Apparatus for detecting a sample

The present invention relates to a detecting apparatus, and more particularly, to a detecting apparatus capable of precisely detecting and calibrating the geometric information of a sample.

The critical dimension of semiconductor device is continuously decreased, such that the damage induced by any defect on a chip is continuously increased. Hence, high resolution examination (both review and inspection) is required to properly find and check the defect. For example, scanning electron microscope (SEM), as a more advanced examination system, is popularly used for examining chips. In general, a sample (wafer or photomask or semiconductor substrate) is located under a charged particle beam during the examination process. Clearly, whether the sample is correctly located is a key factor of the examining result. In general, one detector is located under the sample and on a base (such as the Z-stage of SEM). The detector will project or emit a light to the sample and analyze a reflected light from the sample. According to the analyzing result, the detector could acquire the geometric information (such as position, direction and angle) of the sample.

There are some drawbacks in the conventional design of the examination system. First, the detector is fixed on the base. Hence, once the base is improperly located (such as the top surface of the base is not parallel to the bottom surface of the sample located on a predetermined position), the detector usually can not properly detect the sample (such as the light is not properly projected from the detector onto the sample, such that the quality of the reflected light is degraded.) Second, only one detector is used to detect the geometric information of the sample. Hence, once the sample has a displacement around the light (or around an axis parallel to the light), the detector usually can not find the displacement.

Therefore, it is desired to develop some new designs of examination system to improve the above drawbacks.

An apparatus for detecting the geometric information of a sample in an examination system. The apparatus includes an elastic supporting assembly and an optical-electronic assembly. The optical-electronic assembly could project a light beam to the sample, receive a reflected light beam from the sample, and analyze the received reflected light beam to acquire messages about the geometric information (such as position, direction, and tilt angle) of the sample. The elastic supporting assembly could fix the optical-electronic assembly on a base (such as the Z-stage) and adjust the geometric condition of the optical-electronic assembly (such as moving along X-axis, moving along Y-axis, rotating on X-Y plane, tilting on X-Z plane and tilting on Y-Z plane.)

An application of the proposed detecting apparatus is exemplified herein. By adjusting the elastic supporting assembly, the geometric condition of the optical-electronic assembly could be adjusted, for example, the distance between optical-electronic assembly and sample and/or the direction of the light projected by the optical-electronic assembly. Thus, after the geometric condition of the optical-electronic assembly is adjusted to achieve an optimal reflected light from the sample, the elastic supporting assembly could be locked to fix geometric condition of the optical-electronic assembly corresponding to the base. After that, whenever a new sample is appeared to be detected, by comparing the difference(s) between the new reflected light and the optimal reflected light, it is easy to adjust the geometric condition of the new sample, until the new reflected light also is optimized. Moreover, when the examination system (such as SEM) is maintained, the apparatus also could be used to calibrate the relative geometric relation (such as relative distance, relative angle and relative direction) between the base (such as Z-stage) and the sample to be tested. For example, when the location of the sample is not changed but the location of the base might be changed during the maintain process, the apparatus could be used to calibrate the location of the maintained base by comparing the difference(s) between the new reflected light and the optimal reflected light.

Another application of the proposed detecting apparatus is exemplified herein. Because the proposed apparatus usually only projects a light to the sample along only one direction (such as Z-axis), the proposed apparatus only can detect the displacement (or motion) that has a non-zero displacement (or motion) along the direction but can not detect displacement (or motion) totally on a plane vertical to the direction (such as X-Y plane). Therefore, to effectively detect the displacement (or motion) of the sample, it is worth to use two apparatuses that separately projects lights to the sample along two different directions (such as one along X-axis and another along Y-axis).

Some optional improvements of the proposed apparatus are exemplified herein. The elastic supporting assembly could comprise a planar structure and cubic structure. The planar structure may make a restricted linear motion and/or restricted pivot motion relative to a base where the proposed apparatus is located. The cubic structure may make a restricted deformation. Hence, the optical-electronic assembly on the elastic supporting apparatus could be linear moved, pivot moved or tilted.

Some optional improvements of the proposed apparatus are exemplified herein. The optical-electronic assembly could comprise a light source module and an analyzing module. The optical-electronic assembly also could have other improvements, such as beam-splitting module, automatic gain control circuit, background eliminating circuit, and so on. Hence, not only the receive light could be effectively analyzed, but also the generation of light and elimination of noise could be effectively adjusted.

These and other aspects, features and advantages of the present invention can be further understood from the accompanying drawings and description of embodiments.

FIG. 1 is a schematic side-view diagram illustrating a system for detecting the geometric information of a sample in accordance with one embodiment of the present invention.

FIG. 2 is a schematic side-view diagram illustrating an elastic supporting assembly in accordance with one embodiment of the present invention.

FIG. 3A is a schematic diagram illustrating the relative motion freedom(s) of the planar structure and the base by linear motion in accordance with one embodiment of the present invention.

FIG. 3B is a schematic diagram illustrating the relative motion freedom(s) of the planar structure and the base by rotation in accordance with one embodiment of the present invention.

FIG. 4A is a schematic side-view diagram illustrating a cubic structure in accordance with one embodiment of the present invention. FIG. 4B is a top view of the exemplary cubic structure in FIG. 4A .

FIG. 4C is a first side view of the exemplary cubic structure in FIG. 4A .

FIG. 4D is a second side view of the exemplary cubic structure in FIG. 4A .

FIG. 4E is a third side view of the exemplary cubic structure in FIG. 4A .

FIG. 4F is a fourth side view of the exemplary cubic structure in FIG. 4A .

FIG. 4G , FIG. 4H , FIG. 4I , FIG. 4J , and FIG. 4K are top, a first side, a second side, a third side, and a fourth side views respectively of FIG. 4A when in operation in accordance with one embodiment of the present invention.

FIG. 5 is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention.

FIG. 6 is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention.

FIG. 7 is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention.

FIG. 8 is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention.

FIG. 1 is a schematic side-view diagram illustrating a system for detecting the geometric information of a sample in accordance with one embodiment of the present invention. The exemplary system 10 comprises a holding apparatus 101 and at least one detecting apparatus 103 . The holding apparatus 101 is configured for holding a sample 23 . The detecting apparatus 103 separated from the sample 23 is for detecting the geometric information of the sample 23 . The detecting apparatus 103 comprises an elastic supporting assembly 20 and an optical-electronic assembly 21 . The optical-electronic assembly 21 projects a light beam 103 a on the sample 23 , and then receives a reflected light beam 103 a from the sample 23 and analyzes the reflected light beam 103 a . The elastic supporting assembly 20 supports the optical-electronic assembly 21 , fixes the optical-electronic assembly 21 to a base 201 (such as fixing on the top surface of the Z-stage) and adjusts a relative geometric relation (such as relative distance, relative angle and relative direction) between the optical-electronic assembly 21 and the sample 23 . Therefore, by using the elastic supporting assembly 20 to adjust the geometric condition of the optical-electronic assembly 21 , the light path of the light beam 103 a can be adjusted to optimize the quality of the received reflected light beam 103 a.

As an example, the exemplary system 10 is equipped with a first detecting apparatus 103 for detecting the displacement/motion of the sample 23 on an X-Y plane. A second detecting apparatus 105 may be set such that a second light beam 105 a is projected on another surface (such as the side of the sample 23 ) allowing the second detecting apparatus 105 to detect the position variation of the sample 23 on an X-Z plane or a Y-Z plane. In other words, because the sample 23 is a 3-dimensional object having a first edge, a second edge, and a third edge crossing a specific vertex of the sample 23 , at least two detecting apparatus 103 / 105 may be used to separately detect different displacements/motions of the sample 23 . For example, one detecting apparatus 103 which projects a light beam is used for detecting the displacement/motion on one plane defined by the first edge and the second edge, and another detecting apparatus 105 which projects another light beam is used for detecting the displacement/motion on another plane defined by the first edge and the third edge. Of course, the shape of the sample 23 is not restricted. Therefore, the first edge and the second edge could be the same edge if the shape of the surface defined by the first edge and the second edge is chosen from a group consisting of the following: circle, ellipse, oval, and combination thereof.

FIG. 2 is a schematic side-view diagram illustrating an elastic supporting assembly in accordance with one embodiment of the present invention. The elastic supporting assembly 20 comprises a planar structure 202 and a cubic structure 203 . The optical-electronic assembly (not shown in the figure) may be loaded and fixed on the elastic supporting assembly 20 . In one option, the planar structure 202 is positioned between the base and the cubic structure 203 . Herein, the area between the planar structure 202 and the base is larger than the area between the cubic structure 203 and the planar structure 202 , such that the cubic structure 203 is fixed on the base through the planar structure 202 . Alternatively, the cubic structure 203 may be positioned between the base and the planar structure 202 . Herein, the area between the cubic structure 203 and the base is larger than the area between the planar structure 202 and the cubic structure 203 , such that the planar structure 202 is fixed on the base 201 through the cubic structure 203 . Clearly, the key is how to use both the planar structure 202 and the cubic structure 203 to provide the required motion freedom, how to combine the planar structure 202 and the cubic structure 203 is not a key of the invention. As an example, the planar structure 202 could be mounted with the cubic structure 203 by a way selected from a group consisting of the following: screw, glue, nail, tack, electric welding, and combination therefore.

Continuing the above description, the planar structure 202 is equipped with a plurality of fasteners 202 b positioned within a plurality of holes 202 a respectively. It is noted that all of the holes 202 a usually are not designed on only one side of the planar structure 202 . For example, the holes 202 a may be separately located but not limited to on the two opposite edges of the planar structure 202 . Alternatively, the holes 202 a may all be located but not limited to on the same edge of the planar structure 202 . Moreover, the size of a hole 202 a is larger than the size of a body of a fastener 202 b passing through the hole 202 a and is smaller than the size of an end of the fastener 202 b . Clearly, when the fastener 202 is located in the hole 202 a but not locked, it is allowed to move in the hole 202 a (for the body of fastener 202 is narrower than the hole 202 a ) to provide at least one motion freedom. Of course, when the fastener 202 is located in the hole 202 a and locked (because the end of the fastener 202 b is wider than the hole 202 a ), there is no motion freedom. As an example, the shape, the size and the geometric relation of the holes 202 a and the fasteners 202 b are adjusted to allow the optical-electronic assembly (not shown in the figure) loaded on the elastic supporting assembly to have at least one motion freedom before all of the fasteners 202 b are locked. Herein, FIG. 3A and FIG. 3B shows an embodiment with two possible motion freedoms. Herein, the two motion freedoms may be chosen from a group consisting of the following: rotation/pivot on the locked fastener 202 b (the dotted arc line with an arrow), rotation/pivot on a point between the fastener 202 b and the planar structure 202 , linear motion along a direction parallel to a line crossing both of the holes 202 a , linear motion along a direction vertical to a line crossing both of holes 202 a (the dotted straight line with an arrow), and combination thereof. Thus, the planar structure 202 may be crossed with or offset from the base as shown in FIG. 3A and FIG. 3B , respectively. As an example, to provide the planar structure 202 with a significant motion freedom along the first direction ‘X’, the body of the fastener 202 can be made to be significantly smaller than the hole 202 a along a first direction ‘X’ and slightly narrower than the hole 202 a along a second direction ‘Y.” Furthermore, as an example, the shape of each hole 202 a could be chosen from a group consisting of the following: quadrangle, oblong, circle, square, and the combination thereof, and each of the fasteners 202 b may be chosen from a group consisting of the following: screw with nut, nail, tack and the combination thereof.

FIG. 4A is a schematic side-view diagram illustrating a cubic structure in accordance with one embodiment of the present invention. FIG. 4B is a top view, FIG. 4C is a first side view, FIG. 4D is a second side view, FIG. 4E is a third side view, and FIG. 4F is a fourth side view of the exemplary cubic structure in FIG. 4A . The cubic structure 203 is equipped with a first cavity 203 a , a second cavity 203 b , a first adjusting device 203 c and a second adjusting device 203 d . The first cavity 203 a is positioned between a top plate 205 b and a bottom plate 205 a . The second cavity 203 b is positioned between a top plate 205 c and a bottom plate 205 b . The corresponding adjusting device, for example, the first adjusting device 203 c comprises a first fastener (not shown in the figure) capable of passing through the top plate 205 b to a top surface of the second plate (plate 205 a ) and a second adjusting device 203 d comprises a second fastener (not shown in the figure) capable of passing through the top plate 205 c and the second plate 205 b to reach into a hole being terminated inside the bottom plate 205 a . Each of the adjusting devices ( 203 c and 203 d ) could be chosen from a group consisting of the following: screw with nut, nail, tack and the combination thereof. The first fastener increases the angular magnitude of a corresponding opening when the first fastener is locked (the end of the first fastener contacts with the second plate, such that the second plate is pushed away when the first fastener is locked into the first plate), and the second fastener is capable of decreasing decreases the angular magnitude of the corresponding opening when the second fastener is locked (the end of the first fastener could be embedded into the second plate, such that the distance between the first plate and the second plate is decreased when the fastener is locked into the first plate). Further, the first portion of the cubic structure 203 forming the wall 203 e of the first cavity 203 a is partially overlapped with a second portion of the cubic structure forming the wall 203 f of the second cavity 203 b . Herein, the first cavity 203 a is with a first opening oriented towards a first direction and a second cavity 203 b is with a second opening oriented towards a second direction that is different from the first direction, so that the deformation induced from the first cavity and the deformation induced from the second cavity is distributed over two different planes (or together forming a 3-dimension deformation).

Referring to FIG. 4B , FIG. 4C , FIG. 4D , FIG. 4E , and FIG. 4F , the first adjusting device 203 c adjusts an angular magnitude of a first angle θ 1 of the first opening and the second adjusting device 203 d adjusts an angular magnitude of a second angle θ 2 of the second opening. The first cavity 203 a and the second cavity 203 b are arranged along a specific direction (for example “Z”) to interact with the planar structure (not shown in the figure). Therefore, the deformation of the cubic structure 203 is not totally parallel to the top surface of the planar structure (i.e., the motion freedom(s) induced by the deformation is not totally parallel to the top surface of the planar structure). Herein, the angular magnitudes are in-measured along the specific direction.

FIG. 4G , FIG. 4H , FIG. 4I , FIG. 4J , and FIG. 4K are a top view, a first side, a second side, a third side, and a fourth side views respectively of FIG. 4A when the cubic structure is in operation in accordance with one embodiment of the present invention. In the case of compressing the angular magnitude of the second angle θ 2 , the first cavity 203 a is compressed along the Y-Z plane. Similarly, in the case of stressing the angular magnitude of the first angle θ 1 , the second cavity 203 b is de-compressed on the X-Z plane. According to the foregoing description in reference to FIGS. 4A to 4K , the exemplary elastic supporting assembly may provide more freedoms for the adjustment of the optical-electronic assembly to enhance the qualities and precision of the alignment for the optical-electronic assembly.

Furthermore, the cubic structure 203 could be made of elastic material or could be formed to become an elastomer or an elastic structure. According to the configuration of the cubic structure 203 aforementioned, the shape, the size and the geometric relation of the cavities ( 203 a and 203 b ) cooperated with the adjusting devices ( 203 c and 203 d ) are adjusted to allow the optical-electronic assembly (not shown in the figure) loaded on the elastic supporting assembly 20 in FIG. 2 to have at least one motion freedom before the adjusting devices ( 203 c and 203 d ) are locked. The motion freedom is chosen from a group consisting of the following: tilting by varying the first angle θ 1 of the first opening, tilting by varying the second angle θ 2 of the second opening, and the combination thereof.

Accordingly, the adjustment of the relative geometric relation (such as relative position and relative angle) between the optical-electronic assembly 21 and the sample 23 may be achieved by cooperating the cubic structure 203 and the planar structure 202 .

FIG. 5 is a schematic diagram illustrating an exemplary optical-electronic assembly in accordance with the present invention. The optical-electronic assembly 21 comprises a light source module 211 capable of emitting a light beam 214 to the sample 23 , and an analyzing module 212 capable of analyzing a reflected light beam 215 from the sample 23 .

FIG. 6 is a schematic diagram illustrating an exemplary optical-electronic assembly 21 in accordance with the present invention. In the example, the light source module 211 comprises an electrostatic discharge device 211 a electrically coupled with at least one external signal line that receives at least one external signal from an external environment, such that the noise (or the damages induced by electrostatic discharge) from the external environment through the external signal line is effectively blocked. Furthermore, as an example, the light source module 211 comprises a laser diode 211 b driven and controlled by a laser diode driver. The laser diode 211 b is configured for emitting a laser beam as the light beam 214 .

Further, the optical-electronic assembly 21 optionally comprises a beam splitting module 216 capable of splitting the light beam 214 and the reflected light beam 215 . The beam splitting module 216 could be positioned between the sample 23 and the light source module 211 , and/or between the sample 23 and the analyzing module 212 . As one example, as shown in FIG. 7 , the beam splitting module 216 comprises a first beam splitter 216 a which reflects the first portion 214 a of the light beam 214 and reflects the first portion 215 a of the reflected light beam 215 , and allows the second portion 214 b of the light beam 214 to pass through for projecting on the sample 23 and forms the reflected light beam 215 . As another example, as shown in FIG. 8 , the beam splitting module 216 may comprise a second beam splitter 216 b and a third beam splitter 216 c located separately and in sequence between the light source module 211 and the sample 23 . The second portion 214 c of the light beam 214 is reflected by the second beam splitter 216 b . The third portion 214 d of the light beam 214 passes through the second beam splitter 216 b and the third beam splitter 216 c and projects on the sample 23 to form the reflected light beam 215 . Then the first portion 215 c of the reflected light beam 215 is reflected by the third beam splitter 216 c , the second portion 215 d of the reflected light beam 215 passes through the third beam splitter 216 c and the third portion 215 e of the reflected light beam 215 is reflected by the second beam splitter 216 b . Different light splitting modules 216 correspond to different designs of the optical-electronic assembly 21 , especially correspond to different designs of the analyzing module 212 .

Next, as an example, the analyzing module 212 comprises a position sensor device 212 a and an automatic gain control (AGC) circuit 212 b coupled with the position sensor device 212 a as shown in FIG. 6 or coupled with a first detector 212 d capable of receiving the third portion 215 e of the reflected light beam 215 as shown in FIG. 8 . The position sensor device 212 a the first portion 215 a of the reflected light beam 215 and outputs a processed detected signal 218 which is a function of both the incident angle of the second portion 214 b of the light beam 214 on the sample 23 and a projected position of the second portion 214 b of the light beam 214 on the sample 23 . Herein, by using proper position sensor device 212 , such as a commercial position sensor device 212 having four detectors for providing quadrantal detection independently, it is easy to decide whether the second portion 214 b of the light beam 214 is properly projected on the sample 23 and whether the sample 23 is properly located on the predetermined position with predetermined angle. The automatic gain control circuit 212 b outputs an adjusting signal 219 to the light source module 211 according to a light intensity of the first portion 215 a of the reflected light beam 215 or the third portion 215 e of the reflected light beam 215 . Then, by referring to the output of the automatic gain control circuit 212 b , the light source module 211 decreases the light intensity of the light beam 214 when the light intensity of the light beam 214 is larger than a higher threshold. Similarly, the light source module 211 increases the light intensity of the light beam 214 when the light intensity of the light beam 214 is smaller higher than a lower threshold. Thus, the light source module 211 adjusts the light intensity of the light beam 214 according to the adjusting signal 219 , such that the light intensity of the first portion 215 a of the reflected light beam 215 could be optimal for proper operation of the analyzing module 212 .

Furthermore, as an example, the analyzing module 212 may further comprise a background eliminating circuit 212 c electrically coupled with the position sensor device 212 a . The background eliminating circuit 212 c eliminates the effect of a background light which is received with the first portion 215 a of the reflected light beam 215 by the position sensor device 212 a simultaneously. There are different approaches to achieve the object of the background eliminating circuit 212 c , based on the fact that the light source module 211 usually use laser as the light source. According to a first example, the background eliminating circuit 212 c filters to obtain the required first portion 215 a of the reflected light beam 215 by only allowing a portion of the received light within specific frequencies (corresponding to the frequencies of the light source module 211 ) to pass and blocking the other portion of the received light. According to a second example, background eliminating circuit 212 c divides the received light into a continuous portion which spans over continuous frequencies (corresponding to the backlight) and a discrete portion which discretely distributes only within some specific frequencies (corresponding to the reflected light). Then, the background eliminating circuit 212 c also produces a simulated light which is essentially out-phase with the continuous portion over all frequencies, such that the continuous portion is cancelled by the simulated light and only the discrete portion is passed.

Furthermore, as an example shown in FIG. 7 , for properly adjusting the light intensity of the light beam 214 with reference to the reflected portion of the light beam 214 and the operation of the light source module 211 , the optical-electronic assembly 21 may further comprise a photo receiver 220 capable of receiving the first portion 214 a of the light beam 214 and producing a corresponding output signal 220 a . A focus lens 222 may be optionally set for focusing the first portion 214 a of the light beam 214 on the photo receiver 222 . Optionally, the a power limitation circuit 221 produces a power limitation signal 221 a according the output signal 220 a (which is detected) and a reflection-transmission ratio of the first beam splitter 216 a (which is known when a specific beam splitter is used to form the first beam splitter 216 a ). The power limitation signal 221 a is proportional to the actual intensity of the light beam 214 . according to which the light source module 211 adjusts the light intensity of the light beam 214 . For example, to avoid the risk that only a very small portion of the second portion 214 b of the light beam 214 is reflected (the sample 23 might have a very low reflection coefficient) and then the automatic gain control (AGC) circuit 212 b generates the adjusting signal 219 driving the light source module 211 to overly increase the light intensity of the light beam 214 , the power limitation signal 221 a could be used to restrict the adjusted light intensity of the light beam 214 to be smaller than or equal to a maximum allowable light intensity of the light source module 211 .

Alternatively, as shown in FIGS. 5˜8 , the optical-electronic assembly 21 may comprise a light adjusting module 217 capable of adjusting the propagation of the light beam 214 and the reflected light beam 215 . The light adjusting module 217 may be positioned between the sample 23 and the light source module 211 , and/or between the sample 23 and the analyzing module 212 . In one example, the light adjusting module 217 comprises a collimator lens 217 a capable of adjusting propagation of the light beam 214 for ensuring propagation of the light beam 214 with less divergence. The light adjusting module 217 may comprise a first plate 217 b with a first aperture for ensuring the uniform light intensity of the light beam 214 within a specific cross-sectional area, such that only essentially parallel light is projected on the sample 23 (or such that only incident light within a specific cross-section area and with a specific light strength intensity could pass through the first plate 217 b ). The light adjusting module 217 may further comprise a second plate 217 c with a second aperture for ensuring the uniform light intensity of the reflected light beam 215 within a specific cross-sectional area (e.g. only incident light within a specific cross-section area and with a specific light intensity could pass through the second plate 217 c ). Hence, if the sample 23 is significantly improperly located (such as the sample 23 is far away from the predetermined position or the sample 23 is significantly tilted), the reflected light beam 215 will be blocked by second plate 217 c and then the light adjusting module 217 will receive no light, such that it easily finds the significantly displacement of the sample 23 . Alternatively, the light adjusting module 217 may further comprises a first focusing lens 217 d located between the second beam splitter 216 b and the first detector 212 d , which focuses the third portion 215 e of the reflected light beam 215 into the first detector 212 d.

The optical-electronic assembly means an assembly of the optical device, optoelectronic device and the electronic device. In one embodiment of the present invention, the optical-electronic assembly 21 , as shown in FIG. 6 to FIG. 8 , may include an optical device including the light adjusting module 217 and the beam splitting module 216 , an optoelectronic device including the laser diode 211 b and the position sensor device 212 a , and an electronic device including the electrostatic discharge device 211 a , the automatic gain control (AGC) circuit 212 b and the background eliminating circuit 212 c

Although the present invention has been explained in relation to some embodiments, it is to be understood that other modifications and variation can be made without departing the spirit and scope of the invention as hereafter claimed.