Apparatus and method for controlling etch depth

• US 20040084406A1
• Filed: 09/25/2002
• Published: 05/06/2004
• Est. Priority Date: 09/25/2002
• Status: Active Grant

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Venugopal, Vijayakumar C., Kamp, Tom A., Miller, Alan J.
• Granted Patent: US 6,939,811 B2
• Time in Patent Office: Days
• US Class Current: 216/59
• CPC Class Codes: H01J 37/321 the radio frequency energy being inductively coupled to the plasma
• CPC Class Codes: H01J 37/32963 End-point detection
• CPC Class Codes: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H01L 21/67069 for drying etching
• CPC Class Codes: H01L 21/67253 Process monitoring, e.g. flow or thickness monitoring

Abstract

An apparatus and method for etching a feature in a wafer with improved depth control and reproducibility is described. The feature is etched at a first etching rate and then at a second etching rate, which is slower than the first etching rate. An optical end point device is used to determine the etching depth and etching is stopped so that the feature has the desired depth. Two different etching rates provides high throughput with good depth control and reproducibility. The apparatus includes an etching tool in which a chuck holds the wafer to be etched. An optical end point device is positioned to measure the feature etch depth. An electronic controller communicates with the optical end point device and the etching tool to control the tool to reduce the etch rate part way through etching the feature and to stop the etching tool, so that that the feature is etched to the desired depth.

Claims

1. A method for etching a feature having a feature depth in a layer of a wafer, the method comprising:

etching to a first depth of the feature at a first etching rate;

etching from the first depth to a second depth at a second etching rate, the second etching rate being slower than the first etching rate;

optically determining when the second depth has reached the feature depth; and

stopping etching the feature.

2. The method of claim 1, wherein etching to a first depth includes forming a desired profile of the feature.

3. The method of claim 2, wherein etching from the first depth to the second depth substantially retains the desired profile of the feature.

4. The method of claim 1, wherein the first etch depth is in the range of approximately 65 to 85 percent of the feature depth.

5. The method of claim 1, wherein the feature is a trench.

6. The method of claim 1, wherein the layer is a crystalline silicon layer.

7. The method of claim 1, wherein the etching depth is optically determined throughout the method.

8. The method of claim 7, further comprising optically determining when the first depth has been reached.

9. The method of claim 1, wherein the etching rate is changed by changing the composition of an etchant.

10. The method of claim 1, wherein the layer does not have an associated etch stop indicator.

11. The method of claim 1, wherein the layer does not have an etch stop layer.

12. The method of claim 1, wherein the optical determination is carried out using an optical end point technique.

13. The method of claim 12, wherein the optical end point technique is selected from the group comprising interferometric end point and broadband reflectometry based end point.

14. The method of claim 1, wherein the method is part of a process selected from the group comprising recess and shallow trench isolation.

15. The method of claim 1, wherein an absolute feature depth is optically determined.

16. A method for etching a trench having an end point in a silicon layer of a wafer, comprising:

etching at a first etch rate;

etching at a second etch rate less than the first etch rate;

optically determining a current etch depth; and

stopping etching so that the trench depth reaches the end point.

17. The method of claim 16, wherein etching at a first etch rate forms a desired trench profile.

18. The method of claim 17, wherein etching at the second etch substantially retains the desired etch profile.

19. The method of claim 16, comprising optically determining when to change the etch rate.

20. Apparatus for etching a feature having a feature depth in a layer of a wafer, the apparatus comprising:

an etching tool including a chuck for holding the wafer;

an optical end point device adjacent the etching tool and positioned to measure an etch depth of the feature to be etched; and

an electronic controller in communication with the optical end point device and etching tool and configured to reduce the etch rate of the etching tool at a first etch depth less than the feature depth and stop the etching tool from etching such that the etch depth reaches the feature depth.