Method and apparatus for alignment of submicron lithographic features

• US 5,343,292 A
• Filed: 10/19/1990
• Issued: 08/30/1994
• Est. Priority Date: 10/19/1990
• Status: Expired due to Term

• Current Assignee: UNM Rainforest Innovations (f/k/a STC.UNM) (The University of New Mexico)
• Original Assignee: The University of New Mexico
• Inventors: Brueck, Steven R. J., Zaidi, Saleem H.
• Primary Examiner(s): Turner, Samuel A.
• Application Number:
  US07/599,949
• Time in Patent Office: 1,411 Days
• Field of Search: 356/356, 356/401, 356/363, 356/128, 250/237 G, 250/231
• US Class Current: 356/509
• CPC Class Codes: G03F 9/70 for microlithography measuring printed patterns for monitoring overlay G03F7/70633 or focus G03F7/70641; projection system adjustment G03F7/70258; position control G03F7/70775

Abstract

In the manufacture of microelectronic and optoelectronic circuitry, an arrangement for aligning submicrometer lithographic features on a wafer illuminating a diffraction grating on the wafer with an interferometrically established radiation intensity pattern having a predetermined relationship to the lithographic features in another level of the wafer that is to be exposed, the radiation diffracted from the illuminated grating forming moire interference pattern providing spatial amplification of the grating period for alignment purposes by the ratio of the moire fringe spacing to the grating period.

Claims

1. In the manufacture of microelectronic and optoelectronic integrated circuitry, the method of enabling alignment of submicron lithographic features on surfaces at each level of the circuitry to within about one-third the critical dimension or less comprising the steps of:

a) establishing a pattern of images corresponding to waves diffracted from the surface of the level containing the lithographic features by passing a beam of radiation through a first diffraction grating associated with a reference body, said grating having a first periodicity characteristic, and impinging said pattern on a specimen diffraction grating of a periodicity different from that of said first diffraction grating, said specimen diffraction grating being located on the level of circuitry containing the lithographic features, changes in said pattern of images occurring at a rate which is a multiple of the rate of change of the relative displacement of the level of circuitry from a reference body, and

b) analyzing the changes in the pattern of images to determine the extent of actual displacement between the reference body and the level of circuitry to thereby enable alignment of the level with the body.

2. The method of claim 1 further including the step of:

a. removing zero order diffraction levels from said pattern.

3. The method of claim 1 wherein the pattern of images is a moire fringe pattern.

4. The method of claim 1 wherein the reference and specimen diffraction gratings each have a plurality of sets of parallel lines, each set being at angle to the other set.

5. The method of claim 1 wherein the first and second periodicity characteristics are constant.

6. The method of claim 1 wherein the first and second periodicity characteristics are aperiodic.

7. In the manufacture of microelectronic and optoelectronic circuitry, the method of enabling alignment of submicrometer lithographic features on two levels of a semiconductor or other wafer to within about one-third the critical dimension or less, comprising the steps of:

a. providing a submicrometer diffraction grating on the surface of one level of the wafer, said grating having a known positional relation with the lithographic features of the wafer;

b. illuminating said grating with an interferometrically established radiation intensity pattern having a predetermined relationship to the lithographic features in a subsequent level that is to be exposed, the radiation intensity pattern being selected so that the radiation diffracted from the illuminated grating forms a moire interference pattern with one or more moire fringes across the aperture of said grating, the phase of the moire interference pattern varying by up to about 360 degrees as the relative positions in the plane transverse to the radiation intensity pattern and the grating are varied, thus providing spatial amplification of the grating period for alignment purposes by the ratio of the moire fringe spacing to the grating period, and

c. monitoring the phase of the moire interference pattern to enable adjustment of the wafer relative to the radiation intensity pattern at the position of the grating on the wafer to provide the phase of the moire interference pattern that corresponds to an overlap or alignment of the corresponding features on the two lithography levels.

8. The method of claim 7 wherein the step of providing the radiation intensity pattern comprises the steps of:

a. passing a beam of radiation through a structure on a reference body with a transmission function having a first periodicity characteristic, and

b. impinging the radiation intensity pattern onto the diffraction grating, said diffraction grating having a periodicity characteristic different from said first periodicity characteristic.

9. Apparatus for aligning submicron lithographic features in the manufacture of microelectronic and optoelectronic levels of circuitry to within about one third of the critical dimension comprising:

a. first means having a fixed positional relation to a reference body for creating in response to radiation a first pattern of images having first periodicity characteristic;

b. second means located on a surface of a level of circuitry for creating in response to said radiation a second pattern of images having periodicity characteristic essentially slightly different from said first pattern, whereby in response to radiation projecting said first pattern onto said second means, there is diffracted from the surface of the second means a pattern of images of predetermined characteristics which, with relative movement between the first and second means, varies at a higher rate of change than the rate of change of the displacement of the second means from the first means, thereby providing a measure of relative displacement between the reference body and said second means with enhanced accuracy.

10. Apparatus for aligning submicron lithographic features in the manufacture of microelectronic and optoelectronic levels of circuitry to within about one third of the critical dimension comprising:

a) first means having a fixed positional relation to a reference body for creating in response to radiation in the optical range a first pattern of images;

b) second means located on a surface of a level of circuitry for creating in response to said radiation a second pattern of images essentially slightly different from said first pattern, whereby in response to radiation projecting said first pattern onto said second means, there is diffracted from the surface of the second means a pattern of images of predetermined characteristics which, with relative movement between the first and second means, varies at a higher rate of change than the rate of change in the displacement of the second means from the first means, thereby providing a measure of relative displacement between the reference body and said second means with enhanced accuracy.

11. Apparatus as in claim 10 wherein said first and second means each comprise one or more diffraction gratings.

12. Apparatus as in claim 11 wherein said first means further includes means for focusing said first pattern of images onto said second means.

13. Apparatus as in claim 11 wherein said first means further includes means for blocking zero order portions of the first pattern of images.

14. Apparatus as in claim 13 further comprising:

c. Means for receiving and analyzing changes in the interference pattern to provide a direct, real time measure of displacement.