Optics: measuring and testing – Plural test
Reexamination Certificate
2001-05-30
2003-10-14
Pyo, Kevin (Department: 2878)
Optics: measuring and testing
Plural test
C356S237500, C250S234000
Reexamination Certificate
active
06633372
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to optical instruments and can be particularly used to develop new and improve existing devices for analysis of a surface of semiconductor wafers, and to integrate the devices into the manufacturing equipment, as well as to examine the uniformity degree of a surface of other articles.
BACKGROUND OF THE INVENTION
During the manufacture of semiconductor devices, no dust particles and other defects can be tolerated on the surface of semiconductor wafers. It is desirable to reveal such defects as early as possible to remove at once a source of their origin. To solve this problem a method is widely used utilizing the known fact that any particle on a smooth surface, or a surface defect scatters the light incident onto the surface.
For example, a method for inspection of an analyzed surface is known from U.S. Pat. No. 4,314,763 (Int.Cl. G 01 N 21/88, 09.02.82), comprising the steps of: rotating the analyzed surface about a center of rotation, forming a light spot on the analyzed surface, and sensing a light scattered from the analyzed surface using an optical system.
The same U.S. Pat. No. 4,314,763 discloses a surface scanning analyzer comprising: a light source for illuminating an analyzed surface by a light spot at an angle close to the normal to the analyzed surface; a photodetector for sensing the light scattered from the analyzed surface; and a rotary table for mounting and rotating an article with the analyzed surface thereon about an axis of revolution parallel to the normal to the analyzed surface.
In the analyzer implementing the above method, the rotated analyzed surface is being moved along a straight line relative to a point at which the light spot is formed on the surface. This is the shortage of the method and the analyzer implementing the method since it is necessary to provide movement of a large object, i.e. the rotary table for mounting a semiconductor wafer (up to 300 mm in diameter), equipped with a rotation actuator, which leads to increased size and cost of the device.
The closest prior art is a method for inspection of an analyzed surface comprising the steps of rotating an object having the analyzed surface about a first center of rotation; forming a light spot on the analyzed surface sensing a light scattered from the analyzed surface at the incidence point of the light spot (Altendorfer H. et al. <<Unpatterned surface inspection for next-generation devices>>.—Solid State Technology, 1996, v. 39, N
o
8, pp.
93-97).
The same reference discloses a surface scanning analyzer comprising: a rotary table for mounting and rotating an object with an analyzed surface about a first axis of revolution that is perpendicular to the analyzed surface; a light source for illuminating the analyzed surface by a light spot at an angle close to the normal to the analyzed surface; a collecting mirror in the form of a truncated body of revolution formed by revolving an ellipse about a second axis of revolution which is parallel to the first axis of revolution and substantially coincides with the normal to the analyzed surface erected at the incidence point of said light spot, said incidence point being at the focus of said truncated body of revolution, a first section plane of the body of revolution being perpendicular to the second axis of revolution in the immediate proximity to said focus, and a second section plane being parallel to the first section plane; a photodetector for sensing the light scattered from the analyzed surface and reflected from the collecting mirror.
In this method a progressive movement of the rotated analyzed surface is remained, i.e. as before it is necessary to move a massive object, which results, as mentioned before, in increased size and cost of the device, hampering substantially integration of the device into the process equipment.
Recent developments of a cluster type equipment in the semiconductor industry have enabled several operations to be carried out simultaneously and ensured the cleanness grade infeasible with conventional equipment. The appearance of new process equipment poses the problem to develop a new measurement equipment capable of operating in the cluster process conditions. The demands imposed on such devices differ significantly from the demands placed on conventional devices. One of the most important requirements is a minimal size of the device, which is dictated by a small volume of clean environment inside the cluster. module. Since the cluster measurement devices are integrated into each individual module, they must be also manufactured and serviced at a low cost.
Thus, the object of this invention is to develop such methods for inspection of an analyzed surface, and a surface scanning analyzer that would be free from the indicated drawbacks.
SUMMARY OF THE INVENTION
The above object and the indicated technical result of the present invention are achieved in the following manner.
In one aspect, the invention relates to a method for inspection of an analyzed surface, comprising the steps of: rotating an object having the analyzed surface about a first center of rotation; forming a light spot on the analyzed surface; sensing separately a light mirror-reflected and a light scattered from the analyzed surface at the incidence point of the light spot, wherein in accordance with the present invention, the method includes the steps of: moving the light spot relative to the analyzed surface through an arc about a second center of rotation which lies outside the analyzed surface; and aligning, at least in one predetermined position, the light spot having an elongated form on the analyzed surface with its maximum size along a radius extending from the first center of rotation through the light spot.
A feature of this method is that in the predetermined position the light spot is located substantially in the middle of said analyzed surface radius extending from the first center of rotation, or the light spot, during its movement through said arc, is turned so as to retain its alignment along the radius extending from the first center of rotation thought the light spot all along the scanning line.
One more feature of this method is that the light scattered from the analyzed surface is collected using a system of mirrors, wherein one of the mirrors is in the form of a truncated ellipsoid of revolution having one axis of revolution substantially coinciding with the normal to the analyzed surface erected at the incidence point of said light spot, said incidence point being at a first focus of said truncated ellipsoid of revolution, a first section plane of the ellipsoid being located perpendicularly to its axis of revolution in the immediate proximity to said first focus, and a second section plane being parallel to the first section plane, and another mirror is a flat mirror having an aperture at the center, arranged at an angle to the axis of revolution of the truncated ellipsoid of revolution, and intended for passing therethrough the light from the light source to the analyzed surface and the light mirror-reflected therefrom, and for reflecting the light scattered from the analyzed surface and reflected from the collecting mirror, wherein the light reflected from the flat mirror is passed through a light filter and then diaphragmed at a point corresponding to the second focus of said ellipsoid of revolution with regard of reflection from said flat mirror.
In one embodiment of the method, the light scattered from the analyzed surface is collected using a system of mirrors, wherein one of the mirrors is in the form of a truncated paraboloid of revolution having an axis of revolution substantially coinciding with the normal to the analyzed surface erected at its incidence point of said light spot, said incidence point being at the focus of said truncated paraboloid of revolution, a first section plane of the paraboloid being located perpendicularly to the axis of revolution in the immediate proximity to said focus, and a second section plane being parallel to the first
Ladas & Parry
Obschestvo S Ogranichennoi Otvetstvennostiju “Reflex Lait”
Pyo Kevin
Sohn Seung C.
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