Abstract:
The present invention relates to a high-sensitivity defect inspection method, apparatus, and system adapted for the fine-structuring of patterns; wherein, in addition to a cleaning tank which chemically cleans a sample and rinses the sample, a defect inspection apparatus having a liquid-immersion element by which the interspace between the sample and the objective lens of an optical system is filled with a liquid, and a drying tank which dries the sample, the invention uses liquid-immersion transfer means from said cleaning tank through said liquid-immersion means of said defect inspection apparatus to said drying tank so that the sample is transferred in a liquid-immersed state from said cleaning tank to said liquid-immersion means.

Description:
BACKGROUND OF THE INVENTION 
   The present invention relates to a defect inspection method, defect inspection apparatus, and defect inspection system used to inspect and observe defects, foreign particles, and the like, on the micropatterns formed on substrates through a thin-film forming process represented by manufacturing processes for semiconductors and/or flat-panel displays. 
   Fine-structuring of the patterns formed with photolithography is progressing with the enhancement of semiconductor integration density and the improvement of flat-panel display resolution. During the manufacturing processes for these products, the formation of the patterns is followed by defect inspection and/or the like in order to improve production yields. During the defect inspection, the patterns are detected as images by an optical system and then defects are extracted by comparing these images with those of adjacent dies (or cells). When it comes to the generation of sub-100 nm in terms of pattern size, however, optical systems lack resolution and pattern images become difficult to accurately detect. In the field of defect inspection optical systems, therefore, the resolution enhancement technology described in Japanese Patent Laid-Open No. 2000-155099 (corresponding to U.S. application Ser. No. 09/397,334) is known as an ultrahigh-resolution detection technology that uses wavelength reduction, numerical aperture (NA) enhancement, and light polarization. 
   In response to fine-structuring of technical nodes, wavelength reduction and NA enhancement are also progressing in the field of lithography. At present, the exposure apparatus that uses ArF laser light of a 193 nm wavelength is in practical use, and for further reduction in wavelength, F2 laser light with a wavelength of 157 nm is expected as a promising light source. However, the exposure with F2 laser light, presents problems such as increases in apparatus costs because the construction of an optical system becomes complex and decreases in exposure margins due to decreases in the depth of focus during exposure. For this reason, WO Patent Publication No. WO99/49504 describes the exposure technology that achieves the improvement of resolution and the suppression of decreases in exposure margins at the same time by applying the liquid immersion exposure that uses, for example, ArF laser light as exposure light. 
   In the above ultrahigh-resolution detection technology that uses light polarization, when a sample is irradiated with specific polarized light via a dry-system objective lens by incident illumination, the light thus reflected/diffracted is captured by the same objective lens and an image of the sample is detected using an image sensor. This conventional technology has had the characteristic that an optical image of the sample can be obtained with high contrast by detecting this image using only specific polarized components of the reflected/diffracted light. However, in a sample, represented by a semiconductor wafer, that has undergone a thin-film forming process, a transparent film made of silicon dioxide (SiO 2 ), for example, is formed as an interlayer-insulating film. This insulating film has thickness unevenness in the wafer. During the inspection, such film thickness unevenness should originally not be detected since it has no fatal influence on device characteristics. During observation through a dry-system lens, however, thin-film interference on the transparent film causes the unevenness of the film thickness to appear as the unevenness of brightness on the image detected. For example, during comparative inspection with respect to adjacent dies, if the transparent films on these adjacent dies are uneven in film thickness, differences in the brightness of the respective images detected will occur and an image of the object will be incorrectly detected as a defect image. Increasing an inspection threshold value in an attempt to avoid such incorrect detection will pose the problem that total inspection sensitivity decreases. 
   Also, etched patterns are usually subjected to defect inspection. During defect inspection, therefore, sufficient consideration must be given to the fact that the pattern materials varying in type and form and in surface roughness (surface irregularities in level) are used in semiconductor processes. 
   SUMMARY OF THE INVENTION 
   In order to solve the above problems, the present invention relates to a defect inspection method, defect inspection apparatus, and defect inspection system which enables defects that are ultrafine than patterns of about sub-100-nm or less to be optically inspected and observed by increasing effective NA for improved resolution. 
   In one aspect, the present invention is a defect inspection method for detecting with an image sensor the optical image of a sample that has been enlarged and projected by an optical system, and thus detecting defects present on the sample; wherein an object of the present invention is to improve the optical system in resolution by filling the interspace between an objective lens and the sample with a liquid, and increasing effective NA (numerical aperture). 
   In another aspect, the present invention is constructed so that even when a transparent interlayer-insulating film is formed on the surface of a sample, the unevenness of brightness due to thin-film interference can be reduced since immersion of the interspace between an objective lens and the sample, in a liquid of a refractive index (ideally, 1.3 to 1.7) close to that of the interlayer-insulating film, suppresses amplitude splitting at the interface between the liquid and the insulating film. 
   Also, in order to prevent air bubbles from sticking to very small pattern surface irregularities (or the like) of the sample, the present invention uses an alcohol-containing liquid to fill the interspace between the objective lens and the sample. 
   In yet another aspect, the present invention is constructed so that particularly for the liquid immersion inspection that uses pure water, the sample is kept free of air from completion of liquid immersion inspection to that of drying in order to prevent water marks from being formed on the sample by the liquid left thereon. 
   In addition, the present invention has the features that while being immersed in pure water, the sample that has been inspected by an inspection apparatus is transferred to a cleaning apparatus so as not to form a three-layer interface by the sample, the pure water, and air, and that a drying function of the cleaning apparatus is used as drying means. 
   That is to say, the present invention is a defect inspection system including: a cleaning tank which chemically cleans a sample and rinses the sample; a defect inspection apparatus equipped with an optical system which illuminates the sample and forms an image thereof, an image sensor which detects the image of the sample, an image processor unit which detects defects by using the image detected by the image sensor, and liquid immersion means by which, at least when the image of the sample is detected, the interspace between the sample and an objective lens of the optical system is filled with a liquid; and a drying tank (a drying means) which dries the sample. 
   The defect inspection system further has liquid-immersion transfer means which transfers the sample until the sample has been returned from the cleaning tank through the liquid immersion means of the detect inspection apparatus to the drying tank so that the sample is transferred in a liquid-immersed state at least between said cleaning tank and said liquid-immersion means. 
   The present invention also has the feature that the above-mentioned liquid-immersion transfer means is constructed using a conveyor internally filled with a liquid. In addition, the present invention has the feature that the liquid-immersion transfer means is adapted to accommodate the sample in a liquid-filled cartridge and transfer this cartridge. 
   In a further aspect, the present invention is a defect inspection apparatus including: an optical system which illuminates a sample and forms an image thereof; an image sensor which detects the image of the sample; an image processor unit which detects defects by using the image detected by the image sensor; local liquid immersion means by which, at least when the image of the sample is detected, a liquid is locally supplied and discharged and the interspace between the sample and an objective lens of the optical system is locally immersed in the liquid; and drying means which dries the sample locally immersed in the liquid by the local liquid immersion means. 
   Furthermore, the present invention has the feature that the above-mentioned liquid immersion means is adapted to have a supply window for supplying isopropyl alcohol (IPA) as the above-mentioned liquid, and a discharge window for discharging IPA, on peripheral portions at a front end of the objective lens. 
   Besides, the present invention has the features that the local liquid immersion means formed in a further aspect is adapted to have a pure-water supply window for supplying pure water as the above-mentioned liquid, and a pure-water discharge window for discharging the pure water, in a flange on the periphery of the front end of the objective lens, and locally immerse the flange in the pure water, and that the above-mentioned drying means is adapted to have, on a peripheral portion of the flange, an alcohol-containing liquid supply window for evaporating the pure water left on the sample, and externally to the alcohol-containing liquid supply window, a hot-air window for blasting hot air to dry the sample. 
   Another object of the present invention is to prevent the flow of a liquid onto the reverse side of a sample by providing discharge means by which, when a peripheral section of the sample is inspected, the droplets of the liquid that leak are held between the sample and an objective lens and then leak from an edge of the sample onto a lateral face thereof are discharged by being taken in by a sample chuck. 
   According to the present invention, immersing in a liquid the interspace between the objective lens and the sample makes it possible to improve resolution in proportion to refractive index “n” of the liquid, and to suppress the unevenness in the brightness of images of adjacent dies or adjacent cells due to thin-film interference. Hence, inspection threshold values can be reduced and both the above-mentioned resolution improvement and unevenness suppression are effective for improving inspection sensitivity. 
   Furthermore, according to the present invention, it becomes possible to prevent damage to the sample due to the immersing in a liquid. 
   These and other objects, features, and advantages of the invention will be apparent from the following more particular description of preferred embodiments of the invention, as illustrated in the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a configuration diagram of the inspection apparatus that uses total liquid immersion in a first embodiment of the present invention; 
       FIG. 2A  is a sectional view of a conventional dry-system objective lens and a sample, and  FIG. 2B  is a sectional view of an objective lens and a sample, explaining the thin-film interference suppression effect obtained from liquid immersion according to the present invention; 
       FIG. 3A  is a flowchart showing the flow of the process steps, from cleaning to inspection, that use a conventional technology,  FIG. 3B  is a flowchart showing the flow of process steps in a first example of the present invention, and  FIG. 3C  is a flowchart showing the flow of process steps in a second example of the present invention; 
       FIG. 4  is a configuration diagram of a cleaning/inspection linking system based on the first example of the first embodiment of the present invention; 
       FIG. 5  is a conceptual diagram of the wafer transfer using a liquid immersion cartridge in the first embodiment; 
       FIG. 6  is a configuration diagram of a cleaning/inspection linking system based on the second example of the first embodiment of the present invention; 
       FIG. 7A  is a sectional view of a liquid immersion cartridge, showing a state in which the wafer in the second example is chucked using a wafer chucker, and  FIG. 7B  is a sectional view of a liquid immersion cartridge when it is lifted above the liquid level, on the assumption that the cartridge is a pure-water cartridge; 
       FIG. 8  is a configuration diagram of a local liquid immersion inspection apparatus which is a second embodiment of the present invention; 
       FIG. 9  is an explanatory diagram of the liquid supplying and discharging structure that uses the local liquid immersion method in the second embodiment; 
       FIG. 10  is a perspective view showing an example of a front-end shape of an objective lens for local liquid immersion; 
       FIG. 11A  is a view showing a particular example of a front-end shape of a local liquid immersion objective lens when the front end is observed from the sample side, with the front end being formed with one liquid supply port and one liquid discharge port symmetrically across a window,  FIG. 11B  shows a structure with a plurality of liquid supply ports and liquid discharge ports, and  FIG. 11C  shows a ring-like formation of the stepped surface closest to the wafer; 
       FIG. 12A  is a front view showing the mechanism of a front-end lens section in an objective lens group, and  FIG. 12B  is a schematic diagram of the front-end lens section when viewed from the wafer side; 
       FIG. 13A  is a front view showing a second example of a front end of an objective lens for local liquid immersion, and  FIG. 13B  is a schematic diagram of the front end when viewed from the wafer side; 
       FIG. 14A  is a front view showing a third example of a front end of an objective lens for local liquid immersion, and  FIG. 14B  is a schematic diagram of the front end when viewed from the wafer side; 
       FIG. 15  is a view showing the construction intended to prevent liquid leakage from a wafer edge in the local liquid immersion method according to the present invention; 
       FIG. 16  is a configuration diagram of an optical system in an inspection apparatus which is a third embodiment of the present invention; and 
       FIG. 17  is a schematic block diagram of an image processor unit in an inspection apparatus according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Embodiments of defect inspection of a liquid immersion scheme according to the present invention will be described using the accompanying drawings. 
   First Embodiment 
   A first embodiment in which the total liquid immersion method that forms part of the liquid immersion technology according to the present invention is applied to an optical-type visual inspection apparatus for semiconductor wafers will be described using  FIG. 1 . Wafers to be inspected are stored in a cassette  80 , and each of the wafers is transferred to an inspection preparation chamber  90  by a wafer transfer robot  85  and then mounted on a wafer notch (or orientation flat) detector unit  95 . The wafer is prealigned in a desired direction by the wafer notch detector unit  95 . Next, the wafer is transferred to an inspection station  3 . In the inspection station  3 , wafer  1  is fixed by a chuck  2 , and the wafer  1  is totally immersed in a liquid  5  with which a liquid tank (a liquid vessel)  7  is filled. The liquid tank  7  is connected to a liquid supply/discharge unit  10  by a pipe  15 , and the liquid tank  7  supplies the liquid  5  after loading of the wafer  1 , and discharges the liquid  5  before unloading of the wafer. The chuck  2  and the liquid tank  7  are mounted on a Z-direction stage  200 , a θ (rotational)-direction stage  205 , an X-direction stage  210 , and a Y-direction stage  215 . These stages and an optical system  20  which forms an image of the wafer  1  are further mounted on a stone surface plate  220 . 
   Illumination light  24  that has been emitted from a light source  22  of the optical system  20  is reflected by a beam splitter  40  and irradiated onto the wafer  1  via an objective lens  30  and the liquid  5  by means of incident illumination. The light, after being reflected/diffracted from the surface of the wafer  1 , passes through the liquid  5  and the objective lens  30  once again and reaches the beam splitter  40 . After passing through the beam splitter  40 , the light enters a beam splitter  41  that branches a focus detection optical path  45  and an image detection optical path  46 . Light that has passed through the beam splitter  41  reaches an image sensor  44  to form an image of the wafer  1  thereon. The image sensor  44  may use the reverse-side irradiation type of charge-coupled device (CCD) array that has high quantum efficiency toward the short-wavelength side. Also, light that has been reflected by the beam splitter  41  is light used to detect an out-of-focus level between the wafer  1  and the objective lens  30 , and the light enters a focus detection sensor  43 . Focus is detected by, for example, projecting onto the wafer  1  a striped pattern  47  disposed on an illumination optical path, and then detecting with the focus detection sensor  43  an image of the striped pattern  47  reflected by the wafer  1 . It is desirable that this image of the striped pattern  47  be spatially separated from the field-of-view detected by the image sensor  44 . That is to say, the image of the striped pattern  47  is projected across the field-of-view detected by the image sensor  44  on the wafer  1 . A mechanical controller unit  58  calculates contrast of the image thus detected and if defocusing is occurring, the Z-stage  200  is driven for focusing. An optical image formed on the image sensor  44  is thus focused. In the focus detection scheme that uses liquid immersion, high focus-detection accuracy can be obtained by detecting focus with a through-the-lens (TTL) scheme so that the influence of a focus positional change due to unevenness of surface shape of the liquid  5  and temperature of the liquid  5  is not received. Desirably, the light used for focus detection is either light whose wavelength region is equivalent to that of the image formed on the image sensor  44 , or light whose chromatic aberration has been corrected for by the objective lens  30 . 
   The image, after being detected by the image sensor  44 , is converted into a digital image by an A/D converter  50  and then transferred to an image processor unit  54 . In the image processor unit  54 , images of adjacent dies (or cells) are compared to extract defects. If the image sensor  44  is of a linear image sensor type such as a TDI (Time Delay Integration) type, images are detected while the wafer  1  is being scanned at a fixed speed. The above-mentioned stages, the wafer transfer robot  85 , the liquid supply/discharge unit  10 , and the like are controlled by the mechanical controller unit  58 . The mechanical controller unit  58  controls the mechanical system in accordance with commands from an operating controller unit  60  which controls the entire apparatus. After defects have been detected by the image processor unit  54 , information on the defects is stored into a data server  62 . The defect information stored includes defect coordinates, defect sizes, defect classification information, and the like. The defect information can be displayed/searched for using the operating controller unit  60 . 
   While it has been described above that the optical system for illumination uses incident illumination (bright-field illumination scheme), the optical system may use oblique illumination (off-axis illumination: dark-field illumination scheme). 
   Two advantageous effects obtained from liquid immersion inspection, namely, (1) a resolution improvement effect and (2) a thin-film interference suppression effect, will be described next. 
   (1) Resolution Improvement Effect 
   Equation (1) is known as a general equation for calculating resolution R of an optical system.
 
 R =λ/(2 NA )  (1)
 
   where λ denotes illumination wavelength and NA denotes a numerical aperture of the objective lens. 
   Also, NA is refractive index “n” between the objective lens and the wafer, and “n” is determined by equation (2).
 
 NA=n ·sin θ  (2)
 
   where θ denotes an angle range in which the objective lens  30  can capture the lights diffracted/scattered at one point on the wafer  1 . 
   For an ordinary dry-system objective lens, only air is present between the objective lens and a wafer to be inspected, and a refractive index is therefore 1. 
   Effective NA, however, can be increased by filling an interspace between the objective lens and the wafer, with a liquid whose refractive index “n” is greater than 1. 
   For example, if the interspace between the objective lens  30  and the wafer  1  is filled with pure water, since a refractive index of pure water is 1.35 (at a wavelength of 365 nm), NA becomes 1.35 times as great as that of the dry-system objective lens. In association with this, resolution also improves by 1.35 times. 
   An upper limit of NA which can be increased using the liquid-immersion objective lens  30  has a relationship with a total reflection angle of an interface at which the objective lens  30  and the liquid  5  come into contact. If the objective lens  30  uses quartz as a glass material for its front end, refractive index “n 1 ” at a wavelength of 365 nm is 1.48. If pure water is used as the liquid  5 , refractive index “n” is 1.35 (at the wavelength of 365 nm). The present embodiment assumes that the surface of the quartz at the front end of the objective lens  30  is parallel to the surface of the wafer  1  facing the lens. When light enters the objective lens  30  from the light source  22 , an incident angle of the light totally reflected by the quartz at the front end is defined as a critical angle “θc” determined by refractive index “n 1 ” of the quartz and refractive index “n” of the liquid  5  (here, pure water), as shown in equation (3).
 
θ c ≧sin −1 ( n 1/ n )  (3)
 
   The critical angle θc is equivalent to an incident angle of 66°. At this critical angle, no light is allowed to pass through to the liquid  5 . For practical purposes, 90% or more of the light passed from the quartz at the front end of the objective lens  30  to the liquid  5  is required (for random polarizing), and the incident angle (angle of incidence from the quartz, on the liquid) in this case becomes about 56°. This angle of 56° is equivalent to an incident angle of 65° on the wafer  1 . Accordingly, NA in the liquid  5  is equivalent to 0.91. When converted into an equivalent of a dry-system objective lens, the NA value of 0.91 becomes equal to 1.23. For practical use, therefore, the NA value of 1.23, obtained by the above conversion, is the upper-limit value obtainable at the wavelength of 365 nm. By virtue of the above-described NA enhancement effect obtained using the liquid-immersion objective lens  30 , microfine defects unable to be imaged with a dry-system objective lens can be detected as high-contrast images via the liquid-immersion objective lens  30 . Hence, defect detection sensitivity can be improved. 
   (2) Thin-Film Interference Suppression Effect 
   The thin-film interference suppression effect is shown using  FIGS. 2A and 2B . A comparative example of thin-film interference suppression using a dry-system objective lens is shown in  FIG. 2A . A wafer  1  is illuminated via an objective lens  30 . The wafer  1  has a deposited insulating film  1   a ′ (formed of SiO 2 , for example) on its seed layer silicon  1   b ′. The insulating film  1   a ′ is optically transparent, and illumination light  24  is amplitude-split into light  46   a  reflected by a top layer of the insulating film  1   a ′, and light passing through the insulating film  1   a ′. Light that has passed through the insulating film  1   b ′ is further split into light  46   b  reflecting from the seed layer  1   b ′ and passing through an interface between air and the insulating film, and light reflecting from the interface. Light that has reflected from the interface between air and the insulating film  1   a ′ repeats multiple reflecting to generate the light, such as light  46   c , that comes out into the air. Quality of an optical image formed by the objective lens is determined by interference intensity of the light passed through into the air, such as  46   a ,  46   b , and  46   c . The interference is referred to as thin-film interference. Since the intensity of the thin-film interference is a function of a film thickness “d” of the insulating film  1   a ′, if the film thickness “d” becomes uneven, the optical image also becomes uneven in brightness. The unevenness of the film thickness has no fatal influence on device characteristics, and should originally not be detected as a defect. For defect inspection based on die comparisons, however, if the unevenness of the insulating film  1   a ′ in film thickness exists between adjacent dies, since the brightness of the image will also be uneven, the unevenness of the film thickness is more likely to be incorrectly detected as a defect. Although a defect inspection threshold value needs to be increased to prevent such incorrect detection, increasing the threshold value poses the problem that inspection sensitivity decreases. 
   For this reason, a method for suppressing thin-film interference for improved inspection sensitivity has been desired. This method is shown in  FIG. 2B . This method is the same as the liquid immersion method described in above item ( 1 ), in which the interspace between the objective lens  30  and the wafer  1  is immersed in the liquid having a refractive index close to that of the insulating film  1   a ′. In this method, although illumination light  24  illuminates the insulating film  1   a ′ via the liquid  5 , if the liquid  5  and the insulating film  1   a ′ have the same refractive index, amplitude splitting at the interface between the liquid  5  and the insulating film  1   a ′ does not occur and all light enters the insulating film  1   a ′. Light that has passed through the insulating film  1   a ′ reflects from a seed layer  1   b ′ and is captured by the objective lens  30 . Accordingly, amplitude splitting does not occur at a top layer of the insulating film  1   a ′, and thin-film interference does not occur, either. Hence, it becomes possible to suppress unevenness of an image in brightness due to unevenness of the insulating film  1   a ′ in film thickness, and thus to suppress incorrect detection of defects due to the unevenness of the film thickness. Consequently, high-sensitivity inspection can be implemented since a trifle small inspection threshold value can be set. If the insulating film  1   a ′ is formed of SiO 2 , a refractive index thereof is 1.47 at a wavelength of 365 nm. Therefore, the liquid  5  for suppressing thin-film interference due to the unevenness of the insulating film  1   a ′ is preferably a liquid having a refractive index equivalent to that of the insulating film  1   a ′. However, even when pure water having a refractive index of 1.35 at a wavelength of 365 nm is used as the liquid  5  by way of example, the refractive index of the insulating film  1   a ′ at its top-layer interface does not differ too significantly, compared with the refractive index obtained when a dry-system objective lens is used. A sufficient suppression effect against thin-film interference can thus be obtained. Therefore, the liquid immersion technology using a liquid  5  whose refractive index is greater than that of air (i.e., using a liquid  5  having a refractive index greater than 1) is within the scope of the present invention. 
   While defect inspection effects based on liquid immersion have been described above, the following three factors need to be considered when a liquid  5  is selected: 
   (a) In terms of resolution improvement, a liquid higher in refractive index is preferable. 
   (b) In terms of thin-film interference suppression, a liquid having a refractive index equivalent to that of the insulating film  1   a ′ is preferable. 
   (c) Since the wafer  1  is to be immersed, a liquid less influential on device characteristics is preferable (this does not apply to destructive inspection.). 
   Pure water, an alcohol-containing liquid (such as isopropyl alcohol), a fluorine-containing liquid, or even an oil-containing liquid or a mixture of these liquids is likely to be usable as the liquid for liquid-immersion inspection. 
   Also, the illumination light used for the liquid-immersion inspection is effective anywhere in the range from a visible region to a vacuum ultraviolet region (e.g., 700 to 150 nm in wavelength). The usable types of light sources include a mercury lamp, a Xenon lamp, and other discharge tubes, or a laser light source. In addition, the illumination light can have either a single wavelength width or a broadband wavelength (multispectrum included). 
   Section  4  ( 4   a ,  4   b ) provided on a lateral face of the stage  200 ,  205  is an ultraviolet (UV) light irradiating unit for modifying surface characteristics of a front end of the objective lens  30  by surface activation, and/or an objective-lens cleaning tank for cleaning the front end of the objective lens  30 . The surface characteristics of the objective lens  30  are modified to prevent air bubbles from sticking to the lens surface, and to create a smooth flow of liquid  5 . For these purposes, the lens surface and a lens holder at the lens front end are surface-modified beforehand. For example, the front end of the lens is precoated with a titanium-oxide film to provide hydrophilic treatment. Since the hydrophilic treatment varies characteristics with time, ultraviolet (UV) light irradiating unit  4   a  for irradiating UV light is disposed at a peripheral portion of liquid tank  7 . When the wafer  1  is being unloaded from the chuck  2 , the front end of the objective lens  30  is irradiated with UV light from the UV light irradiating unit  4   a . This produces a photocatalyzing effect, making it possible to maintain a hydrophilic property. Consequently, it becomes possible to prevent air bubbles from sticking to the lens surface, and to suppress entrainment of the bubbles by making the liquid  5  flow smoothly between the wafer  1  and the objective lens  30 . In addition, it becomes possible to prevent false detection of defects without a bubble-laden image being formed in the optical image detected by the image sensor  44  after enlarged projection of the optical image by the objective lens  30 . 
   Furthermore, while the wafer  1  is being unloaded, the front end of the objective lens  30  is immersed in an internal liquid of objective-lens cleaning tank  4   b , such as a cleaning liquid (this liquid can be an alcohol-containing liquid, pure water, a fluorine-containing liquid, or liquid  5  for liquid immersion). At the same time, the hydrophilic property is also improved by irradiating UV light from the UV light irradiating unit  4   a  onto the front end of the objective lens  30  through a transparent window provided at the bottom of the objective-lens cleaning tank  4   b . As a result, the front end of the objective lens  30  is protected from dirt and the like. Deterioration of optical image quality can also be prevented. 
   The above is described in U.S. application Ser. No. 10/893,988. 
   Features of the first embodiment of the present invention will be described next. 
   Semiconductor wafer pattern processing steps from cleaning to inspection are shown in  FIG. 3A . In these processing steps, the pattern formed on a wafer  1  undergoes etching and chemical-mechanical polishing (CMP) and then the wafer is cleaned. In a cleaning apparatus  300 , after removal of contamination by chemical cleaning (step S 31 ), the wafer  1  is rinsed in pure water or the like (step S 32 ). After this, the wafer surface is dried using a drying function (step S 33 ). The dried wafer  1  is transferred to an inspection apparatus  20  (step S 41 ). After liquid-immersion inspection by the inspection apparatus  20  (step S 51 ), there is a need to prevent watermarks from occurring. To implement this, the wafer  1  needs to be sufficiently dried when lifted off from a liquid tank  7 . When a section to be inspected is a transistor layer of LSI, in particular, insufficient drying is liable to result in watermarks occurring. Therefore, a drying function also needs to be added to the inspection apparatus  20 . Adding this function increases an apparatus cost of the inspection apparatus. 
   Accordingly, a first example  400  of a method for suppressing the apparatus cost in the liquid-immersion inspection which is a feature of the present invention will be described using  FIG. 3B . Flow of processing with a system  400  which is the first example is shown in  FIG. 3B . The system  400  is a system in which a cleaning/drying function and an inspection function are merged. Chemical cleaning (step S 31 ) of the wafer  1  is followed by rinsing in, for example, pure water (step S 32 ). After rinsing, the wafer  1  is carried in a water-immersed state to inspection station  20  and undergoes liquid-immersion inspection (step S 51 ). After the inspection, the wafer  1  is dried using a drying function of a drying tank (step S 61 ). This makes the liquid-immersion inspection executable without adding a drying function to the inspection apparatus  20 . An increase in the apparatus cost of the inspection apparatus, associated with the liquid-immersion inspection, can be suppressed as a result. 
   Next, a second example  410  of a method for suppressing the apparatus cost in the liquid-immersion inspection which is a feature of the present invention will be described using  FIG. 3C . A system  410  that is the second example is shown in  FIG. 3C . The system  410  is a system having a cleaning apparatus  300  and an inspection apparatus  20  linked to each other. The cleaning apparatus  300  is operated to conduct chemical cleaning (step S 31 ) and rinsing (step S 32 ). After rinsing, the wafer  1  is carried in a pure-water immersed state (step S 71 ) to the inspection station  20  (step S 72 ). The pure-water immersed state is called “pure-water packed state” (step S 71 ). The wafer that has been transferred in the pure-water packed state is set up in a liquid tank (a liquid vessel)  7   b  of an inspection station  20  and undergoes liquid-immersion inspection (step S 51 ). After the inspection, the wafer  1  is once again placed in the pure-water packed state (step S 71 ) and transferred to the cleaning apparatus  300  (step S 73 ). In step S 81 , the wafer is dried using a drying function of the drying tank  305  mounted on the cleaning apparatus  300 . In this linking system  410 , wafers  1   b  and  1   c  remain in a liquid-immersed atmosphere during process steps from chemical cleaning to inspection. For this reason, the wafers do not come into contact with air up until completion of a drying process by the cleaning apparatus  300  (cleaning tank  330 /drying tank  305 ), based on an isopropyl alcohol (IPA) vapor scheme or the like. This makes it unnecessary to add a drying function to the inspection apparatus  20  and allows watermarks to be prevented from occurring during the liquid-immersion inspection. 
   Next, an apparatus configuration of the cleaning/inspection process merge system  400  which is the first example will be described in detail using  FIG. 4 . After wafers store into a cassette  80  following completion of a resist removal process and a CMP process, the each wafer is independently carried from the cassette  80  into a cleaning chamber  330  by a transfer system  85 . Depending on the kind of wafer to be cleaned, cleaning chamber  330  has a plurality of liquid tanks (cleaning tanks)  330   a ,  330   b ,  330   c  (water-washing tank included) and conducts cleaning and water-washing processes on a wafer  1   b  (although a multi-bath configuration is shown in  FIG. 4 , the above description also applies to a single-bath configuration). A cleaning liquid is supplied from the tank  335   a . After final rinsing in pure water, a gate  340  of the liquid tank  330   a  is opened by an opening/closing unit  341 . Through the gate  340 , the wafer  1   b  is carried to a notch detector unit  95  by a liquid-immersion transfer system (liquid-immersion transfer means)  342  (such as the belt conveyor of water that transfers the wafer while keeping it immersed in water  5 ). The wafer, after being transferred to the notch detector unit  95  by the liquid-immersion transfer system  342 , is prealigned in its θ-direction  127 . Next, the wafer is carried to an inspection station  20  by the liquid-immersion transfer system  342 . At this time, the gate  136  of the notch detector unit  95  and a gate  146  of the inspection station  20  are already opened by respective opening/closing units  137  and  147 . The gates  136  and  146  are closed after a wafer  1   c  has been carried into a liquid tank (a liquid vessel)  7   a  of the inspection station  20 . Since each wafer  1   c  that has thus been carried into the liquid tank  7   a  is mounted on an X-stage  215 , a Y-stage  210 , a θ-stage  205 , and a Z-stage  200 , the surface of the wafer  1   c  is visually inspected while an interspace between the objective lens  30  and the wafer remains immersed in pure water  5 . After the inspection, the wafer  1   c  is unloaded through the liquid-immersion transfer system  342 . Unloaded wafer  1   a  is transferred to cleaning/drying chamber  300  (constituted by the drying tank), in which, for example, depressurized/superheated IPA (isopropyl alcohol) vaporizing is then conducted to dry the wafer. A heating plate  320  regulates an internal temperature of a drying chamber (drying tank)  305  to a required value, then vapors of IPA  315  are fed into the chamber  305 , and this chamber is depressurized by a vacuum pump  310 . This makes it possible to dry the moisture sticking to the wafer pattern, essentially without bringing the wafer into contact with the atmosphere. After the drying process, the wafer is returned to cassette  80 . 
   The usable methods of drying with the drying tank  305  include (1) depressurized IPA (isopropyl alcohol) vaporizing, (2) wafer spinning, (3) gas jet spraying, and others. 
   Also, the liquid-immersion transfer system  342  may have (provide) a wafer interfacial bubble-removing element for removing the air bubbles sticking to the wafer  1 . Wafer-in-liquid ultrasound vibration by an ultrasound vibration source, wafer-in-liquid spinning by a rotating unit, a depressurizing process for reducing an internal pressure of an inspection preparation chamber provided with the notch detector unit  95 , or others can be used for the above bubble-removing element. It becomes possible, by providing such a bubble-removing element in the liquid-immersion transfer system  342 , to prevent false detection of defects by preventing air bubbles from sticking to the wafer  1  during its actual inspection. Also, when the wafer  1  to be inspected has a formed contact hole on the surface, an interfacial shape of the liquid  5  on a top layer of the contact hole can be made qualitatively even, which allows an even optical image to be detected from the contact hole and false detection of defects to be prevented. 
   Next, an apparatus configuration of the cleaning apparatus/inspection apparatus linking system  410  which is the second example will be described in detail using  FIGS. 5 ,  6 , and  7 A,  7 B.  FIG. 5  is a conceptual diagram showing the apparatus configuration of the second example. A wafer  1   b  is placed in the liquid cartridge (liquid-immersion transfer element)  156  located between the cleaning apparatus  300  and the inspection apparatus  20  and filled with a liquid (e.g., pure water), and the cartridge  156  with the wafer  1   b  contained therein is transferred.  FIG. 6  is a diagram showing a more specific apparatus configuration of the second example. After wafers store into a cassette  80  following completion of a resist removal process and a CMP process, the each wafer is independently carried from the cassette  80  into a cleaning chamber (cleaning tank)  330  by a transfer system  85 . Depending on the kind of wafer to be cleaned, the cleaning chamber  330  has a plurality of liquid tanks  330   a ,  330   b  and  330   c  (water-washing tank included) and conducts cleaning and water-washing processes (although a multi-bath configuration is shown in  FIG. 6 , the above description also applies to a single-bath configuration). A cleaning liquid is supplied from the tank  335   a . After final rinsing in pure water, wafer  1   b  is stored into a pure-water cartridge (pure-water pack)  156 . A gate  340  of the cleaning tank and a gate  350  of a transfer system  360  are opened by respective opening/closing units  341  and  351 , and thus the pure-water cartridge (liquid-immersion transfer element)  156  is carried to a transfer chamber  361 . 
   The pure-water cartridge  156  is carried to a station of a notch detector unit  116 , in which a θ-rotation stage  126  is then rotated to detect a notch in the wafer and prealign this wafer in a θ-direction thereof. The pure-water cartridge  156  containing the thus-prealigned wafer is carried into the inspection station  20 , then the wafer  1   c  remaining immersed in pure water  5  is transferred intact from the pure-water cartridge  156  to a liquid tank (a liquid vessel)  7   b , and the wafer  1   c  is fixed to a chuck of the liquid tank  7   b . That is to say, the liquid tank  7   b  has with a function of chuck  2 . In this state, the wafer  1   c  undergoes liquid-immersion inspection, and after undergoing the inspection, the wafer  1   c  is returned to the pure-water cartridge  156  and unloaded. During this unloading operation, the pure-water cartridge  156  remains the state filled with the pure water. The system is therefore adapted to keep the wafer not to touch air until it has been dried by a drying function of a drying tank  305 . Since the drying tank  305  is internally depressurized by a vacuum pump  310 , the wafer is kept almost not to touch air. 
   Next, a mechanism for storing the wafer  1   b  into the pure-water cartridge  156  located in the liquid tank  330   a  of the cleaning chamber, within a rinsing tank, is shown in  FIG. 7A . The wafer  1   b  has a bevel section held by a wafer moving unit  380 . After rinsing in pure water  5 , a moving arm  381  is slid to chuck the wafer  1   b  using a chuck  159  of the pure-water cartridge  156 . Using an electrostatic chuck or mechanically gripping the bevel section of the wafer  1   b  is possible as a chucking method. The chuck  159  is driven by the electric power supplied from a battery  158 ,  161 . Next, the wafer moving unit  380  withdraws from the liquid tank  330   a  and as shown in  FIG. 7B , the pure-water cartridge  156  is rotated to place the wafer  1  in a horizontal position. The pure-water cartridge  156  is lifted from the liquid surface by a vertical drive  391 . A liquid level of the liquid  5  in the pure-water cartridge  156  is adjusted according to a particular position of a gate  371 . After the liquid level in the pure-water cartridge  156  has been adjusted, the gate  371  is closed by a vertical drive  372  in accordance with a wireless signal. In the example of  FIG. 7B , the section above, or an upper section of, the pure-water cartridge  156  is not closed. Accordingly, height from the water surface to the top of the pure-water cartridge  156  needs to be controlled considering the occurrence of waves on the water surface due to acceleration during movement. 
   As described above, according to the first and second examples, since the wafer  1  is kept not to touch air from completion of rinsing by means of the cleaning apparatus  300  to completion of drying, the occurrence of watermarks during liquid-immersion inspection can be prevented without adding a drying function to the inspection apparatus  20 . Damage to devices by the occurrence of watermarks can be prevented as a result. 
   Second Embodiment 
   A second embodiment in which the local liquid immersion method that forms part of the liquid immersion technology according to the present invention is applied to an optical-type visual inspection apparatus for semiconductor wafers will be described using  FIG. 8 . Unlike the total liquid immersion method shown in  FIG. 1 , the local liquid immersion method is used to immerse only the interspace between the objective lens  30  and the wafer  1 , in a liquid. A basic configuration of the second embodiment is much the same as that of the first embodiment, except for the inside of the inspection station  3 . For example, for a linear type of image sensor  44 , images are acquired while the wafer  1  is being moved at a fixed speed. A liquid  5  is fed from a liquid supply/discharge unit  10  into a liquid supply controller  181  at a specific pressure. The liquid, after having its flow rate, temperature, and other factors controlled by the liquid supply controller  181 , is supplied to the surface of the wafer  1  through a pipe  170  disposed in front of a position at which the wafer  1  moves past the objective lens  30 . 
   The liquid  5  that has been supplied to the wafer  1  flows under the objective lens  30 , in a moving direction of the wafer  1  (here, on the drawing, from left to right). After flowing through the objective lens  30 , the liquid  5  is introduced into a liquid discharge controller  179  through a pipe  175   a  and discharged. The liquid thus discharged into the liquid discharge controller  179  flows out into the liquid supply/discharge unit  10 , whereby, even when the wafer  1  is moving, the interspace between the objective lens  30  and the wafer  1  can be filled with the liquid  5  at all times. When the wafer  1  moves in an opposite direction (here, on the drawing, from right to left), the liquid  5  is supplied to the surface of the wafer  1  through a pipe  170   a , flows under the objective lens, and is forcibly taken into a pipe  175 . When an image is to be acquired during the movement of the wafer  1 , therefore, the liquid  5  is supplied in front side of a wafer scanning direction of the objective lens  30  and after flowing through the lens  30 , the liquid  5  is discharged. The liquid supply controller  181  and the liquid discharge controller  179  are piped at respective specific water pressures to the liquid supply/discharge unit  10 . 
   A modification of the local liquid immersion method in the second embodiment is shown in  FIG. 9 . A flow route of the liquid  5  from the liquid supply controller  181  is branched into two pipes,  170  and  170   a . For example, when the wafer  1  is moving at a fixed speed in a direction of arrow  211 , a valve  171  on the pipe  170  is open and a valve  171   a  on the pipe  170   a  is in a closed state. Hence, the liquid is supplied to the wafer  1  only through the pipe  170 . After the liquid  5  has been supplied to the surface of the wafer  1  through the pipe  170 , the fluid flows between the objective lens  30  and the wafer  1 , and then the fluid is introduced into the liquid discharge controller  179  through the pipe  175   a  having an open valve  176   a . At this time, a valve  176  on the pipe  175  is in a closed state. When the wafer  1  is moving in an opposite direction to that of arrow  211 , the valve  171   a  at the supply side is open and the valve  171  is in a closed state, whereas the valve  176  at the discharge side is open and the valve  176   a  is in a closed state. Even when the moving direction of the wafer  1  is reversed, the interspace between the objective lens  30  and the wafer  1  can be filled with the liquid at all times by controlling valve opening and closing. The liquid supply controller  181  includes a regulator  182  for regulating a supply rate of the liquid, an in-liquid oxygen concentration regulator  183 , and a liquid temperature controller  184 . The liquid discharge controller  179  has a mounted regulator  177  for regulating a discharge rate of the liquid. 
   It is desirable that the oxygen concentration regulator  183  (also having a bubble removal function based on pressure reduction) should be necessary for purposes such as (1) preventing oxidation of the wafer  1  due to the presence of the liquid  5 , and (2) removing any microbubbles contained in the liquid supplied. For instance, a device that utilizes Henry&#39;s law would be usable as the in-liquid oxygen concentration regulator  183 . Also, the liquid  5  changes in refractive index with a change in temperature. Since the objective lens  30  is optically designed with the refractive index of the liquid as a specific value, aberration increases as the refractive index changes more significantly. The temperature controller  184  is therefore required for suppression of changes in the refractive index of the liquid  5 . For example, a device that utilizes the Peltier effect (thermoelectric cooling) would be usable as the temperature controller  184 . Desirably, even in the wafer total liquid immersion scheme shown in  FIG. 1 , the oxygen concentration regulator  183  and the temperature controller  184  are provided in the system that supplies the liquid to the liquid tank  7  ( 7   a ,  7   b ), or in the tank  335   a.    
   In particular, when an outer edge portion of the wafer is inspected based on local liquid immersion, since a difference in level for a thickness of the wafer is caused at the outer edge, the liquid flows out from the peripheral edge of the wafer onto the surface of the chuck  2 . For this reason, the interspace between the objective lens  30  and the wafer  1  cannot be filled with the liquid. A stepped portion  6  commensurate with the thickness of the wafer  1 , therefore, needs to be provided in proximity to an outer portion of the wafer  1  as shown in  FIG. 8 . Thus, even when the outer portion of the wafer  1  is to be inspected through a pupil of the objective lens  30 , the interspace between the objective lens  30  and the wafer  1  can be locally filled with the liquid  5  since a slight clearance is only left between the outer portion of the wafer  1  and the stepped portion  6 . 
   An external view of the plane of the objective lens  30  that faces the wafer  1  is shown in  FIG. 10 . Glass  31  is a window that transmits illumination light and the light reflected/diffracted by a pattern. Liquid supply and discharge ports  185  are arranged symmetrically at both sides of the window  31 . A groove formed as an interspace having width Yd and depth Zd is a region to be filled with the liquid supplied. Of all faces of the objective lens  30 , the plane  188  is brought closest to the wafer  1 , and an interspace between the plane  188  and the wafer  1  acts as a working distance (WD). It is desirable that the amount of liquid left on the wafer  1  should be minimized. It is necessary, therefore, for the liquid to be reduced in the amount of overflow reaching a portion other than the groove (e.g., in a direction within a horizontal face, orthogonal to a traveling direction of the wafer  1 ). A reduction effect against the amount of liquid left on the wafer  1  is expected to be obtainable by conducting hydrophilic surface treatment of grooved portion  32  which is to be filled with the liquid, and hydrophobic (water-repellent) surface treatment of the plane  188  other than the groove. A similar reduction effect is likewise anticipated by adjusting WD. A desirable WD value is up to about 0.7 mm (further desirably, up to about 0.3 mm). A relational expression relating to the amount of liquid supplied and the amount of its discharge, is shown as equation (4) below. When dimension Z for filling the region with the liquid is taken as Zd+WD, dimension Y for filling the region with the liquid as Yd, a stage-scanning velocity as Vst, a liquid supply rate as Vin, and a liquid discharge rate as Vout, liquid supply rate Vin should be greater than liquid discharge rate Vout. This relational expression is shown as equation (4).
 
 Vin≧Vout =( Zd+WD )× Yd×Vst   (4)
 
   As described above, the groove (interspace)  32  to be filled with the liquid is entirely walled by the plane  188 . 
   As shown in  FIGS. 11A ,  11 B, and  11 C, the plane of the objective lens  30  that faces the wafer  1  can take various shapes. At the groove  32  to be filled with the liquid  5 , the place  188  is also stepped in a traveling direction of the stage. Examples of shapes of the groove  32  are shown in  FIGS. 11A to 11C . In  FIG. 11A , two liquid supply and discharge ports  185 , one at each side of the window  31 , are formed symmetrically thereacross. In  FIG. 11B , a plurality of holes are formed as liquid supply and discharge ports  185  at each side. In  FIG. 1C , the stepped plane  188  closest to the wafer  1  is formed into a shape of a ring  188   a  to allow for a two-dimensional movement of the wafer. Internally to this ring, liquid supply ports  185   a  are formed to supply the liquid  5 . Supply of the liquid through an inner-diameter portion of the objective lens results in the liquid overflowing from the stepped plane  188 . In order to discharge the overflow, a plurality of discharge ports  185   b  are arranged externally to the stepped face  188   a . The shape thus formed makes it possible, even when the wafer  1  moves in various directions in the plane, to fill an internal section of the stepped face  188   a  with the liquid and to discharge the liquid. This shape is also effective for purposes such as observing detected defects. 
   The above is described in U.S. application Ser. No. 10/893,988. 
   Features of the second embodiment of the present invention will be described next. 
   An objective lens peripheral construction for local liquid-immersion inspection will be described using  FIGS. 12A ,  12 B,  13 A,  13 B, and  14 A,  14 B. 
   First, a first example of the objective lens and periphery will be described using  FIGS. 12A ,  12 B.  FIG. 12A  is a front view showing a mechanism of a front-end lens portion  31  of the objective lens  30 , and  FIG. 12B  is a schematic diagram of this mechanism when observed from the wafer side. The conceivable kind of liquid would be pure water or isopropyl alcohol (IPA). If pure water is used, watermarks could occur if the water is left on the surface of the wafer  1 . When IPA is used as the liquid, however, even if the IPA is left on the wafer  1 , the occurrence of watermarks is likely to be suppressible since the IPA evaporates within a short time. In addition, since IPA is most commonly used as a solvent in the drying process that follows cleaning, there is no need to worry about the possible damage to the semiconductor device. Accordingly, the construction that uses IPA as the liquid is shown below. 
   An IPA supply system  500  supplies IPA to an interspace between the front-end lens portion  31  and the wafer  1 . The wafer  1  is scanned in an arrow-marked direction, and IPA is discharged by an IPA discharge system  510 . For this reason, there is a liquid immersion effect since the interspace between the front-end lens  31  and the wafer  1  is filled with IPA. However, not all of IPA is completely discharged by the IPA discharge system  510  and part of IPA is left on the wafer  1 . Hot air  551  is sprayed onto the wafer  1  by a hot-air blower  550  to evaporate the IPA left on the wafer  1 . A schematic diagram of this mechanism when observed from the wafer side is shown in  FIG. 12B . The scanning direction of the wafer  1  is from left to right on the drawing. In this case, IPA is supplied from an IPA supply window  500   a  provided in front side of the wafer scanning direction. The IPA that has passed through the lens is discharged from an IPA discharge window  510   a . Furthermore, evaporation of the IPA left on the wafer  1  is accelerated by the hot air  551  blasted through a hot-air window  550   a.    
   When the scanning direction of the wafer  1  is reversed, a function of the IPA supply window  500   a  and that of the IPA discharge window  510   a  are changed over to each other and the IPA discharge window  510   a  and the IPA supply window  500   a  function as an IPA supply window  500   b  and an IPA discharge window  510   b , respectively. The construction shown in  FIG. 9  makes the changeover realizable. A similar changeover also applies to hot-air windows  550   a  and  550   b , and the hot air  551  is blasted from the hot-air window  550   b  after the wafer  1  has moved past the front-end lens  31 . A changeover valve mechanism is also required for the hot air. 
   Next, second and third examples of the objective lens and periphery will be described using  FIGS. 13A ,  13 B,  14 A, and  14 B.  FIGS. 13A and 13B  show the second example in which an area to be filled with IPA is formed into a flange shape.  FIG. 13A  is a front view of the second example, and  FIG. 13B  is a schematic diagram of the second example when observed from the wafer side. In a construction of the second example, a wall  39  ( 188   a ) is provided on outer surfaces of both an IPA supply window  500  and an IPA discharge window  510 . 
   A construction of the third example in use of pure water as the liquid is shown in  FIGS. 14A and 14B .  FIG. 14A  is a front view of the third example, and  FIG. 14B  is a schematic diagram of the third example when observed from the wafer side. A pure-water supply window  520  and a pure-water discharge window  530  are provided on an outer surface of the front-end lens  31 , and a flange  39  ( 188   a ) is internally filled with pure water. That is, when a scanning direction of the wafer  1  is from left to right on the drawing, the flange  39  ( 188   a ) is internally filled with pure water by supplying the water from a pure-water supply window  520   a  and discharging the water from a pure-water discharge window  530   a . IPA supply windows  500   a  and  500   b  for early evaporation of the pure water left on the wafer  1  are provided externally to the flange  39 , and IPA  501  is supplied from these supply windows. Furthermore, hot air  551  is sprayed from a hot-air window  550   a  onto the wafer previously supplied with IPA. The wafer is thus dried within a short time. 
   Next, an example of preventing the liquid from flowing around to the reverse side of the wafer will be described using  FIG. 15 . During inspection of an outer surface of the wafer  1 , the liquid is likely to leak to a bevel section of the wafer when the interspace between the objective lens  30  and the wafer  1  is locally immersed in the liquid by supplying it from a liquid supply system  185  through a liquid supply window  190  to a groove  32  at the front end of the objective lens  30  and discharging the liquid from the groove  32  through a liquid discharge window  191  to a liquid discharge system  186 . If the liquid leaks, it will flow around to the reverse side of the wafer and contaminate the bevel section thereof and/or the reverse side of the wafer. However, providing a discharge system  2   c  by which the liquid  600  that has leaked is taken into a discharge hole  2   b  of a wafer chuck  2   a  and discharged makes it possible to prevent the liquid from flowing around to the reverse side of the wafer  1  and contaminating the reverse side thereof. 
   Third Embodiment 
   Next, an example of configuration of a visual inspection optical system which uses liquid immersion, and a method for improving this optical system in resolution will be described below using  FIG. 16 . 
   (1) An interspace between an objective lens  30  and a wafer  1  is immersed in a liquid  5  and thus, resolution is improved. 
   (2) In an incident illumination/bright-field detection scheme, when Koheler illumination is applied, an image of a light source  22  is formed on an aperture stop (an aperture diaphragm)  425 . This image is further formed on a pupil of the objective lens  30 . If the aperture stop  425  has a ring-form (zonal) aperture portion, light that illuminates one point on the wafer  1  becomes oblique illumination light not having a vertical illumination light component. Use of the illumination light improves high-frequency MTF (Modulation Transfer Function) of a spatial frequency. 
   (3) Furthermore, when a polarizing type of beam splitter  40   a  is used, the light reflected from the beam splitter  40   a  changes into linearly polarized light. On passing through a wavelength plate  430 , the linearly polarized light further changes into elliptically polarized light to conduct the wafer  1  with incident illumination. After the illumination, the polarized light suffers modulation of its polarized state when the light is reflected, diffracted, and/or scattered from a pattern on the wafer  1 . These light beams pass through the wavelength plate  430  once again and enter the polarizing-type beam splitter  40   a . The P-polarized light that has passed through the polarizing-type beam splitter  40   a  forms an optical image of the wafer  1 , and the image is detected by an image sensor  44 . In this way, the polarizing-type beam splitter  40   a  functions as a light analyzer. Therefore, the polarized state of the illumination light is preadjusted according to the polarized state existing when the light is reflected, diffracted, and/or scattered from the pattern of the wafer  1 . Thus, the optical image formed by the regular reflected light, high-order diffracted light, and/or scattered light passing through the polarizing-type beam splitter  40   a , is adjusted to become an image advantageous for defect detection. The image advantageous for defect detection refers to an image whose defective portions can be improved in contrast. 
   (4) When the wafer  1  is illuminated using the ring-form aperture stop  425  described in above item (2), zeroth-order light (regular reflected light) and high-order diffracted light are separated at the pupil of the objective lens  30 . For this reason, the patterns on the wafer  1  can be detected in an edge-enhanced state by disposing, at a position of the pupil, a spatial filter  420  for adjusting transmittivity and a relative phase difference for both the zeroth-order light and the high-order diffracted light (first-order or higher). The above is based on the principles of phase contrast microscopy. The pupil of the objective lens  30  is usually formed therein, and therefore, there is no space available to dispose the spatial filter. Hence, a position conjugate to the pupil of the objective lens  30  is provided and the spatial filter  420  is provided at this conjugate position. This makes it possible to enhance optical images in resolution and to form images advantageous for defect detection. 
   A liquid immersion method is described in above item (1), and a resolution improvement method is described in above items (2) to (4). Combining these methods allows further enhancement of the optical system in resolution and provides a greater advantage in high-sensitivity inspection. 
   Next, a more specific example of the image processor unit  54  shown in  FIGS. 1 and 8  will be described using  FIG. 17 . The image of a wafer  1  that has been detected by an image sensor  44  (in the present example, a linear image sensor) is input as a digital image to the image processor unit  54  via an A/D converter  50 . The input image is branched into a position deviation detector unit  710  and a delay memory  700 . The delay memory  700  sends an image delayed by either a time associated with adjacent dies (in the case of die comparison), or a time associated with adjacent cells (in the case of cell comparison), to the position deviation detector unit  710 . The image sent to the position deviation detector unit  710  is therefore an image of an adjacent die (or cell) having the same design pattern formed on the wafer  1 . The amount of deviation in position between the above two images is detected by the position deviation detector unit  710  and then the deviation is adjusted for accurate position matching at an image alignment unit  720 . Position matching at the image alignment unit  720  is conducted in sub-pixel units. 
   A differential image between the position-matched images is acquired by a differential-image arithmetic unit  730 . Based on characteristic values of the differential image, a judgment is conducted on a defect candidate  750  by a defect-judging unit  740 . The characteristic values serving as the base for defect judgment by the defect-judging unit  740  include a gray scale difference, a size (including a area and a projection length) exceeding a gray scale difference threshold, brightness of the detected image, contrast of the image, and defect coordinate information. After being detected by the defect-judging unit  740 , the defect candidate  750  has its defect coordinate information input to a defect classification unit  770 . The images of the adjacent dies that were branched from the image alignment unit  720  are temporarily prestored in an image memory  760 , and images associated with the coordinates of the defect candidate that have been input to the defect classification unit  770  can be read out from the image memory  760 . The defect classification unit  770  classifies defects or defect candidate by using the images of the adjacent dies that have been read out. The information of the classification results and the defect candidate  750  are stored into a data server  62 . The presence/absence of foreign particles and pattern defects, fatal influence on device characteristics due to the defect, and the like are judged at the defect sorter  770 . The coordinate information and size of and classification results on the defect candidate  750 , therefore, are stored into the data server  62 , from which various defect information is then further sent for a defect observation step. 
   While defect inspection methods based on liquid immersion, liquid-immersion inspection sequences, and the like have been described above, combinations of respective embodiments/examples, use of composite illumination, modification and omission of an inspection sequence, and the like are easily devisable and details of these combinations and others are embraced in the present invention. 
   The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiment is therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.