KR102534756B1 - Polishing with measurement prior to deposition - Google Patents

Abstract

A method of controlling polishing includes storing a base measurement, the base measurement comprising depositing at least one layer on a substrate and prior to depositing an outer layer on the at least one layer. is a measure of After deposition of the outer layer and during polishing of the outer layer on the substrate, a sequence of raw measurements of the substrate during polishing is received from the in situ monitoring system. Each raw measurement is normalized to create a sequence of normalized measurements using the raw and base measurements. Based on at least one normalized measurement from the sequence of normalized measurements, at least one of an adjustment to the polishing rate or a polishing endpoint is determined.

Description

POLISHING WITH MEASUREMENT PRIOR TO DEPOSITION}

[0001] The present disclosure relates to polishing control methods, for example during chemical mechanical polishing of substrates.

[0002] Typically, an integrated circuit is formed on a substrate by sequential deposition of conductive, semiconducting, or insulating layers on a silicon wafer. One fabrication step involves depositing a filler layer over a non-planar surface and planarizing the filler layer. For certain applications, the filler layer is planarized until the top surface of the patterned layer is exposed. For example, an oxide filler layer may be deposited on the patterned insulating layer to fill trenches or holes in the insulating layer. After planarization, the filler layer is planarized until a predetermined thickness remains over the non-planar surface or until the top surface of the underlying layer is exposed. For other applications, the filler layer is planarized until a predetermined thickness remains above the underlying patterned layer. Also, planarization of the substrate surface is generally required for photolithography.

[0003] Chemical mechanical polishing (CMP) is one accepted planarization method. These planarization methods typically require the substrate to be mounted on a carrier head. Typically, the exposed surface of the substrate is placed against a rotating polishing pad. The carrier head provides a controllable load on the substrate to push the substrate against the polishing pad. Typically, a polishing liquid, such as a slurry with abrasive particles, is supplied to the surface of the polishing pad.

[0004] One problem in CMP is determining whether the polishing process is complete, eg, whether a substrate layer has been planarized to a desired flatness or thickness, or when a desired amount of material has been removed. is to do Variations in the initial thickness of the substrate layer, the slurry composition, the polishing pad condition, the relative speed between the polishing pad and the substrate, the thicknesses of each deposited layer and the load on the substrate will cause variations in material removal rates. can These variations cause variations in the time needed to reach the polishing endpoint. Therefore, it may not be possible to determine the polishing endpoint only as a function of polishing time.

[0005] In some systems, the substrate is optically monitored in-situ during polishing, for example through a window in the polishing pad. However, existing optical monitoring techniques may not be able to meet the increasing demands of semiconductor device manufacturers.

[0006] In some optical monitoring processes, a spectrum measured in situ, for example during the polishing process of CMP, is compared to a library of reference spectra to find the best matching reference spectrum. Spectra measured in situ can contain a number of noise components that can distort the results, making comparisons with a library of reference spectra inaccurate. One significant noise component is the variation of the underlayer. That is, due to process variations, the various material layers beneath the layer being polished may differ from substrate to substrate in refractive indices and thicknesses.

[0007] A normalization method that can solve these problems is to determine the base spectrum of the substrate after depositing one or more dielectric layers, but before depositing the outer layer(s) to be polished. includes measuring The measured base spectrum is used to normalize each measured spectrum obtained during polishing, which can then be compared to a library of reference spectra to find the best matching reference spectrum.

[0008] In one aspect, a computer program product tangibly embodied on a machine readable storage device includes instructions for performing a method of controlling polishing. The method includes storing a base spectrum, wherein the base spectrum is deposited on a substrate after deposition of a plurality of deposited dielectric layers overlying a metal layer or semiconductor wafer and prior to depositing a non-metallic layer over the plurality of deposited dielectric layers. is the spectrum of light reflected from After depositing a non-metallic layer over a plurality of deposited dielectric layers and during polishing of the non-metallic layer on the substrate, in situ optical monitoring measures the sequence of raw spectra of light reflected from the substrate during polishing. It is received from the system (in-situ optical monitoring system). Each raw spectrum in the sequence of raw spectra is normalized to produce a sequence of normalized spectra using the raw spectrum and the base spectrum. At least one of an adjustment to the polishing rate or a polishing endpoint is determined based on at least one normalized predetermined spectrum from the sequence of normalized spectra.

[0009] In another aspect, a method for manufacturing a substrate includes depositing at least one dielectric layer on a semiconductor wafer or metal layer of the substrate. A base spectrum reflected from the substrate is measured by an optical metrology system after depositing at least one dielectric layer, but before depositing the outermost layer. An outermost layer is deposited on at least one dielectric layer, an outermost layer of the substrate is polished, and during polishing of the outermost layer, a sequence of raw spectra reflected from the substrate is measured by an in situ optical monitoring system. Each raw spectrum in the sequence of raw spectra is normalized to produce a sequence of normalized spectra, using the raw spectrum and the post deposition base spectrum, and at least one of the adjustment to the polishing rate or the polishing endpoint One is determined based on at least one normalized predetermined spectrum from the sequence of normalized spectra.

[0010] In another aspect, an integrated circuit manufacturing system includes a deposition system, a metrology system, and a polishing system. The deposition system is configured to receive a substrate and deposit a stack of layers overlying a metal layer or semiconductor substrate, the stack of layers including a non-metal layer to be polished and at least one dielectric layer underlying the non-metal layer. includes The metrology system is configured to produce measurements of a spectrum of light reflected from the substrate after deposition of the at least one dielectric layer and prior to deposition of the non-metallic layer. The polishing system includes a controller configured to receive a substrate and polish a non-metallic layer on the substrate, and configured to perform operations comprising: receiving a measurement of a spectrum of light from a metrology system, and converting the measurement to a base spectrum to store as; receiving, by an in situ optical monitoring system, measurements of a sequence of raw spectra of light reflected from a substrate during polishing; normalizing each raw spectrum in the sequence of raw spectra to produce a sequence of normalized spectra using the raw spectrum and the base spectrum; and based on at least one normalized predetermined spectrum from the sequence of normalized spectra, determining at least one of an adjustment to the polishing rate or a polishing endpoint.

[0011] In another aspect, a polishing system includes a carrier, a platen, an in situ optical monitoring system, and a controller. The carrier is configured to mount a substrate, the substrate including a metal layer or a stack of layers overlying a semiconductor substrate, the stack of layers comprising a non-metal layer to be polished and a plurality of layers underlying the non-metal layer. Deposited dielectric layers. The platen receives a polishing pad configured to contact the substrate. The controller is configured to perform operations including: storing a post-deposition base spectrum, which is a spectrum of light reflected from the substrate after deposition of the plurality of deposited dielectric layers and prior to deposition of the non-metallic layer; receiving, by an in situ optical monitoring system, measurements of a sequence of raw spectra of light reflected from a substrate during polishing; normalizing each raw spectrum in the sequence of raw spectra to produce a sequence of normalized spectra using the raw spectrum and the post-deposited base spectrum; and based on at least one normalized predetermined spectrum from the sequence of normalized spectra, determining at least one of an adjustment to the polishing rate or a polishing endpoint.

[0012] In another aspect, a computer program product tangibly embodied on a machine-readable storage device provides instructions that, when executed by one or more computers, cause the one or more computers to perform operations. wherein the operations include: receiving a base measurement, wherein the base measurement measures a measurement of a substrate after deposition of at least one layer overlying a semiconductor wafer and prior to depositing a conductive layer over the at least one layer. It is an eddy current measurement. After depositing the conductive layer over the at least one layer and during polishing of the conductive layer on the substrate, a sequence of raw measurements of the substrate is received from the in situ eddy current monitoring system. Using the raw measurement and the base measurement, each raw measurement in the sequence of raw measurements is normalized to generate a sequence of normalized measurements, and based on at least the sequence of normalized measurements, an adjustment to the polishing rate or and determining at least one of the polishing endpoints.

[0013] Implementations can optionally include one or more of the following advantages. Accuracy in determining the polishing endpoint of a substrate may be improved by filtering out noise from deviations in refractive indices and/or thicknesses of underlying deposited layers on the substrates. During polishing, by obtaining spectral measurements of the substrate, the thickness of the outermost material layer being polished can be tracked.

[0014] Figures 1A-1E are schematic cross-sectional views of an exemplary substrate before, during, and after polishing.
2 illustrates a schematic cross-sectional view of an example of a polishing apparatus.
[0016] Figure 3 illustrates a schematic plan view of a substrate having multiple zones.
[0017] FIG. 4 illustrates a top view of a polishing pad and shows locations on a substrate at which in situ measurements are taken.
[0018] FIG. 5 illustrates different stages of fabrication of an exemplary substrate in which base spectra may be measured after deposition.
6 illustrates a sequence of values generated from a measured spectrum.
[0020] FIG. 7 illustrates a linear function that is fit over a sequence of values.
[0021] FIG. 8 is a flow diagram of an exemplary process for manufacturing a substrate and detecting a polishing endpoint.
9 is a schematic illustration of a fabrication facility.
[0023] Like reference numbers and designations in the various drawings indicate like elements.

[0024] The substrate may include a metal layer or a stack of layers overlying the semiconductor substrate, the stack of layers including an outermost layer being polished and a plurality of deposited layers overlying the outermost layer. In some implementations, the outermost layer is a non-metallic layer. By way of example, reference is generally made to a substrate having alternating layers of dielectric materials, such as, for example, a 3D NAND structure. It should be understood that other substrates may be used and the substrate described in FIG. 1 is one example.

[0025] As an example, referring to substrate 10 in FIG. 1A, a substrate base 12, such as a glass sheet or semiconductor wafer, optionally includes an intermediate layer structure 14, such an intermediate layer structure 14 may include one or more patterned or unpatterned metal, oxide, nitride or polysilicon layers.

[0026] At least one additional dielectric layer is deposited between the outermost layer and the middle layer structure 14 (or, if there is no middle layer structure, the substrate base 12). In some implementations, the at least one additional dielectric layer is a single layer. In some implementations, the at least one dielectric layer includes a plurality of alternating layers deposited over layer structure 14 , for example over a conductive material. Alternating layers alternate between the first layer of material 16 and the second layer of material 18 . For example, a first layer 16, for example an oxide or nitride, is deposited over the conductive layer 14. A second layer 18, for example nitride or oxide, is deposited over the first layer. For example, the first dielectric layer can be silicon oxide and the second dielectric layer can be silicon nitride. The deposition is repeated once or more times to create alternating layers of materials. Also, either the first layer 16 or the second layer 18 may be polysilicon rather than a dielectric.

[0027] FIG. 1B illustrates the substrate 10 after an etching process has been performed. Substrate 10 has been etched to create a stepped structure, for example, the substrate has been patterned and etched according to a pattern. Patterning may include applying photoresist to the substrate 10 illustrated in FIG. 1A , which defines a structure after etching, for example a step structure. After etching, if the photoresist was used to pattern the substrate, a plasma ashing process may remove the remaining photoresist on the substrate 10 .

[0028] FIG. 1C illustrates the substrate 10 after depositing the layer 20 over the step structure. Layer 20 may be a nitride, for example silicon nitride. Depending on the substrate 10, the nitride layer 20 can act as an insulator, barrier or charge trap in a 3D NAND flash memory structure.

[0029] FIG. 1d shows a substrate after depositing an outer gap filler layer 30 thick enough to fill recesses, eg, recesses left by a stepped structure ( 10) is exemplified. The outer gap filler layer 30 is a non-metallic layer, for example an oxide. For example, layer 30 may be silicon oxide. 1E illustrates the substrate 10 after undergoing a chemical mechanical planarization process. Chemical mechanical polishing may be used to planarize the substrate until the nitride layer 20 is exposed.

2 illustrates an example of a polishing apparatus 100 . The polishing apparatus 100 includes a rotatable disk-shaped platen 120 on which a polishing pad 110 is positioned. The platen is operable to rotate about an axis 125 . For example, the motor 121 may rotate the drive shaft 124 to rotate the platen 120 . The polishing pad 110 may be a two-layer polishing pad having an outer polishing layer 112 and a softer backing layer 114 .

[0031] The polishing apparatus 100 may include a port 130 for dispensing a polishing liquid 132, such as a slurry, onto the polishing pad 110. The polishing apparatus may also include a polishing pad conditioner for abrading the polishing pad 110 to maintain the polishing pad 110 in an abrasive state.

[0032] The polishing apparatus 100 includes one or more carrier heads 140. Each carrier head 140 is operable to hold the substrate 10 against the polishing pad 110 . Each carrier head 140 may have independent control of the polishing parameters, eg pressure, associated with each individual substrate.

In particular, each carrier head 140 may include a retaining ring 142 to retain the substrate 10 under the flexible membrane 144 . Each carrier head 140 also includes a plurality of independently controllable pressurizable chambers defined by a membrane, for example three chambers 146a-146c, which chambers are flexible membrane 144 ) and thus to the associated zones 148a - 148c on the substrate 10 (see FIG. 3 ). Referring to FIG. 3 , central zone 148a may be substantially circular, and remaining zones 148b - 148c may be concentric annular zones around central zone 148a . Although only three chambers are shown in FIGS. 2 and 3 for ease of illustration, there may be one or two chambers, or four or more chambers, for example five chambers.

[0034] Returning to FIG. 2, each carrier head 140 is suspended by a support structure 150, for example a carousel or track, and a carrier by a drive shaft 152. It is connected to a head rotation motor 154, so that the carrier head can rotate about an axis 155. Optionally, each carrier head 140 may be, for example, on sliders on the carousel 150; Or it can oscillate laterally, either by rotational vibration of the carousel itself, or by translation along the track. In operation, the platen is rotated about its central axis 125, and each carrier head is rotated about its central axis 155 and translated laterally across the top surface of the polishing pad. (translated).

[0035] Although only one carrier head 140 is shown, more carrier heads may be provided to hold additional substrates so that the surface area of the polishing pad 110 may be used efficiently. Thus, the number of carrier head assemblies adapted to hold substrates for a concurrent polishing process may be based, at least in part, on the surface area of the polishing pad 110 .

[0036] The polishing apparatus also determines whether or not to adjust the polishing rate or an adjustment to the polishing rate or an in situ optical monitoring system 160 that can be used for endpoint detection, e.g., spectroscopic monitoring, as discussed below. It may include a spectrographic monitoring system. Optical access through the polishing pad is provided by including an aperture (ie, a hole that runs through the pad) or a solid window 118 .

[0037] The optical monitoring system 160 transmits and transmits signals between a light source 162, a light detector 164, and a controller 190, eg, a computer, and the light source 162 and light detector 164. It may include circuitry 166 for receiving. One or more optical fibers, such as bifurcated optical fiber 170, may be used to transmit light from light source 162 to an optical access within the polishing pad, and substrate 10 Light reflected from the detector 164 may be transmitted.

[0038] The output of the circuitry 166 may be a digital electronic signal, such a signal may be a controller 190 for the optical monitoring system via a rotary coupler 129 in the drive shaft 124, for example a slip ring. ) is passed on. Similarly, in response to control commands in digital electronic signals passed from controller 190 through rotary coupler 129 to optical monitoring system 160 , the light source may be turned on or off. Alternatively, circuitry 166 may communicate with controller 190 by radio signals.

[0039] The light source 162 may be operable to emit white light. In one embodiment, the white light emitted includes light with wavelengths of 200-800 nanometers. A suitable light source is a xenon lamp or a xenon mercury lamp. In some other implementations, the emitted light includes light having wavelengths in the near infrared spectrum, eg, wavelengths of 800-1400 nanometers.

[0040] The light detector 164 may be a spectrometer. A spectrometer is an optical instrument for measuring the intensity of light over a portion of the electromagnetic spectrum. A suitable spectrometer is a grating spectrometer. A typical output for a spectrometer is the intensity of light as a function of wavelength (or frequency).

[0041] As noted above, light source 162 and light detector 164 may be coupled to a computing device, eg, controller 190, operable to control their operation and to receive their signals. there is. The computing device may include a microprocessor, eg a programmable computer, located near the polishing apparatus. Regarding control, the computing device may, for example, synchronize activation of a light source with rotation of the platen 120 .

[0042] In some implementations, the light source 162 and detector 164 of the in situ monitoring system 160 are installed within the platen 120 and rotate with the platen 120. In this case, the motion of the platen will cause the sensor to scan across each substrate. In particular, as the platen 120 rotates, the controller 190 can cause the light source 162 to emit a series of flashes starting just before the optical access passes under the substrate 10 and ending just after. . Alternatively, the computing device may cause the light source 162 to continuously emit light starting immediately before each substrate 10 passes over the optical access and ending immediately thereafter. In either case, the signal from the detector may be integrated over the sampling period to produce spectral measurements at the sampling frequency.

[0043] In operation, the controller 190 carries information describing the spectrum of light received by the light detector, for example, for a particular flash of a light source or during a time frame of the detector. signal can be received. Thus, this spectrum is a spectrum measured in situ during polishing.

[0044] As shown by FIG. 4, when the detector is installed within the platen, rotation of the platen (shown by arrow 204) causes the window 108 to move under the carrier head, An optical monitoring system that performs spectral measurements at the sampling frequency will cause spectral measurements to be made at locations 201 in an arc across the substrate 10 . For example, each of points 201a to 201k represents a location of a spectrum measurement by the monitoring system (the number of points is exemplary; depending on the sampling frequency, more or fewer measurements than shown may be made). there is). The sampling frequency may be selected such that between 5 and 20 spectra are collected per sweep of window 108 . For example, the sampling period may be 3 to 100 milliseconds.

[0045] As shown, over one revolution of the platen, spectra are acquired from different radii on the substrate 10. That is, some spectra are acquired from locations closer to the center of the substrate 10 and some closer to the edge. Thus, for any given scan of the optical monitoring system across the substrate, based on the timing, motor encoder information, and optical detection of the edge of the substrate and/or retaining ring, the controller 190 determines each measured value from the scan. The radial position (relative to the center of the substrate being scanned) can be calculated for the spectrum. The polishing system also includes a flange attached to the edge of the platen that will pass a rotary position sensor, e.g., a stationary optical interrupter, to determine which substrate and the location on the substrate of the measured spectrum. Additional data can be provided for Accordingly, the controller can associate the measured various spectra with controllable zones 148b - 148e (see Fig. 2) on substrates 10a and 10b. In some implementations, the time of measurement of the spectrum can be used as a substitute for accurate calculation of radial position.

[0046] A sequence of spectra may be acquired over time, for each zone, over multiple rotations of the platen. Without being limited to any particular theory, the spectrum of light reflected from the substrate 10 is due to changes in the thickness of the outermost layer (e.g., not during a single sweep across the substrate, but rather across multiple across rotations) as the polishing progresses, yielding a sequence of time-varying spectra. Also, specific spectra are exhibited by specific thicknesses of the layer stack.

[0047] In some implementations, a controller, eg, a computing device, receives the measured post-deposition base spectrum of the substrate 10, measured after deposition but before polishing, and the measured base spectrum from each zone. It can be programmed to normalize a sequence of spectra. The controller will then be programmed to compare each normalized spectrum from the sequence of normalized measured spectra from each zone to a number of reference spectra to generate a sequence of best matching reference spectra for each zone. can

[0048] As used herein, a reference spectrum is a predefined spectrum generated prior to polishing of a substrate. The reference spectrum may have a predefined association with a value representing the time in the polishing process at which the spectrum is expected to appear, under the assumption that the actual polishing rate follows the expected polishing rate, i.e. defined prior to the polishing operation. It can be. Alternatively or additionally, the reference spectrum may have a predefined correlation with a value of a substrate property, such as the thickness of the outermost layer, eg the layer to be polished.

[0049] A reference spectrum may be empirically generated, for example, by measuring spectra from a test substrate, eg, a test substrate comprising deposited layers of known layer thicknesses. For example, to generate a plurality of reference spectra, the setup substrate is polished while the sequence of spectra is being collected using the same polishing parameters to be used during polishing of the device wafers. For each spectrum, a value representing the time in the polishing process at which the spectrum was collected is recorded. For example, the value can be elapsed time or number of platen revolutions.

[0050] In addition to being determined empirically, some or all of the reference spectra may be calculated from theory, for example using an optical model of the substrate layers. For example, an optical model can be used to calculate a reference spectrum for a given substrate comprising deposited layers of known thicknesses, and a given outer layer thickness (D). A value representative of the time in the polishing process at which the reference spectrum will be collected can be calculated, for example, by assuming that the outer layer is removed at a uniform polishing rate.

[0051] A measured spectrum of a substrate undergoing polishing may be compared against reference spectra from one or more libraries.

[0052] In some implementations, each reference spectrum is assigned an index value. In general, each library will contain many reference spectra 320, eg one or more, eg exactly one reference spectrum, for each platen rotation over the expected polishing time of the substrate. can This index may be a value representing the time in the polishing process at which the reference spectrum is expected to be observed, for example a number. Spectra can be indexed such that each spectrum in a particular library has a unique index value. Indexing may be implemented such that the index values are sequenced in the order in which the spectra of the test substrate were measured. As polishing progresses, the index value may be selected to change monotonically, eg increase or decrease. In particular, the index values of the reference spectra (provided that the polishing rate follows the polishing rate of the test substrate or model used to generate the reference spectra in the library), such index values are dependent on time or platen rotations. can be chosen to form a linear function of a number. For example, the index value may be proportional to, eg equal to, the number of platen rotations for which reference spectra have been measured for the test substrate or will appear in the optical model. Accordingly, each index value may be a whole number. The index number may indicate an expected platen rotation at which the associated spectrum will appear.

[0053] Reference spectra and their associated index values may be stored in a library of reference spectra. For example, each reference spectrum and its associated index value may be stored in a record in a database. The database of reference libraries of reference spectra may be implemented in the memory of the computing device of the polishing apparatus.

[0054] As noted above, for each region of each substrate, based on the sequence of spectra measured for that region of the substrate, the controller 190 may be programmed to generate a best matching sequence of spectra. there is. A best matching reference spectrum can be determined by comparing the measured spectrum obtained during polishing with reference spectra from a particular library.

[0055] The raw spectra to be measured are normalized using the post-deposition base spectrum measured from the substrate. Acquisition of the base spectrum after deposition is described below with respect to FIG. 5 . The base spectrum may be obtained prior to polishing the substrate. In particular, the base spectrum can be measured after depositing one or more dielectric layers on the substrate, but before depositing the layer to be polished. The base spectrum can be measured after depositing the entire stack of alternating oxide and nitride layers. For example, the stack of alternating layers can be an ONON stack (ie, a stack of alternating oxide and nitride layers) deposited in the creation of a 3D NAND memory. In some implementations, the base spectrum is measured prior to etching the substrate, eg, prior to creating the stepped structure. In some implementations, the base spectrum is measured after etching the substrate, but before depositing an intermediate layer, eg, a nitride layer. In some implementations, the base spectrum is measured after depositing the intermediate layer, but before depositing a gap filler layer, eg, an oxide layer, that is thick enough to fill the etched aperture. After normalizing the raw spectrum, the normalized spectrum is then compared to the reference spectra to determine the best match, e.g., by calculating cross-correlation, sum of squared differences, etc. do.

[0056] The base spectrum is measured in a stand-alone metrology station, for example a system from Nova Measuring Instruments or Nanometrics, or integrated into a deposition or etch system responsible for performing the deposition or etch processes described with respect to FIG. 5. - Can be measured at the line measuring station.

[0057] Normalization may include a division operation, where the raw spectrum is in the numerator and the base spectrum is in the denominator. The base spectrum may be the spectrum of light reflected from the bottom layer of material and multiple dielectric layers from which the light is expected to reach. Measurement of the base spectrum has been described above with respect to three process points for measurement, eg after deposition of a layer stack, after etching, and after deposition of an intermediate layer.

[0058] The measured spectrum can be normalized as follows:

R=(A-DA)/(B-DB)

where R is the normalized spectrum, A is the raw spectrum, DA and DB are dark spectra obtained under dark conditions, and B is the base spectrum. A dark spectrum is a spectrum measured by an in situ optical monitoring system when the substrate is not being measured by the in situ optical monitoring system. In some implementations, DA and DB are the same spectrum. In some implementations, DA is the dark spectrum collected when the raw spectrum is collected, eg, at the same platen rotation, and DB is the dark spectrum collected when the raw spectrum is collected, eg, at the same platen rotation. This is the dark spectrum being collected.

[0059] Figure 5 illustrates different fabrication stages at which base spectra may be measured after deposition. 5 shows different stages from the initial stage 502, to the post-deposition stage 504 (eg, the substrate 502 having layers of deposited dielectric materials) and to the final post-polishing stage 506. An exemplary substrate 502 at manufacturing stages is illustrated. Spectra may be measured by the optical monitoring system to obtain a post-deposition base spectrum, eg, a spectrum of the substrate at the post-deposition stage, ie, stage 504 and thereafter. As described above, the post-deposition base spectrum can also be obtained from material (e.g., deposition 510) from the post etch substrate 512, e.g., one or more layers deposited on the substrate. material that is then removed from the substrate) can be obtained from the spectrum of the substrate after removal. Also, the post-deposition base spectrum can be obtained from a pre gap fill substrate 514, e.g., after etching 512, but prior to deposition of a gap fill layer (e.g., thick oxide). may be obtained from the spectrum of a substrate having a layer of material applied thereto (eg, a nitride deposited layer).

[0060] Referring now to FIG. 6, which illustrates only results for a single region of a single substrate, to generate a time-varying sequence of index values 212, the index value of each of the best matching spectra in the sequence may be determined. . This sequence of index values may be referred to as index trace 210 . In some implementations, an index trace is generated by comparing each normalized measured spectrum, eg, normalized to a measured post-deposition base spectrum, to reference spectra from exactly one library. In general, index trace 210 may include one, eg exactly one, index value per sweep of the optical monitoring system under the substrate.

[0061] For a given index trace 210 where a number of spectra (referred to as "current spectra") are measured and normalized for a particular area in a single sweep of the optical monitoring system, the current normalized A best match may be determined between each of the measured spectra and reference spectra of one or more, eg exactly one, library. In some implementations, each selected current spectrum is compared against respective reference spectra of the selected library or libraries. Alternatively, in some implementations, the current spectra may be combined, eg averaged, and the resulting combined spectrum compared to the reference spectra to determine a best match and thus an index value. do.

[0062] In summary, each index trace comprises a sequence 210 of index values 212, each particular index value 212 of the sequence closest to, from a given library, the normalized measured spectrum. It is created by selecting the index of the reference spectrum to be fit. The time value for each index of the index trace 210 may be the same as the time at which the normalized measured spectrum was measured.

[0063] As shown in Figure 7, a function, e.g. a polynomial function of known order, e.g. a first-order function (e.g. line 214), The spectra are fitted to a sequence of index values, for example using robust line fitting. Lines provide ease of computation, although other functions can be used, for example second-order polynomial functions. Polishing may be stopped at an endpoint time TE where line 214 crosses target index IT.

[0064] Figure 8 shows a flow diagram of a method of manufacturing and polishing a product substrate. The product substrate may have at least the same layer structure and the same pattern as the test substrates used to generate the library's reference spectra. In some implementations, the method of FIG. 8 can be performed using the manufacturing facility described below with respect to FIG. 9 . 8 illustrates a method of fabricating and polishing an exemplary substrate, such as, for example, a 3D NAND structure, although step 804 and steps 808-816 may be applied to any suitable fabricated substrate. You have to understand.

9 is a schematic illustration of a manufacturing facility 900 . Manufacturing facility 900 includes a deposition system 902 that optionally includes an in-line metrology system 904, eg, a chemical vapor deposition system or a plasma enhanced chemical vapor deposition system. In some implementations, manufacturing facility 900 can include standalone metrology system 906 .

[0066] The manufacturing facility 900 further includes an etching system 908 capable of receiving a substrate, patterning the substrate, and performing an etching process. Etching system 908 can include inline metrology system 910 .

[0067] The manufacturing facility 900 also includes a polishing system 912 capable of receiving a substrate and polishing, eg, removing an outer material layer on the substrate. The polishing system 912 is configured with an in situ optical metrology system 914 and a controller 916 configured to perform operations.

[0068] Layers of material are deposited on the substrate (step 802). As noted above with respect to FIGS. 1A and 5 , a substrate base 12 , such as a glass sheet or semiconductor wafer, includes a conductive layer 14 disposed thereon, such as a metal, such as copper, tungsten. or aluminum.

[0069] The substrate is transported to the deposition system 902. In some implementations, alternating layers, eg, alternating first layer material and second layer material, are deposited by deposition system 902 over the substrate, or over conductive layer 14 in some implementations. . For example, a first dielectric layer 16, eg an oxide or nitride, is deposited over the conductive layer, and a second dielectric layer, eg an oxide or nitride, is deposited over the first layer. For example, the first dielectric layer can be silicon oxide and the second dielectric layer can be silicon nitride. The deposition is repeated once or more times to create a stack of alternating layers of materials. As described above with respect to FIG. 1 , one of the layers, eg the first layer material or the second layer material, may be polysilicon.

[0070] As described in step 804, the spectrum reflected from the substrate may be measured at this point in the fabrication process and stored as a base spectrum after deposition. The substrate may be measured by an in-line metrology system 904 within the deposition system 902 or by a standalone metrology system 906 .

[0071] Next, the substrate is patterned and etched, for example to create a stepped structure. To perform etching, the substrate may be transported to an etching system 908. Alternatively, after removing any remaining photoresist, the spectrum reflected from the substrate can be measured at this point in the fabrication process and stored as a post-deposition base spectrum. The substrate may be measured by an in-line metrology system 910 within the etching system 908 or by a standalone metrology system 906 .

[0072] Next, an intermediate layer, eg, a nitride layer 20 as in FIG. 1, such as silicon nitride, is deposited over the alternating material layers with etched apertures. Deposition of the intermediate layer may be performed by the same deposition system 902 that deposited the stack of alternating layers or by a different deposition system. Alternatively, the spectrum reflected from the substrate may be measured at this point in the fabrication process, prior to deposition of the outer gap fill layer 30, and stored as a base spectrum after deposition. The substrate may be measured by an in-line metrology system, eg, in-line metrology system 904 within deposition system 902, or by stand-alone metrology system 906.

[0073] Consequently, the product substrate is measured after deposition but before polishing and before deposition of the layer to be polished (step 804). The spectrum reflected from the product substrate is measured for use in normalizing the spectra measured during polishing, as described below. The product substrate is measured to obtain a post-deposition base spectrum, eg, a spectrum of the substrate at the post-deposition stage that is used to normalize the raw spectra measured during polishing. The post-deposition base spectrum can be measured from the spectrum of the product substrate after deposition and prior to etching. The post-deposition base spectrum can also be measured after etching, eg, after removing material from one or more layers deposited on the product substrate to create a stepped structure. Also, the post-deposition base spectrum can be measured after etching and depositing the nitride layer on the product substrate, but before polishing.

[0074] After measuring the post-deposition base spectrum, an outer gap fill layer, for example a thick oxide, is deposited on the substrate (step 806). Deposition of the intermediate layer may be performed by the same deposition system 902 that deposited the stack of alternating layers, and/or by the same deposition system 902 that deposited the intermediate layer, or by a different deposition system. can

[0075] The product substrate is polished to remove the gap fill layer (step 808). For example, the gap fill layer may be polished and removed using a polishing pad in the polishing system 912 , eg, the polishing apparatus described in FIG. 2 . Of course, steps 802-806 could be performed elsewhere, so the process for a particular operator of polishing system 912 begins at step 808.

[0076] The in situ metrology system 914 is used to detect the measured spectra of the product substrate during polishing (step 810), using the in situ monitoring system 914 described above.

[0077] The controller 916 in the polishing system 912 normalizes the measured spectra using the measured post-deposition base spectrum, as discussed above (step 812). In some implementations, a function, eg a linear function, is fit to a sequence of index values for spectra collected after the time TC at which the clearance of the gap fill layer is detected.

[0078] The normalized measured spectra are analyzed to generate a sequence of index values, and a function is fitted to the sequence of index values. In particular, for each measured spectrum in the sequence of measured spectra, an index value for the best fitting reference spectrum is determined to produce a sequence of index values (step 814). That is, the normalized measured spectra are analyzed to generate a sequence of index values, and a function is fitted to the sequence of index values.

[0079] When an index value (eg, a computed index value generated from a linear function fitted to a new sequence of index values) reaches the target index, polishing may be stopped (step 816). The target thickness IT may be set and stored by a user prior to the polishing operation. Alternatively, a target amount for removal may be set by the user, and a target index IT may be calculated from the target amount for removal.

[0080] detecting a clearance of an outermost layer, e.g., a gap fill layer, to adjust polishing parameters, e.g., to adjust a polishing rate of one or more zones on a substrate, to improve polishing uniformity. It is also possible to use a function that is fitted to the index values from spectra collected after they have been collected.

[0081] In some implementations, an index trace may be generated for each zone. Alternatively or in addition to those used to detect the polishing endpoint, the index traces can be used such that different zones reach their target thickness closer to the target thickness reducing polishing, e.g. As described in application Ser. No. 13/094,677, it can be used to calculate adjustments to polishing parameters that will adjust the polishing rate for one or more of the zones to improve polishing uniformity.

[0082] Although the discussion above assumes a rotating platen with an optical endpoint monitor installed within the platen, the system may be applicable for other types of relative motion between the monitoring system and the substrate. For example, in some implementations, for example in orbital motion, the light source traverses different locations of the substrate, but not the edge of the substrate. In such cases, the collected spectra may still be grouped, eg spectra may be collected with a certain frequency and spectra collected within a certain time period may be considered part of the group. The time period should be long enough so that 5 to 20 spectra can be collected for each group.

[0083] Further, although the discussion above focused on using the base spectrum for normalization, the base spectrum may be used for other applications. As a first example, rather than normalization, the base spectrum can be used as a reference spectrum during the polishing process.

[0084] As a second example, the location of valleys or peaks in the base spectrum can be determined. This data can be used to adjust targets in a spectral feature tracking algorithm. For example, the algorithm described in US Pat. No. 7,998,358, incorporated herein by reference, can be tuned by changing the target location by a predetermined amount based on the location of a valley or peak in the base spectrum.

[0085] As a third example, rather than division, one can subtract the base spectrum from the measured spectrum.

[0086] As a fourth example, one of several stored endpoint algorithms may be automatically selected by the controller based on the base spectrum. For example, prior to polishing, a base spectrum can be compared to a plurality of spectra, and a best matching spectrum can be identified. Each of the plurality of spectra may have an associated algorithm type, such as Fourier transform, spectral feature tracking, difference tracking relative to a reference spectrum, or identification of a matching reference spectrum from a library. After the controller determines which spectrum best matches, the controller can automatically select an endpoint algorithm associated with that spectrum.

[0087] Further, although the discussion above focused on normalization of spectra measured during polishing of dielectric layers, this approach would also be applicable to normalization of eddy current measurements during polishing of conductive layers. In this case, the outermost layer is a conductive layer, for example a metal such as copper. For example, an eddy current monitoring system as described in US Patent Publication No. 2012/0276661 replaces the optical monitoring system and is used to monitor the substrate during polishing. A stand-alone or in-line eddy current measurement device is used to generate a base measurement of the substrate after deposition of a conductive layer overlying the semiconductor wafer, but prior to deposition of an outermost conductive layer. Eddy current measurements can be normalized as follows:

R=(A-DA)/(B-DB)

where R is the normalized measurement, A is the raw measurement during polishing, DA and DB are measurements made by the in situ eddy current monitoring system when the sensor is not under the substrate, and B is the outside It is a base measurement made prior to the deposition of the outermost conductive layer.

[0088] As used herein, the term substrate may include, for example, a product substrate (eg, containing multiple memory or processor dies), a test substrate, and a gating substrate. can The term substrate can include circular disks and rectangular sheets.

[0089] Embodiments and all functional operations of the invention described herein may be implemented in digital electronic circuitry or in computer software, firmware, or the structural means disclosed herein and their structural equivalents. It can be implemented in hardware, including, or in combinations thereof. Embodiments of the invention may be directed to one or more data processing apparatus, eg, for execution by, or for controlling the operation of, a data processing apparatus, a programmable processor, a computer, or multiple processors or computers. may be implemented as computer program products of, ie, as one or more computer programs tangibly embodied in a machine-readable storage medium. A computer program (also known as a program, software, software application, or code) may be written in any form of programming language, including compiled or interpreted languages, and stand-alone. may be deployed in any form, such as a program alone, or including such as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program may reside within a portion of a file that holds other programs or data, within a single file dedicated to that program, or within multiple coordinated files (e.g., one or more modules, subprograms). , or files that store parts of code). A computer program can be deployed to be executed on one computer or on multiple computers distributed at one site or across multiple sites and interconnected by a communication network. The processes and logic flows described in this specification may be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. there is. The processes and logic flows may also be performed by special purpose logic circuitry, such as a field programmable gate array (FPGA) or application specific integrated circuit (ASIC), and the apparatus may also be implemented as such an FPGA or ASIC. there is.

[0090] The above-described polishing apparatus and methods can be applied in various polishing systems. The polishing pad or the carrier heads, or both, may be moved to provide relative motion between the polishing surface and the substrate. For example, the platen may orbit rather than rotate. The polishing pad may be a circular (or any other shaped) pad fixed to the platen. Some aspects of the endpoint detection system may be applicable for linear polishing systems, for example where the polishing pad is continuous or a linearly moving reel-to-reel belt. The polishing layer can be a standard (eg polyurethane with or without fillers) polishing material, a soft material, or a fixed-abrasive material. Terms of relative positioning are used; It should be understood that the polishing surface and substrate may be held in a homeotropic orientation or any other orientation.

[0091] Certain embodiments of the invention have been described. Other embodiments are within the scope of the following claims.

Claims (24)

A computer program stored on one or more computer storage media,
the computer program includes instructions that, when executed by one or more computers, cause the one or more computers to perform operations;
The above actions are:
storing a base measurement - the base measurement is an eddy current measurement of a substrate comprising a semiconductor wafer and at least one layer overlying the semiconductor wafer, wherein the eddy current measurement is a measurement of the eddy current of the at least one layer performed prior to deposition of the above conductive outer layer;
in-situ a sequence of raw measurements of eddy currents of the substrate after deposition of the conductive outer layer on the at least one layer and during polishing of the conductive outer layer on the substrate; receiving from a monitoring system, wherein the in-situ monitoring system is an in-situ eddy current monitoring system;
generating a sequence of adjusted measurements using the raw measurements and using the base measurement to reduce noise in the raw measurements; and
determining at least one of an adjustment to a polishing rate or a polishing endpoint based on at least the adjusted sequence of measurements.
A computer program stored on one or more computer storage media. According to claim 1,
The base measurement may be performed after deposition of the at least one layer but prior to etching of the at least one layer, or after etching of the at least one layer but prior to deposition of a barrier layer, or deposition of the barrier layer. an eddy current measurement of the substrate measured after or prior to deposition of the outer layer,
A computer program stored on one or more computer storage media. A computer program stored on one or more computer storage media,
the computer program includes instructions that, when executed by one or more computers, cause the one or more computers to perform operations;
The above actions are:
storing a base measurement - wherein the base measurement is a spectrographic measurement of a substrate comprising a semiconductor wafer and at least one layer overlying the semiconductor wafer, the spectrographic measurement comprising an outer surface over the at least one layer performed prior to deposition of an outer layer, wherein the at least one layer includes at least one dielectric layer, and wherein the base measurement is a base spectrum representing a spectrum of light reflected from the substrate;
receiving from an in situ monitoring system a sequence of raw measurements of spectra of light reflected from the substrate after deposition of the outer layer over the at least one layer and during polishing of the outer layer on the substrate - the in situ monitoring The system is an in situ optical monitoring system;
generating a sequence of adjusted measurements using the raw measurements and using the base measurement to reduce noise in the raw measurements; and
determining at least one of an adjustment to a polishing rate or a polishing endpoint based on at least the adjusted sequence of measurements.
A computer program stored on one or more computer storage media. According to claim 3,
wherein the outer layer is a non-metallic layer;
A computer program stored on one or more computer storage media. According to claim 4,
wherein the base spectrum is a spectrum of light reflected from the substrate after deposition of a plurality of dielectric layers overlying a metal layer or semiconductor wafer and prior to depositing the non-metallic layer over the plurality of deposited dielectric layers;
A computer program stored on one or more computer storage media. According to claim 5,
The base spectrum may be applied after deposition of the plurality of dielectric layers but prior to an etching process, or after the etching process but prior to deposition of a nitride layer, or after deposition of the nitride layer but depositing the non-metallic layer undergoing polishing. The spectrum of the light reflected from the substrate measured before
A computer program stored on one or more computer storage media. According to any one of claims 1 to 6,
Generating the adjusted sequence of measurements comprises:
normalizing each raw measurement in the sequence of raw measurements to produce a sequence of normalized measurements using the raw measurement and the base measurement;
A computer program stored on one or more computer storage media. According to claim 7,
normalizing comprises a division operation, wherein the raw measure is in the numerator and the base measure is in the denominator;
A computer program stored on one or more computer storage media. According to claim 8,
The division operation is

Calculate a normalized measure (R) that satisfies
where A is a raw measurement, B is a base measurement, and D _A and D _B are measurements made by the in situ monitoring system when the substrate is not being measured by the in situ monitoring system.
A computer program stored on one or more computer storage media. As a method of manufacturing a substrate,
depositing at least one layer over the semiconductor wafer;
obtaining a base measurement of a substrate, wherein the base measurement is an eddy current measurement of the substrate after deposition of the at least one layer and prior to deposition of an outer layer over the at least one layer, wherein the outer layer is a conductive layer. -;
depositing the outer layer on the at least one layer;
polishing the outer layer of the substrate;
during polishing of the outer layer, acquiring a sequence of raw measurements of eddy currents of the substrate by an in situ monitoring system, wherein the in situ monitoring system is an in situ eddy current monitoring system;
generating a sequence of adjusted measurements using the raw measurements and using the base measurement to reduce noise in the raw measurements; and
determining at least one of an adjustment to a polishing rate or a polishing endpoint based on at least one adjusted measurement from the sequence of adjusted measurements.
How to make a substrate. According to claim 10,
wherein the at least one layer is a plurality of layers including at least one underlying conductive layer and at least one dielectric layer over the semiconductor wafer;
How to make a substrate. According to claim 11,
The base measurement is taken after depositing a plurality of alternating layers on the substrate but before etching the substrate, or after etching the substrate but before depositing a barrier layer, or after depositing a barrier layer. or before depositing the conductive layer, the eddy current measurement of the substrate,
How to make a substrate. According to claim 12,
wherein the plurality of alternating layers comprises polysilicon and silicon oxide.
How to make a substrate. As a method of manufacturing a substrate,
depositing at least one layer over the semiconductor wafer, the at least one layer comprising at least one dielectric layer;
obtaining a base measurement of a substrate, the base measurement being a measurement of the substrate after deposition of the at least one layer and prior to deposition of an outer layer over the at least one layer, the base measurement comprising: is a base spectrum representing the spectrum of reflected light;
depositing the outer layer on the at least one layer;
polishing the outer layer of the substrate;
during polishing of the outer layer, acquiring a sequence of raw measurements of spectra of light reflected from the substrate by an in situ monitoring system, wherein the in situ monitoring system is an in situ optical monitoring system;
generating a sequence of adjusted measurements using the raw measurements and using the base measurement to reduce noise in the raw measurements; and
determining at least one of an adjustment to a polishing rate or a polishing endpoint based on at least one adjusted measurement from the sequence of adjusted measurements.
How to make a substrate. According to claim 14,
wherein the outer layer is a non-metallic layer;
How to make a substrate. According to claim 15,
wherein the base spectrum is a spectrum of light reflected from the substrate after deposition of a plurality of dielectric layers overlying a metal layer or semiconductor wafer and prior to depositing a non-metallic layer over the plurality of deposited dielectric layers;
How to make a substrate. According to any one of claims 14 to 16,
depositing alternating non-metallic layers on the substrate, the alternating non-metallic layers comprising at least one dielectric layer;
etching the substrate to create a stepped structure;
depositing an intermediate layer on the etched substrate; and
depositing an outermost layer on the intermediate layer;
How to make a substrate. According to claim 17,
Measuring the base spectrum may be done after depositing alternating oxide and nitride layers on the substrate, but before etching the substrate, or after etching the substrate, but before depositing a nitride layer, or after etching the nitride layer. measuring the base spectrum after depositing, but before depositing the outermost layer;
How to make a substrate. According to any one of claims 10 to 16,
Generating the adjusted sequence of measurements comprises:
normalizing each raw measurement in the sequence of raw measurements using the raw measurement and the base measurement to produce a sequence of normalized measurements;
How to make a substrate. As an integrated circuit manufacturing system,
A deposition system configured to receive a substrate and deposit a stack of layers on the substrate, the stack of layers including an outer layer to be polished and at least one layer underlying the outer layer, the outer layer being a conductive layer. — ;
a metrology system configured to generate eddy current measurements of the substrate after deposition of the at least one layer and prior to deposition of the outer layer; and
a polishing system configured to receive the substrate and polish the outer layer on the substrate;
The polishing system includes a controller configured to perform operations;
The above actions are:
receiving the measurement from the metrology system and storing the measurement as a base measurement;
receiving a sequence of raw measurements of eddy currents in the substrate during polishing from an in situ eddy current monitoring system;
generating a sequence of adjusted measurements using the raw measurements and using the base measurement to reduce noise in the raw measurements; and
determining at least one of an adjustment to a polishing rate or a polishing endpoint based on at least one adjusted measurement from the adjusted sequence of measurements.
Integrated circuit manufacturing system. As an integrated circuit manufacturing system,
A deposition system configured to receive a substrate and deposit a stack of layers on the substrate, the stack of layers including an outer layer to be polished and at least one layer underlying the outer layer, the at least one layer comprising: including at least one dielectric layer;
a metrology system configured to produce a measurement of a spectrum of light reflected from the substrate after deposition of the at least one layer and prior to deposition of the outer layer; and
a polishing system configured to receive the substrate and polish the outer layer on the substrate;
The polishing system includes a controller configured to perform operations;
The above actions are:
receiving the measurement from the metrology system and storing the measurement as a base measurement;
receiving a sequence of raw measurements of spectra of light reflected from the substrate during polishing from an in situ optical monitoring system;
generating a sequence of adjusted measurements using the raw measurements and using the base measurement to reduce noise in the raw measurements; and
determining at least one of an adjustment to a polishing rate or a polishing endpoint based on at least one adjusted measurement from the adjusted sequence of measurements.
Integrated circuit manufacturing system.
According to claim 20 or 21,
wherein the metrology system is an in-line metrology station within the deposition system;
Integrated circuit manufacturing system. According to claim 20 or 21,
The measurement system is an independent measurement system,
Integrated circuit manufacturing system. According to claim 20 or 21,
Generating the adjusted sequence of measurements comprises:
normalizing each raw measurement in the sequence of raw measurements using a raw measurement and the base measurement to generate a sequence of normalized measurements;
Integrated circuit manufacturing system.

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