JP3262565B2 - Reference body for optical surface scanner - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD This invention relates to the testing of optical scanners and, more particularly, to reference standards for establishing particle counts for scanners.

[0002]

BACKGROUND ART El Galbrais (L. Galbrai)
An optical scanner of the type shown in U.S. Pat. No. 4,512,659 of the th) is used to measure the contamination of bare semiconductor wafers before the chip fabrication process begins. Contamination is often in the form of particulate matter of sizes ranging from very large flakes of particles to submicron specifications of powder or dust.

In surface scanning, the general state of contamination is an important consideration, but more specifically, the actual particle count is the desired information. Many surface scanners scan back and forth in one direction, while the wafer being inspected is moved vertically under a scanning beam.
This establishes an xy scan on the wafer surface. The scan controller typically establishes a wafer-shaped scan pattern such that the scan beam is always on the wafer surface and does not encounter the wafer edge.

One of the problems encountered in optical surface scanning
First, the light scattered from features on the surface varies with the position of the features with respect to the scan center of the beam. There are at least two reasons for such a change. The first reason is that the light intensity from the center of the scan falls off as the square of the distance from that center. Thus, features that scatter light closer to the scan center will present a stronger scatter signal to the remote detector than the same feature further away. The second reason is that the scanning beam spot falling on the surface changes cross-sectional shape across the surface. A beam that is circular in shape at the center of the surface becomes elliptical at the edges of the surface. Such a change in beam spot shape causes a change in the amount of light scattered from the feature. Further, if the scan center is not just above the center of the surface, there will be a significant difference in scattering from the opposite edge of the surface. These problems are solved in telecentric scanners,
Many of the surface scanners currently in use are not telecentric.

[0005] There is a need for a reference substrate for examining particle counts in a surface scanner where beam irradiation varies on the surface and the surface edges may be misaligned with respect to the scan center.

[0006]

SUMMARY OF THE INVENTION The above needs are met by a reference wafer having a group of light scattering features disposed in spaced concentric rings. A regular group of light-scattering elements is disposed in each annulus and the groups are spaced around each annulus. A group of light-scattering features of the same size are aligned to receive a scanning beam at the same scan location but at different scans. With this arrangement, the scanner should see features of the same dimensions in different scans and scatter the same amount of light at the same relative positions.

[0007] The operator may size the light scattering features in various groups within the scan line. Changes in dimensions will inform the operator of a system error.

[0008] The scattering pattern over multiple scans will tell the user if the scan center is centered on the wafer. In this situation, there will be significant differences in the scattering from each edge.

Bands containing light-scattering elements are spaced apart from adjacent similar bands by empty bands, allowing wafer edge simulation and rejection by the scanner.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Referring to FIG. 1, a wafer having a pattern of light scattering features is shown. This pattern includes a hierarchical organization of features. At the lowest level, called the group level, there is an array of elements that scatter individual light. A first such group 11 is arranged at the geometric center 15 of the wafer 13. Circles 21 and 2 surround the first group
7 is an empty annular band 17 having an edge indicated by 7. The inner circle 21 is about 10 m from the geometric center 15
m, while circle 27 is at a radius of 13 mm from the center. In this application, the crosshairs marking the center 15 of the wafer, as well as all the circular dotted lines indicating the annular boundary, are overhead lines. The wafer is completely bare except for the pattern of light scattering features.

Next, the first feature including the annular band 25 is that an inner overhead band edge 27 and an outer overhead band edge 29 are respectively provided.
Having. This first band comprises light scattering features 31, 33, 3
5, and 4 groups of 37. The distance from the geometric center 15 to the center of the group is 18 mm. The radius of the outer band edge 29 is 22 mm. Second
An empty annular band 39 is defined between the band edge 29 and the band edge 41. The radius of the band edge 41 is 26 mm.

Next, the second light scattering feature including the band 43 is:
It is defined between edges 41 and 45. The radius of the edge 45 is 34 mm. Group of features, for example, Group 4
7 is disposed in the second band.

Beyond the second feature, including band 43, there is another empty annular band 49 having band edges 45 and 51. The radius of the band edge 51 is 38 mm. The empty annular band 49
It fulfills the same purpose as other empty annular zones and allows for edge removal for scanning over reduced zones. The radius of the empty annular band corresponds to the outer radius of the wafer of predetermined dimensions. This embodiment assumes a 100 millimeter wafer, but other dimensions can be used, as well as 3 inch and 6 inch wafers. A third including an annular band 53,
And the outermost feature is defined between the band edges 51 and 55. The group of light scattering features 57 is at a radius of 40 mm from the geometric center, while the band edge 55 is 46 m
m radius. The outer edge 59 of the wafer has a radius of 50 m
m.

The overall distribution of the group on the wafer, like the previously measured annular distribution, is one of the rows and columns.
And there are at least four groups in any row or column. The innermost group in the first annular band 25 differs from the group in the second band 43 with respect to the center, but has the same angular orientation as the third band 53.
By collinearly aligning the groups, light scattering features in different groups of different bands will be seen in the same line scan.

Referring to FIG. 2, another pattern of a group of light scattering elements will be seen. Again, the groups are distributed in an annular band around the geometric center 65. Annular bands 71, 7 having a common geometric center 65
3 and 75 are spaced by empty bands 81, 83 and 85 having the same radius size as the empty band of FIG. Bands 71, 73 and 75 each include a plurality of spaced groups of light scattering features. The distribution of groups is also in rows and columns, with the spacing between groups being greater than twice the width size of the groups. Since there are 12 light scattering features per group, there will also be 12 light scattering elements just near the geometric center 65. If the edges are chosen to be locked out by a first empty annular band 81 so that all groups within the annular band 71 are counted, 48 features in the first annular band, plus 12 features in the center. , There are a total of 60 light scattering features, which should be counted in one scan including all light scattering elements in the empty annular band 81. If the closure of the annular edge is pushed out to the second empty annular band 83,
There will be an additional 8 groups that will be scanned, or a total of 96 light scattering elements. With an additional 96 elements, there are a total of 156 light scattering elements to be scanned.

If the exclusion area were pushed further into the third empty annular band 85, the twelve additional groups present in the annular band 75 would be counted in the total number of groups. . The twelve groups in the outermost belt are
With an additional 144 or a total of 300 light scattering elements.

Each of the light scattering features is created by patterning a reflective bare semiconductor wafer. The bare wafer is coated with a photoresist, and the coated wafer is then patterned into a precise pattern by a photomask containing light scattering elements. The photomask may be made by a step and repeat camera to homogenize the light scattering elements. Once the wafer has been patterned, it may be etched to the desired depth, and all photoresist is then removed. A typical desired depth is 675 °. The diameter of the etched pit is 1.5 microns. These magnitudes are selected so that the light scattered from any light scattering feature approximates the amount of light scattered by a 0.269 micron latex sphere. Polystyrene latex spheres of these sizes
As a reference reference material known as SRM-1691,
National Institute of Standards and Technology
itute of Standards andTec
hnology). Other thicknesses are
Will be used to mimic the response from 0.364 micron and 0.496 micron spheres. Therefore, the absolute contamination standards are: test wafer, SRM-169
It may be mimicked by comparing the light scattering features created by etching, with reference to an absolute standard created by distributing one type of polystyrene latex sphere.

The details of the shape structure of each light scattering group will be understood with reference to FIG. Light scattering element 8
The distance between 7 and 91 is 2 mm. But 1 to 3
It can be in the millimeter range. Similarly, the distance between the light scattering elements 87 and 93 is also 2 mm.
Since the spacing along the rows and columns of the array is the same, the size across the array is 6 mm. Similarly, the height of the array is also 6 mm. The array is symmetric about the xy axes 95, 97, which are merely fictitious axes and not etched lines. This also applies to the axis seen in the center of FIGS.

The spacing of the light scattering features is such that the illuminating beam spot illuminates less than all members of the group. Preferably, only one spot, or a portion of the spot, is irradiated at a time. then,
Other spots are illuminated and recorded as the beam sweeps across the surface of the wafer. In this way, the number of spots may be counted. If more than one spot is illuminated at once, counting the spots is more difficult and must rely on information obtained from repeated passes over the spot.

[Brief description of the drawings]

FIG. 1 is a top plan view of a reference standard according to the present invention.

FIG. 2 is a top plan view of another reference according to the present invention.

FIG. 3 is a detailed view of the reference standard of FIG. 1;

[Explanation of symbols]

(15, 65) Center (25, 43, 53, 71, 73, 75) Annular band (17, 39, 49, 81, 83, 85) Empty annular band (41, 51, 55, 59) Wafer edge (11, 31, 33, 35, 37, 47, 57) Light scattering feature group

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-60-38827 (JP, A) JP-A-61-108950 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/66

Claims (9)

(57) [Claims] An optical surface scanner reference body disposed in first and second annular bands surrounding a center of a wafer.
Multiple groups of multiple light scattering features
It includes wafer to said first and second annular bands does not include the light scattering characteristic object
Are separated from each other by an empty annular band, said empty annular band corresponding to a radius of a wafer of a predetermined size.
A reference body for an optical surface scanner having a radius. 2. A plurality of light scattering features in each said group.
Are arranged in a row and column pattern.
Reference body described in. 3. The groups in different annular zones.
2. The criterion of claim 1, wherein are aligned linearly.
body. 4. A reference for an optical surface scanner, comprising a plurality of light scattering features, radiating around a common center.
Includes wafers with multiple groups
Seen, a plurality of light-scattering characteristic of said each group, the beam is grayed
Simultaneously less light scattering features in the entire loop
In a row and column pattern, spaced as if illuminated
An array of empty rings that do not include the light scattering features.
Wherein the empty annular band includes the plurality of radially distributed glues.
Circle corresponding to the radius of a wafer of a predetermined size
A reference body having a radius. 5. The light-scattering feature according to claim 1, wherein the light-scattering features are 1 to 3 mm.
The reference body according to claim 4, wherein the reference body has an interval in the range of: 6. The light scattering feature is provided on the wafer surface.
5. The pit of claim 4, wherein the pit is etched.
Reference body. 7. The light-scattering feature is provided in a plurality of annular zones.
And wherein a first annular band of the plurality of annular bands is light scattering.
5. The method of claim 4, comprising four groups of features.
Reference body. 8. A second annular band of the plurality of annular bands.
Includes eight groups of light scattering features .
A reference body according to claim 7. 9. A third annular band of the plurality of annular bands.
Comprises 12 groups of light scattering features,
A reference body according to claim 8.