1. Field of Invention
The present invention relates to a high voltage device and a manufacturing method of a high voltage device; particularly, it relates to such device and manufacturing method wherein the breakdown voltage is increased.
2. Description of Related Art
FIGS. 1A and 1B show a cross-section view and a 3D (3-dimensional) view of a prior art double diffused drain metal oxide semiconductor (DDDMOS) device, respectively. As shown in FIGS. 1A and 1B, a P-type substrate 11 has multiple isolation regions 12 by which a device region 100 is defined. The isolation region 12 for example is a shallow trench isolation (STI) structure or a local oxidation of silicon (LOCOS) structure, the former being shown in the figures. The DDDMOS device is formed in the device region 100, which includes a gate 13, a drift region 14, a drain 15, and a source 16. The drift region 14, drain 15 and the source 16 are formed by a lithography process and an ion implantation process, wherein the lithography process defines the implantation regions by a photoresist mask together with a self-alignment effect provided by all or part of the gate 13 and the isolation regions 12, and the ion implantation implants N-type impurities to the defined regions in the form of accelerated ions. The drain 15 and the source 16 are beneath the gate 13 and at different sides thereof respectively. Part of the drift region 14 is located beneath the gate 13 near the drain. The DDDMOS device is a high voltage device designed for applications requiring higher operation voltages. However, if it is required for the DDDMOS device to be integrated with a low voltage device in one substrate, the high voltage device and the low voltage device should adopt the same manufacturing process steps with the same ion implantation parameters, and thus the flexibility of the ion implantation parameters for the DDDMOS device is limited; as a result, the DDDMOS device will have a lower breakdown voltage and therefore a limited application range. To increase the breakdown voltage of the DDDMOS device, additional manufacturing process steps are required, that is, an additional lithography process and an additional ion implantation process are required in order to provide different ion implantation parameters, but this increases the cost.
FIGS. 2A and 2B show a cross-section view and a 3D view of a prior art lateral diffused metal oxide semiconductor (LDMOS) device. Compared to the prior art shown in FIGS. 1A and 1B, the LDMOS device shown in FIGS. 2A and 2B has a body region 17 and a body electrode 18, and part of its gate 13 is located on the isolation region 12. Still similarly, when the LDMOS device is integrated with a low voltage device in one substrate, the high voltage device and the low voltage device should adopt the same manufacturing process steps with the same ion implantation parameters, and thus the flexibility of the ion implantation parameters for the LDMOS device is limited; as a result, the LDMOS device will have a lower breakdown voltage and therefore a limited application range. To increase the breakdown voltage of the LDMOS device, additional manufacturing process steps are required, that is, an additional lithography process and an additional ion implantation process are required in order to provide different ion implantation parameters, but this increases the cost.
In view of above, to overcome the drawbacks in the prior art, the present invention proposes a high voltage device and a manufacturing method thereof which provide a higher breakdown voltage so that the high voltage device may have a broader application range, in which additional manufacturing process steps are not required such that the high voltage device can be integrated with and a low voltage device and manufactured by common manufacturing process steps.