Method and apparatus for inspecting a substrate

In a method and an apparatus for inspecting defects on a substrate using a light beam, a light source irradiates light beams having different wavelengths onto the substrate. A detector detects first lights scattered from a surface of the substrate and second lights scattered from impurities on the substrate by irradiation of the light beams. An operation unit compares first intensities of the first lights with second intensities of the second lights in order to produce differential values therebetween, and selects a wavelength corresponding to a maximum value of the differential values. An inspection process for inspecting the defects on the substrate is performed using a light beam having the selected wavelength.

RELATED APPLICATION

The present application claims priority from Korean Patent Application No. 2003-12824, filed Feb. 28, 2003, the disclosure of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

The present invention relates to a method and an apparatus for inspecting a substrate, and more particularly, to a method and an apparatus for inspecting defects on a semiconductor substrate using a light scattered from a surface of a semiconductor substrate by irradiation of a light beam.

DESCRIPTION OF THE RELATED ART

Generally, semiconductor devices are manufactured through a three-step process. First, a fabrication process is performed for forming electronic circuits on a silicon wafer used as a semiconductor substrate. Second, an electrical die sorting (EDS) process is performed for inspecting electrical characteristics of the semiconductor devices on the semiconductor substrate. Third, a packaging process is performed for packaging the semiconductor devices in epoxy resins and individuating the semiconductor devices.

The fabrication process for producing a semiconductor device may include any of the following: a deposition process for depositing a layer of a selected material onto the semiconductor substrate, a chemical mechanical polishing (CMP) process for planarizing a surface of the layer, a photolithography process for forming a photoresist pattern on the layer, an etching process for forming a predetermined pattern using a patterned photoresist material in the semiconductor substrate, an ion implantation process for implanting predetermined ions into predetermined portions of the semiconductor substrate, a cleaning process for removing impurities from the semiconductor substrate, an inspection process for inspecting defects on the semiconductor substrate on which the layer or the pattern is formed, or other similar processes.

Defects, such as impurities remaining on the surface of the semiconductor substrate, deteriorate the performance of the semiconductor devices as well as lower yields in the manufacturing of the semiconductor devices. Recently, as the degree of integration of the semiconductor devices has increased, the inspection process for these defects has become increasingly important in the manufacturing of the semiconductor devices.

For example, U.S. Pat. No. 6,215,551 (Nikoonahad, et al.) discloses a scanning system for inspecting anomalies on surfaces. The scanning system directs a focused beam of light at a grazing angle toward the surface to be inspected, and collects the light scattered along the scan path for detecting the anomalies.

While the light beam is irradiated onto the semiconductor substrate, an intensity of a light scattered from the semiconductor substrate is varied in accordance with materials of layers or patterns on the semiconductor and a wavelength of a light beam.

FIG. 1is a line graph showing a light deflection rate and a light absorption rate on a silicon wafer.FIG. 2is a line graph showing a light deflection rate and a light absorption rate on a nitride layer.FIG. 3is a line graph showing a light deflection rate on an oxide layer.

Referring toFIGS. 1 to 3, a light deflection rate and a light absorption rate are varied in accordance with a wavelength of a light beam and materials of objects. Thus, a light scattering rate of a light beam having a specific wavelength is varied in accordance with the materials of the objects.

A conventional apparatus employs a laser beam having a predetermined specific wavelength, and thus the reliability of the inspection process is deteriorated. That is, an intensity of a light scattered from the semiconductor substrate by irradiation of the laser beam having the specific wavelength is varied in accordance with the layers or the patterns formed on the semiconductor substrate. For example, an intensity of a light scattered from the oxide layer on the semiconductor substrate, and an intensity of a light scattered from the nitride layer on the semiconductor substrate, are different from each other. Accordingly, detection rates of the impurities remaining on the oxide layer and the nitride layer become different from each other. The reliability of the inspection process is also deteriorated because the intensity of the light scattered from the semiconductor substrate is varied in accordance with the specific materials which comprise the impurities.

SUMMARY OF THE INVENTION

According to embodiments of the present invention, a method and an apparatus may be provided to select a wavelength of a light beam in accordance with materials of layers or patterns formed on a semiconductor substrate and materials of impurities remaining on the semiconductor substrate, and to inspect defects on the semiconductor substrate using a light beam having the selected wavelength.

According to method embodiment of the present invention, a method for inspecting a substrate comprises irradiating first light beams onto the substrate, the first light beams having different wavelengths, detecting first intensities of first lights scattered from a surface of the substrate and detecting second intensities of second lights scattered from impurities on the substrate, comparing the first intensities of the first lights with the second intensities of the second lights in order to produce differential values between the first and second intensities, irradiating a second light beam onto the substrate, the second light beam having a wavelength corresponding to a maximum value of the differential values, and inspecting the substrate for defects by examining a third light scattered from the surface of the substrate and a fourth light scattered from the impurities on the substrate.

The substrate may include a semiconductor substrate such as a semiconductor wafer, and laser beams may be employed as the first light beams and second light beam. The first light beams are preferably sequentially irradiated by a predetermined wavelength onto the substrate. Lights scattered from the substrate can be detected by a detector. The first intensities and second intensities are varied in accordance with the wavelengths of the first light beams.

The selected wavelength corresponds to the maximum value of the differential values between the first and second intensities. Thus, when an inspection process for inspecting the defects on the substrate is performed using the second light beam having the selected wavelength, the efficiency of the inspection process may be improved. That is, the impurities on the substrate may be easily detected using the third light scattered from the surface of the substrate and the fourth light scattered from the impurities on the substrate by irradiation of the second light beam.

According to another embodiment of the present inventing, an apparatus for inspecting a substrate comprises a light source for irradiating a plurality of light beams onto the substrate, the plurality of light beams having different wavelengths, a detector for detecting lights scattered from the substrate, an operation unit for comparing first intensities of first lights scattered from a surface of the substrate with second intensities of second lights scattered from impurities on the substrate, for producing differential light intensity values between the first intensities and the second intensities, and for selecting a wavelength corresponding to a maximum value of the differential values, a controller for controlling operation of the light source such that the plurality of light beams is sequentially irradiated onto the substrate, and a selected light beam having the selected wavelength is irradiated onto the substrate, and an image processing unit for acquiring an image representing the substrate using a light scattered from substrate by irradiation of the selected light beam, and for inspecting defects of the substrate from the image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring toFIG. 4, the substrate inspection method preferably includes a first process for selecting an inspection wavelength among first wavelengths of first light beams, and a second process for inspecting defects, such as impurities on the substrate surface, using a second light beam having a selected wavelength. Laser beams having different wavelengths are preferably employed as the first light beams and for the second light beam. The substrate preferably comprises a semiconductor substrate, such as a silicon wafer, on which layers and/or patterns are formed.

The first process includes steps S110to S150.

In step S110, a light source irradiates a first laser beam onto a predetermined sampling area of the semiconductor substrate. The first laser beam scans the sampling area in an x-direction. The semiconductor substrate is moved in a y-direction. The x-direction and the y-direction cross each other perpendicularly. A tunable optical parametric oscillator laser system may be used as the light source.

In next step S120, a detector detects a first light scattered from a surface of the sampling area and a second light scattered from impurities remaining on the sampling area in response to the irradiation of the first laser beam.

Subsequently, in step S130, an operation unit compares a first intensity of the first light with a second intensity of the second light in order to produce a differential value between the first and second light intensities.

The steps S110to S130are repeatedly performed when a first wavelength of the first light beam is sequentially varied by a predetermined wavelength in step S140. The first wavelength may be varied between about 250 nm to about 700 nm. Preferably, the first wavelength may be varied between about 250 nm to about 400 nm. More preferably, the first wavelength can be varied between the above wavelengths by a predetermined wavelength of about 10 nm.

In step S150, the operation unit then selects a second wavelength corresponding to a maximum value of the differential values produced during the steps S110to S140above.

The second process includes steps S210to S240.

In step S210, the light source irradiates a second laser beam having the second wavelength onto the entire semiconductor substrate. The second laser scans the entire semiconductor substrate in the x-direction, and the semiconductor substrate moves in the y-direction.

In sequent step S220, the detector detects a third light scattered from a surface of the semiconductor substrate and a fourth light scattered from impurities on the semiconductor substrate by irradiation of the second laser beam.

An image processing unit acquires an image representing the semiconductor substrate in step S230. A third intensity of the third light and a fourth intensity of the fourth light are converted into electric signals by the detector, respectively. The image processing unit acquires the image based on the electric signals, and a display unit displays the image.

The image processing unit inspects the defects on the semiconductor substrate by analyzing the image in step S240. A differential value between the third and fourth intensities corresponds to the maximum value of the differential values between the first and second intensifies. Thus, the impurities on the semiconductor substrate may be readily detected, and the efficiency of the inspection process may be improved.Referring toFIGS. 5 to 7B, the substrate inspection apparatus100preferably includes a laser source110for generating a laser beam20, a detector120for detecting a light30scattered from a semiconductor substrate10, an operation unit130for analyzing intensities of the scattered light30, a controller140for controlling the operation of the laser source110, and an image processing unit150for receiving an image representing the semiconductor substrate10using the intensity of the scattered light30.

The laser source110irradiates laser beams having different wavelengths onto the semiconductor substrate10. For example, the laser source110sequentially varies a wavelength of the laser beam20by a predetermined wavelength while the laser beam20is irradiated onto semiconductor substrate10. A turnable optical parametric oscillator laser system may be preferably used as the laser source110. The tunable optical parametric oscillator laser system is able to vary the wavelength of the laser beam20at discrete intervals either by a predetermined wavelength or linearly. The wavelength of the laser beam20may be varied between about 250 nm to about 700 nm, preferably between about 250 nm to about 400 nm. More preferably, the wavelength of the laser beam20may be varied by a predetermined wavelength of about 10 nm.

A moving stage160supports the semiconductor substrate10thereon. The moving stage160moves the semiconductor substrate10in a horizontal direction so that the laser beam20scans a surface10aof the semiconductor substrate10. A driving shaft162connects the moving stage160with a driving unit164for moving the moving stage160.

The driving unit164preferably includes a Cartesian robot. The driving unit164moves the moving stage160in the x-direction and the y-direction so that the laser beam20scans a predetermined sampling area12of the semiconductor substrate10or an entire surface of the semiconductor substrate10.

A beam expander112expands a cross-sectional area of the laser beam20agenerated by the laser source110. A beam deflector114deflects the laser beam20bexpanded by the beam expander112so that the laser beam20scans the surface10aof the semiconductor substrate10. A focusing lens116focuses the deflected laser beam20conto the surface10aof the semiconductor substrate10such that a spot size of the laser beam20dirradiated onto semiconductor substrate10may be evenly maintained.

The detector120detects the lights30scattered from the semiconductor substrate10by irradiation of the laser beams, converts the detected lights30into electric signals, and sends the electric signals to the operation unit130and the image processing unit150.

The operation unit130compares the first intensities of the first lights31scattered from the surface10aof the semiconductor substrate10with second intensities of second lights32scattered from the impurities14on the semiconductor substrate10based on the respective electric signals. Also, the operation unit130produces differential values between the first and second intensities, and then selects an inspection wavelength corresponding to a maximum value of these differential values.

The controller140is connected to the operation unit130. The controller140controls operation of the laser source110so as to irradiate the laser beams onto the sampling area12sequentially by the predetermined wavelength, and to irradiate an inspection laser beam having the selected inspection wavelength onto the entire surface of the semiconductor substrate10. Also, the controller140controls operations of the beam deflector114and the driving unit164such that the laser beams and the inspection laser beam scan the surface of the sampling area12and the entire surface of the semiconductor substrate10, respectively, as shown inFIG. 6.

The image processing unit150acquires the image representing the semiconductor substrate10, and the display unit170displays the image. Also, the image processing unit150detects positions and sizes of the impurities remaining on the semiconductor substrate10from the image.

A method for inspecting defects, such as the impurities, on the semiconductor substrate10using the substrate inspection apparatus100will be described hereinafter with reference toFIGS. 5 to 7B.

The semiconductor substrate10is supported on the moving stage160. The beam expander112expands the cross-section area of the first laser beam generated from the laser source110. The expanded first laser beam is irradiated onto the sampling area12through the beam deflector114and the focusing lens116. The beam deflector114deflects the first laser beam so that the first laser beam scans the sampling area12in the x-direction. The driving unit164moves the moving stage160so that the first laser beam scans the sampling area12in the y-direction.

The detector120detects the first light scattered from the surface of the sampling area12and the second light scattered from the impurities on the sampling area12. Also, the detector120converts the first intensity of the first light and the second intensity of the second light into first electric signals, and sends the first electric signals to the operation unit130.

The operation unit130compares the first electric signals to each other in order to produce the differential value between the first electric signals.

The laser source110increases the first wavelength of the first laser beam by the predetermined wavelength. The first laser beam having an increased first wavelength is irradiated onto the sampling area12through the beam expander112, the beam deflector114and the focusing lens116. The differential value corresponding to the increased first wavelength may be produced by the detector120and analyzed by the operation unit130in such a manner as described herein.

The differential values between the first lights and the second lights are produced sequentially during the variation of the first wavelength. The detector120detects the first intensity variation of the first light and the second intensity variation of the second light during the variation of the first wavelength.

The operation unit130produces a plurality of differential values from the first and second intensity variations, and selects the maximum value from the plurality of differential values thus produced.

The controller140controls the operation of the laser source110so as to generate the second laser beam having the second wavelength corresponding to the maximum value. Also, the controller140controls the operation of the beam deflector114so that the second laser beam scans the surface of the semiconductor substrate10in the x-direction. Furthermore, the controller140controls operation of the driving unit164so that the second laser beam scans the entire surface of the semiconductor substrate10in the x and y directions as shown inFIG. 6.

The detector120detects the third light scattered from the surface of the semiconductor substrate10and the fourth light scattered from the impurities on the semiconductor substrate10. Also, the detector120converts the third intensity of the third light and the fourth intensity of the fourth light into second electric signals, and sends the second electric signals to the image processing unit150.

The image processing unit150acquires the image representing the semiconductor substrate10using the second electric signals, and the display unit170displays the image. The image processing unit150detects the impurities remaining on the semiconductor substrate10by analyzing the image.

A differential value between the third intensity and the fourth intensity is typically larger than the differential values between the first intensities and the second intensities. As a result, the impurities on the semiconductor substrate10may be readily detected.

According to exemplary embodiment of the present invention, the inspection laser beam having the selected inspection wavelength may improve the efficiency and reliability in the process for inspecting the defects on the semiconductor substrate.