JP4408244B2 - Substrate polishing method and substrate polishing apparatus - Google Patents

Description

  The present invention relates to a technique for polishing a substrate.

  In order to ensure a certain quality of a semiconductor product, in a semiconductor manufacturing process, for example, in a polishing process using chemical mechanical polishing (hereinafter abbreviated as “CMP”), a semiconductor substrate (for example, silicon ( Si) substrate, hereinafter referred to as “substrate”), the polishing rate is obtained by measuring the thickness of the thin film formed on the surface before and after polishing, and is used for processing the next substrate (or lot). A technique for suppressing variations in the film thickness of the substrate after polishing is known (for example, see Patent Document 1).

The film thickness is measured by irradiating the substrate with white light and spectrally analyzing the reflected light from the substrate to obtain the spectral reflectance, and calculating the thickness of the film based on the spectral reflectance. An interference type film thickness measuring apparatus is conventionally used.
JP 11-186204 A

  By the way, since the polishing rate of the substrate changes depending on the state of the polishing table, the slurry concentration, the temperature, the decrease of the polishing pad, etc., the polishing time is determined based only on the polishing rate obtained in the immediately preceding process. Even if the substrate is polished, it is not easy to accurately polish the substrate film to the target film thickness. Therefore, when the pattern on the substrate is further miniaturized, it becomes difficult to satisfy the required accuracy of the film thickness.

  The present invention has been made in view of the above problems, and an object thereof is to accurately polish a film formed on the surface of a substrate to a target film thickness.

The invention according to claim 1 is a substrate polishing method for polishing a substrate, wherein a first measurement step of measuring a thickness of a film formed on a surface of the substrate to obtain a first film thickness, A first polishing step for polishing the substrate for a predetermined time; a second measurement step for obtaining a second film thickness of the film after the first polishing step; and the first film thickness and the second film. The additional polishing time based on the corrected polishing rate obtained by correcting the polishing rate derived from the thickness and the predetermined time using a correction coefficient, and the difference between the second film thickness and the target film thickness A second polishing step for further polishing the substrate for the additional polishing time, a third measurement step for obtaining a third film thickness of the film after the second polishing step, and the second The value obtained by dividing the difference between the film thickness and the third film thickness by the difference between the second film thickness and the target film thickness is And a step of modifying the correction coefficient by multiplying the correction coefficient with respect to another substrate, and a step of repeating from the first measurement step up to the step of the modification.

The invention according to claim 2 is a substrate polishing apparatus for polishing a substrate, and a film thickness for obtaining a film thickness by measuring a thickness of a polishing unit for polishing a substrate and a film formed on the surface of the substrate The first thickness of the film formed on the surface of the measurement unit and the substrate before polishing, the second thickness of the film after being polished for a predetermined time by the polishing unit, and the predetermined time In the polishing portion, only the additional polishing time determined based on the corrected polishing rate obtained by correcting the polishing rate using the correction coefficient and the difference between the second film thickness and the target film thickness. A controller for further polishing the substrate, and the difference between the second film thickness and the third film thickness of the film after polishing for the additional polishing time, The correction coefficient is corrected by multiplying the correction coefficient by a value obtained by dividing by the difference from the target film thickness. After treatment of the substrate in the substrate polishing apparatus, another substrate is Ru are processed.

According to the first and second aspects of the invention, the film formed on the surface of the substrate can be accurately polished to the target film thickness.

  FIG. 1 is a diagram showing a configuration of a substrate polishing apparatus 1 according to an embodiment of the present invention. The substrate polishing apparatus 1 shown in FIG. 1 is used, for example, in a damascene process in a circuit forming process, and performs polishing (for example, CMP) on a substrate having a laminated film (multilayer film constituting a circuit pattern). Measure the film thickness of the substrate.

  A substrate polishing apparatus 1 in FIG. 1 performs a disk-shaped substrate holding unit 2 that holds a substrate 9, a film thickness measuring unit 3 that measures the thickness of a film of the substrate 9, and obtains the film thickness, and performs various arithmetic processes. An overall control unit 4 configured by a CPU, a memory for storing various information, and the like, and a polishing unit 5 connected to the overall control unit 4 are provided. In FIG. 1, the structure of the film thickness measuring unit 3 is illustrated, but the structure of the polishing unit 5 is not illustrated.

  A substrate rotation mechanism 21 having a motor and a rotation support shaft is attached to the substrate holding unit 2 on the side opposite to the substrate 9. The film thickness measuring unit 3 is a film formed on the surface of the substrate 9 at the time of film thickness measurement (a film to be polished on the uppermost layer among the films formed on the surface is hereinafter referred to as “target film”). A head unit 31 that irradiates illumination light and receives reflected light from the substrate 9, a spectroscope 32 that acquires the spectral intensity of reflected light from the substrate 9 that enters the head unit 31, and a CPU that performs various arithmetic processes, The computer 33 includes a memory for storing various information.

  The head unit 31 receives illumination light from a lamp (for example, a xenon lamp) 311 through an optical fiber 312 and guides it to a half mirror 314 through a lens 313. The illumination light reflected by the half mirror 314 is applied to the surface of the substrate 9 through the lens 315. Reflected light from the substrate 9 is taken into the head portion 31 by the lens 315, passes through the half mirror 314, and then guided to the spectroscope 32 by the optical fiber 316. The computer 33 is connected to the spectroscope 32 via an I / O board, and obtains the thickness of the film on the substrate 9 based on the output from the spectroscope 32.

  FIG. 2 is a diagram schematically showing the substrate polishing apparatus 1 when the substrate 9 is polished. As shown in FIG. 2, the polishing unit 5 includes a polishing table 51 having a polishing pad attached to the upper surface and a lower surface connected to a motor 52. The polishing table 51 is a film thickness measuring unit 3 (in FIG. 2, a circle). It is provided adjacent to. The substrate holding unit 2 is attached to a holding unit moving mechanism (not shown), and when the substrate 9 is polished, the substrate holding unit 2 moves onto the polishing table 51 and moves to the lower surface of the substrate 9 (that is, the target film). The surface) comes into contact with the surface of the polishing table 51. The substrate rotation mechanism 21 is connected to the overall control unit 4 (see FIG. 1), and the substrate rotation mechanism 21 is driven to rotate the substrate 9 on the polishing table 51 at a constant angular velocity. The polishing table 51 is also rotated by a motor 52, and a polishing agent (also called slurry) is supplied on the surface thereof. Thereby, the surface of the rotating substrate 9 on the polishing table 51 is polished by the rotating polishing table 51. When polishing the substrate 9, the substrate holding unit 2 swings between the inside and the outer peripheral portion of the polishing table 51 by a holding unit moving mechanism (not shown).

  FIG. 3 is a diagram showing a flow of processing in which the substrate polishing apparatus 1 polishes the substrate 9. In FIG. 3, the steps included in the right dashed rectangle indicate steps in the film thickness measurement unit 3, and the steps included in the left dashed rectangle indicate steps in the polishing unit 5.

  In the substrate polishing apparatus 1, first, a measurement recipe indicating the type of measurement method of the film thickness of the substrate 9, parameters used for measurement, and the like is created in the computer 33 of the film thickness measurement unit 3 (step S <b> 11). As will be described later, in the substrate polishing process, three film thickness measurements are performed on each substrate 9 in different processing (polishing) stages, and the film thickness measuring unit 3 uses a measurement recipe used for each film thickness measurement. Are created individually. For example, when the substrate 9 has a two-layer film, the computer 33 uses a measurement recipe for measuring both film thicknesses of the two-layer film for the first measurement of the three film thickness measurements. For the second and third measurements, only the film thickness of the target film is measured, and the film thickness of the other film (that is, the lower layer film) is created using the first measurement value. Is done. Note that the film thickness (predicted value) of the lower layer film may be set in advance in the measurement recipe, and only the target film may be quickly measured while using the film thickness of the lower layer film. The computer 33 individually designates whether or not the lower layer film thickness measurement is necessary for each of the first to third measurements by an input from the operator. Of course, the film on the substrate 9 may be three or more layers. In this case, the lower layer film in the following description is a multilayer film.

  Subsequently, the substrate 9 transported to the substrate standby stage (indicated by reference numeral 71 in FIG. 2) by the external transport device is held by the substrate holding unit 2 by suction, and the holding unit moving mechanism holds the substrate. The part 2 is moved to the film thickness measuring part 3. Then, the first film thickness measurement in the film thickness measurement unit 3 is performed under the control of the overall control unit 4. Specifically, the illumination light from the head unit 31 is irradiated onto the surface of the substrate 9, and the spectral intensity of the reflected light from the substrate 9 is acquired by the spectrometer 32. In the film thickness measuring unit 3, the spectral intensity of the reflected light is acquired in advance on another substrate (reference substrate) on which no film is formed, and the relative spectral reflection of the substrate 9 is made using the spectral intensity of the reference substrate. A rate is required. FIG. 4 is a diagram showing an example of the spectral reflectance obtained by measurement with a solid line denoted by reference numeral 81.

  In the computer 33, by executing a program prepared in advance, various film thicknesses in the film configuration of the substrate 9 are calculated based on a predetermined film thickness calculation formula of optical interference considering multiple reflection of the multilayer film of the substrate 9. Spectral reflectance for the combination is obtained by calculation. Then, by matching the spectral reflectances obtained in advance with the spectral reflectances obtained by measurement, the spectral reflectance most approximate to the spectral reflectance obtained by measurement (for example, in FIG. 4). , The film thickness combination indicating the spectral reflectance shown by the broken line 82 is specified, and the film thickness of the target film (hereinafter referred to as “first film thickness”) and the film thickness of the lower layer film are acquired. (Step S12). The acquired film thickness data is stored in the computer 33 and is output to the overall control unit 4 as necessary.

  When the first film thickness is acquired, the substrate holding unit 2 moves onto the polishing table 51, and the rotation and swinging of the substrate holding unit 2 and the rotation of the polishing table 51 are started. The substrate 9 is polished for the initial polishing time (step S13). Note that the initial polishing time is sufficiently shorter than the time required for the target film of the substrate 9 to reach a predetermined target film thickness.

  When the initial polishing time has elapsed, the polishing unit 5 finishes polishing, and the substrate holding unit 2 moves away from the polishing table 51 and moves to the film thickness measuring unit 3. Then, the film thickness is measured for the second time, and the film thickness (hereinafter referred to as “second film thickness”) of the target film of the substrate 9 after the initial polishing time is acquired (step S14). At this time, the film thickness measurement unit 3 uses the value obtained in the first film thickness measurement for the film thickness of the lower layer film according to the measurement recipe, and only the film thickness of the target film is obtained. It can be done in a short time.

  When the second film thickness is acquired, the computer 33 obtains the polishing rate Ri by performing the calculation shown in Equation 1 with the first film thickness d1, the second film thickness d2, and the initial polishing time Ti. Step S15).

  Subsequently, the polishing rate Ri is corrected by multiplying the polishing rate Ri by the correction coefficient X, and the corrected polishing rate Rc is obtained (step S16). Here, the correction coefficient X is set to 1.0 for the first substrate 9, and the polishing rate Ri is handled as it is as the corrected polishing rate Rc. When the corrected polishing rate Rc is acquired, the additional polishing time Tc for the substrate 9 after polishing in the initial polishing time is a number where the second film thickness is d2, the corrected polishing rate is Rc, and the target film thickness is d0. 2 is obtained by the calculation shown in FIG. 2 (step S17).

  Thus, the additional polishing time Tc is based on the polishing rate Rc derived from the first film thickness d1, the second film thickness d2, and the initial polishing time Ti, and the difference between the second film thickness d2 and the target film thickness d0. Is required. The additional polishing time Tc is output to the overall control unit 4, and the substrate 9 moves again onto the polishing table 51. Then, the substrate 9 is further polished by the additional polishing time Tc under the control of the overall control unit 4 (step S18). As a result, the substrate 9 is accurately polished to the target film thickness d0 based on the result of polishing for the same substrate 9 during the initial polishing time.

  When the additional polishing is completed, the substrate holding unit 2 moves to the film thickness measuring unit 3 to perform the third film thickness measurement, and the film thickness of the target film of the substrate 9 after the additional polishing (hereinafter referred to as “the first film”). 3) ”is acquired (step S19). As described above, in the third film thickness measurement, as in the second film thickness measurement, the first measurement value is used for the film thickness of the lower layer film. Then, by substituting the second film thickness d2, the third film thickness d3, the target film thickness d0, and the current correction coefficient X (indicated by Xc in Equation 3) into the right side of Equation 3, the next substrate 9 The corrected correction coefficient X used for the process is acquired (step S20).

  In Equation 3, the difference between the second film thickness d2 and the third film thickness d3, which is the actual polishing amount due to the additional polishing, is set to the second film thickness d2 that is the predicted polishing amount for the additional polishing and the target. The correction coefficient is easily corrected by multiplying the correction coefficient X by a value obtained by dividing by the difference from the film thickness d0.

  When the correction coefficient X is corrected (or while correcting the correction coefficient X), the substrate holding unit 2 moves to the substrate standby stage 71 and the substrate 9 is placed thereon, and the substrate polishing apparatus 1 is moved by an external transfer mechanism. Will be paid out. Thereafter, the substrate 9a to be processed next is placed on the substrate standby stage 71.

  The next substrate 9a is held by the substrate holding unit 2, and the first film thickness of the uppermost target film is acquired by the film thickness measuring unit 3 (steps S21 and S12). After the acquisition of the first film thickness, the substrate 9a is polished by the polishing unit 5 for the same initial polishing time Ti as that of the first substrate 9 (step S13), and the target film of the substrate 9a after the initial polishing time is polished. Two film thicknesses d2 are acquired (step SS14). Then, the polishing rate Ri of the substrate 9a is calculated by substituting the first film thickness d1 and the second film thickness d2 of the substrate 9a and the initial polishing time Ti into Equation 1 (step S15).

  The computer 33 further multiplies the polishing rate Ri of the substrate 9a by the correction coefficient X corrected based on the ratio between the actual additional polishing amount of the first substrate 9 and the predicted polishing amount, thereby obtaining the substrate 9a. The corrected polishing rate Rc of the substrate 9a in consideration of the result of the additional polishing is acquired (step S16). Then, an additional polishing time Tc for the substrate 9a is obtained by substituting the corrected polishing rate Rc, second film thickness d2 and target film thickness d0 of the substrate 9a into Equation 2 (step S17), and the substrate 9a is additionally polished. Further polishing is performed for the time Tc (step S18).

  When the additional polishing is completed, the third film thickness d3 of the substrate 9a after the additional polishing is acquired (step S19), and by using Equation 3, the second film thickness d2, the third film thickness d3 of the substrate 9a, and The correction coefficient X is further modified based on the target film thickness d0 (step S20). That is, the correction coefficient X is corrected to a value reflecting the result of the additional polishing of the second substrate 9a. After the second substrate 9a has moved to the substrate standby stage 71, it is unloaded from the substrate polishing apparatus 1, and the next substrate is loaded into the substrate standby stage 71, and the above steps S12 to S20 are repeated (step S21). ).

  As described above, in the substrate polishing apparatus 1, the substrate 9 is polished by the polishing unit 5 for a predetermined initial polishing time, and then the first film thickness and initial polishing time of the uppermost layer film of the substrate 9 before polishing. The substrate 9 is further polished for the additional polishing time determined based on the polishing rate derived from the second film thickness and the initial polishing time of the film after polishing only, and the difference between the second film thickness and the target film thickness. The Thus, the uppermost layer film of the substrate 9 can be accurately polished to the target film thickness by using the polishing rate in the polishing of the initial polishing time. In general, it is not easy to obtain the optimum polishing rate, and even if the polishing rate is obtained only from the result of the last polishing, it is experiential that a certain deviation from the actual polishing rate occurs. However, in the substrate polishing apparatus 1, the substrate 9 can be polished more accurately by correcting the polishing rate using the correction coefficient. Further, before the next substrate is processed, the correction coefficient is corrected based on the result of polishing the immediately preceding substrate 9, so that the next substrate can be polished more accurately.

  Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications can be made.

  In the above embodiment, the additional polishing time is obtained by the film thickness measurement unit 3. For example, the first film thickness, the second film thickness, and the third film thickness are input from the film thickness measurement unit 3 to the overall control unit 4. Thus, the additional polishing time may be obtained by the overall control unit 4. In addition, the function of calculating the film thickness in the computer 33 may be realized by the overall control unit 4, and the overall control unit 4 may play a part of the function of the film thickness measurement unit 3.

  The film thickness measuring unit 3 does not necessarily need to measure the film thickness by acquiring the spectral reflectance of the film, and may be an ellipsometer that acquires the film thickness by polarization analysis, for example. .

  The substrate 9 may have a single layer film formed thereon. The substrate 9 is not necessarily a semiconductor substrate, and may be another type of substrate such as a printed wiring board or a glass substrate.

It is a figure which shows the structure of a board | substrate polish apparatus. It is a figure which simplifies and shows the substrate polishing apparatus at the time of the grinding | polishing of a board | substrate. It is a figure which shows the flow of the process which grind | polishes a board | substrate. It is a figure which shows an example of a spectral reflectance.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Substrate polisher 3 Film thickness measurement part 4 Overall control part 5 Polishing part 9 Substrate S12-S21 Step

Claims (2)

A substrate polishing method for polishing a substrate,
A first measurement step of measuring a thickness of a film formed on the surface of the substrate to obtain a first film thickness;
A first polishing step of polishing the substrate for a predetermined time;
A second measurement step of obtaining a second film thickness of the film after the first polishing step;
The corrected polishing rate obtained by correcting the polishing rate derived from the first film thickness, the second film thickness, and the predetermined time using a correction coefficient , the second film thickness, and the target A step of obtaining an additional polishing time based on the difference from the film thickness;
A second polishing step of further polishing the substrate for the additional polishing time;
A third measurement step of obtaining a third film thickness of the film after the second polishing step;
The correction coefficient is obtained by multiplying the correction coefficient by a value obtained by dividing the difference between the second film thickness and the third film thickness by the difference between the second film thickness and the target film thickness. A process of correcting
Repeating the steps from the first measuring step to the correcting step for another substrate;
A substrate polishing method comprising: A substrate polishing apparatus for polishing a substrate,
A polishing section for polishing the substrate;
A film thickness measuring unit for measuring the thickness of the film formed on the surface of the substrate and obtaining the film thickness;
The film thickness of the first formed on the surface of the substrate before the polishing film, the second film thickness and the polishing rate derived from the predetermined time of the film after the polishing by a predetermined time by the polishing unit The substrate is held at the polishing section for the additional polishing time determined based on the corrected polishing rate determined by correcting using the correction coefficient and the difference between the second film thickness and the target film thickness. A control unit for further polishing;
Equipped with a,
The difference between the second film thickness and the third film thickness after the polishing for the additional polishing time is obtained by dividing the difference between the second film thickness and the target film thickness. The correction factor is modified by multiplying the correction factor by the value
After treatment of the substrate in the substrate polishing apparatus, another substrate is processed substrate polishing apparatus according to claim Rukoto.

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