JPH0125233B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of Industrial Application The present invention relates to improvements in diodes incorporated in monolithic integrated circuits.

(b) Prior Art A diode with Zener characteristics that is incorporated into a conventional monolithic integrated circuit, as shown in FIG. A P ⁺ type isolation region 4 that penetrates the layer 2 and forms a plurality of island regions 3, 3, and the isolation region 4 is connected to an anode region 5.
An N ⁺ type cathode region 6 is provided in the anode region 5 and is composed of an anode electrode 7 and a cathode electrode 8 which are in ohmic contact with each region 5 and 6.

(c) Problems to be Solved by the Invention However, in such a structure, since the anode region 5 is also used as the separation region 4, many crystal defects occur on the surface of the anode region 5 when high concentration impurities are diffused. That is, since the isolation region 4 is diffused so as to penetrate the epitaxial layer 2, it is necessary to carry out high-concentration impurity diffusion for a long time, and crystal defects are extremely likely to occur on the surface thereof. As a result, as shown by the dotted line in FIG. 4, leakage current and the like occur due to crystal defects, resulting in deterioration of Zener characteristics.

(d) Means for Solving the Problems The present invention has been made in view of the above-mentioned drawbacks, and by forming an anode region 15 formed by diffusion of a low concentration impurity overlapping the surface of the isolation region 14 formed by diffusion of a high concentration impurity, it is possible to solve the problem by The purpose of this invention is to realize a method of manufacturing a diode incorporated in a monolithic integrated circuit which eliminates the drawbacks described above.

(e) Effect According to the present invention, crystal defects generated on the surface of the isolation region 14 are annealed and reduced by the diffusion of low concentration impurities in the anode region 15. As a result, good Zener characteristics can be obtained.

(f) Embodiment An embodiment of the present invention will be described in detail below with reference to FIGS. 1 and 3.

The diode according to the present invention is as shown in FIG.
A P type semiconductor substrate 11, an N type epitaxial layer 12 provided on the substrate 11, and a P ⁺ type separation that penetrates the epitaxial layer 12 and separates the epitaxial layer 12 into a plurality of island regions 13, 13. Area 1
4, and was in ohmic contact with each of the regions 15 and 16, with a P-type anode region 15 formed by low concentration impurity diffusion from the surface of the isolation region 14 and an N ⁺ type cathode region 16 diffused on the surface of the anode region 15. It is composed of an anode electrode 17 and a cathode electrode 18. 19 is an oxide film.

A feature of the present invention is that an anode region 15 is formed on the surface of the isolation region 14 by diffusing low concentration impurities. For the separation region 14, a general thermal diffusion process of boron B deposit and drive-in is used, and first, a high concentration impurity deposit with a sheet resistance Rs = 20 Ω cm ^-2 and near the solid solubility limit of boron B is performed ( initial diffusion), followed by a long drive-in (extension diffusion) at 1200°C for 10-15 hours.
The diffusion depth is 15 to 20 μm. In order to carry out such high-concentration impurity diffusion for a long time, the isolation region 1
Many crystal defects are generated on the surface of No. 4. In addition, since the initially diffused impurities are diffused by prolonged diffusion over a long period of time, the impurity concentration on the surface of the isolation region 14 is considerably lower than that at the time of deposition.
This becomes a diffusion region where the surface concentration is about 10 ¹⁹ atoms·cm ^-3 . Furthermore, in the planar technology, the formation of the oxide film 19 at the same time as the diffusion is unavoidable, and the diffusion of boron B into the oxide film 19 is also unavoidable.As a result, the impurity concentration at the outermost surface of the isolation region 14 is reduced. It decreases to 10 ¹⁷ to 10 ¹⁸ atoms cm ^-3 (surface depletion).

An anode region 15 is again formed overlying the isolation region 14 formed in this manner by a common diffusion method of depositing boron B and drive-in. That is, the anode diffusion first increases the sheet resistance.
Boron B is deposited (initial diffusion) at an impurity concentration of Rs = 200 Ω cm ^-2 , which is lower than that during separation diffusion, and then heat treatment (extension diffusion) at 1200°C for 3 to 4 hours increases the diffusion depth. Form a diffusion region of 1-2 μm. At this time, since the surface concentration of the separation region 14 is reduced to below the solid solubility due to stretching diffusion, it is possible to deposit impurities for forming the anode region 15. Specifically, base diffusion of an NPN transistor can be used, and the surface concentration of the anode region 15 after diffusion is about 5×10 ¹⁸ atoms·cm ⁻³ . As a result, separation region 14 and anode region 1
The impurity concentration of boron B in the overlapped part with 5 is:
Boron B of both is added and becomes 5.1×10 ¹⁶ ~6×
10 ¹⁸ atoms・cm ^-3 . After that, the surface concentration is again applied to the surface of the anode region 15 by thermal diffusion.
By forming a cathode region 16 of about 10 ²⁰ atoms·cm ^-3 , a diode of the present invention having a concentration profile as shown in FIG. 3 is manufactured.

In this way, since the anode region 15 and the epitaxial layer 12 are formed shallower than the anode region 15 and the epitaxial layer 12, the isolation region 1
4, it is formed in a shorter time by diffusion of impurities at a lower concentration. Therefore, no new crystal defects are generated on the surface of the epitaxial layer 12 in the process of forming the anode region 15, and many crystal defects that have occurred on the surface of the isolation region 14 are annealed during the diffusion of low concentration impurities in the anode region 15. Therefore, it decreases. Therefore, although the anode region 15 is formed overlapping the isolation region 14 and the impurity concentration in the overlapping portion is higher than that of the isolation region 14, the crystal defects on its surface are significantly reduced compared to the surface of the isolation region 14. As a result, good Zener characteristics can be obtained as shown by the solid line in FIG. 4, and the characteristics can be significantly improved compared to the conventional one.

Further, other reasons why the characteristics of the diode of the present application are improved include (1) the concentration profile of the anode region 15 compensates for surface depletion of the isolation region 14, and (2) silicon crystal on the surface of the isolation region 14 having crystal defects. is the oxide film 19 when forming the anode region 15
One example is that it is consumed for the purpose of production.

(g) Effects of the Invention As explained above, according to the present invention, the anode region 15 is formed overlapping the surface of the isolation region 14, and crystal defects in the isolation region 14 are annealed and removed by the anode diffusion. As shown in FIG. 4, a diode having good Zener characteristics with little surface leakage can be obtained. Furthermore, the present invention is advantageous in that it can contribute to improving the degree of integration of monolithic integrated circuits by obtaining a good Zener diode in the isolation region.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of the diode of the present invention, FIG. 2 is a cross-sectional view of a conventional diode, FIG. 3 is a characteristic diagram showing the concentration profile of the diode of the present invention, and FIG. 4 is a cross-sectional view of the diode of the present invention. FIG. 3 is a characteristic diagram showing the Zener characteristics of the invention. 11 is a semiconductor substrate, 12 is an epitaxial layer,
13 is an island region, 14 is a separation region, 15 is an anode region, 16 is a cathode region, 17 is an anode electrode, and 18 is a cathode electrode.

Claims (1)

[Claims] 1 A semiconductor substrate of one conductivity type, an epitaxial layer of an opposite conductivity type provided on the substrate, and an isolation region of one conductivity type formed by high concentration impurity diffusion penetrating the epitaxial layer to form a plurality of island regions. In a monolithic integrated circuit comprising: an anode region of one conductivity type and diffused with a low concentration impurity so as to overlap the isolation region; crystal defects in the isolation region are removed by annealing during the diffusion of the low concentration impurity; A method of manufacturing a diode incorporated into a monolithic integrated circuit, characterized in that a cathode region of opposite conductivity type is formed within an anode region.