A wafer high-K metal gate chemical mechanical polishing method and semiconductor device

Abstract

The present invention provides a wafer high-K metal gate chemical mechanical polishing method and a semiconductor device, belonging to the field of semiconductor wafer processing technology. The present invention can divide the high-K metal gate chemical mechanical polishing into two stages, namely, preliminary polishing and fine polishing. In the preliminary polishing stage, a constant polishing rate control method is adopted to quickly remove most of the polishing layer to ensure the overall polishing efficiency. The initial polishing pressure during fine polishing is determined based on the remaining film thickness after the preliminary polishing to ensure that the polishing is completed at the same time as much as possible, reduce the total polishing time difference of each area at the polishing end point, and reduce over-polishing and under-polishing defects. In the fine polishing stage, constant pressure polishing is performed, and when a certain area reaches the polishing end point, the polishing pressure of the area is adjusted to a smaller level to stop polishing the area, so as to avoid constantly adjusting the pressure when approaching the polishing end point and avoid causing the polishing rate to drift, thereby improving the accuracy of the end point control and reducing over-polishing and under-polishing defects.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor wafer processing, and in particular to a wafer high-K metal gate chemical mechanical polishing method and a semiconductor device. Background Art

[0002] Wafer high-k metal gate (HKMG) is an advanced semiconductor manufacturing technology widely used in the production of high-performance integrated circuits. With the continuous development of semiconductor technology, the line width of ultra-large-scale integrated circuit manufacturing has been continuously reduced, resulting in higher requirements for planarization. Whether in advanced processes such as W-gate processes or multi-layer three-dimensional Cu wiring processes, chemical mechanical polishing (CMP) processes are required to efficiently remove excess metal materials on the wafer surface and globally planarize the wafer surface to ensure the accuracy of lithography process overlay and high-quality realization of multi-layer metal interconnection.

[0003] Currently, the size of wafers is getting larger and larger, and the polishing speed of each area on the wafer is not the same. Traditional chemical mechanical polishing methods usually adjust the polishing pressure of each area in real time during polishing, with the aim of adjusting the polishing rate of each area so that each area can be polished at the same time, improving polishing production efficiency and reducing polishing defects. However, when approaching the end point of polishing, the film thickness of the remaining polishing layer is relatively thin. Due to the delay and uncertainty of control, it is difficult to accurately control the polishing rate in a timely manner by adjusting the polishing pressure, which results in more polishing defects in high-K metal gate chemical mechanical polishing. Summary of the invention

[0004] The present invention provides a wafer high-K metal gate chemical mechanical polishing method and a semiconductor device, so as to solve the problems of low accuracy and many polishing defects in the existing high-K metal gate chemical mechanical polishing control method.

[0005] In a first aspect, the present invention provides a method for chemical mechanical polishing of a wafer high-K metal gate, comprising:

[0006] A constant polishing rate control method is used to perform preliminary polishing on the polishing layer of the wafer until the average residual film thickness of the polishing layer is reduced to a preset thickness; the residual film thickness of the polishing layer in each area of ​​the wafer surface after preliminary polishing is obtained; based on the residual film thickness of each area, the initial polishing pressure of each area is determined with the same remaining polishing time as the target; based on the initial polishing pressure of each area, a constant polishing pressure control method is used to perform fine polishing on the wafer after the initial polishing; during the fine polishing process, if any area reaches the polishing endpoint, the polishing pressure of the area is reduced from the initial polishing pressure to the preset pressure to stop polishing the area until all areas reach the polishing endpoint.

[0007] In one possible implementation, the initial polishing pressure of each area is determined based on the residual film thickness of each area and takes the same remaining polishing time as the target, including: for any area on the wafer surface, dividing the residual film thickness of the area by the target remaining polishing time to obtain the target polishing rate of the area; based on the target polishing rate of the area, determining the polishing pressure corresponding to the target polishing rate as the initial polishing pressure of the area.

[0008] In a possible implementation, the polishing endpoint detection method includes an eddy current endpoint detection method.

[0009] In a possible implementation, the method further includes:

[0010] During the fine polishing process, for any area, based on the real-time scanning results of the eddy current sensor, it is determined whether there is any polishing layer residue in the area; if no polishing layer residue is scanned in the area for a preset number of consecutive times, it is determined that the area has reached the polishing endpoint.

[0011] In a possible implementation, the preset number of times ranges from 10 to 20 times.

[0012] In a possible implementation, the preset pressure ranges from 0.3 to 0.8 psi.

[0013] In a possible implementation, after determining the initial polishing pressure of each area, it also includes: obtaining a preset upper limit and a preset lower limit of the initial polishing pressure; obtaining a historical usage time of the polishing pad, wherein the polishing pad is a polishing pad used in a fine polishing process; based on the historical usage time of the polishing pad, correcting the preset upper limit and the preset lower limit of the initial polishing pressure to obtain a corrected upper limit and lower limit, wherein the longer the historical usage time, the smaller the range of the corrected upper limit and lower limit; if the initial polishing pressure of any area is greater than or equal to the corrected upper limit, the corrected upper limit is used as the initial polishing pressure of the area; if the initial polishing pressure of any area is less than or equal to the corrected lower limit, the corrected lower limit is used as the initial polishing pressure of the area.

[0014] In a possible implementation manner, the polishing layer is a metal layer, and the lower layer of the polishing layer is a dielectric layer.

[0015] In a possible implementation manner, the metal layer includes a copper layer, a tungsten layer or an aluminum layer.

[0016] In a second aspect, the present invention provides a semiconductor device, which is manufactured based on the chemical mechanical polishing method of high-K metal gate on a wafer in any possible implementation manner as described above.

[0017] The present invention provides a wafer high-K metal gate chemical mechanical polishing method and a semiconductor device. The present invention divides the high-K metal gate chemical mechanical polishing into two stages, namely, preliminary polishing and fine polishing. In the preliminary polishing stage, a constant polishing rate control method is adopted to quickly remove most of the polishing layer to ensure the overall polishing efficiency. The initial polishing pressure during fine polishing is determined based on the remaining film thickness after the preliminary polishing to ensure that the polishing is completed at the same time as much as possible, reduce the total polishing time difference of each area at the polishing end point, and reduce over-polishing and under-polishing defects. In the fine polishing stage, constant pressure polishing is performed, and when a certain area reaches the polishing end point, the polishing pressure of the area is adjusted to a smaller level to stop polishing the area, so as to avoid constantly adjusting the pressure when approaching the polishing end point and avoid causing the polishing rate to drift, thereby improving the accuracy of the end point control and reducing over-polishing and under-polishing defects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0019] Figure 1 Schematic diagram of the structure of Dishing and Erosion polishing defects provided by an embodiment of the present invention;

[0020] Figure 2 It is a flow chart of an implementation method of a wafer high-K metal gate chemical mechanical polishing method provided by an embodiment of the present invention;

[0021] Figure 3 is a schematic structural diagram of a polishing head provided by an embodiment of the present invention;

[0022] Figure 4 is a graph showing the change of wafer grinding time and pressure provided by an embodiment of the present invention;

[0023] Figure 5 Schematic diagram of the eddy current endpoint detection principle provided by an embodiment of the present invention;

[0024] Figure 6 Schematic diagram of the structure of an eddy current metal film thickness measurement system provided by an embodiment of the present invention;

[0025] Figure 7 is a schematic diagram of scanning trajectories after 8 scans provided by an embodiment of the present invention;

[0026] Figure 8 is a schematic diagram of scanning trajectories after 16 scans provided by an embodiment of the present invention;

[0027] Fig. 9is a schematic diagram of the relationship between the use time of the polishing pad and the polishing rate provided by an embodiment of the present invention;

[0028] Fig.10 Schematic diagram of the relationship between the use time of the polishing pad provided by an embodiment of the present invention and the Dishing defect of tungsten metal;

[0029] Fig.11 It is a schematic diagram of the relationship between film removal rate and pressure of different materials provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0030] In order to enable people in the technical field to better understand the present solution, the technical solution in the embodiment of the present solution will be clearly described below in conjunction with the drawings in the embodiment of the present solution. Obviously, the described embodiment is an embodiment of a part of the present solution, not all of the embodiments. Based on the embodiments in the present solution, all other embodiments obtained by ordinary technicians in the field without creative work should fall within the scope of protection of the present solution.

[0031] The term "including" and any other variations in the specification and claims of this solution and the above drawings mean "including but not limited to", and is intended to cover non-exclusive inclusions and is not limited to the examples listed in the text. In addition, the terms "first" and "second" are used to distinguish different objects, not to describe a specific order.

[0032] The following is a detailed description of the implementation of the present invention in conjunction with the specific drawings:

[0033] The chemical mechanical polishing (CMP) process is a surface flattening method that combines chemical corrosion and mechanical grinding. It achieves trace removal of workpiece surface material through the organic combination of the physical grinding effect of nano-scale particles and the chemical corrosion effect of the polishing liquid to obtain an ultra-smooth, low-damage processed surface. The basic working principle of CMP technology is to drive the wafer to rotate through the polishing head, and then use the polishing pad to polish the wafer surface to achieve the desired smoothness. In this process, the polishing pad and the abrasive particles in the polishing liquid work together to remove excess surface material and achieve flattening through the synergistic effect of friction and corrosion.

[0034] There are multiple steps in the high-k metal gate (HKMG) process that require CMP process for planarization. For example, the Metal Clear process of the HKMG process can use CMP process, that is, growing a metal layer on the oxide layer to fill the key structure, but the surface of the entire wafer oxide layer is covered with a metal layer, and the excess metal layer can be removed by CMP process.

[0035] In the existing high-K metal gate chemical mechanical polishing method, the polishing pressure is continuously adjusted during the polishing process to adjust the polishing rate of each area, with the goal of completing polishing in each area at the same time. Due to the delay and uncertainty of control, it is difficult to accurately control the polishing rate during the polishing process. Before the polishing is completed, the impact of this problem is not prominent. When the film thickness of the remaining polishing layer is thin when approaching the polishing end point, continuous adjustment of the polishing pressure will cause the polishing rate to drift, and the polishing rate cannot be accurately controlled, resulting in over-polishing and under-polishing defects. In other words, it is impossible to control the consistency of the metal thickness removed from the wafer surface by adjusting the pressure in each area in real time. The following first explains the polishing defects.

[0036] Figure 1 Schematic diagram of the structure of Dishing and Erosion polishing defects provided by the embodiment of the present invention. Figure 1 For example, due to the difference in thickness of the metal layer in different areas on the wafer surface, when the metal material in a local area on the wafer surface is removed cleanly in a short time, if the pressure in this area cannot be controlled and adjusted in real time and the original set pressure is still used for polishing, this area will be over-polished, which is prone to larger defects such as Dishing and Erosion.

[0037] For example, since the contact area between the edge of the wafer and the polishing pad is small, the edge removal rate is low. This edge is difficult to remove during the CMP process, which may result in under-polishing and easily cause metal residue, such as WResidue, which can easily cause leakage in the device.

[0038] The embodiment of the present invention divides the chemical mechanical polishing of the high-K metal gate into two stages, namely, preliminary polishing and fine polishing. The preliminary polishing stage adopts a constant polishing rate control method, and the fine polishing stage adopts a constant pressure polishing, so as to solve the problems of low accuracy and many polishing defects in the existing high-K metal gate chemical mechanical polishing control method.

[0039] Figure 2 A flowchart of a wafer high-K metal gate chemical mechanical polishing method provided by an embodiment of the present invention. Figure 2 , the method comprising:

[0040] Step 201 , using a constant polishing rate control method to perform preliminary polishing on the polishing layer of the wafer until the average remaining film thickness of the polishing layer is reduced to a preset thickness.

[0041] Figure 3 It is a schematic structural diagram of a polishing head provided in an embodiment of the present invention. Figure 3 This is a schematic diagram of the longitudinal section of the polishing head. Figure 3The polishing head includes a retaining ring and a pressure membrane. The pressure membrane is placed inside the retaining ring, and the bottom of the pressure membrane is used to fix the wafer, wherein the back of the wafer faces the pressure membrane and the front of the wafer faces the polishing pad below.

[0042] During the wafer polishing process, the polishing head first brings the wafer to the polishing pad. At the same time, the polishing head applies pressure to the back of the wafer in different areas through the edge polishing guard ring and pressure membrane to control it, and polishes the wafer by rotation.

[0043] The pressure membrane includes a plurality of annular regions, each of which is concentrically arranged and arranged in sequence from the inside to the outside. Exemplarily, each annular region of the pressure membrane corresponds to each region of the wafer surface. For example, it can be divided into 7 annular regions. The polishing pressure applied to the wafer by each annular region of the pressure membrane can be adjusted separately. For another example, the number of region divisions can also be 3, 4 or 5.

[0044] In some embodiments, the constant polishing rate control method is to polish each area with the same polishing rate as the control target. Exemplarily, the polishing pressure of each area on the surface of the wafer is adjusted so that the polishing rate of each area is the target polishing rate. It should be noted that the wafer size is large, and the polishing rates of each area under the same polishing conditions will not be the same. Polishing pressure refers to the pressure applied by the polishing head on the wafer. The polishing pressure also determines the magnitude of the interaction force between the wafer surface and the polishing pad, which in turn affects the polishing rate. Therefore, adjusting the polishing pressure in a certain area can adjust the polishing rate of that area.

[0045] It should be further explained that the film thickness of each region before polishing is different. Even if the polishing rate is the same, the remaining film thickness of each region may not be exactly the same, and the film thickness of each region fluctuates within a certain range. Therefore, the average remaining film thickness is used to characterize the overall remaining thickness after polishing.

[0046] In some embodiments, the preset thickness is smaller than the thickness before polishing. For example, it can be one tenth of the original thickness. Exemplarily, the preset thickness can range from 100 to 300 angstroms. That is, the average remaining film thickness after preliminary polishing can range from 100 to 300 angstroms.

[0047] In some embodiments, the polishing layer is a metal layer, and the lower layer of the polishing layer is a dielectric layer.

[0048] In some embodiments, the metal layer includes a copper layer, a tungsten layer, or an aluminum layer.

[0049] In some embodiments, when tungsten (W) polishing is performed in the HKMG CMP process, a Hardness Shore D: 47-63 polishing pad is generally used in the preliminary polishing to remove a large amount of tungsten metal film, and eddy current endpoint detection can be used to stop polishing at a preset thickness.

[0050] In some embodiments, after preliminary polishing, the thickness non-uniformity of the tungsten metal film within the wafer surface is required to be NU% < 3%, and the thickness of the tungsten metal film on the wafer is < 100 angstroms.

[0051] In some embodiments, since the thickness of the tungsten metal film is relatively thick, about 1500~2500 angstroms, during the initial polishing process, the polishing rate can be controlled within a certain range during the polishing process. Through the eddy current control system, the polishing pressure of each area of ​​the polishing head is adjusted in real time on the software side, so that each area of ​​the wafer can reach the preset target thickness at the same time, thereby achieving nano-level flattening of the wafer.

[0052] In some embodiments, the diameter size of the wafer includes 6 inches, 8 inches, or 13 inches.

[0053] Step 202, obtaining the remaining film thickness of the polishing layer in each area of ​​the wafer surface after preliminary polishing.

[0054] For example, an eddy current detection method can be used to determine the remaining film thickness of the polishing layer in each area. The principle of eddy current detection will be described in the following embodiments.

[0055] In the above steps, the wafer is initially polished to obtain the residual film thickness of each partition. The film thickness of each partition is used to determine the initial polishing pressure in the next polishing stage in the subsequent steps.

[0056] Step 203 , based on the remaining film thickness of each region and with the same remaining polishing time as the target, determine the initial polishing pressure of each region.

[0057] It should be noted that after the initial polishing, the remaining film thickness of each area is not necessarily the same. In this step, the polishing pressure of the next stage is determined with the same remaining polishing time as the target, which can ensure that the polishing is completed at the same time as much as possible, reduce the difference in the total polishing time of each area at the end of the polishing, and reduce over-polishing and under-polishing defects. Here, the size of the remaining polishing time can be determined in advance. For example, a suitable remaining polishing time can be determined based on the average remaining film thickness, the expected production efficiency target, and other equipment factors.

[0058] In a possible implementation, based on the remaining film thickness of each region and with the same remaining polishing time as a target, determining the initial polishing pressure of each region includes:

[0059] Step 2031 , for any area on the wafer surface, divide the remaining film thickness of the area by the target remaining polishing time to obtain the target polishing rate of the area.

[0060] Step 2032: Based on the target polishing rate of the region, determine the polishing pressure corresponding to the target polishing rate as the initial polishing pressure of the region.

[0061] It should be noted that there is a correlation between the polishing rate and the polishing pressure. Generally, the greater the polishing pressure, the greater the polishing rate. Therefore, the polishing pressure corresponding to the target polishing rate can be determined based on the given target polishing rate and the correlation between the polishing rate and the polishing pressure.

[0062] In some embodiments, steps 2031 - 2032 are performed on each region to obtain an initial polishing pressure for each region.

[0063] After obtaining the initial polishing pressure of each area, the next stage of fine polishing is carried out.

[0064] Step 204 , based on the initial polishing pressure of each area, a constant polishing pressure control method is adopted to perform fine polishing on the wafer after the initial polishing.

[0065] After the initial polishing of the wafer is completed, the remaining polishing layer is removed, which is fine polishing. Fine polishing is close to the end point, and the requirements for polishing defects are higher. For example, the specification requirement for tungsten metal dishing defects is less than 20nm.

[0066] Since the remaining film thickness after the initial polishing is relatively thin, for example, 100 to 300 angstroms, the time for fine polishing to remove the remaining film is relatively short. The polishing rate is difficult to control during the fine polishing process, and it is impossible to control the consistency of the metal removal thickness on the wafer surface by adjusting the polishing pressure in each area in real time, which can easily lead to the generation of defects on the wafer surface.

[0067] In some embodiments, the constant polishing pressure control method is to polish the wafer with a constant initial polishing pressure. The initial polishing pressure of each region is obtained through step 203. The initial polishing pressure of each region is not necessarily the same.

[0068] In some embodiments, during fine polishing, the polishing pad specification used is PAD Dynamic Compressibility: 8.5~20.5%.

[0069] The following steps explain how to perform stop polishing during constant pressure polishing during the fine polishing stage.

[0070] Step 205 , during the fine polishing process, if any region reaches the polishing endpoint, the polishing pressure of the region is reduced from the initial polishing pressure to a preset pressure to stop polishing the region until all regions reach the polishing endpoint.

[0071] In some embodiments, the polishing endpoint detection method includes an optical online detection method, a drive motor current change detection method, or an eddy current endpoint detection method. Exemplarily, at the polishing endpoint, the upper metal layer has been polished away, exposing the underlying oxide layer.

[0072] In some embodiments, when a certain area reaches the polishing end point, the polishing pressure of the area is reduced to a very small preset pressure to stop applying force to the area of ​​the wafer, thereby stopping polishing the area. The polishing method of the embodiment of the present invention, which is completed by polishing a certain area and reducing the pressure to a small pressure, can greatly reduce the generation of Dishing and Erosion defects on the wafer surface.

[0073] In some embodiments, the preset pressure ranges from 0.3 to 0.8 psi.

[0074] In some embodiments, endpoint detection is performed using an eddy current endpoint detection method, and polishing is performed using an input initial pressure at the polishing equipment end. Before polishing is completed and when there is tungsten metal residue on the wafer surface, each area is polished without pressure adjustment during the polishing process and at a constant pressure. After it is detected that the metal has been removed from a certain area, the pressure in that area is reduced to a low pressure (0.3~0.8) psi until all areas are polished.

[0075] For example, the following table shows the initial polishing pressure and the pressure after the polishing end point of each zone. Among them, the guard ring is the polishing guard ring at the edge of the polishing head. Zone 1-7 is the corresponding Figure 3 There are seven annular areas represented by Z1-Z7 on the pressure membrane of the middle polishing head.

[0076]

[0077] Figure 4 A graph showing the change in wafer grinding time and pressure provided by an embodiment of the present invention. Figure 4 The horizontal axis represents time in seconds, and the vertical axis represents polishing pressure in psi. Fine polishing starts at 0 seconds, and the initial polishing pressure of each zone is different. As fine polishing proceeds, some zones reach the polishing end point first. For example, after zone 5 reaches the polishing end point, the polishing pressure is reduced to 0.5 psi until the last zone (for example, zone 1) reaches the polishing end point, and fine polishing ends.

[0078] It should be noted that the value of the preset pressure is not equal to 0. The reason is that if the polishing pressure is adjusted to 0, the pressure membrane is prone to wrinkles without pressure. Therefore, the polishing pressure is adjusted to the minimum pressure that satisfies the pressure membrane without wrinkles. It should be further noted that "stopping polishing of the area" here cannot completely achieve a polishing rate of 0. On the one hand, the polishing pressure cannot be adjusted to 0; on the other hand, even if the polishing pressure is adjusted to 0, the polishing rate will be slow due to the existence of chemical reactions. Of course, the time for fine polishing is very short, and the polishing pressure after reaching the polishing end point is very small. The impact on the wafer surface at an extremely small polishing rate is relatively small, and the resulting polishing defects are also very small. In addition, since the initial polishing pressure is determined with the same remaining polishing time as the target in step 203, the time difference of the polishing end points of each area in step 205 is also small, which also makes the over-polishing time of the area that is polished first shorter, and the resulting polishing defects are also very small.

[0079] The embodiment of the present invention divides the chemical mechanical polishing of the high-K metal gate into two stages, namely, preliminary polishing and fine polishing. In the preliminary polishing stage, a constant polishing rate control method is adopted to quickly remove most of the polishing layer to ensure the overall polishing efficiency. The initial polishing pressure during fine polishing is determined based on the remaining film thickness after the preliminary polishing to ensure that the polishing is completed at the same time as much as possible, reduce the difference in the total polishing time of each area at the polishing end point, and reduce over-polishing and under-polishing defects. Constant pressure polishing is performed in the fine polishing stage, and when a certain area reaches the polishing end point, the polishing pressure of the area is adjusted to a smaller level to stop polishing the area, thereby avoiding continuous pressure adjustment when approaching the polishing end point and avoiding polishing rate drift, thereby improving the accuracy of end point control and reducing over-polishing and under-polishing defects.

[0080] One of the most important requirements in the CMP process is to determine when to stop the polishing process, namely endpoint detection (EPD). It is used to determine when the polishing process is completed, that is, when the expected flatness and thickness are achieved, while reducing defects during the polishing process and improving the yield and performance of the device. The detection methods for the polishing endpoint include optical online detection methods, drive motor current change detection methods, or eddy current endpoint detection methods.

[0081] First, let's explain the optical online detection method. During the CMP process, due to the different intensities of reflected light from different materials, when the metal layer, barrier layer, and dielectric layer produce changes in film type, the optical signal will change significantly. Detecting this intensity change can determine the end point of CMP. For example, in the tungsten (W) process, the surface material of the wafer will change from tungsten to an oxide layer near the end of polishing. The reflectivity of metal tungsten is high, and the reflectivity of the non-metallic oxide layer is relatively much lower. This change can be detected optically, thereby monitoring the end point of CMP.

[0082] Secondly, the detection of the current change of the drive motor is explained. When the wafer polishing reaches the end point, the film material contacted by the polishing pad is different, which directly leads to a significant change in the friction coefficient between the wafer and the polishing pad. For example, the tungsten on the wafer is removed, and the oxide layer with a relatively slow polishing speed is exposed. The friction between the wafer and the polishing pad changes, causing the rotation torque of the polishing head or polishing machine to change, and the current of its drive motor also changes accordingly. The sensor on the polishing machine monitors the change in the drive motor current to detect whether the polishing end point has been reached.

[0083] In a possible implementation, the polishing endpoint detection method includes an eddy current endpoint detection method.

[0084] Eddy current endpoint detection principle: Figure 5 Schematic diagram of the eddy current endpoint detection principle provided by an embodiment of the present invention. Figure 5 According to the electromagnetic principle, when the sensor coil is passed through a sinusoidal alternating current I1, a sinusoidal alternating magnetic field H1 will be generated in the space around the coil, causing an induced eddy current I2 to be generated in the metal conductor placed in the magnetic field. The induced eddy current I2 will generate a new alternating magnetic field H2 (such as Figure 4 ), the magnetic field H2 will have mutual induction with the circuit of the original magnetic field H1, causing the electrical parameters of the original magnetic field H1 circuit to change. According to electromagnetic theory, the equivalent impedance of the excitation coil that generates the alternating magnetic field can be obtained when it is affected by the eddy current in the metal in the magnetic field. For a specific detection target, after the coil and the measuring device are installed, the change in the coil impedance is mainly determined by the thickness of the metal film in its magnetic field. Therefore, the impedance value of the excitation coil is measured, and then the thickness of the corresponding metal film to be measured can be calculated.

[0085] Figure 6 Schematic diagram of the structure of the eddy current metal film thickness measurement system provided by the embodiment of the present invention. Figure 6 The main structure of the eddy current metal film thickness measurement system consists of an eddy current sensor, a signal conditioning circuit module, a data acquisition and communication module, and a host computer algorithm software. The drive circuit is responsible for outputting a sinusoidal AC signal of a specific frequency, collecting the measurement signal output by the signal amplifier, completing the lock-in amplification operation, and returning the measurement signal to the superior controller. The change in the apparent impedance of the sensor is measured to reflect the change in the metal film thickness of the wafer. This method can not only monitor the changes in the polished material on the wafer, but also detect the flatness of the polished surface of the wafer.

[0086] The embodiment of the present invention adopts an eddy current endpoint detection control method, which can monitor the wafer thickness online in real time during the polishing process and detect the flatness of the wafer polishing surface at the same time.

[0087] The following embodiment illustrates how to determine the polishing endpoint based on the eddy current endpoint detection method.

[0088] In a possible implementation, the method further includes: during the fine polishing process, for any area, based on the real-time scanning result of the eddy current sensor, determining whether there is any polishing layer residue in the area. If no polishing layer residue is found in the area for a preset number of consecutive scans, it is determined that the area has reached the polishing endpoint.

[0089] The polishing method of the present invention uses an eddy current sensor to scan the wafer surface during the wafer fine polishing process, and performs multiple all-round scans on the wafer to identify whether there is polishing layer residue on the wafer surface, such as tungsten metal residue (Wresidue), to avoid polishing layer residue in the wafer surface, especially at the edge.

[0090] Figure 7 It is a schematic diagram of the scanning trajectory after 8 scans provided by an embodiment of the present invention. Figure 8 FIG. 1 is a schematic diagram of a scanning trajectory after 16 scans provided by an embodiment of the present invention. Figure 7 and Figure 8 If the number of monitoring scans is small, some areas on the edge of the wafer may not be monitored, which may lead to the risk of residual polishing layer. By increasing the number of monitoring scans, the wafer can be monitored more comprehensively and the occurrence of defects can be reduced.

[0091] In some embodiments, the preset number of times ranges from 10 to 20 times.

[0092] Fig. 9 Schematic diagram of the relationship between the use time and polishing rate of the polishing pad provided in an embodiment of the present invention. Fig. 9 During wafer processing, under different lifespan conditions of the polishing pad, the removal rates of different materials to be polished have significant differences. For example, using the existing EPD detection method and conditions for endpoint detection process will result in large differences in W Dishing within the wafer surface, affecting the wafer yield. Fig.10 Schematic diagram of the relationship between the use time of the polishing pad provided by the embodiment of the present invention and the tungsten metal Dishing defect. Fig.10 As the polishing pad is used for a longer time, the tungsten metal Dishing defect increases.

[0093] Due to the limitations of existing EPD (End Point Detection) technology, the high-K metal gate CMP process is prone to produce larger Dishing and Erosion defects in the center of the wafer after CMP processing, and W Residue problems are prone to occur in the edge area. Furthermore, under the influence of different use time of the polishing pad, it is easy to cause differences in W Dishing.

[0094] During wafer processing, the removal rate of polishing will change as the polishing pad is used for a longer period of time. For example, in the early stage of the use of the polishing pad (less wear, generally the initial PAD groove depth Depth is above 20mil), the removal rate of the tungsten metal film in the high-K metal gate CMP process is high, the polishing will be completed relatively early, and the hydrogen peroxide wet etching time in the polishing liquid is relatively short. At this time, the Dishing defect in the tungsten metal structure is relatively small. At the end of the use of the polishing pad (the grooves on the PAD surface are more worn, the groove depth at the end of the PAD is less than 10mil, and it is generally believed that the grooves on the PAD surface are 5mil as a safety line), the situation is the opposite.

[0095] Based on the above situation, it is found in actual verification that when the polishing pressure changes, the removal rate changes of different material films are different. Fig.11 Schematic diagram of the relationship between film removal rate and pressure of different materials provided by the embodiment of the present invention. Fig.11 For example, when comparing tungsten metal film and oxide film, the removal rate of oxide film is relatively more sensitive to the same unit pressure change.

[0096] Therefore, when setting the pressure parameters for fine polishing during wafer processing, the upper limit of the pressure should be controlled at the beginning of the use of the polishing pad (for example, about 1.2 times the current input pressure) to further speed up the isolation and reduce the time of Dishing. As the use time of the polishing pad increases, the pressure can be appropriately reduced to reduce the selectivity of W to Oxide in the tungsten metal structure. At the end of the use of the polishing pad, the lower limit of the pressure should be controlled (for example, about 0.8 times the current input pressure) to prevent Dishing from being amplified due to excessive polishing time. This method can be used to adjust the initial input pressure during polishing for different use times of the polishing pad, which can greatly improve the occurrence of defects in CMP processing.

[0097] The initial polishing pressure of each region is determined in step 203. The initial polishing pressure of each region is usually different, and the multiple pressures may have preset upper and lower limits.

[0098] In a possible implementation, after determining the initial polishing pressure of each region, the method further includes:

[0099] Step 301, obtaining a preset upper limit and a preset lower limit of an initial polishing pressure.

[0100] Step 302, obtaining the historical usage time of the polishing pad, wherein the polishing pad is a polishing pad used in a fine polishing process.

[0101] Step 303, based on the historical usage time of the polishing pad, correct the preset upper limit and preset lower limit of the initial polishing pressure to obtain the corrected upper limit and lower limit, wherein the longer the historical usage time, the smaller the range of the corrected upper limit and lower limit.

[0102] Step 304: If the initial polishing pressure of any region is greater than or equal to the corrected upper limit, the corrected upper limit is used as the initial polishing pressure of the region.

[0103] Step 305: If the initial polishing pressure of any region is less than or equal to the corrected lower limit, the corrected lower limit is used as the initial polishing pressure of the region.

[0104] The embodiments of the present invention can greatly improve the defect problem caused by the increase of the life of the CMP polishing pad consumables during the high-K metal gate CMP process.

[0105] In a second aspect, the present invention provides a semiconductor device, which is manufactured based on the chemical mechanical polishing method of high-K metal gate on a wafer in any possible implementation manner as described above.

[0106] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A wafer high-K metal gate chemical mechanical polishing method, characterized in that: include: Performing preliminary polishing on the polishing layer of the wafer by adopting a constant polishing rate control method until the average remaining film thickness of the polishing layer is reduced to a preset thickness; Obtaining the remaining film thickness of the polishing layer in each area of ​​the wafer surface after preliminary polishing; Based on the remaining film thickness of each area, the initial polishing pressure of each area is determined with the same remaining polishing time as the target; Based on the initial polishing pressure of each area, a constant polishing pressure control method is adopted to finely polish the wafer after initial polishing; During the fine polishing process, if any area reaches the polishing endpoint, the polishing pressure of the area is reduced from the initial polishing pressure to a preset pressure to stop polishing the area until all areas reach the polishing endpoint; The determining of the initial polishing pressure of each region based on the remaining film thickness of each region and taking the same remaining polishing time as a target comprises: For any area on the wafer surface, the remaining film thickness of the area is divided by the target remaining polishing time to obtain the target polishing rate of the area; Based on the target polishing rate of the region, a polishing pressure corresponding to the target polishing rate is determined as an initial polishing pressure of the region.

2. The wafer high-K metal gate chemical mechanical polishing method according to claim 1, characterized in that: The polishing endpoint detection method includes an eddy current endpoint detection method.

3. The wafer high-K metal gate chemical mechanical polishing method according to claim 2, characterized in that: The method further comprises: During fine polishing, for any area, based on the real-time scanning results of the eddy current sensor, determine whether there is any polishing layer remaining in the area; If no polishing layer residue is found in the area after a preset number of consecutive scans, it is determined that the area has reached the polishing endpoint.

4. The wafer high-K metal gate chemical mechanical polishing method according to claim 3, characterized in that: The preset number of times ranges from 10 to 20 times.

5. The wafer high-K metal gate chemical mechanical polishing method according to claim 1, characterized in that: The preset pressure ranges from 0.3 to 0.8 psi.

6. The wafer high-K metal gate chemical mechanical polishing method according to claim 1, characterized in that: After determining the initial polishing pressure of each region, the method further includes: obtaining a preset upper limit and a preset lower limit of an initial polishing pressure; Obtaining a historical usage time of a polishing pad, wherein the polishing pad is a polishing pad used in a fine polishing process; Based on the historical usage time of the polishing pad, correct the preset upper limit and the preset lower limit of the initial polishing pressure to obtain the corrected upper limit and lower limit, wherein the longer the historical usage time, the smaller the range of the corrected upper limit and lower limit; If the initial polishing pressure of any area is greater than or equal to the corrected upper limit, the corrected upper limit is used as the initial polishing pressure of the area; If the initial polishing pressure of any region is less than or equal to the corrected lower limit, the corrected lower limit is used as the initial polishing pressure of the region.

7. The wafer high-K metal gate chemical mechanical polishing method according to claim 1, characterized in that: The polishing layer is a metal layer, and the lower layer of the polishing layer is a dielectric layer.

8. The wafer high-K metal gate chemical mechanical polishing method according to claim 7, characterized in that: The metal layer includes a copper layer, a tungsten layer or an aluminum layer.

9. A semiconductor device, characterized in that: The method is prepared based on the chemical mechanical polishing method for high-K metal gate on a wafer as described in any one of claims 1 to 8.

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