TW201802621A - Device and method for measuring overlay error - Google Patents

Abstract

Disclosed is a device and method for measuring an overlay error. A measuring light adjustment assembly for adjusting measuring light to be centrosymmetric relative to the optical axis of a microobjective is added to the device, so that the measuring light forms positive and negative level diffraction light by passing through this device and through an overlay measurement mark, and finally a diffraction spectrum of the positive and negative level diffraction light is displayed on a detector, wherein the spectrum of the positive level diffraction light and the negative level diffraction light on the diffraction spectrum are staggered to each other. A control system calculates an overlay error according to the diffraction spectrum, such that a broadband light source can be used during resource selection. Therefore, by means of this device and method, the wavelength range of measuring light is wider and any light spot-shaped light source can be used, such that the acquired measuring signals are more abundant, the precision of measurement is improved and the utilization rate of light energy is higher. A small-sized overlay measurement mark also can receive measuring light, and the device and method are also suitable for small-sized measured objects, thereby being better adapted to fine semiconductor products.

Description

Device and method for measuring overlap error

The present invention relates to the field of semiconductor lithography, and in particular, to a device and method for measuring overlapping errors.

According to the lithography measurement technology roadmap given by ITRS (International Technology Roadmap for Semiconductor), with the critical size of lithography patterns entering 22nm and below process nodes, especially the extensiveness of Double Patterning technology In the application, the measurement accuracy requirements for the overlay of lithographic process parameters have entered the field of sub-nanometers. Due to the limitation of imaging resolution, the traditional Imaging-Based overlay (IBO) technology based on imaging and image recognition has gradually failed to meet the requirements of new process nodes for overlay measurement. Diffraction-Based overlay (DBO) based on diffracted light detection is gradually becoming the main method of overlay measurement.

Because the diffraction angle of the diffracted light changes with the incident angle of the incident light, the incident light of different angles is diffracted by the diffraction grating mark to form the diffraction light of each diffraction order, and the diffraction light of each diffraction order is formed. The light intensity distribution is the angle-resolved spectrum of reflected light. For example, in Chinese patent CN1916603A (application number: 200510091733.1, published on February 21, 2007), in a ring illumination mode, the angle-resolved spectrum of reflected light formed by diffraction light of each diffraction order is on a CCD detector Distribution.

Based on the above principles, a US patent US7791727B2 (application number: 10/918742, published on December 16, 2006) discloses a DBO technology that measures the formation of light by diffraction and reflection by overlapping marks. In the angle-resolved spectrum of the diffracted light, the asymmetry between the same diffraction orders gives the stacking error of the stacking mark.

The patent discloses the device structure diagram of this technical means. As shown in FIG. 1, the light emitted from the light source 2 passes through the lens group L2 and the filter device 30 in order to form a narrow-band incident light, and the objective lens L1 focuses the incident light. Onto the overlay mark of the substrate 6. The detector 32 is located on the back focal plane of the objective lens L1. The diffracted light of the overlapping marks is collected by the objective lens L1 and reflected by the reflecting surface 34 to be received by the detector 32. The detector 32 measures the angle-resolved spectrum of the reflected light formed by the diffraction and reflection of the light at various angles by the overlapping marks. In order to obtain a wide range of angle-resolved spectra, a large numerical aperture (NA) objective lens L1 is used in this scheme. Because the diffraction angles of the diffracted light of different wavelengths are different, in order to prevent overlap between different wavelength angular spectra, the solution uses a filter device 30 to filter the light emitted from the light source 2 to form a narrow-band measurement light. In principle, this solution can only measure the resolution angle of reflected light at one wavelength at a time. In order to perform multi-wavelength measurement, a solution provided in the patent for the pupil surface 40 of the objective lens L1 can be used to measure the angular resolution spectrum at multiple discrete wavelengths simultaneously. Nonetheless, the patent can only measure a limited number of discrete wavelengths.

It can be known from this that the wavelength range of the measurement light used for overlapping error measurement in the conventional technology is limited. In the face of complex semiconductor manufacturing processes, there may be certain process adaptability problems. For example, if the light wavelength of the measurement light is exactly four times the thickness of the thin film film covered on the semiconductor, interference effects are likely to occur and the reflectance of the light reflected from the superimposed mark is greatly reduced, resulting in a decrease in measurement accuracy. Secondly, the large NA objective lens scheme used in the conventional technology has a smaller focal depth range. Generally speaking, the effective numerical aperture used for measuring light is greater than 0.9. Based on a typical measuring light wavelength of 600 nm, the effective focal depth range is less than 1 μm. Therefore, during the measurement process, the position of the focal plane must be controlled with high precision, which will affect the measurement speed and accuracy. In addition, in this case, if the focal plane is not well controlled, the spot of the measurement light will easily spread to the measured object. A lot of stray light is formed outside the overlapping marks, which seriously interferes with the measurement process.

Therefore, it is necessary to invent a device and method for measuring overlapping errors, which can not only adapt to a wider range of measurement light, but also better adapt to semiconductors that are becoming more refined.

In order to solve the above problems, the present invention proposes a device and method for measuring overlapping errors. A measurement light adjustment element capable of adjusting measurement light to be symmetrical about the optical axis center of a microscope objective lens is added to the device, so that the measurement light passes through the device. After passing through the pair of measurement marks to form positive and negative order diffraction light, and finally display the diffraction spectrum of the positive and negative order diffraction light on the detector, the control system calculates the stacking error based on the diffraction spectrum, so the device and method can be used A wider band of light source is used to measure the stacking error, so that the wavelength range of the measurement light is wider, and the diffraction spectrum is a spectrum of positive and negative orders of diffraction light, so the measurement signals obtained are more abundant, the measurement accuracy is improved, and the utilization rate of light energy Higher, it can adapt to the small size of the test object, making it more suitable for modern semiconductor products that are becoming more refined.

In order to achieve the above object, the present invention provides a device for measuring overlapping errors, including an illumination system for generating measurement light; a measurement light adjustment element; a measurement beam splitter for splitting the measurement light, the illumination system, The measuring light adjusting element and the measuring beam splitter are arranged on the first straight line in sequence; a micro objective lens is used to collect the measuring light and project it to the surface of the object to be measured with a grating structure and stacked measurement marks; a detector is used After detecting the diffraction spectrum formed by the diffraction of the measurement light incident on the stack of measurement marks, the detector is located on the pupil surface of the microscope objective lens, and the detector, the measurement beam splitter, the microscope objective lens, and the measured object Arranged in sequence on a second straight line, the first straight line intersects the second straight line; a control system, connected to the detector signal, and used to form a winding formed by overlapping measurement marks displayed on the detector The measurement light adjustment element is used to adjust the measurement light to be symmetrical about the optical axis center of the microscope objective lens, so that the formed diffraction spectrum is positive The spectra of negative order diffracted light and diffracted light are staggered.

Preferably, a straight line passing through the center of the measurement light adjustment element and perpendicular to the measurement light adjustment element and the optical axis of the microscope objective lens are symmetrical with respect to a normal line of the measurement beam splitter.

Preferably, the measurement light adjusting element is a ring-shaped diaphragm or a slit, and the ring-shaped diaphragm is composed of two quarter rings that are symmetrical about the center of the circle.

Preferably, it further includes an incident beam splitter located between the illumination system and the measurement light adjusting element.

Preferably, the measurement light adjusting element is an optical fiber cluster having a linear exit surface.

Preferably, the exit surfaces of the optical fiber clusters are linearly arranged optical fiber end faces.

Preferably, the exit surface of the optical fiber cluster further includes a collimating element, which is located on an optical path from which the measurement light exits from the exit surface of the optical fiber cluster, and the collimating element is used to collimate light emitted from the optical fiber cluster.

Preferably, the collimating element is a concave lens array or a self-focusing system.

Preferably, the incident surface of the optical fiber cluster is a two-dimensional rectangular surface or a three-dimensional structure.

Preferably, the three-dimensional structure is a hemisphere or an ellipsoid.

Preferably, it further comprises a monitoring light element located on an optical path after the measurement light penetrates the measurement beam splitter, and the control system further measures a measurement light signal formed by reflecting and diffracting the measurement light from the measured object. Normalize the monitoring light signal formed with the measurement light reflected or diffracted from the monitoring light element.

Preferably, the monitoring light element includes, in order: a lens group, located on an optical path after the measurement light penetrates the measurement beam splitter; a monitoring optical element, located on an optical path after the measurement light penetrates the lens group, For reflecting or diffracting the measurement light and passing at least a part of the reflected light or the diffracted light thus generated through the lens group.

Preferably, the monitoring optical element is a monitoring grating, and the period of the monitoring grating is the same as the period of the grating of the pair of measurement marks, and the monitoring grating is placed obliquely so that only the diffracted light from the monitoring grating is diffracted. The -1 order diffraction light can pass through the lens group, reach the measurement beam splitter after passing through the lens group, and be reflected by the measurement beam splitter to the detector.

Preferably, the monitoring optical element is two reflecting mirrors placed perpendicular to each other, and the measuring light passing through the lens group is reflected by the two reflecting mirrors to the measuring beam splitter and is measured by the measuring beam splitting mirror. Reflected to the detector.

Preferably, the measured object is carried by a film carrier.

Preferably, it further comprises a polarizing device, which is located on an optical path where the measurement light is incident on the detector.

Preferably, the polarizing device includes a polarizer located between the measurement light adjusting element and the measurement beam splitter; and an analyzer located between the measurement beam splitter and the detector.

Preferably, it further comprises a compensator, which is located on the optical path from which the measurement light exits from the polarizer, and is used for measuring the reflectance change and the phase change of the measurement light having a polarization state.

Preferably, the measurement light generated by the illumination system is at least one of ultraviolet light, visible light, and infrared light.

The invention also provides a method for measuring overlapping errors. A measurement light is emitted by an illumination system, and a measurement light adjustment element is provided between the illumination system and the measurement beam splitter. The measurement light adjustment element forms the measurement light into the display light. After the center of the optical axis of the micro-objective lens is symmetrical, it is reflected by the measuring beam splitter and incident on the measured object after passing through the micro-objective lens. The measuring light is diffracted by the measured object to form positive and negative orders of diffraction light. When the microscope objective lens and measuring beam splitter reach the detector to form a diffraction spectrum in which the positive diffraction spectrum and the negative diffraction spectrum are staggered from each other, the control system calculates the stack of the measured object based on the diffraction spectrum on the detector. On error.

Preferably, a monitoring light element is provided on the optical path after the measurement light exits from the measurement light adjustment element and penetrates the measurement beam splitter, and then the measurement light passes through the measurement light adjustment element and the measurement beam splitter and then enters the measurement beam. The monitoring light element is reflected or diffracted by the monitoring light element, and at least a part of the reflected light or diffracted light generated by the monitoring light element passes through the measuring beam splitter and is reflected by the measuring beam splitter to the detector, and will be transmitted from the measured object. The measurement light signal formed by the reflected and diffracted measurement light and the monitoring light signal formed by the reflected or diffracted measurement light from the monitoring light element are normalized to eliminate the interference of the light intensity fluctuation on the measurement stacking error.

Preferably, the method specifically includes the following steps: Step 1: Calculate the sensitivity of each primitive point on the diffraction spectrum displayed by the detector, set a threshold for the sensitivity, and filter out the primitive points whose sensitivity on the diffraction spectrum is less than the threshold. Step 2: Generate the relationship between the difference between the intensity of the positive-order diffracted light and the intensity of the negative-order diffracted light and the error value of the step unit overlap; Step 3: The positive-order diffracted light obtained according to step 2. The graph of the relationship between the difference between the light intensity and the negative diffraction light intensity and the step unit stacking error value is repeated iteratively. Each iterative operation produces an intermediate image. When the iterative operation calculates a symmetrical intermediate image, Then the iterative operation is completed, and the total step size formed by the iterative operation is the overlay error of the overlay measurement mark.

。Preferably, two stacked measurement marks arranged in a row are made on the measured object, which are a first stacked measurement mark and a second stacked measurement mark, respectively, and the first stacked measurement mark sets a location of the first stacked measurement mark. The overlap error between the patterned photoresist of the upper layer and the patterned photoresist of the upper layer is 0, and the offset of the patterned photoresist of the upper layer and the patterned photoresist of the second layer of the pair of measurement marks is set as

.

，其中

為照射在第一疊對測量標記上的光強，

為照射在第二疊對測量標記上的光強。Preferably, the method of calculating the sensitivity of each primitive point on the diffraction spectrum displayed by the detector in step 1 is:

,among them

In order to illuminate the light intensity on the first stack of measurement marks,

The intensity of the light irradiated on the second pair of measurement marks.

，其中

為運行一個步進單位疊對誤差

時所對應的探測器接收到的光強變化量在控制系統上的圖像。Preferably, in the step 2, the relationship diagram between the difference between the positive diffraction light intensity and the negative diffraction light intensity of the measurement light and the step unit stacking error value is generated according to the formula:

,among them

Overlap error for running one step unit

The image of the change in light intensity received by the corresponding detector at the time on the control system.

，其中m為反覆運算的迴圈次數，當

值為0時，m所對應的值為n，則疊對測量標記的疊對誤差OV_value=n×OV_step。Preferably, the intermediate image value corresponding to the intermediate image generated by each iterative operation in step 3

, Where m is the number of loops of the iteration, when

When the value is 0 and the value corresponding to m is n, the overlap error of the overlap measurement mark is OV_value = n × OV_step.

Compared with the conventional technology, the present invention has the following beneficial effects: the present invention provides a device for measuring overlapping errors, including an illumination system for generating measurement light; a measurement light adjustment element; a measurement beam splitter for Measuring light splitting, the illumination system, measuring light adjusting element, and measuring beam splitter are arranged on the first straight line in sequence; a micro objective lens is used to collect the measuring light and project it to the measured mark with a pair of measuring marks having a grating structure The surface of the object; a detector for detecting the diffraction spectrum formed by the diffraction of the measurement light after it is incident on the pair of measurement marks, the detector is located on the pupil surface of the microscope objective lens, and the detector and the measurement beam The mirror, the micro objective lens and the measured object are arranged in order on a second straight line, and the first straight line intersects the second straight line; a control system is connected to the signal of the detector and is used for displaying according to the display on the detector The diffraction spectrum formed by the overlapping measurement marks to calculate the overlapping error; the measuring light adjusting element is used for adjusting the measuring light to be symmetrical about the optical axis center of the microscope objective lens, so that Formed on the diffraction spectra of the spectra of negative order diffracted light and positive order diffracted light are staggered.

The present invention further provides a method for measuring overlapping errors. A measurement light is emitted by an illumination system, and a measurement light adjustment element is provided between the illumination system and the measurement beam splitter. The measurement light adjustment element forms the measurement light into the display light. After the center of the optical axis of the micro-objective lens is symmetrical, it is reflected by the measuring beam splitter and incident on the measured object after passing through the micro-objective lens. The measuring light is diffracted by the measured object to form positive and negative orders of diffracted light. When the microscope objective lens and measuring beam splitter reach the detector to form a diffraction spectrum in which the positive diffraction spectrum and the negative diffraction spectrum are staggered from each other, the control system calculates the stack of the measured object based on the diffraction spectrum on the detector. On error.

The invention provides a device and method for measuring stacking errors. A measuring light adjustment element capable of adjusting measurement light to be symmetrical about the optical axis center of the microscope objective lens is added to the device, so that the measurement light passes through the device after passing through the set of devices. Positive and negative order diffraction light is formed on the measurement mark, and the diffraction spectrum of the positive and negative order diffraction light is finally displayed on the detector, and the spectra of the positive order diffraction light and the negative order diffraction light on the diffraction spectrum are staggered from each other, so There is no interference between them. The control system calculates the overlap error based on the diffraction spectrum. In this way, when selecting the light source, a wide-band light source such as infrared light, ultraviolet light, visible light, or a combination of these lights can be used. With measuring light adjustment element, surface light source, line light source or point light source can be used. Therefore, this device and method can measure a wider range of light wavelengths and can use any spot shape light source. This way, the measurement signals obtained are more abundant and the measurement accuracy is improved. And because the utilization of light energy is high, the measurement light can also be received for small-sized overlapping measurement marks, so this A method and apparatus are also adapted to suit the size of a small object, it tends to make it more suitable for fine modern semiconductor products.

In order to make the foregoing objects, features, and advantages of the present invention more comprehensible, specific embodiments of the present invention are described in detail below with reference to the drawings.

Example one

Referring to FIG. 2, the present invention provides a device for measuring overlap error, including:

An illumination system for generating measurement light. The illumination system includes at least one light source 41. The light source 41 is a broadband light source, which can be a surface light source, a line light source, or a point light source, and a light source having other light spot shapes. The measurement light is at least one of ultraviolet light, visible light, and infrared light.

A measuring light adjusting element, a straight line passing through the center of the measuring light adjusting element and perpendicular to the measuring light adjusting element and the optical axis of the microscope objective lens 46 are symmetrical with respect to the normal of the measuring beam splitter 45, and such an incident angle is used to make the light The light reflected on the mirror 45 can be incident on the microscope objective lens 46 vertically to ensure the maximum collection of the incident light.

In this embodiment, the measurement light adjusting element is an optical fiber cluster 43. Please refer to FIG. 11. The optical fiber cluster 43 has a linear exit surface 44. Specifically, the end faces of the optical fiber 437 are linearly arranged.

A measuring beam splitter 45 is used for splitting the measuring light and is arranged in a first straight line with the illumination system and the measuring light adjusting element in order.

A micro-objective lens 46 is used to collect measurement light and project it onto the surface of the object 47 to be measured with a grating structure.

；更包括一探測器411，用於探測由疊對測量標記形成的繞射光譜，探測器411位於顯微物鏡46的瞳面，且與測量分光鏡45、顯微物鏡46、被測對象47依次排列成第二直線，上述第一直線與第二直線相交，因此形成了第2圖的結構；更包括一控制系統（未圖示），與探測器411訊號連接，用於根據探測器411上顯示的由疊對測量標記形成的繞射光譜，計算疊對誤差；測量光調整元件也就是光源整形系統，用於將測量光整形為關於顯微物鏡46光軸中心對稱，使得形成的繞射光譜上正級繞射光的光譜與負級繞射光的光譜相互錯開，也就是使兩者互不干擾，這樣控制系統在計算時可避免很多誤差。The stacked measurement marks on the measured object 47 are used to reflect and diffract the measurement light. The stacked measurement marks are generally on the mask plate and are located in the non-patterned area on the mask plate. The stacked measurement marks include two arranged in a row. Of the first stack of measurement marks 471 and the second stack of measurement marks 472, when making a mask, the first stack of measurement marks 471 is set to be the same as the first stack of measurement marks 471 on the previous mask. The overlay error is 0, and the second overlay measurement mark 472 is set to a preset offset from the second overlay measurement mark 472 on the previous mask version as

; Further comprising a detector 411 for detecting the diffraction spectrum formed by the pair of measurement marks, the detector 411 is located on the pupil surface of the micro objective lens 46, and is connected with the measuring beam splitter 45, the micro objective lens 46, and the measured object 47; A second straight line is arranged in sequence, and the first straight line intersects the second straight line, thus forming the structure of FIG. 2; it further includes a control system (not shown), which is connected to the signal of the detector 411 and is used for The diffraction spectrum formed by the overlapping measurement marks is displayed to calculate the overlapping error; the measuring light adjusting element, that is, the light source shaping system, is used to shape the measuring light to be symmetrical about the optical axis center of the microscope objective lens 46, so that the formed diffraction On the spectrum, the spectrum of the positive-order diffracted light and the spectrum of the negative-order diffracted light are staggered from each other, that is, the two do not interfere with each other, so that the control system can avoid a lot of errors in the calculation.

In this embodiment, please refer to FIGS. 10 and 11. The measuring light adjusting element is an optical fiber cluster 43 having a linear exit surface 44. The optical fiber cluster 43 has several optical fibers 437. The optical fiber 437 is generally small in diameter and can reach several 100 micron, because the direction of the light emitted from the optical fiber 437 after passing through the optical fiber 437 is disordered, a collimating element (not shown) is provided on the exit surface 44 of the fiber cluster 43. A more common collimating element such as a concave lens array or self-focusing is used. In the system, the collimating element shapes the light emitted from the optical fiber 437 into mutually parallel light, so that the light incident on the measured object 47 is uniform during the measurement, and the error is reduced from the source.

Preferably, referring to FIG. 12, the incident surface 432 of the optical fiber cluster 43 is a two-dimensional rectangular surface, that is, the end surfaces incident on the optical fiber 437 are arranged to form a rectangle.

Preferably, in order to improve the measurement accuracy, a device capable of providing reference light is provided, specifically a monitoring light element. Please refer to FIG. 2, the monitoring light element is located on the optical path after the measurement light penetrates the measurement beam splitter 45. Specifically, a lens group 49 is located on the optical path after the measurement light penetrates the measurement beam splitter 45; a monitoring optical element is located on the optical path after the measurement light penetrates the lens group 49, and is used to reflect or diffract the measurement light and reflect the reflection The light or diffracted light passes through the lens group 49. Specifically, the monitoring optical element in this embodiment is a monitoring grating 410. The period of the monitoring grating 410 is the same as the period of the grating overlapping the measurement marks, and the monitoring grating 410 is placed obliquely so that Of the diffracted light diffracted from the monitoring grating 410, only the -1 order diffracted light can pass through the lens group 49, and the other 0 and +1 order diffracted light paths do not pass through the lens group 49. When the -1 order diffracted light passes through The lens group 49 reaches the measurement beam splitter 45 and is reflected by the measurement beam splitter 45 to the detector 411.

Referring to FIG. 14, the measurement light reflected and diffracted from the measured object 47 is a measurement light signal. In this embodiment, a linear light source is used, so the spectrum displayed on the detector 411 is the first diffraction spectrum. 4151. The measurement light reflected and diffracted from the monitoring light element is a monitoring light signal, which is displayed as a monitoring spectrum 414 on the detector 411. The monitoring light signal is used as a reference contrast, and the control system compares the measurement light signal with the monitoring light. The signal is normalized. After normalization, the calculated stacking error can eliminate the influence of the perturbation of partial band light intensity in the wide-band light source on the stacking error measurement.

Please refer to Figs. 2 and 3, the measuring device provided by the present invention is mainly used to measure the stacking error of the measured object 47. The measured object 47 is a silicon wafer, which is placed on the stage 48 of the lithography machine work table. There are at least two layers of patterned photoresist on the chip, and the overlap error measured is the coverage error between the two layers of patterned photoresist at the same location. After the first layer of patterned photoresist is fabricated on the silicon wafer, it is necessary to apply a layer of photoresist again in the subsequent process and pattern the layer of photoresist, but it is masking during the second patterned photoresist. The film may not be aligned with the pattern of the first patterned photoresist when the film is aligned, so the coverage error of the patterned photoresist will be caused.

Please refer to Figure 4. When there is a pairing error between the two layers of patterned photoresist, the light diffracted from the photoresist will change. When the value of the pairing error is equal to zero, the positive and negative high-order diffraction light intensity is equal. When the stacking error value is not equal to zero, the positive and negative high-order diffraction light intensities are not equal, and when the stacking error value is near zero, the diffraction light intensity and the stacking error value have a linear relationship.

Based on the above principles, the present invention provides a method for measuring overlapping errors based on the above measurement device. The measurement light is emitted by the light source 41, and the measurement light is adjusted to be symmetrical about the optical axis center of the microscope objective lens 46 by the measurement light adjustment element. The spectroscope 45 reflects and passes through the microscope objective lens 46 and is incident on the stacked measurement marks of the measured object 47. The measurement light is diffracted by the stacked measurement marks to form positive and negative orders of diffracted light. When the microscope objective lens 46 and the measuring beam splitter 45 reach the detector 411, the diffraction spectrum of the positive order diffraction light spectrum and the spectrum of the negative order diffraction light are staggered from each other. The control system calculates the diffraction spectrum based on the diffraction spectrum on the detector 411. The stacking error of the measurement object 47.

，因此第一疊對測量標記471與下層光阻之間的偏移量為0+

=

，設定第二疊對測量標記472與下層光阻之間具有預設偏移量

，那麼經過第二次掩膜曝光後，實際上形成的偏移量即為

+

。Please refer to FIG. 5 and FIG. 6. Using the measurement method provided by the present invention requires that the measured object 47 has at least two pairs of measurement marks, namely a first measurement pair 471 and a second measurement pair 472. The two marks are located on both sides of the silicon wafer, in the non-patterned area, with an effective pattern area spaced between the two. When designing the mask, set the first stack of measurement marks 471 and the lower layer of photoresist. The error is 0, but because there must be an alignment error between the two mask exposures, there must be an overlap error

, So the offset between the first stack of measurement marks 471 and the underlying photoresist is 0+

=

, Set a preset offset between the second stack of measurement marks 472 and the lower layer photoresist

, Then after the second mask exposure, the offset actually formed is

+

.

Using the overlapping measurement marks described above, measuring the overlapping error specifically includes the following steps:

，其中

為照射在第一疊對測量標記471上的光強，

為照射在第二疊對測量標記472上的光強，對於照射在第一疊對測量標記471上的正負光強分別為

，

，對於照射在第二疊對測量標記472上的正負光強分別為

，

，其中k為該裝置的測量製程參數，b為光強的基本值，也就是疊對誤差值為0時的光強值，

為疊對誤差值。Step 1: Refer to Figures 7 and 8 to calculate the sensitivity of each pixel point on the diffraction spectrum displayed by the detector 411

,among them

In order to irradiate the light intensity on the first pair of measurement marks 471,

In order to irradiate the light intensity on the second stack of measurement marks 472, the positive and negative light intensities on the first stack of measurement marks 471 are

,

, For the positive and negative light intensities on the second pair of measurement marks 472 are

,

, Where k is the measurement process parameter of the device, and b is the basic value of the light intensity, that is, the light intensity value when the overlapping error value is 0,

Is the overlap error value.

Please refer to Fig. 7. For the point with poor sensitivity in the figure, the vertical coordinate does not change greatly with the change of the horizontal coordinate. Therefore, it needs to be filtered out. The filtering method is to set the threshold of sensitivity based on experience. The pixel points whose calculated sensitivity is less than the threshold are filtered out, as shown in Figure 8 after filtering.

Step 2: Please refer to Figure 9 to generate a map (image) generated in the control system when the difference between the positive and negative diffraction light intensity of the measurement light and the step unit overlap error value. Relationship.

，其中

為運行一個步進單位

疊對誤差時所對應的探測器411接收到的光強變化量在控制系統上的圖像，其對應的圖像請參照第13圖所示，其中

是個常數值。The formula for generating the relationship diagram is:

,among them

For running one step unit

The image of the change in light intensity received by the corresponding detector 411 during the overlap error on the control system. For the corresponding image, please refer to FIG. 13, where

Is a constant value.

，其中m為反覆運算的迴圈次數，當計算得到的

對應的中間圖像map接近於無偏差時，也就是

的值接近於0時，得到此時m所對應的值為n，則疊對測量標記的疊對誤差OV_value=n×OV_step。Step 3: Use the iterative calculation of the computer system to recursively calculate the overlap error value, that is, repeat the relationship between the difference in the intensity of the positive-order diffraction light and the intensity of the negative-order diffraction light obtained in step 2 and the unit overlap error value. Recursive operation, specifically calculating the calculated value corresponding to the intermediate image map generated by each iterative operation

, Where m is the number of loops of the iterative operation, when calculated

When the corresponding intermediate image map is close to unbiased, that is,

When the value of is close to 0, it is obtained that the value corresponding to m at this time is n, and the overlap error of the overlap measurement mark is OV_value = n × OV_step.

In addition, in order to improve the measurement accuracy, please refer to FIG. 2 and FIG. 14. A monitoring light element is provided on the optical path after the measurement light exits from the measurement light adjustment element and penetrates the measurement beam splitter 45. After the measuring beam splitter 45 enters the monitoring light element, and is reflected and diffracted by the monitoring beam element, it reaches the measuring beam splitter 45, is reflected by the measuring beam splitter 45 to the detector 411, and is reflected and scattered from the measured object 47. The measurement light signal formed by the measurement light and the monitoring light signal formed by the reflection and diffraction measurement light from the monitoring light element are normalized to eliminate the interference of stray light on the measurement stackup error.

Example two

Please refer to FIG. 15. The difference between this embodiment and the first embodiment is that the incident surface 432 of the optical fiber cluster 43 is a three-dimensional structure. As shown in FIG. 15, the hemispherical shape can also be an ellipsoid. 432 can increase the surface area of the incident surface 432 and can collect more incident light.

Example three

Please refer to FIG. 16. The difference between this embodiment and the first embodiment lies in that the measurement light adjusting element is a ring-shaped first diaphragm 4171, and the ring-shaped first diaphragm 4171 is composed of two quarter rings that are symmetrical about the center of the circle. That is, the two quarter-circles are shaded, and the rest are transparent.

Embodiment 4

Referring to FIG. 17, the difference between this embodiment and the third embodiment is that the monitoring light element is two reflecting mirrors 419 having an angle of 90 ° with each other, and the measurement light passing through the lens group 49 is reflected by the two reflecting mirrors 419 To the measuring beam splitter 45 and reflected by the measuring beam splitter 45 to the detector 411. Since the monitoring spectrum 414 is formed by the reflecting mirror 419, the second diffraction spectrum 4152 formed by the formed monitoring spectrum 414 and the measuring light signal is as described in Section 18 As shown.

Example 5

Referring to FIG. 19, the difference between this embodiment and the third embodiment is that the shape of the second diaphragm (not shown) used is two half-strings symmetrical about the center, and the monitoring light element is the same as that of the fourth embodiment, so The third diffraction spectrum 4153 formed by the obtained monitoring spectrum 414 and the measurement optical signal is shown in FIG. 19.

Example Six

Please refer to FIG. 20. The difference between this embodiment and the fifth embodiment is that the third diaphragm (not shown) used is formed by rotating the second diaphragm of the fifth diaphragm 90 ° clockwise, and the obtained monitoring spectrum 414 and measurement The fourth diffraction spectrum 4154 formed by light is shown in FIG. 20.

Example Seven

The difference between this embodiment and the first embodiment lies in that the measurement light adjusting element is a slit (not shown).

Example eight

The difference between this embodiment and Embodiment 7 is that it has two slits. An incident beam splitter (not shown) is provided between the illumination system and the measurement light adjustment element. The incident beam splitter divides the measurement light into two identical beams and separates them. Enter two slits.

Example Nine

The difference between this embodiment and the eighth embodiment is that a shutter (not shown) is provided between the slit and the measurement beam splitter 45 to block non-measurement light beams that interfere with the measurement.

Example 10

The difference between this embodiment and the first embodiment is that a filter device (not shown) is added to the device. The filter device is located on the light path where the measurement light is incident on the measured object 47. For example, it can be set on the lighting system. After the light source 41 emits the measurement light and passes through the filtering device, the measurement light with a narrower bandwidth can be filtered out, which is more favorable for measurement.

Example 11

The difference between this embodiment and the first embodiment is that a polarization device (not shown) is further included, which is located on the optical path where the measurement light enters the detector 411, so that the measurement light becomes light having a polarization state.

Specifically, the polarizing device includes a polarizer located between the measurement light adjusting element and the measurement beam splitter 45; an analyzer is located between the measurement beam splitter 45 and the detector 411.

Preferably, it further comprises a compensator, which is located on the optical path from which the measurement light exits from the polarizer, and is used to measure the reflectance change and phase change of the measurement light having a polarization state.

放大而實現在測得的光強值中，從而容易被控制系統計算得到，這樣提高了測量精度，因此需要根據測量製程以及被測物體選擇不同性質的偏振光。A polarizer is added to the device, so that the measurement light becomes polarized light with a TE mode or a TM mode, but the TE mode or the TM mode is selected according to the condition of the measured object 47. Since the TE mode and the TM mode are for the same measured object, The reflectance of the object 47 is not the same. If the measured object is a metal and has a linear grating structure, the TE mode is more easily absorbed by the linear grating, so the reflection efficiency is low, and finally it affects the measurement process parameter k. In general, the larger k, the higher the error

Amplification is realized in the measured light intensity value, which is easily calculated by the control system. This improves the measurement accuracy. Therefore, it is necessary to select polarized light of different properties according to the measurement process and the measured object.

The present invention has been described in the above embodiments, but the present invention is not limited to the above embodiments. Obviously, those skilled in the art can make various changes and modifications to the invention without departing from the spirit and scope of the invention. In this way, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalent technologies, the present invention also intends to include these modifications and variations.

2‧‧‧ light source
30‧‧‧ filter device
32‧‧‧ Detector
34‧‧‧Reflective surface
40‧‧‧ pupil surface
6‧‧‧ substrate
L1‧‧‧ Objective
L2‧‧‧ lens group
41‧‧‧light source
43‧‧‧fiber cluster
432‧‧‧ incident surface
437‧‧‧optical fiber
44‧‧‧ exit surface
45‧‧‧ measuring beamsplitter
46‧‧‧Micro Objective
47‧‧‧Measured object
471‧‧‧The first pair of measurement marks
472‧‧‧Second pair of measurement marks
48‧‧‧ film stage
49‧‧‧ lens group
410‧‧‧Monitoring Grating
411‧‧‧ Detector
414‧‧‧Monitoring Spectrum
4151‧‧‧First diffraction spectrum
4152‧‧‧second diffraction spectrum
4153‧‧‧ Third diffraction spectrum
4154‧‧‧ Fourth diffraction spectrum
4171‧‧‧First stop
419‧‧‧Reflector

FIG. 1 is a schematic structural diagram of a device for measuring overlap error in the conventional technology.

FIG. 2 is a schematic structural diagram of an apparatus for measuring overlap error according to a first embodiment of the present invention.

FIG. 3 is a schematic cross-sectional view of a measured object according to a first embodiment of the present invention.

FIG. 4 is a schematic diagram of measuring the change of the diffracted light intensity with the change of the overlap value according to the first embodiment of the present invention.

FIG. 5 is a schematic diagram of a first stack of measurement marks according to a first embodiment of the present invention.

FIG. 6 is a schematic diagram of a second stack of measurement marks according to a first embodiment of the present invention.

FIG. 7 is a relationship diagram between positive and negative order diffraction light and diffraction efficiency according to the first embodiment of the present invention.

FIG. 8 is a schematic diagram of a change after filtering out pixel points with poor sensitivity according to the first embodiment of the present invention.

FIG. 9 is a relationship diagram between the overlapping error and the positive and negative order light intensity differences generated in the first embodiment of the present invention.

FIG. 10 is a schematic structural diagram of an optical fiber cluster according to an embodiment of the present invention.

Fig. 11 is a schematic diagram of the arrangement of the end faces of the optical fiber exits in Fig. 10.

FIG. 12 is a schematic diagram of the incident surface structure in FIG. 10.

FIG. 13 is a light intensity change diagram of a step unit stacking error according to an embodiment of the present invention.

FIG. 14 is a diagram showing a measurement optical signal and a monitoring optical signal on a detector according to the first embodiment of the present invention.

FIG. 15 is a schematic structural diagram of an optical fiber cluster according to the second embodiment of the present invention.

FIG. 16 is a schematic structural diagram of a third diaphragm according to an embodiment of the present invention.

FIG. 17 is a schematic structural diagram of a device for measuring overlap error according to the fourth embodiment of the present invention.

FIG. 18 is a display diagram of a monitoring optical signal and a measuring optical signal according to the fourth embodiment of the present invention.

FIG. 19 is a display diagram of a monitoring optical signal and a measuring optical signal according to the fifth embodiment of the present invention.

FIG. 20 is a display diagram of a monitoring optical signal and a measuring optical signal according to the sixth embodiment of the present invention.

41‧‧‧light source

43‧‧‧fiber cluster

45‧‧‧ measuring beamsplitter

46‧‧‧Micro Objective

47‧‧‧Measured object

48‧‧‧ film stage

49‧‧‧ lens group

410‧‧‧Monitoring Grating

411‧‧‧ Detector

Claims (26)

A device for measuring overlapping errors includes: an illumination system for generating measurement light; a measurement light adjustment element; a measurement beam splitter for splitting measurement light; the illumination system, the measurement light adjustment element and the The measuring beamsplitters are arranged on a first straight line in sequence; a micro objective lens is used for collecting measuring light and projecting it onto a surface of a pair of measuring marks having a grating structure on a surface of a measured object; a detector for A diffraction spectrum formed by detecting and diffracting the measurement light after it enters the stack of measurement marks, the detector is located on the pupil surface of the microscope objective lens, and the detector, the measurement beam splitter, the microscope objective lens, and the measured object The objects are sequentially arranged on a second straight line, the first straight line intersects the second straight line; a control system connected to the detector signal, and used for the winding formed by the stack of measurement marks displayed on the detector; And the measurement light adjustment element is used to adjust the measurement light to be symmetrical about the center of the optical axis of the microscope objective lens, so that the positive diffraction around the diffraction spectrum is formed. The spectrum of the emitted light and the spectrum of the negative diffraction light are staggered from each other. The device for measuring overlap error according to item 1 of the scope of patent application, wherein a straight line passing through the center of the measurement light adjustment element and perpendicular to the measurement light adjustment element and an optical axis of the microscope objective lens with respect to the measurement beam splitter Normals are symmetrical. The device for measuring double-layer error according to item 2 of the scope of the patent application, wherein the measuring light adjusting element is an annular diaphragm or a slit, and the annular diaphragm is composed of two quarter rings that are symmetrical about the center of the circle. composition. The device for measuring overlapping error as described in the first item of the patent application scope further includes an incident beam splitter located between the illumination system and the measurement light adjusting element. The device for measuring overlap error according to item 2 of the scope of the patent application, wherein the measuring light adjusting element is a fiber cluster having a linear exit surface. The device for measuring double-layer error as described in item 5 of the scope of patent application, wherein the exit surface of the optical fiber cluster is a linearly arranged optical fiber end face. According to the device for measuring overlap error described in item 5 of the scope of the patent application, wherein the exit surface of the fiber cluster further includes a collimating element, which is located on the optical path of the measurement light exiting from the exit surface of the fiber cluster, the collimating element Used to collimate the light exiting the fiber cluster. The device for measuring overlap error according to item 7 of the scope of patent application, wherein the collimating element is a concave lens array or a self-focusing system. According to the device for measuring overlap error described in item 5 of the scope of the patent application, wherein the incident surface of the optical fiber cluster is a two-dimensional rectangular surface or a three-dimensional structure. The device for measuring overlap error as described in item 9 of the scope of patent application, wherein the three-dimensional structure is a hemisphere or an ellipsoid. According to the device for measuring overlap error described in item 1 of the patent application scope, it further comprises a monitoring light element, which is located on the optical path after the measuring light penetrates the measuring beam splitter, and the control system further detects the error from the measured object. The measurement light signal formed by the reflected and diffracted measurement light is normalized with the monitoring light signal formed by the reflected or diffracted measurement light from the monitoring light element. The device for measuring double-layer error according to item 11 of the scope of patent application, wherein the monitoring light component comprises: a lens group, which is located on an optical path after the measurement light penetrates the measurement beam splitter; a monitoring optical element, which is located in the measurement The light passes through the optical path of the lens group, and is used to reflect or diffract the measurement light and pass at least a part of the reflected light or diffracted light generated thereby through the lens group. According to the device for measuring overlap error described in item 12 of the scope of the patent application, wherein the monitoring optical element is a monitoring grating, the period of the monitoring grating is the same as the period of the grating of the stack measuring mark, and the monitoring grating is placed obliquely. So that only -1 order diffraction light from the diffraction light diffracted from the monitoring grating can pass through the lens group, reach the measurement beam splitter after passing through the lens group, and be reflected by the measurement beam splitter to the detector. The device for measuring double-layer error according to item 12 of the scope of the patent application, wherein the monitoring optical element is two mirrors placed perpendicular to each other, and the measurement light passing through the lens group is reflected by the two mirrors to the The measuring beam splitter is reflected by the measuring beam splitter to the detector. The device for measuring overlap error according to item 1 of the scope of the patent application, wherein the object to be measured is carried by a stage. The device for measuring overlap error as described in item 1 of the scope of patent application, further comprising a polarizing device, which is located on an optical path where the measurement light is incident on the detector. The device for measuring overlapping errors according to item 16 of the scope of patent application, wherein the polarizing device comprises: a polarizer located between the measuring light adjusting element and the measuring beam splitter; and an analyzer located at the Measure between the spectroscope and the detector. The device for measuring overlapping error according to item 16 of the scope of patent application, further comprising a compensator, which is located on the optical path of the measuring light exiting the polarizer, and is used for measuring the reflectance change of the measuring light having a polarization state. And phase change. The device for measuring double-layer error according to item 1 of the scope of patent application, wherein the measurement light generated by the lighting system is at least one of ultraviolet light, visible light, and infrared light. A method for measuring overlapping errors, comprising: emitting measurement light by an illumination system, setting a measurement light adjustment element between the illumination system and a measurement beam splitter, and measuring the measurement light by the measurement light adjustment element to form the measurement light. After the optical axis of the micro-objective lens is symmetrical, it is reflected by the measuring beam splitter and enters the measured object after passing through the micro-objective lens. The measuring light is diffracted into positive and negative order diffraction light after being diffracted by a measured object. The secondary diffracted light reaches a detector through the microscope objective lens and the measuring beam splitter in turn to form a diffraction spectrum in which the positive-order secondary diffracted light spectrum and the negative-order diffracted light spectrum are staggered from each other. A control system based on the The diffraction spectrum is calculated to obtain the overlap error of the measured object. According to the method for measuring the overlap error described in item 20 of the patent application scope, wherein a monitoring light element is provided on the optical path after the measurement light exits from the measurement light adjustment element and penetrates the measurement beam splitter, the measurement light is sequentially passed through The measuring light adjusting element and the measuring beam splitter are incident on the monitoring light element and reflected or diffracted by the monitoring light element. At least a part of the reflected light or diffracted light generated by the measuring light beam passes through the measuring beam splitter and is The measurement beam splitter reflects to the detector, and normalizes the measurement light signal formed by reflecting and diffracting the measurement light from the measured object with the monitoring light signal formed by reflecting or diffracting the measurement light from the monitoring light element. Processing, used to eliminate the interference of light intensity fluctuations on measurement stackup errors. The method for measuring overlap error as described in item 21 of the patent application scope includes the following steps: Step 1: Calculate the sensitivity of each primitive point on the diffraction spectrum displayed by the detector, set the threshold of sensitivity, and set The element points with sensitivity less than the threshold value on the diffraction spectrum are filtered out. Step 2: Generate the relationship between the difference between the intensity of the positive-order diffraction light and the intensity of the negative-order diffraction light that characterizes the measurement light and the step unit pairing error value. Figure 3: Step 3: According to the relationship between the difference between the positive-order diffracted light intensity and the negative-order diffracted light intensity obtained in step 2 and the step unit overlap error value, iterative operations are repeated, and each intermediate operation produces an intermediate For images, when the symmetric intermediate image is calculated by iterative calculation, the iterative operation is completed, and the total step formed by the iterative operation is the overlay error of the overlay measurement mark. The method for measuring overlap error as described in item 22 of the scope of patent application, wherein two stacked measurement marks arranged in a row are made on the object under test, which are a first stacked measurement mark and a second stacked respectively. For the measurement mark, the first stack of measurement marks sets the overlap error between the patterned photoresist of the first stack of measurement marks and the upper patterned photoresist to 0, and the second stack of measurement marks sets the patterning of the upper layer. The offset between the photoresist and the patterned photoresist where the second pair of measurement marks is located is

. According to the method for measuring the overlap error described in item 23 of the patent application scope, wherein the method of calculating the sensitivity of each primitive point on the diffraction spectrum displayed by the detector in step 1 is

,among them

In order to irradiate the light intensity on the first pair of measurement marks,

The intensity of light irradiated on the second pair of measurement marks. The method for measuring the overlap error as described in item 24 of the scope of the patent application, wherein in step two, the difference between the positive diffraction light intensity and the negative diffraction light intensity of the measurement light and the step unit overlap error value are generated. The relationship between them is based on the formula:

,among them

Overlap error for running one step unit

The image of the change in light intensity received by the detector at the time on the control system. The method for measuring overlap error as described in the scope of the patent application No. 25, wherein the intermediate image value corresponding to the intermediate image generated by each iterative operation in step 3

, Where m is the number of loops of the iteration, when

When the value is 0 and the value corresponding to m is n, the stacking error of the overlay measurement mark is OV_value = n × OV_step.