Patent ID: 6872631

Claim:
A method of forming a trench isolation in a substrate, said method comprising the steps of: forming a trench groove in a substrate; forming a first electrically insulating layer which fills said trench groove and extends over an upper surface of said substrate, wherein said first electrically insulating layer has a first surface coverage, and an upper surface of said first electrically insulating layer has a first hollow positioned over said trench groove; forming a second electrically insulating layer over said first electrically insulating layer, wherein said second electrically insulating layer fills said first hollow, and an upper surface of said second electrically insulating layer has a second hollow positioned over said trench groove; carrying out a heat treatment to cause a surface re-flow of said second electrically insulating layer, whereby said second hollow is reduced in size; and carrying out an etch back to said first and second electrically insulating layers after said heat treatment, whereby said second hollow is reduced in size, wherein a taper angle of said hollow after said etch back is not more than 20 degrees.