Method for forming trench

Abstract

Provided is a method for forming a trench, capable of rounding a top corner without adding a separate mask or process. In the method, first and second insulating layers are stacked on a substrate having an isolation region and an active region. Subsequently, a photoresist pattern is formed on the second insulating layer, and the first and second insulating layers are patterned using the photoresist pattern as a mask to expose a portion of a substrate in the isolation region. After that, the substrate is etched using the first and second pad insulating layers as a mask to form an STI region such that an upper width of the STI region is greater than a lower width of the STI region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a further understanding of the invention and are incorporated in and constitute a part of this application, illustrate embodiment(s) of the invention and together with the description serve to explain the principle(s) of the invention. In the drawings:

FIG. 1 is a related art profile photo when an STI region is surface-oxidized at temperature of 1000° C.;

FIG. 2 is a related art profile photo when an STI region is re-oxidized at a temperature of 950° C.;

FIG. 3 is a view a method for rounding an STI corner according to the present invention; and

FIG. 4 is a cross-sectional view illustrating a related art STI region having an oxide layer whose pullback length is short, which is provided for comparison with the STI region of FIG. 3.

Claims

1. A method for forming a trench, the method comprising: sequentially stacking a first insulating layer and a second insulating layer on a substrate having an isolation region and an active region therein;forming a photoresist pattern on the second pad insulating layer;sequentially patterning the second pad insulating layer and the first pad insulating layer using the photoresist pattern as a mask to expose a portion of a substrate in the isolation region; andetching the substrate using the first and second pad insulating layers as a mask to form a trench such that an upper width of the trench is greater than a lower width of the trench.

2. The method according to claim 1, wherein further comprising rounding a top corner of the trench.

3. The method according to claim 2, wherein rounding the top corner of the trench comprises increasing an inner angle θ and a radius of an inscribed circle at the top corner by controlling an upper diameter and a lower diameter of the trench.

4. The method according to claim 3, wherein rounding the top corner of the trench further comprises controlling a slope of the trench.

5. The method according to claim 1, further comprising increasing a pullback length of the first insulating layer.

6. The method according to claim 2, wherein rounding the top corner of the trench comprises controlling a time of dipping the top corner in an HF-containing medium during a cleaning process.

7. The method according to claim 3, wherein the radius of the top corner of the trench is calculated using R=tan{[(θα/2)][aβ+b]}, where θ=tan−1[{(e−f)/2}/g]+π/2, a is a pullback length of the first pad insulating layer, b is a pullback length of the second insulating layer, a={(C1×T1)2−C2}0.5, b=C2×T2, α and β are weight factors of an oxidation process on the trench, C1 is an etching rate (Å/sec) of the first insulating layer, C2 is an etching rate (Å/sec) of the second insulating layer, T1 is an etching time (sec) of the first insulating layer, and T2 is an etching time (sec) of the second insulating layer.

8. The method according to claim 1, further comprising depositing an oxide layer in the trench.

9. The method according to claim 8, further comprising growing a liner oxide along sidewalls of the trench before depositing the oxide layer in the trench.

10. The method according to claim 8, further comprising polishing the oxide layer to remove the oxide layer from areas other than the trench.

11. The method according to claim 10, further comprising removing the second insulating layer.

12. The method according to claim 1, wherein the second insulating layer comprises a nitride layer.

13. The method according to claim 1, wherein the first insulating layer comprises a pad oxide layer.