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Recessed Oxidation Isolation Structures

IP.com Disclosure Number: IPCOM000048597D
Original Publication Date: 1982-Feb-01
Included in the Prior Art Database: 2005-Feb-08
Document File: 3 page(s) / 58K

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Malaviya, SD: AUTHOR


These structures and the process for making them relate to various ways of introducing diffused regions under the recessed oxide isolation (ROI) structures.

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Recessed Oxidation Isolation Structures

These structures and the process for making them relate to various ways of introducing diffused regions under the recessed oxide isolation (ROI) structures.

Figs. 1A through 1C depict cross-sectional views of a device and illustrate the various steps of the first isolation scheme. The starting point is illustrated in Fig. 1A which shows a P-type semiconductor substrate 10 with an overlying epitaxial layer 12, N+ sub-collector regions 14, and ROI regions 16 surrounding monocrystalline N-epi regions 18. The spacing between regions 16 is made such that the separation between them after outgrowth of the regions is very small, i.e., on the order of 0.5 micron. Regions 16 have been formed by depositing an oxidation-resistant masking layer consisting of thermal oxide layer 20 with an overlying layer 22 of silicon nitride. Regions 16 were formed by removing a portion of the unmasked silicon of epitaxial layer 12, and subsequently oxidizing the silicon. The technique for forming this structure is well known in the art.

The first step of this process for forming an improved isolation scheme consists of forming a block-out mask 30 that leaves exposed the portions of oxidation-resistant masks 20 and 22 that overlie the monocrystalline crystalline epi region between regions 16. The exposed masking layers are removed by chemically etching with a suitable etch. As indicated in Fig. 1B, the portion of epitaxial layer 12 between regions 16 is subsequently etched down to the dotted line 32 and subsequently down to the solid line 34 by reactive ion etching (RIE). After the block-out mask 30 has been removed, the, depression is oxidized, forming a thin layer of thermal oxide 36, and a boron implant made to form P+ pocket 38. The opening is subsequently filled with chemically vapor deposited oxide 40, as shown in Fig. 1C.

An alternate technique is to extend the thermal re-oxidation cycle used to form layer 36 to fill up and seal the hole in the epitaxial layer. This option has the advantage that the corners can be sealed with a suitably extended oxidizing cycle. The CVD oxide layer can then be used to fill the remaining hole between the ROI walls. Yet another option is to use a layer of polycrystalline silicon followed by a polysilicon silicon re-o...