Patent ID: 8652931

Claim:
A method of Dual-depth STI formation, said method comprising the following steps of: step S1. form a pad oxide layer, a first mask layer and a poly-silicon layer in sequence from the bottom up on a substrate which contain a first region and a second region; The poly-silicon layer comprises at least a first overlapping portion with the first region and a second overlapping portion with the second portion; step S2. coat a first photoresist layer on said poly-silicon layer and a first opening pattern is then formed in the first photoresist layer to expose said second overlapping portion; step S3. inject dopant to said second overlapping portion along said first opening pattern by using the first photoresist layer as a mask; step S4. deposit a second mask layer on said poly-silicon layer after removing the first photoresist, said second mask layer includes a thick mask layer portion located on the first overlapping portion and a thin mask layer which have step difference relative to said thick mask layer located on the second overlapping portion; step S5. coat a second photoresist layer on said second mask layer, then a second opening pattern which exposed at least a portion area on the upper surface of said thick mask layer is formed in the second photoresist layer and a third opening pattern which exposed at least a portion area on the upper surface of said thin mask layer is formed; step S6. etch said thick mask layer portion, said poly-silicon layer and said first mask layer along said second opening pattern to form a first type trench by using the second photoresist layer as a mask and etch said thin mask layer portion, said poly-silicon layer, said first mask layer and said pad oxide layer along said second opening pattern to form a second type trench; wherein the forming time of the second type trench is shorter than the first trench's and thus to etch a second STI with a first depth D 1 on the upper surface of said substrate's second region which exposed in said second type trench; step S7. etch the region of said pad oxide layer which exposed in the first type trench along said first type trench after removing said second photoresist layer and then etch the first region of said substract to form a first STI with a third depth D 3 along the first trench; and etch the portion of said substrate's second region which located on the below part of the second SPI with a first depth D 1 to the first SPI with a second depth D 2 , wherein the second depth D 2 is deeper than the first depth D 1 and the third depth D 3 .