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Epi-Isolated Substrate Contact to Polycrystalline Silicon Trench

IP.com Disclosure Number: IPCOM000043161D
Original Publication Date: 1984-Jul-01
Included in the Prior Art Database: 2005-Feb-04
Document File: 2 page(s) / 89K

Publishing Venue

IBM

Related People

Lange, RC: AUTHOR [+2]

Abstract

In polycrystalline silicon (poly-Si)-filled trench isolation for substrate application, the trench poly-Si frequently tends to be overplanarized. This is caused by excessive poly-Si etch back and insufficient poly-Si. The active N-epi region 1 adjacent to the trench could be exposed and shorted to poly-Si by substrate contact (Fig. 1). The transistor collector in this N-epi region would then be shorted to the substrate. The active N-epi region can still be isolated from the substrate even if the back-fill poly-Si is overplanarized. In this method, two floating N-epi islands 2 and 3 (Fig. 2) are provided for the substrate contact area 4, one at each adjacent side of the poly-Si trench.

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Epi-Isolated Substrate Contact to Polycrystalline Silicon Trench

In polycrystalline silicon (poly-Si)-filled trench isolation for substrate application, the trench poly-Si frequently tends to be overplanarized. This is caused by excessive poly-Si etch back and insufficient poly-Si. The active N-epi region 1 adjacent to the trench could be exposed and shorted to poly-Si by substrate contact (Fig. 1). The transistor collector in this N-epi region would then be shorted to the substrate. The active N-epi region can still be isolated from the substrate even if the back-fill poly-Si is overplanarized. In this method, two floating N-epi islands 2 and 3 (Fig. 2) are provided for the substrate contact area 4, one at each adjacent side of the poly-Si trench. These floating epi islands are achieved by closing a small area of epi within a closed poly-Si trench loop formed by 5 and 6, as shown by top view (Fig. 3). Although the floating epi islands are shorted to the substrate (Fig. 2), they do not affect the active epi region because they are electrically isolated by the poly-Si trench loop. Since the minimum island area required is determined by the requirement that no two parallel trenches merge, the impact on integration density is insignificant. With this epi- isolated substrate contact method for poly-Si trench application, the yield would be greatly improved and the planarization tolerance becomes an insignificant factor for successful trench isolation. This method is...