JPH0138379B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to semiconductor devices, and in particular to improved power transistors with improved secondary breakdown resistance (Es/b) for use in electronic ignition devices (igniters) for automobiles, motorcycles, etc. Regarding.

Generally, a method of connecting a clip diode between the collector and base in order to increase this secondary breakdown resistance (Es/b) or to protect the transistor from surge voltage is well known.

Figure 1 shows the equivalent circuit of a Darlington-connected power transistor with a monolithic built-in diode. In this diagram, Q ₁ is the front stage (drive)
_Q2 is a transistor for the latter stage (output). D is a diode for the purpose of dissipating the energy applied to the transistor _Q2 when a reverse voltage is applied, and R1 _{and R2} are resistors connected between the emitter and base for the purpose of stabilizing leakage current. D _A is a built-in clip diode for the purpose of increasing secondary breakdown resistance (Es/b). This diode _DA is designed to break down at a value lower than the collector-emitter sustaining voltage V _CE (sus) of the transistor itself. Furthermore, this diode D _A
The effect of this will be explained.

When applied to a fully transistorized igniter circuit, the power transistor is turned off by an applied voltage V _CC and then turned on when an input signal is applied to the base, and the collector current flows through the ignition coil (not shown). flowing. Then, when the base current is cut off, the collector current is cut off, but at this time, a high kickback voltage is applied to the transistor due to the energy stored on the primary side of the ignition coil. If the clip diode _DA is not used, the operating point at this time is the V _CE (sus) value of the transistor, which tends to exceed the safe operating area. When the clipping diode _DA is included, the kickback voltage is clipped by the breakdown voltage V _A of the clipping diode _DA , so the operating point is relatively low, compared to the case without the clipping diode _DA . The secondary breakdown resistance (Es/b) can be increased.

FIG. 2 shows a cross-sectional structure of a conventional chip of a Darlington-connected power transistor in which a clip diode _DA having the above-mentioned effects is monolithically built-in.

In this figure, 1 is an n-type (n ⁺ type) collector region with a high impurity concentration, 2 is an n-type (n ^- type) collector region with a low impurity concentration, and 3 is two transistors Q ₁ , Q forming a Darlington connection. p common to ₂
The p-type base region 4 is directly under and in contact with the base portion of the transistor _Q1 of the p-type base region 3 to form a clip diode D _A.
n ^- type region formed in n-type collector layer 2, 5
is the n ⁺ type emitter region of transistor Q ₁ , 6 is the n ⁺ type emitter region of transistor Q ₂ , 7 is the base electrode of transistor Q ₁ , and 8 is the n + type emitter region of transistor Q ₁ .
Electrode wiring formed across the n ⁺ type emitter region 5 and the base part of the transistor Q ₂ in the p type base region 3, 9 is the emitter electrode of the transistor Q ₂ , and 10 is the collector electrode common to the transistors Q ₁ and Q _2. , 11 is a passivation film that protects the ends of each bond exposed on the main surface of this device.

FIG. 3 is a profile diagram of impurity concentration in a cross section taken along the dashed line of the conventional structure shown in FIG. In the profile of the conventional clip diode D _A built-in part, an example of each region is shown as follows: The surface impurity concentration N _s of the p-type base region 3 is
2×10 ¹⁸ atoms/cm ² , depth x _j =20 μm, n
The type region 4 is formed by diffusion before the formation of the p-type base region 3, and its impurity concentration is 1×10 ¹⁵ atoms/
cm ³ , impurity concentration of n ^-type collector region 2 1.2×
The depth of the n-type region 4 until it becomes equivalent to 10 ¹⁴ atoms/cm ³ is 10 μm. The distance from directly below the p-type base region 3 to the n ⁺ -type collector region 1 is 60 μm.

In such a profile, the breakdown voltage V _A of the clipping diode D _A is determined by the resistivity of the highest impurity concentration portion of the n-type region 4 directly below the p-type base region 3 . In this way, a power transistor having a clipping diode _DA with a desired breakdown voltage can be realized.

However, the conventional structure described above has a drawback in that the clip voltage V _A has a large positive temperature dependence. Curve A shown by a solid line in FIG. 4 shows the characteristics of the clip voltage V _A of the built-in clip diode in the conventional example of FIG. 2 with respect to the ambient temperature T _a . As mentioned above, in the conventional structure, the n-type region 4
The change in specific resistance with respect to temperature has a large effect on the clip voltage of the clip diode. That is,
Since the impurity concentration of n-type region 4 is 1×10 ¹⁵ atoms/cm ³ , its specific resistance is 5 Ωcm at room temperature and at -30°C.
3Ωcm, changes to 10Ωcm at +150℃. Therefore,
The clip voltage varies widely over the range 270V to 500V.

The allowable range of clip voltage is determined by its lower limit in relation to the secondary output voltage of the ignition coil, and its upper limit in relation to secondary breakdown resistance (Es/b). Also, this relationship applies to the entire temperature range (-30℃ to +130℃) loaded on the igniter.
It is necessary to ensure that Therefore, in addition to selecting a clip diode D _{A whose clip voltage V A} at room temperature is within the desired range, for practical use, it is necessary to select a clip diode D _A taking into account low-temperature characteristics, high-temperature characteristics, and room-temperature characteristics. However, as mentioned above, changes in characteristics due to temperature may become a problem in actual use.

The purpose of this invention is to eliminate the above-mentioned drawback (temperature dependence of clip voltage V _A ) of a transistor with a built ^- in clip diode ^. is formed to constitute the diode, and a clip voltage adjustment region is formed in the n ^- type region, and the distance between the region and the p-type base region is equal over the entire circumference of the adjustment region. An n ⁺ -type region is formed, and a base electrode is further formed with an insulating film interposed therebetween so as to completely cover the diode region.

Examples of the present invention will be described below.

FIG. 5 is a cross-sectional structural diagram showing an embodiment of the present invention. FIG. 6 is a profile diagram of the impurity concentration in a cross section taken along the dashed line in FIG. 5, and the same reference numerals as in the conventional example indicate the same regions. In this example,
The n-type region 4 provided under and in contact with the p-type base region 3 in the conventional example is not formed, and the lower surface and the entire circumferential surface of the p-type base region 3 are all in contact with the n ^- type collector region 2. and, moreover,
The n ^- type collector region 2 protrudes into the base portion of the transistor Q ₁ of the p type base region 3 and reaches the surface, thereby causing the p type base region 3 and n The junction with the surface of the ^{n -} type collector region serves as a clipping diode, and the gap between the n-type collector region and the p-type base region 3 serves as a clip voltage adjustment region on the surface of the n-type collector region. n ⁺ shaped area 4a so that it is equal over the entire circumference of the adjustment area
is formed. In the figure, the p-type base region 3 separated on both sides by the entry of the n ^- type collector region 2 is connected to each other by a metal electrode 7a, and the n ^- type collector region 2 and the n ⁺ -type region exposed on the surface. The surface of the electrode 4a is covered with an insulating film so as not to come into contact with the metal electrode 7a, and the metal electrode 7a completely covers the surface thereof. The other parts are the same as the conventional row.

Next, the effects will be explained.

The breakdown voltage value V of this example configuration is V=(2/X _nB W _C −W _C ² /X _nB )V _B , where, X _nB : Theoretical width of the depletion layer at breakdown V _B : Theoretical Breakdown value V _C : Given by the range of actual high resistance values. The theoretical breakdown value refers to the withstand voltage when W _C is sufficiently larger than X _nB . In this case, resistance has temperature dependence, and even if V _B changes, the increase in resistance is proportional to the increase in x _nB , so temperature changes in breakdown voltage V are suppressed.

To ^give a specific numerical example, in ^the embodiment shown in FIG.
The impurity concentration of n ^- type collector region 2 is 1.2×10 ¹⁴ atoms/cm ² (specific resistance ρ at room temperature ₎ .
= 60 Ωcm), the change in specific resistance ρ in the temperature range of -30°C to +150°C is 40 to 100 Ωcm, and the change in the above-mentioned X _nB is 100 to 150 μm. Therefore, the maximum change in breakdown voltage value V is 300 to 380V, which is significantly improved over the conventional example described above. Ambient temperature of clip voltage V _A in an example using such a clip diode
In order to compare the characteristics with respect to T _a with those of the conventional example, the broken line curve B is shown in FIG. From this figure, it can be seen that in the device of this embodiment, the clip voltage hardly changes with respect to temperature changes.

Furthermore, since the diode region and the clip voltage adjustment region are incorporated into the base region 3, the chip area can be used effectively. Furthermore, since the n ^- type collector region surrounded by the p-type base region 3 is completely covered by the base electrode 7a via the insulating film 11, the insulating film is not deteriorated or degraded by outside air.
That is, it is possible to prevent the clip voltage from changing over time and furthermore to prevent the influence of an external electric field on the diode region and the adjustment region.

Note that the entire portion of the n ^- type region 2 sandwiched between the p type base region 3 and the n ⁺ type region 4a is covered with the insulating film 11.
By completely covering the metal electrode 7a through the metal electrode 7a, the influence of ionic contamination from the outside can be prevented, and a highly reliable clip diode can be obtained.

FIG. 7a is a plan view of only the clipping diode portion of this embodiment, and FIG. 7b is a plan view showing a modified example of the pattern of the n ⁺ type region 4. In either case, it goes without saying that similar effects can be obtained even if a more complicated pattern is used.

As described above, according to the semiconductor device according to the present invention, in a semiconductor device having a clip diode for increasing the secondary breakdown resistance of an element, a p-type base region of a transistor is connected to an n ^- type collector layer. An n ^- type region is formed to configure the diode, and within the n ^- type region,
An n ⁺ -type region is formed as a clip voltage adjustment region so that the distance between the region and the p-type base region is equal over the entire circumference of the adjustment region, and an insulating region is formed so as to completely cover the diode region. Since the base electrode is formed through the film, it is possible to reduce the chip area, and it is also possible to reduce fluctuations in clip voltage due to temperature changes, as well as to suppress fluctuations in clip voltage over time and due to external electric fields. There is.

[Brief explanation of drawings]

Figure 1 is an equivalent circuit diagram of a Darlington-connected power transistor with a built-in voltage clip diode.
FIG. 2 is a cross-sectional view showing a conventional semiconductor device in which the above structure is integrated, and FIG. 3 is a profile diagram of impurity concentration in a cross section taken along the dashed line in FIG.
FIG. 4 is a characteristic diagram showing the temperature dependence of the clipping voltage of a clipping diode, FIG. 5 is a cross-sectional view showing an embodiment of the present invention, and FIG. FIG. 7a is a plan view of only the clipping diode portion of this embodiment, and FIG. 7b is a plan view showing another embodiment. In the figure, 2 is an n ^- type collector region, and 3 is a p-type collector region.
4a is an n ⁺ type (first conductivity type high impurity concentration) region, 5 and 6 are n ⁺ type emitter regions,
7a is a metal electrode (low resistance conductor layer), and 11 is an insulating film. Note that the same reference numerals in the figures indicate the same or equivalent parts.

Claims (1)

[Scope of Claims] 1. A semiconductor device having a function of increasing secondary breakdown resistance of an element, comprising: a first conductivity type low concentration collector layer formed on a first conductivity type high concentration collector layer; and the low concentration collector layer. A transistor comprising a second conductivity type base region formed in a surface region of a layer, and a first conductivity type emitter region formed in the base region, the second conductivity type base region and in the base region. a clipping diode for clipping the base-collector voltage to a predetermined potential; and a first conductive type high concentration region formed so that the distance to the second conductive type base region is equal over the entire circumference, and for adjusting the clip voltage within a predetermined range. and a base electrode formed on the first conductivity type low concentration region through an insulating film so as to completely cover the first conductivity type low concentration region.