JPS63131564A - Protective circuit for output - Google Patents

Abstract

PURPOSE:To increase breakdown strength by static electricity by forming a contact section between a diffusion layer used as a source or a drain for an output transistor pair connected to an output pin and a metallic wiring layer in metal-polysilicon-diffusion layer and deepening a diffusion section under the contact section. CONSTITUTION:A contact section to a diffusion layer 13 on the output terminal side connected in common in an output transistor is shaped in laminated structure of a metallic wiring layer 16-a polysilicon layer 21-a diffusion layer 13. The contact of polysilicon and the diffusion layer is brought to ohmic connection by diffusing an impurity or implanting ions from the upper section of polysilicon. Consequently, a section just under the contact section can be formed in a diffusion region 131 deeper than the diffusion layer in other regions. Accordingly, an output protective circuit can be made to resist against static electricity, and the aluminum layer 16 is not connected directly to the diffusion layer 13, thus eliminating the trouble of the 'whisker' of aluminum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention (Field of Industrial Application) The present invention relates to an output protection circuit in a semiconductor integrated circuit.

- (Prior Art) Conventionally, in MOS type semiconductor integrated circuits, the phenomenon of destruction at input/output pins due to static electricity has been a big problem. This problem is especially noticeable because input pins have high impedance, and input protection circuits against electrostatic damage have been considered more frequently than before, and are relatively powerful.

However, the current situation is that nothing has been done to protect the output circuit. Even if there is one, it will only require an extremely small resistance between the output pin and the output transistor. The reason for this is that the output pin is connected to a relatively large diffusion layer (the source and drain of the output transistor), and a large current can momentarily flow through this diffusion layer. Therefore, due to this current capacity and output protection resistance, the structure is relatively strong against destruction of the output bin due to static electricity.

(Problem to be solved by the invention) Is the output circuit an interface circuit to be connected? Direct driving requires a large current drive capability, and it is impossible to improve the output protection capability by increasing the output protection resistance. Particularly in modern devices that require high-speed performance, it is necessary to minimize resistance.

On the other hand, highly integrated VLSI devices require scaling (reduction) in order to increase the integration density. From a two-dimensional perspective, it is possible to avoid problems caused by high integration (for example, the distance between diffusion layers becomes smaller, which increases the likelihood of punch-through) by allowing a large pattern allowance for such input/output circuits. . However, this is difficult to avoid when it comes to vertical scaling. For example, if the xj (depth) of the diffusion layer becomes shallow, the surface of the silicon will also be etched or etched during contact etching and etching, especially under the contact area, and if the xj (depth) of the diffusion layer becomes shallow, the surface It becomes difficult for current (instantaneous current due to static electricity) to flow from the metal wiring layer to the substrate through this diffusion layer. This is because the resistance at the contact portion increases. Furthermore, if a high voltage is applied to this part and an attempt is made to flow a current, there is a problem in that this part will be destroyed.

As a result, the breakdown voltage due to static electricity is lowered.

FIG. 5 is a connection diagram of output transistors of a typical output circuit. MOS) Transistors Tl and T2 are connected in series, the source terminal of the transistor T1 and the drain terminal of the transistor T2 are commonly connected, and the output protection resistor 1 is connected.
1 to an external output terminal 2. The drain terminal of the transistor T1 is connected to the power supply vec, and the source terminal of the transistor T2 is connected to the ground Vll.

Figure 6 shows the conventionally used output transistor (T
I or TI), No. 1 is a one-conductivity type substrate,
12 is an opposite conductivity type diffusion layer that becomes a source or drain;
13 is an opposite conductivity type diffusion layer which becomes a drain or source;
14 is a dirt electrode made of polysilicon, 15 is a power supply (
■The electrode of the diffusion layer 12 connected to (ec or Vsa)
For example, aluminum), 16 is an electrode of the diffusion layer 13 connected to the output terminal. The features of this configuration are the drain,
The diffusion layer that serves as the source is directly contacted by the output terminal and the metal wiring (for example, aluminum) that serves as the power source. The problem in this case is that if a strong electric field is applied to the diffusion layer (12 or 13 for fc) under the contact portion, it is likely to be destroyed. Furthermore, if aluminum is brought into direct contact with the diffusion layer, folds of the aluminum tend to be introduced into the diffusion layer, and in this case too, it is likely to be destroyed by a strong electric field.

The present invention has been made in view of the above-mentioned circumstances, and it is an object of the present invention to provide an output protection circuit that is resistant to static electricity in a signal output circuit of a semiconductor integrated circuit.

[Structure of the Invention] (Means and Effects for Solving the Problems) The present invention provides a contact portion between a diffusion layer and a metal wiring layer that serves as a source or drain of a pair of output transistors connected to an output pin.
By using a metal-polysilicon-diffusion layer structure and making the diffusion layer deep under the contact, static electricity can be reduced.
It has improved breakdown voltage.

(Example) The present invention will be described in detail below with reference to the drawings. FIG. 1 is a cross-sectional view of the output transistor section of the first embodiment, but since this is an example corresponding to that in FIG. 6, corresponding parts will be given the same reference numerals and explained. This will be omitted, and the main points will be explained. The feature of this embodiment is that the contact portion to the diffusion layer 13 on the output terminal side to which the output transistors are commonly connected is made of a metal wiring layer (for example, aluminum).
16-polysilicon layer 21-diffusion layer 13.

The contact between polysilicon and the diffusion layer has a structure commonly called a pared contact, and an ohmic connection is made between the polysilicon and the diffusion layer by diffusing a thin film or implanting ions onto the polysilicon. It is something to do. By adopting this structure, it is possible to form the diffusion layer 131 deeper than the diffusion layers in other regions directly under the contact portion, and it can be made strong against strong electric fields caused by static electricity. Also, the aluminum layer 16 is the diffusion layer 13
Since it is not directly connected to the aluminum, the above-mentioned "whiskers" problem of aluminum can be eliminated.

FIG. 2 shows a second embodiment in which the features of the structure shown in FIG. 1 are applied to contacts on the power and ground sides. This is metal wiring 1
When a strong electric field due to static electricity is applied to the output terminal side connected to the power source 6 and a large amount of current is injected to the substrate 11 side, this current needs to be absorbed by the power supply or ground line 15 side.

At that time, since the contact portion between the metal wiring 15 and the diffusion layer 12 is easily destroyed, a polysilicon layer 22 is placed between them.
The above problem is prevented by inserting a deep diffusion layer 121.

FIG. 3 shows a third embodiment. That is, in the embodiments shown in FIGS. 1 and 2, the polysilicon layer 2 used as the dart electrode 14 and the polysilicon layer 2 used as the contact portion are the same. It is difficult to bring the parts close together and requires a relatively large area. In order to solve this problem, the first polysilicon layer is used for the r-upper electrode 14, and the second polysilicon layer 31 is used for the contact part (i.e., a two-layer structure) 1. Polysilicon layer The structure allows 14 and 31 to overlap, so that the dart electrode and the contact portion can be brought close to each other. At this time, by using a low resistance wiring material such as polycide as the second polysilicon layer 31, the source of the output transistor,
At the same time, the resistance of the drain portion can be reduced.

FIG. 4 shows a fourth embodiment in which the structure explained in FIG. 3 is applied to the power supply and ground side contacts, as in the case of FIG. silicon layer, 1
21*131 is the deep part of the diffusion layer.

[Effects of the Invention] As explained above, according to the present invention, the contact portion to the diffusion layer constituting the source and drain of the output transistor and one metal wiring layer-polysilicon layer-diffusion layer, and the diffusion layer immediately below the contact portion. Since the layer is deep, it can be strengthened against strong electric fields caused by static electricity. Furthermore, since the metal wiring, especially aluminum, is not connected to the diffusion layer, the problem of aluminum "folds" can be completely eliminated.

[Brief explanation of the drawing]

1 to 4 are cross-sectional views of a transistor section for explaining each embodiment of the present invention, FIG. 5 is an output circuit diagram, and FIG.
The figure is a cross-sectional view of the output transistor of the same circuit. 11...Substrate, 12.13...Diffusion layer, 121. 131...Deep part of diffusion layer, 14...f-) electrode, 15.16...Metal wiring layer, 21, 22, 31°3
2...Polysilicon layer. SS 50 Figure 6

Claims (3)

[Claims] (1) In the output section of a semiconductor integrated circuit, a contact portion between a diffusion layer and a metal wiring layer of an output terminal that commonly connects the sources and drains of a pair of output transistors connected to an output pin for external output of the integrated circuit. . An output protection circuit characterized in that it has a metal-polysilicon-diffusion layer structure, and the diffusion layer directly under the contact portion is deeper than the surrounding diffusion layers. (2) The contact portion between the diffusion layer and the metal wiring layer on the power supply side or ground side of the output transistor is connected to the metal wiring layer.
The output protection circuit according to claim 1, characterized in that it has a structure of polysilicon-diffusion layer. (3) Output protection according to claim 1 or 2, wherein a second polysilicon different from the first polysilicon for gate wiring is used as the polysilicon. circuit.