JP2009074802A - Inspection device, inspection method, and manufacturing method of pattern substrate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a mask inspection device having small power consumption, and a simple structure dispensing with control for synchronizing accurately a two-dimensional imaging device with a laser light source. <P>SOLUTION: The mask inspection device 1 in one embodiment is equipped with a two-dimensional optical sensor 208 for imaging a defect on a mask 220, and a mode-lock fundamental wave laser 101 for irradiating the mask 220 with light having the larger number of repetition than a line rate of the two-dimensional optical sensor 208. The number of the repetition of light emitted from the fundamental wave laser 101 is 100 times as large as the line rate of the two-dimensional optical sensor 208 or larger. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inspection apparatus, an inspection method, and a pattern substrate manufacturing method, and in particular, a photomask (hereinafter simply referred to as a mask) used in a semiconductor manufacturing process or an inspection apparatus used when detecting defects in a wafer. The present invention relates to an inspection method and a pattern substrate manufacturing method.

  In general, in a defect inspection apparatus for a mask, an observation region (generally, a micro region having a diameter of 100 to 200 μm) on a pattern surface of a mask that is an inspection object is enlarged and observed. In this case, it is necessary to illuminate the observation area with light. The light source (referred to as a mask inspection light source. Here, simply referred to as a light source) is roughly classified into a case of using a lamp and a case of using a laser. In an inspection apparatus using a laser, a continuous laser that generates continuous laser light is generally used.

  With the progress of semiconductor technology, that is, miniaturization, the defect size required to be detected is decreasing year by year. In order to increase the defect detection sensitivity, it is necessary to shorten the wavelength of the inspection light source. Therefore, conventionally, commercialized inspection apparatuses use an argon laser having a wavelength of 364 nm as a light source. Recently, a mask inspection apparatus using a continuous laser beam having a wavelength of 257 nm (this is a second harmonic wave having a wavelength of 514 nm, which is the maximum output line in an argon laser) is commercially available. However, from the viewpoint of improving detection sensitivity, further shortening of the wavelength of the inspection light source is desired. A conventional mask inspection apparatus using such a continuous laser beam having a wavelength of 257 nm is disclosed in Non-Patent Document 1 or Non-Patent Document 2, for example.

  Since the pattern on the mask becomes finer as the semiconductor becomes finer, the light source of the mask inspection apparatus is also required to have a shorter wavelength in order to improve the defect detection sensitivity. As a next generation mask inspection light source, a light source having a wavelength of 200 nm or less is required. Therefore, for example, a mask inspection apparatus that generates 198.5 nm ultraviolet laser light, which is the sum frequency of the second harmonic of an argon laser with a wavelength of 488 nm and a fiber laser with a wavelength of 1064 nm, and uses this as a mask inspection light source. Has been developed.

  FIG. 7 shows a configuration of a conventional mask inspection light source 800. This conventional mask inspection light source 800 includes an argon laser 801a having a wavelength of 488 nm and a fiber laser 801b having a wavelength of 1064 nm. As shown in FIG. 7, 198.5 nm ultraviolet laser light is generated by the sum frequency generation of the second harmonic of an argon laser 801 a having a wavelength of 488 nm and a fiber laser 801 b having a wavelength of 1064 nm. Such a mask inspection apparatus is disclosed in Patent Document 1 or Non-Patent Document 3, for example.

  However, a conventional light source that generates ultraviolet light having a wavelength of 198.5 nm uses a large water-cooled argon laser. For this reason, not only the apparatus becomes huge, but also power consumption of several tens of kW is required. Furthermore, there is a problem that the running cost is high due to the replacement of the laser tube of the argon laser.

  Therefore, a compact and low power consumption solid-state laser that can generate ultraviolet light having a wavelength of 193 nm by wavelength conversion as much as about 100 mW has been developed. FIG. 8 shows a configuration of a conventional wavelength conversion type 193 nm solid-state laser 900. In this conventional wavelength conversion type 193 nm solid-state laser 900, a fiber laser having a wavelength of about 1547 nm is used as the fundamental laser 901, and a laser beam having a wavelength of 193 nm is generated using a wavelength conversion method as shown in FIG. Yes. This is shown in Patent Document 2, for example. This solid-state laser is called a conventional 193 nm solid-state laser.

  In the conventional 193 nm solid-state laser, a fiber laser is used as a fundamental wave laser. Further, this fiber laser is a combination of an oscillation stage and an amplification stage. A semiconductor laser (LD) is used for the oscillation stage. This LD is in a pulse operation by repeating ON / OFF. For this reason, the finally obtained laser beam with a wavelength of 193 nm is also pulsed, but the pulse repetition rate is around 100 kHz, and is said to be 2 MHz at the maximum.

  Here, the repetition number of a general solid-state laser will be described. In general, a solid-state laser can perform CW operation if excited by an LD or the like that emits light continuously (CW). Further, a pulse operation can be performed by exciting with a light source that emits pulses, such as a flash lamp. However, the flash lamp has a limit of about 100 Hz at most. On the other hand, it is known that the number of repetitions can be increased by operating the Q switch while CW excitation. For example, an Nd: YAG laser (referred to simply as a YAG laser), which is a typical solid-state laser, can perform a repetitive operation of 1 to 20 kHz. However, it is known that even a solid-state laser can be repeatedly operated up to about 300 kHz with an Nd: YVO4 laser.

  On the other hand, a laser oscillation mode of a solid-state laser includes what is called mode lock. Mode lock is a mode in which lasers are oscillated simultaneously in a number of longitudinal modes and the phases of the respective modes are aligned. This mode-locked solid-state laser can be operated in pulses at a time interval of period T = 2L / c, where L is the cavity length and c is the speed of light. Since the resonator length is generally around 1 m, the period is around 6.67 ns. That is, laser operation is performed at a repetition rate of around 150 MHz.

However, since the mode-locking operation needs to oscillate a number of longitudinal modes simultaneously, only lasers with a relatively wide laser spectral width (more precisely, a spectral band that provides a gain that enables laser oscillation) are possible. Operation. Therefore, this operation mode is often used in a fiber laser, a titanium sapphire laser, or the like that is known to have a relatively wide spectrum width.
JP 2006-73970 A JP-A-2005-351919 Proceedings of SPIE Vol. 446, pp. 265-278, 2004. Toshiba Review, Vol. 58, No. 7, pp. 58-61, 2003 Proceedings of SPIE Vol. 5592, pp. 43, 2005.

  The present inventors have discovered that when a pulse laser having a repetition rate of about several hundred kHz is used as a mask inspection light source, as in the case of a conventional 193 nm solid-state laser, the following problems occur.

  That is, in a two-dimensional photosensor (an image sensor in which light receiving elements are arranged two-dimensionally in the vertical and horizontal directions, that is, an imaging device) used in a mask inspection apparatus, the sensor is used at a line rate of 200 to 300 kHz. The charge generated in the inside is transferred. Usually, the two-dimensional photosensor accumulates electric charge for about 80% of the light receiving period for one line of about 3 to 5 μsec, and transfers electric charge for the remaining period of about 20%. In such a two-dimensional optical sensor, the sensitivity of the sensor may decrease with respect to light incident on the sensor during charge transfer. For this reason, when a pulsed laser such as a Q-switch type that can be repeatedly operated at about 300 kHz is used as a light source, the laser must be oscillated in synchronization with the line rate of the two-dimensional photosensor, and extra control is required. There was a problem that would be necessary.

  An object of the present invention is to provide an inspection apparatus, an inspection method, and a pattern substrate manufacturing method having a simple structure that is small in size and low in power consumption and does not require control for accurately synchronizing a two-dimensional imaging device and a laser light source. It is.

  The inspection apparatus according to the first aspect of the present invention irradiates the inspection object with a two-dimensional imaging apparatus that images a defect on the inspection object and a light having a repetition rate higher than a line rate of the two-dimensional imaging apparatus. A mode-locked laser light source. As described above, since the number of repetitions of the laser light source is higher than the line rate of the two-dimensional imaging device, the inspection performance of the inspection object can be improved without controlling the two-dimensional imaging device and the laser light source accurately. It becomes possible.

  The inspection apparatus according to a second aspect of the present invention is characterized in that, in the above-described inspection apparatus, the number of repetitions of light emitted from the laser light source is 100 times or more the line rate of the two-dimensional imaging apparatus. To do. In this way, by increasing the number of repetitions of the laser light source by 100 times or more of the line rate of the two-dimensional imaging device, light that is received during a light receiving period for one line in the two-dimensional imaging device other than during charge transfer. The number of pulses can be increased. Therefore, the unevenness for each line can be suppressed to 1/100 or less, and an accurate inspection can be performed.

  In the inspection apparatus according to the third aspect of the present invention, in the above-described inspection apparatus, the timing at which the image of the inspection object of the two-dimensional imaging apparatus is captured is a relative position between the inspection object and the two-dimensional imaging apparatus. It is characterized by being determined by. According to the present invention, the charge transfer timing in the two-dimensional imaging apparatus is determined so that the amount of movement of the inspection object actually observed becomes a constant amount for each period until the charge transfer in the light receiving period of each line. However, the variation in light quantity due to this can be made small enough to be ignored.

  An inspection apparatus according to a fourth aspect of the present invention is the inspection apparatus described above, further comprising an objective lens for observing the inspection object, wherein a working distance of the objective lens is 3 mm or more. To do. Thereby, interference of light does not occur between the mask surface and the objective lens, and generation of pseudo defects can be suppressed.

  An inspection apparatus according to a fifth aspect of the present invention is the inspection apparatus according to the above aspect, wherein the laser light source irradiates a laser beam obtained by wavelength-converting a laser beam from a solid-state laser or a fiber laser that oscillates in a wavelength of 1.06 μm band. It is characterized by doing. The present invention is particularly effective in such a case.

  An inspection method according to a sixth aspect of the present invention is an inspection method in which a defect on an inspection object is imaged and inspected by a two-dimensional imaging device, and the line of the two-dimensional imaging device is detected from a mode-locked laser light source. The inspection object is irradiated with light having a repetition rate higher than the rate, and the light transmitted through or reflected by the inspection object is imaged by the two-dimensional imaging device. Accordingly, it is possible to improve the inspection performance of the inspection object without performing control for accurately synchronizing the two-dimensional imaging device and the laser light source.

  An inspection method according to a seventh aspect of the present invention is characterized in that, in the above inspection method, light having a repetition number of 100 times or more a line rate of the two-dimensional imaging device is emitted from the laser light source. Thereby, the number of pulses of light received other than during charge transfer can be increased within the light receiving period for one line in the two-dimensional imaging device. Therefore, the unevenness for each line can be suppressed to at least 1/100 or less, and an accurate inspection can be performed.

  According to an eighth aspect of the present invention, there is provided an inspection method according to the above-described inspection method, wherein a timing at which the object to be inspected of the two-dimensional imaging device is imaged by a relative position between the object to be inspected and the two-dimensional imaging device. It is characterized by determining. As a result, even when the charge transfer timing in the two-dimensional imaging device is determined so that the amount of movement of the inspection object actually observed becomes a constant amount for each period until the charge transfer in the light receiving period of each line, The variation in the amount of light due to can be made so small that it can be ignored.

  The inspection method according to a ninth aspect of the present invention is characterized in that, in the above inspection method, the inspection object is observed with an objective lens having a working distance of 3 mm or more. Thereby, interference of light does not occur between the mask surface and the objective lens, and generation of pseudo defects can be suppressed.

  An inspection method according to a tenth aspect of the present invention is the above-described inspection method, wherein the laser light source converts the wavelength of a laser beam from a solid-state laser or a fiber laser that oscillates in a wavelength of 1.06 μm and converts the wavelength. A laser beam is irradiated to the inspection object. The present invention is particularly effective in such a case.

  A pattern substrate manufacturing method according to an eleventh aspect of the present invention includes a step of detecting a defect of a mask or a substrate that is the inspection object by any of the inspection methods described above. Thereby, the manufacturing yield of the pattern substrate can be improved.

  According to the present invention, it is possible to provide an inspection apparatus, an inspection method, and a pattern substrate manufacturing method having a simple structure that is small in size and low in power consumption and does not require control for accurately synchronizing a two-dimensional imaging device and a laser light source. Can do.

  Embodiments of the present invention will be described below with reference to the drawings. The following description shows preferred embodiments of the present invention, and the scope of the present invention is not limited to the following embodiments. In the following description, the same reference numerals denote the same contents.

  An inspection apparatus according to an embodiment of the present invention will be described with reference to FIGS. Here, as an example of an inspection apparatus, an inspection apparatus for a photomask (hereinafter simply referred to as a mask) used in a semiconductor manufacturing process will be described. FIG. 1 is a diagram showing a basic configuration of a mask inspection apparatus 1 according to the present embodiment. FIG. 2 is a diagram showing a configuration of the mask inspection light source 100 used in the mask inspection apparatus 1 according to the present embodiment. FIG. 3 is a diagram showing a configuration of the mask inspection apparatus main body 200.

  As shown in FIG. 1, the mask inspection apparatus 1 includes a mask inspection light source 100 and a mask inspection apparatus main body 200. The mask inspection light source 100 includes a mode-locked fundamental wave laser 101 and a wavelength conversion unit 102. As the fundamental wave laser 101, for example, a general high-power fiber laser can be used. The fundamental wave laser 101 performs a mode lock operation. Note that the mode-locking operation refers to making a short pulse train by performing phase synchronization between a plurality of longitudinal modes in laser oscillation. A mode-locked solid-state laser can be operated at a pulse repetition rate of 50 to 200 MHz. In the present embodiment, the fundamental laser 101 emits laser light L1 having a wavelength of 1064 nm at a repetition rate of 100 MHz, for example.

  The wavelength conversion unit 102 performs wavelength conversion of the laser beam L1 from the input fundamental wave laser 101. As illustrated in FIG. 2, the wavelength conversion unit 102 includes three nonlinear optical crystals 121, 122, and 123. The laser beam L 1 emitted from the fundamental laser 101 enters the wavelength conversion unit 102. Then, the wavelength is converted three times by the nonlinear optical crystals 121, 122, and 123, and the laser beam L2 is a linearly polarized laser beam having a wavelength of 213 nm in the ultraviolet region. This laser beam L2 advances to the mask inspection apparatus main body 200 and is used for mask defect inspection.

  Details of the configuration of the wavelength conversion unit 102 in the mask inspection light source 100 will be described with reference to FIG. The laser beam L 1 extracted from the fundamental laser 101 first enters the nonlinear optical crystal 121. As a result, a laser beam L12 having a wavelength of 532 nm, which is the second harmonic, is generated. As the nonlinear optical crystal 121, an LBO crystal or the like can be used. However, the laser light L12 includes unconverted laser light having a wavelength of 1064 nm.

  The laser beam L12 is incident on the nonlinear optical crystal 122. As a result, an ultraviolet laser beam L13 having a wavelength of 266 nm, which is the second harmonic, that is, the fourth harmonic of the laser beam L1, is generated. As the nonlinear optical crystal 122, a BBO crystal or the like can be used. However, the laser light L13 includes unconverted laser light with a wavelength of 1064 nm and laser light with a wavelength of 532 nm.

  The laser beam L13 is incident on the nonlinear optical crystal 123. As a result, the sum frequency is generated by the near-infrared laser beam having a wavelength of 1064 nm and the ultraviolet laser beam having a wavelength of 266 nm, and an ultraviolet laser beam L2 having a wavelength of 213 nm is generated. Since the laser beam L2 is generated by wavelength conversion, the pulse operation with the same repetition rate of 100 MHz as the laser beam L1 that is the fundamental wave is performed. As the nonlinear optical crystal 123, a BBO crystal or the like can be used.

  Next, the configuration of the mask inspection apparatus body 200 in the mask inspection apparatus 1 according to the present embodiment will be described with reference to FIG. As shown in FIG. 3, the mask inspection apparatus main body 200 includes a beam splitter 201, mirrors 202a and 202b, λ / 4 wavelength plates 203a and 203b, a condenser lens 204, a polarizing beam splitter 205, an objective lens 206, an imaging lens 207, It has a two-dimensional optical sensor 208, precision stages 210a and 210b, movable parts 211a and 211b, fixed parts 212a and 212b, a control device 213, and the like. The mask inspection apparatus 1 according to the present embodiment is attached to a pellicle frame 220c that is disposed so as to surround the outside of the pattern surface 220b formed on the mask substrate 220a, as an example of an inspection target. The mask 220 made of the pellicle 220d is inspected.

  The laser beam L2 that is linearly polarized light with a wavelength of 213 nm emitted from the mask inspection light source 100 strikes the beam splitter 201 and is split. About 30% of the laser light L 2 is reflected by the beam splitter 201. The reflected laser light L3 is used as transmitted illumination. Further, the remaining 70% of the laser light L2 passes through the beam splitter 201. The transmitted laser beam L4 is used as reflected illumination.

  The laser beam L3 is reflected by the mirrors 202a and 202b and travels upward in FIG. 3 like the laser beam L5. The laser light L5 passes through the λ / 4 wavelength plate 203a and becomes circularly polarized laser light L6. The laser light L6 travels while being narrowed down through the condenser lens 204, passes through the mask substrate 220a of the mask 220, and is focused on the observation region of the mask pattern surface 220b.

  On the other hand, the laser light L4 that is reflected illumination hits the polarization beam splitter 205 and is reflected, and proceeds downward in FIG. 3 like the laser light L8. The laser beam L8 passes through the λ / 4 wavelength plate 203b and becomes circularly polarized laser beam L9. The laser light L9 enters the objective lens 206 and travels while being narrowed down, and is focused on the observation area of the pattern surface 220b, similar to the transmitted illumination.

  Of the diffracted light generated from the observation area illuminated by the transmission illumination and the reflection illumination as described above, the diffracted light traveling upward in FIG. 3 passes through the objective lens 206, passes through the λ / 4 wavelength plate 203b, and travels upward. move on. The polarization of the laser light traveling upward through the λ / 4 wavelength plate 203b will be described below.

  Of the diffracted light generated from the observation region, the light generated by the transmitted illumination irradiated from below the mask 220 is circularly polarized light as described above, and thus linearly polarized light passes through the λ / 4 wavelength plate 203b. Return to. However, the polarization direction is such that the light passes through the polarizing beam splitter 205 with high transmittance. Therefore, the laser light passes through the imaging lens 207 and reaches the two-dimensional optical sensor 208.

  In addition, among the diffracted light generated from the observation region, the light generated by the reflected illumination irradiated from above the mask 220 is the one reflected by the laser light L9. Therefore, when the light passes through the λ / 4 wavelength plate 203a again, The light travels upward in the polarization direction orthogonal to the circularly polarized laser beam L9 traveling downward. As a result, the laser light passes through the polarization beam splitter 205, passes through the imaging lens 207, and reaches the two-dimensional optical sensor 208.

  As the two-dimensional optical sensor 208, for example, a TDI sensor that operates at a line rate of 300 kHz can be used. Note that the observation area of the pattern surface 220 b of the mask 220 is enlarged and projected onto the two-dimensional optical sensor 208 by the objective lens 206 and the imaging lens 207. Thereby, a minute defect can be detected by magnifying and observing a minute observation region.

  The mask 220 of the object to be inspected is placed and sucked on the movable parts 211a and 211b of the precision stages 210a and 210b having a linear scale. These movable portions 211a and 211b are configured to smoothly reciprocate (reciprocate scan) on the fixed portions 212a and 212b. The real-time position of the mask 220 by this scanning can be detected by monitoring the movement of the movable parts 211a and 211b. That is, in FIG. 3, the arrows protruding from the fixing portions 212a and 212b indicate the laser light. The laser light strikes the side surfaces of the movable portions 211a and 211b, and the reflected light is detected there, whereby the positions of the movable portions 211a and 211b are detected in real time.

  In the present embodiment, the timing for capturing an image of the mask 220 of the two-dimensional photosensor 208 that is a two-dimensional imaging device is determined by the relative position between the mask 220 and the two-dimensional photosensor 208. The position information of the movable parts 211a and 211b detected as described above is transmitted to the control device 213 as indicated by arrows in FIG. The control device 213 controls the line rate of the two-dimensional photosensor 208, that is, the imaging timing, based on the position information of the movable parts 211a and 211b.

  Conventionally, in a conventional light source that operates at several hundred kHz, it may be difficult to control the laser oscillation timing from the outside depending on the structure of the light source. In such a case, on the contrary, an attempt was made to operate the line rate of the two-dimensional photosensor in accordance with the timing of laser oscillation, but the following problems occurred. In other words, if the timing of laser oscillation is exactly constant, the two-dimensional photosensor needs to be fixed at a line rate with exactly constant timing. However, when the line rate of the two-dimensional photosensor is fixed and the speed of the stage during constant-speed scanning fluctuates, the optical image of the mask pattern surface acquired by the two-dimensional photosensor is stretched or reduced. Will end up. For this reason, the inspection performance may be deteriorated. As described above, controlling the line rate of the two-dimensional photosensor by the operation of the light source cannot compensate for variations in scan speed, and has been a factor that deteriorates inspection performance.

  For this reason, as described above, the line rate of the two-dimensional photosensor 208 is fine based on the information of the scanning speed of the mask 220 (more precisely, the real-time positions of the movable parts 211a and 211b of the precision stages 210a and 210b). Adjusted. As a result, an accurate optical image can be obtained, and a decrease in inspection performance can be suppressed.

  As described above, as a method of determining the charge transfer timing in the two-dimensional photosensor 208, the amount of movement of the mask 220 to be actually observed is constant for each period (charge accumulation period) until the charge transfer in the light receiving period of each line. If determined to be, the length of the light receiving period of one line may vary. FIG. 4 is a diagram for explaining the line rate of the two-dimensional photosensor 208. As shown in FIG. 4A, the period of normal light reception (charge accumulation period) is the period other than the period for transferring charges in the light reception period for one line. Since the light receiving period for one line varies depending on the amount of movement of the mask 220, the length of the charge accumulation period for normal light reception may vary as shown in FIG. 4B.

  Conventionally, when a 300 kHz light source having the same number of repetitions as a two-dimensional photosensor is used, if the length of the light receiving period for one line varies, no pulse is emitted within the light receiving period, or two shots are emitted. Sometimes. Therefore, conventionally, it has been necessary to control the laser oscillation of the light source in synchronization with the line rate in the two-dimensional photosensor.

  However, the line rate of the two-dimensional optical sensor 208 used in the mask inspection apparatus 1 according to the present embodiment is 300 kHz, whereas the pulse repetition number of the laser light L2 that is illumination light is 100 MHz. Thus, in the present invention, the mode-locked mask inspection light source 100 irradiates the mask 220 with light having a pulse repetition rate that is 300 times higher than the line rate of the two-dimensional optical sensor 208. As described above, since the repetition rate of the laser light source is higher than the line rate of the two-dimensional imaging device, the light receiving period for one line is long even if control for accurately synchronizing the two-dimensional imaging device and the laser light source is not performed. When there is a fluctuation, there is no problem that no pulse is irradiated within the charge accumulation period. Therefore, in the present invention, a control system for accurately synchronizing the two-dimensional imaging device and the laser light source is not required, and the configuration of the inspection apparatus can be simplified. In addition, the mask 220 can be imaged satisfactorily, and the inspection performance can be improved.

  The pulse repetition number of the laser light emitted from the mask inspection light source 100 is preferably 100 times or more the line rate of the two-dimensional optical sensor 208. In the present embodiment, the line rate of the two-dimensional optical sensor 208 is 300 kHz, whereas the pulse repetition number of the laser light L2 that is illumination light is 100 MHz. For this reason, the observation region is irradiated with about 333 pulses of pulsed laser light within the light receiving period for one line of the two-dimensional optical sensor 208. As described above, the number of pulses of light received other than during charge transfer within the light receiving period for one line in the two-dimensional imaging device (the number of pulses within the period of normal light reception (charge accumulation period), hereinafter effective) Called the number of pulses).

  Therefore, even if there is a variation of 10% in each pulse energy, the variation in the amount of light (total light energy) corresponding to the number of effective pulses for each line can be reduced to 1% or less. Further, even if the length of the light receiving period for one line may vary by about 1%, for example, the variation of the total energy of the pulsed laser light incident within the light receiving period for one line can be reduced. Can do. Therefore, according to the present invention, the amount of movement of the inspected object that is actually observed for the charge transfer timing in the two-dimensional photosensor 208 is made constant for each period until the charge transfer in the light receiving period of each line. Even if determined, the variation in the amount of light of each line due to this can be made so small that it can be ignored.

  As described above, in the present embodiment, it is not necessary to synchronize the two-dimensional photosensor 208 and the mask inspection light source 100. This eliminates the need for a control system that accurately synchronizes the two-dimensional imaging device and the laser light source, thereby simplifying the configuration of the inspection apparatus. Further, the line rate of the two-dimensional photosensor 208 can be finely adjusted by monitoring the position of the mask 220. Therefore, the mask 220 can be imaged well, and the inspection performance can be improved.

  Here, the working distance (WD) of the objective lens 206 will be described with reference to FIG. The working distance is the distance between the observation area of the mask 220 that is an object to be inspected and the tip of the objective lens 206 focused on this. That is, as shown in FIG. 5, the distance from the most advanced lens 206a of the objective lens 206 to the pattern surface 220b of the mask 220 is the working distance. In the present embodiment, since the height of the pellicle frame 220c is 6 mm, a general objective lens having a working distance of 8 to 10 mm is used.

  In this regard, when the working distance of the objective lens 206 is shorter than the coherence length of the laser light emitted from the mask inspection light source 100, the objective lens 206 is reflected on the surface of the most advanced lens 206a (the lens closest to the mask 220). There may be a case where slight light and light reflected by the pattern surface 220b of the mask 220 interfere with each other.

Table 1 shows the coherent lengths of a conventional continuous CW laser, a Q-switched solid-state laser, a pulse laser based on ON / OFF of a semiconductor laser, and a mode-locked solid-state laser used in the present invention. The coherent length shown in Table 1 is calculated by a general formula where the speed of light c is divided by the spectral width Δν of each type of laser. The spectral width of each type of laser varies depending on the detailed structure of each laser. For example, in the case of a continuous CW laser that is an ultraviolet laser having a wavelength close to 200 nm, Optics Letters, Vol. 8, no. 2, pp. 73-75. Δν is about 1 MHz. Therefore, the coherent length of the continuous CW laser is about 300 m. In the case of a Q-switch solid state laser, SPIE, Vol. 3679, pp. 497-503. Δν is about 0.2 pm. For this reason, the coherent length of the Q-switched solid-state laser is about 19 cm.

  As shown in Table 1, the conventional light source has a coherent length of several tens to several hundreds of mm. For this reason, when a general objective lens 206 having a working distance of 8 to 10 mm is used, the working distance is almost equal to or shorter than the coherent length. As a result, interference occurs between the light generated from the pattern surface 220b of the mask and the light slightly reflected from the lower surface of the most advanced lens 206a of the objective lens 206. The acquired optical image may be disturbed, and the inspection performance may be deteriorated.

  On the other hand, the spectral width of the laser light extracted from the mode-locked solid-state laser is extremely wide as 100 GHz or more. For example, Laboratory for Laser Energys, Vol. 97, pp. 36-39. The wavelength is about 1055 nm, and the wavelength width is about 0.9 nm. Therefore, the coherent length of this mode-locked solid-state laser is as short as about 1.24 mm. However, in the mask inspection light source 100 according to the present embodiment, the wavelength of the laser light is converted and ultraviolet light having a wavelength of about 211 nm, which is a fifth harmonic wave, is generated. . Therefore, in the mask inspection light source 100 according to the present embodiment in which the wavelength of the laser beam of the mode-locked solid-state laser is converted, the coherent length is further shortened to about 0.25 mm.

  Thus, in the present invention, the mode-locked laser is used as the fundamental laser. For this reason, the spectral width of the laser beam L2 extracted from the mask inspection light source 100 of the present invention is 100 to 1000 GHz, which is an order of magnitude larger than that of other types of laser beams. Accordingly, the coherent length is as small as 0.3 to 3 mm. For this reason, the working distance (WD), which is the distance between the objective lens 206 and the pattern surface 220b of the mask 220, can be made longer than the coherent length.

  Therefore, even when a general objective lens 206 having a working distance of about 8 to 10 mm is used, no light interference occurs between the pattern surface 220b of the mask 220 and the objective lens 206. Thereby, deterioration of inspection performance can be controlled. Even if the working distance of the objective lens used in the mask inspection apparatus main body is shorter than 8 to 10 mm, it can be used as long as it is longer than 3 mm. Therefore, when inspecting an EUV mask that is not provided with a pellicle, it is possible to use the objective lens 206 having a shorter working distance.

  Next, another configuration of the mask inspection light source suitable for the mask inspection apparatus 1 of the present invention will be described with reference to FIG. FIG. 6 is a diagram illustrating a configuration of the mask inspection light source 300. As shown in FIG. 6, the mask inspection light source 300 includes a mode-locked fundamental wave laser 301 and a wavelength conversion unit 302. In the mask inspection light source 300, a mode-locked titanium sapphire laser is used as the fundamental laser 301. The laser beam L31 extracted from the fundamental laser 301 is a pulsed laser beam having a wavelength of 820 nm and a repetition rate of about 80 MHz.

  The wavelength converter 302 performs wavelength conversion of the laser beam L31 from the input fundamental wave laser 301. As illustrated in FIG. 6, the wavelength conversion unit 302 includes three nonlinear optical crystals 321, 322, and 323. The laser beam L31 emitted from the fundamental laser 301 enters the wavelength converter 302. Then, the wavelength is converted three times by the nonlinear optical crystals 321, 322, and 323 to become a linearly polarized laser beam L 34 in the ultraviolet region having a wavelength of 205 nm. This laser beam L3 advances to the mask inspection apparatus main body 200 and is used for mask defect inspection.

  Specifically, the laser beam L31 is incident on the nonlinear optical crystal 321 of the wavelength conversion unit 302. Thereby, the laser beam L32 having a wavelength of 410 nm, which is the second harmonic, is emitted. As the nonlinear optical crystal 321, an LBO crystal or the like can be used. However, the laser light L32 includes unconverted laser light having a wavelength of 820 nm.

  The laser beam L32 is incident on the nonlinear optical crystal 322. As a result, a laser beam L33 having a wavelength of 273.3 nm, which is the sum frequency of the wavelength of 410 nm and the wavelength of 820 nm, is emitted. As the nonlinear optical crystal 322, a BBO crystal or the like can be used. However, the laser light L33 includes unconverted laser light having a wavelength of 820 nm. When this laser beam L33 enters the nonlinear optical crystal 323, a laser beam L34 having a wavelength of 205 nm is emitted. This laser beam L34 is guided to the mask inspection apparatus main body. As the nonlinear optical crystal 323, a BBO crystal or the like can be used. Since the laser beam L34 is generated by wavelength conversion, the pulse operation with the same number of repetitions as the laser beam L31 that is the fundamental wave is performed.

  The line rate of the two-dimensional optical sensor 208 used in the mask inspection apparatus 1 according to the present embodiment is 300 kHz, whereas the pulse repetition rate of the laser light L34 extracted from the mask inspection light source 300 is 80 MHz. . That is, the pulse repetition number of the laser beam L34 extracted from the mask inspection light source 300 is higher than the line rate of the two-dimensional photosensor 208. Therefore, the mask 220 can be imaged satisfactorily and the inspection performance can be improved even if the control for accurately synchronizing the two-dimensional imaging device and the laser light source is not performed as described above. In the mask inspection light source 300 of this embodiment, a typical titanium sapphire laser is used as a wavelength tunable laser. Therefore, depending on the type of nonlinear optical crystal used in the wavelength conversion unit, the laser beam L34 can be further shortened.

  As described above, according to the present invention, since it is not necessary to control the light source for each line rate of the two-dimensional photosensor used in the inspection apparatus main body, the control function of the entire system can be simplified. Even if an objective lens having a working distance of 8 to 10 mm is used, no interference occurs with the mask pattern surface, so that the number of pseudo defects generated during inspection can be greatly reduced.

  Furthermore, since the working distance can be shortened to nearly 3 mm particularly in the light source of the present invention, for example, when configuring a mask inspection apparatus dedicated to inspection of a mask that does not use a pellicle, such as an EUV mask, it is 3 to 5 mm. An objective lens with a short working distance can be used.

  In the light source of the present invention, since it becomes easy to operate at a pulse repetition rate of 50 to 200 MHz, the energy of one pulse is as extremely small as 1 to 4 pJ. Therefore, it becomes 1/100 or less as compared with a pulse light source adjusted to 200 to 300 kHz of the line speed of a general two-dimensional photosensor. For this reason, not only the optical components of the light source itself but also the optical components in the mask inspection apparatus main body can be greatly reduced.

  In addition, by using the inspection apparatus of the present invention for inspection of masks and mask blanks, or inspection processing of semiconductor wafers, the defect inspection of the substrate is performed and the pattern substrate is manufactured, thereby improving the manufacturing yield of semiconductor devices. Can do. In manufacturing a typical semiconductor device, a mask original plate is set in an exposure apparatus, and a resist-formed wafer is exposed using light, an ion beam, an electron beam, or the like. The semiconductor wafer subjected to the exposure process is subjected to a development process, and a resist pattern is formed on the wafer. Thereby, a pattern substrate is manufactured.

  With the mask inspected using the inspection apparatus or inspection method of the present invention, or the mask using mask blanks, the exposure process in the manufacture of the semiconductor device can be carried out. In addition, a semiconductor device can be manufactured by subjecting a wafer inspected using the inspection apparatus or inspection method of the present invention to a widely known semiconductor device manufacturing process. In addition, you may perform defect correction using a well-known defect correction apparatus.

It is a figure which shows the structure of the mask inspection apparatus which concerns on embodiment. It is a figure which shows the structure of the mask test | inspection light source which concerns on embodiment. It is a figure which shows the structure of the mask inspection apparatus main body which concerns on embodiment. It is a figure for demonstrating the line rate of a two-dimensional photosensor. It is a figure for demonstrating the working distance of an objective lens. It is a figure which shows the other structure of the mask inspection light source which concerns on embodiment. It is a figure which shows the structure of the conventional mask inspection light source. It is a figure which shows the structure of the conventional mask inspection light source.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Mask inspection apparatus 100 Mask inspection light source 101 Fundamental wave laser 102 Wavelength conversion part 121,122,123 Nonlinear optical crystal 200 Mask inspection apparatus main body 201 Beam splitter 202a, 202b Mirror 203a, 203b (lambda) / 4 wavelength plate 204 Lens 205 Polarization beam splitter 206 Objective lens 206a State-of-the-art lens 207 Imaging lens 208 Two-dimensional optical sensors 210a and 210b Precision stages 211a and 211b Movable parts 212a and 212b Fixed part 213 Controller 220 Mask 220a Mask substrate 220b Pattern surface 220c Pellicle frame 220d Pellicle frame 220 Mask inspection Light source 301 Fundamental wave laser 321, 322, 323 Nonlinear optical crystal L1 Laser light L2, L3, L4, L5, L6, L7, L8, L9 with a wavelength of 1064 nm Laser beam L12 having a wavelength of 213 nm Laser beam L13 including a wavelength of 532 nm and a wavelength of 1064 nm Laser beam L31 including a wavelength of 266 nm, a wavelength of 532 nm, and a wavelength of 11064 nm Laser beam L32 having a wavelength of 820 nm Laser beam L33 having a wavelength of 410 and a wavelength of 820 nm Laser beam L34 including 3 nm and wavelength 820 nm Laser beam with wavelength 205 nm

Claims (11)

A two-dimensional imaging device for imaging defects on the inspection object;
A mode-locked laser light source that irradiates the inspection object with light having a repetition rate higher than the line rate of the two-dimensional imaging device;
An inspection apparatus comprising:   The inspection apparatus according to claim 1, wherein the number of repetitions of light emitted from the laser light source is 100 times or more a line rate of the two-dimensional imaging apparatus.   The inspection apparatus according to claim 1, wherein a timing at which the image of the inspection object of the two-dimensional imaging apparatus is captured is determined by a relative position between the inspection object and the two-dimensional imaging apparatus. An objective lens for observing the inspection object;
The inspection apparatus according to claim 1, wherein a working distance of the objective lens is 3 mm or more.   The said laser light source irradiates the laser beam which converted the wavelength of the laser beam from the solid-state laser or fiber laser which oscillates in a wavelength 1.06 micrometer band, The any one of Claims 1-5 characterized by the above-mentioned. Inspection device. An inspection method for inspecting the inspection object by imaging a defect on the inspection object with a two-dimensional imaging device,
The test object is irradiated with light having a repetition rate higher than the line rate of the two-dimensional imaging device from a mode-locked laser light source,
An inspection method in which light transmitted through or reflected by the inspection object is imaged by the two-dimensional imaging device.   The inspection method according to claim 6, wherein the laser light source emits light having a repetition rate of 100 times or more a line rate of the two-dimensional imaging device.   The inspection method according to claim 6 or 7, wherein a timing at which the inspection object of the two-dimensional imaging device is imaged is determined based on a relative position between the inspection object and the two-dimensional imaging device.   9. The inspection method according to claim 6, 7 or 8, wherein the inspection object is observed with an objective lens having a working distance of 3 mm or more.   The laser light source performs wavelength conversion on laser light from a solid-state laser or fiber laser that oscillates in a wavelength of 1.06 μm band, and irradiates the object to be inspected with the wavelength-converted laser light. 10. The inspection method according to any one of 9 above.   The manufacturing method of a pattern board | substrate including the process of detecting the defect of the mask which is the said to-be-inspected object, or a board | substrate with the inspection method of any one of Claims 6-10.

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