JPH07123140B2 - Method for manufacturing semiconductor integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (A) Field of Industrial Application The present invention relates to a semiconductor integrated circuit including a transistor that can satisfy all of Icmax, breakdown voltage, and h _FE .

(B) Conventional technology Since the basic technical idea is to use each diffusion region in common in a semiconductor integrated circuit to simplify the process, each circuit element is configured with a common diffusion region, and the same chip is used. All of the above elements (NPN transistors) had the same characteristics.

However, in consumer ICs, especially audio ICs, etc., power system transistors in the output stage are often incorporated at the same time as various signal processing circuits, and due to circuit requirements, small signal transistors for signal processing and output stage transistors are used. There is a demand to make the current amplification factor h _FE different from that of the large signal transistor. That is a request that the h _FE of the small signal Torajisuta when 100 to 200, to increase the maximum collector current Icmax lowers the h _FE of the large-signal transistor to about 50.

As means for changing h _FE as described above, for example, Japanese Patent Laid-Open No.
There is a means for separately forming the base region as described in Japanese Patent Publication No. 70756.

That is, as shown in FIG. 3, each island (3) obtained by separating the epitaxial layer (1) by the separation region (2) has a base region (5) for the small signal transistor ( 4 ) and a large signal transistor ( 6 ). And the base region (7) of the above are individually formed. At this time, two methods can be considered for the base region (7) of the large signal transistor ( 6 ). One is a method to reduce the h _FE by setting a high impurity concentration (Fig. 4, Fig. 1).
2) Deepen the diffusion depth (widen the base width)
It is a technique to reduce the h _FE (second draft Figure 4).

(C) Problem to be Solved by the Invention However, the above-mentioned method has a drawback in that it cannot be increased so much due to the saturation limit of boron with respect to silicon crystals, and thus there is a limit in reducing h _FE . Besides, there is a concern that the breakdown voltage may be deteriorated due to the Zener breakdown, and when the base region (7) is formed by ion implantation, the treatment time becomes long due to the increase of the dose amount, which complicates the process. On the other hand,
Although the latter method meets the purpose of lowering h _FE , there is a close relationship between the impurity concentration and the diffusion depth, and the impurity concentration of the base decreases, which causes conductivity modulation, so that Icmax does not increase. was there. Therefore, if h _FE same base concentration is the higher can be increased Icmax. Even if both the impurity concentration and the base width are controlled, it is still difficult to satisfy both h _FE and Icmax.

(D) Means for Solving the Problems The present invention has been made in view of the above-mentioned conventional drawbacks, and a base region (26) is formed at the bottom of the base region (26) of a large signal transistor ( 25 ) having a relatively high impurity concentration. By forming the low-concentration base region (28) having a lower impurity concentration, a large-signal transistor ( 25 ) having a smaller h _FE than the small-signal transistor ( 16 ) coexists and the low-concentration base region (28) is formed. 28) and IIL ( 20 ) well area (2
By simultaneously forming 3) and 3), it is possible to coexist with IIL.

According to (e) acts present invention, since the base width of the large signal transistor by superimposed low concentration base region (28) (25) widens less than the h _FE of the h _FE small signal transistor (16) And it can be controlled to an appropriate value. Moreover,
Since a part of the base is composed of the base region (26) having a relatively high impurity concentration, the maximum collector current Icmax can be increased. Since the low-concentration base region (28) of the large signal transistor ( 25 ) and the low-concentration well region (23) of the IIL ( 20 ) are simultaneously formed, they can coexist efficiently.

(F) Embodiment One embodiment of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a sectional view showing a semiconductor integrated circuit according to the present invention. In the figure, (11) is a P-type silicon single crystal substrate,
(12) is an N ⁻ type epitaxial layer formed by epitaxial growth on the surface of the substrate (11), (13) is an N ⁺ type buried layer, and (14) surrounds the buried layer (13) and penetrates the epitaxial layer (12). The P ⁺ -type isolation region (15) is an island individually isolated by the isolation region (14).

One of the islands (15) has a small signal transistor ( 16 )
To form the P type base region (17) and the N ⁺ type emitter region (18), the island (15) is used as a collector to form a vertical NPN transistor. (19) is an N ⁺ type collector contact region.

On the other island (15), a P-type injector region (21), an extrinsic base region (22), and P ⁻ are formed to form IIL ( 20 ).
Type well region (23) and N ⁺ type collector region (24) are formed, and IIL is formed using the well region (23) as the base of the reverse vertical inverter transistor. Well area (2
By using 3) as a base, a high reverse β can be obtained because the base is close to the N ⁺ type buried layer (13) which is a main carrier injection from the emitter of the inverter transistor to the base.

Then, in another island (15), a P-type base region (26) and an N ⁺ -type emitter region (27) are formed in order to form a large signal transistor ( 25 ), and the island is overlaid on the base region (26). A P ^- type low concentration base region (28) was formed. (29)
Is an N ⁺ collector contact region, (30) is a silicon oxide film, and (31) is each electrode. The base regions (17) (26) and the emitter regions (18) (27) were formed in the same process. The well region (23) of the IIL ( 20 ) and the low concentration base region (28) of the large signal transistor ( 25 ) were formed simultaneously.

Since the IIL well region (23) is intended to have the base-emitter junction close to the buried layer (13) as described above, it has a deep diffusion depth and a low impurity concentration in order to increase the inverse β. There is. Specifically, the base area (17)
(26) has a surface concentration of 10 ¹⁸ atoms · cm ^-2 and a diffusion depth of 1.0 to 1.5
well region (23) has a surface concentration
10 ¹⁶ to 10 ¹⁷ atoms · cm ^-2 and a diffusion depth of 2.0 to 3.0 μ are formed.

Since the well region (23) and the low-concentration base region (28) of the large signal transistor ( 25 ) are formed simultaneously, the low-concentration base region (28) naturally has the above-mentioned impurity concentration and depth. When the impurity concentration is lowered as described above, the increase in the leak current due to the surface depletion of impurities is feared, so the low concentration base region (28) is formed so as not to protrude from the base region (26). That is, the entire surface of the low-concentration base region (28) is superposed so as to be covered with the base region (26).

Since the large signal transistor ( 25 ) has the base region (26) and the low concentration base region (28) below the emitter region (27), its impurity concentration profile has a distribution as shown in FIG. That is, it has a two-step inclination, a relatively steep inclination formed by the base region (26) having a relatively high impurity concentration and a gentle inclination formed by the low concentration base region (28) having a relatively low impurity concentration. . As a result, the base width W _B of the large signal transistor ( 25 ) is determined by the diffusion depth of the low-concentration base region (28) as shown in FIG.
The base width can be made larger and the current amplification factor h _FE can be made smaller than that of the small signal transistor (17) having only 6). Since it is a low impurity concentration region, h _FE will not drop too much. At the same time, the base of the large signal transistor ( 25 ) has a relatively high impurity concentration in the base region (2
Since 6) overlaps, the influence of the conductivity modulation of the base is small, and therefore the increase in Icmax obtained by lowering h _FE can be maximized.

2A to 2D show a method of manufacturing the integrated circuit of the present application.

First, as shown in FIG. 2A, an epitaxial layer (12) is formed on a substrate (11) on which a buried layer (13) and a lower isolation region (14) are formed, and boron (B) is added to a low concentration base region ( 2
8) and the well region (23) are selectively ion-implanted in a necessary dose amount, and heat treatment is applied to the entire substrate (11) as shown in FIG. The doped boron (B) is driven in to a desired depth to form an upper isolation region (14) as shown in FIG. 2C, and then boron (B) is selectively ion-implanted and driven in again. As a result, the base region (17) of the small signal transistor ( 16 ), the base region (27) of the large signal transistor ( 25 ), the external base region (22) of the IIL ( 20 ) and the injector region (21) are all formed simultaneously. Then, as shown in FIG. 2D, the emitter regions (18) and (27) of the small signal transistor ( 16 ) and the large signal transistor ( 25 ) and the collector region (2 of the IIL ( 20 ) are diffused by the emitter diffusion.
4) to form.

According to the configuration of the present application, the small signal transistor ( 16 ) and the large signal transistor ( 25 ) are formed by subjecting the diffused low-concentration base region (28) to base diffusion to prevent the diffusion depth from fluctuating even if some heat treatment is applied. Therefore, the base diffusion can be controlled and diffused for the small signal transistor ( 16 ). Therefore, it is extremely easy to control the characteristics of both the small signal transistor ( 16 ) and the large signal transistor ( 25 ).

(G) Effect of the Invention As described above, according to the present invention, by superimposing the low-concentration base region (28) on the large-signal transistor ( 25 ), the small-signal transistor ( 16 ) and _hFE having a high h _{FE can be obtained.} Has the advantage that it can easily coexist with a large signal transistor ( 25 ) having a small size. In addition, since the base of the large signal transistor ( 25 ) is overlapped with the base region (26) having a relatively high impurity concentration, the decrease in Icmax due to conductivity modulation is small, and therefore the advantage that Icmax can be maximized is obtained. Have.
Furthermore, there is an advantage that ASO can be increased by lowering the h _FE of the large signal transistor ( 25 ) and that the transistor can be manufactured to have appropriate characteristics as an output stage transistor. And further,
The use of the low-concentration base region (28) also has an advantage that characteristics of both large signals and small signals can be easily controlled.

Furthermore, since the low-concentration base region (28) of the large-signal transistor ( 25 ) is shared with the well region (23) of the IIL ( 20 ), there is an advantage that three types of devices can coexist without increasing the manufacturing process. Also has.

[Brief description of drawings]

FIG. 1 is a sectional view for explaining the present invention, and FIGS. 2A to 2D.
Is a cross-sectional view for explaining the manufacturing method thereof, FIG. 3 is a cross-sectional view for explaining a conventional example, FIG. 4 is a view showing a conventional impurity concentration distribution, and FIG. 5 is a impurity concentration distribution of the present application. It is a figure.

Claims (1)

[Claims] 1. A large signal transistor in which a step of forming an epitaxial layer of opposite conductivity type on a semiconductor substrate of one conductivity type is carried out, impurities of one conductivity type are ion-implanted into the surface of the epitaxial layer and diffused to a desired depth. Low concentration base region and IIL
A well region of the epitaxial layer is selectively diffused into the surface of the epitaxial layer, and is shallower than the base region for the small-signal transistor and the low-concentration base region for the large-signal transistor. A step of forming a base region having an impurity concentration higher than that of the low-concentration base region, and an injector region and an external base region of IIL, selectively introducing an impurity of a reverse conductivity type, and a surface of the base region of the small signal transistor. And a collector region on the surface of the well region of the IIL, wherein the emitter region is formed in a portion where the low-concentration base region and the base region of the large signal transistor overlap each other, and the collector region is formed on the well region surface of the IIL. Manufacturing method of semiconductor integrated circuit.