JP2022170119A - Polishing method - Google Patents

Abstract

To provide a polishing method that can improve the uniformity of wafer thickness.SOLUTION: A polishing method includes a second polishing step for polishing a substrate under second polishing conditions. The second polishing conditions include a polishing condition determined to form a second polishing profile having an opposite distribution to the distribution of a first polishing profile.SELECTED DRAWING: Figure 7

Description

The present invention relates to a polishing method.

Chemical mechanical polishing (CMP) is known as a technique in the manufacturing process of semiconductor devices. A polishing apparatus for performing CMP includes a polishing table that supports a polishing pad and a polishing head that holds a wafer.

When polishing a wafer using such a polishing apparatus, the wafer is held by the polishing head and pressed against the polishing surface of the polishing pad with a predetermined pressure. At this time, the wafer is brought into sliding contact with the polishing surface by relatively moving the polishing table and the polishing head, and the surface of the wafer is polished.

Furthermore, a signal corresponding to the film thickness of the wafer is detected by a film thickness sensor to acquire the film thickness distribution of the wafer. Based on the film thickness distribution of the wafer, the pressure of a plurality of airbags provided concentrically on the polishing head is controlled. The film thickness sensor rotates together with the polishing table, and the polishing head holding the wafer also rotates. Normally, the movement path of the film thickness sensor across the surface of the wafer is different for each revolution of the polishing table. As an index value for controlling the pressure of each airbag, the film thickness measured at different measurement points of each concentric airbag is averaged to calculate a numerical value representative of the film thickness inside each airbag. ing.

WO2015/163164 Japanese Patent Application Laid-Open No. 2005-11977

In recent years, the required degree of film thickness uniformity has increased. In the region of the wafer corresponding to one of the concentrically arranged airbags, the variation in film thickness in the radial direction of the wafer becomes large, and even if the pressure of the airbag corresponding to that region is adjusted, it will not exceed a certain level. However, there is a problem that the uniformity of the film thickness cannot be improved.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a polishing method capable of improving the uniformity of the film thickness of a wafer.

In one aspect, a polishing method is provided in which a polishing head having a plurality of pressure chambers including specific pressure chambers presses a substrate against a polishing surface of a polishing pad. The polishing method corresponds to a first polishing step of polishing the substrate under a first polishing condition, and the specific pressure chamber obtained by previously polishing a substrate different from the substrate under the first polishing condition. and a second polishing step of polishing the substrate under second polishing conditions determined based on a first polishing profile along the radial direction of a specific region of the substrate, wherein the second polishing conditions are the second polishing conditions. The second polishing step is performed after the first polishing step, including polishing conditions predetermined to form a second polishing profile having a distribution opposite to the distribution of the first polishing profile.

In one aspect, the specific pressure chamber includes an edge pressure chamber that presses the outermost periphery of the substrate.
In one aspect, the second polishing conditions include polishing conditions determined by adjusting pressures in pressure chambers other than the specific pressure chamber.
In one aspect, the second polishing condition includes a polishing condition determined by adjusting pressure in an adjacent pressure chamber adjacent to an edge pressure chamber that presses the outermost periphery of the substrate.

In one aspect, the second polishing condition includes a polishing condition determined by adjusting a pressing force against the polishing surface of a retainer ring arranged to surround the outermost periphery of the substrate.
In one aspect, the first polishing condition is based on the film thickness of the substrate corresponding to each of the plurality of pressure chambers, which is measured using a film thickness sensor during polishing. It includes polishing conditions for polishing the substrate while feedback-controlling each pressure.
In one aspect, the substrate is polished under the first polishing condition, and after a predetermined switching condition is satisfied, the substrate is polished under the second polishing condition.

In one aspect, as the switching condition, when the difference between the maximum value and the minimum value of the film thickness of the specific region becomes larger than a predetermined threshold value, the change from the first polishing condition to the second polishing condition is performed. switch to
In one aspect, as the switching conditions, the time required to eliminate the difference between the maximum value and the minimum value of the film thickness of the specific region by polishing under the second polishing condition, and the time required to reach the final target film thickness. The first polishing condition is switched to the second polishing condition based on the remaining polishing time.
In one aspect, the specific pressure chamber includes an edge pressure chamber that presses the outermost periphery of the substrate, and the pressure in the edge pressure chamber is controlled based on the second polishing condition while the pressure of the edge pressure chamber is controlled under the first polishing condition. is used to control the pressure of the pressure chambers other than the edge pressure chamber.

The polishing method includes a second polishing step of polishing the substrate under second polishing conditions. By polishing the substrate in the second polishing step, it is possible to improve the uniformity of the film thickness in a specific region of the wafer.

1 is a schematic diagram showing an embodiment of a polishing apparatus; FIG. 1 is a cross-sectional view of a polishing head; FIG. It is a figure which shows an example of the spectrum produced|generated by the operation control part. FIG. 4 is a diagram showing an example of a process of acquiring a plurality of reference spectra; FIG. FIG. 4 is a diagram showing a plurality of pressing regions of a wafer divided according to a plurality of pressure chambers; FIG. 10 is a diagram showing a polishing profile of a wafer when the wafer is polished under the first polishing conditions; It is a figure which shows 2nd polishing conditions. FIG. 4 is a diagram showing polishing rates of wafers polished under first polishing conditions and second polishing conditions; It is a figure which shows an example of the process of polishing the wafer of polishing object.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic diagram showing one embodiment of a polishing apparatus. As shown in FIG. 1, the polishing apparatus includes a polishing table 3 that supports a polishing pad 2, a polishing head 1 that presses a wafer W (such as a substrate) having a film against the polishing pad 2, and a table motor that rotates the polishing table 3. 6, a polishing liquid supply nozzle 5 for supplying polishing liquid such as slurry onto the polishing pad 2, and a film thickness sensor 40 (optical film thickness sensor 40 in this embodiment) for measuring the film thickness of the wafer W. and an operation control unit 9 for controlling the operation of the polishing apparatus. The upper surface of the polishing pad 2 constitutes a polishing surface 2a for polishing the wafer W. As shown in FIG.

The polishing head 1 is connected to a head shaft 10, and the head shaft 10 is connected to a polishing head motor (not shown) via connecting means such as a belt. The polishing head motor rotates the polishing head 1 together with the head shaft 10 in the direction indicated by the arrow. The polishing table 3 is connected to a table motor 6, and the table motor 6 is configured to rotate the polishing table 3 and the polishing pad 2 in the directions indicated by the arrows.

Wafer W is polished as follows. While rotating the polishing table 3 and the polishing head 1 in the direction indicated by the arrow in FIG. While the wafer W is rotated about the head shaft 10 by the polishing head 1 , the wafer W is pressed against the polishing surface 2 a of the polishing pad 2 by the polishing head 1 while the polishing liquid is present on the polishing pad 2 . The polishing table 3 rotates around its center CP. The surface of the wafer W is polished by the chemical action of the polishing liquid and the mechanical action of the abrasive grains contained in the polishing liquid or the polishing pad 2 .

The operation control unit 9 is composed of at least one computer. The operation control unit 9 includes a storage device 9a in which programs are stored, and an arithmetic device 9b that executes calculations according to instructions included in the programs. The arithmetic device 9b includes a CPU (Central Processing Unit) or GPU (Graphic Processing Unit) that performs calculations according to instructions included in programs stored in the storage device 9a. The storage device 9a includes a main storage device (eg, random access memory) accessible by the arithmetic unit 9b and an auxiliary storage device (eg, hard disk drive or solid state drive) for storing data and programs.

The motion controller 9 is electrically connected to the film thickness sensor 40 . In this embodiment, the film thickness sensor 40 guides light to the surface of the wafer W, detects reflected light from the wafer W, and outputs a signal corresponding to the film thickness of the wafer W to the operation controller 9 . The operation control unit 9 measures the film thickness of the wafer W based on the signal sent from the film thickness sensor 40 (more specifically, intensity measurement data of the reflected light from the wafer W).

In this embodiment, the film thickness sensor 40 is an optical film thickness sensor, but other film thickness sensors may be used as long as the film thickness of the wafer W can be measured by the operation control unit 9 . In other words, the film thickness sensor 40 is a sensor that detects a physical quantity related to the film thickness of the wafer W. FIG. As an example, film thickness sensor 40 may be an eddy current sensor. The eddy current sensor detects an eddy current corresponding to the film thickness of the wafer W and outputs an eddy current signal by having its sensor coil pass magnetic flux through the conductive film of the wafer W to generate an eddy current. . The motion controller 9 measures the film thickness of the wafer W based on this eddy current signal.

In this embodiment, the film thickness sensor 40 includes a light source 44 that emits light, a spectroscope 47 , and an optical sensor head 7 coupled to the light source 44 and the spectroscope 47 . The optical sensor head 7 , light source 44 and spectroscope 47 are attached to the polishing table 3 and rotate together with the polishing table 3 and polishing pad 2 . The position of the optical sensor head 7 is the position across the surface of the wafer W on the polishing pad 2 each time the polishing table 3 and polishing pad 2 make one revolution.

The storage device 9a stores therein a program for generating a spectrum and detecting the film thickness of the wafer W, which will be described later. Light emitted from the light source 44 is transmitted to the optical sensor head 7 and guided to the surface of the wafer W from the optical sensor head 7 . The light reflects off the surface of wafer W, and the reflected light from the surface of wafer W is received by optical sensor head 7 and sent to spectroscope 47 . A spectroscope 47 decomposes the reflected light according to wavelength. In this manner, the film thickness sensor 40 detects the intensity of the reflected light at each wavelength and sends the intensity measurement data of the reflected light to the operation control section 9 .

FIG. 2 is a cross-sectional view of the polishing head. As shown in FIG. 2, the polishing head 1 includes an elastic film 65 for pressing the wafer W against the polishing surface 2a of the polishing pad 2, a head main body 21 holding the elastic film 65, and a An annular drive ring 62 is disposed and an annular retainer ring 60 is secured to the lower surface of the drive ring 62 .

The elastic membrane 65 is attached to the lower portion of the head body 21 . The head body 21 is fixed to the end of the head shaft 10, and the head body 21, the elastic membrane 65, the drive ring 62, and the retainer ring 60 are configured to rotate together as the head shaft 10 rotates. there is The retainer ring 60 and the drive ring 62 are configured to be vertically movable relative to the head body 21 . The head main body 21 is made of resin such as engineering plastic (for example, PEEK).

A lower surface of the elastic film 65 constitutes a substrate pressing surface 65 a that presses the wafer W against the polishing surface 2 a of the polishing pad 2 . The retainer ring 60 is arranged to surround the substrate pressing surface 65 a , and the wafer W is surrounded by the retainer ring 60 . Four pressure chambers 70 , 71 , 72 and 73 are provided between the elastic membrane 65 and the head body 21 .

The pressure chamber 70 is a circular central pressure chamber located at the center, the pressure chamber 73 is an annular edge pressure chamber located at the outermost periphery, and the pressure chambers 71 and 72 are the pressure chambers 70 and 72, respectively. It is an intermediate pressure chamber positioned between chamber 73 .

The pressure chambers 70 , 71 , 72 , 73 are formed by the elastic membrane 65 and the head body 21 . The central pressure chamber 70 is circular and the other pressure chambers 71, 72, 73 are annular. These pressure chambers 70, 71, 72, 73 are concentrically arranged (divided). In this embodiment, the elastic membrane 65 forms four pressure chambers 70 to 73, but the above number of pressure chambers is an example and may be changed as appropriate.

Gas transfer lines F1, F2, F3 and F4 are connected to the pressure chambers 70, 71, 72 and 73, respectively. One end of the gas transfer lines F1, F2, F3, F4 is connected to a compressed gas supply (not shown) as a utility provided in the factory where the polishing apparatus is installed. Compressed gas such as compressed air is supplied to pressure chambers 70, 71, 72 and 73 through gas transfer lines F1, F2, F3 and F4, respectively. The compressed gas is supplied to the pressure chambers 70 to 73 to expand the elastic film 65, and the compressed gas in the pressure chambers 70 to 73 presses the wafer W against the polishing surface 2a of the polishing pad 2 via the elastic film 65. . Pressure chambers 70 - 73 function as actuators for pressing wafer W against polishing surface 2 a of polishing pad 2 .

The retainer ring 60 is an annular member arranged around the elastic film 65 and in contact with the polishing surface 2 a of the polishing pad 2 . The retainer ring 60 is arranged so as to surround the outermost periphery of the wafer W, prevents the wafer W from jumping out of the polishing head 1 during polishing of the wafer W, and allows the polishing pad 2 to behave elastically ( Rebound) can be adjusted to adjust the film thickness distribution of the outermost periphery of the wafer W.

The upper portion of the drive ring 62 is connected to an annular retainer ring pressing device 80 . The retainer ring pressing device 80 applies a downward load to the entire upper surface 60 b of the retainer ring 60 via the drive ring 62 , thereby pressing the lower surface 60 a of the retainer ring 60 against the polishing surface 2 a of the polishing pad 2 .

The retainer ring pressing device 80 includes an annular piston 81 fixed to the upper portion of the drive ring 62 and an annular rolling diaphragm 82 connected to the upper surface of the piston 81 . A retainer ring pressure chamber 83 is formed inside the rolling diaphragm 82 . The retainer ring pressure chamber 83 is connected to the compressed gas supply source via a gas transfer line F5. Compressed gas is supplied into the retainer ring pressure chamber 83 through the gas transfer line F5.

When compressed gas is supplied from the compressed gas supply source to the retainer ring pressure chamber 83, the rolling diaphragm 82 pushes the piston 81 downward, the piston 81 pushes the drive ring 62 downward, and the drive ring 62 pushes the entire retainer ring 60 downward. down to In this manner, the retainer ring pressing device 80 presses the lower surface 60 a of the retainer ring 60 against the polishing surface 2 a of the polishing pad 2 . The drive ring 62 is detachably connected to the retainer ring pressing device 80 . In one embodiment, the retainer ring pressing device 80 may have a structure that presses the lower surface 60 a of the retainer ring 60 against the polishing surface 2 a of the polishing pad 2 by applying the downward force of the polishing head 1 to the retainer ring 60 . good.

The gas transfer lines F1, F2, F3, F4, F5 extend through a rotary joint 25 attached to the head shaft 10. As shown in FIG. The polishing apparatus further includes pressure regulators R1, R2, R3, R4 and R5, which are provided in gas transfer lines F1, F2, F3, F4 and F5, respectively. ing. Compressed gas from a compressed gas supply is supplied independently into pressure chambers 70-73 and retainer ring pressure chamber 83 through pressure regulators R1-R5. Pressure regulators R 1 -R 5 are configured to regulate the pressure of compressed gas within pressure chambers 70 - 73 and retainer ring pressure chamber 83 . The pressure regulators R1-R5 are connected to the operation controller 9. FIG.

The pressure regulators R1-R5 are capable of varying the internal pressures of the pressure chambers 70-73 and the retainer ring pressure chamber 83 independently of each other, thereby adjusting the four corresponding regions of the wafer W, namely the central region. The pressing force against the polishing surface 2a of the wafer W at the edge portion, the inner intermediate portion, the outer intermediate portion, and the edge portion, and the pressing force of the retainer ring 60 against the polishing pad 2 can be adjusted independently. The gas transfer lines F1, F2, F3, F4, and F5 are also connected to atmospheric release valves (not shown), so that the pressure chambers 70 to 73 and the retainer ring pressure chamber 83 can be opened to the atmosphere. . In this embodiment, the elastic membrane 65 forms four pressure chambers 70-73, but in one embodiment, the elastic membrane 65 may form less than four pressure chambers or more than four pressure chambers. good.

FIG. 3 is a diagram showing an example of a spectrum generated by an operation control section; In FIG. 3, the horizontal axis represents the wavelength of light reflected from the wafer, and the vertical axis represents the relative reflectance derived from the intensity of the reflected light. The relative reflectance is an index value indicating the intensity of reflected light, and is the ratio of the intensity of light to a predetermined reference intensity. By dividing the light intensity (actually measured intensity) at each wavelength by a predetermined reference intensity, unnecessary noise such as variations in intensity specific to the optical system of the apparatus and the light source can be removed from the measured intensity.

The reference intensity is the pre-measured intensity of light for each wavelength, and the relative reflectance is calculated at each wavelength. Specifically, the relative reflectance is obtained by dividing the light intensity (measured intensity) at each wavelength by the corresponding reference intensity.

The operation controller 9 is configured to generate a reflected light spectrum from the reflected light intensity measurement data. The spectrum of reflected light is represented as a line graph (that is, spectral waveform) showing the relationship between the wavelength and intensity of reflected light. The intensity of reflected light can also be expressed as a relative value such as reflectance or relative reflectance.

ここで、λは基板から反射した光の波長であり、Ｅ（λ）は波長λでの強度であり、Ｂ（λ）は波長λでの基準強度であり、Ｄ（λ）は光を遮断した条件下で測定された波長λでの背景強度（ダークレベル）である。 In actual polishing, the dark level (background intensity obtained under the condition that light is blocked) is subtracted from the measured intensity to obtain the corrected measured intensity, and the dark level is further subtracted from the reference intensity to obtain the corrected reference intensity. , and the relative reflectance is obtained by dividing the corrected measured intensity by the corrected reference intensity. Specifically, the relative reflectance R(λ) can be obtained using the following formula (1).

where λ is the wavelength of the light reflected from the substrate, E(λ) is the intensity at wavelength λ, B(λ) is the reference intensity at wavelength λ, and D(λ) blocks the light. is the background intensity (dark level) at wavelength λ measured under the condition of

The operation control unit 9 generates a spectrum as shown in FIG. 3 from the reflected light intensity measurement data. Furthermore, the operation control unit 9 determines the film thickness of the wafer W from the spectrum of the reflected light. The spectrum of the reflected light changes according to the film thickness of the wafer W. FIG. Therefore, the operation control section 9 can determine the film thickness of the wafer W from the spectrum of the reflected light. Hereinafter, the spectrum generated from the reflected light from the wafer W to be polished is referred to as the measured spectrum in this specification.

The operation control unit 9 is configured to determine the film thickness from a comparison between the measured spectrum (ie measured data) and a plurality of reference spectra (ie reference data). The operation control unit 9 compares the measured spectrum generated during polishing with a plurality of reference spectra to determine the reference spectrum closest in shape to the measured spectrum, and the film associated with the determined reference spectrum. Get thickness. The reference spectrum that is closest in shape to the measured spectrum is the spectrum with the smallest difference in relative reflectance between the reference spectrum and the measured spectrum.

A plurality of reference spectra are obtained in advance by polishing a reference wafer having an initial film thickness that is the same as or equivalent to the wafer to be polished (hereinafter, wafer W corresponds to the wafer to be polished in this specification). Each reference spectrum can be associated with a film thickness at which the reference spectrum was acquired. That is, each reference spectrum is acquired at different film thicknesses, and multiple reference spectra correspond to multiple different film thicknesses. Therefore, the current film thickness can be estimated by determining the reference spectrum that is closest in shape to the measured spectrum.

FIG. 4 is a diagram showing an example of a process of acquiring a plurality of reference spectra. First, a reference wafer having the same or equivalent film thickness as the wafer W is prepared. The reference wafer is transferred to the film thickness measuring device 170 (see FIG. 1), and the initial film thickness of the reference wafer is measured by the film thickness measuring device 170 (see step S101). The film thickness measuring device 170 is electrically connected to the operation controller 9 .

Next, the reference wafer is polished while slurry as a polishing liquid is supplied to the polishing pad 1 (see step S102). During polishing of the reference wafer, the surface of the reference wafer is irradiated with light, and the spectrum of reflected light from the reference wafer (ie, the reference spectrum) is obtained (see step S103).

A reference spectrum is acquired each time the polishing table 3 rotates once. Thus, multiple reference spectra are acquired during polishing of the reference wafer. After finishing the polishing of the reference wafer, the reference wafer is transferred to the film thickness measuring device 170 again, and the film thickness (that is, the final film thickness) of the polished reference wafer is measured (see step S104).

If the polishing rate of the reference wafer is constant, the film thickness decreases linearly with polishing time. The polishing rate can be calculated by dividing the difference between the initial film thickness and the final film thickness by the polishing time required to reach the final film thickness. As described above, the reference spectrum is periodically acquired each time the polishing table 3 rotates once. Therefore, the polishing time when each reference spectrum is acquired can be calculated from the rotational speed of the polishing table 3. can be done. Thus, the operation controller 9 determines the film thickness corresponding to each reference spectrum (see step S105).

Each reference spectrum can be related (bound) to the corresponding film thickness. Therefore, the motion control unit 9 determines the current film thickness of the wafer W from the film thickness associated with the reference spectrum that is closest in shape to the measured spectrum during polishing of the wafer W. be able to.

The process of polishing the wafer W to be polished will be described below. First, it is necessary to determine the first polishing condition (in other words, the final target film thickness flat condition) under which the film thickness uniformity of the wafer W to be polished is within a predetermined allowable range.

The first polishing condition may be a polishing condition (control of pressure in each of the plurality of pressure chambers 70, 71, 72, 73, 83) determined in advance so that the final target film thickness is flat. The operation control unit 9 is configured to polish the wafer W while controlling the respective pressures of the plurality of pressure chambers 70, 71, 72, 73, 83 based on the first polishing conditions.

FIG. 5 is a diagram showing a plurality of pressing regions of a wafer divided according to a plurality of pressure chambers. As shown in FIG. 5, the operation control unit 9 divides the wafer W into a plurality of pressing areas A1 to A4 according to the plurality of pressure chambers 70, 71, 72, and 73. As shown in FIG. These pressing areas A1 to A4 are arranged concentrically with the center CPW of the wafer W. As shown in FIG. A notch Nt is formed in the outer edge of the wafer W. As shown in FIG.

In one embodiment, the first polishing condition is based on the film thickness measured by the film thickness sensor 40 during polishing of the wafer W, and the film thickness (average film thickness) of each region A1 to A4 of the wafer W is The polishing conditions (CLC: closed loop control) may be such that the pressure in each of the pressure chambers 70 to 73 is feedback-controlled in real time so that the average film thickness of the entire film is obtained. More specifically, the operation control unit 9 calculates the average film thickness value in each of the pressing areas A1 to A4 based on the film thickness of the wafer W measured based on the signal output from the film thickness sensor 40. do. After that, the operation control unit 9 controls the pressure regulators R1 to R4 so that the difference between the average film thickness value of each of the pressing areas A1 to A4 and the average film thickness value of the entire wafer W is reduced. Thereby, the pressure in the pressure chambers 70 to 73 corresponding to the pressing areas A1 to A4 is controlled.

The operation control section 9 may control the pressure in the retainer ring pressure chamber 83 by controlling the pressure regulator R5 based on the same method as described above.

FIG. 6 is a diagram showing a polishing profile of a wafer when the wafer is polished under the first polishing conditions. 6, the horizontal axis represents the radial distance of the wafer W, and the vertical axis represents the film thickness distribution of the wafer W. In FIG. The thick line in FIG. 6 indicates the boundary line between the pressing area A4 corresponding to the pressure chamber 73 located at the outermost periphery of the wafer W and the pressing area inside the pressing area A4. In the embodiment shown in FIG. 6, the film thickness distribution in the radial direction of the wafer W after polishing the wafer W for a predetermined period of time will be described as the polishing profile of the wafer W. A polishing rate distribution in the radial direction of W may be included.

When the wafer W is polished under the first polishing condition, the uniformity of the film thickness of the wafer W is within a predetermined allowable range in other regions including the central portion of the wafer W (that is, regions other than the outermost periphery). In a specific region including the outermost periphery of the wafer W, the residual film (film thickness after polishing) of the wafer W may vary greatly in the radial direction. That is, within the specific region including the outermost periphery of the wafer W, the film thickness difference between the large film thickness portion and the small film thickness portion is large. The outermost periphery of the wafer W tends to have a steep and asymmetrical polishing profile due to the influence of rebound of the polishing pad 2, etc., and a flat film cannot be obtained simply by adjusting the pressure of the pressure chamber in a specific region including the outermost periphery of the wafer W. Obtaining a thickness distribution is difficult. Variation in the film thickness after polishing within a specific region including the outermost periphery of the wafer W (so-called residual film range) tends to increase as the polishing time under the first polishing condition increases.

Therefore, in the present embodiment, the operation control unit 9 is configured to polish the wafer W based on the second polishing condition for reducing the variation in film thickness in the radial direction of the wafer W at the outermost periphery of the wafer W. there is In the embodiment shown below, as an example of the specific region of the wafer W, an embodiment for reducing the variation in the film thickness of the wafer W at the outermost periphery of the film thickness of the wafer W will be described. It is not limited to the outermost circumference of W. In other regions of the wafer W than the outermost periphery, there is a possibility that the film thickness of the wafer W may vary.

FIG. 7 is a diagram showing second polishing conditions. In FIG. 7, the horizontal axis represents the radial distance of the wafer W, and the vertical axis represents the film thickness distribution of the wafer W. As shown in FIG. In the embodiment shown in FIG. 7, the film thickness distribution in the radial direction of the wafer W after polishing the wafer W for a predetermined time will be described as the polishing profile of the wafer W. A polishing rate distribution in the radial direction of W may be included.

The operation control unit 9 polishes a wafer having an initial film thickness equal to or equivalent to that of the wafer W to be polished, based on the first polishing conditions. After that, the operation control unit 9 determines the second polishing conditions based on the first polishing profile (film thickness distribution or polishing rate distribution of the wafer W after polishing) obtained by polishing under the first polishing conditions. The second polishing conditions form a second polishing profile having a distribution opposite to the distribution of the first polishing profile (more specifically, the distribution of pressed areas on the wafer W corresponding to specific pressure chambers). are predetermined (adjusted) polishing conditions.

In other words, under the second polishing conditions, the thicker portion of the outermost periphery of the wafer W polished under the first polishing condition is more actively polished, and the outermost periphery of the wafer W after polishing is thickened. The polishing conditions are such that polishing of thin portions of the film is suppressed. The second polishing profile has a distribution in which the positive and negative signs of the numerical values indicating the thickness of the film thickness of the wafer W or the polishing rate are inverted with respect to the distribution of the first polishing profile. Ideally, the curve representing the distribution of the second polishing profile and the curve representing the distribution of the first polishing profile are axisymmetrical to each other.

In the embodiment shown in FIG. 7, in the film thickness distribution on the coordinate system specified by the distance in the radial direction of the wafer W and the film thickness of the wafer W corresponding to the distance, the film thickness distribution of the outermost periphery of the wafer W (curve showing the distribution of the second polishing profile) is a curve showing the film thickness distribution of the outermost periphery of the wafer W polished under the first polishing condition centering on the reference line (see the dashed line in FIG. 7). is axisymmetric with respect to In addition, in the embodiment shown in FIG. 7, the curve showing the distribution of the second polishing profile is drawn as an ideal curve.

The second polishing conditions are determined by polishing a wafer having an initial film thickness equal to or equivalent to that of the wafer W to be polished. First, the wafer W is polished in advance under the first polishing conditions, and the first polishing profile is confirmed. After that, another wafer is polished, and the second polishing conditions are experimentally determined so that the polishing profile after polishing has a distribution opposite to that of the first polishing profile. Alternatively, in one embodiment, the wafer W is first polished under the first polishing condition, and then the polishing condition is switched from the first polishing condition to polish the wafer W. The second polishing conditions, which are conditions for switching from the first polishing conditions, are experimentally determined so that the polishing profile after polishing has a flat distribution. In one embodiment, the second polishing conditions may be selected from a database of polishing conditions and polishing profiles stored in advance in the storage device 9a, and/or may be determined by polishing simulation. good.

The operation control unit 9 stores second polishing conditions in its storage device 9a, and is configured to polish the wafer W based on the second polishing conditions. More specifically, the operation control unit 9 controls the pressure of a specific pressure chamber out of the pressure chambers 70, 71, 72, 73, 83 with a predetermined fixed value based on the second polishing condition. while polishing the wafer W. The second polishing conditions include polishing conditions for polishing the wafer W while controlling the pressure of a specific pressure chamber at a predetermined fixed value based on the second polishing profile.

In this embodiment, the specific pressure chambers include the edge pressure chamber 73 that presses the outermost periphery of the wafer W and adjacent pressure chambers adjacent to the edge pressure chamber 73 . The adjacent pressure chambers include at least one of intermediate pressure chamber 72 and retainer ring pressure chamber 83 . In this embodiment, the adjacent pressure chambers are both the intermediate pressure chamber 72 and the retainer ring pressure chamber 83 . In one embodiment, the specific pressure chamber may be edge pressure chamber 73 only.

The second polishing conditions include polishing conditions determined by adjusting the pressure of specific pressure chambers. In one embodiment, the second polishing conditions may include polishing conditions determined by adjusting pressures in pressure chambers other than specific pressure chambers. For example, if the specific pressure chamber is the edge pressure chamber 73 , the second polishing conditions include polishing conditions determined by adjusting the pressure of the adjacent pressure chamber adjacent to the edge pressure chamber 73 .

In one embodiment, the second polishing conditions may include polishing conditions determined by adjusting the pressing force of the retainer ring 60 arranged to surround the outermost periphery of the wafer W against the polishing surface 2a. In this case, the operation control section 9 controls the retainer ring pressing device 80 that applies the downward force of the polishing head 1 to the retainer ring 60 based on the second polishing condition.

In this embodiment, the operation control unit 9 controls the pressures of the edge pressure chamber 73 and the adjacent pressure chambers 72 and 83 based on the second polishing conditions, while controlling the edge pressure chamber 73 and the adjacent pressure chambers 72 . , 83 are feedback-controlled based on the first polishing condition.

The first polishing conditions are the average film thickness value of the regions corresponding to the other pressure chambers 70 and 71 and the average film thickness value of the entire wafer W based on the signal output from the film thickness sensor 40 during polishing. This is a polishing condition for feedback-controlling the respective pressures of the pressure chambers 70 and 71 so as to reduce the difference between .

FIG. 8 is a diagram showing polishing rates of wafers polished under the first polishing condition and the second polishing condition. In FIG. 8, the horizontal axis represents the radial distance of the wafer W, and the vertical axis represents the polishing rate of the wafer W. In FIG. FIG. 8 shows the polishing rate of the outer portion of the wafer W in an enlarged manner. As shown in FIG. 8, the polishing rate at the pressed area A4 on the wafer W under the first polishing condition and the polishing rate at the pressed area A4 on the wafer W under the second polishing condition are opposite to each other. Therefore, the operation control unit 9 can improve the uniformity of the film thickness of the outermost periphery of the wafer W by polishing the wafer W under the combination of the first polishing condition and the second polishing condition.

FIG. 9 is a diagram showing an example of a process of polishing a wafer to be polished. As shown in step S201 of FIG. 9, the operation control unit 9 polishes the wafer W under the first polishing conditions (first polishing step). Thereafter, the operation control unit 9 determines whether or not a predetermined switching condition is satisfied (see step S202), and if the switching condition is not satisfied (see "No" in step S202), continues step S201. If the switching condition is satisfied ("Yes" in step S202), the operation control unit 9 switches the polishing condition from the first polishing condition to the second polishing condition (see step S203), and polishes the wafer W under the second polishing condition. is polished (second polishing step).

In a state where the variation in the remaining film thickness (more specifically, the difference between the maximum value and the minimum value of the film thickness) of the outermost periphery (that is, the specific region) of the wafer W is too large, the polishing conditions are changed to the first polishing. Even if the condition is switched to the second polishing condition, there is a possibility that the variation in the film thickness of the outermost periphery of the wafer W will not be eliminated. Therefore, as the switching condition, the operation control unit 9 sets the difference between the maximum value and the minimum value of the film thickness of the outermost periphery of the wafer W during polishing of the wafer W under the first polishing condition (so-called residual film range). exceeds a predetermined threshold value, the polishing condition may be switched from the first polishing condition to the second polishing condition (first switching condition).

If there is a large variation in film thickness within a specific region of the wafer W corresponding to a specific pressure chamber, the variation in film thickness may not be eliminated even if the pressure in the specific pressure chamber is adjusted. Therefore, in the above-described embodiment, the operation control unit 9 changes the polishing condition from the first polishing condition to Switch to the second polishing condition.

Even if the polishing condition is switched from the first polishing condition to the second polishing condition in a state where the remaining polishing time is too short, there is a possibility that the film thickness variation in the specific region of the wafer W will not be eliminated. Therefore, the operation control unit 9 sets, as the switching conditions, the time required to eliminate the difference between the maximum value and the minimum value of the film thickness of the outermost periphery of the wafer W by polishing under the second polishing condition, The polishing condition may be switched from the first polishing condition to the second polishing condition based on the remaining polishing time until the final target film thickness (second switching condition).

The polishing rate when the wafer W is polished under the second polishing conditions is known in advance by the process of determining the second polishing conditions. Therefore, when the wafer W is polished under the second polishing condition, the operation control unit 9 reduces (eliminates) the residual film range of the wafer W during polishing of the wafer W under the first polishing condition. time can be calculated. Therefore, in one embodiment, when the required polishing time under the second polishing condition reaches or approaches the predetermined remaining time, the operation control unit 9 changes the polishing condition from the first polishing condition to the second polishing condition. You can switch to The predetermined remaining time is, for example, the same as the time required for the film thickness of the wafer W to reach the final target film thickness when the wafer W is polished under the second polishing conditions after the switching timing.

More specifically, the operation control unit 9 controls the time required to reduce the residual film range of the wafer W under the second polishing condition (that is, the required time) during polishing of the wafer W under the first polishing condition. polishing time) and the remaining polishing time (that is, the remaining time) are calculated. The remaining polishing time is calculated based on the following formula. Remaining polishing time=(current film thickness of wafer W−target film thickness of wafer W)/assumed polishing rate under the second polishing condition

If the required polishing time is shorter than the remaining time (required polishing time <<remaining time), the polishing time under the second polishing condition becomes longer, and the residual film profile of the wafer W deteriorates. When the required polishing time and the remaining time are the same (required polishing time=remaining time), the remaining film thickness range of the wafer W is eliminated and the film thickness of the wafer W reaches the target film thickness (ideal state). If the required polishing time is longer than the remaining time (required polishing time>remaining time), the film thickness of the wafer W reaches the target film thickness before the remaining film range is resolved, and the remaining film range cannot be completely resolved. do not have. If polishing is continued as it is, overpolishing will occur. Therefore, it is desirable that the operation control section 9 switches the polishing condition from the first polishing condition to the second polishing condition when the required polishing time and the remaining time are the same.

According to the second switching condition, when there is a difference in the total polishing amount, it is possible to change the residual film range allowable in polishing under the first polishing condition. can be optimized accordingly. In the case of polishing for removing the film on the wafer W, the "time required to reach the final target film thickness" means that the final target film thickness is zero, that is, the time required to clear the excess film. time means

In one embodiment, the operation control section 9 may switch the polishing condition from the first polishing condition to the second polishing condition based on the first switching condition and the second switching condition. In one embodiment, the operation control unit 9 may switch the polishing condition from the first polishing condition to the second polishing condition when the average film thickness of the entire wafer W reaches a predetermined film thickness. In one embodiment, the operation control unit 9 may switch the polishing condition from the first polishing condition to the second polishing condition when the polishing time of the wafer W reaches a predetermined polishing time.

After executing step S203 in FIG. 9, the operation control unit 9 determines whether the average film thickness of the entire wafer W reaches the target film thickness or the material formed on the wafer W reaches the interface with the different material. Upon receiving an end point detection signal indicating that the polishing has been completed from the film thickness sensor 40 (see "Yes" in step S204), the polishing of the wafer W is completed (see step S205). If the end point detection signal has not been received (see "No" in step S204), the operation control unit 9 continues polishing the wafer W under the second polishing conditions. When the end point detection signal is received, the operation control unit 9 may continue polishing the wafer W under the second polishing condition if the residual film range in the specific region is not equal to or less than the predetermined value. Further, the operation control unit 9 may issue an alarm when the remaining film range in the specific region is not equal to or less than a predetermined value when receiving the end point detection signal.

In the embodiment described above, the polishing head 1 has a plurality of pressure chambers (airbags), but the pressing element for pressing the wafer W is not limited to this. The technical idea of the present invention is applicable when a plurality of pressing elements that apply the same pressure to the wafer W are arranged in the radial direction of the wafer W. A piezoelectric element, for example, can be used as the pressing element.

The above-described embodiments are described for the purpose of enabling a person having ordinary knowledge in the technical field to which the present invention belongs to implement the present invention. Various modifications of the above embodiments can be made by those skilled in the art, and the technical idea of the present invention can be applied to other embodiments. Accordingly, the present invention is not limited to the described embodiments, but is to be construed in its broadest scope in accordance with the technical spirit defined by the claims.

REFERENCE SIGNS LIST 1 polishing head 2 polishing pad 2a polishing surface 3 polishing table 5 polishing liquid supply nozzle 6 table motor 7 optical sensor head 9 operation control section 9a storage device 9b arithmetic device 10 head shaft 21 head body 25 rotary joint 40 film thickness sensor 44 light source 47 Spectrometer 60 Retainer ring 60a Lower surface 60b Upper surface 62 Drive ring 65 Elastic film 65a Substrate pressing surface 70 Central pressure chamber 71 Intermediate pressure chamber 72 Intermediate pressure chamber 73 Edge pressure chamber 80 Retainer ring pressing device 81 Piston 82 Rolling diaphragm 83 Retainer ring pressure chamber 170 film thickness measuring instrument

Claims (10)

A polishing method for pressing a substrate against a polishing surface of a polishing pad with a polishing head having a plurality of pressure chambers including specific pressure chambers,
The polishing method is
a first polishing step of polishing the substrate under a first polishing condition;
determined based on a first polishing profile along the radial direction of a specific region of the substrate corresponding to the specific pressure chamber, which is obtained by previously polishing a substrate different from the substrate under the first polishing conditions. a second polishing step of polishing the substrate under a second polishing condition;
the second polishing conditions include polishing conditions predetermined to form a second polishing profile having a distribution opposite to the distribution of the first polishing profile;
The polishing method, wherein the second polishing step is performed after the first polishing step. 2. The polishing method according to claim 1, wherein said specific pressure chamber includes an edge pressure chamber that presses the outermost periphery of said substrate. 3. The polishing method according to claim 1, wherein said second polishing conditions include polishing conditions determined by adjusting pressures in pressure chambers other than said specific pressure chamber. 4. The second polishing condition according to any one of claims 1 to 3, wherein the second polishing condition includes a polishing condition determined by adjusting pressure in an adjacent pressure chamber adjacent to an edge pressure chamber that presses the outermost periphery of the substrate. The polishing method described in . 5. The second polishing condition according to any one of claims 1 to 4, wherein the second polishing condition includes a polishing condition determined by adjusting a pressing force against the polishing surface of a retainer ring arranged to surround the outermost periphery of the substrate. or the polishing method according to item 1. The first polishing condition adjusts the pressure of each of the plurality of pressure chambers based on the film thickness of the substrate corresponding to each of the plurality of pressure chambers, which is measured using a film thickness sensor during polishing. The polishing method according to any one of claims 1 to 5, comprising polishing conditions for polishing the substrate under feedback control. The polishing method according to any one of claims 1 to 6, wherein the substrate is polished under the first polishing condition, and after a predetermined switching condition is satisfied, the substrate is polished under the second polishing condition. . wherein, as the switching condition, the first polishing condition is switched to the second polishing condition when a difference between the maximum value and the minimum value of the film thickness of the specific region increases beyond a predetermined threshold value. Item 8. The polishing method according to Item 7. As the switching conditions, the time required to eliminate the difference between the maximum value and the minimum value of the film thickness in the specific region by polishing under the second polishing condition, and the remaining polishing time to reach the final target film thickness. 8. The polishing method according to claim 7, wherein said first polishing condition is switched to said second polishing condition based on. the specific pressure chamber includes an edge pressure chamber that presses the outermost periphery of the substrate;
According to the second polishing condition, the pressure of the edge pressure chamber is controlled, and based on the first polishing condition, the pressure of the pressure chambers other than the edge pressure chamber is controlled. Item 10. The polishing method according to any one of Items 9.

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