JPH01272151A - Semiconductor element with guard ring and manufacture thereof - Google Patents

Abstract

PURPOSE:To enable higher breakdown strength by forming a guard ring in dig-in type structure and deepening the depth of the dig-in of the guard ring with separation from a main junction. CONSTITUTION:A surface film 3 composed of an oxide film is formed onto the surface of an N<-> type semiconductor substrate 1, and the surface film 3 on guard rings 4a, 4b, 4c is removed through etching, etc., thus shaping concentric opening windows. The semiconductor substrate 1 is etched through the opening windows, and grooves 2a, 2b, 2c are formed first. Only the groove 2a nearest to a central section is protected by the surface film 3 such as the oxide film, a resist, etc., and the semiconductor substrate 1 is further dug in through etching. No.1 and No.2 guard rings 2a, 2b from the central section are protected by the surface films 3 such as the oxide films, the resists, etc., the semiconductor substrate 1 is further dug in, P<+> type impurity diffusion layers are shaped to the dug-in each groove 2a, 2b, 2c, and the guard rings 4a, 4b, 4c are acquired while a P<+> type impurity diffusion layer 5 is also formed at the central section, thus forming a main junction.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a semiconductor device having a guard ring and a method for manufacturing the same, and is particularly suitable for manufacturing high voltage diodes, transistors, thyristors, etc. .

[Prior Art] Conventionally, it has been proposed to form a guard ring to surround the main junction in order to increase the breakdown voltage of a semiconductor element (
(Special Publication No. 40-12739).

FIG. 3 is a diagram showing a cross-sectional structure of a diode having a guard ring. A P+ type diffusion layer 5 is formed on the N- type semiconductor substrate 1, forming a main junction of the diode. A plurality of guard rings 4a, 4b, 4c made of P+ type diffusion layers are formed concentrically to surround this main junction. Such guard rings 4a, 4b,
4c was formed by opening concentric diffusion windows on the surface of the semiconductor substrate 1 and performing thermal diffusion.

[Problems to be Solved by the Invention] In the above structure, in order to achieve high breakdown voltage, it is necessary to: 1) increase the resistivity of the semiconductor substrate 1, 2) guard rings 4a and 4b.
, increase the diffusion depth t of 4c, ■ guard ring 4a,
Increase the number of 4b and 4c, ■ Guard rings 4a and 4b
, 4c interval d, , d2. It is conceivable to optimize d according to the above-mentioned items (1) and (2). However, if there are constraints such as, for example, the resistivity of the semiconductor substrate 1 cannot be changed due to the quality of the semiconductor element, or the area of the chip cannot be easily increased due to the cost of the semiconductor element, then the above
Measures are difficult to implement, and guard ring 4a,
It is conceivable to increase the diffusion depth t of 4b and 4c.

However, when the guard rings 4a, 4b, 4c are formed by thermal diffusion as in the past, there is a problem in that the drive (diffusion) time becomes extremely long if the diffusion depth t is increased. was there. By the way, when the temperature of thermal diffusion is 1150℃, the diffusion time is about 4 hours to make the diffusion depth 9μm, but if the diffusion depth is 15μm.
m, the diffusion time is approximately 20 hours and the diffusion depth is 20μ.
The diffusion time would be approximately 45 hours, making it difficult to implement in reality.

The present invention has been made in view of these points, and its purpose is to achieve deep diffusion of the guard ring by digging into the semiconductor substrate, and to increase the diffusion depth of the guard ring from the main junction. It is an object of the present invention to provide a semiconductor device having a guard ring that is deepened as the distance increases, thereby making it possible to further increase the withstand voltage, and a method for manufacturing the same.

[Means for Solving the Problems] In the present invention, in order to solve the above problems, the first
As shown in Figure (d), a semiconductor substrate 1 of a first conductivity type has a main junction in which a diffusion layer 5 of a second conductivity type is formed on one surface side, and a diffusion layer 5 of a second conductivity type is formed around this main junction. Totally surrounding the second
A plurality of guard rings 4a, 4 made of diffusion layers of a conductivity type of
b, 4c, the guard ring 4
a, 4b, and 4e have a dug-in structure, and guard rings 4a, 4b.

4c is characterized in that the depth of the digging is increased as the distance from the main joint increases.

In addition, as a manufacturing method particularly suitable for obtaining the above structure, as shown in FIGS. 2(a) to (c), a surface film 3 is formed on a semiconductor substrate 1 of the first conductivity type, and this surface Leather WA
3, a plurality of concentric opening windows 6 a, whose radial opening widths a, b, and c become longer as they move away from the center.
After forming grooves 6b and 6c, anisotropic etching is performed to form a plurality of concentric grooves 2a, 2b, and 2c that become deeper toward the periphery, and the innermost groove 2
A second conductivity type diffusion layer 5 is formed in a portion surrounded by a, and guard rings 4m, 4b formed of the second conductivity type diffusion layer are formed in each groove 2a, 2b, 2c.

4c.

[Function] In the present invention, as described above, the guard rings 4m, 4
Since b and 4c have a dug-in structure, the diffusion depth can be increased without using a long thermal diffusion process, and therefore a high breakdown voltage can be achieved. Further, since the depth of the guard rings 4a, 4b, and 4c is increased as the distance from the main junction increases, it is possible to increase the breakdown voltage of the - layer.

Furthermore, as shown in FIGS. 2(a) to 2(c), in the surface film 3 formed on the semiconductor substrate 1 of the first conductivity type, the opening widths a, b, and c in the radial direction increase as the distance from the center increases. Therefore, the plurality of concentric opening windows 6 a, 6 b become longer.

If anisotropic etching is performed after forming the grooves 6c, a plurality of concentric grooves 2a, which become deeper toward the periphery, can be formed.
2b, 2c can be easily formed, and a semiconductor element having guard rings 4a, 4b, 4c having the above structure can be easily manufactured.

[Example 1] FIGS. 1(a) to 1(d) are diagrams showing the manufacturing process of a semiconductor element having a guard ring according to the present invention. After forming a surface film 3 made of an oxide film such as silicon dioxide on the surface of the N-type semiconductor substrate 1, guard rings 4a, 4b,
The surface film 3 on 4c is removed by etching or the like to form concentric opening windows.

The semiconductor substrate 1 is etched through this opening window,
First, as shown in FIG. 1(a), 12a and 2b.

2c is obtained. Here, the etching method may be wet etching or dry etching, and the method is not limited.
After protecting only 2a with a surface film 3 such as an oxide film or resist, the semiconductor substrate 1 is further etched to obtain the state shown in FIG. 1(b). In the same way, after protecting the first and second guard rings 2a and 2b from the center with a surface film 3 such as an oxide film or a resistor, the semiconductor substrate 1 is further etched and etched as shown in FIG.
) obtain the state shown. After that, each of these grooves 2a is dug.

2b and 2c are provided with P+ type impurity diffusion layers to obtain guard rings 4a, 4b, and 4c, and a P+ type impurity diffusion layer 5 is also formed in the center to form a main junction.
The structure shown in d) is obtained.

[Example 2] FIGS. 2(a) to 2(c) are diagrams showing another manufacturing process of a semiconductor element having a guard ring according to the present invention.

In the manufacturing process shown in FIG. 1 described above, it was necessary to perform etching and surface protection alternately, but in this example, by using anisotropic etching, etching and surface protection can be performed in one step each. It's done. As the semiconductor substrate 1, a silicon single crystal <100> substrate is used. After forming a surface film 3 made of an oxide film such as silicon dioxide on the surface of this semiconductor substrate 1, guard rings 4a and 4b are formed.
, 4e, concentric diffusion windows 6a, 6b, 6c are provided in the surface film 3, as shown in FIG. 2(a). Etching consists of 40% potassium hydroxide and 800cc water.
800ccI
Anisotropic etching was performed using an etching solution of 134 cc of PA (isopropyl alcohol) and 67 cc of ethanol.
The semiconductor substrate 1 is etched while maintaining the temperature at 0 to 73°C. At this time, if the opening widths of the diffusion windows 6 a, 6 b, and 6 c are a, b, and c, then the etching depths al and b are
l and l are respectively a'=o, 7Xa, b'=Q, 7x
b, e'=o, 7Xe, so the diffusion window 6 is adjusted to obtain the necessary depths a', b', and c' of machining and cutting.
a.

The opening widths a, b, and c of 6b and 6e are set so that they become wider toward the periphery. In this way, you can protect the surface once and
With only one anisotropic etching process, multiple concentric grooves 2, which become deeper toward the periphery, are formed as shown in FIG. 2(b).
a, 2 b, 2 e can be obtained.

After that, each of these dug grooves 2a, 2b,
2C by providing a P+ type impurity diffusion layer to guard ring 4
a.

4b and 4c, a P+ type impurity diffusion layer 5 is also formed in the center to form a main junction, and the structure shown in FIG. 2(c) is obtained.

[Effects of the Invention] In the semiconductor device having the guard ring according to the present invention, since the guard ring has a recessed structure, the diffusion depth can be increased, and therefore a high breakdown voltage can be achieved. It has the effect of becoming.

Further, since the depth of the guard ring is increased as the distance from the main junction increases, there is an effect that it is possible to increase the withstand voltage of the - layer.

In addition, if such a guard ring is dug by anisotropic etching, multiple concentric grooves that become deeper toward the periphery can be easily formed by simply changing the opening width in the surface film. This has the effect that a semiconductor element having a guard ring structure can be easily manufactured.

[Brief explanation of the drawing]

FIGS. 1(a) to (d) are cross-sectional views showing the manufacturing process of one embodiment of the present invention, and FIGS. 2(a) to (c) are cross-sectional views showing the manufacturing process of another embodiment of the present invention. , FIG. 3 is a sectional view of a conventional example. 1 is a semiconductor substrate, 2 a, 2 b, 2 c are grooves, 3
4a, 4b, 4c are guard rings, 5 is a diffusion layer, and 6a, 6b, 6c are open windows.

Claims (2)

[Claims] (1) A main junction in which a diffusion layer of a second conductivity type is formed on one surface side of a semiconductor substrate of a first conductivity type, and a diffusion layer of a second conductivity type completely surrounds this main junction. In a semiconductor device having a plurality of guard rings made of diffusion layers,
1. A semiconductor device having a guard ring, wherein the guard ring has a recessed structure, and the depth of the recess of the guard ring increases as the distance from the main junction increases. (2) forming a surface film on a first conductivity type semiconductor substrate;
After forming multiple concentric opening windows in which the radial opening width increases as the distance from the center increases, anisotropic etching is performed to form multiple concentric grooves that become deeper toward the periphery. and forming a second conductivity type diffusion layer in a portion surrounded by the innermost groove,
A method for manufacturing a semiconductor device having a guard ring, the method comprising forming a second conductivity type diffusion layer in each groove.