JP4739393B2 - Method for creating diagram used for light wavelength selection for polishing end point detection, light wavelength selection method, polishing end point detection method, polishing end point detection device, and polishing device - Google Patents

Description

  The present invention relates to a method and an apparatus for selecting a wavelength of light used for optical polishing end point detection of a substrate having a transparent insulating film. The present invention also relates to a method and apparatus for detecting a polishing end point using light of a selected wavelength.

  In a semiconductor device manufacturing process, various materials are repeatedly formed in a film shape on a silicon wafer to form a laminated structure. In order to form this laminated structure, a technique for flattening the surface of the uppermost layer is important. As a means for such planarization, a polishing apparatus that performs chemical mechanical polishing (CMP) is used.

  This type of polishing apparatus generally includes a polishing table that supports a polishing pad, a top ring that holds a substrate (a wafer on which a film is formed), and a nozzle that supplies a polishing liquid onto the polishing pad. When polishing the substrate, while supplying the polishing liquid from the nozzle onto the polishing pad, the substrate is pressed against the polishing pad by the top ring, and the top ring and the polishing table are moved relative to each other to polish the substrate. Flatten the top film. The polishing apparatus usually includes a polishing end point detection device. The polishing end point detection device determines that the polishing end point has been reached when the film is removed to a predetermined thickness.

  As an example of the polishing end point detection device, there is a so-called optical polishing end point detection device that irradiates light on the surface of a substrate and determines the polishing end point based on information contained in reflected light. An optical polishing end point detection device generally includes a light projecting unit, a light receiving unit, and a spectroscope. The spectroscope decomposes the reflected light from the substrate according to the wavelength and measures the reflection intensity for each wavelength. This optical polishing end point detection device is often used when polishing a substrate on which a light-transmitting film is formed. For example, in the method disclosed in Patent Document 1, a characteristic value is generated by performing a predetermined process for removing a noise component on the intensity (reflection intensity) of reflected light returning from the substrate. The polishing end point is detected from the characteristic point (maximum point or minimum point) of the change.

  As shown in FIG. 1, the characteristic value generated from the reflection intensity changes periodically with the polishing time, and the maximum point and the minimum point appear alternately. This is a phenomenon caused by interference between lights. That is, the light irradiated to the substrate is reflected at the interface between the medium and the film and the interface between the film and the underlying layer of the film, and the lights reflected at these interfaces interfere with each other. The manner of interference of light varies depending on the thickness of the film (that is, the optical path length). For this reason, the intensity of the reflected light returning from the substrate (that is, the reflection intensity) periodically changes according to the thickness of the film.

  As shown in FIG. 1, the optical polishing end point detection apparatus described above counts the number of characteristic points (maximum points or minimum points) of the characteristic value change that appears after the start of polishing, and the number of feature points is set to a predetermined number. Detect when it is reached. Then, the polishing is stopped when a predetermined time elapses from the detected time.

The characteristic value is an index obtained based on the reflection intensity or the relative reflectance. The relative reflectance is a ratio between the intensity (reference value) of certain predetermined light and the intensity of reflected light. For example, the relative reflectance is measured in the absence of a reflection object from the reflection intensity at each wavelength during polishing of the substrate to be polished and the reference reflection intensity at each wavelength acquired under a certain polishing condition. The obtained background intensity is subtracted, and the former of the two obtained reflection intensities is divided by the latter. Specifically, the relative reflectance is obtained from the following equation.
Relative reflectance R (λ) = {E (λ) −D (λ)} / {B (λ) −D (λ)} (1)
Here, λ is the wavelength, E (λ) is the reflection intensity of the substrate to be polished, B (λ) is the reference reflection intensity, and D (λ) was acquired in the absence of the substrate. Background intensity (dark level). As the reference reflection intensity B (λ), for example, when the silicon substrate is water-polished while pure water is supplied onto the polishing pad, the intensity of light returning from the silicon substrate can be used.

Then, using relative reflectances at a plurality of wavelengths λk (k = 1,..., K), a characteristic value S (λ1, λ2,..., ΛK) is obtained from the following equation.
X (λk) = ∫R (λ) · Wk (λ) dλ (2)
S (λ1, λ2,..., ΛK) = X (λ1) / {X (λ1) + X (λ2) +.
+ X (λK)} = X (λ1) / ΣX (λk) (3)
Here, Wk (λ) represents a weighting function centered at the wavelength λk (that is, the maximum value is indicated at the wavelength λk). FIG. 2 shows an example of the weight function. The maximum value and width of the weight function shown in FIG. 2 can be changed as appropriate. In equation (2), the integration interval is from the minimum wavelength to the maximum wavelength that can be measured by the spectroscope of the optical polishing end point detection device. For example, if the wavelength that can be measured by the spectroscope is 400 nm or more and 800 nm or less, the integration interval of Equation (2) is [400, 800]. The number of wavelengths λ of light used for calculating the characteristic value is preferably two or three.

  In Equation (3), the relative reflectance is divided by the relative reflectance, so that even if the received light amount fluctuates due to a minute change in the distance between the substrate, the light projecting unit, and the light receiving unit, or mixing of slurry, the effect is suppressed. be able to. Therefore, it is possible to obtain a more stable time-change waveform related to the characteristic value. Note that the characteristic value can be obtained from the reflection intensity instead of the relative reflectance according to the same method.

  In order to detect an accurate polishing end point, it is necessary to select a wavelength at which the maximum point or the minimum point of the characteristic value appears when the target film thickness is approached or the target film thickness is reached. However, in practice, it is a fact that an optimum wavelength is found by trial and error, and a long time is required for wavelength selection.

Japanese Patent Laid-Open No. 2004-154928

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide a diagram creation method capable of efficiently selecting a wavelength of light optimal for optical polishing end point detection. Another object of the present invention is to provide a method for efficiently selecting a wavelength of light optimal for optical polishing end point detection. A further object of the present invention is to provide a method and apparatus for detecting the polishing end point using light of a selected wavelength.

In order to achieve the above-described object, one embodiment of the present invention is a method for creating a diagram used for selecting a wavelength of light in optical polishing end point detection, and polishing a surface of a substrate having a film with a polishing pad, During the polishing, the surface of the substrate is irradiated with light, and the reflected light returning from the substrate is received, the relative reflectance of the reflected light is calculated for each wavelength, and the relative reflectance that changes with the polishing time is calculated. On the coordinate system having the coordinate axes representing the wavelength of light and the polishing time, determining the wavelength when the wavelength indicating the maximum point and the minimum point is determined, determining the wavelength of the reflected light indicating the maximum point and the minimum point in comprising the step of creating a diagram by plotting the coordinates specified by the time when the determined wavelength and corresponding coordinates on the diagrams, known eye polishing end point detection Characterized in that it comprises a coordinate that exists within a predetermined time range around the time.

In a preferred aspect of the present invention, the step of determining the wavelength of the reflected light indicating the local maximum point and the local minimum point calculates an average value of the relative reflectance for each wavelength, and calculates the relative reflectance at each time point as the average. It is a step of correcting the relative reflectance by dividing by a value, and determining the wavelength of the reflected light indicating the maximum point and the minimum point of the corrected relative reflectance.
In a preferred aspect of the present invention, the step of obtaining the wavelength of the reflected light indicating the maximum point and the minimum point calculates an average value of the relative reflectance for each wavelength, and calculates the average from the relative reflectance at each time point. The relative reflectance is corrected by subtracting a value, and the wavelength of the reflected light indicating the maximum point and the minimum point of the corrected relative reflectance is obtained.

Another aspect of the present invention is a method of selecting a wavelength of light used for optical polishing end point detection, wherein a surface of a substrate having a film is polished with a polishing pad, and light is applied to the surface of the substrate during the polishing. The reflected light returning from the substrate is received, the relative reflectance of the reflected light is calculated for each wavelength, and the reflected light indicating the maximum and minimum points of the relative reflectance that change with the polishing time is calculated. The wavelength is obtained, the time point when the wavelength is obtained is specified, and the coordinates specified by the obtained wavelength and the corresponding time point are plotted on the coordinate system having the coordinate axis representing the wavelength of the light and the polishing time. To create a diagram, search for coordinates existing within a predetermined time range centered on a known target time for polishing end point detection on the diagram, and select a plurality of wavelengths from among the wavelengths constituting the searched coordinates Wavelength And selects.

In a preferred aspect of the present invention, the step of selecting a plurality of wavelengths from among the wavelengths constituting the searched coordinates generates a plurality of combinations of a plurality of wavelengths using the wavelengths constituting the searched coordinates. Then, from the relative reflectance at each of the plurality of wavelengths in each combination, a characteristic value that periodically changes as the film thickness changes is calculated, and a score of the plurality of combinations is calculated using a wavelength evaluation formula And a step of selecting a plurality of wavelengths constituting the combination having the highest score.
In a preferred aspect of the present invention, the wavelength evaluation formula includes, as evaluation elements, a time point at which a maximum point or a minimum point of the characteristic value appears and an amplitude of a graph drawn by the characteristic value with polishing time. To do .

  Another aspect of the present invention is a polishing end point detection method, in which a surface of a substrate having a film is polished with a polishing pad, and during the polishing, the surface of the substrate is irradiated with light and reflected back from the substrate. Receiving light, calculating the relative reflectance of the reflected light at a plurality of wavelengths selected according to the wavelength selection method described above, and periodically from the calculated relative reflectance as the thickness of the film changes A characteristic value that changes is calculated, and a polishing end point of the substrate is detected by detecting a maximum point or a minimum point of the characteristic value that appears during polishing.

  Another aspect of the present invention is a polishing end point detection device, wherein during polishing, a light projecting unit that irradiates light onto a surface of a substrate having a film, a light receiving unit that receives reflected light returning from the substrate, From the spectroscope that measures the reflection intensity for each wavelength of the reflected light, and the reflection intensity measured by the spectroscope, a characteristic value that periodically changes as the film thickness changes is calculated, and the characteristic value is calculated. A monitoring device for monitoring, the monitoring device calculates a relative reflectance from the reflection intensities at a plurality of wavelengths selected according to the wavelength selection method described above, and from the calculated relative reflectance, the thickness of the film A characteristic value that periodically changes with a change in the value is calculated, and a polishing end point of the substrate is detected by detecting a maximum point or a minimum point of the characteristic value that appears during polishing.

  In another aspect of the present invention, a polishing table that supports the polishing pad and rotates the polishing pad, a top ring that holds a substrate having a film and presses the substrate against the polishing pad, and a polishing end point of the substrate is provided. A polishing end point detection device for detecting, the polishing end point detection device, during polishing, a light projecting unit for irradiating the surface of the substrate having a film, a light receiving unit for receiving the reflected light returning from the substrate, A spectroscope that measures the reflection intensity for each wavelength of the reflected light, and a characteristic value that periodically changes as the film thickness changes from the reflection intensity measured by the spectroscope. The monitoring device calculates a relative reflectance from the reflection intensities at a plurality of wavelengths selected according to the wavelength selection method described above, and from the calculated relative reflectance, As the thickness changes Calculate the periodically varying characteristic value, a polishing apparatus and detecting the polishing end point of the substrate by detecting a maximum point or minimum point of the characteristic value which appears in polishing.

  The diagram prepared according to the present invention shows the relationship between the maximum and minimum points distributed according to the polishing time and the wavelength of light. Therefore, by searching for a maximum point and a minimum point that appear at a known target polishing end point detection time or a time in the vicinity thereof, the wavelength of the corresponding light can be easily selected.

Hereinafter, embodiments of the present invention will be described. FIG. 3A is a schematic diagram for explaining a polishing end point detection method according to an embodiment of the present invention, and FIG. 3B is a plan view showing a positional relationship between the substrate and the polishing table. As shown in FIG. 3A, a substrate W to be polished includes a base layer (for example, a silicon layer or a tungsten film) and a film formed thereon (for example, light-transmitting SiO ₂ or the like). Insulating film). The light projecting unit 11 and the light receiving unit 12 are arranged to face the surface of the substrate W. During polishing of the substrate W, as shown in FIG. 3B, the polishing table 20 and the substrate W rotate, and a relative movement between a polishing pad (not shown) on the polishing table 20 and the substrate W causes the substrate W to move. The surface is polished.

  The light projecting unit 11 emits light substantially perpendicularly to the surface of the substrate W, and the light receiving unit 12 receives light returning from the substrate W. The light projecting unit 11 and the light receiving unit 12 move across the substrate W every time the polishing table 20 rotates once. At this time, the light projecting unit 11 projects light to a plurality of measurement points including the central portion of the substrate W, and the light receiving unit 12 receives reflected light. A spectroscope 13 is connected to the light receiving unit 12, and the spectroscope 13 measures the intensity of reflected light (that is, the reflection intensity) for each wavelength. More specifically, the spectroscope 13 decomposes the reflected light according to the wavelength, and generates spectral data representing the reflection intensity for each wavelength.

FIG. 4 shows spectral data when an oxide film (SiO ₂ ) having a uniform thickness of 600 nm formed on a silicon wafer is polished. In the graph shown in FIG. 4, the horizontal axis represents the wavelength of light, and the vertical axis represents the relative reflectance calculated from the reflection intensity according to the above formula (1). As shown in FIG. 4, as the film thickness decreases (that is, the polishing time increases), the positions of the maximum point and the minimum point of the relative reflectance change. In general, as the film thickness decreases, the maximum point moves to the short wavelength side, and the interval between the maximum points increases.

  A monitoring device 15 is connected to the spectrometer 13. As the monitoring device 15, a general-purpose or dedicated computer can be used. During the polishing, the monitoring device 15 calculates the relative reflectance and the characteristic value from the spectral data, monitors the time variation of the characteristic value, and detects the polishing end point based on the maximum or minimum point of the characteristic value ( (See FIG. 1). The calculation of the relative reflectance and the characteristic value is performed using the above-described Expression (1), Expression (2), and Expression (3).

  In FIG. 3A, the refractive index of the film is n, the refractive index of the medium in contact with the film is n ′, and the refractive index of the underlayer is n ″. The refractive index n of the film is the refractive index n of the medium. If the refractive index n ″ of the underlayer is larger than the refractive index n of the film (n ′ <n <n ″), the light is reflected at the interface between the medium and the film and the interface between the film and the underlayer. The phase of the light is shifted by π with respect to the incident light, and the reflected light returning from the substrate is light that is reflected by the light reflected at the interface between the medium and the film and the light reflected at the interface between the film and the underlayer. Therefore, the intensity of the reflected light changes depending on the phase difference between the two lights, so that the characteristic value described above changes periodically according to the change in the thickness of the film (that is, the change in the optical path length) ( (See FIG. 1).

The maximum and minimum points (that is, feature points) of the characteristic value that change according to the thickness of the film, that is, the polishing time, are defined as points that indicate the maximum and minimum values of the characteristic value. The maximum point and the minimum point are points where the light reflected at the interface between the medium and the film and the light reflected at the interface between the film and the underlayer are strengthened and weakened. Therefore, the thickness of the film when the maximum point appears and the thickness of the film when the minimum point appears are expressed by the following equations (4) and (5).
Maximum point: 2nx = mλ (4)
Minimum point: 2nx = (m−1 / 2) λ (5)
Here, x is the thickness of the film, λ is the wavelength of light, and m is a natural number. Note that m represents the phase difference between the lights strengthened by interference (the number of waves on the optical path in the film).

  As described above, the wavelength indicating the maximum point and the minimum point of the relative reflectance changes according to the change in the film thickness (polishing time). Therefore, the monitoring device 15 acquires the spectral data of the reflection intensity during polishing of the sample substrate having the same structure (the same wiring pattern and the same film) as the substrate to be polished, and sets the wavelength of the reflected light indicating the maximum point and the minimum point. Determine the polishing time when the wavelength is determined. The monitoring device 15 stores the obtained wavelength and the corresponding polishing time in a storage device (not shown) built in the monitoring device 15. Further, the monitoring device 15 plots the coordinates of the stored wavelength and the corresponding polishing time on a coordinate system in which the vertical axis indicates the wavelength and the horizontal axis indicates the polishing time, and a diagram as shown in FIG. Create Hereinafter, this diagram is referred to as a distribution map of local maximum points and local minimum points, or simply a distribution map. It should be noted that the distribution map may be created by taking the spectrum data acquired by the monitoring device 15 into another computer and using this computer.

  In the distribution diagram shown in FIG. 5A, the symbol ◯ represents the coordinates of the maximum point, and the symbol × represents the coordinates of the minimum point. As can be seen from FIG. 5 (a), the positions of the coordinates indicating the maximum point and the minimum point with the polishing time show a downward trend. Therefore, it can be said that the distribution diagram shown in FIG. FIG. 5B is a graph showing the relative reflectance that varies with the polishing time. As can be seen from FIGS. 5 (a) and 5 (b), the maximum and minimum points of relative reflectance at each wavelength shown in FIG. 5 (b) are the maximum and minimum points on FIG. 5 (a). Appears at approximately the time corresponding to. When the film thickness x in the expressions (4) and (5) is replaced with the polishing time, the straight line connecting the maximum points and the straight line connecting the minimum points in FIG. 5A are expressed by the expressions (4) and (5), respectively. Can be represented.

The above-described spectral data of FIG. 4 is obtained when a substrate having a film having a uniform thickness formed on an underlayer is polished. Next, spectral data obtained by polishing a substrate on which a film is formed on a base layer having a level difference will be described. FIG. 6 is a cross-sectional view showing a part of a substrate on which a film is formed on a base layer having a step. In this example, the underlayer is a tungsten film that is sufficiently thick to prevent light from passing therethrough, and the step formed on the surface thereof is about 100 nm. An oxide film (SiO ₂ ) having a thickness of 600 nm to 700 nm is formed on the base layer.

  FIG. 7A shows spectral data obtained by polishing a substrate having such a structure. As can be seen from FIG. 7A, due to the underlying layer, the longer the wavelength of light, the larger the relative reflectance, and the relative reflectance maximum and minimum points do not appear clearly. FIG. 7B is a diagram obtained by plotting on the coordinate system the coordinates of the wavelength and the polishing time indicating the local maximum point and the local minimum point in accordance with the same manner as in FIG. As shown in FIG. 7B, the coordinates indicating the local maximum point and the local minimum point change substantially horizontally without showing a downward-sloping tendency.

  Therefore, in order to remove the influence of the underlayer, the monitoring device 15 calculates the average value of the relative reflectance for each wavelength, and divides the relative reflectance at each time point by the average value corresponding to the wavelength. Generate normalized spectral data (normalized relative reflectance). The average value of relative reflectance is the average value of relative reflectance over the total polishing time from the start of polishing to the end point of polishing, and is obtained for each wavelength. FIG. 8 shows normalized relative reflectance spectral data. As can be seen from FIG. 8, each graph showing the normalized relative reflectance shows clear local maximum points and local minimum points.

  FIG. 9A is a distribution diagram created based on the normalized relative reflectance, and coordinates of the wavelength and polishing time indicating the maximum and minimum points are coordinated according to the same manner as in FIG. 5A. It is a distribution map obtained by plotting on the system. As shown in FIG. 9 (a), the positions of the coordinates indicating the maximum point and the minimum point on the normalized relative reflectance show a downward trend as in FIG. 5 (a). Therefore, the distribution diagram shown in FIG. 9A can visually provide a state in which the film thickness decreases as the polishing time elapses.

  The normalized relative reflectance is obtained by dividing the relative reflectance by the average value of the relative reflectance at the corresponding wavelength. Therefore, the positions (time points) of the maximum point and the minimum point on the normalized relative reflectance when viewed along the time axis coincide with the positions (time points) of the maximum point and the minimum point on the relative reflectance. FIG. 9B is a graph showing the relative reflectance that varies with the polishing time. As can be seen from FIGS. 9 (a) and 9 (b), the maximum and minimum points of the normalized relative reflectance shown in FIG. 9 (a) are approximately the maximum and minimum points on FIG. 9 (b). Appears at the corresponding time.

  Even if the average value of the relative reflectance at each wavelength is subtracted from the relative reflectance for each wavelength calculated at each time point, the same spectrum data and the same maximum as in the case of the normalized relative reflectance described above are used. A distribution map of points and local minimum points is obtained. FIG. 10A is a diagram showing spectral data obtained by subtracting the average value of the relative reflectance from the relative reflectance at each time point, and FIG. 10B is shown in FIG. It is a distribution map of a maximum point and a minimum point created using spectrum data. As can be seen from FIG. 10 (a) and FIG. 10 (b), also in this case, the same spectrum data and distribution diagram as those in FIG. 9 (a) and FIG. 9 (b) are obtained.

  FIG. 11A is a contour map of relative reflectance corresponding to FIG. 7A, and FIG. 11B is a contour map of normalized relative reflectance corresponding to FIG. From FIG. 11 (b), it can be seen that as the polishing time increases, the normalized relative reflectance tends to decrease to the right as a whole.

  Here, a method of selecting two wavelengths using the distribution diagram of the maximum points and the minimum points will be described with reference to FIG. In FIG. 12, a symbol tI indicates a target time for detecting the polishing end point (hereinafter referred to as a detection target time). The wavelength to be selected is a wavelength at which a maximum point or a minimum point appears within a predetermined time range centered on the detection target time tI. The detection target time tI reaches the target film thickness by polishing a sample substrate having the same structure as the substrate to be polished, measuring the film thickness after polishing (preferably also with the film thickness before polishing). It can be determined by obtaining the time when

  Next, a detection time lower limit tL and a detection time upper limit tU are set for the detection target time tI. These detection time lower limit tL and detection time upper limit tU define a time range Δt in which detection of the maximum point or the minimum point of the characteristic value is allowed in the polishing end point detection process. The detection time lower limit tL and the detection time upper limit tU also define the search range for the maximum point and the minimum point of relative reflectance. That is, all local maximum points and local minimum points existing in this time range Δt are searched, and wavelengths corresponding to these local maximum points and local minimum points are selected as candidates. Next, a wavelength combination is generated from the selected wavelengths. The number of wavelength combinations generated depends on the number of wavelengths selected as candidates.

When there are two wavelengths to be finally selected, a combination of two wavelengths is generated using a plurality of wavelengths selected as candidates. For example, in the example shown in FIG. 12, λ _P1 , λ _P2 , λ _V1 , and λ _V2 are selected as the wavelength candidates, so that the combinations of the generated two wavelengths are [λ _P1 , λ _V1 ], [ λ _P1 , λ _V2 ], [λ _P2 , λ _V1 ], [λ _P2 , λ _V2 ] and the like.

  The distribution diagram of the maximum points and minimum points described above is a diagram showing the relationship between the maximum points and minimum points distributed according to the polishing time and the wavelength of light. Therefore, by searching for local maximum points and local minimum points that appear within a predetermined time range centered on a known detection target time, the wavelength of light corresponding to the local maximum points and local minimum points can be easily selected. Such selection of the wavelength may be performed by an operator, or may be performed by the monitoring device 15 or another computer. Although this example is a description of a method of selecting two wavelengths, a similar method can be used when three or more wavelengths are selected.

  FIG. 13 is a distribution diagram of local maximum points and local minimum points created based on spectrum data measured when a substrate on which a wiring pattern is formed is polished. As shown in FIG. 13, when the pattern substrate is polished, the maximum point and the minimum point change in a complicated manner with the polishing time. However, also in this case, the maximum point and the minimum point change relatively regularly in the region surrounded by the dotted line in FIG. In such a region, a characteristic value having a good S / N ratio (that is, drawing a smooth sinusoidal waveform with a large amplitude) is often obtained.

  FIG. 14 is a diagram showing changes in characteristic values calculated using a set of wavelengths selected based on the distribution diagram shown in FIG. In this example, a combination of two wavelengths [745 nm, 775 nm] and a combination of two wavelengths [455 nm, 475 nm] are selected, and two characteristic values obtained from these combinations are shown in FIG. As can be seen from FIGS. 13 and 14, the characteristic value corresponding to the area surrounded by the dotted line in FIG. 13 has a large amplitude and draws a smooth sine wave. Therefore, based on the distribution diagram shown in FIG. 13, an optimum wavelength can be selected according to the target time for detecting the polishing end point.

Next, an example of a method for determining the wavelength of light as a parameter of the characteristic value based on the above distribution map of the maximum point and the minimum point using software (computer program) will be described with reference to FIG. .
In step 1, a sample substrate having the same structure (the same wiring pattern and the same film) as the substrate to be polished is polished, and spectral data measured during the polishing is read into the monitoring device 15. The sample substrate is polished under the same polishing conditions as the substrate to be polished (the same rotation speed of the polishing table 20 and the same kind of slurry). Note that it is preferable that the sample substrate is polished until a time point slightly after the target time for detecting the polishing end point is reached.

  In step 2, a measurement point for film thickness monitoring is designated. As shown in FIG. 3B, the reflection intensity is measured at a plurality of measurement points each time the polishing table 20 rotates once. Therefore, in this step, it is specified which measurement point to use among a plurality of preset measurement points. For example, five measurement points that are symmetric with respect to the center of the sample substrate are designated. This measurement point designation is performed by inputting the number of measurement points to the monitoring device 15 via an input device (not shown). The monitoring device 15 calculates the average value of the measurement values at the designated measurement point. This average value is an average value of a plurality of reflection intensities (or relative reflectances) obtained each time the polishing table 20 rotates once. Further, in step 2, the average value as time series data is smoothed using a moving average method. The moving average time (the number of time-series data to be averaged) is input in advance to the monitoring device 15, and the monitoring device 15 calculates the average of the time-series data acquired within the specified time.

  In step 3, using the spectral data obtained during the polishing of the sample substrate, the distribution map of the above-described maximum points and minimum points is created by the monitoring device 15. The relative reflectance of each wavelength constituting the spectrum data is averaged based on the smoothing condition defined in Step 2. The obtained distribution map is displayed on the display unit of the monitoring device 15 or another display device. If a desired distribution map cannot be obtained, the conditions in step 2 (for example, the number of measurement points and the moving average time) may be changed and step 2 may be executed again.

  In step 4, the number of wavelengths of light used for calculating the characteristic value is designated. For example, when selecting to calculate a characteristic value using two wavelengths, “2” which is the number of the wavelengths is input to the monitoring device 15. Note that the number of wavelengths corresponds to K in Equation (3).

  In step 5, various conditions for detecting the maximum point or the minimum point of the characteristic value are designated. Specifically, a data area not used for wavelength selection is designated in the spectrum data. This is because, in the initial stage of polishing, a sine wave having a clean characteristic value is often not drawn. Further, in step 5, the above-described detection target time tI, detection time lower limit tL, and detection time upper limit tU (see FIG. 12) that define the detection allowable range of the maximum point or the minimum point of the characteristic value are specified. As described above, the detection time lower limit tL and the detection time upper limit tU are also used for specifying the search range for the maximum point and the minimum point of the relative reflectance.

  In step 6, a wavelength search is executed by the monitoring device 15. In this step, wavelength candidates are searched based on the distribution map of local maximum points and local minimum points created in step 3 and the detection target time tI, detection time lower limit tL, and detection time upper limit tU specified in step 5. Furthermore, a combination of wavelengths (for example, a combination of two wavelengths or a combination of three wavelengths) is generated. The search for these wavelengths and the generation of wavelength combinations are performed in the manner described with reference to FIG. Note that the maximum point and the minimum point on the distribution map may not exactly match the maximum point and the minimum point when the relative reflectance is viewed along the time axis. In consideration of this, a combination of wavelengths may be generated using wavelengths in the vicinity of wavelengths searched according to the method shown in FIG. The monitoring device 15 calculates a corresponding characteristic value from the generated wavelength combination based on the measurement point and the smoothing condition specified in step 2, and the characteristic value is a maximum point or a point within the allowable time range. It is determined whether or not a minimum point is indicated.

  In step 7, a score for each combination of the selected wavelengths is calculated based on the wavelength evaluation formula stored in advance in the monitoring device 15. This score is an index for evaluating each combination of selected wavelengths from the viewpoint of accurate polishing end point detection. The wavelength evaluation formula is used as an evaluation element, for example, the time difference between the time at which the maximum or minimum point of the characteristic value appears and the target detection time, the amplitude of the characteristic value, the stability of the amplitude of the characteristic value, the stability of the period of the characteristic value And the smoothness of the waveform drawn by the characteristic value. The higher the score calculated by this wavelength evaluation formula, the more accurate polishing end point detection is expected.

Specifically, the wavelength evaluation formula is expressed by the following formula.
Evaluation formula J = Σwi ・ Ji
= W1 · J1 + w2 · J2 + w3 · J3 + w4 · J4 + w5 · J5 (6)
here,
w1, J1: Weighting factor and score regarding the time at which the maximum or minimum point of the characteristic value appears,
w2, J2: weighting factor and score regarding the amplitude of the characteristic value,
w3, J3: weighting factor and score regarding the stability of the amplitude of the characteristic value,
w4, J4: weighting factor and score regarding the stability of the period of the characteristic value,
w5, J5: Weight coefficient and score regarding the smoothness of the waveform drawn by the characteristic value.

The weighting factors w1, w2, w3, w4, and w5 described above are predetermined numerical values. The scores J1, J2, J3, J4, and J5 are variables that vary depending on the obtained characteristic values. For example, J1 is represented by the following equation, where t is the time at which the maximum or minimum point of the characteristic value appears.
When t ≦ tI, J1 = (t−tL) / (tI−tL) (7)
When t> tI, J1 = (tU−t) / (tU−tI) (8)

In step 8, the graph drawn by the combination of wavelengths and the corresponding characteristic value is displayed on the display unit in descending order of the calculated score. FIG. 16 is a diagram illustrating a graph drawn by combinations of wavelengths displayed in descending order of scores and corresponding characteristic values.
In step 9, a score is referred to from a plurality of wavelength combinations displayed in step 8, and a wavelength combination having the highest score is designated as a candidate. If a problem is found in the subsequent steps, another wavelength combination is designated as a candidate. Also in this case, in principle, the next wavelength combination is designated in the descending order of score.
The combination of wavelengths specified in Step 9 can be determined as a combination of wavelengths to be finally selected. In order to perform more accurate polishing end point detection, the following fine adjustment of characteristic values and It is preferable to study the reproducibility of the characteristic value.

That is, in step 10, various conditions for fine adjustment of the characteristic value are designated. This fine adjustment of the characteristic value is performed by finely adjusting the wavelength specified in step 9 and the smoothing condition in step 2.
In step 11, the characteristic value is calculated by the monitoring device 15 based on the wavelength and the smoothing condition finely adjusted in step 10, and the time variation of the obtained characteristic value is displayed. If the displayed graph shows good results, proceed to the next step, otherwise return to step 9 or step 10.

  If there is spectral data relating to the same type of substrate as the substrate to be polished other than the sample substrate, the data is read into the monitoring device 15 (step 12). Then, the monitoring device 15 calculates a characteristic value using the relative reflectance at the wavelength finely adjusted in Step 10, and displays a graph of the characteristic value that changes with the polishing time on the display unit (Step 13). If the reproducibility of the characteristic value is good, the wavelength is finally determined (step 14). If the reproducibility is not good, the process returns to Step 9 or Step 10. Note that the process up to the wavelength determination described above may be performed by another computer using spectral data acquired during polishing of the sample substrate, as in the case of the above-described distribution map creation.

  Next, a polishing apparatus incorporating the above polishing end point detection device will be described. FIG. 17 is a cross-sectional view schematically showing a polishing apparatus. As shown in FIG. 17, the polishing apparatus supplies a polishing table 20 that supports the polishing pad 22, a top ring 24 that holds the substrate W and presses against the polishing pad 22, and supplies a polishing liquid (slurry) to the polishing pad 22. The polishing liquid supply nozzle 25 is provided. The polishing table 20 is connected to a motor (not shown) disposed below the polishing table 20 and is rotatable about an axis. The polishing pad 22 is fixed to the upper surface of the polishing table 20.

  The upper surface 22a of the polishing pad 22 constitutes a polishing surface with which the substrate W is slidably contacted. The top ring 24 is connected to a motor and a lifting cylinder (not shown) via a top ring shaft 28. Thereby, the top ring 24 can be raised and lowered and can be rotated around the top ring shaft 28. The substrate W is held on the lower surface of the top ring 24 by vacuum suction or the like.

  The substrate W held on the lower surface of the top ring 24 is pressed by the top ring 24 against the polishing pad 22 on the rotating polishing table 20 while being rotated by the top ring 24. At this time, the polishing liquid is supplied from the polishing liquid supply nozzle 25 to the polishing surface 22 a of the polishing pad 22, and the surface of the substrate W is polished in a state where the polishing liquid exists between the surface of the substrate W and the polishing pad 22. . In the present embodiment, the relative motion mechanism that causes the surface of the substrate W and the polishing pad 22 to slidably contact each other is constituted by the polishing table 20 and the top ring 24.

  The polishing table 20 is formed with a hole 30 that opens on the upper surface thereof. Further, a through hole 31 is formed in the polishing pad 22 at a position corresponding to the hole 30, and the hole 30 and the through hole 31 communicate with each other. The through hole 31 is opened at the polishing surface 22a, and the diameter of the through hole 31 is about 3 to 6 mm. The hole 30 is connected to a liquid supply source 35 via a liquid supply path 33 and a rotary joint 32. During polishing, water (preferably pure water) is supplied from the liquid supply source 35 to the hole 30 as a transparent liquid, fills the space formed by the lower surface of the substrate W and the through hole 31, and the liquid discharge path 34. It is discharged through. The polishing liquid is discharged together with the water, thereby ensuring an optical path of light. The liquid supply path 33 is provided with a valve (not shown) that operates in conjunction with the rotation of the polishing table 20. This valve operates to stop the flow of water or reduce the flow rate of water when the substrate W is not positioned over the through hole 31.

  The polishing apparatus has the above-described polishing end point detection device. The polishing end point detection device includes a light projecting unit 11 that irradiates light on a surface to be polished of a substrate W, an optical fiber 12 that receives light returning from the substrate W, and light received by the optical fiber 12. A spectroscope 13 that decomposes in accordance with the wavelength to acquire spectral data, and a monitoring device 15 that calculates a characteristic value from the spectral data obtained by the spectroscope 13 and monitors a temporal change of the characteristic value are provided. As shown in FIG. 1, the monitoring device 15 detects the polishing end point from the maximum point or the minimum point of the characteristic value.

  The light projecting unit 11 includes a light source 40 and an optical fiber 41 connected to the light source 40. The optical fiber 41 is an optical transmission unit that guides light from the light source 40 to the surface of the substrate W. The optical fiber 41 extends from the light source 40 through the hole 30 and the through hole 31 to a position near the surface to be polished of the substrate W. The respective tips of the optical fiber 41 and the optical fiber 12 are arranged to face the center of the substrate W held by the top ring 24, and light is applied to a region including the center of the substrate W each time the polishing table 20 rotates. It has become. It should be noted that the optical fiber 41 may be installed at a position where the tip of the optical fiber 41 does not protrude from the upper surface of the polishing table 20 and fits in the hole 30 so that the polishing pad 22 can be easily replaced.

  As the light source 40, a light emitting diode (LED), a halogen lamp, a xenon lamp, or the like can be used. The optical fiber 41 and the optical fiber 12 are arranged in parallel with each other. The tips of the optical fiber 41 and the optical fiber 12 are arranged perpendicular to the surface of the substrate W, and the optical fiber 41 irradiates light perpendicularly to the surface of the substrate W.

  During polishing of the substrate W, light is emitted from the light projecting unit 11 to the substrate W, and reflected light from the substrate W is received by the optical fiber 12 serving as a light receiving unit. While the light is irradiated, water is supplied to the hole 30, whereby the space between the tips of the optical fiber 41 and the optical fiber 12 and the surface of the substrate W is filled with water. The spectroscope 13 measures the intensity of reflected light for each wavelength and generates spectral data. Then, the monitoring device 15 calculates the characteristic value from the relative reflectance (or reflection intensity) at the wavelength selected in advance according to the wavelength selection method described above, monitors the characteristic value that changes with the polishing time, and the characteristic value The polishing end point is detected from the local maximum point or the local maximum point.

  18 is a cross-sectional view showing another modification of the polishing apparatus shown in FIG. In the example shown in FIG. 17, a liquid supply path, a liquid discharge path, and a liquid supply source are not provided. Instead, a transparent window 50 is formed in the polishing pad 22. The optical fiber 41 of the light projecting unit 11 irradiates light onto the surface of the substrate W on the polishing pad 22 through the transparent window 50, and the optical fiber 12 as the light receiving unit receives reflected light from the substrate W through the transparent window 50. .

  The embodiment described above is described for the purpose of enabling the person having ordinary knowledge in the technical field to which the present invention belongs to implement the present invention. Various modifications of the above embodiment can be naturally made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Therefore, the present invention should not be limited to the described embodiments, but should be the widest scope according to the technical idea defined by the claims.

It is a graph which shows a mode that a characteristic value changes with grinding | polishing time. It is a figure which shows the example of a weight function. FIG. 3A is a schematic diagram for explaining a polishing end point detection method according to an embodiment of the present invention, and FIG. 3B is a plan view showing a positional relationship between the substrate and the polishing table. Is a diagram showing the spectral data obtained when an oxide film of uniform thickness 600nm was formed on a silicon wafer of (SiO ₂₎ was polished. It is a diagram which shows the distribution map of the maximum point and the minimum point. It is sectional drawing which shows a part of board | substrate with which the film | membrane is formed on the base layer with a level | step difference. FIG. 7A is a diagram showing spectral data obtained by polishing a substrate having the structure shown in FIG. 6, and FIG. 7B is a distribution of local maximum points and local minimum points corresponding to FIG. It is a diagram which shows a figure. It is a figure which shows the spectrum data of a normalized relative reflectance. FIG. 9A is a distribution diagram of local maximum points and local minimum points created based on the normalized relative reflectance, and FIG. 9B is a graph showing the relative reflectance changing with the polishing time. FIG. 10A is a diagram showing spectral data obtained by subtracting the average value of the relative reflectance from the relative reflectance at each time point, and FIG. 10B is shown in FIG. It is a distribution map of a maximum point and a minimum point created using spectrum data. FIG. 11A is a contour map of relative reflectance corresponding to FIG. 7A, and FIG. 11B is a contour map of normalized relative reflectance corresponding to FIG. It is a diagram for explaining a method of selecting two wavelengths using a distribution diagram of local maximum points and local minimum points. FIG. 6 is a distribution diagram of local maximum points and local minimum points created based on spectrum data measured when a substrate on which a wiring pattern is formed is polished. It is a figure which shows the change of the characteristic value calculated using the group of the wavelength selected based on the distribution map shown in FIG. It is a flowchart which shows an example of the method of determining the wavelength of the light as a parameter of a characteristic value based on the distribution map of the maximum point and the minimum point using software (computer program). It is a figure which shows the graph which the group of the wavelength displayed in order with a high score, and the corresponding characteristic value draw. It is sectional drawing which shows a grinding | polishing apparatus typically. It is sectional drawing which shows the other modification of the grinding | polishing apparatus shown in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Light projection part 12 Light reception part 13 Spectrometer 15 Monitoring apparatus 20 Polishing table 22 Polishing pad 24 Top ring 25 Polishing liquid supply nozzle 28 Top ring shaft 30 Hole 31 Through hole 32 Rotary joint 33 Liquid supply path 34 Liquid discharge path 35 Liquid supply Source 40 Light source 41 Optical fiber 50 Transparent window

Claims (11)

A method of creating a diagram used to select the wavelength of light in optical polishing end point detection,
Polish the surface of the substrate with the film with a polishing pad,
During the polishing, the surface of the substrate is irradiated with light, and reflected light returning from the substrate is received,
Calculate the relative reflectance of the reflected light for each wavelength,
Obtain the wavelength of the reflected light indicating the maximum and minimum points of the relative reflectance that change with the polishing time,
Identify the point in time when the wavelength indicating the local maximum and local minimum is determined;
Creating a diagram by plotting the coordinates specified by the determined wavelength and the corresponding point in time on a coordinate system having a coordinate axis representing the wavelength of the light and the polishing time ;
The coordinate on the diagram includes a coordinate existing within a predetermined time range centered on a known target time of polishing end point detection . The step of determining the wavelength of the reflected light indicating the maximum point and the minimum point,
Calculate the average value of the relative reflectance for each wavelength,
Modify the relative reflectance by dividing the relative reflectance at each time point by the average value,
The method of creating a diagram according to claim 1, wherein the method is a step of obtaining a wavelength of the reflected light indicating the corrected maximum point and minimum point of relative reflectance. The step of determining the wavelength of the reflected light indicating the maximum point and the minimum point,
Calculate the average value of the relative reflectance for each wavelength,
Subtract the average value from the relative reflectance at each time point to correct the relative reflectance,
The method of creating a diagram according to claim 1, wherein the method is a step of obtaining a wavelength of the reflected light indicating the corrected maximum point and minimum point of relative reflectance. A method of selecting a wavelength of light used for optical polishing end point detection,
Polish the surface of the substrate with the film with a polishing pad,
During the polishing, the surface of the substrate is irradiated with light, and reflected light returning from the substrate is received,
Calculate the relative reflectance of the reflected light for each wavelength,
Obtain the wavelength of the reflected light indicating the maximum and minimum points of the relative reflectance that change with the polishing time,
Identify the point in time when the wavelength was determined;
On the coordinate system having a coordinate axis representing the wavelength of light and the polishing time, a diagram is created by plotting the coordinates specified by the obtained wavelength and the corresponding time point,
Search the diagram for coordinates that exist within a predetermined time range centered on a known target time for polishing endpoint detection ,
A wavelength selection method, wherein a plurality of wavelengths are selected from wavelengths constituting the searched coordinates. The step of selecting a plurality of wavelengths from among the wavelengths constituting the searched coordinates,
Using the wavelengths constituting the searched coordinates, generating a plurality of combinations of a plurality of wavelengths,
From the relative reflectance at the plurality of wavelengths in each combination, a characteristic value that periodically changes with a change in film thickness is calculated,
Calculate a score of the plurality of combinations using a wavelength evaluation formula,
5. The wavelength selecting method according to claim 4, wherein the wavelength selecting method is a step of selecting a plurality of wavelengths constituting the combination having the highest score.   6. The wavelength evaluation formula includes, as evaluation elements, a time point at which a maximum point or a minimum point of the characteristic value appears and an amplitude of a graph that the characteristic value draws with a polishing time. Wavelength selection method. The step of determining the wavelength of the reflected light indicating the maximum point and the minimum point,
An average value of the relative reflectance indicating the maximum point and the minimum point is calculated for each wavelength,
Modify the relative reflectance by dividing the relative reflectance at each time point by the average value,
5. The wavelength selection method according to claim 4, wherein the wavelength selection method is a step of obtaining a wavelength of the reflected light indicating the corrected maximum point and minimum point of relative reflectance. The step of determining the wavelength of the reflected light indicating the maximum point and the minimum point,
An average value of the relative reflectance indicating the maximum point and the minimum point is calculated for each wavelength,
Subtract the average value from the relative reflectance at each time point to correct the relative reflectance,
5. The wavelength selection method according to claim 4, wherein the wavelength selection method is a step of obtaining a wavelength of the reflected light indicating the corrected maximum point and minimum point of relative reflectance. A polishing end point detection method,
Polish the surface of the substrate with the film with a polishing pad,
During the polishing, the surface of the substrate is irradiated with light, and reflected light returning from the substrate is received,
Calculating a relative reflectance of the reflected light at a plurality of wavelengths selected according to the wavelength selection method according to claim 4;
From the calculated relative reflectance, a characteristic value that periodically changes with a change in the thickness of the film is calculated,
A polishing end point detection method, wherein a polishing end point of the substrate is detected by detecting a maximum point or a minimum point of the characteristic value appearing during polishing. A polishing end point detection device,
A light projecting unit that irradiates light onto the surface of the substrate having a film during polishing;
A light receiving portion for receiving reflected light returning from the substrate;
A spectroscope for measuring the reflection intensity for each wavelength of the reflected light;
From the reflection intensity measured by the spectroscope, a characteristic value that periodically changes as the film thickness changes, and a monitoring device that monitors the characteristic value,
The monitoring device
A relative reflectance is calculated from the reflection intensities at a plurality of wavelengths selected according to the wavelength selection method according to claim 4,
From the calculated relative reflectance, a characteristic value that periodically changes with a change in the thickness of the film is calculated,
A polishing end point detection apparatus, wherein a polishing end point of the substrate is detected by detecting a maximum point or a minimum point of the characteristic value appearing during polishing. A polishing table that supports the polishing pad and rotates the polishing pad;
Holding a substrate having a film and pressing the substrate against the polishing pad;
A polishing end point detection device for detecting the polishing end point of the substrate;
The polishing end point detection device is:
A light projecting unit that irradiates light onto the surface of the substrate having a film during polishing;
A light receiving portion for receiving reflected light returning from the substrate;
A spectroscope for measuring the reflection intensity for each wavelength of the reflected light;
From the reflection intensity measured by the spectroscope, a characteristic value that periodically changes as the film thickness changes, and a monitoring device that monitors the characteristic value,
The monitoring device
A relative reflectance is calculated from the reflection intensities at a plurality of wavelengths selected according to the wavelength selection method according to claim 4,
From the calculated relative reflectance, a characteristic value that periodically changes with a change in the thickness of the film is calculated,
A polishing apparatus, wherein a polishing end point of the substrate is detected by detecting a maximum point or a minimum point of the characteristic value appearing during polishing.

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