JPS5936963A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To increase the degree of freedom for the control of withstand voltage by a method wherein extra field depletion regions are formed between P-N regions which compose a clip diode, and then the former regions are short-circuitted to junction regions according to a desired withstand voltage. CONSTITUTION:The extra field depletion ring regions are previously formed on the main surface of a semiconductor substrate, in a planar type high withstand voltage semiconductor device having at least one junction, e.g., clip diode built-in type power transistor. In other words, the field depletion ring regions 4a and 4b to obtain extra withstand voltage to the desired value of withstand voltage are formed between the P type base region 4 and an N plus type diffused region 3a which form the clip diode DA. These regions are formed to the same conductivity type as the base region 4. The ring regions 4a and 4b are connected to the base region 4 in one side or both sides, based on the evaluation of the withstand voltage of the junction of the diode DA. Since the degree of freedom for the control of withstand voltage increases thereby, the dispersion at the time of manufacture can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a semiconductor device, and more particularly, the present invention relates to a method for manufacturing a semiconductor device, and more specifically, a method for manufacturing a semiconductor device, and more specifically, a method for manufacturing a planar high-voltage semiconductor such as a diode or transistor having at least one junction on the main surface of a semiconductor substrate. The present invention relates to a control method capable of controlling the withstand voltage of a joint when manufacturing a device.

Hereinafter, the case of a power transistor with a built-in clip diode used in an electronic ignition device (igniter) for automobiles and the like will be explained as an example of a planar type high-voltage conductor device.

In general, in circuits with conductive loads such as igniters, the secondary breakdown resistance (
A well-known method is to connect a clipping diode between the collector and base in order to increase the EEIB) or to protect the transistor from surge voltage.

Figure 1 shows the circuit of a Darlington power transistor monolithically incorporating this clipping diode, where (Ql) is the front stage (drive transistor) and (Ql) is the rear stage (output) transistor. CD) is a protection diode to release the energy applied to the transistor (Q2) when reversely connected, and (
R+), (R2) are each transistor (Ql')+ (
Ql! ) is a resistor connected to stabilize the leakage current flowing between the emitter and base of the (
DA) is a built-in clip diode to increase secondary breakdown resistance (E8B), and is made of an energy diode. This clip diode (DA) is designed to break down at a value lower than the collector-emitter sustaining withstand voltage ct (port a 8) of the transistors (Ql) and (Q2) themselves.

Here, the effect of the clip diode (DA) when applied to an igniter will be explained. In general, in a transistor-type igniter circuit, a power transistor is turned on when an input signal is applied to its base from a state cut off by an applied voltage VCC, and the collector current increases.

Then, when the base current is cut off, a high voltage is applied to the transistor due to the energy stored in the primary side of the ignition coil. At this time, the VCx (su8') of the transistor is It takes the value shown by the curve ■ shown in the figure, which is outside the safe operating area.However, if a clip diode is used, the kick bank voltage is the clip voltage (also called plater down voltage) of the clip diode (DA). As a result, the VOR (80B') becomes relatively low as shown in curve l in Figure 2, increasing the secondary breakdown resistance ('EllIB) compared to the case without the clip diode (DA'). It is possible.In addition,
The curve ■ in Figure 2 is the clip voltage V of the clip diode.
yolc(sns), in which case the clip diode no longer performs its function.

Next, a clip diode (DA
) is shown in FIG. 3, which shows the structure of a conventional Darlington power transistor chip. In the figure, (1) is an N-type collector region made of a silicon substrate having a -conductivity type, and (2) is an N-type collector region (1
) is formed by diffusion on one main surface of the transistor (Ql) to reduce its resistance, and (3) is formed directly under the base region of the transistor (Ql) in order to form the clip diode (2). The completed N-type diffusion region (4) represents each transistor (Ql') formed by diffusion on the other main surface of the N-type collector region (1).
l (Qg), (5) is the N+ type emitter region of the transistor (Ql), (6) is the N+ type emitter region of the transistor (Q2), (7) is the base electrode, and (8) is the The N+ type emitter region (5) of the transistor (Ql) and the base electrode (7) of the transistor (Q2)
), (9) is the emitter electrode, (10
) is the collector electrode.

-Also, (11) is a vancipation film that preserves the surface of each PN junction.

In such a structure, a clip diode (DA)
The crimp voltage Vm is determined by the resistivity of the highest concentration portion of the N-type diffusion region (3) directly below the P-type base region (4).

However, the conventional structure described above has the following drawbacks. In other words, the permissible range of the clip voltage Vm is determined by the relationship between the lower limit and the secondary output voltage of the ignition coil in the case of an igniter, and the upper limit based on the secondary breakdown resistance (E
8B), and the main transistor V
determined by the lower bound of the distribution of an(sos').

This range is usually 300 to 450V, but
In the conventional structure, it is very difficult to control the clipping voltage Vm within this range. Unfortunately, the yield during manufacturing is low. The reason for this is that in order to determine the clip voltage Vm, the N-type diffusion region (
This is because the specific resistance of 3) is extremely likely to vary due to structure and manufacturing.

This will be explained using specific numerical examples.

For mass production, an N-type substrate (1
) is usually on the order of 15 cm, and the N-type diffusion region (3) is formed by deep, low-concentration diffusion, but even if ion implantation with small variations is used, variations in surface concentration will cause The variation in resistivity directly under the P-type pace area (4) is ±10 inches, and the variation in the depth direction is also ±1096.
It is. Furthermore, when forming the P-type pace region (4), the variation in resistivity directly under the pace region is 10%, 10%.
Therefore, the specific resistance (impurity concentration) of the N-type diffusion region (3) directly under the P-type base region determines the clip voltage VA.
The total variation range of 1 uJ is as high as 55% if intermediate steps such as re-diffusion are not controlled, and the clip voltage distribution is also distributed from 170 to 580 V with a maximum of 375 V as the center. In actual manufacturing, by controlling the depth of the P-type base region (4),
(adding the re-diffusion step), it becomes 125%, which is 280-47
Although it is possible to improve the voltage to about 0V, the range of freedom of control becomes limited because the pace diffusion is directly related to hym and Vom (st+s) of the main transistor. Therefore, in the above-mentioned conventional device, the crimp voltage varies greatly and the yield rate 9 decreases, making it difficult to manufacture an inexpensive monolithic power transistor with a built-in clip diode.

In order to improve this problem, the applicant has developed a clip diode (DA) as shown in FIGS. 4 and 5.
) is proposed as a reach-through type in which an N+ type diffusion region 3a) is formed between the P type pace regions (4). According to this structure, the clip voltage VA of the clip diode (DA) is determined by variations in the N-type substrate (1), the N4-type diffusion region (3a-), the P-type space region (4a-), and the variation in the N-type substrate (1).
) is determined by the distance t. At this time, N-type board (1)
The variation in specific resistance is 115%, and the N+ type diffused region 3a
) is ±5q6,N with respect to the distance t.
The lateral variations in the diffusion of the +-shape and P shadow regions (3a) and (4) are about ±5%, which is about 5 cm with respect to the distance t, so the overall variation is about ±30%. The breakdown voltage distribution can also be improved from 375v to a maximum of 260 to 490v. However, even in this case, in order to further reduce the overall variation, it is necessary to control intermediate processes such as re-diffusion, as in the case of Figure 3 above, so it is necessary to change the characteristics of the main transistor. There was no change, and I was not completely satisfied.

In view of the above points, the present invention was made in order to eliminate such conventional drawbacks, and aims to increase the degree of freedom in pressure resistance control and to reduce variations in characteristics during manufacturing.

In order to achieve such an object, the present invention provides a method for manufacturing a planar high-voltage semiconductor device having at least one joint on the main surface of a semiconductor substrate, which includes forming an extra field depression ring region in advance, After evaluating the breakdown voltage of the junction, the breakdown voltage is controlled by short-circuiting the depletion ring region and the semiconductor region forming the junction as necessary during electrode formation based on the evaluation results.

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 6 is a sectional view corresponding to FIG. 5 for explaining one embodiment of the manufacturing method according to the present invention, and shows the case where it is applied to a power transistor with a built-in clip diode. The same reference numerals as in FIG. 5 indicate the same or corresponding parts. In this embodiment, an extra withstand voltage is obtained between the P type space region (4) forming the clip diode (DA) and the N+ type diffused region 3a). forming P-type field depression ring regions (4&), (4b) having the same conductivity type as at least one pace region (4);
After completing the diffusion process, evaluate the value of the clipping voltage V^ at the junction of the clip diode (DA), that is, the anode-cathode junction. Based on the difference in breakdown voltage, a contact hole is formed on one extra depression ring region (4a) during the photolithography process for forming the electrode contact region after the passivation film (11) is applied. After that, during electrode formation, the P-type pace region (4)
By connecting and short-circuiting the extra depression ring region (4a) with the pace electrode (7), the withstand voltage is controlled to a predetermined value 1. In this case, the P-type base region (4a) ) and N+ type diffused region 3a)
There are two depression ring regions r4a) between
(4b) is formed, the distance between the ring regions (4a) and (4b) is tb, and the distance from the other depletion ring region M (4b) to the N''-shaped diffusion region (3a) is h.
Then, the value of this distance plus h (To +to
) corresponds to the distance t between the P type base region (4) and the N+ type diffusion region (3a) in FIG.

As described above, the present invention selectively removes one of the depression ring regions (4a) and (4b) formed between the P-type pace region (4) and the N+-type diffusion region (3a). By connecting with the P-type pace region (4), the width or distance on the N-type collector region (2) included up to the connected depression ring region (4a) no longer contributes to determining the withstand voltage, and the electrode The breakdown voltage can be lowered at the time of formation.

Therefore, the clipping force VA of the clipping diode can be controlled without changing the characteristics of the main transistor.

That is, as described above, conventionally, when manufacturing a power transistor with a built-in clip diode, variations in the distance t between the P type space region (4) and the Type 1 diffusion region (3a), which have been set to a desired breakdown voltage in advance, have been avoided. The withstand voltage was determined by variations in the resistivity of the N-type substrate (1) and the resistivity of the N-type substrate (1). In contrast, according to the present invention, the P-type base region (
4) and the N+ type diffusion region (3a) are selectively connected to the P type base region (4), the characteristics of the main transistor can be improved. It is possible to control the withstand pressure without changing it.

Note that Fig. 7 shows the relationship between the applied voltage of the clip diode (DΔ) and the width t of the depletion layer from the junction to the collector region (1), which corresponds to the difference in withstand voltage evaluation. Ring area (4a).

The more (4b) is formed, the more finely the breakdown voltage can be controlled. Also, the interval is 1143°...
・If you want the voltage width of the control to be constant for each unit, you can narrow it down. Therefore, according to the method of the present invention, the degree of freedom in pressure resistance control can be greatly improved.
As shown in Figure 8, the variation in characteristics during manufacturing is shown in the figure (a
) to (b). In Fig. 8(,) and (b), the horizontal axis represents the clip voltage Vm, and the vertical axis represents the frequency, and the symbol A indicates the non-defective range. show the cases of the conventional product and the product of the present invention, respectively.

In the above-described embodiment, a case where the present invention is applied to a power transistor with a built-in clip diode as a planar type high-voltage semiconductor device is shown, but as shown in FIG. 9, the present invention can be similarly applied to a single diode. The one in Figure 9 is N
A resistive cathode region (22) is formed on one main surface of the N-type cathode region (21) to reduce the resistance of the region, and a P-type cathode region (22) is formed on the other main surface of the N-type cathode region (21). P-type field depletion ring regions (23a), (23b) having the same conductivity type as the anode region, and forming a P-type anode region (23) around the anode region (23), (23c
), and the withstand voltage of the anode/cathode junction of the diode 9 is evaluated before the electrode forming process. Thereafter, when forming the electrode, a P-type is formed to suppress the extension from the anode-cathode junction to the depletion layer into the N-type collector region (21), which corresponds to the difference between the breakdown voltage at the time of the evaluation and the desired breakdown voltage. The anode region (23) and at least one depression ring region (23a) are connected to the anode electrode (25).
By short-circuiting at , the breakdown voltage of the diode can be controlled in the same manner as in the above embodiment. In FIG. 9, (24) is a cathode electrode, and (26) is a vancivation film. Furthermore, it goes without saying that the present invention can be similarly implemented with a single transistor in addition to the above-mentioned diode.

As explained above, the present invention provides a method for manufacturing a semiconductor device having at least one junction by forming a semiconductor region of a conductivity type opposite to that of the substrate on the main light side of a semiconductor substrate of a - conductivity type. Around the semiconductor region, there is at least one depletion ring region larger than the depletion ring region required by the predetermined withstand voltage.
Since the semiconductor region and the selected depletion ring region are short-circuited by the electrode metal in the step of forming three or more deep electrodes, the degree of freedom in controlling the withstand voltage is greatly improved, and therefore the characteristics during manufacturing can be improved. Variations can be significantly reduced and yields can be improved.

[Brief explanation of drawings]

Figure 1 is an equivalent circuit diagram of a Darlington power transistor with a built-in clip diode, Figure 2 is a characteristic diagram of the collector-emitter voltage and collector current of the transistor when high voltage is applied, and Figure 3 is an explanation of the conventional manufacturing method. FIG. 4 is a cross-sectional view of another semiconductor device illustrating another conventional manufacturing method; FIG. 5 is an enlarged cross-sectional view of a clip diode portion of the semiconductor device 1a shown in FIG. 4; FIG. 6 is an enlarged sectional view of a clip diode portion of a semiconductor device corresponding to FIG. 5 for explaining an embodiment of the manufacturing method according to the present invention, and FIG. 7 is a relationship between applied voltage and width of the depletion layer. Figure 8 (-) is a distribution diagram of the clip' internal pressure of a semiconductor device manufactured by the conventional method.
b) is a clip voltage distribution diagram of a semiconductor device manufactured by the method of the present invention, and FIG. 9 is a sectional view of the semiconductor device for explaining another embodiment of the manufacturing method according to the present invention. (1)... ・N- type collector region (silicon substrate), (2)... ・N+ type collector region, (3)
...N type diffusion region, (3a)...N+ type diffusion region, (4)...P type base region, (4a), (4b
')...P-type field depression ring region t
(5)...N+ type emitter region of transistor (Ql), (6)...N+ of transistor (Q2)
Shape eminter region, (7)... pace electrode, (8)...
...Internal wiring, (9)... -Emitter electrode, (1
0)... Collector electrode, (11)... Pansivation Il! , (21)... N- type cathode region, (n)... ・N+ type cathode region, (2
3)...P-type cathode region, (23a), (23b
), (23c) P-type field depression ring region, (24) cathode electrode, (25
)... Anode electrode, (26)... Pancipation film. Agent Makoto Kuzuno - Figure 4 Figure 5 Figure 7 Figure 95! ! Ding i, left sleeve +1: :'F (spontaneous) 1i,
i' as Office Director 1 know+, i; Display of l'l f,'+j1g
L'i Showa 57-148708 No. 2, Title of the invention (4, Method for manufacturing a semiconductor device: 3, First i+I: Xi 3 Shin 3 Shi J 11,..."17'l- 5, Details subject to amendment Column 6 of Detailed Description of the Invention of the Book, Contents of Amendment (1) “EsnJ Correct it to "Es/B".
"Avalanche diode" and correct. (3) “Breakdown” on page 4, lines 6-7 of the same book is changed to “
Breakdown” is corrected. (4) "Connect with base electrode (7)" on page 5, line 11 of the same book is corrected to "connect with base region." (5) In the second line of page 7 of the same book, “10%, 10chi” was changed to “10
%, and the variation in the depth direction is 10%.''that's all

Claims (1)

[Claims] 4. On the main surface of a semiconductor substrate of a single conductor type,
1. In a method of manufacturing a semiconductor device having at least one junction by forming a semiconductor region in the shape of A field depletion ring region having the same conductivity type as the above semiconductor region is formed, and the withstand voltage of the junction is evaluated in advance before the electrode forming step, and then, in the electrode forming step, the withstand voltage at the time of evaluation and the desired By short-circuiting the semiconductor region and at least one or more field depletion ring regions with an electrode metal in order to suppress the extension of the depletion layer from the junction portion to the semiconductor substrate corresponding to the difference in breakdown voltage of , a method for manufacturing a semiconductor device characterized by controlling the breakdown voltage to a desired value.