JP2520319B2 - Photo triac - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a means for improving the sensitivity of a commutation element by light utilizing a horizontal junction and increasing dv / dt resistance, and a lateral type It is suitable for improving the performance of the Photo Triac.

(Prior Art) FIG. 13 is a plan view of a conventional lateral photo triac, FIG. 14 is a bottom view thereof, and FIG. 15 is a schematic sectional view thereof. This photo triac is a combination of a pair of photo thyristors. In FIG. 13, an anode diffusion region A1, a cathode diffusion region K1, and a P gate diffusion region are formed on the right side of the surface of the N-type substrate 1. One thyristor is formed by P1 and the like, and the other thyristor is formed by the anode diffusion region A2, the cathode diffusion region K2, the P gate diffusion region P2, and the like that are formed on the left side of the surface of the N-type substrate 1. The anode diffusion region A1 and the P gate diffusion region P2 are connected by a gate resistor R2, and the anode diffusion region A2 and the P gate diffusion region P1 are connected by a gate resistor R1.

FIG. 14 shows its bottom surface, and an N ⁺ type diffusion region 3 is formed over the entire back surface of the N type substrate 1.

As shown in FIG. 15, the cross-sectional structure is such that a P-type anode diffusion region A1 is formed on the right side of the surface of the N-type substrate 1,
Adjacent to this, a P type P gate diffusion region P1 is formed inside the P, and an N ⁺ type cathode diffusion region K1 is formed on a part of the surface thereof. Symmetrically to these, an anode diffusion region A2, a P gate diffusion region P2, and a cathode diffusion region K2 are formed on the left side of the surface of the N-type substrate 1. N ⁺ on the entire back
A mold diffusion region 3 is formed.

Generally, the impurity concentration of the N-type substrate 1 is 10 ¹³ to 10 ¹⁵ cm ⁻³ , and the surface concentration of impurities of the N ⁺ -type cathode diffusion regions K1 and K2 and the N ⁺ -type diffusion region 3 is 5 × 10 ²⁰ cm ^−3. It is a degree.

In FIG. 15, the anode diffusion region A1 and the cathode diffusion region K2 are connected to the terminal T1, and the anode diffusion region A2 and the cathode diffusion region K1 are connected to the terminal T2. Terminal T1
Is positive and terminal T2 is negative, the first channel Ch
1 and vice versa is the second channel Ch2.

The N ⁺ type diffusion region 3 provided on the back surface of the N type substrate 1 is intended for the so-called BSF effect. As a result, the lifetime of minority carriers inside the N-type substrate 1 is equivalently increased. That is, without this N ⁺ type diffusion region 3,
Minority carriers are likely to recombine near the back surface of the N-type substrate 1.
However, in the presence of the N ⁺ type diffusion region 3, minority carriers are reflected, so that the equivalent lifetime is increased. As a result, the following advantages occur.

(1) The h _FE (PNP) of the transistor composed of the anode diffusion region A1 or A2, the N-type substrate 1, the P gate diffusion region P1 or P2 is increased, and the P gate diffusion region P1 or P2 and the cathode diffusion region K1 or K2 are increased. Photodiode photosensitivity (I
_PD ), both of which improve the photosensitivity for the firing of the photo triac.

(2) Since h _FE (PNP) can be increased, the response of the photo triac is delayed. This is the response h _FE (PNP)
Because it is proportional to Therefore, the so-called dv / dt withstand capability, which does not cause a malfunction for steep pulses, is increased.

(Problems to be Solved by the Invention) However, the conventional structure as described above has a drawback that the commutation characteristics are poor because the lifetime of holes, which are minority carriers of the N substrate 1, is long. For example, after half a cycle of alternating current where the channel Ch1 consisting of the anode diffusion region A1, N-type substrate 1, P gate diffusion region P1, cathode diffusion region K1, etc. was conducting, the rise of the applied voltage to the channel Ch2 symmetrical to this In the case of abruptness, even if there is no light incident, the channel Ch2 becomes conductive due to excess holes which are minority carriers in the N substrate 1, and commutation fails. N board 1
If there is no N ⁺ type diffusion region 3 on the back surface of B, there is no BSF effect, so the commutation characteristics are improved, but the sensitivity of the photodiode is reduced and the dv / dt withstand capability is also reduced.

Therefore, it is necessary to improve both of these properties.

(Means for Solving the Problem) In the present invention, in order to solve the above-mentioned problem, an N ⁺ type diffusion region is formed on the back surface of the N type substrate of each thyristor part which is a constituent element of the lateral photo triac. No N ⁺ type diffusion region is formed on the back surface of the N type substrate in the middle of each thyristor.

(Operation) Since the N ⁺ type diffusion region is formed on the back surface of the N type substrate of each thyristor part, each thyristor part can obtain high sensitivity and improved dv / dt withstand capability due to the BSF effect. In addition, since the N ⁺ type diffusion region is not formed on the back surface of the N type substrate in the middle of each thyristor portion, the lifetime of holes in the N type substrate corresponding to this region is shortened to improve the commutation characteristics. improves.

(Embodiment) FIG. 1 is a plan view of an embodiment of the present invention, FIG. 2 is a bottom view thereof, and FIG. 3 is a schematic sectional view taken along line AA ′. The same parts as those in the conventional example shown in FIGS. 13 to 15 are designated by the same reference numerals. The difference from the conventional example is that the N ⁺ type diffusion region 2, on the N type substrate 1 on the back surface of each thyristor part which is an element of the triac,
2 is formed. Further, the arrangement of the P gate diffusion regions P1 and P2 in each thyristor portion is changed to increase the distance between them. By increasing this distance, the effect of excess holes can be prevented and the commutation characteristics can be further improved.

1 to 3, the N-type substrate 1 is, for example, N
-Type silicon single crystal with an impurity concentration of 10 ¹³ to 10 ¹⁵ cm
Use the one from ^-3 .

As shown in FIG. 1, on the surface of the N-type substrate 1, a P-type anode diffusion region A2 is provided on the right side thereof, and a P-type P gate diffusion region P2 is provided on the outside thereof, and a part thereof. And the N ⁺ type cathode diffusion region K2 and the like are formed. These form one thyristor. Further, on the left side of the surface of the N-type substrate 1, a P-type anode diffusion region A1, a P-gate diffusion region P1, a cathode diffusion region K1 and the like are formed symmetrically with the above-mentioned thyristor constituent portion, and the other thyristor is formed. Configure.

The P type portion is simultaneously formed with boron as an impurity, and the N ⁺ type portion is formed with phosphorus, antimony, arsenic or the like as impurities.

Further, providing the gate resistance R2 between the anode diffusion region A1 and the P gate diffusion region P2 and providing the gate resistance R1 between the anode diffusion region A2 and the P gate diffusion region P1 is the same as in the conventional example. .

In FIG. 2, on the back surface of the N-type substrate 1, N ⁺ -type diffusion regions 2, 2 are formed only on the back surface of each thyristor portion. This formation is performed by photolithography at the same time as the cathode diffusion regions K1 and K2. This impurity concentration is 5 ×
It is set to about 10 ²⁰ cm ^-3 .

To form the above P-type or N ⁺ -type diffusion region, a doped CV is used.
D method, thermal diffusion method or ion implantation method is used.

After completion of the diffusion process, the Al film deposited on the surface of the device by the vapor deposition method is selectively etched to form electrode wiring on the surface.

FIG. 3 shows a cross section taken along the line AA 'in FIG. The connection of terminals T1 and T2 is the same as in FIG. The P gate diffusion regions P1 and P2 are arranged outside the cathode diffusion regions K1 and K2, and the N ⁺ type diffusion regions 2 and 2 are provided on the back surface of each thyristor portion, which is different from the conventional example of FIG. . Ch1 and Ch2
Indicates a channel in each mode of AC operation, and when the terminal T1 is positive and the terminal T2 is negative, it is indicated as Ch1.

FIGS. 4 to 6 show another embodiment of the shape and arrangement of the N ⁺ type diffusion regions 2, 2 on the back surface of the N type substrate 1.
The figure shows the back surface of each thyristor portion formed with a large area and shifted, FIG. 5 shows the respective area of FIG. 4 reduced, and FIG. 6 shows the vertical length of FIG. 4 lengthened. In each case, N ⁺ is placed in the middle of each thyristor.
The mold diffusion region 2 is not formed.

FIG. 7 is a plan view of another embodiment, FIG. 8 is a bottom view thereof,
FIG. 9 is a schematic sectional view taken along the line BB ′ of FIG. 7. The arrangement of FIG. 1 is vertically long. P gate diffusion regions P1 and P2
Are arranged in the diagonal direction of the N-type substrate 1, so that the distance between them can be increased. As shown in Fig. 8, the back surface of this element has N ^{+ on} the back surface of each thyristor.
Form diffusion regions 2, 2 are formed. Also, the BB '
The cross section is as shown in FIG. A P-type gate diffusion region P1, an anode diffusion region A1, and a gate resistance R2 are formed on the back surface of the N-type substrate 1, and a cathode diffusion region K1 is formed on the surface of the P-gate diffusion region P1. Further, an N ⁺ type diffusion region 2 is formed on the back surface of the N type substrate 1. 10th
Figures 12 to 12 correspond to Figures 4 to 6, respectively.

(Effect of the Invention) According to the present invention, since the N ⁺ type diffusion region that achieves the BSF effect is present only on the back surface of each thyristor portion, the lateral h _FE (NPN) is increased and the photosensitivity is improved. dv
/ dt tolerance can be increased. Since there is no N ⁺ type diffusion region in the middle of each thyristor part, it is possible to prevent commutation failure due to excess holes.

[Brief description of drawings]

FIG. 1 is a plan view of an embodiment of the present invention, FIG. 2 is a bottom view thereof, FIG. 3 is a schematic sectional view taken along the line AA ′ of FIG. 1, and FIGS. FIG. 7 is a bottom view of another embodiment of the bottom surface of the embodiment, FIG. 7 is a plan view of another embodiment of the present invention, FIG. 8 is its bottom view, and FIG. 9 is a schematic sectional view taken along line BB ′ of FIG. 7. FIGS. 10 to 12 are bottom views of other embodiments of the bottom surface of the embodiment of FIG. 7, FIG. 13 is a plan view of an example of the prior art, FIG. 14 is its bottom view, and FIG. FIG. 14 is a schematic cross-sectional view taken along the line CC ′ of FIG. 13. 1 ... N type substrate, 2,3 ... N ⁺ type diffusion region, A1, A2 ... Anode diffusion region, P1, P2 ... P gate diffusion region, K1, K2 ....
Cathode diffusion region, T1, T2 ...... Terminal

Claims (1)

(57) [Claims] 1. A back surface of a pair of thyristor portions formed by forming a pair of anode diffusion regions, a P gate diffusion region, and a cathode diffusion region on one surface of an N type substrate, and the other surface of the N type substrate. , A photo triac having a pair of N type diffusion layers having an impurity concentration higher than that of the N type substrate.