Structure in a high voltage path of an ultra-high voltage device for providing ESD protection

An ultra-high voltage device has a high voltage path established from a high voltage N-well through a first metal layer to a second metal layer, and a contact plug electrically connected between the high voltage N-well and the first metal layer. The contact plug has a distributed structure on a horizontal layout to improve the uniformity of the ultra-high voltage device such that the current in the high voltage path will be more uniform distributed so as to avoid the localized heat concentration caused by non-uniform current distribution that would damage the ultra-high voltage device. Multiple fuse apparatus are preferably connected to the first metal layer individually. Each the fuse apparatus includes a poly fuse to be burnt down when an over-load current flows therethrough.

FIELD OF THE INVENTION

The present invention is related generally to ultra-high voltage devices and, more particularly, to a structure in a high voltage path of an ultra-high voltage device for providing electro-static discharge (ESD) protection.

BACKGROUND OF THE INVENTION

Ultra-high voltage devices only can use self-protection scheme since they are often huge dimension devices. ESD protection schemes, increasing the dimensions of some critical layouts, are not available for Ultra-high voltage devices since they are already huge dimension devices. Even the dimension of ultra-high voltage devices is very huge, they still cannot meet the minimum ESD requirement. The root cause is that the device is non-uniform triggering on to induce the current localized at a finite region. Typically, a conventional ultra-high voltage device has a vertical cross-sectional view as shown inFIG. 1, in which a P-substrate10has a P-epilayer12thereon, a P-well14and a high voltage N-well16are formed on the P-epilayer12, the high voltage N-well16has an oxide28thereon, and a contact region18is formed by doping the surface of the high voltage N-well16through an opening not covered by the oxide28, and is electrically connected to a high voltage electrode HV through a contact plug20, a first metal layer22, a via26and a second metal layer24, which is the high voltage path of the ultra-high voltage device. The high voltage N-well16raises the breakdown voltage of the ultra-high voltage device, thereby allowing the device to support high voltage operation. InFIG. 2, the drawing in the upper part is a layout of the ultra-high voltage device shown inFIG. 1, the lower drawing is an enlarged view of the area30in the foregoing layout. The contact plug20has a stripe shape in the horizontal cross-section of the ultra-high voltage device, and the terminal32of the contact region18is often the non-uniform portion of the ultra-high voltage device. When there is a great current, such as an ESD current, flowing through the high voltage path, the current intends to concentrate around the terminal32and produce great heat, resulting in localized high temperature to melt down this portion of the ultra-high voltage device. Once any portion of the high voltage path is burnt down, the ultra-high voltage device will lose its high voltage withstanding capability and become no more usable.

To date, there has not been any ESD protection about the ultra-high voltage technology, typically referring to the voltage equal to or higher than 500V, and thus an ultra-high voltage device only can be protected by its structure itself.

SUMMARY OF THE INVENTION

An objective of the present invention is to provide a structure for providing ESD protection for ultra-high voltage devices.

According to the present invention, an ultra-high voltage device has a high voltage path established from a high voltage N-well through a first metal layer to a second metal layer, and a contact plug electrically connected between the high voltage N-well and the first metal layer. The contact plug has a distributed structure on a horizontal layout to improve the uniformity of the ultra-high voltage device such that the current in the high voltage path will be more uniform distributed so as to avoid the localized heat concentration caused by non-uniform current distribution, thereby reducing the possibility of damaging the ultra-high voltage device.

Preferably, multiple fuse apparatus are connected to the first metal layer individually, and each the fuse apparatus includes a poly fuse to be burnt down when an over-load current flows therethrough.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 3shows a first embodiment according to the present invention, which has the same vertical cross-sectional view as that shown inFIG. 1, but has a distributed contact plug20with the contact region18conforming thereto, so that the horizontal layout has a dot-like distribution of discrete islands. This distributed structure helps to improve the uniformity of the ultra-high voltage device and thus allows the current in the high voltage path to be uniform distributed. Therefore, it may avoid the localized heat concentration caused by non-uniform current distribution when a great current, such as an ESD current, flowing the high voltage path, thereby reducing the possibility of damaging the ultra-high voltage device. In this embodiment, the discrete structure of the contact region18and the distributed contact plug20can be easily formed by changing the defined pattern without increasing manufacturing complexity, and will not increase the circuit size.

FIG. 4andFIG. 5are a vertical cross-sectional view and a partial horizontal layout of a second embodiment, respectively. In addition to the contact plug20having a distributed structure on the horizontal layout, a plurality of fuse apparatus40are arranged on the high voltage path, each of which has a poly fuse42with its two ends connected to a first portion48and a second portion50of the first metal layer22through the connections44and46, respectively. The first portion48and the second portion50are parts of the first metal layer22and are separate from each other. Since the second metal layer24is connected to each of the second portions50of the first metal layer22through a respective via26, all the fuse apparatus40are connected in parallel between the contact region18and the second metal layer24. The contact plug20, the connections44and46, the first metal layer22and the second metal layer24are all made of metal, so that when the device encounters an excessively great current, the poly fuse42of a proper length will be first broke before the contact plug20, the connections44and46, the first metal layer22and the second metal layer24are melted down. When the current flowing through any poly fuse42reaches the saturation current of this poly fuse42, this poly fuse42will turn into a resistor of high impedance, and thus force the current to flow toward the other poly fuses42not saturated yet. As a result, for each saturated poly fuse42, although the voltage may keep increasing, the current is prohibit from going up any more, and thereby the current will be uniform distributed over the poly fuses42of all the fuse apparatus40. Even if the current on a poly fuse42exceeds its saturation current, this current will first break this poly fuse42and thus block the current from flowing to the contact region18of this poly fuse42, thereby preventing the contact region18from being damaged to cause short circuit, and the other good poly fuses42will remain supportive to the ultra-high voltage device's normal operation. The poly fuses42may be provided by a polysilicon layer and the connections44and46may be formed together with the contact plug20. Therefore, the structure of this embodiment requires no extra processing step. The fuse apparatus40may be arranged above the oxide28, and thus will not enlarge the circuit layout.

FIG. 6provides a third embodiment as a combination of the above two embodiments, which distributes the contact region18to the distributed contact plug20, thereby forming a plurality of discrete islands, in addition to connect each contact plug20with a fuse apparatus40as that shown inFIG. 5.

As illustrated by the above embodiments, the present invention effectively improves the ESD performance of an ultra-high voltage device to an acceptable level without changing the dimension, IV characteristics and manufacturing process of the Ultra-high voltage device.