Measurement device and measurement method
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- Filing Date
- 2023-09-08
- Publication Date
- 2026-03-18
AI Technical Summary
Existing measuring devices struggle to accurately measure the surface state of subjects, particularly when fine patterns are formed over multiple layers on a silicon wafer, leading to device failure due to increased surface unevenness.
A measuring device that uses a light source to generate first, second, and third light beams, where the second and third light beams are incident perpendicularly on the surface and back surface of a substrate, respectively, allowing for accurate measurement of surface steps by canceling background light and enhancing the detection of reflected light.
The measuring device achieves high accuracy in measuring surface steps and unevenness by effectively canceling background light and isolating the reflected light, thereby improving the reliability of semiconductor device fabrication processes.
Smart Images
Figure 00000000_0000_ABST
Abstract
Description
[Technical field]
[0001] The present embodiment relates to a measurement apparatus and a measurement method. [Background technology]
[0002] Semiconductor devices are manufactured by forming elements and wiring patterns on silicon wafers through processes such as film formation, exposure, and etching. When fine patterns are formed in multiple layers, the unevenness of the wafer surface increases. Such steps can cause device defects, so measuring devices that can measure steps on the wafer surface are becoming increasingly important. [Prior art documents] [Patent documents]
[0003] [Patent Document 1] US Patent Application Publication No. 2018 / 0045506 Summary of the Invention [Problem to be solved by the invention]
[0004] An object of the present embodiment is to provide a measurement apparatus and a measurement method capable of measuring the surface state of a test object with high accuracy. [Means for solving the problem]
[0005] The measurement device of this embodiment is a measurement device that measures a surface of a first film in a specimen having a first film formed on a substrate. The measurement device includes a light source that generates a first light, a beam splitter that splits the first light into a second light and a third light, and a detection unit that receives a signal light generated from the specimen by irradiation with the second light and the third light.
[0006] The first light has a wavelength that can transmit through the substrate. The second light is perpendicularly incident from the surface of the first film. The third light is perpendicularly incident from the rear surface of the substrate coaxially with the second light. The phase of the transmitted light of the third light that has transmitted through the substrate is inverse to the phase of the reflected light that is generated when a portion of the second light transmits through the first film and is reflected at the surface of the substrate. The intensity of the transmitted light is approximately equal to the intensity of the reflected light. [Brief description of the drawings]
[0007] [Figure 1A] 1 is a diagram illustrating the structure of a specimen S. FIG. [Figure 1B] 4 is a diagram illustrating a detected waveform in the detection section 300. FIG. [Figure 1C] 11A and 11B are diagrams illustrating a method of calculating a step based on a detected waveform. [Diagram 2] 1A and 1B are diagrams illustrating light generated in an object having a transparent film formed on its surface. [Figure 3A] 13 is an example of a detected waveform in a test object having a transparent film formed on its surface. [Figure 3B] 13 is an example of a detected waveform in a test object having a transparent film formed on its surface. [Figure 4A] FIG. 10 is a diagram for explaining roughly the light generated in a subject in a comparative example. [Figure 4B] 13 is an example of a detection waveform in a comparative example. [Figure 5A] 3 is a diagram for explaining the outline of light generated in a subject in the present embodiment; FIG. [Figure 5B] 4 is an example of a detection waveform in the present embodiment. [Figure 6] 1 is a block diagram showing an example of the configuration of a measurement device according to an embodiment of the present invention; [Figure 7] FIG. 1 is a schematic diagram illustrating an optical comb. [Figure 8] 4 is a flowchart illustrating an example of a measurement method according to the present embodiment. [Figure 9A] 1 is a block diagram showing an example of the configuration of another measurement device according to the present embodiment. [Figure 9B] 9B is a diagram illustrating a method for measuring the surface shape of a test object using the measurement apparatus shown in FIG. 9A. [Figure 10A] FIG. 1 is a schematic diagram illustrating dual-comb spectroscopy. [Figure 10B] FIG. 1 is a schematic diagram illustrating dual-comb spectroscopy. [Figure 10C] FIG. 13 is a block diagram showing a configuration of a modified example of the measurement device of the present embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0008] Hereinafter, an embodiment will be described with reference to the drawings.
[0009] The measuring device of this embodiment can measure, for example, a step formed on the surface of the specimen S. FIG. 1 is a diagram for explaining an example of the principle of measuring a step using the measuring device according to this embodiment. FIG. 1A is a diagram for explaining the structure of the specimen S. FIG. 1B is a diagram for explaining a detection waveform in the detection unit 300. FIG. 1C is a diagram for explaining a method of calculating a step based on the detection waveform. In the specimen S, a surface on which a step to be measured is formed is defined as a front surface, and a surface opposite to the front surface is defined as a back surface. In the following drawings, two orthogonal directions in a plane parallel to the back surface of the specimen S are defined as a D1 direction and a D2 direction. Furthermore, a direction orthogonal to the back surface of the specimen S is defined as a D3 direction. In the D3 direction, the upper side of the paper is defined as a positive side (upward), and the lower side of the paper is defined as a negative side (downward). In FIG. 1A, the surface formed on the upper side of the surface of the specimen S is defined as a first surface, and the surface formed on the lower side is defined as a second surface.
[0010] As shown in FIG. 1A, a measurement light Li is emitted from a light source 100. The measurement light Li is split into a D1 direction and a D3 direction via a beam splitter 200. The light Li1 split into the D3 direction is perpendicularly incident on the surface of the specimen S. First, when the irradiation area of the light Li1 is set to the first surface, a reflected light Lr1 is generated on the first surface. On the other hand, the light Li2 split into the D1 direction is perpendicularly incident on the surface of the reference mirror 400, and a reflected light Lrs is generated. The reflected lights Lr1 and Lrs are combined by the beam splitter 200 and detected by the detection unit 300. The detection waveform when the irradiation area of the light Li1 is set to the first surface is shown in the upper part of FIG. 1B. The detection times of the reflected lights Lr1 and Lrs differ depending on the optical path difference. When the distance from the beam splitter 200 to the first surface is greater than the distance from the beam splitter 200 to the reference mirror 400, the reflected light Lr1 arrives at the detection unit 300 later than the reflected light Lrs. Therefore, as shown in the waveform in the upper part of Fig. 1B, the detection time t1 of the reflected light Lr1 is later than the detection time t0 of the reflected light Lrs. The time difference Δt1 between the detection times t0 and t1 is multiplied by the speed c of the reflected lights Lr1 and Lrs and divided by 2 to calculate the distance difference ΔZ1 between the distance from the beam splitter 200 to the first surface and the distance from the beam splitter 200 to the reference mirror 400.
[0011] Next, when the subject S is moved in the D1 direction and the irradiation area of the light Li1 is set to the second surface, the reflected light Lr2 is generated on the second surface. Meanwhile, the reflected light Lrs is generated from the reference mirror 400 by the irradiation of the light Li2. The reflected lights Lr2 and Lrs are combined by the beam splitter 200 and detected by the detection unit 300. The lower part of FIG. 1B shows a detection waveform when the irradiation area of the light Li1 is set to the second surface. Since the distance from the beam splitter 200 to the second surface is longer than the distance from the beam splitter 200 to the reference mirror 400, the reflected light Lr2 arrives at the detection unit 300 later than the reflected light Lrs. Therefore, as shown in the waveform shown in the lower part of FIG. 1B, the detection time t2 of the reflected light Lr2 is later than the detection time t0 of the reflected light Lrs. By multiplying the time difference Δt2 between detection time t0 and detection time t2 by the speed c of reflected lights Lr2 and Lrs and dividing by 2, the distance difference ΔZ2 between the distance from the beam splitter 200 to the second surface and the distance from the beam splitter 200 to the reference mirror 400 can be calculated.
[0012] Finally, as shown in FIG. 1C, the step ΔZ between the second surface and the first surface can be calculated from the difference between the distance difference ΔZ2 and the distance difference ΔZ1. That is, in the measurement device of the embodiment, the step of the specimen S is measured by calculating the difference in height between the first surface and the second surface when the reference mirror 400 is used as a reference. When the distance from the beam splitter 200 to the reference mirror 400 is approximately equal when measuring the first surface and the second surface, the detection time t0 of the reflected light Lrs is approximately equal. Therefore, as shown in FIG. 1B, the step ΔZ between the second surface and the first surface can also be calculated by multiplying the time difference Δt12 between the detection time t1 of the reflected light Lr1 and the detection time t2 of the reflected light Lr2 by the speed c of the reflected light Lr1 and Lr2 and dividing the result by 2. Furthermore, when pulsed light is used as the measurement light Li, the time difference Δt1 can be obtained from the phase difference between the reflected light Lr1 and the reflected light Lrs, and the time difference Δt2 can be obtained from the phase difference between the reflected light Lr2 and the reflected light Lrs.
[0013] Next, consider the case of measuring the step of the specimen S having a transparent film S2 formed on the surface of the substrate S1. The substrate S1 is, for example, a silicon substrate. The transparent film S2 is, for example, a silicon oxide film or a silicon nitride film. FIG. 2 is a diagram for explaining light generated in the specimen having a transparent film formed on its surface. When the transparent film S2 is formed on the surface of the specimen S, the measurement light Li1 irradiated from above the transparent film S2 is divided into reflected light Lr reflected on the surface of the transparent film S2 and transmitted light Lt2 transmitted through the transparent film S2. For example, when the transparent film S2 is a silicon oxide film, the proportion of the measurement light Li reflected on the surface of the transparent film S2 is about several percent (for example, 4%), and most of it is transmitted through the transparent film S2. When the transmitted light Lt2 reaches the interface between the transparent film S2 and the substrate S1, it is divided into interface reflected light Lri reflected on the interface and transmitted light Lt1 transmitted through the substrate S1. For example, when the transparent film S2 is a silicon oxide film and the substrate S1 is silicon, the proportion of the transmitted light Lt2 reflected at the interface between the transparent film S2 and the substrate S1 is several tens of percent (for example, about 40%).
[0014] When the interface reflected light Lri reflected at the interface between the transparent film S2 and the substrate S1 reaches the surface of the transparent film S2 (the interface between the transparent film S2 and the air), it is divided into interface reflected light Lri' reflected at the interface and transmitted light transmitted from the surface of the transparent film S2 into the air. This transmitted light is the background light Lb1 generated when the light Li1 irradiated to the specimen S is reflected at the interface between the transparent film S2 and the substrate S1. When the interface reflected light Lri' reaches the interface between the transparent film S2 and the substrate S1, it is divided into interface reflected light reflected again at the interface and transmitted light transmitted through the substrate S1. When the interface reflected light reaches the surface of the transparent film S2 (the interface between the transparent film S2 and the air), it is divided into interface reflected light reflected at the interface and transmitted light transmitted from the surface of the transparent film S2 into the air. This transmitted light is background light Lb2, which is generated when light Li1 irradiated to the specimen S is reflected twice at the interface between the transparent film S2 and the substrate S1 and once at the interface between the transparent film S2 and air. In this manner, background light Lb1, Lb2, etc., which is generated each time the transmitted light Lt2 is repeatedly reflected on the surface of the substrate S1, is detected by the detection unit 300 together with the reflected light Lr. Light Lg shown in FIG. 2 indicates light generated from the specimen S by irradiation with light Li1, and is a combination of the reflected light Lr and background light Lb1, Lb2, etc.
[0015] 3A and 3B are examples of detected waveforms in an object having a transparent film formed on its surface. FIG. 3A shows an example of a detected waveform when the transparent film is thick. When the transparent film S2 is thick, the delay time of the background light Lb1 relative to the reflected light Lr is large. In this case, as shown in FIG. 3A, the reflected light Lr and the background light Lb1 are detected at a predetermined interval. In this way, when the waveforms of the reflected light Lr and the background light Lb1 are detected separately, it is possible to extract the waveform of the reflected light Lr from the detected waveform. Therefore, the detection time of the reflected light Lr on the surface of the object S can be measured with high accuracy.
[0016] FIG. 3B shows an example of a detection waveform when the transparent film is thin. When the transparent film S2 is thin, the delay time of the background light Lb1 relative to the reflected light Lr is small. In this case, as shown in FIG. 3B, the waveforms of the reflected light Lr and the background light Lb1 overlap. In this way, when the waveform of the reflected light Lr and the waveform of the background light Lb1 are detected overlapping, it is difficult to extract the waveform of the reflected light Lr in the detection waveform. Therefore, the reflected light Lr on the surface of the specimen S cannot be measured with high accuracy. In semiconductor devices, some transparent films (silicon oxide films and silicon nitride films) formed on silicon substrates are very thin, for example, with a film thickness of several tens of nm. When measuring a step formed on the surface of such a thin film, there is a high possibility that the reflected light Lr and the background light Lb1 overlap, as shown in FIG. 3B.
[0017] As a method for removing background light Lb1 that becomes noise, a method of combining light that is approximately equal in intensity and has an opposite phase to the background light Lb1 with light Lg generated from the subject S is considered. FIG. 4 is a diagram for explaining an example of light generated in a comparative example. FIG. 4A is a diagram for explaining light generated in a subject in a comparative example. FIG. 4B is an example of a detection waveform in the comparative example. As shown in FIG. 4A, light Lb1_inv that is approximately equal in intensity and has an opposite phase to the background light Lb1 is combined with light Lg generated from the subject S using a beam splitter 200'. Since the background light Lb1 is offset by the light Lb1_inv, the light Lg' output from the beam splitter 200' does not contain a component of the background light Lb1. Therefore, the background light Lb1 is not detected in the detection unit 300. However, in the comparative example, the background light Lb2... generated by multiple reflections of the interface reflected light Lri' cannot be removed.
[0018] 4B, the detection unit 300 detects the background light Lb2 in addition to the reflected light Lr. When the transparent film S2 is thin, the reflected light Lr and the background light Lb2 overlap, making it difficult to extract the waveform of the reflected light Lr from the detected waveform. Therefore, the method of the comparative example also cannot accurately measure the reflected light Lr from the surface of the specimen S.
[0019] In contrast, the measurement device of the embodiment irradiates light from the back surface of the specimen S upward in the D3 direction with light that is approximately equal in intensity to and in opposite phase to the reflected light Lri. FIG. 5 is a diagram for explaining an example of light generated by the measurement device of the embodiment. FIG. 5A is a diagram for explaining the light generated by the specimen in the embodiment. FIG. 5B is an example of a detection waveform in the embodiment. As shown in FIG. 5A, the back surface incident light Lib is incident in the opposite direction to the measurement light Li, that is, from below in the D3 direction toward the surface of the transparent film S2. The light of the back surface incident light Lib that passes through the substrate S1 and is incident on the transparent film S2 is referred to as the transmitted light Libt. The intensity of the back surface incident light Lib is set so that the intensity of the transmitted light Libt is approximately equal to the intensity of the interface reflected light Lri. In addition, the phase of the back surface incident light Lib is adjusted so that the phase of the transmitted light Libt is in opposite phase to the interface reflected light Lri. Since the interface reflected light Lri is offset by the back surface incident light Lib, the background light Lb1 is not generated. Furthermore, because the interface reflected light Lri is cancelled out, the interface reflected light Lri' is not generated either. That is, the background light Lb2... is not generated either. Therefore, the light Lg generated from the subject S is substantially equal to the reflected light Lr, and the reflected light Lr can be extracted in the detection waveform as shown in FIG. 5B. Therefore, according to the measurement device of this embodiment, the reflected light Lr from the surface of the subject S can be measured with high accuracy.
[0020] Next, the configuration of the measurement device according to this embodiment will be described. Fig. 6 is a block diagram showing an example of the configuration of the measurement device according to this embodiment. The measurement device according to this embodiment includes a light source 1, beam splitters 2 and 5, a variable ND (Neutral Density) filter 3, a plurality of mirrors 4, 8, 9 and 11, a reference mirror 6, a delay line 10, and a detection unit 7. The measurement device according to this embodiment also includes a control and calculation unit 12 and a specimen holder 13.
[0021] A light source 1 generates and emits light (light L1) to be irradiated onto a specimen S, which is a measurement target. For example, an optical frequency comb (optical comb) is used as the light L1. FIG. 7 is a schematic diagram for explaining an optical comb. In FIG. 7, the upper part shows the electric field distribution on the time axis, and the lower part shows the intensity distribution on the frequency axis. In an optical comb, ultrashort pulsed light having an extremely short time width of several fs to several ps is arranged at regular intervals on the time axis. Its spectrum is a comb-like arrangement of many narrow linewidth frequency modes arranged at regular intervals on the frequency axis.
[0022] As shown in the upper part of Fig. 7, the repetition time of the optical pulse train, T rep and repetition frequency f rep The relationship between them is expressed as equation (1).
[0023] f rep =1 / T rep …… (1) An optical pulse train is composed of a carrier wave (thick line in the upper part of Fig. 7), which is a superposition wave of many thin spectra, and a wave packet that constitutes the envelope of the carrier wave (dash line in the upper part of Fig. 7). If the above-mentioned optical pulse train on the time axis is Fourier transformed and observed on the frequency axis, as shown in the lower part of Fig. 7, it is found that the repetition time T rep The repetition frequency f corresponds to the inverse of rep The optical comb is a frequency comb with a given carrier envelope offset (CEO, offset frequency) f with respect to zero on the frequency axis. CEO and a predetermined repetition frequency f rep Multiple optical frequency modes f spaced at intervals of an integer multiple of n The frequency f(n) of the nth spectrum of the optical comb is the repetition frequency f rep and carrier envelope offset f CEO With parameters, it is expressed as in equation (2).
[0024] f(n) = n × f rep +f CEO ... (2) Optical combs can measure frequency and distance with high accuracy and are widely used as "precise rulers." In other words, by using an optical comb as the measurement light, steps formed on the surface of the specimen S can be measured with high accuracy.
[0025] The beam splitter 2 splits the light L1 emitted from the light source 1 into a first probe light L2 and a second probe light L3. The first probe light L2 is incident on a variable neutral density filter 3, which is a variable neutral density filter. The second probe light L3 is incident on a delay line 10 after its optical path direction is adjusted by mirrors 8 and 9.
[0026] The variable ND filter 3 reduces the amount of light of the first probe light L2 incident from the beam splitter 2. The amount of light attenuation in the variable ND filter 3 is set by the control and calculation unit 12. The first probe light L2 emitted from the variable ND filter 3 is incident on the beam splitter 5 after the optical path direction is adjusted by the mirror 4.
[0027] The beam splitter 5 splits the first probe light L2 emitted from the variable ND filter 3 into a measurement light L2a and a reference light L2b. The measurement light L2a is incident perpendicularly to the surface of the specimen S. The reference light L2b is incident on a reference mirror 6.
[0028] The reference mirror 6 is a mirror installed at a predetermined distance from the beam splitter 5. The reference light Lb2 is reflected by the reference mirror 6 to generate a reflected reference light L5. The reference mirror 6 may be made of a material that does not easily scatter the reflected reference light L5. For example, the reference mirror 6 may be made of resin or ceramic instead of a mirror. Alternatively, the reference mirror 6 may be a transparent film S2 formed thickly (for example, about several μm) on a substrate S1.
[0029] The delay line 10 delays the second probe light L3 by a set time. The delay line 10 includes two total reflection prisms 11a and 11b with their reflecting surfaces facing each other. When the delay line 10 moves along the arrow D, the optical path length of the second probe light L3 changes and a predetermined delay time is added. The delay time added in the delay line 10 is set in a control and calculation unit 12. The second probe light L3 output from the delay line 10 has its optical path direction adjusted by a mirror 11, and is then perpendicularly incident on the back surface of the specimen S. The measurement light L2a and the second probe light L3 are incident on the specimen S so that the optical axis of the measurement light L2a and the optical axis of the second probe light L3 coincide with each other.
[0030] 2, the specimen S has a transparent film S2 formed on the surface of a substrate S1. A step is formed on the surface of the transparent film S2, and the measurement device of the embodiment measures the step. The specimen S is held by a specimen holder 13, and its position is fixed during measurement. The specimen holder 13 may be a clamp that holds two opposing side surfaces of the specimen S to fix the position, or may be a stage that supports the back surface of the specimen S.
[0031] A part of the measurement light L2a incident on the surface of the specimen S is reflected by the surface of the transparent film S2 of the specimen S (reflected light Lr). A part of the measurement light L2a is transmitted through the transparent film S2 (transmitted light Lt2), and then reflected at the interface between the transparent film S2 and the substrate S1, becoming the interface reflected light Lri. When the refractive index of the substrate S1 is larger than that of the transparent film S2, the interface reflected light Lri undergoes phase inversion with respect to the transmitted light Lt2. For example, when the substrate S1 is silicon and the transparent film S2 is a silicon oxide film or a silicon nitride film, the interface reflected light Lri undergoes phase inversion. On the other hand, at least a part of the second probe light L3 incident on the back surface of the specimen S, i.e., the back surface incident light Lib, transmits through the substrate S1 and is incident into the transparent film S2 (transmitted light Libt).
[0032] In the path from the light L1 to the generation of the interface reflected light Lri, the light L1 is reflected by the mirror 4, the beam splitter 5, and the interface between the transparent film S2 and the substrate S1. That is, in this path, there are three reflections, and a phase inversion occurs in each reflection. Therefore, the phase of the interface reflected light Lri is the opposite phase to the phase of the light L1. On the other hand, in the path from the light L1 to the generation of the back-incident light Lib, the light L1 is reflected by the beam splitter 2, the mirrors 8, 9, and 11, and the total reflection prisms 11a and 11b. That is, in this path, there are six reflections, and a phase inversion occurs in each reflection. Therefore, the phase of the back-incident light Lib is the same phase as the phase of the light L1. In this way, in the measurement device of the embodiment, the number of reflections in each path is set to an even / odd relationship so that the phase of the interface reflected light Lri and the phase of the back-incident light Lib are in opposite phase.
[0033] The interface reflected light Lri can be cancelled by adjusting the phase of the back-incident light Lib so that the intensity of the transmitted light Libt is substantially equal to the intensity of the interface reflected light Lri and the phase of the interface reflected light Lri is in opposite phase to the phase of the transmitted light Libt. The variable ND filter 3 is adjusted to increase or decrease the amount of the measurement light L2a, and the intensity of the interface reflected light Lri can be substantially equal to the intensity of the transmitted light Libt. Furthermore, the optical path length of the second probe light L3 can be adjusted by the delay line 10 with respect to the phase of the interface reflected light Lri and the phase of the transmitted light Libt, so that the transmitted light Libt can be locked to the interface reflected light Lri. The variable ND filter 3 may be disposed in the optical path of the second probe light L3. The delay line 10 may be disposed in the optical path of the first probe light L2. In this way, since the interface reflected light Lri is cancelled out by the transmitted light Libt, the signal light L4, which is a combination of the light generated in the subject S by the measurement light L2a and the light generated in the subject S by the second probe light L3, can be regarded as equivalent to the reflected light Lr.
[0034] The signal light L4 and the reflected reference light L5 are combined by the beam splitter 5 to become combined signal light L6, which is received by the detection unit 7. The detection unit 7 includes, for example, a photodiode, and detects the waveform of the combined signal light L6.
[0035] In the control and calculation unit 12, the phase difference between the reflected reference light L5 and the signal light L4 is calculated from the waveform of the combined signal light L6 detected by the detection unit 7. The calculation of the step in the control and calculation unit 12 is performed, for example, as follows. First, the phase difference between the signal light L4 (=Lr1) and the reflected reference light L5 (=Lrs) is calculated from the waveform of the combined signal light L6 obtained when the measurement light L2a is irradiated onto the first surface of the specimen S. The time difference Δt1 between the signal light L4 and the reflected reference light L5 is calculated from the phase difference between the signal light L4 and the reflected reference light L5. Next, the phase difference between the signal light L4 (=Lr2) and the reflected reference light L5 (=Lrs) is calculated from the waveform of the combined signal light L6 obtained when the measurement light L2a is irradiated onto the second surface of the specimen S. The time difference Δt2 between the signal light L4 and the reflected reference light L5 is calculated from the phase difference between the signal light L4 and the reflected reference light L5. The difference between the time difference Δt1 and the time difference Δt2 is calculated to obtain the time difference Δt12 between the signal light Lr1 and the signal light Lr2. The time difference Δt12 is multiplied by the speed of the signal light L4 and divided by 2 to calculate the step ΔZ between the first surface and the second surface.
[0036] Based on the waveform of the combined signal light L6 detected by the detector 7, the control and calculation unit 12 also instructs the variable ND filter 3 to increase or decrease the amount of light attenuation and instructs the delay line 10 to increase or decrease the optical path length.
[0037] Next, a method for measuring a step using the measurement device of the embodiment will be described with reference to Fig. 8. Fig. 8 is a flow chart for explaining an example of the measurement method of the embodiment. First, a step to be measured in the subject S is identified, and an irradiation area is set so that the first surface, i.e., the upper surface of the step, is irradiated with measurement light L2a (S1). Next, light L1 (e.g., an optical comb) is emitted from the light source 1 (S2).
[0038] As described above, the light L1 is split into the first probe light L2 and the second probe light L3 by the beam splitter 2. The measurement light L2a split from the first probe light L2 by the beam splitter 5 is perpendicularly incident on the irradiation area of the subject S from the front side (upper side in the direction D3). The second probe light L3 is perpendicularly incident on the irradiation area of the subject S from the back side (lower side in the direction D3) coaxially with the measurement light L2a. The signal light L4 generated from the subject S by irradiation with the measurement light L2a and the second probe light L3 is incident on the detection unit 7 via the beam splitter 5. The detection unit 7 observes the waveform component of the signal light L4 in the combined signal light L6 (S3). The amount of light attenuation of the variable ND filter 3 and the amount of delay of the delay line 10 are adjusted (S4) so that the output signal of the detection unit 7 approaches a minimum value (the wording of FIG. 8 is also modified in the same way).
[0039] When the output signal of the detection unit 7 becomes sufficiently small and adjustment of the light attenuation amount of the variable ND filter 3 and the delay amount of the delay line 10 is completed, the phase difference between the reflected reference light L5 and the signal light L4 is obtained based on the waveform component of the reflected reference light L5 in the combined signal light L6 and the waveform component of the signal light L4. Furthermore, the time difference Δt between the reflected reference light L5 and the signal light L4 is calculated from the phase difference (S5). Here, since the irradiation area is the first surface of the subject S, the time difference Δt1 is calculated.
[0040] If the time difference Δt between the first surface and the reference surface has not been calculated for either the first surface or the second surface of the specimen S (S6, NO), the irradiation area is moved (S7) and a series of steps from S3 to S5 are repeated. Since only the time difference Δt1 on the first surface of the specimen S has been calculated in the above, the process proceeds to S7 and the irradiation area on the specimen S is set to the second surface (the lower surface of the step). Then, the series of steps from S3 to S5 are executed for the second surface to calculate the time difference Δt2 on the second surface.
[0041] If the time difference Δt between the first and second surfaces of the specimen S and the reference surface has been calculated (S6, YES), the step ΔZ is calculated from the time differences Δt1 and Δt2 (S8), and the series of procedures is terminated.
[0042] In this way, according to the measurement device of the embodiment, when measuring the step on the surface of the transparent film S2 of the specimen S in which the transparent film S2 is formed on the substrate S1, the second probe light L3 as the backside incident light Lib is also irradiated from the backside of the specimen S when the measurement light L2a is irradiated from the front side of the specimen S. Of the second probe light L3, the transmitted light Libt that is transmitted through the substrate S1 and incident on the transparent film S2 has a complementary intensity relationship with the interface reflected light Lri in the opposite phase. Since the interface reflected light Lri is offset by the transmitted light Libt whose phase and intensity are adjusted in this way, the generation of the background light Lb1 and the interface reflected light Lri' is suppressed. Therefore, the reflected light Lr from the surface of the transparent film S2 can be detected without being affected by the background light Lb1 and the interface reflected light Lri', and the step on the surface of the specimen S can be measured with high accuracy.
[0043] Moreover, according to the measurement method of the embodiment, the waveform component of the signal light L4 from the specimen S is observed while irradiating the front surface of the specimen S with the measurement light L2a and the rear surface of the specimen S with the second probe light L3. Until the background light Lb1 is sufficiently removed from the waveform component of the signal light L4 and the waveform of the reflected light Lr can be extracted, the phase of the second probe light L3 is adjusted by the delay line 10 and the intensity of the measurement light L2a is adjusted by the variable ND filter 3. Therefore, the reflected light Lr from the surface of the transparent film S2 can be detected with the background light Lb1 sufficiently removed, and the step on the surface of the specimen S can be measured with high accuracy.
[0044] The light L1 is not limited to the optical comb described above. Any light having a wavelength that can be transmitted through the substrate S1 may be used, for example, a pulsed laser or a CW laser may be used. The transparent film S2 is not limited to the silicon oxide film or silicon nitride film described above. Any film that transmits the measurement light L2a and does not scatter the transmitted light Lt2 may be used, for example, a resin film or a ceramic film.
[0045] In the above, the measurement of the step between two points on the specimen S has been described, but the measurement device of the embodiment can also measure the uneven shape of the surface in a measurement region set on the specimen S. Fig. 9A is a block diagram showing an example of the configuration of another measurement device according to the present embodiment. Fig. 9B is a diagram explaining a method of measuring the surface shape of the specimen by the measurement device shown in Fig. 9A.
[0046] The measurement device shown in FIG. 9 further includes a holder driving mechanism 14 in addition to the configuration of the measurement device shown in FIG. 6. In FIG. 9, the same components as those shown in FIG. 6 are denoted by the same reference numerals and will not be described. The holder driving mechanism 14 moves the specimen holding part 13 in the D1 direction and the D2 direction. During measurement, by moving the specimen holding part 13 in the D1 direction and / or the D2 direction while holding the specimen S, the irradiation area can be moved while the optical axes of the measurement light L2a and the second probe light L3 are aligned. Even if the irradiation area is moved, the distance between the beam splitter 5 and the reference mirror 6 does not change, so the optical path length of the reflected reference light L5 can be kept constant. The operation of the holder driving mechanism 14 is controlled by the control and calculation unit 12.
[0047] FIG. 9B shows an enlarged measurement area of the uneven shape of the surface of the specimen S. As shown in FIG. 9B, for example, in a measurement area set in a rectangular shape with one side of several hundred μm, N areas of irradiation target areas Ri (i=1, 2, ... N) are set as irradiation areas (for example, several μm in diameter) of the measurement light L2a. The specimen holding part 13 is moved by the holding part driving mechanism 14 so that the measurement light L2a is irradiated to the first irradiation target area R1, and the position of the specimen S is set. After the position of the specimen S is fixed, the composite signal light L6 in the irradiation target area R1 is obtained by the above-mentioned measurement method, and the time difference Δt1 with respect to the reference surface is obtained. After the measurement of the irradiation target area R1 is completed, the specimen holding part 13 is moved so that the measurement light L2a is irradiated to the next irradiation target area R2. Then, the composite signal light L6 in the irradiation target area R2 is obtained by the above-mentioned measurement method, and the time difference Δt2 with respect to the reference surface is obtained. In this way, by acquiring the composite signal light L6 while shifting the position of the irradiation area, the time difference Δti with respect to N reference surfaces is acquired. From these time differences Δti, the distance difference ΔZi with respect to the reference surface in each irradiation target area Ri is calculated. By mapping the distance difference ΔZi using the coordinates of each irradiation target area Ri, the uneven shape of the surface within the measurement area can be measured.
[0048] In the measurement device shown in FIG. 6, the optical comb of the light L1 emitted from the light source 1 has a center frequency fc of several hundred THz and a repetition frequency f rep The repetition frequency f is about 100MHz to GHz. rep Because the time interval between optical pulses is too narrow, it is difficult to observe them using a spectrometer. In addition, the interval between optical pulses is also very narrow, ranging from a few femtoseconds to a few ps, making it difficult to measure the phase. Therefore, it is possible to perform measurements using dual-comb spectroscopy using a measurement device equipped with two optical comb light sources.
[0049] 10A and 10B are schematic diagrams illustrating dual-comb spectroscopy. Dual-comb spectroscopy is a technique for acquiring information on each optical frequency mode of an optical comb, and can be used to measure the physical properties of a sample with high accuracy. As shown in FIG. 10A, the repetition frequency frep Optical comb A with repetition rate f rep +Δf rep The optical comb B is passed through the sample. When the optical comb C, which passes through the sample and contains the optical information of the sample, interferes with the optical comb A, a beat is generated and the beat signal has a repetition frequency of Δf rep For example, the repetition rate of optical comb A is f rep 100.000MHz, and the repetition rate of the optical comb B, f rep +Δf rep is set to 100.001 MHz. Also, the i-th optical frequency mode of optical comb A is controlled to match the j-th optical frequency mode of optical comb B. In this case, the beat between the i+1-th spectrum of optical comb A and the j+1-th spectrum of optical comb C is at a frequency Δf rep = 1kHz. Similarly, the i+mth spectrum of optical comb A appears at mkHz. This means that the repetition rate of 100MHz in optical frequency is expressed as 10 ―5 Since the frequency can be reduced by 1x (=1 kHz), the waveform of optical comb C, which contains the optical information of the sample, can be observed as an electrical signal, making it possible to separate and observe each optical frequency mode.
[0050] In addition, if the two optical combs A and C shown in FIG. 10A are represented on the time axis, as shown in FIG. 10B, the pulses of optical comb A and optical comb C are separated by a time ΔT rep There is a difference in the periods by only 1. The waveform (interferogram) produced by interfering two such optical combs A and C is a waveform that is a stretched-out version of optical comb C. Optical comb C has a short period and is difficult to measure. In contrast, the waveform produced by interfering two optical combs has a long period. Since the interference waveform can be observed using an oscilloscope, the waveform of optical comb C can be measured, and optical information of the sample can be obtained with high accuracy.
[0051] 10C is a block diagram showing the configuration of a modified example of the measurement device of this embodiment. The measurement device of the modified example includes a second light source 1A in addition to the components shown in FIG. 6. Furthermore, both the light L1 emitted from the light source 1 and the light L1A emitted from the second light source 1A are optical combs. The repetition frequency f rep_1A is the repetition frequency f of light L1 rep_1 The light L1A corresponds to the optical comb A described above, and the light L1 corresponds to the optical comb B described above.
[0052] The optical beat signal L7 is generated by interfering the signal light L6 corresponding to the optical comb C with the light L1A. As described above, the optical beat signal L7 has a waveform obtained by stretching the signal light L6 in time. The repetition frequency f rep_1A and repetition frequency f rep_1 The difference between rep_1 Then, the optical beat signal L7 is Δf rep_1 As mentioned above, Δf rep_1 When a frequency in the radio frequency band is set as , the optical beat signal L7 becomes an electrical signal and can be observed with high accuracy using an oscilloscope or the like. This allows the delay time to be measured with high accuracy. In this way, by configuring the measurement device with a dual comb configuration, the step on the surface of the specimen S can be measured with high accuracy.
[0053] In the above, the measurement device of the embodiment is described as an example of measuring the step on the surface of the specimen S, but the measurement device of the embodiment can be applied to monitor not only the shape of the step, but also the film quality (e.g., refractive index, absorptance, etc.) on the surface of the specimen S. For example, when there is no light absorption in the transparent film S2, it is possible to obtain the refractive index of the transparent film S2 from the intensity ratio of the reflected light Lg to the incident light Li. The measurement device of the embodiment can also be applied to a process monitor. For example, it can be applied to inspecting the uneven shape of the surface of a wafer after a predetermined process such as a film formation process in the manufacturing process of a semiconductor device. In addition, it is also possible to apply it to monitoring the amount of film formation by measuring the surface of the wafer using the measurement device of the embodiment at each of two points in the film formation process and calculating the distance difference from the reference surface.
[0054] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]
[0055] 1...light source, 2, 5...beam splitter, 3...variable ND filter, 4, 8, 9, 11...mirror, 6...reference mirror, 7...detection unit, 10...delay line, 12...control and calculation unit, 13...subject holder, S...subject, S1...substrate, S2...transparent film
Claims
1. A measurement apparatus for measuring a surface of a first film on a test object having a substrate on which a first film is formed, comprising: A light source that generates a first light; a beam splitter that splits the first light into a second light and a third light; a detection unit that receives signal light generated from an object by irradiation with the second light and the third light; Equipped with the first light has a wavelength that can be transmitted through the substrate, the second light is perpendicularly incident on a surface of the first film, the third light is incident perpendicularly to the second light from the rear surface of the substrate and is coaxial with the second light; a phase of transmitted light of the third light that has been transmitted through the substrate is inverse to a phase of reflected light that is generated when a portion of the second light is transmitted through the first film and reflected on a surface of the substrate; The intensity of the transmitted light is approximately equal to the intensity of the reflected light.
2. 2. The measurement apparatus according to claim 1, wherein the first light is an optical frequency comb having a component of a predetermined offset frequency with respect to zero on a frequency axis, and a plurality of frequency components spaced apart from the offset frequency by an integer multiple of a first repetition frequency.
3. The measurement apparatus according to claim 1 , further comprising a variable neutral density filter, the variable neutral density filter being disposed in an optical path of either the second light or the third light.
4. The measurement apparatus according to claim 1 , further comprising a delay line capable of delaying transmission of light, the delay line being disposed in an optical path of either the second light or the third light.
5. 1. A method for measuring a surface of a first film on a test object having a substrate on which a first film is formed, comprising: generating a first light having a wavelength capable of being transmitted through the substrate; splitting the first light into a second light and a third light; The second light is perpendicularly incident on a surface of the first film; The third light is incident perpendicularly to the second light from a rear surface of the substrate and is coaxial with the second light; adjusting the intensities and delay times of the second light and the third light such that a transmitted light of the third light that has been transmitted through the substrate and a reflected light generated by a portion of the second light being transmitted through the first film and reflected on the surface of the substrate have an inverse phase and complementary intensity relationship with each other; detecting signal light generated from an object by irradiating the object with the second light and the third light; monitoring a surface of the first film based on the signal light; Measurement methods, including