Methods for forming fully segmented salicide ballasting (FSSB) in the source and/or drain region
View Patent ↗Transistor structures for relatively even current balancing within a device and methods for fabricating the same are disclosed. These devices can be used in relatively compact MOSFET Electrostatic Discharge (ESD) protection structures, such as in snapback devices. One embodiment utilizes a salisided exclusion layer for segmentation of the source and/or drain diffusion areas, while the others utilize poly for segmentation of the source and/or drain area. Also, diffusion is used generically herein and, for example, includes implants. These techniques provide relatively good ESD tolerance while consuming a relatively small amount of area, and provide significant area and parasitic capacitance reduction over the state of the art without sacrificing ESD performance. These techniques are also applicable to current balancing within relatively high current devices, such as drivers.
1. A method of forming a semiconductor device, the method comprising:
providing a semiconductor substrate assembly;
forming a patterned mask for excluding saliside diffusion from corresponding portions of the substrate assembly;
performing a saliside diffusion process to form a salisided diffusion for a source and a salisided diffusion for a drain, and leaving non-salisided areas corresponding at least to the patterned masks; and
forming contacts on the substrate assembly, the contacts including two or more contacts of the same drain or source, wherein the contacts are spaced apart along a side of the gate;
wherein the mask is formed such that the non-salisided regions remain between the two or more contacts of the same drain and/or between the two or more contacts of the same source.
2. The method as defined in claim 1 , further comprising removing the mask.
3. The method as defined in claim 1 , wherein the patterned mask is formed in strips of material having a longer axis and a shorter axis, wherein the longer axis is approximately perpendicular to an adjacent gate.
4. The method as defined in claim 1 , wherein the patterned mask is formed in strips approximately parallel to a desired direction of current flow, and wherein the contacts are formed in a plurality of rows having axes approximately parallel to the desired direction of current flow.
5. The method as defined in claim 4 , wherein the contacts are formed such that the contacts comprise sets of two or more contacts each, wherein a strip of saliside-excluded material is disposed between sets of contacts.
6. The method as defined in claim 1 , further comprising forming the pattern mask only in one or more areas that become drains.
7. The method as defined in claim 1 , further comprising forming the pattern mask only in one or more areas that become sources.
8. The method as defined in claim 1 , further comprising forming the pattern mask in areas that become drains and sources.
9. The method as defined in claim 1 , further comprising forming ballasting resistors in series with the drain.
10. The method as defined in claim 1 , wherein the semiconductor device is an N-type snapback device, further comprising coupling a drain of the snapback device to a terminal to protect the terminal from a positive voltage transient.
11. The method as defined in claim 1 , wherein the semiconductor device is a P-type snapback device, further comprising coupling a drain of the snapback device to a terminal to protect the terminal from a negative voltage transient.