Semiconductor device
View Patent ↗In a conventional semiconductor device, protection of a to-be-protected element from a surge voltage is difficult because the to-be-protected element is turned on before a protection element due to variations in manufacturing conditions. In a semiconductor device of the present invention, a protection element and a MOS transistor have part of their structures formed under common conditions. N type diffusion layers of the protection element and the MOS transistor are formed in the same process, while the N type diffusion layer of the protection element has a larger diffusion width than the N type diffusion layer of the MOS transistor. With this structure, when a surge voltage is applied to an output terminal, the protection element is turned on before the MOS transistor, and thereby the MOS transistor is protected from an avalanche current.
1. A semiconductor device comprising:
a MOS transistor comprising a back-gate diffusion region of a first general conductivity type, a source diffusion layer of a second general conductivity type and a drain diffusion layer of the second general conductivity type; and
a protection element electrically connected to the MOS transistor in parallel and comprising a first diffusion layer of the first general conductivity type, a second diffusion layer of the second general conductivity type formed in the first diffusion layer and a third diffusion layer of the second general conductivity type surrounding the first diffusion layer in plan view of the semiconductor device,
wherein a lateral diffusion width of the second diffusion layer of the protection element is larger than a lateral diffusion width of the source diffusion layer of the MOS transistor.
2. The semiconductor device of claim 1 , wherein a separation distance between the first diffusion layer and the third diffusion layer is equal to a separation distance between the back-gate diffusion layer and the drain diffusion layer.
3. The semiconductor device of claim 1 , wherein the protection element further comprises a fourth diffusion layer of the second general conductivity type disposed outside the third diffusion layer with respect to the first diffusion layer and electrically connected to a drain electrode of the MOS transistor, and at least the first diffusion layer and the second diffusion layer are shorted to each other and are electrically connected to a source electrode of the MOS transistor.
4. The semiconductor device of claim 2 , wherein the protection element further comprises a fourth diffusion layer of the second general conductivity type disposed outside the third diffusion layer with respect to the first diffusion layer and electrically connected to a drain electrode of the MOS transistor, and at least the first diffusion layer and the second diffusion layer are shorted to each other and are electrically connected to a source electrode of the MOS transistor.
5. The semiconductor device of claim 3 , wherein the protection element further comprises a buried layer of the second general conductivity type and connected to the fourth diffusion layer.
6. The semiconductor device of claim 3 , wherein the fourth diffusion layer surrounds the third diffusion layer in the plan view of the semiconductor device, and the third diffusion layer is configured to be floating.
7. The semiconductor device of claim 1 , further comprising an isolation region of the first general conductivity type surrounding the third diffusion layer and comprising an upper diffusion layer and a lower diffusion layer connected to each other, a diffusion depth of the upper diffusion layer being smaller than a diffusion depth of the lower diffusion layer.
8. The semiconductor device of claim 3 , further comprising an isolation region of the first general conductivity type surrounding the fourth diffusion layer and comprising an upper diffusion layer and a lower diffusion layer connected to each other, a diffusion depth of the upper diffusion layer being smaller than a diffusion depth of the lower diffusion layer.
9. The semiconductor device of claim 1 , wherein an avalanche voltage between the first diffusion layer and the third diffusion layer of the protection element is equal to an avalanche voltage between the back-gate diffusion layer and the drain diffusion layer of the MOS transistor.
10. The semiconductor device of claim 1 , wherein at least part of the back-gate diffusion region is disposed under the source diffusion layer.