JPH04111359A - Semiconductor device - Google Patents

Abstract

PURPOSE:To strengthen an electrostatic breakdown strength without changing the size of an output buffer by a method wherein a noise is made to escape by a P-N junction avalanche breakdown or a punchthrough. CONSTITUTION:Regarding the breakdown strength of an NMOS transistor at an output buffer part, the breakdown strength of the output buffer is strenthened even by using the transistor formed of an impurity layer which has been made fine when a P-N junction avalanche breakdown at a drain part or a channel length caused by a punchthrough at a channel part is selected. The figure shows the following: an electric current value at which the drain part has been broken down permanently when an electric current is injected into the drain part of the NMOS transistor of an LDD structure; and a channel length of the NMOS transistor at this time. When the channel length is set at 4mum or higher or 1.2mum or lower, the breakdown current of the transistor becomes large. Inversely, when it is set at 4mum or lower and 1.2mum or higher, the transistor is broken down permanently by a small electric current. Consequently, when the L length of the transistor used in the output buffer is set at 4mum or higher or 1.2mum or lower, it is possible to obtain the output buffer which is resistant to a noise.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an output buffer circuit that can improve resistance to electrostatic damage of an IC.

[Summary of the invention]

In the present invention, when noise enters the output part of the output buffer, that is, the drain part of the MOS transistor, the device is prevented from being destroyed by letting the noise escape to ground through avalancinilla breakdown due to the PN junction of the drain part or punch-through between the source and drain. It is something to prevent.

[Conventional technology]

Conventionally, as a technique to increase resistance to electrostatic discharge damage in the output buffer section, the space between the contact and the gate, which serve as the source/drain electrodes, is widened. Known methods include increasing the area of the drain and source, increasing the concentration of the drain and source, making the concentration gradient of diffusion gentler and deeper, loosening the electric field, and lowering avalanche breakdown.

[Problem to be solved by the invention]

However, in conventional methods, as miniaturization occurs, impurity diffusion becomes shallow in the drain and source, resulting in a steep concentration gradient and a strong electric field at the drain end, making hot electrons more likely to be generated. Therefore, miniaturized MOS has the disadvantage that when large noise is applied to the output transistor, the snap bank phenomenon caused by these hot electrons causes permanent destruction of the drain.

[Means to solve the problem]

In order to solve the above problems, the present invention has been developed so that the withstand voltage of the NMO5I-transistor in the output hammer core section is PN at the toru-in section.
By selecting a channel length where junction avalanche breakdown occurs due to punch-through in the channel portion, the breakdown voltage of the output buffer can be increased even when using a transistor formed with a miniaturized impurity layer.

[Effect]

When noise enters the output buffer formed by the transistor with the optimized channel length, it first breaks down due to avalanche or punch-through at the drain, so a buffer that does not cause permanent damage can be obtained. Ta.

〔Example〕

The present invention will be explained below based on specific examples.

Figure 1 shows the current value when the drain is permanently destroyed when a current is injected into the drain part of an NMO3 transistor with an LDD structure manufactured using a known method for manufacturing a semiconductor device 1, and the channel length of the MOS transistor at that time. It is something that When the channel length is 4 or more or 1.2 or less, the transistor breakdown xfL increases; conversely, if the channel length is 4 or less, 1.
It can be seen that transistors with a value of 2 or more are permanently destroyed by a small current. Therefore, if the L length of the transistor used in the output buffer is set to 4 or more or 1.2 or less, an output buffer that is resistant to noise can be obtained.

As described above, by optimizing the channel length, an output buffer that is resistant to noise was obtained without changing the depth or concentration of the impurity layer or the area of the drain part.

〔Effect of the invention〕

The present invention has the effect of increasing the electrostatic breakdown voltage without changing the size of the output buffer by releasing noise through PN junction avalanche breakdown or punch-through.

[Brief explanation of drawings]

FIG. 1 shows the permanent breakdown current and channel length when a current is injected into the drain of a MOS transistor according to an embodiment of the present invention. that's all

Claims (1)

[Claims] An output buffer circuit characterized in that it uses a MOS transistor whose source-drain breakdown voltage is determined by avalanche breakdown or punch-through of a PN junction by controlling the channel length.