Abstract:
Disclosed is an adaptive groove focusing and leveling device for measuring the height and the inclination of the surface of a measured object ( 400 ). The measured object ( 400 ) is provided with cyclic grooves ( 401 ) in the surface and supported by a moving table; the focusing and leveling device sequentially comprises an illumination unit, a projection unit, a detection unit and a detector ( 212 ); the measured object ( 400 ) is positioned between the projection unit and the detection unit along the light path, the projection unit comprises a projection slit ( 203 ) and is used for forming a plurality of measuring points ( 501 ) on the measured object ( 400 ), and each measuring point ( 501 ) comprises at least three measuring child light spots ( 502 ), wherein the at least three measuring child light spots ( 502 ) are arranged at unequal intervals, so that when the plurality of measuring points ( 501 ) are projected to the surface of the measured object ( 400 ), at least two of the at least three measuring child light spots ( 502 ) of each measuring point ( 501 ) can be positioned outside the grooves ( 401 ), and then the height and the inclination of the surface of the measured object ( 400 ) are measured.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a projection lithography tool and, more particularly, to an focusing and leveling apparatus and method adaptable to trenches for use in a projection lithography tool. 
       BACKGROUND 
       [0002]    Projection lithography tools are ones of those used as core processing equipment in the field of liquid crystal display (LCD). Through-silicon vias (TSVs) represent the latest technique for interconnection of chips by means of vertical conductive vias fabricated between the chips or wafers. TSVs offer the advantages of small package size, fast signal transmission, low power consumption and etc. Standard wafers subjected to a number of TSV processes often exhibit, at their edge portions, bonding inconsistencies, non-concentricities, wears, scribe lines, sputtered metals or insulating material on the surface or warps. Under such complex conditions, apparatuses for focusing and leveling are often incapable of measurement. 
         [0003]    As shown in  FIG. 1 , a conventional detection device for focusing and leveling comprises a measuring optical path extending on both sides of an optical axis of a projection objective  20 . In the measuring optical path, there are disposed an illumination unit, a projection unit, a detection unit and a relay unit in a sequence. Light emanated from a light source  21  of the illumination unit is converged at a light-source lens group  22  and then guided by an optical fiber to the projection unit, so as to provide lighting for the entire detection device. The projection unit is composed of a projection slit  23 , a front projection lens group  24 , a projection reflector group  25 , a rear projection lens group  26  and the like. After propagating through the projection slit and the lens  24 , being reflected by the reflector  25  and passing through the lens  26 , the light forms a measuring light spot in the current exposure area on the surface of a glass substrate. The detection unit is made up of a front detection lens group  27 , a detection reflector group  28 , a rear detection lens group  29  and others. The relay unit is constituted of a relay reflector  30 , a relay lens group  31 , a detector  32 , an arithmetic unit  33 , a controller  34  and others. Light from the light spot travels through the relay unit and is received by the detector which thereby forms a light intensity signal carrying surface height information of the object under measurement (e.g., a glass substrate). This measurement approach requires the surface of the object under measurement to be flat, but the object under measurement  36 , such as a wafer or a glass substrate, carried on the movable carrier stage  35  has trenches  41  (see  FIG. 3 ) due to different processed layers. 
         [0004]    As shown in  FIGS. 2A and 2B , a solution has been proposed in order to address the issue of trenches  41 , in which, an illumination numerical aperture A is designed to be greater than or equal to the product of a projection numerical aperture B multiplied by a detection numerical aperture M, which is, in turn, designed to be greater than or equal to the sum of the detection numerical aperture M and a tilt W of the object under measurement (i.e., A≧B*M≧M+W), in order to reduce shadows in images caused by the surface irregularities of the object under measurement which may lead to measurement errors. In many cases, interlaced patterns and wires are formed on a wafer surface. As a result, deviations in various directions are also generated from reflections. A projection aperture stop  50  may be shaped like a cross so that a distance d is created between the detection and projection light beams, ensuring easy reception of the detection light beam  51  with reduced measurement errors. Although this solution can mitigate the consequences of the object&#39;s surface irregularities to a certain extent, for a relative large trench  41  (as shown in  FIG. 3 ), the measurement will be still impossible if the projection light beam is incident on the inner wall surface of the trench. 
         [0005]    In the surface of an actual object  36  such as a wafer or the glass substrate, are often formed periodic trenches typically at a pitch on the order of millimeters, e.g., 5 mm, which are unfavorable to the measurement. Since the trenches themselves are sized on the order of hundreds of microns, e.g., 100 μm, it is likely for the measuring light spot to be formed partially or entirely within one of the trenches. This may introduce measurement errors or even make the measurement impossible. As shown in  FIG. 3 , when the measuring light spot is formed in part or as a whole within one of the trenches, the reflection in the optical path will occurs in an undesirable way in which the reflected light cannot be collected and the measurement of the object is thus affected adversely. When the reflected light is entirely reflected away by the trench, the measurement will be disabled. 
       SUMMARY OF THE INVENTION 
       [0006]    It is an object of the present invention is to provide a focusing and leveling apparatus adaptable to trenches, for use in measuring a height and a tilt of an object under measurement. 
         [0007]    In order to achieve this object, the present invention provides a focusing and leveling apparatus adaptable to trenches, used to measure a height and a tilt of a surface of an object under measurement. The trenches are formed in the surface of the object under measurement which is carried on a movable stage. The focusing and leveling apparatus comprises, disposed sequentially, an illumination unit, a projection unit, a detection unit and a detector. The object under measurement is disposed between the projection unit and the detection unit along an optical path. The projection unit comprises a projection slit configured to form a plurality of measuring points onto the object under measurement, each of the plurality of measuring points comprising at least three measuring light spots which are arranged in a non-equidistant manner such that upon projection of the plurality of measuring points on the surface of the object under measurement, at least two of the at least three measuring light spots of each of the plurality of measuring points are located outside the trenches, thereby allowing the measurement of the height and the tilt of the surface of the object under measurement. 
         [0008]    Further, a size of each of the at least three measuring light spots may be greater than a width of each of the trenches. 
         [0009]    Further, each of the plurality of measuring points may comprise three, four or five measuring light spots. 
         [0010]    Further, a distance between a first and a last measuring light spots in each of the plurality of measuring points may be not equal to a multiple of a pitch of the trenches. 
         [0011]    Further, s distance between any adjacent two of the at least three measuring light spots may be not equal to a multiple of the pitch of the trenches. 
         [0012]    Further, a distance between any two of the at least three measuring light spots may be not equal to a multiple of a pitch of the trenches. 
         [0013]    Further, the trenches have a pitch of 2 mm, wherein each of the plurality of measuring points comprises three measuring light spots and the distances between adjacent ones of the measuring light spots are 1.5 mm and 1 mm, respectively. 
         [0014]    Further, upon projection of the plurality of measuring points onto the surface of the object under measurement, for each of the plurality of measuring points, at least two of the at least three measuring light spots that are located out of the trenches may be identified based on distance(s) between measuring light spots that are detected by the detector. 
         [0015]    Further, the illumination unit may sequentially comprise a light source and a light-source lens group, wherein the projection unit comprises a projection slit, a front projection lens group, a projection reflector group and a rear projection lens group, disposed sequentially along the optical path, wherein the detection unit comprises a front detection lens group, a detection reflector group and a rear detection lens group, disposed sequentially along the optical path, and wherein the focusing and leveling apparatus further comprises a relay unit between the detection unit and the detector, the relay unit comprising a relay reflector and a relay lens group, disposed sequentially along the optical path. 
         [0016]    In the focusing and leveling apparatus adaptable to trenches according to the present invention, as the illumination unit projects light onto the surface of the object under measurement via a projection slit in the projection unit which splits each measuring point into a number of non-equidistant sections, each measuring point projected on the surface of the object under measurement accordingly contains the same number of non-equidistant measuring light spots. Reflected light from the measuring light spots on the surface of the object under measurement is collected by the detection unit and is then input to the detector. In case of any of the measuring light spots located in one of the trenches, the detector identifies effective ones of the measuring light spots based on detected distance(s) between them, thereby enabling the height and tilt measurement of the object under measurement in which the trenches are formed, based on the effective measuring light spots. Herein, an effective measuring light spot refers to a measuring light spot located out of the trenches in the object under measurement, and an ineffective measuring light spot refers to a measuring light spot formed in one of the trenches in the object under measurement. 
         [0017]    The present invention also provides a focusing and leveling method adaptable to trenches, used to measure a height and a tilt of the surface of an object under measurement. The trenches are formed periodically in the surface of the object under measurement which is carried on a movable stage. The method comprises the steps of: forming, by an focusing and leveling apparatus, a plurality of measuring points on the surface of the object under measurement, each of the plurality of measuring points comprising at least three measuring light spots arranged in a non-equidistant manner; moving the movable stage and hence the object under measurement carried thereon such that upon projection of the plurality of measuring points on the surface of the object under measurement, at least two of the at least three measuring light spots of each of the plurality of measuring points are located outside the trenches; and measuring the height and the tilt of the surface of the object under measurement by the focusing and leveling apparatus. 
         [0018]    Further, the focusing and leveling method adaptable to trenches may further comprise: moving the movable stage to an initial position; detecting distances between the at least three measuring light spots by the focusing and leveling apparatus; and in the event of at least one of the at least three measuring light spots located in one of the trenches, relocating the at least three measuring light spots on the surface of the object under measurement by moving the object under measurement through the movable stage such that at least two of them are located outside the trenches. 
         [0019]    Further, moving the object under measurement through the movable stage may comprise: moving the movable stage in a first horizontal direction by a distance that is equal to 1/10 to ½ of a pitch at which the trenches are distributed along the first horizontal direction; and moving the movable stage in a second horizontal direction by a distance that is equal to 1/10 to ½ of a pitch at which the trenches are distributed along the second horizontal direction. 
         [0020]    Further, upon projection of the plurality of measuring points onto the surface of the object under measurement, for each of the plurality of measuring points, at least two of the at least three measuring light spots that are located out of the trenches may be identified based on distance(s) between them detected by the detector. 
         [0021]    In the focusing and leveling method adaptable to trenches according to the present invention, the focusing and leveling apparatus as defined above is employed such that when any of the measuring light spot is located in one of the trenches, effective ones of the measuring light spots can be identified based on the distance(s) between measuring light spots that are detected by the focusing and leveling apparatus, thus enabling the height and tilt measurement of the object under measurement in which the trenches are formed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0022]      FIG. 1  is a structural schematic diagram of an apparatus for focusing and leveling according to the prior art. 
           [0023]      FIG. 2A  is a diagram schematically showing a projected light spot according to the prior art. 
           [0024]      FIG. 2B  is a diagram schematically showing a tolerance measurement on the projected light spot according to the prior art. 
           [0025]      FIG. 3  schematically illustrates how a trench affects an optical path in accordance with the prior art. 
           [0026]      FIG. 4  is a structural schematic diagram of an apparatus for focusing and leveling according to the present invention. 
           [0027]      FIG. 5  schematically shows an arrangement of measuring points and measuring light spots according to the present invention. 
           [0028]      FIG. 6  is an enlarged view of one of the measuring light spots shown in  FIG. 5 . 
           [0029]      FIG. 7A  schematically shows an arrangement of three equidistant light spots. 
           [0030]      FIG. 7B  is an image obtained when the three equidistant light spots shown in  FIG. 7A  are each located in a trench. 
           [0031]      FIG. 7C  schematically shows an arrangement of three non-equidistant light spots in accordance with one embodiment of the present invention. 
           [0032]      FIG. 7D  is an image obtained when part of the three non-equidistant light spots shown in  FIG. 7C  are each located in a trench. 
           [0033]      FIG. 7E  schematically shows an arrangement of four non-equidistant light spots in accordance with one embodiment of the present invention. 
           [0034]      FIG. 7F  is an image obtained when part of the four non-equidistant light spots shown in  FIG. 7E  are each located in a trench. 
           [0035]      FIG. 7G  schematically shows an arrangement of five non-equidistant light spots in accordance with one embodiment of the present invention. 
           [0036]      FIG. 7H  is an image obtained when part of the non-equidistant light spots shown in  FIG. 7G  are each located in a trench. 
           [0037]      FIG. 8  schematically shows a positional relationship of three light spots and trenches spaced apart at a 2-mm pitch in accordance with the present invention. 
           [0038]      FIG. 9  schematically shows periodic trenches. 
           [0039]      FIG. 10  is a flowchart graphically illustrating a method for focusing and leveling in accordance with one embodiment of the present invention. 
       
    
    
       [0040]    In the figures depicting the prior art,  20  denotes a projection objective;  21 , a light source;  22 , a light-source lens group;  23 , a projection slit;  24 , a front projection lens group;  25 , a projection reflector group;  26 , a rear projection lens group;  27 , a front detection lens group;  28 , a detection reflector group;  29 , a rear detection lens group;  30 , a relay reflector;  31 , a relay lens group;  32 , a detector;  33 , an arithmetic unit;  34 , a controller;  35 , a movable carrier stage;  36 , an object under measurement;  41 , a trench;  50 , a projection aperture stop; and  51 , a detection light beam. 
         [0041]    In the figures depicting the present invention,  100  denotes a projection objective;  201 , a light source;  202 , a light-source lens group;  203 , a projection slit;  204 , a front projection lens group;  205 , a projection reflector group;  206 , a rear projection lens group;  207 , a front detection lens group;  208 , a detection reflector group;  209 , a rear detection lens group;  210 , a relay reflector;  211 , a relay lens group;  212 , a detector;  213 , an arithmetic unit;  214 , a controller;  300 , a movable carrier stage;  400 , an object under measurement;  401 , a trench;  500 , a light beam;  501 , a measuring point;  502 , a measuring light spot; P 1 , a first light spot; P 2 , a second light spot; P 3 , a third light spot; P 4 , a fourth light spot; and P 5 , a fifth light spot. 
       DETAILED DESCRIPTION 
       [0042]    The present invention will be described below in detail with reference to the accompanying drawings. 
         [0043]    Referring to  FIGS. 4 to 6 , the present invention provides a focusing and leveling apparatus adaptable to trenches, comprising a measuring optical path extending on both sides of an optical axis of a projection objective  100 , along which there are disposed an illumination unit, a projection unit, a detection unit, a relay unit and a detector in a sequence. 
         [0044]    With reference to  FIG. 4 , the illumination unit includes, sequentially disposed, a light source  201  and a light-source lens group  202 . The light source  201  is a light source provided by the present invention. The light-source lens group  202  is adapted to transform a light beam from the light source  201  into a parallel light beam. 
         [0045]    With reference to  FIGS. 4, 5 and 6 , the projection unit includes a projection slit  203 , a front projection lens group  204 , a projection reflector group  205  and a rear projection lens group  206 , disposed sequentially in the optical path. By means of the projection slit  203 , a number of measuring points  501  are formed on an object under measurement  400  (e.g., a wafer or a glass substrate). An exemplary distribution of the measuring points  501  is schematically illustrated in  FIG. 5 . Each of the measuring points  501  includes a number of measuring light spots  502  distributed in a non-equidistant manner, for example, as illustrated in  FIG. 6 . After propagating through the projection slit  203 , the front projection lens group  204 , the projection reflector group  205  and the rear projection lens group  206 , the parallel light beam forms the measuring points  501  and hence the measuring light spots  502  in an exposure area on the surface of the object under measurement  400  such as a wafer. 
         [0046]    With reference to  FIG. 4 , the detection unit includes a front detection lens group  207 , a detection reflector group  208  and a rear detection lens group  209 , disposed sequentially in the optical path. The front detection lens group  207  is configured to collect light from the measuring points  501  and hence from the measuring light spots  502  formed on the surface of the object under measurement  400 . The direction of the optical path of the light collected from the measuring points  501  and hence from the measuring light spots  502  is deflected by the detection reflector group  208  and is then focused by the rear detection lens group  209  by passing therethrough. 
         [0047]    With reference to  FIG. 4 , the relay unit includes a relay reflector  210  and a relay lens group  211 , disposed sequentially along the optical path. The relay reflector  210  is adapted to bend the focused light such that it passes through the relay lens group  211  and is thereby further focused and is then incident on the detector  212 . The detector  212  is adapted to identify effective one(s) in the measuring light spots  502  based on detected distance(s) therebetween so as to determine a height and a tilt of the object under measurement. 
         [0048]    With reference to  FIG. 4 , the apparatus for focusing and leveling further includes an arithmetic unit  213  and a controller  214 . The controller  214  contains a circuit that is connected to a movable carrier stage  300  on which the object under measurement  400  is carried. The arithmetic unit  213  is capable of converting an optical signal corresponding to the effective measuring light spots  502  detected by the detector  212  into an electrical signal. Based on a value of the electrical signal, the controller  214  determines whether to adjust the height and tilt of the object under measurement  400  through changing its six degree-of-freedom (DoF) directions. The six DoFs of the movable carrier stage  300  represent the freedom of translation on the three orthogonal coordinate axes X, Y and Z and rotation about these coordinate axes. 
         [0049]    When no effective measuring light spot  502  is detected through the detector  212 , it is known that the object under measurement  400  has excessive positional deviations and adjustments of its position are required to be made by the movable carrier stage  300  so as to relocate the measuring light spots  502  on the surface of the object under measurement  400 . In this case, the positional adjustments of the object under measurement  400  may be accomplished by the arithmetic unit  213  and the controller  214  provided for the apparatus for focusing and leveling. 
         [0050]    When only one effective measuring light spot  502  is detected by the detector  212 , it will be unable to determine an identifier of the measuring light spot  502  based on its distance from another effective measuring light spot that is absent and hence which of the measuring light spots  502  corresponds to the effective one. In this case, in order to obtain more accurate measurement results, the position of the object under measurement  400  may be adjusted by the movable carrier stage  300  in order to relocate the measuring light spots  502  on the surface of the object under measurement  400  so that two or more effective measuring light spots  502  are detectable based on the distance between the effective light spots. 
         [0051]    According to the present invention, each lens group may consist of one or more lenses, and each reflector group may consist of one or more reflectors. 
         [0052]    With reference to  FIGS. 8 and 9 , in the focusing and leveling apparatus adaptable to trenches, each measuring light spot  502  is sized larger than a width Lg of the trenches  401 . For example, if the measuring light spots  502  are circular, their diameter may be larger than the width of the trenches  401 , and if the measuring light spots  502  are square, their side length may be larger than the width of the trenches  401 . 
         [0053]    In a projection lithography tool, a detection device for focusing and leveling is often employed for height and tilt measurement of specific areas of the surface of a wafer. This detection device is usually required to provide a high accuracy while not causing damages on the wafer during its operations. Topographic irregularities (i.e., heights and tilts) of the wafer are measured in order to enable control of the wafer&#39;s gesture so as to ensure the wafer surface to be located within an effective focal depth range of the projection objective. The apparatus for focusing and leveling has at least three measuring points, four in this embodiment. A spatial plane defined by these measuring points is considered as representing the surface of the object under measurement, and the process of focusing and leveling is intended to bring this plane into an optimum focal plane of the projection objective. In accordance with the present invention, it is required that there are at least three measuring light spots in each measuring point and the light spots are spaced from one another non-equidistantly. 
         [0054]      FIG. 3  schematically shows how a trench affects the optical path. With reference to  FIG. 3 , when there is a trench in the surface of the object under measurement, it is likely for the reflected light to fail to pass through the detection unit and reach the detector.  FIG. 9  schematically illustrates trenches formed in the surface of the object under measurement. With reference to  FIG. 9 , during exposure by the projection lithography tool, periodic trenches  401  are formed in the surface of the object under measurement due to various processes, and the direction of the trenches  401  typically parallel or perpendicular to a direction of the movable carrier stage. Generally, the trenches are spaced apart at a pitch on the order of millimeters, and their widths and depths are on the order of hundreds of microns. During measurement by the apparatus for focusing and leveling, if any measuring point is located in one of the trenches, the measurement may fail. In addition, the trench areas are usually not supposed to be measured by the apparatus for focusing and leveling, because they cannot reflect the topography of the whole exposure area on the surface of the object under measurement  400 . 
         [0055]    In this embodiment, principles in measurement are explained with each measuring point encompassing three equidistant measuring light spots, three non-equidistant measuring light spots, four non-equidistant measuring light spots, and five non-equidistant measuring light spots as examples. 
         [0056]    With reference to  FIGS. 7A, 7C, 7E and 7G  measuring light spots  502  totally span a distance of 6 mm in each case. In order to discuss the consequences of location of measuring light spot(s)  502  in trench(es)  401 , it is assumed that the pitch of the trenches  401  is 3 mm and that, in each case, the two outermost measuring light spots are located in respective trenches  401 . 
         [0057]    With reference to  FIGS. 7A and 7B , three equidistant measuring light spots (hereinafter referred to as the “light spots”)  502  are given the identifiers P 1 , P 2 , P 3 , where |P 1 −P 2 |=3 and |P 2 −P 3 |=3. In this case, each of the three light spots P 1 , P 2 , P 3  is located in a respective trench  401 . As a result, no light spot appears in an image obtained by the detector as shown in  FIG. 7B . 
         [0058]    With reference to  FIGS. 7C and 7D , three light spot P 1 , P 2 , P 3  are arranged non-equidistantly, where |P 1 −P 2 |=2 and |P 2 −P 3 |=4. In this case, each of the two outermost light spots P 1 , P 3  is located in a respective trench  401 . As a result, only one of the light spots is detected by the detector, i.e., being effective, as shown in FIG.  7 D. However, as the identifier of the detected light spot remains unknown, the measurement is still impossible. 
         [0059]    With reference to  FIGS. 7E and 7F , four non-equidistant light spots P 1 , P 2 , P 3 , P 4  are arranged, where |P 1 −P 2 |=2, |P 2 −P 3 |=3 and |P 3 −P 4 |=1. In this case, each of the two outermost light spots P 1 , P 4  is located in a trench  401 , and an image obtained by the detector is shown in  FIG. 7F . From the image, two of the light spots are identifiable. Based on the distance between these effective light spots, it can be known that their identifiers are P 2  and P 3 . The measurement can be carried out based on positional information carried by these known effective light spots. 
         [0060]    With reference to  FIGS. 7G and 7H , five non-equidistant light spots P 1 , P 2 , P 3 , P 4 , P 5  are arranged, where |P 1 −P 2 |=1.7, |P 2 −P 3 |=1, |P 3 −P 4 |=1.3 and |P 3 −P 4 |=2. In this case, each of the two outermost light spots P 1 , P 5  is located in a respective trench  401 , and an image obtained by the detector is shown in  FIG. 7H . Based on the distances between the effective light spots  502  identifiable from the image, it can be known that their identifiers are P 2 , P 3  and P 4 . The measurement can be conducted based on positional information carried by these known effective light spots. 
         [0061]    As apparent from the above-described arrangements of non-equidistant light spots and detection results, the present invention eliminates the impact of trenches on the results of height and tilt measurement on the object under measurement  400 . In particular, better measurement results can be obtained from the arrangements with four or five non-equidistant light spots. With the number of effective light spots increasing, it will be easier to determine the identifiers of the light spots. In addition, more effective light spots result in higher credibility and accuracy of the results. 
         [0062]    Analyzed above are several scenarios with trenches spaced at a certain pitch and with 3 to 5 or more non-equidistant light spots in which two or more are each located in one of the trenches. In cases where trenches are formed in the object under measurement at a pitch that is greater than 5 mm, if the apparatus for focusing and leveling is configured to form measuring light spots of which adjacent ones are spaced apart from each other by a distance of about 3 mm and the trenches  401  are formed with their widths smaller than the size of each single light spot, it will not happen that two or more of the light spots are simultaneously ineffective. As such, more accurate measurement results can be obtained by determining the identifiers of the effective ones of the light spots  502  based on the distance(s) between them. 
         [0063]    In order to further describe the benefits of the present invention, an embodiment is set forth below in which under the conditions that trenches are formed at a pitch of 2 mm and each measuring points contains only three light spots, regardless of their locations, the light spots are always guaranteed to be as far from the trenches as possible while the identifiers of them are easily determinable based on the distance(s) between them.  FIG. 8  schematically depicts three of the vertically-oriented periodic trenches. Wherein, among the three measuring light spots  502 , those with the identifiers P 1  and P 2  are spaced apart by a distance of 1.5 mm, and those with the identifiers P 2  and P 3  are spaced apart by 1 mm. In case of the light spot P 1  being located in a trench  401 , i.e., being ineffective, P 2  and P 3  are effective, and the shortest one of the distances between the effective light spots and the trenches  401  is 0.5 mm. For example, P 3  is 0.5 mm away from the second leftmost trench. In case of the light spot P 2  being ineffective, i.e., being located in a trench  401 , P 1  and P 3  are effective, and the shortest one of the distances between the effective light spots and the trenches  401  is 0.5 mm. For example, P 1  is 0.5 mm away from the leftmost trench. In case of the light spot P 3  being ineffective, i.e., being located in a trench  401 , P 1  and P 2  are effective, and the shortest one of the distances between the effective light spots and the trenches  401  is 0.5 mm. For example, P 1  is 0.5 mm away from the second leftmost trench. In summary, even when a certain one of the light spots is ineffective, it is always guaranteed that one of the effective light spots is always 0.5 mm away from the nearest trench. In addition, the difference between the distances between the light spots is also 0.5 mm. This ensures no impact on the measurement signal as well as easy determination of the light spots&#39; identifiers, enabling the height and tilt measurement on the object under measurement  400 . 
         [0064]    In the focusing and leveling apparatus adaptable to trenches according to the present invention, as each measuring point  501  is split by the projection slit  203  into a number of non-equidistant measuring light spots  502 , each measuring point projected on the surface of the object under measurement  400  also contains the same number of non-equidistant measuring light spots. In case of any of the measuring light spots  502  located in one of the trenches  401 , identifiers of effective ones of the measuring light spots  502  that are formed out of the trenches can be determined based on detected distance(s) between them, and the height and tilt of the object under measurement can be determined based on positional information carried by these effective measuring light spots  502 . 
         [0065]    In accordance with the present invention, as the measuring light spots are non-equidistantly arranged, it is easy to determine the identifiers of detected measuring light spots and hence obtain the height and tilt of the object under measurement at the locations corresponding to them. In addition, their non-equidistant arrangements preclude the possibility of simultaneous location of two or more of them in trenches, achieving adaptation of the height and tilt measurement on the object under measurement to the trenches. 
         [0066]    According to the present invention, the number of the non-equidistant measuring light spots  502  is at least three. This avoids incapability of adaptation of the height and tilt measurement on the object under measurement to the impact of the trenches due to employment of one measuring point or location of all equidistant light spots in trenches  401 . 
         [0067]    In a preferred embodiment, in the focusing and leveling apparatus adaptable to trenches according to the present invention, the distance between the first and last measuring light spots  502  in each measuring point  501  is not equal to a multiple of a pitch of the trenches  401 . As such, it is prevented that either the first or last measuring light spot  502  is located in one of the trenches  401 . 
         [0068]    In a preferred embodiment, in the focusing and leveling apparatus adaptable to trenches according to the present invention, the distance between any adjacent two of the measuring light spots  502  is not equal to a multiple of the pitch of the trenches  401 . As such, it is prevented that any adjacent two of the measuring light spots  502  are both located in respective ones of the trenches  401 . 
         [0069]    In a preferred embodiment, in the focusing and leveling apparatus adaptable to trenches according to the present invention, the distance between any two of the measuring light spots  502  is not equal to a multiple of the pitch of the trenches  401 . As such, it is prevented that any two of the measuring light spots  502  are both located in respective ones of the trenches  401 . 
         [0070]    As can be perceived from the above three relationships of measuring light spots  502  and multiples of the trench pitch, the non-equidistant arrangements of the measuring light spots  502  according to the present invention are intended to stagger the measuring light spots  502  from the periodic trenches  401  in order to increase the number of effective measuring light spots  502  so that more effective measuring light spots can serve as the basis for the height and tilt measurement of the object under measurement. 
         [0071]    With reference to  FIG. 10 , the present invention also provides a method for focusing and leveling adaptable to trenches, using the focusing and leveling apparatus adaptable to trenches as described above. It is based on the concept that the apparatus for focusing and leveling forms a plurality of measuring points  501  on the surface of an object under measurement  400 , each comprising a number of measuring light spots  502  arranged in a non-equidistant manner, following by moving the movable carrier stage  300  to an initial position, detecting the measuring light spots  502  with the detector  212  of the apparatus for focusing and leveling, in case of any of the measuring light spots  502  located in one of the trenches  401 , identifying effective ones of the measuring light spots  502  based on the distance(s) between them detected by the apparatus for focusing and leveling, and measuring the height and tilt of the object under measurement. 
         [0072]    In case of two or more measuring light spot  502  located outside the trenches  401  in the object under measurement  400 , i.e., two or more effective measuring light spots, the height and tilt of the object under measurement  400  are measured based on these effective measuring light spots  502 . Otherwise, the measuring light spots  502  formed on the surface of the object under measurement  400  are relocated away from the trenches  401 . In accordance with the present invention, the six DoF directions of the movable carrier stage are adjusted based on the height and tilt of the object under measurement  400  so as to accomplish adjusting the object under measurement  400 . Herein, an effective measuring light spot refers to a measuring light spot located out of the trenches in the object under measurement, whilst an ineffective measuring light spot refers to a measuring light spot that is situated, in part or as a whole, in one of the trenches in the object under measurement, and is thus deformed and undetectable. 
         [0073]    In a preferred embodiment, in the proposed method for focusing and leveling adaptable to trenches, in the event of any of the measuring light spots  502  located in one of the trenches  410 , the measuring light spots  502  projected on the surface of the object under measurement  400  are relocated from the trench  401  by adjusting the movable carrier stage  300  that carries the object under measurement  400 . The relocation of the light spots  502  on the object under measurement  400  is accomplished by changing the horizontal and vertical DoF directions of the movable carrier stage  300  that carries the object under measurement  400 . Relocation of the light spots  502  on the object under measurement  400  is eventually relocation of the measuring points. 
         [0074]    In this embodiment, adjusting the movable carrier stage  300  may be specifically accomplished by horizontally moving the movable carrier stage  300  a distance that is equal to ½ of a pitch Lx at which the trenches  401  are distributed along the horizontal direction and vertically moving the movable carrier stage  300  a distance that is equal to ½ of a pitch Ly at which the trenches  401  are distributed along the vertical direction. In  FIG. 9 , Lg represents a width of the trenches  401 . That is, the positional adjustments of the movable carrier stage  300  in the horizontal and vertical DoF directions are related to the horizontal and vertical pitches of the trenches  401  distributed on the object under measurement  400 . During the horizontal or vertical positional adjustment, the distance moved is not limited to ½ of the trench pitch, as it may also be ⅓, ¼, ⅕, ⅙, 1/7, ⅛, 1/9, 1/10 or the like thereof. Additionally, the distance actually moved may be adjusted according to the pitches of the trenches. 
         [0075]    In the method for focusing and leveling adaptable to trenches according to the present invention, the apparatus for focusing and leveling as defined above is employed so that when any of the measuring light spot is formed in one of the trenches, effective ones of the measuring light spots can be identified based on the distance(s) between them detected by the apparatus for focusing and leveling, thus enabling the height and tilt measurement of the object under measurement in which the trenches are formed.