the main cell unit and the combined resistance of the operating resistance of the sense cell unit and the current detection resistor. Flow in response. For this reason, in order to suppress the difference in the change rate with time of the main current and the sense current, the change rate with time of the operating resistance of the main cell unit and the combined resistance of the operation resistance of the sense cell unit and the current detection resistor It is only necessary to suppress the difference from the rate.

  In such a semiconductor device, since the resistivity of the current detection resistor does not change with time, the operation resistance of the main cell unit and the operation resistance of the sense cell unit may be adjusted. For example, when the heavy metal diffuses, the change rate with time of the operating resistance of the main cell unit is 1.1 times, the initial operating resistance of the sense cell unit is 40Ω, and the current detection resistance is 10Ω, Consider a case where the initial operating resistance is 5Ω and the current detection resistance is 10Ω. That is, consider the case where the combined resistance before the change with time is 50Ω and the case where it is 15Ω.

  In this case, assuming that the change rate with time of the sense cell unit is 1.3 times, when the initial operation resistance of the sense cell unit is 40Ω, the operation resistance of the sense cell unit after change with time is 52Ω, and the operation resistance of the sense cell unit is And the combined resistance of the current detection resistor is 62Ω. That is, the rate of change of the combined resistance with time is 1.24 times. When the initial operating resistance of the sense cell portion is 5Ω, the operating resistance of the sense cell portion after the change with time is 6.5Ω, and the combined resistance of the operating resistance of the sense cell portion and the current detection resistor is 16.5Ω. That is, the rate of change with time of the combined resistance is 1.1 times.

  In other words, in such a semiconductor device, the initial change resistance of the main cell portion and the sense cell portion is set to a predetermined value although the change rate with time of the operation resistance of the main cell portion is different from the change rate with time of the operation resistance of the sense cell portion. By doing so, it is possible to suppress the difference between the rate of change over time of the operating resistance of the main cell unit and the rate of change over time of the combined resistance of the operating resistance of the sense cell unit and the current detection resistor. The operating resistance of the main cell unit and the operating resistance of the sense cell unit are determined according to the cell number ratio between the main cell unit and the sense cell unit, that is, the cell ratio that is the area ratio of current flow.

  From the above, the present inventors conducted an experimental study on the difference between the cell ratio of the main cell portion and the sense cell portion and the rate of change with time of the voltage across the current detection resistor. Note that the rate of change with time of the voltage across the current detection resistor is the same as the difference in rate of change with time of the main current and the sense current. FIG. 4 is a diagram showing the relationship between the cell ratio between the main cell portion and the sense cell portion and the rate of change with time of the voltage across the current detection resistor after 2000 hours. After 2000 hours is a state in which the heavy metal is sufficiently diffused to reach a saturated state. In FIG. 4, the solid line represents a drift layer resistivity of 30 Ω · cm, the dotted line represents a drift layer resistivity of 70 Ω · cm, and the alternate long and short dash line represents a drift layer resistivity of 100 Ω · cm. Is shown.

  As shown in FIG. 4, by changing the cell ratio between the main cell portion and the sense cell portion, it is confirmed that the rate of change with time of the voltage across the current detection resistor changes, and the cells of the main cell portion and the sense cell portion are changed. When the ratio is a predetermined value, it is confirmed that the rate of change with time of the voltage across the current detection resistor is almost 0%. That is, by setting the cell ratio between the main cell portion and the sense cell portion to a predetermined value, it is possible to suppress the rate of change with time of the main current and the sense current, and to suppress a decrease in detection accuracy of the semiconductor device. It will be possible.

ところで、従来の半導体装置では、一般的に、ドリフト層の抵抗率が３０Ω・ｃｍとされ、（センスセル部／メインセル部）^１／２が約０・０５とされていたため、２０００時間後の電流検出抵抗の両端電圧の経時変化率が約−８％であった。このため、本発明では、ドリフト層の抵抗率が３０Ω・ｃｍ以上であり、電流検出抵抗の両端電圧の経時変化率が−５〜５％の範囲を満たすセル比とされていることを特徴としている。 For this reason, the present inventors perform a multiple regression analysis using multivariate analysis based on FIG. 4, where the resistivity of the drift layer is ρ, and the change rate with time of the voltage across the current detection resistor after 2000 hours is calculated. It has been found that the cell ratio between the main cell portion and the sense cell portion is derived by the following equation, where x is x.

By the way, in the conventional semiconductor device, since the resistivity of the drift layer is generally 30 Ω · cm and (sense cell portion / main cell portion) ^1/2 is about 0.05, the current after 2000 hours The rate of change with time of the voltage across the detection resistor was about -8%. For this reason, in the present invention, the resistivity of the drift layer is 30 Ω · cm or more, and the cell ratio in which the time-dependent change rate of the voltage across the current detection resistor satisfies the range of −5 to 5%. Yes.

That is, in the invention described in claim 1, the ratio of the number of cells of the main cell portion (10a) and the sense cell portion (10b) is defined as the cell ratio, the resistivity of the drift layer (3) is defined as ρ, and the current detection resistance When the change rate with time of the voltage at both ends in (9) is x, the cell ratio of {sense cell portion (10b) / main cell portion (10a)} is {(x + 0.22ρ + 10.08) /224.38} ² . It is a derived value, and the resistivity ρ of the drift layer (3) is 30 Ω · cm or more, and the time-dependent rate x of the voltage across the current detection resistor (9) is +5 to −5%. It is said.

  In such a semiconductor device, the cell ratio between the main cell portion (10a) and the sense cell portion (10b) is derived from the rate of change with time of the resistivity of the drift layer (3) and the voltage across the current detection resistor (9). The cell ratio is such that the resistivity of the drift layer (3) is 30 Ω · cm or more and the change rate with time is −5 to 5%.

  Therefore, the rate of change with time of the voltage across the current detection resistor (9) can be reduced as compared with the conventional semiconductor device, that is, the operating resistance of the main cell portion (10a) and the sense cell portion (10b). The difference in the rate of change with time of the combined resistance of the operating resistance and the current detection resistance (9) can be reduced. Therefore, the difference in the rate of change with time of the main current and the sense current can be reduced, and a decrease in detection accuracy can be suppressed. Moreover, since the resistivity of the drift layer (3) is 30 Ω · cm or more, the breakdown voltage of the semiconductor device can be improved as compared with the conventional semiconductor device.

  In addition, the code | symbol in the bracket | parenthesis of each means described in this column and the claim shows the correspondence with the specific means as described in embodiment mentioned later.

1 is a top surface layout of a semiconductor device according to a first embodiment of the present invention. It is a figure which shows the cross-sectional structure of the semiconductor device shown in FIG. It is a figure which shows the circuit structure of the semiconductor device shown in FIG. It is a figure which shows the relationship between the cell ratio of a main cell part and a sense cell part, and the time-dependent change rate of the both-ends voltage of the current detection resistance after 2000 hours.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 1 is a top surface layout of the semiconductor device according to the present embodiment, and FIG. 2 is a diagram showing a cross-sectional configuration of the semiconductor device shown in FIG.

  As shown in FIG. 1, the semiconductor device of the present embodiment includes a main cell unit 10a and a sense cell unit 10b electrically connected to a current detection resistor (not shown). IGBTs having the same basic structure are formed in the portion 10a and the sense cell portion 10b.

Specifically, as shown in FIG. 2, the main cell portion 10a and the sense cell portion 10b are formed with IGBTs using a p ⁺ type substrate 1 as a collector layer. The p ⁺ -type substrate 1 is formed with a gettering layer 1a containing many crystal defects. In this embodiment, the gettering layer 1a is an intrinsic gettering layer formed by depositing an enzyme. On the gettering layer 1a, a defect-free layer 1b formed by forming the gettering layer 1a is formed. Although not particularly limited, the p ⁺ type substrate 1 has a resistivity of 0.01 to 0.03 Ω · cm and a thickness of 500 to 580 μm.

Then, an n ⁺ type buffer layer 2 having a high impurity concentration layer is formed on the main surface of the p ⁺ type substrate 1, and an n ⁻ type drift layer 3 having a low impurity concentration is formed on the n ⁺ type buffer layer 2. Is formed. Although not particularly limited, the n ⁺ -type buffer layer 2 has a resistivity of 0.04 to 0.06 Ω · cm and a thickness of 14 to 16 μm. The n ⁻ type drift layer 3 has a resistivity of 30 Ω · cm or more and a thickness of 65 to 100 μm.

A p-type base region 4 is formed in the surface layer portion of the n ⁻ -type drift layer 3. Further, an n ⁺ -type emitter region 5 having a higher impurity concentration than that of the n ⁻ -type drift layer 3 is formed in the surface layer portion of the p-type base region 4 so as to be separated from the n ⁻ -type drift layer 3 by a predetermined distance. In the surface of the p-type base region 4, a channel region is formed at a portion disposed between the n ⁺ -type emitter region 5 and the n ⁻ -type drift layer 3.

Further, a gate insulating film (not shown) is formed by thermal oxidation or the like on the surface of the p-type base region 4 serving as the channel region and the surface of the n ⁻ -type drift layer 3 where the p-type base region 4 is not formed. In addition, a gate electrode 6 made of polysilicon or the like is formed through this gate insulating film. The gate electrode 6 is covered with an interlayer insulating film 7, and an emitter electrode (not shown) is formed on the interlayer insulating film 7. The emitter electrode is configured to be electrically connected to the n ⁺ -type emitter region 5 and the p ⁺ -type base region 4 through a contact hole formed in the interlayer insulating film 7.

  Further, the emitter electrode of the main cell unit 10a and the emitter electrode of the sense cell unit 10b are separated from each other, and the emitter electrode of the sense cell unit 10b is electrically connected to the current detection resistor. The current detection resistor is made of polysilicon, like the gate electrode 6.

Further, a common collector electrode 8 corresponding to the back surface electrode of the present invention is provided on the back surface of the p ⁺ type substrate 1 with respect to the main cell portion 10a and the sense cell portion 10b.

  FIG. 3 is a diagram illustrating a circuit configuration of the semiconductor device. As shown in FIG. 3, in such a semiconductor device, the main current flowing through the main cell unit 10a can be detected by detecting the sense current flowing through the sense cell unit 10b. That is, the current value flowing through the main cell portion 10a can be detected by detecting the voltage across the current detection resistor 9.

  In the present embodiment, the cell ratio between the main cell portion 10a and the sense cell portion 10b is a value based on the following (Equation 2). As described above, the initial operating resistance of the main cell unit 10a and the initial operating resistance of the sense cell unit 10b are set to a predetermined value, that is, the cell ratio between the main cell unit 10a and the sense cell unit 10b is set to a predetermined value. This is because the difference between the temporal change rate of the operating resistance of the main cell unit 10a and the temporal change rate of the combined resistance of the operating resistance of the sense cell unit 10b and the current detection resistor 9 can be suppressed. In other words, it is possible to suppress the difference in the rate of change with time of the main current and the sense current.

  FIG. 4 is a diagram showing the relationship between the cell ratio of the main cell portion 10a and the sense cell portion 10b and the change rate with time of the voltage across the current detection resistor 9 after 2000 hours, as described above. As shown in FIG. 4 and as described above, by setting the cell ratio between the main cell portion 10a and the sense cell portion 10b to a predetermined value, the rate of change of the voltage across the current detection resistor 9 with time can be suppressed. Then, when multiple regression analysis is performed using multivariate analysis based on FIG. 4, if the resistivity of the drift layer 3 is ρ, the rate of change x with time of the voltage across the current detection resistor 9 after 2000 hours is It is expressed by a formula.

すなわち、上記式より、（センスセル部／メインセル部）は次式で表される。

そして、本実施形態では、メインセル部１０ａとセンスセル部１０ｂとのセル比が、ドリフト層３の抵抗率ρが３０Ω・ｃｍ以上であり、電流検出抵抗９の両端電圧の経時変化率ｘが−５〜５％である数値を代入した値とされている。例えば、ドリフト層３の抵抗率を７０Ω・ｃｍとし、電流検出抵抗９の両端電圧の経時変化率を約０となる半導体装置とする場合には、メインセル部１０ａとセンスセル部１０ｂとのセル比が約７８とされる。

That is, from the above equation, (sense cell portion / main cell portion) is expressed by the following equation.

In the present embodiment, the cell ratio between the main cell portion 10a and the sense cell portion 10b is such that the resistivity ρ of the drift layer 3 is 30 Ω · cm or more and the rate of change x with time of the voltage across the current detection resistor 9 is − It is a value obtained by substituting a numerical value of 5 to 5%. For example, in the case of a semiconductor device in which the resistivity of the drift layer 3 is 70 Ω · cm and the time-dependent change rate of the voltage across the current detection resistor 9 is about 0, the cell ratio between the main cell portion 10a and the sense cell portion 10b. Is about 78.

  As described above, in the semiconductor device of the present embodiment, the cell ratio between the main cell portion 10a and the sense cell portion 10b is a value derived from the change rate with time of the resistivity of the drift layer 3 and the voltage across the current detection resistor 9. The cell ratio is such that the resistivity of the drift layer 3 is 30 Ω · cm or more and the rate of change with time is −5 to 5%.

  Therefore, the rate of change with time of the voltage across the current detection resistor 9 can be reduced, that is, the operation resistance of the main cell unit 10a and the combined resistance of the operation resistance of the sense cell unit 10b and the current detection resistor 9 with time. The difference in change rate can be reduced. Therefore, the difference in the rate of change with time of the main current and the sense current can be reduced, and a decrease in detection accuracy can be suppressed. Moreover, since the resistivity of the drift layer 3 is 30 Ω · cm or more, the breakdown voltage of the semiconductor device can be improved.

(Other embodiments)
In the first embodiment, the first conductivity type region is assumed to be p-type and the second conductivity type region is assumed to be n-type. However, the first conductivity type region is assumed to be n-type and the second conductivity type region is assumed to be p-type. Is also possible. Also in this case, the difference in the rate of change with time of the main current and the sense current can be suppressed by appropriately adjusting the cell ratio between the main cell portion 10a and the sense cell portion 10b.

1 p ⁺ type substrate 1a gettering layer 2 buffer layer 3 drift layer 4 base region 5 emitter region 6 gate electrode 7 interlayer insulating film 8 collector electrode 9 current detection resistor 10a main cell unit 10b sense cell unit

Claims (2)

A semiconductor device having a main cell portion (10a) for flowing a main current and a sense cell portion (10b) for flowing a sense current smaller than the main current,
Both the main cell portion (10a) and the sense cell portion (10b)
A first conductivity type semiconductor substrate (1);
A gettering layer (1a) formed on the semiconductor substrate (1);
A second conductivity type buffer layer (2) formed on the semiconductor substrate (1);
A drift layer (3) of a second conductivity type formed on the buffer layer (2);
A first conductivity type base region (4) formed in a surface layer of the drift layer (3);
A second conductivity type emitter region (5) formed in a surface layer portion of the base region (4);
A gate insulating film formed on the channel region when a surface of a portion of the base region (4) sandwiched between the emitter region (5) and the drift layer (3) is a channel region When,
A gate electrode (7) formed on the gate insulating film;
An emitter electrode electrically connected to the emitter region (5);
A backside electrode (8) formed on the backside of the semiconductor substrate (1), and an insulated gate bipolar transistor comprising:
The emitter electrode of the sense cell portion (10b) is connected to a current detection resistor (9) for flowing the sense current,
The ratio of the number of cells between the main cell part (10a) and the sense cell part (10b) is the cell ratio, the resistivity of the drift layer (3) is ρ, and the voltage of both ends of the current detection resistor (9) is timed. When the rate of change is x, the cell ratio of {the sense cell portion (10b) / the main cell portion (10a)} is a value derived from {(x + 0.22ρ + 10.08) /224.38} ² . The semiconductor device, wherein the drift layer (3) has a resistivity ρ of 30 Ω · cm or more and the temporal change rate x is +5 to −5%.
The semiconductor device according to claim 1, wherein the current detection resistor is made of polysilicon.

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