Low cost application of oxide test wafer for defect monitor in photolithography process

• US 6,171,737 B1
• Filed: 02/03/1998
• Issued: 01/09/2001
• Est. Priority Date: 02/03/1998
• Status: Expired due to Fees

• Current Assignee: Advanced Micro Devices, Inc.
• Original Assignee: Advanced Micro Devices, Inc.
• Inventors: Punjabi, Shobhana R., Singh, Bhanwar, Phan, Khoi A., Chiu, Robert J.
• Primary Examiner(s): Young, Christopher G.
• Application Number:
  US09/017,695
• Time in Patent Office: 1,071 Days
• Field of Search: 430/30, 430/311, 257/48, 438/18, 702/117, 702/118, 702/121, 356/302, 356/305, 356/389, 356/390, 356/394, 382/145, 382/149, 382/151
• US Class Current: 430/30
• CPC Class Codes: G03F 7/7065 Defects, e.g. optical inspection of patterned layer for defects
• CPC Class Codes: H01L 22/20 Sequence of activities consisting of a plurality of measurements, corrections, marking or sorting steps
• CPC Class Codes: H01L 22/34 Circuits for electrically characterising or monitoring manufacturing processes, e. g. whole test die, wafers filled with test structures, on-board-devices incorporated on each die, process control monitors or pad structures thereof, devices in scribe line switching, multiplexing, gating devices G01R19/25; process control with lithography, e.g. dose control, G03F7/20; structures for alignment control by optical means G03F7/70633

Abstract

A low cost technique for detecting defects in photolithography processes in a submicron integrated circuit manufacturing environment combines use of a reusable test wafer with in-line processing to monitor defects using a pattern comparator system. A reusable test wafer having an oxide layer overlying a silicon substrate and having a thickness corresponding to a minimum reflectance for an exposure wavelength used for photolithography is patterned using a prescribed photolithographic fabrication process to form a repetitive pattern according to a prescribed design product rule. The pattern is formed using a reticle having a repetitive pattern array with a similar design rule as the product to be developed by the lithography processes. The patterned test wafer is then inspected using image-based inspection techniques, where the image has high resolution pixels of preferably 0.25 microns per pixel. An optical review station and scanning electron microscope system are used to review defect and classify defect types. The test wafer can then be reused by cleaning the photolithographic pattern by removing the photoresist, and then removing polymer particles adhering to the oxide layer following removal of the photoresist.

Claims

1. A method of monitoring defects generated during formation of a pattern on a wafer, comprising:

(a) forming a reusable test wafer having an oxide layer overlying on a silicon substrate of the wafer;

(b) forming a repetitive pattern on the oxide layer according to a prescribed fabrication process, the repetitive pattern related to a prescribed design product rule by depositing a photoresist layer on the oxide layer according to the prescribed fabrication process, exposing regions of the photoresist layer with a reticle, having the pattern, at a wavelength specified by the prescribed fabrication process, and developing the photoresist layer to form the repetitive pattern in the photoresist layer;

(c) inspecting the repetitive pattern to detect a defect on the repetitive pattern;

(d) classifying the defect to a defect type and defect cause;

(e) determining whether the repetitive pattern has a defect density below a prescribed threshold acceptable for wafer fabrication; and

(f) removing the repetitive pattern from the oxide layer following the determining step by;

(i) removing photoresist forming the repetitive pattern from the oxide layer; and

(ii) removing polymer particles loosely adhering to the oxide layer following the photoresist removing step, wherein steps (b) through (f) are repeated following the removing step (f) at least once.

2. The method of claim 1, wherein the test wafer forming step comprises growing the oxide layer on the silicon substrate to a thickness corresponding to a minimum reflectance for an exposure wavelength used during the repetitive pattern forming step.

3. The method of claim 2, wherein the oxide layer growing step comprises growing the oxide to a thickness substantially equal to 1200 Angstroms for an I-line wavelength as said exposure wavelength.

4. The method of claim 2, wherein the oxide layer growing step comprises growing the oxide to a thickness substantially equal to 1600 Angstroms for a deep ultraviolet wavelength as said exposure wavelength.

5. The method of claim 1, wherein the prescribed design product rule specifies a smallest design rule as a product.

6. The method of claim 1, wherein the inspecting step comprises:

generating an image of the test wafer having the pattern in an optical inspection tool;

generating a wafer map specifying locations and sizes of the detected defect from the image of the test wafer.

7. The method of claim 6, wherein the inspecting step further comprises detecting a defect undetectable by the optical inspection tool using a scanning electron microscope inspection system.

8. The method of claim 1, wherein the classifying step comprises compiling the defects by the defect type and defect cause to prioritize the defect causes causing the defect density.

9. The method of claim 1, wherein:

the photoresist removing step comprises applying a first solution having sulfuric acid and hydrogen peroxide at a first prescribed temperature for a first prescribed interval; and

the polymer particles removing step comprises applying a second solution having ammonium hydroxide and hydrogen peroxide at a second prescribed temperature for a second prescribed interval.

10. The method of claim 1, wherein the removing step removes a maximum of 2 angstroms from the oxide layer.

11. The method of claim 1, wherein the removing step removes the pattern without changing a reflectivity of the test wafer.

12. The method of claim 1, wherein the inspecting step includes performing a pixel-based comparison between adjacent patterns of the repetitive pattern to detect the defect.