Method for forming an ESD protection device
View Patent ↗An ESD protection device ( 20 ) comprises an N-type epitaxial collector ( 21 ), a first, lightly doped, deep base region ( 221 ) and second, highly doped, shallow base region ( 222 ) that extends a predetermined lateral dimension. The device responds to an ESD event by effecting vertical breakdown between the base regions and the N-type epitaxial collector. The ESD response is controlled by the predetermined lateral dimension, S, which, in one embodiment, may be is determined by a single masking step. Consequently, operation of the ESD protection device is rendered relatively insensitive to the tolerances of a fabrication process, and to variations between processes.
1. A method of fabricating an ESD protection device, the method comprising:
providing collector layer of a first conductivity type;
forming a first base region in the collector layer, the first base region having a second conductivity type;
forming a second base region in the first base region, the second base region having the second conductivity type;
wherein the first base region and the second base region are formed so that the first base region has a depth that is greater than a depth of the second base region and so that the second base region is more highly doped than the first base region;
and wherein the second base region is formed by:
patterning, with a single mask layer, photoresist on the first base region so as to leave exposed a central area having a predetermined lateral dimension; and
implanting the central area to form the second base region that has a depth less than the depth of the first base region and has a dopant concentration greater than a dopant concentration of the first base region.
2. A method of fabricating an ESD protection device as defined in claim 1 , wherein the first conductivity type is N-type and the second conductivity type is P-type.
3. A method of fabricating an ESD protection device as defined in claim 1 , wherein the first base area and the second base area are formed so that the first base area only partially surrounds the second base area.
4. A method of fabricating an ESD protection device as defined in claim 1 , wherein the patterning establishes a predetermined lateral dimension that is effective to cause an ESD response in which vertical breakdown between the collector region and the first base region predominates with respect to vertical breakdown between the collector region and the second base region.
5. A method of fabricating an ESD protection device as defined in claim 1 , wherein the patterning establishes a predetermined lateral dimension that is effective to cause an ESD response in which vertical breakdown between the collector region and the second base region predominates with respect to vertical breakdown between the collector region and the first base region.
6. A method of fabricating an ESD protection device as defined in claim 1 further comprising:
placing the ESD protection device in an integrated circuit;
providing a conductive pin for coupling the integrated circuit to external signals;
coupling an active semiconductor device coupled to the conductive pin; and
coupling the ESD protection device to the conductive pin.
7. A method of fabricating an ESD protection device comprising:
providing a first base area, the first base area having a first conductivity type and having a first dopant concentration;
providing a second base area formed within the first base area, the second base area having the first conductivity type, having a second dopant concentration, wherein the second base area is formed by:
patterning, with a single mask layer, photoresist on the first base area so as to leave exposed a central area having a predetermined lateral dimension; and
implanting the central area to form the second base area that has a depth less than the depth of the first base area and has a dopant concentration greater than a dopant concentration of the first base area; and
providing a collector area of a second conductivity type and positioned beneath the first and the second base areas.
8. A method of fabricating an ESD protection device as defined in claim 7 , further comprising:
coupling an ESD event to the ESD protection device; and
effecting vertical breakdown between the collector area and one or both of the first and the second base areas in response to the ESD event.
9. A method of fabricating an ESD protection device as defined in claim 8 , further comprising:
controlling occurrence of the vertical breakdown in response to the ESD event by the predetermined lateral dimension of the second base area.
10. A method of fabricating an ESD protection device as defined in claim 8 , further comprising:
forming a relatively wide lateral dimension so that vertical breakdown between the second base area and the collector area predominates over vertical breakdown between the first base area and the collector area in response to the ESD event.
11. A method of fabricating an ESD protection device as defined in claim 8 , further comprising:
forming a relatively narrow lateral dimension so that vertical breakdown between the first base area and the collector area predominates over vertical breakdown between the second base area and the collector area in response to the ESD event.
12. A method of fabricating an ESD protection device as defined in claim 8 , further comprising:
forming an equivalent Zener diode between the collector area and one or both of the first and the second base areas in response to vertical breakdown between the collector area and one or both of the first and the second base areas.