Abstract:
A particle detecting apparatus for testing a substrate with a film on its surface includes a light source section, an optical system, a light quantity measuring section and an operation section. The light source section emits first and second light beams respectively having first and second wavelengths which are different from each other. The optical system directs the first and second light beams to an incident point on the substrate, wherein the first and second light beams are scattered on the substrate to produce first and second scattered light beams. The light quantity measuring section measures a quantity of the first scattered light beam and a quantity of the second scattered light beam. The operation section detects a foreign particle on or in the film based on the first scattered light beam quantity and the second scattered light beam quantity measured by the light quantity measuring section.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a particle detecting apparatus for a substrate with a film on its surface, and more particularly a particle detecting apparatus which can distinguish and detect a foreign substance on or in the film. 
     2. Description of the Related Art 
     With high integration of a semiconductor device, formation of a fine wiring pattern and fine gate pattern is requested. When there is a foreign substance on the pattern, a short circuit is sometimes formed due to the foreign substance. Also, the flatness of an interlayer insulating film is sometimes degraded by the foreign substance so that an upper wiring pattern is broken. With the high integration of the semiconductor device, even if the foreign substance has a small diameter, the foreign substance influences severely on the break of the wiring pattern. 
     In order to prevent such an influence, a particle detecting method is requested which can detect a particle with a smaller size. The particle with the smaller size could be detected by use of a laser beam with a shorter wavelength. For example, a particle with the size of 0.1 μM can be detected by an Ar laser beam. However, when there is a film of a material such as SiO 2  and SiN formed on a Si substrate, a scattered light beam by the foreign substance is hidden in a scattered light beam by the film, because the laser beam is reflected, absorbed or refracted. As a result, the scattered light beam by the film functions as noise so that it is difficult to detect the foreign substance in a high precision. 
     It is supposed that the maximum voltage corresponding to a quantity of scattered light beam by the foreign substance is represented by V 1  and the maximum voltage of the noise is represented by V 2 . In this case, the foreign substance cannot be distinguished from the noise, if V 1 /V 2  is not larger than 1 at least. This value is desirably equal to or more than 3. Therefore, the laser wavelength should be changed in accordance with the film thickness and the material of the film. However, it is impossible to cope with problems such as different light absorption and reflectivity depending on the film thickness and the film material only by changing the laser wavelength. 
     When the wavelength is made short, the light beam quantity transmitting a silicon film formed on a wafer surface sometimes decreases remarkably, so that the existence of a foreign substance particle in the silicon film cannot be detected. A laser unit with at least 2 wavelengths must be used to detect the existence of the foreign substance particle with a small size from the scattered light beam which is influenced by 2 variables of the film thickness and the particle diameter. 
     A method of detecting a particle by use of such a laser unit with 2 wavelengths is described in Japanese Laid Open Patent Application (JP-A-Heisei 6-148085). In this method, the degradation of the detection precision of a foreign substance particle in the wafer surface due to the interference depending upon the change of the film thickness can be prevented. That is, the method can obtain information relating to the change of the film thickness, but can not obtain information in the direction of the depth in the film. The information which is more important than the film thickness change is existence or non-existence of a foreign substance particle in the film, e.g., a hole in the film. Because the intensity of a light beam scattered by the hole is local but large, it is a detection object which is more important than the film thickness change. When the light beam is scattered by the hole, the film thickness information is not substantively gotten. A method of detecting the existence or non-existence of a foreign substance particle in the substrate surface can be surely is demanded even if the film thickness information is not obtained. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a particle detecting apparatus which can obtain information of a foreign substance particle in a film to reliably detect the foreign substance particle in a substrate surface. 
     Another object of the present invention is to provide a particle detecting apparatus which can reliably detect a foreign substance particle in a substrate surface by removing information in the direction of the thickness of the substrate. 
     Still another object of the present invention is to provide a particle detecting apparatus which can reliably detect a foreign substance particle in a film and a foreign substance particle on a film surface. 
     Yet still another object of the present invention is to provide a particle detecting apparatus which can obtain information of a foreign substance particle in a film formed on a substrate to detect the foreign substance particle with the size equal to or less than 0.1 μm on a film surface. 
     In order to achieve an aspect of the present invention, a particle detecting apparatus for testing a substrate with a film on its surface includes a light source section, an optical system, a light quantity measuring section and an operation section. The light source section emits first and second light beams respectively having first and second wavelengths which are different from each other. The optical system directs the first and second light beams to an incident point on the substrate, wherein the first and second light beams are scattered on the substrate to produce first and second scattered light beams. The light quantity measuring section measures a quantity of the first scattered light beam and a quantity of the second scattered light beam. The operation section detects a foreign particle on or in the film based on the first scattered light beam quantity and the second scattered light beam quantity measured by the light quantity measuring section. 
     The first and second light beams may be directed to the substrate at a same time. In this case, the light quantity measuring section includes a beam collecting section for collecting the first scattered light beam and the second scattered light beam, a light wave guide for guiding the first scattered light beam and the second scattered light beam, a spectroscope for separating the first scattered light beam and the second scattered light beam guided by the light wave guide, a first measuring section for measuring the quantity of the first scattered light beam separated by the spectroscope, and a second measuring section for measuring the quantity of the second scattered light beam separated by the spectroscope. The beam collecting section may include a set of optical fibers, wherein an end of each of the optical fibers is arranged on a semi-spherical surface having the incident point as a center and the other end is connected to the light wave guide. Also, the beam collecting section and the light wave guide are made as a unit, and the light wave guide includes the set of optical fibers. Instead, the beam collecting section may include a set of optical fibers and a set of lenses, each of which is provided for one of the optical fibers in front of the end. An end of each of the optical fibers is provided on a semi-spherical surface having the incident point as a center and the other end is connected to the light wave guide. 
     The first and second light beams may be alternatively directed to the substrate. In this case, it is desirable that the light quantity measuring section includes a beam collecting section for collecting the first scattered light beam and the second scattered light beam, a light wave guide for guiding the first scattered light beam and the second scattered light beam, and a measuring section for measuring the quantity of the first scattered light beam and the quantity of the second scattered light beam by the light wave guide. Also, the beam collecting section may include a set of optical fibers. An end of each of the optical fibers is arranged on a semi-spherical surface having the incident point as a center and the other end is connected to the light wave guide. Instead, the beam collecting section may include a set of optical fibers and a set of lenses, each of which is provided for one of the optical fibers in front of the end. An end of each of the optical fibers is provided on a semi-spherical surface having the incident point as a center and the other end is connected to the light wave guide. 
     It is preferable that the wavelength of the first light beam is smaller than a grain diameter of the foreign particle. Especially, the wavelength of the first light beam is preferably shorter than 488 nm. 
     The wavelength of the first light beam may be smaller than that of the second light beam, and the wavelength of the second light beam may be smaller than a grain diameter of the foreign particle. 
     In order to achieve another aspect of the present invention, a method of detecting a foreign particle on or in a film formed on a substrate, includes: 
     emitting a first light beam a first wavelength; 
     emitting a second light beam having a second wavelength which is different from the first wavelength; 
     directing the first and second light beams to an incident point on the substrate; 
     scattering the first and second light beams by the substrate with the film; 
     measuring a quantity of the first scattered light beam and a quantity of the second scattered light beam; and 
     detecting a foreign particle on or in the film based on the first scattered light beam quantity and the second scattered light beam quantity measured by the light quantity measuring section. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram of an optical system of a particle detecting apparatus according to a first embodiment of the present invention; 
     FIG. 2 is a diagram showing relation between light beams with different wavelengths and scattered light beams; 
     FIG. 3 is a diagram showing a light collecting section of the particle detecting apparatus according to a second embodiment of the present invention; and 
     FIG. 4 is another light collecting section of the particle detecting apparatus according to a second embodiment of the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     A particle detecting apparatus of the present invention will be described below with reference to the attached drawings. 
     FIG. 1 is a block diagram showing the particle detecting apparatus according to the first embodiment of the present invention. Referring to FIG. 1, a movement body  1  can be moved to an optional position on the two-dimensional plane by an X-Y drive mechanism  2 . A substrate  3  for a semiconductor circuit device is fixed and supported on the movement body  1 . The substrate  3  for the semiconductor circuit structure is formed from a semiconductor substrate  4  and a silicon film  5  formed on the semiconductor substrate  4 . The silicon film  5  is formed of material such as silicon oxide and silicon nitride. 
     A laser source is composed of a short wavelength laser source  6  and a long wave length laser source  7 . The wavelength of the laser beam emitted from the short wavelength laser source  6  is shorter than that of the laser beam emitted from the long wave length laser source  7 . The wavelength of 337 nm, 488 nm, 532 nm, or 810 nm are known as the wavelength of the used laser beam source. First laser beam  8  and second laser beam  9  are emitted from the short wavelength laser source  6  and the long wave length laser source  7  through lenses  13  and  14 , respectively, and are synthesized into a synthetic laser beam  12  by a transmission type reflection mirror  11 . As the transmission type reflection mirror  11 , a usual beam splitter can be used. The first laser beam  8  transmits the transmission type reflection mirror  11  just as it is, and the second laser beam  9  is all reflected by the transmission type reflection mirror  11 . A first focus adjusting lens  13  is disposed between the short wavelength laser source  6  and the transmission type reflection mirror  11 . Also, a second focus adjusting lens  14  is disposed between the long wave length laser source  7  and the transmission type reflection mirror  11 . 
     The synthetic laser beam  12  is irradiated to the semiconductor device substrate  3  when a shutter  15  is opened. The synthetic laser beam  12  is not irradiated when the shutter  15  is closed. 
     The synthetic laser beam  12  is irradiated to the surface of the silicon film  5  in a direction orthogonal to the silicon film surface. The synthetic laser beam  12  is not always collected in an incident point or an incident area like a point P (hereinafter, to be referred to as an incident point). However, it is desirable that the synthetic laser beam  12  is collected to have an about tens-of-μm area. The degree of the beam collection can be adjusted by moving the first focus adjusting lenses  13  and the second focus adjusting lenses  14 . 
     The synthetic laser beam  12  is scattered or irregularly reflected at the incident point P to have a corn shape and is inputted to a plurality of optical fibers  17 . An end of each of the plurality of optical fibers  17  is provided to surround the incident point P on a semi-spherical surface having the incident point P as a center position. The plurality of optical fibers form a bundle wave guide. The other ends of all the optical fibers  17  are connected with an optical transmission path  18 . Thus, all the incident light beams which are inputted to optical fibers  17  is transferred to the light beam transmission path  18 . The light beam transmission path  18  is connected with a photo-multiplier  19 . That is, most of the light beams inputted to the optical fibers  17  is supplied to the photo-multiplier  19 . It should be noted that the optical fibers  17  and optical transmission path  18  may be made as a unit. 
     A spectroscope  21  is disposed between the photo-multi plier  19  and the light beam transmission path  18 . The spectroscope  21  can separate the first laser beam and second laser beam with different wavelengths spatially. For example, a prism can be used as the spectroscope  21 . As the spectroscope  21 , various spectroscopes such as a wavelength separating lattice and a resonance parallel plane board are well known and can be used in place of the prism. The photo-multiplier section  19  is composed of a first photo-multiplier  22  and a second photo-multiplier  23 . The first laser beam and second laser beam are separated by the spectroscope  21  and are inputted to the first photo multiplier  22  and second photo-multiplier  23 , respectively. 
     The first photo-multiplier  22  and second photo-multiplier  23  output a first voltage signal  24  and a second voltage signal  25  proportional to the quantities of light beams which are inputted to the first photo-multiplier  22  and second photo-multiplier  23 , respectively. The first voltage signal  24  and the second voltage signal  25  are supplied to a CPU  26 . The CPU  26  is provided with an arithmetic and logic operation circuit  27 . A shutter drive mechanism  28  is disposed between the CPU  26  and the shutter  15 . 
     The CPU  26  drives the X-Y drive mechanism  2  in accordance with a program inputted to the CPU  26 . Also, the CPU  26  drives the shutter drive mechanism  28  once in correspondence to the driving operation of the X-Y drive mechanism  2  such that the shutter  15  is opened for a predetermined time. 
     FIG. 2 is a diagram showing the state in which the synthetic laser beam  12  is irradiated to the silicon film  5  to be reflected regularly and irregularly, and then collected. This figure shows that a foreign substance fine particle  31  is adhered on the surface of the silicon film  5 , and a hole  32  as another foreign substance particle is present in the silicon film  5 . 
     The synthetic laser beam  12  is separated into a first regularly reflected light beam  12   a , a second regularly reflected light beam  12   b , a first irregularly reflected light beam  12   c  and a second irregularly reflected light beam  12   d . The first regularly reflected light beam  12   a  is reflected on the first interface between air and the silicon oxide film  5 . The second regularly reflected light beam  12   b  is refracted at the interface to be inputted to the silicon oxide film  5 , reflected at a second interface between the silicon oxide film  5  and the substrate  4 , and then refracted at the first interface again to be outputted into the air. The first irregularly reflected light beam  12   c  is irregularly reflected by the foreign substance file particle  31  and the second irregularly reflected light beam  12   d  is irregularly reflected by the hole  32 . 
     It is supposed that the film thickness of the silicon film  5  is constant, and the light beam quantity 2Q of the synthetic laser pulse beam  12  is constant. In this case, the light quantity 2Q is a summation of the first laser light beam quantity and the second laser light beam quantity. Also, it is supposed that the first laser light beam quantity and the second laser light beam quantity are equal to each other. 
     The reflectivity K 1  in the first interface for the first laser beam and the reflectivity K 2  in the first interface for the second laser are different from each other. The reflected light beam quantity Q 1  is Q 1 =K 1 Q, which is approximately constant, when the first laser beam is reflected in the first interface. The reflected light beam quantity Q 2  is Q 2 =K 2 Q, which is approximately constant, when the second laser beam is reflected in the first interface. Thus, thee light beam quantity  12   a  of the first regularly reflected light beam and the light beam quantity  12   c  of the first irregularly reflected light beam are constant. 
     In the silicon film  5 , the attenuation factor L 1  of the first laser beam and the attenuation factor L 2  of the second laser beam are different from each other. The light beam quantity Q 3  when the first laser beam travels in the silicon film  5  and goes out from the silicon film  5  is approximately constant. That is, 
     
       
           Q   3   =L   1 ( Q−K   1   Q ) =L   1   Q (1 −K   1 ) 
       
     
     Also, the light beam quantity Q 4  when the second laser beam travels in the silicon film  5  and goes out from the silicon film  5  is approximately constant. That is, 
     
       
           Q   4   =L   2 ( Q−K   2   Q ) =L   2   Q (1 −K   2 ) 
       
     
     The light beam quantity Q 5  of the first laser beam which is irregularly scattered or reflected by a foreign substance fine particle  31  is represented by X 1 . Also, the light beam quantity Q 6  of the second laser beam which is irregularly reflected by the foreign substance fine particle  31  is represented by X 2 . Also, the light beam quantity Q 7  of the first laser beam which is irregularly reflected by a hole particle  32  is represented by Y 1 . Also, the light beam quantity Q 8  of the second laser beam which is irregularly reflected by the hole particle  32  is represented by Y 2 . A variable attenuation factor in the silicon film  5  of the first laser beam is represented by V 1 . Also, a variable attenuation factor in the silicon film  5  of the second laser beam is represented by V 2 . In this case, the light beam quantity of the first laser beam which goes out of the silicon film  5  is V 1 Y 1 . Also, the light beam quantity of the second laser beam which goes out of the silicon film  5  is V 2 Y 2 . 
     Therefore, the light beam quantity Q 1  of the first laser beam and the light beam quantity Q 2  of the second laser beam which are measured by the first photo-multiplier  22  and second photo-multiplier  23  are obtained as follows. 
     
       
           Q   1   =K   1   Q+L   1 ( Q−K   1   Q ) +X   1   +V   1   Y   1 . 
       
     
     
       
           Q   2   =K   2   Q+L   2 ( Q−K   2   Q ) +X   2   +V   2   Y   2 . 
       
     
     In this case, the light beam quantity X 1  and light beam quantity X 2  satisfy X 1 =kX 2  using a proportional constant k. Also, the light beam quantity Y 1  and the light beam quantity Y 2  satisfy Y 1 =sY 2 , using a proportional constant s. The variables in the simultaneous equations are only X and Y. Therefore, if measured values Q 1  and Q 2  are substituted for the simultaneous equations, the light beam quantity of the first laser beam and the light beam quantity of the second laser beam can be determined, when the first and second laser beams are reflected by the foreign substance fine particle  31  and the hole particle  32  and then inputted to the first photo-multiplier  22  and the second photo-multiplier  23 . 
     The quantity V 1 Y 1  and light beam quantity V 2 Y 2  of the laser beams which are irregularly reflected by the hole particle  32  are different from each other. When a dimensionless quantity Z which is defined by the following equation is used, 
     
       
           Z =ln ( V   1   Y   1 / V   2   Y   2 )=ln ( sV   1 / V   2 ) 
       
     
     the values which are represented by the attenuation factors V 1  and V 2  correspond to the depth. Therefore, this dimensionless quantity Z is a data which shows the depth of the hole particle  32  in the silicon film  5 . In this way, even if the foreign substance fine particle  31  and the hole particle  32  exist at the same time, the existence or non-existence of the foreign substance  31  on the silicon film  5  surface and the hole particle  32  in the silicon film  5  can be detected distinguishably by use of 2 wavelength laser beams. Also, the depth of the hole particle can be known. 
     Moreover, the grain diameter of the foreign substance  31  and that of the hole particle  32  can be determined from the reflected laser beam quantities X 1  and Y 1  which are determined through the above calculation. That is, the reflected laser beam quantity is calculated by the light beam scattering theory based on the grain diameter. When 3 wavelength laser beams can be used even if the film thickness of the silicon film  5  is not constant, the simultaneous equations are composed of 3 equations. Thus, the film thickness data can be obtained, in addition to existence or non-existence of both of the hole particle  32  and the foreign substance particle  31  and those grain diameters. 
     The quantity of laser beam irregularly reflected on the silicon film  5  surface which is not a mirror surface increases when the reflectivity is large and the refract factor is large. When surface irregular reflection as noise is more than the irregular reflection quantity by the foreign substance, the detection precision decreases. In such a case, in order to make surface irregular reflection quantity little, use of a laser beam with a longer wavelength is desirable. 
     If an absorption quantity of the laser beam in the silicon film  5  increases by making the wavelength of the laser beam short, only the data near the silicon film  5  surface is obtained. Thus, the data in the direction of the depth can be removed. If the wavelength of the laser beam becomes long, the grain diameter of the particle to be possible to detect becomes large. Generally, it is possible to distinguishably detect existence of a particle, if the grain diameter is about a quarter of the wavelength, as shown in FIG.  3 . 
     For this reason, it is desirable to use an Ar laser beam with the wavelength of 488 nm for the foreign substance with the gain diameter of 0.1 μm on the silicon film. If a N 2  laser with the wavelength of 337 nm is used, it is possible to detect a foreign substance with the grain diameter equal to or less than 0.1 μm. By controlling an irregular reflection quantity by using the laser beams with various wavelength, the detection accuracy can be improved. The laser beam with the wavelength of 1.3 μm penetrates into Si. 
     A laser beam with the wavelength of 810 nm is absorbed up to the depth of about 5 μm. Also, a laser beam with the wavelength of 532 nm is absorbed up to the depth of about 0.5 μm. Therefore, it is necessary to use a laser beam with a longer wavelength to obtain information in the direction of the depth. However, it is difficult to detect a foreign substance with a small grain diameter when a laser beam with a longer wavelength is used. 
     By changing the wavelength of each of the 2 wavelength laser beams, the detection accuracy can be improved. That is, when the 2 wavelength laser beams are used, the information in the direction of the depth can be obtained. In addition, the detection precision can be improved. Also, when the information of a defect or hole in the silicon film  5  can be obtained when the laser beam with a longer wavelength is used. 
     By making the wavelength short to remove the information of the hole in the silicon film  5 , only the foreign substance particle  31  on the film surface  5  can be detected, resulting in the improved detection accuracy of a surface foreign substance particle  31 . In this way, when the wavelength of the first laser beam and the wavelength of the second laser beam are changed or controlled at the same time, the existence of the surface foreign substance particle and inner foreign substance particle and the detection of the grain diameters of particles can be improved. 
     FIG. 4 shows the second embodiment of the reflected beam collecting section. The reflected beam collecting section shown in the figure is composed of a lot of small beam collecting lenses  41 . Each of the lot of beam collecting lenses  41  is arranged on a semi-spherical surface centered on the incident point P of the synthetic laser beam  12 . The light axis of each beam collecting lens  41  passes through the incident point P. 
     One optical fiber is provided for each beam collecting lens  41 . A light wave guide bunch  42  is a set of one or more optical fibers. The centerline of an end of each optical fiber turns to pass through the incident point P. The method of directing the laser beams which are inputted to the beam collecting lenses  41  to the spectroscope section  21  is same as that described with reference to FIG.  1 . 
     FIG. 4 shows 2 examples that the focal distances of the beam collecting lenses  41  are different. In one example, the irregular reflection light beam which passes the beam collecting lens  41  is collimated. In the other example, the irregular reflection light beam which passed the beam collecting lens  41  is collected for the optical fiber bundle  42 . 
     The irradiation of the first laser beam and the second laser beam on the silicon film  5  may be performed separately. In this case, the shutter  15  is removed and, instead, two shutters (not illustrated) which operate independently are provided in the light beam path of the first laser beam  8  and the light beam path of the second laser beam  9 . The two shutters are independently driven to be opened and closed by the shutter drive mechanism  28 . In this case, the spectroscope section  21  is unnecessary and a single photo-multiplier  19  is only used. It is not necessary to say that the film thickness information can be obtained so that the detection precision can be improved, if 3 wavelength laser beams are used. It should be noted that accuracy of information of the film thickness and particle depth can be improved by selecting 2 or 3 wavelength laser beams from 3 or 4 wavelength laser beams or by sequentially selecting one of the 3 or 4 wavelength laser beams. 
     The measuring section for measuring a quantity of scattered light beam is composed of an photo-multiplier as a light beam quantity detecting section, a light transfer section for gathering and transferring the scattered light beam and a collecting section for collecting the scattered light beam. A combination of the lens for the collection and the optical fiber is illustrated as the collecting section. However, the lens for the collection is not always necessary. The collecting section may be composed of optical fibers, each of which has an end opening surface arranged on the semi-spherical surface to face the incident point P. Also, if the light beam receiving surface of the photo-multiplier is formed to have a semi-spherical shape so that the scattered light beams are directly received on the spherical surface, it is not necessary to use a light beam transmission path (optical fibers). 
     The detection precision of a foreign substance on the surface can be improved. For example, (1) it is possible to test a film formed wafer and to detect a foreign substance of 0.1 μm. The foreign substance of 0.1 nm can be detected by use of a laser beam with the wavelength shorter than 488 nm as one of the laser beams of 2 wavelengths. Also, (2) the irregular reflection quantity of the other wavelength laser beam as noise from the irregular surface becomes little because the wavelength of the other laser beam is long. Therefore, the noise can be removed from the difference between irregular reflection quantities with 2 wavelengths. Thus, the foreign substance particle on the film can be detected. It is possible to determine the data in the direction of the depth from the attenuation quantity of the scattered light beam by the film by use of the laser beams with 2 wavelengths. For instance, in case of the laser beam with the wavelength of 1.3 μm, the light beam passes through the silicon film, but the laser beams with the wavelength of 810 nm and 532 nm are absorbed up to the depth of about 5 μm and 0.5 μm. Thus, it is necessary to use a laser beam with a longer wavelength. The foreign substance particle with a small grain diameter can be detected by use of the laser beams of 2 wavelengths to inspect the foreign substance particle in the direction of the depth. Also, information in the direction of the depth can be removed such that the information of the hole particle in the silicon film can be removed, by making a wavelength short. That is, only the information of the film can be obtained, resulting in improvement of the foreign substance detection reliability.