JPH0332064A - Semiconductor device - Google Patents

Abstract

PURPOSE:In a transistor being formed within the silicon film on an insulating film, to absorb positive holes generated by collision ionization phenomena so as to improve breakdown strength by providing a region having a concentration higher than the substrate concentration. CONSTITUTION:When a source electrode 42 is grounded and positive voltage is applied to a gate electrode 5, a transistor becomes ON conditions. When positive voltage is applied to a drain electrode 41 in this condition, electrons flow from a source diffusion layer 32 to a drain diffusion layer 31. Moreover, when the electrons get energy enough being accelerated by an electric field, they collide against a silicon lattice and generate electron-hole pairs, and the electrons generated here are absorbed in a layer 31 along a drain electric field. the positive holes flow in a substrate and are absorbed in a P<+> diffusion layer 33 in high positive hole density. Hereby, they do not accumulate in the vicinity of the layer 32, and also potential barriers between the source and the substrate cease to be low. As a result, kink phenomena become small or cease to appear.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transistor made of a silicon layer formed on an insulating film, in which the substrate is not grounded to an electrode.

[Conventional technology]

FIG. 2 is a cross-sectional view showing a conventional semiconductor device, in which (1) is a silicon substrate, (2) is a silicon oxide film, (
3) is a silicon layer, 0υ, ■ are silicon layers (3
) are the drain diffusion layer and source diffusion layer. @
υ is a drain electrode, (6) is a source electrode, (5) is a gate electrode, and (6) is a gate oxide film.

Next, the operation will be explained. When the source electrode (6) is grounded and a positive voltage is applied to the gate electrode (5), an inversion layer is formed on the surface of the silicon layer (3) directly under the gate oxide film (6). In this state, when a positive voltage is applied to the drain electrode (c), a potential gradient is created in the inversion layer along the source-drain direction, and electrons flow from the source diffusion layer (2) to the drain diffusion rmC3υ. The drain voltage-drain current characteristics at this time are as shown in FIG. Electrons flowing out of the source diffusion diagram 11 are accelerated by the potential gradient, and when their energy increases, they collide with the lattice in the silicon substrate (3), generate electron-hole pairs, and lose energy. This phenomenon is called impact ionization phenomenon. The electrons generated by this collision [separation phenomenon] are attracted by the drain electric field and enter the drain diffusion meX), resulting in a drain current. On the other hand, holes have no place to be absorbed and are accumulated in the substrate region. In the vicinity of the drain diffusion layer, holes are driven away by the drain electric field, and holes gather in the vicinity of the source diffusion layer □. As a result, the potential barrier between the source and the substrate becomes smaller, more electrons flow out of the source, and the drain current increases,
A first kink shown in FIG. 3 occurs. As the voltage applied to the drain becomes higher, this phenomenon becomes more pronounced, and the transistor operates in a bipolar manner. This is the second kink.

[Problem to be solved by the invention]

As described above, in the conventional semiconductor device formed in SOI, the substrate is not connected to the electrode, so holes tend to gather near the source, and a kink phenomenon tends to occur, resulting in a low breakdown voltage.

The present invention was made to solve the above-mentioned problems, and an object of the present invention is to obtain a high internal voltage transistor formed in SOI.

[Means to solve the problem]

A semiconductor device according to the present invention has an r-diffusion region formed at the bottom of a substrate.

[Effect]

The P diffusion region in this invention collects holes generated by impact ionization.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. 1st
In the figure, (1) is a silicon substrate, <2) is a silicon oxide film, <3) is a silicon layer, 0υ is a drain diffusion layer,
(2) is the source diffusion layer, (to) is the P diffusion layer, OD is the drain electrode, 04 is the source electrode, (5) is the gate electrode, (
6) is a gate oxide film.

Next, the operation will be explained. When the source electrode (6) is grounded and a positive voltage is applied to the gate electrode (5), the transistor is turned on. When a positive voltage is applied to the drain electrode 0 in this state, the source diffusion layer (
Electrons flow from 2) to the drain diffusion MO]). Also,
When the electrons gain enough energy, they collide with the silicon lattice and generate electron-hole pairs.

The electrons generated here are absorbed into the drain diffusion layer 0υ along the drain electric field. Holes flow through the substrate and are absorbed by the P4'' diffusion layer (2), which has a high hole density.This prevents them from accumulating near the source diffusion layer (2) and lowers the potential barrier between the source and the substrate. As a result,
The kink phenomenon becomes smaller or does not appear.

Note that in the above embodiment, the P+ diffusion layer (to) is replaced by a silicon layer (
3) Although the case where it is placed at the bottom is shown, the P"411 diffused layer Q may be placed only in the vicinity of the source region. Also, a part of the silicon oxide film (2) is slid down and a P+ diffused layer is provided. You can.

〔Effect of the invention〕

As described above, according to the present invention, since the P+ diffusion layer is disposed on the substrate, it is possible to absorb holes generated by impact ionization phenomenon, and it is possible to improve the breakdown voltage of the transistor in SOI.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a semiconductor device according to an embodiment of the present invention, FIG. 2 is a sectional view showing a conventional semiconductor device, and FIG. 3 is a diagram showing drain current-drain voltage characteristics of the conventional semiconductor device. be. In the figure, (1) is a silicon substrate, (2) is a silicon oxide film, (3) is a silicon layer, 00 is a drain diffusion layer, ■ is a source diffusion layer, (to) is a P1 diffusion layer, 4 is a drain electrode, (6) is the source electrode, (5) is the gate electrode, (
6) shows the gate oxide film. In addition, in the figures, the same reference numerals indicate the same or equivalent parts. Agent Masuo Oiwa Figure 1 17 2 Sheath Electrical Machinery No. 2 Section 2 Figure 3 Toray:, tFL 16 Display of Cases Plain Patent Application 11ii 1-167597 No. 2, Title of Invention Semiconductor Device 3, Person Who Makes Amendment Case connection of

Claims (1)

[Claims] A semiconductor device characterized in that a transistor is manufactured in a silicon layer formed on an insulating film, and includes a region having a higher concentration than the substrate.