Reduction of electric field effect in the bird's beak region of a DRAM cell following expansion of active region through local encroachment reduction
US4959325A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Feb 24, 1989 |
| Grant date | Sep 25, 1990 |
| Priority date | — |
| Expiry date | Feb 24, 2009 |
Classification
- Technology area (CPC Y)Emerging Cross-Sectional Technologies
- CPC primaryY10S438/936
- WIPO fieldSemiconductors
- WIPO sectorElectrical engineering
Abstract
The present invention constitutes an improvement of the Local Encroachment Reduction (LER) process developed by Tyler Lowrey at Micron Technology, Inc. of Boise, Idaho. LER consists of selectively etching a portion of the field oxide which has encroached into a DRAM cell's active area and then subjecting the cell to a high-energy boron implant to maintain adequate active area isolation. Although the boron implant effectively decreases the width of the depletion region between n+ active areas and p+ substrate, it has the undesirable effect of reducing the breakdown voltage at the n-p junctions in the bird's beak regions at the edges of the active regions, thus increasing the cell's susceptibility to gated-diode breakdown following creation of the cell plate. The present invention solves this problem by creating a graded junction in the bird's beak regions of the cell. The graded junction reduces the electric field intensity in the junction region, resulting in an increase in the breakdown voltage. The graded junction also minimizes the effect of gated-diode breakdown and band-band tunneling leakage.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.