Method and apparatus for improving accuracy of plasma etching process

• US 6,270,622 B1
• Filed: 04/10/2000
• Issued: 08/07/2001
• Est. Priority Date: 09/30/1998
• Status: Expired due to Term

• Current Assignee: Lam Research Corporation
• Original Assignee: Lam Research Corporation
• Inventors: Kadavanich, Vikorn Martin, Klippert, Walter E II
• Primary Examiner(s): Mills, Gregory
• Assistant Examiner(s): Hassonzadeh, P.
• Application Number:
  US09/546,428
• Time in Patent Office: 484 Days
• Field of Search: 156/345, 156/643.1, 156/657.1, 156/626.1, 156/627.1, 118/712, 118/715
• US Class Current: 156/345.12
• CPC Class Codes: G01B 11/06 for measuring thickness ; e.g. of sheet material thickness measurement by thermal means G01B21/085
• CPC Class Codes: G01B 11/0675 using interferometry
• CPC Class Codes: G01B 11/22 for measuring depth
• CPC Class Codes: H01L 21/3065 Plasma etching; Reactive-ion etching
• CPC Class Codes: H01L 21/32137 of silicon-containing layers
• CPC Class Codes: H01L 22/12 for structural parameters, e.g. thickness, line width, refractive index, temperature, warp, bond strength, defects, optical inspection, electrical measurement of structural dimensions, metallurgic measurement of diffusions electrical measurement of diffusions H01L22/14
• CPC Class Codes: H01L 22/26 Acting in response to an ongoing measurement without interruption of processing, e.g. endpoint detection, in-situ thickness measurement endpoint detection arrangements in CMP apparatus B24B37/013, in discharge apparatus H01J37/32

Abstract

The invention provides a process and apparatus for improving the accuracy of plasma etching processes such as trench and recess etch processes. In such processes, a trench or recess is etched into a layer of material which does not have a stop layer at the desired depth of the etched openings. Instead, the etching process is carried out for a set time period calculated to achieve a desired etch depth on the basis of measured or estimated etching rates. For example, the duration of etching to achieve a target depth may be based on statistical analysis or real-time measurements of etch depths by interferometry. However, use of estimated etching rates or interferometry to control when etching should be terminated to achieve a desired etch depth can result in defective structures due to etched openings which are too deep or too shallow. According to the invention, a technique is provided for controlling the etching process in a manner which achieves more accurate etch depths in a more reproducible way by conducting a masking layer thickness measurement as part of the etching process.

Claims

1. An apparatus for etching openings in a semiconductor substrate in a plasma chamber, comprising:

a plasma etching chamber including a gas supply for supplying an etching gas into an interior of the chamber;

a substrate support for supporting a semiconductor substrate in the interior of the plasma chamber, the semiconductor substrate including a masking layer and openings in the masking layer containing a material to be etched;

an energy source which energizes the etching gas into a plasma which etches the material in the openings of the masking layer during an etching step;

a thickness measuring device which measures a thickness of the masking layer and outputs a signal representative of the measured masking layer thickness prior to etching of the material in the openings in the masking layer; and

a controller which receives the signal outputted from the thickness measuring device and automatically adjusts the etching step to achieve a target etch depth relative to an underside of the masking layer, the controller terminating the etching step when the target etch depth of the openings is obtained.

2. The apparatus as set forth in claim 1, wherein the thickness measuring device is an interferometer and the energy source generates a high density plasma.

3. The apparatus as set forth in claim 1, further comprising a detector which detects exposure of an upper surface of the masking layer during etching of a layer of material overlying the masking layer, the detector outputting a thickness measuring signal to the controller when a chemical species in the plasma is detected.

4. The apparatus as set forth in claim 3, wherein the masking layer is of silicon nitride and the chemical species detected by the detector is silicon chloride or the masking layer is a photoresist and the chemical species detected by the detector is CO.

5. The apparatus as set forth in claim 1, wherein the thickness measuring device measures the thickness of the masking layer during an etching process which includes clearing a layer of material overlying the masking layer.

6. The apparatus as set forth in claim 1, wherein the thickness measuring device measures the thickness of a masking layer which has been chemically-mechanically polished.

7. The apparatus as set forth in claim 1, wherein the controller terminates the etching step during etching of material in the openings wherein a stop layer is not present at the target etch depth.

8. The apparatus as set forth in claim 1, wherein the masking layer consists essentially of silicon nitride and the material in the openings consists essentially of polysilicon.

9. The apparatus as set forth in claim 1, wherein the masking layer comprises two or more layers of material or a photoresist.

10. The apparatus as set forth in claim 1, wherein the thickness measuring device is an interferometer which determines the thickness of the masking layer by measuring light reflected from upper and lower surfaces of the masking layer.

11. The apparatus as set forth in claim 10, wherein the thickness measuring device determines the thickness of the masking layer by comparing the actual signal generated by the reflected light to a stored signal derived for a given thickness of the masking layer.

12. The apparatus as set forth in claim 10, wherein light is reflected from the surface of the substrate during etching and wherein the signal created by light reflected from upper and lower surfaces of the masking layer is subtracted from the total signal created by the reflected light to determine the etch depth.

13. The apparatus as set forth in claim 1, wherein the thickness measuring device determines the thickness of the masking layer by comparing a stored curve profile with a measured curve profile.