Optics: measuring and testing – Inspection of flaws or impurities
Reexamination Certificate
2000-06-08
2004-05-11
Smith, Zander V. (Department: 2877)
Optics: measuring and testing
Inspection of flaws or impurities
Reexamination Certificate
active
06734960
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a defect measuring method and apparatus for an object to be measured. Particularly, the present invention is concerned with a defect measuring method suitable as a method for measuring and evaluating defects in crystal present in a surface layer of a semiconductor wafer, as well as an apparatus using the method.
RELATED ART
Heretofore, a method and an apparatus for non-destructively measuring defects in crystal present in a surface layer of a semiconductor wafer have been publicly known.
For example, for the observation of defects present in a surface layer portion not deeper than 5 &mgr;m, there has been made available a visible laser scattering tomography, for example, such as MO521 of Mitsui-Kinzoku-Kozan. According to this tomography, it is possible to observe defects up to a depth of 5 &mgr;m on an average from silicon wafers, but the depth and size of each individual surface layer defect cannot be obtained.
Also, in Japanese Patent Laid Open No. 64136/97 there are disclosed a method and an apparatus for determining an intensity distribution of scattered beams which reflect actual sizes of defects present in a surface layer of a semiconductor wafer. According to this method, defects present in a semiconductor wafer are measured on the basis of scattered beams generated from these defects. More particularly, light having a silicon absorbing wavelength is radiated to the wafer from a light source through an optical system, allowing scattered light to be generated from the wafer. This scattered light,is received by a detector and the optical system. Such an operation is performed for the whole area of the wafer and the results of scanning are processed as defect indicating information by means of a computer. At this time there is made correction for eliminating the influence of light absorption by silicon. The results of measurement are corrected taking the attenuation rate of light into account.
There also has been proposed an apparatus wherein plural laser beams of different wavelengths are radiated to a wafer, and on the basis of a difference in absorbance between the wavelengths there is obtained a scattered light intensity which reflects the size of a defect or information relating to the depth of a defect from a polished specular surface.
If the conventional laser scattering tomography of a two-wavelength type is used for the same purpose, the depth of a defect up to 0.5 &mgr;m right beneath the surface of silicon wafer can be measured by utilizing the wavelength dependence of absorption coefficient. For example, in OSDA (optical shallow crystal defect analyzer) of Hitachi there are used two laser beams of 532 nm and 810 nm in wavelength.
According to the conventional infrared laser scattering tomography, it is possible to measure defects in silicon wafers present at a position deeper than about 10 &mgr;m from the surface, but the measurement at the shallower region is impossible. An example of laser beam wavelength is 1.06 &mgr;m.
The semiconductor wafer defect measuring method and apparatus disclosed in Japanese Patent Laid Open No. 64136/97 are for making correction with respect to a scattered light intensity distribution obtained by measurement and not for correcting the intensity of a scattered light with respect to each detect. Thus, the depth from a polished specular surface, as well as a relative dimensional factor, of each crystal defect cannot be measured.
On the other hand, in a measuring apparatus using plural laser beams of different wavelengths, the optical system used is complicated, which is very disadvantageous in point of detection accuracy and cost.
The above conventional apparatuses are lacking in a method for obtaining, with a high accuracy, information relating to the depths and sizes of defects present in a surface layer up to a depth of 10 &mgr;m from the surface. For example, it has been difficult to determine which of two defects is the larger.
In the case where a high accuracy is not so strictly required for the depth of a subsurface defect and it suffices roughly to know a defect density up to a certain depth, the measurement concerned can be effected by changing the laser wavelength. In this case, however, it is necessary to provide plural lasers in advance. Thus, this method is also compelled to use a complicated optical system, which is disadvantageous in point of detection sensitivity and cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method and apparatus for measuring defects of an object (especially a semiconductor wafer) to be measured which method and apparatus can measure the depth of each individual defect and the number of defects in a non-destructive manner.
It is another object of the present invention to provide a semiconductor wafer defect measuring method and apparatus capable of comparing sizes of defects.
It is a further object of the present invention to provide a semiconductor wafer crystal defect measuring method and apparatus using an optical system not complicated, advantageous in point of detection sensitivity and cost, and capable of measuring defects in a non-destructive manner.
According to the present invention, crystal defect measuring method and apparatus for an object (especially a semiconductor wafer) to be measured are described in the appended claims. The defects include not only oxygen precipitates, but also voide defects, stacking faults and others that produce scattered beams upon receipt of laser beams.
The present invention is to improve a method and apparatus for non-destructively measuring defects present in a subsurface layer of an object to be measured.
According to the present invention, the phenomenon that the intensity of a scattered light varies depending on temperature is utilized, and the intensities of scattered beams are measured at two or more temperatures, thereby determining the depths of defects from the surface of an object (especially a semiconductor wafer) to be measured, as well as relative dimensional factors of the defects.
In the present invention, the phenomenon that the penetration depth of a laser beam varies depending on temperature is utilized, and the intensity of a scattered beam is measured at any of plural temperatures, thereby determining the number of crystal defects present in a region from the wafer surface up to an arbitrary depth.
In a preferred example of the defect measuring method and apparatus according to the present invention, the intensities of scattered beams of a laser at two or more temperatures of an object to be measured are measured, thereby determining the depths of defects from the surface of the object to be measured. In comparing the sizes of defects, the intensities of scattered beams of a laser at two or more temperatures of an object to be measured are measured to determine a relative dimensional factor of each defect in the object. In determining the number of defects, a laser beam is radiated to the surface of an object to be measured to scan the same surface and the intensity of scattered beam from the object is measured at any of plural temperatures of the object, thereby calculating the number of defects present in a region from the object surface up to an arbitrary depth. A typical and preferred example of the object to be measured is a semiconductor wafer, particularly a silicon wafer, provided the present invention is also applicable to other objects than wafer.
In one preferred mode for carrying out the present invention, the intensities of scattered beams of a single laser are measured at two or more temperatures, thereby measuring defects present in a surface layer of a semiconductor wafer in a non-destructive manner. For example, by measuring the intensities of scattered beams generated from defects in a semiconductor wafer at two different temperatures, there are determined the depths of defects from the surface of the wafer, as well as relative dimensional factors of these defects.
In another mode for carrying out the present inv
Fujinami Makiko
Goto Hiroyuki
Saito Hiroyuki
Shirai Hiroshi
Foley & Lardner LLP
Smith Zander V.
Stock, Jr. Gordon J.
Toshiba Ceramics Co. Ltd.
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