Overlay measurement device

Abstract

The present invention relates to an overlay measurement device, and more particularly to an overlay measurement device having an auto focus system using light sources of different wavelengths. The present invention provides an overlay measurement device, which measures the error between a first overlay mark and a second overlay mark respectively formed on different layers of a wafer, the overlay measurement device comprising: a first light source, which irradiates a first light beam; a first detector, which obtains a signal of the first light beam emitted from the first light source and reflected at a measurement position of the wafer; a second light source, which irradiates a second light beam having a wavelength different from that of the first light beam; a second detector, which obtains a signal of the second light beam emitted from the second light source and reflected at the measurement position of the wafer; an objective lens, which collects the first light beam and the second light beam at the measurement position of the wafer and collects the light beams reflected at the measurement position; an actuator, which adjusts the relative position of the objective lens in the optical axis direction relative to the wafer; a control unit, which controls the actuator; and a height detection unit, which detects the height of the first overlay mark based on a change in a signal of the first detector corresponding to a change in the relative position of the objective lens in the optical axis direction relative to the wafer, and detects the height of the second overlay mark based on a change in a signal of the second detector corresponding to a change in the relative position of the objective lens in the optical axis direction relative to the wafer.

Description

Technical Field

[0001] The present invention relates to an overlay measurement device, and more particularly to an overlay measurement device having an auto focus system using light sources of different wavelengths. Background Art

[0002] As technology develops, the size of semiconductor devices decreases, and the density of integrated circuits is required to increase. In order to meet such requirements, various conditions need to be met, among which overlay tolerance is one of the important indicators.

[0003] Semiconductor devices are manufactured through multiple manufacturing processes. In order to form an integrated circuit on a wafer, multiple manufacturing processes are required to sequentially form the desired circuit structures and elements at specific locations. The manufacturing process causes patterned layers to be formed on the wafer in sequence. Through such repeated lamination processes, electrically activated patterns are generated within the integrated circuit. At this time, if each structure is not aligned within the tolerance range allowed in the production process, interference will occur between the electrically activated patterns, and this phenomenon may cause problems with the performance and reliability of the manufactured circuit. In order to measure and verify the alignment errors between these layers, an overlay measurement tool is used.

[0004] General overlay metrology and methods measure and verify whether the alignment between two layers is within the allowable error range. One of the methods is to form a structure called an overlay mark at a specific position on the substrate, and use an optical image acquisition device to photograph the structure to measure the overlay. The structure used for measurement is designed to measure the overlay in at least one direction of the X direction and the Y direction in each layer. Each structure is designed as a symmetrical structure, and the center value between the structures arranged in the symmetrical direction is calculated to use it as the representative value of the layer, and the relative difference between the representative values ​​of each layer is calculated to derive the overlay error.

[0005] When measuring the overlay of two layers, such as Figure 1 and Figure 2 As shown, after a first set of engraved marks 1 substantially in the form of a box and a second set of engraved marks 2 substantially in the form of a box smaller than the first set of engraved marks 1 are formed on two consecutive layers, Figure 3 and Figure 4 As shown, a waveform representing the intensity variation of the signal at different positions obtained with the first overlay mark 1 as the focal plane is obtained to obtain the center value C1 of the first overlay mark 1, and a waveform representing the intensity variation of the signal at different positions obtained with the second overlay mark 2 as the focal plane is obtained to obtain the center value C2 of the second overlay mark 2, thereby measuring the overlay error between the two layers.

[0006] However, the problem with this method is that it does not take into account that the first set of engraved marks 1 and the second set of engraved marks 2 are formed of different materials in different layers, and the first set of engraved marks 1 is covered by the layer formed with the second set of engraved marks 1, etc., and the heights of the first set of engraved marks 1 and the second set of engraved marks 2 are measured using an autofocus device using a single light source.

[0007] The autofocus device measures the heights of the first overlay mark 1 and the second overlay mark 2 using the size change of the detector signal corresponding to the distance from the wafer. For example, the heights of the first overlay mark 1 and the second overlay mark 2 can be measured using the contrast change of the overlay mark image.

[0008] Figure 5 This is a diagram showing the change in the magnitude of the detector signal according to the distance between the wafer and the objective lens when a light source with a single wavelength is used. Figure 5 (a) is the case of using a short-wavelength light source, and (b) is the case of using a long-wavelength light source.

[0009] like Figure 5 As shown in (a) and (b), since the first set of engraved marks 1 is located in the previous layer formed first, the detector signal based on the first set of engraved marks 1 has a maximum value in the area where the distance between the wafer and the objective lens is close; and since the second set of engraved marks 2 is located in the current layer formed on the previous layer, the detector signal based on the second set of engraved marks 2 has a maximum value in the area where the distance between the wafer and the objective lens is far.

[0010] However, as from Figure 5 As can be seen from (a) and (b), there is a large difference in the size of the maximum value depending on the type of light source. When a short-wavelength light source is used, the maximum value of the detector signal based on the second set of engraved marks 2 is large, while the maximum value of the detector signal based on the first set of engraved marks 1 is small. Therefore, when a short-wavelength light source is used, there is a problem that it is difficult to accurately measure the height of the first set of engraved marks 1. On the contrary, when a long-wavelength light source is used, there is a problem that it is difficult to accurately measure the height of the second set of engraved marks 2.

[0011] As semiconductor process technology develops, the height difference becomes larger, and at present, it is necessary to accurately measure the overlay error between layers with different optical properties, and the demand for solving this problem is increasing.

[0012] Prior art literature

[0013] Korean Publication Patent No. 2003-0054781

[0014] Korean Patent No. 10-0689709

[0015] Korean Patent No. 10-1564312 Summary of the invention

[0016] Technical issues

[0017] The present invention aims to improve the above-mentioned problem, and its object is to provide a new overlay measurement device capable of accurately measuring the overlay error between layers having a large height difference and different optical properties.

[0018] Technical Solution

[0019] In order to achieve the above-mentioned object, the present invention provides an overlay measurement device, which measures the error between a first overlay mark and a second overlay mark respectively formed on different layers of a wafer, the overlay measurement device comprising: a first light source, which irradiates a first light beam; a first detector, which obtains a signal of the first light beam emitted from the first light source and reflected at a measurement position of the wafer; a second light source, which irradiates a second light beam having a wavelength different from that of the first light beam; a second detector, which obtains a signal of the second light beam emitted from the second light source and reflected at the measurement position of the wafer; an objective lens, which collects the first light beam and the second light beam at the measurement position of the wafer and collects the light beams reflected at the measurement position; an actuator, which adjusts the relative position of the objective lens in the optical axis direction relative to the wafer; a control unit, which controls the actuator; and a height detection unit, which detects the height of the first overlay mark based on a change in a signal of the first detector corresponding to a change in the relative position of the objective lens in the optical axis direction relative to the wafer, and detects the height of the second overlay mark based on a change in a signal of the second detector corresponding to a change in the relative position of the objective lens in the optical axis direction relative to the wafer.

[0020] In addition, the provided overlay measurement device further includes a hot mirror, which is disposed between the first light source and the objective lens and reflects the long-wavelength light in the first light beam from the first light source toward the objective lens.

[0021] In addition, the provided overlay measurement device further includes a cold mirror, which is disposed between the second light source and the objective lens and reflects the short-wavelength light in the second light beam from the second light source toward the objective lens.

[0022] In addition, the provided overlay measurement device further includes a first aperture, which changes the shape of the first light beam emitted from the first light source into a shape corresponding to the shape of the first overlay mark.

[0023] In addition, the provided overlay measurement device further includes a second aperture which changes the shape of the second light beam emitted from the second light source into a shape corresponding to the shape of the second overlay mark.

[0024] In addition, the provided overlay measurement device further includes a first cylindrical lens, which changes the first light beam from the first light source into a line beam.

[0025] In addition, the provided overlay measurement device further includes a second cylindrical lens which changes the second light beam from the second light source into a line beam.

[0026] Furthermore, in the provided overlay measurement device, the first light beam is a light beam in an infrared region, and the second light beam is a light beam in an ultraviolet region.

[0027] Effects of the Invention

[0028] The overlay measurement device of the present invention uses light of different wavelengths to measure the height of each layer, so it can accurately measure the height, and therefore has the advantage of being able to accurately measure the overlay error between layers with large height differences and different optical properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a plan view of the overlay mark.

[0030] Figure 2 yes Figure 1 Side view of the overlay mark shown.

[0031] Figure 3 Shown with Figure 1 The first set of markings shown is a waveform showing changes in the intensity of a signal acquired at each position of the focal plane.

[0032] Figure 4 Shown with Figure 1 The second set of markings shown is a waveform showing the intensity variation at each position of the signal acquired from the focal plane.

[0033] Figure 5 3 is a diagram showing changes in the magnitude of a detector signal according to the distance between a wafer and an objective lens when a light source having a single wavelength is used.

[0034] Figure 6 It is a conceptual diagram of an overlay measurement device according to an embodiment of the present invention.

[0035] Figure 7 : is a graph showing changes in the magnitude of the first detector signal corresponding to the distance between the wafer and the objective lens when the first light source is used.

[0036] Figure 8 : is a graph showing changes in the magnitude of the second detector signal corresponding to the distance between the wafer and the objective lens when the second light source is used.

[0037] Fig. 9 It is a diagram showing an example of the first light beam.

[0038] Fig.10 It is a diagram showing an example of the second light beam. DETAILED DESCRIPTION

[0039] An embodiment of the present invention is described in detail below with reference to the accompanying drawings. However, the embodiments of the present invention can be deformed into a variety of different forms, and it should not be interpreted that the scope of the present invention is limited to the embodiments described in detail below. The embodiments of the present invention are provided to more completely illustrate the present invention to the general technicians in the art. Therefore, the shapes of the elements in the figures are exaggerated in order to emphasize a clearer description, and the elements marked with the same reference numerals in the figures mean the same elements.

[0040] Figure 6 1 is a conceptual diagram of an overlay measurement device according to an embodiment of the present invention. The overlay measurement device is a device for measuring an error between a first overlay mark and a second overlay mark respectively formed on different layers of a wafer w.

[0041] For example, Figure 1 and Figure 2 As shown, the first overlay mark 1 may be an overlay mark formed on a previous layer, and the second overlay mark 2 may be an overlay mark formed on a current layer. When a layer for forming a semiconductor device is formed in a die region, the overlay mark is formed on a scribe line. For example, the first overlay mark 1 may be formed together with an insulating film pattern, and the second overlay mark 2 may be formed together with a photoresist pattern formed on the insulating film pattern.

[0042] In this case, the second overlay mark 2 is exposed to the outside, but the first overlay mark 1 is in a state of being blocked by the photoresist layer and is composed of an oxide having optical properties different from those of the second overlay mark 2 made of the photoresist material. In addition, the height of the first overlay mark 1 and the height of the second overlay mark 2 are different from each other.

[0043] In the present invention, in order to measure the height of the first set of engraved marks 1 and the second set of engraved marks 2, light beams of different wavelengths are used. That is, the height of each mark is measured using a light beam of a wavelength suitable for the optical properties of the material constituting each mark, the height of each mark, and the shape. For example, the height of the first set of engraved marks 1 can be measured using an infrared light beam, and the height of the second set of engraved marks 2 can be measured using an ultraviolet light beam.

[0044] As the overlay mark, various forms of overlay marks currently in use can be used, such as box in box (BIB, see Figure 1 ), advanced imaging metrology (AIM) overlay marks, etc. The following description will be mainly based on the overlay marks in the form of a simple box-in-box structure.

[0045] like Figure 6 As shown, the overlay measurement device according to an embodiment of the present invention comprises a first light source 11 for measuring the height of a first overlay mark 1 , a first beam splitter 13 , a hot mirror 16 , and a first detector 18 .

[0046] Furthermore, a second light source 21 for measuring the height of the second set of engraved marks, a second beam splitter 23, a cold mirror 26, and a second detector 28 are included.

[0047] In addition, an objective lens 31 , an actuator 32 , a control unit 41 , and a height detection unit 42 , which are commonly used for measuring the height of the first set of engraved marks 1 and measuring the height of the second set of engraved marks 2 , are included.

[0048] First, the configuration related to the measurement of the height of the first overlay mark 1 by the overlay measurement device will be described.

[0049] As the first light source 11, a halogen lamp, a xenon lamp, a supercontinuum laser, a light emitting diode, a laser induced lamp, etc. can be used. The first light source 11 is used as a light source for irradiating light to the first set of engraved marks 1 formed in the previous layer.

[0050] The first beam splitter 13 plays a role of splitting the light beam from the first light source 11 into two light beams. That is, the first beam splitter 13 transmits a part of the light beam from the first light source 11 and reflects the other part, thereby splitting the light beam from the first light source 11 into two light beams.

[0051] The hot mirror 16 is disposed at 45° with respect to the path of the light beam transmitted through the first beam splitter 13. The hot mirror 16 reflects a light beam with a long wavelength among the light beams transmitted through the first beam splitter 13, and transmits a light beam with a short wavelength.

[0052] The objective lens 31 plays the role of focusing the long-wavelength light beam reflected by the heat mirror 16 at the measurement position of the wafer w and collecting the light beam reflected at the measurement position. The objective lens 31 is provided on an actuator 32 (actuator) configured to enable the objective lens 31 to move linearly along the optical axis direction. The control unit 41 controls the actuator 32 to adjust the relative position of the objective lens 31 in the optical axis direction relative to the wafer w.

[0053] The first detector 18 detects the first light beam which is collected by the objective lens 31 , passes through the cold mirror 26 , and is reflected by the hot mirror 16 and then reflected by the first beam splitter 13 .

[0054] The height detection unit 42 can detect the height of the first overlay mark 1 based on a change in the signal of the first detector 18 corresponding to a change in the relative position of the objective lens 31 in the optical axis direction with respect to the wafer w.

[0055] For example, Figure 7 As shown, the change in the magnitude of the signal acquired by the first detector 18 can be confirmed, and the height of the first overlay mark 1 can be detected using the relative position of the objective lens 31 in the optical axis direction relative to the wafer w when the magnitude of the signal is at the highest point.

[0056] like Figure 7 As shown, when the first light source 11 is used, the maximum value of the signal of the first detector 18 based on the first overlay mark 1 is greater than the maximum value of the signal of the first detector 18 based on the second overlay mark 2. Therefore, the height of the first overlay mark 1 can be accurately measured using the first light source 11.

[0057] Next, the configuration for measuring the height of the second set of engraved marks 2 will be described.

[0058] Like the first light source 11, the second light source 21 may also use a halogen lamp, a xenon lamp, a supercontinuum laser, a light emitting diode, a laser induced lamp, etc. The second light source 21 is used as a light source for irradiating light to the second set of engraved marks 2 formed on the current layer. It is preferred that the light beam of the second light source 21 is a light beam with a shorter wavelength than the light beam of the first light source 11. As described above, the light beam of the first light source 11 may be a light beam in the infrared region, and the light beam of the second light source 21 may be a light beam in the ultraviolet region.

[0059] The second beam splitter 23 serves to split the light beam from the second light source 21 into two light beams.

[0060] The cold mirror 26 is disposed at 45° with respect to the path of the light beam transmitted through the second beam splitter 23. The cold mirror 26 reflects a light beam with a short wavelength among the light beams transmitted through the second beam splitter 23, and transmits a light beam with a long wavelength.

[0061] The objective lens 31 focuses the short-wavelength light beam reflected by the cold mirror 26 at the measurement position of the wafer w and collects the light beam reflected at the measurement position. The control unit 41 controls the actuator 32 to adjust the relative position of the objective lens 31 with respect to the wafer w in the optical axis direction.

[0062] The second detector 28 detects the second light beam collected by the objective lens 31 and then reflected by the cold mirror 26 and then reflected by the second beam splitter 23 .

[0063] The height detection unit 42 can detect the height of the second overlay mark 2 based on a change in the signal of the second detector 28 corresponding to a change in the relative position in the optical axis direction of the objective lens 31 with respect to the wafer w.

[0064] For example, Figure 8 As shown, the change in the size of the signal of the second set mark 2 obtained by the second detector 28 can be confirmed, and the height of the second set mark 2 can be detected using the relative position in the optical axis direction of the objective lens relative to the wafer w when the signal size is the highest point.

[0065] like Figure 8 As shown, when the second light source 21 is used, the maximum value of the signal of the second detector 28 based on the second overlay mark 2 is much greater than the maximum value of the signal of the second detector 28 based on the image of the first overlay mark 1. Therefore, the height of the second overlay mark 2 can be accurately measured using the second light source 21.

[0066] In addition, in order to measure the overlay error, the overlay measuring device further includes a third illumination 51 for photographing the first overlay mark 1 and the second overlay mark 2 , a third detector 53 , and a tube lens 52 .

[0067] The overlay error can be measured by the following method.

[0068] First, the focal plane is located between the first set of engraved marks 1 and the second set of engraved marks 2 using the height of the first set of engraved marks 1 and the height of the second set of engraved marks 2 obtained previously. The focal plane can be located between the first set of engraved marks 1 and the second set of engraved marks 2, for example.

[0069] Next, images of the first set of engraved marks 1 and the second set of engraved marks 2 are acquired together.

[0070] The overlay error can then be measured by comparing the center of the image of the first overlay mark 1 and the center of the image of the second overlay mark 2 with each other.

[0071] In addition, the overlay error can also be measured by comparing the two images after respectively acquiring the image of the first overlay mark 1 and the image of the second overlay mark 2.

[0072] In more detail, when photographing the first set of engraved marks 1, after the focal plane is located at the first set of engraved marks 1 using the height of the first set of engraved marks 1 obtained by the height detection unit 42, the light beam used to acquire the image is irradiated by the third illumination 51, and the reflected light beam is detected by the third detector 53 to acquire a clear image of the first set of engraved marks 1.

[0073] Next, when photographing the second set of engraved marks 2 , the height of the second set of engraved marks 2 is utilized to make the focal plane located behind the second set of engraved marks 2 , so as to obtain a clear image of the second set of engraved marks 2 .

[0074] Then, the centers of the image of the first overlay mark 1 and the image of the second overlay mark 2 are compared with each other to measure the overlay error.

[0075] In addition, the overlay measurement device further includes a first aperture 12 and a second aperture 22 to more accurately measure the height of the first overlay mark 1 and the height of the second overlay mark 2 .

[0076] The first aperture 12 is located between the first light source 11 and the first beam splitter 13. The second aperture 22 is disposed between the second light source 21 and the second beam splitter 23.

[0077] The first aperture 12 plays a role in changing the first light beam into a form suitable for photographing the first set of engraved marks 1 .

[0078] For example, Fig. 9 As shown, when the first engraved mark 1 is an outer box of a box-in-box (BIB) engraved mark, the first light beam B1 can be changed into a circular ring shape. Since the center of the first engraved mark 1 of the BIB engraved mark is an empty four-frame shape, there is no need to irradiate the first light beam B1 to the center.

[0079] The second aperture 22 plays a role in changing the second light beam into a form suitable for photographing the second set of engraved marks 2 .

[0080] For example, Fig.10 As shown, when the second overlay mark 2 is an inner box of a box in box (BIB) overlay mark, the second light beam B2 can be changed into a circle having a diameter equal to the length of the diagonal line of the inner box.

[0081] In addition, the overlay measurement device includes a first cylindrical lens 14 and a second cylindrical lens 24 to more accurately measure the height of the first overlay mark 1 and the height of the second overlay mark 2 .

[0082] When a line beam is required, a cylindrical lens is used. A cylindrical lens is a lens with a curved surface on only one side, and the light beam that passes through the cylindrical lens becomes a line beam. When a line beam is used, the sensitivity increases due to optical astigmatism, allowing for more precise height measurement.

[0083] In addition, the overlay measurement device may also include polarizing plates 15, 25 (waveplates) arranged at the front end of the hot mirror 16 and the cold mirror 26 to convert the passing light into a polarization state, and lenses 17, 27 arranged at the front end of the first detector 18 and the second detector 28 to collect light.

[0084] The embodiments described above only illustrate preferred embodiments of the present invention. The scope of rights of the present invention is not limited to the described embodiments, and those skilled in the art will be able to make various changes, deformations or substitutions within the scope of the technical ideas and claims of the present invention, and such embodiments should be understood to be within the scope of the present invention.

Claims

1. An overlay measurement device for measuring an error between a first overlay mark and a second overlay mark respectively formed on different layers of a wafer, the overlay measurement device comprising: a first light source emitting a first light beam; a first detector for acquiring a signal of the first light beam emitted from the first light source and reflected at a measurement position of the wafer; a second light source emitting a second light beam having a wavelength different from that of the first light beam; a second detector for acquiring a signal of the second light beam emitted from the second light source and reflected at the measurement position of the wafer; an objective lens, which collects the first light beam and the second light beam at the measurement position of the wafer and collects the light beam reflected at the measurement position; an actuator that adjusts a relative position of the objective lens in the direction of the optical axis with respect to the wafer; a control unit that controls the actuator; a height detection unit that detects the height of the first overlay mark based on a change in a signal of the first detector corresponding to a change in a relative position of the objective lens in the optical axis direction relative to the wafer, and detects the height of the second overlay mark based on a change in a signal of the second detector corresponding to a change in a relative position of the objective lens in the optical axis direction relative to the wafer; a third illumination that irradiates a light beam for acquiring an image of the first set of engraved marks and the second set of engraved marks; as well as A third detector detects the light beam reflected from the third illumination to acquire images of the first overlay mark and the second overlay mark.

2. The overlay measurement device according to claim 1, characterized in that: Also included is a heat mirror disposed between the first light source and the objective lens, and reflecting the light with a long wavelength in the first light beam emitted from the first light source toward the objective lens.

3. The overlay measurement device according to claim 1, characterized in that: Also included is a cold mirror disposed between the second light source and the objective lens, and reflecting the light of short wavelength in the second light beam emitted from the second light source toward the objective lens.

4. The overlay measurement device according to claim 1, characterized in that: Also included is a first aperture that changes the shape of the first light beam from the first light source into a shape corresponding to the shape of the first overlay mark.

5. The overlay measurement device according to claim 1, characterized in that: Also included is a second aperture that changes the shape of the second light beam from the second light source into a shape corresponding to the shape of the second overlay mark.

6. The overlay measurement device according to claim 1, characterized in that: Also included is a first cylindrical lens which changes the first light beam from the first light source into a line light beam.

7. The overlay measurement device according to claim 1, characterized in that: The invention also includes a second cylindrical lens which changes the second light beam emitted from the second light source into a line light beam.

8. The overlay measurement device according to claim 1, characterized in that: The first light beam is a light beam in an infrared region, and the second light beam is a light beam in an ultraviolet region.

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