Chemical mechanical polishing film thickness real-time control method, device and equipment

Abstract

The invention provides a chemical mechanical polishing film thickness real-time control method, device and equipment, and relates to the technical field of chemical mechanical polishing equipment. According to the invention, the optical sensing module is arranged in the vertical hole of the polishing disk, so that the reflected light intensity of the wafer can be monitored in real time in the CMP process. By adopting the optical sensing module, the corresponding relationship between the film thickness of samples with different thicknesses and the reflected light intensity is obtained. Therefore, the real-time film thickness can be determined in the CMP process according to the corresponding relation and the reflected light intensity monitored in real time, and chemical mechanical polishing film thickness real-time control is carried out on the target wafer. Time waste caused by multiple times of shutdown for film thickness detection in a traditional method is avoided, and the chemical mechanical polishing efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of chemical mechanical polishing equipment, and particularly to a method, device and equipment for real-time control of chemical mechanical polishing film thickness. Background Art

[0002] Chemical-Mechanical Polishing (CMP for short) is a process used to planarize the surface of materials and is widely applied in the field of semiconductor manufacturing. During chemical mechanical polishing, the polishing pad contacts the surface of the wafer, and the wafer is subjected to chemical mechanical grinding driven by the polishing platen. The polishing liquid contains chemical reagents and abrasives, which play a dual role of chemical corrosion and mechanical assisted grinding during the CMP process. A thin film grows on the surface of the wafer, and the purpose of chemical mechanical polishing is to precisely control the thickness and flatness of the thin film.

[0003] CMP film thickness monitoring refers to measuring the thickness of the thin film on the surface of the wafer during chemical mechanical polishing. Combining CMP film thickness monitoring can achieve control of the polishing process. The existing method uses the method of off-line measurement. For example, after a certain stage of polishing is completed, the wafer is removed from the CMP equipment and placed on a special measurement platform for film thickness measurement. The traditional method requires multiple off-line detections of the film thickness, and the off-line interruption of the polishing process wastes time, resulting in low efficiency of the existing chemical mechanical polishing film thickness control method. Summary of the Invention

[0004] Embodiments of the present invention provide a method, device and equipment for real-time control of chemical mechanical polishing film thickness to solve the problem of low efficiency of the existing chemical mechanical polishing film thickness control method.

[0005] In a first aspect, embodiments of the present invention provide a method for real-time control of chemical mechanical polishing film thickness, which is applied to a film thickness monitoring device; the film thickness monitoring device includes an optical sensing module disposed in a vertical hole of the polishing platen, wherein the vertical hole penetrates the polishing platen and the polishing pad; the method includes:

[0006] Obtaining the film thicknesses of a plurality of thin film samples made of the same material; the film thicknesses of each thin film sample are different;

[0007] For each thin film sample, controlling the optical sensing module to vertically irradiate the thin film sample with a preset light intensity and obtaining the reflected light intensity of the thin film sample;

[0008] Based on the film thicknesses and reflected light intensities of each thin film sample, determining the corresponding relationship between the film thickness and the reflected light intensity;

[0009] Based on the corresponding relationship, performing real-time control of the chemical mechanical polishing film thickness of the target wafer according to the reflected light intensity of the surface of the target wafer monitored in real time.

[0010] In a possible implementation, based on the corresponding relationship, real-time control of the chemical mechanical polishing film thickness of the target wafer according to the reflected light intensity of the surface of the target wafer monitored in real time includes:

[0011] During the chemical mechanical polishing of the target wafer, the reflected light intensity of the surface of the target wafer is monitored in real time through the optical sensing module;

[0012] Based on the corresponding relationship, the real-time remaining film thickness of the surface of the target wafer is determined according to the reflected light intensity of the surface of the target wafer monitored in real time;

[0013] Based on the real-time remaining film thickness and the target remaining film thickness of the surface of the target wafer, real-time control of the chemical mechanical polishing film thickness of the target wafer is performed.

[0014] In a possible implementation, a light-transmitting cover plate is further provided at one end of the vertical hole close to the polishing pad;

[0015] The light-transmitting cover plate is used to isolate the optical sensing module from the polishing liquid.

[0016] In a possible implementation, before performing real-time control of the chemical mechanical polishing film thickness of the target wafer based on the corresponding relationship according to the reflected light intensity of the surface of the target wafer monitored in real time, it further includes:

[0017] Obtain the reflected light intensity of the surface of the target wafer monitored in real time;

[0018] Obtain the polishing temperature, the concentration of the polishing liquid, and the surface roughness of the light-transmitting cover plate;

[0019] Based on the polishing temperature and the concentration of the polishing liquid, determine the first influence coefficient of the polishing liquid on the transmittance;

[0020] Based on the polishing temperature and the surface roughness of the light-transmitting cover plate, determine the second influence coefficient of the light-transmitting cover plate on the transmittance;

[0021] According to the first influence coefficient and the second influence coefficient, correct the reflected light intensity, and use the corrected reflected light intensity as the reflected light intensity of the surface of the target wafer.

[0022] In a possible implementation, the light-transmitting cover plate is a convex mirror;

[0023] The highest point of the convex mirror is lower than the polishing pad.

[0024] In a possible implementation, a light-transmitting heat-insulating unit is further provided between the light-transmitting cover plate and the optical sensing module in the vertical hole.

[0025] In a possible implementation, for each thin film sample, controlling the optical sensing module to vertically irradiate the thin film sample with a preset light intensity and obtaining the reflected light intensity of the thin film sample includes:

[0026] For each thin film sample, the thin film sample faces a polishing pad with deionized water added; the rotating polishing disk drives the polishing pad and the thin film sample to move relative to each other;

[0027] During the relative movement of the polishing pad and the thin film sample, control the optical sensing module to vertically irradiate the thin film sample with a preset light intensity and obtain the reflected light intensity of the thin film sample.

[0028] In a possible implementation, determining the correspondence between the film thickness and the reflected light intensity based on the film thickness and the reflected light intensity of each thin film sample includes:

[0029] Perform linear fitting based on the film thickness and the reflected light intensity of each thin film sample to obtain the linear relationship between the film thickness and the reflected light intensity;

[0030] Determine the linear relationship as the correspondence between the film thickness and the reflected light intensity.

[0031] In a second aspect, an embodiment of the present invention provides a chemical mechanical polishing film thickness real-time control device, which is applied to a film thickness monitoring device; the film thickness monitoring device includes an optical sensing module disposed in a vertical hole of a polishing disk, wherein the vertical hole penetrates the polishing disk and the polishing pad; the device includes:

[0032] A film thickness acquisition module, configured to acquire the film thicknesses of multiple thin film samples made of the same material; the film thicknesses of each thin film sample are different;

[0033] A reflected light intensity acquisition module, configured to, for each thin film sample, control the optical sensing module to vertically irradiate the thin film sample with a preset light intensity and obtain the reflected light intensity of the thin film sample;

[0034] A correspondence determination module, configured to determine the correspondence between the film thickness and the reflected light intensity based on the film thickness and the reflected light intensity of each thin film sample;

[0035] A real-time control module, configured to perform real-time control of the chemical mechanical polishing film thickness of the target wafer based on the correspondence and according to the reflected light intensity of the surface of the target wafer monitored in real time.

[0036] In a third aspect, an embodiment of the present invention provides a chemical mechanical polishing device, including a memory and a processor, where the memory stores a computer program, and when the processor executes the computer program, the chemical mechanical polishing film thickness real-time control method described in any item of the first aspect is implemented.

[0037] An embodiment of the present invention provides a method, device, and equipment for real-time control of the film thickness in chemical mechanical polishing. By arranging an optical sensing module in the vertical hole of the polishing platen in the present invention, the reflected light intensity of the wafer can be monitored in real time during the CMP process. Using the above optical sensing module, the corresponding relationship between the film thickness of different thickness samples and the reflected light intensity is obtained. Thus, during the CMP process, the real-time film thickness can be determined according to the corresponding relationship and the reflected light intensity monitored in real time, and real-time control of the film thickness in chemical mechanical polishing of the target wafer can be performed. This avoids the time waste caused by multiple downtime detections of the film thickness in the traditional method and improves the efficiency of chemical mechanical polishing. Description of the Drawings

[0038] Figure 1 FIG. is a schematic structural diagram of a chemical mechanical polishing equipment provided by an embodiment of the present invention;

[0039] Figure 2 FIG. is a flowchart for implementing a method for real-time control of the film thickness in chemical mechanical polishing provided by an embodiment of the present invention;

[0040] Figure 3 FIG. is a schematic structural diagram of a real-time film thickness monitoring system provided by an embodiment of the present invention;

[0041] Figure 4 FIG. is a diagram showing the relationship between the reflected light intensity and the wafer thickness provided by an embodiment of the present invention;

[0042] Figure 5 FIG. is a schematic diagram of the real-time change of the non-metal film thickness provided by an embodiment of the present invention;

[0043] Figure 6 FIG. is a schematic diagram of the real-time change of the polishing head pressure in the non-metal thin film control system provided by an embodiment of the present invention;

[0044] Figure 7 FIG. is a schematic diagram of the comparison between the feedback data and the measurement data of the CMP machine provided by an embodiment of the present invention;

[0045] Figure 8 FIG. is a schematic structural diagram of a device for real-time control of the film thickness in chemical mechanical polishing provided by an embodiment of the present invention. Detailed Embodiments

[0046] In order to enable those skilled in the art to better understand this solution, the technical solutions in the embodiments of this solution will be clearly described below in conjunction with the accompanying drawings in the embodiments of this solution. Obviously, the described embodiments are some, but not all, of the embodiments of this solution. Based on the embodiments in this solution, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this solution.

[0047] In the description and claims of this solution, as well as in the above-mentioned drawings, the term "including" and any other variations thereof mean "including but not limited to", intending to cover non-exclusive inclusion and not limited to the examples listed in the text. In addition, terms such as "first" and "second" are used to distinguish different objects rather than to describe a specific order.

[0048] The implementation of the present invention will be described in detail below with reference to specific drawings:

[0049] Chemical mechanical polishing, also known as mechanical chemical grinding, CMP, has a profound impact on integrated circuits and is one of the core technologies in integrated circuit manufacturing. CMP technology is mainly used for planarization in the process of integrated circuit manufacturing. Especially in the multi-layer wiring process, it plays a crucial role in eliminating various problems caused by unevenness between wiring layers. With the continuous extension of Moore's Law and the continuous reduction of chip size, the requirements for the surface quality of wafers have also increased. The mechanical chemical grinding (CMP) technology can remove impurities and defects on the surface of integrated circuits, improve the smoothness and finish of the surface, thereby ensuring the stability and reliability of integrated circuits. In addition, the CMP technology can also effectively reduce the resistance and capacitance in integrated circuits and optimize the circuit performance.

[0050] Mechanical chemical grinding (CMP) grinds the surface of the wafer through the interaction between the polishing head, polishing pad, polishing liquid, and grinder, thereby controlling the surface roughness and flatness of the wafer to meet the production requirements of high-order process chips and higher wafer surface quality. In special process procedures, it is necessary to use mechanical chemical grinding to remove the non-metallic layer or ultra-thin metal film on the wafer surface. For example, the non-metallic layer includes SiO 2 , SiN, Poly, etc. Another example is that the ultra-thin metal film includes W, Cu, Al, etc. with a thickness less than 200 angstroms. For the methods of controlling the thickness of these non-metallic films and ultra-thin metals, special measurement machines are generally used for measurement. By comparing the film thickness data measured before and after wafer grinding, parameters such as polishing pressure, polishing speed, and polishing duration are adjusted to obtain the production requirements that meet high-process wafers.

[0051] In semiconductor processes, the quality of non-metallic thin films (SiO 2 , SiN, Poly, TiN, …) has a great impact on the yield and performance of devices. Therefore, when using mechanical chemical grinding for non-metallic thin films (SiO 2When processing non-metallic films (such as SiN, Poly, etc.), it is necessary to inspect the films, and the measurement of thickness is one of the important contents of film quality inspection. The interference method for measuring the thickness of non-metallic films is a commonly used measurement method in production. Its principle is to use monochromatic light to vertically irradiate the surface of the non-metallic layer. Since most non-metallic layers are light-transmitting materials, the incident light is reflected at the surface of the non-metallic layer and the non-metallic layer - Si interface respectively. According to the principle of light interference, the thickness of the non-metallic film can be calculated.

[0052] During the processing of non-metallic films by traditional mechanical chemical polishing, first, it is necessary to measure the wafers coated with non-metallic film thickness. For example, an optical measurement device can be used to measure the initial value of the non-metallic film. Generally, a linear measurement pattern is adopted, with a total of 81 measurement points. After measurement, the wafers are placed on a mechanical chemical polishing machine table. The polishing head carries the wafers, places them on the polishing pad to make relative movements, and grinds them with a fixed pressure. After grinding, the non-metallic film on the wafers is measured as the final value. According to the measured initial and final thickness values, the following formula is used to calculate the removal rate of the non-metallic film per unit time, and parameters such as the initial value, final value, and removal rate are observed to judge the flatness of the wafers after grinding. Finally, the pressure of the polishing head is adjusted, and the above operations are repeated.

[0053] Removal rate of non-metallic film = (Initial value of non-metallic film - Final value) / Time

[0054] In traditional chemical mechanical polishing (CMP), the control of the flatness of the wafer surface is mainly achieved by changing the pressure of the polishing head and the area of the air pressure distribution of the polishing head, such as 12-inch 5Zone head and 12-inch 7zone head. To meet the flatness requirements of the wafers, it is necessary to repeatedly measure the non-metallic film thickness and match the appropriate polishing head pressure. This process consumes a large amount of time, manpower, and wafers coated with non-metallic films. At the same time, for metal films, when the metal film thickness is very thin, the eddy current signal will generate a large error, and the thickness of the ultra-thin metal film cannot be accurately and real-time feedback.

[0055] In the embodiments of the present invention, by setting an optical sensing module in the polishing disk to realize real-time monitoring of the reflected light intensity, and determining the real-time film thickness according to the corresponding relationship between the sample film thickness of different thicknesses and the reflected light intensity, it avoids the time waste caused by multiple downtime detections of the film thickness in the traditional method and improves the chemical mechanical polishing efficiency.

[0056] Figure 1 It is a schematic structural diagram of a chemical mechanical polishing device provided by the embodiments of the present invention. Refer to Figure 1 , this chemical mechanical polishing device includes: a polishing head, a polishing pad, and a polishing disk. The polishing disk drives the polishing pad to rotate synchronously. The polishing head drives the wafer to make relative movements on the polishing pad and continuously passes through the area above the optical sensing module.

[0057] Exemplarily, a light-transmitting cover plate is provided above the optical sensing module. For example, the light-transmitting cover plate can be made of a light-transmitting resin material and has light-transmitting properties.

[0058] Exemplarily, a light-transmitting heat-insulating unit can also be provided below the light-transmitting cover plate. The light-transmitting heat-insulating unit can prevent the heat generated by friction and chemical reactions during the wafer grinding process from being transmitted to the optical sensing module.

[0059] Exemplarily, a cast iron bracket is provided below the optical sensing module. The bracket can be used to adjust the distance between the optical sensing module and the wafer.

[0060] Exemplarily, the control module is placed inside the polishing platen and is used to process the emitted light intensity signals collected by the optical sensing module and convert them into the corresponding wafer surface film thickness. Further, the control module is connected to an external host computer, can process the wafer film thicknesses collected at different times, and draw them into a 2D image. At the same time, it can also adjust the pressure of each area of the polishing head in real time according to the collected thickness values, so as to adjust the change of the thickness value in real time during the wafer grinding process and improve the flatness of the non-metallic film on the wafer.

[0061] Regarding the film thickness acquisition method, it should be noted that during the chemo-mechanical polishing process, the polishing platen rotates counterclockwise, and the polishing head carries the wafer and presses it against the polishing pad with pressure and rotates clockwise. The optical sensing module will form an arc-shaped acquisition area following the polishing platen when passing by the polishing head. When the wafer passes through the acquisition area, the optical sensing module will irradiate the wafer, collect the reflection data, and calculate the film thickness through the control module.

[0062] An embodiment of the present invention provides a method for real-time control of chemo-mechanical polishing film thickness, which is applied to a film thickness monitoring device; the film thickness monitoring device includes an optical sensing module disposed in a vertical hole of the polishing platen, wherein the vertical hole penetrates the polishing platen and the polishing pad.

[0063] The above describes the structure and operation mode of the film thickness monitoring device. The following describes the method for real-time control of chemo-mechanical polishing film thickness.

[0064] Figure 2 This is a flowchart for implementing a method for real-time control of chemo-mechanical polishing film thickness provided by an embodiment of the present invention. Refer to Figure 2 , the method includes:

[0065] Step 201, obtain the film thicknesses of multiple thin film samples made of the same material; the film thicknesses of each thin film sample are different.

[0066] Exemplarily, prepare multiple thin film samples, and the thin film materials of these samples are the same. The thin film samples can be wafers with thin films grown on their surfaces. For example, on multiple wafers, silicon dioxide (SiO 2)The film is made of a material. It should be noted that the film material here is the material that needs to be chemically mechanically polished in the subsequent steps.

[0067] Exemplarily, the thickness of each film sample is different. For example, during physical vapor deposition, by changing parameters such as deposition time and deposition rate, film samples with different thicknesses can be obtained. In this way, a set of film samples with a gradient change in film thickness can be obtained, so that the change law of the reflected light intensity of different film thicknesses can be determined in the subsequent steps.

[0068] Exemplarily, the film can be a light-transmitting non-metallic film. For example, silicon oxide or silicon nitride. Exemplarily, the film can be an ultra-thin metal film with a thickness less than 200 angstroms. For example, films of materials such as W, Cu, and Al with a thickness less than 200 angstroms. When the thickness of the ultra-thin metal film is small enough, it also exhibits film interference characteristics similar to those of light-transmitting non-metallic films.

[0069] Step 202: For each film sample, control the optical sensing module to vertically irradiate the film sample with a preset light intensity and obtain the reflected light intensity of the film sample;

[0070] It should be noted that the optical sensing module can both emit light and receive light. The light emitted by the optical sensing module is reflected by the film sample to generate reflected light. Due to film interference, the light intensity of the reflected light is positively correlated with the thickness under certain conditions.

[0071] Furthermore, the conditions for obtaining the reflected light intensity here need to be as close as possible to the conditions of the subsequent actual chemical mechanical polishing. The following embodiments simulate the real chemical mechanical polishing to obtain the reflected light intensity of the film samples.

[0072] In a possible implementation manner, the step of, for each film sample, controlling the optical sensing module to vertically irradiate the film sample with a preset light intensity and obtain the reflected light intensity of the film sample includes:

[0073] Step 2021: For each film sample, the film sample faces the polishing pad with deionized water added; the polishing disk rotates to drive the polishing pad and the film sample to move relative to each other;

[0074] It should be noted that the film sample is placed facing the polishing pad, and deionized water is added to the polishing pad. The polishing disk rotates to drive the polishing pad and the film sample to move relative to each other. Since only deionized water is used and no abrasive and other corrosive chemical agents are added, during the relative movement of the film sample and the polishing pad, the film thickness of the film sample remains basically unchanged within a certain period of time. Therefore, the accuracy of the reflected light intensity measured for the film sample is higher, and the corresponding relationship obtained in the subsequent steps is more in line with the actual situation.

[0075] Step 2022: During the relative movement of the polishing pad and the thin film sample, control the optical sensing module to vertically irradiate the thin film sample with a preset light intensity, and obtain the reflected light intensity of the thin film sample.

[0076] It should be noted that by simulating the actual chemical mechanical polishing process, the accuracy of the measured reflected light intensity is higher.

[0077] Step 203: Based on the film thickness and the reflected light intensity of each thin film sample, determine the corresponding relationship between the film thickness and the reflected light intensity.

[0078] Exemplarily, use the reflected light intensity as the abscissa and the film thickness of the thin film sample as the ordinate. Plot the film thickness and the corresponding reflected light intensity data points of each thin film sample on a coordinate graph, and use mathematical methods to fit these data points.

[0079] In a possible implementation manner, the determining the corresponding relationship between the film thickness and the reflected light intensity based on the film thickness and the reflected light intensity of each thin film sample includes: performing linear fitting based on the film thickness and the reflected light intensity of each thin film sample to obtain the linear relationship between the film thickness and the reflected light intensity; determining the linear relationship as the corresponding relationship between the film thickness and the reflected light intensity.

[0080] It should be noted that when the change range of the film thickness is small, usually much smaller than the wavelength of light, the change in the reflected light intensity is approximately a linear relationship.

[0081] Step 204: Based on the corresponding relationship, perform real-time control of the film thickness of the target wafer during chemical mechanical polishing according to the reflected light intensity of the surface of the target wafer monitored in real time.

[0082] Exemplarily, during the chemical mechanical polishing (CMP) of the target wafer, use the optical sensing module to measure the reflected light intensity of the surface of the target wafer in real time. The optical sensing module continuously emits light with a preset light intensity and vertically irradiates the surface of the target wafer, and obtains the reflected light intensity in real time.

[0083] Furthermore, according to the reflected light intensity of the surface of the target wafer monitored in real time, using the corresponding relationship between the film thickness and the reflected light intensity determined in Step 203, the current film thickness of the target wafer can be deduced. For example, if the corresponding relationship is a linear function, then substituting the value of the real-time reflected light intensity into the function can calculate the current film thickness.

[0084] During the chemical mechanical polishing process, the film thickness is a critical process parameter that needs to be controlled within a specific range. Based on the calculated current film thickness, it is compared with the pre-set target film thickness. If the current film thickness is greater than the target film thickness, it indicates that the polishing needs to continue, and the polishing process parameters can be appropriately adjusted, such as increasing the polishing pressure, increasing the flow rate of the polishing liquid, etc., to accelerate the polishing speed; if the current film thickness is close to or reaches the target film thickness, the polishing speed can be correspondingly reduced to avoid over-polishing.

[0085] In a possible implementation manner, based on the corresponding relationship, real-time control of the chemical mechanical polishing film thickness of the target wafer according to the reflected light intensity of the surface of the target wafer monitored in real time includes: during the chemical mechanical polishing of the target wafer, the reflected light intensity of the surface of the target wafer is monitored in real time through the optical sensing module; based on the corresponding relationship, the real-time remaining film thickness of the surface of the target wafer is determined according to the reflected light intensity of the surface of the target wafer monitored in real time; based on the real-time remaining film thickness and the target remaining film thickness of the surface of the target wafer, real-time control of the chemical mechanical polishing film thickness of the target wafer is performed.

[0086] It should be noted that during the chemical mechanical polishing process, precise control of the film thickness is crucial for the performance and quality of the wafer. By monitoring the reflected light intensity in real time and performing real-time control of the film thickness based on the corresponding relationship, deviations in the polishing process can be detected and corrected in a timely manner, ensuring the film thickness uniformity and accuracy of the target wafer, improving production efficiency and product yield, and reducing the product rejection rate caused by the non-compliance of the film thickness.

[0087] In the embodiment of the present invention, by arranging an optical sensing module in the vertical hole of the polishing platen, the reflected light intensity of the wafer can be monitored in real time during the CMP process. Using the above optical sensing module, the corresponding relationship between the film thickness of different thickness samples and the reflected light intensity is obtained. Thus, during the CMP process, the real-time film thickness can be determined according to the corresponding relationship and the reflected light intensity monitored in real time, and real-time control of the chemical mechanical polishing film thickness of the target wafer is performed. It avoids the time waste of multiple downtime detections of the film thickness in the traditional method and improves the chemical mechanical polishing efficiency.

[0088] In a possible implementation manner, a light-transmitting cover plate is further provided at one end of the vertical hole close to the polishing pad; the light-transmitting cover plate is used to isolate the optical sensing module from the polishing liquid.

[0089] It should be noted that the polishing liquid usually contains chemical reagents, abrasive particles and impurities. If it directly contacts the optical sensing module (such as a light source, a detector), it may cause sensor corrosion, optical path contamination or device short circuit. The light-transmitting cover plate completely separates the polishing liquid from the sensor through a physical barrier, extending the life of the device. The fine particles generated during the polishing process may impact the surface of the optical sensor along with the liquid flow. The light-transmitting cover plate can prevent the particles from directly scratching the optical elements, maintaining the measurement stability. The light-transmitting cover plate needs to be made of a material with a high light transmittance (such as quartz glass, sapphire) to ensure that the transmission losses of the incident light and the reflected light are extremely small, and to avoid measurement errors in the reflected light intensity caused by material absorption or scattering.

[0090] In a possible implementation, the highest point of the light-transmitting cover plate is lower than the polishing pad.

[0091] It should be noted that the flow of the polishing liquid may cause liquid surface fluctuations or bubbles, affecting the stability of the optical path. The cover plate confines the polishing liquid to a specific area, reducing the interference of the liquid dynamic changes on the optical signal and ensuring the accuracy of the reflected light intensity data.

[0092] It should be noted that during the polishing process, if the cover plate protrudes from the polishing pad, it may be continuously scoured by the abrasive particles, resulting in wear of the cover plate material or an increase in surface roughness, which in turn affects the light transmittance or introduces particle contamination. Setting the light-transmitting cover plate lower than the polishing pad can prevent abnormal wear.

[0093] In a possible implementation, the light-transmitting cover plate is a convex mirror; the highest point of the convex mirror is lower than the polishing pad.

[0094] It should be noted that the curved surface design of the convex mirror can reflect and converge the light signals diffusely reflected from the wafer surface to the optical sensor (such as a CCD or a photodetector). Compared with a flat cover plate, the convex mirror reduces the divergence loss of light energy through reflective focusing, significantly increasing the light intensity per unit area. For example, when the light source is vertically incident, the convex mirror can redirect the originally divergent reflected light to the sensor, and the light intensity may increase by 30%-50%, thereby improving the signal-to-noise ratio and reducing the difficulty of weak signal detection.

[0095] The converging function of the convex mirror can be equivalent to introducing a pre-focusing element for the optical system, allowing the lens to achieve the same spot size at a shorter working distance (WD). For example, a traditional flat cover plate requires the lens to be 10 mm away from the wafer to obtain a clear image, while the convex mirror design may reduce the WD to 5 mm while keeping the spot diameter unchanged. The convex mirror light-transmitting cover plate significantly increases the light intensity through reflective focusing, and at the same time allows the optical lens to be closer to the wafer, breaking through the performance bottleneck of the traditional flat design while ensuring physical isolation.

[0096] In a possible implementation, within the vertical hole, a light-transmitting heat-insulating unit is further provided between the light-transmitting cover plate and the optical sensing module.

[0097] It should be noted that during the CMP process, heat is generated by the friction between the polishing pad and the wafer, and the local temperature is too high. If the optical module is directly exposed to the thermal environment, it may cause the lens to thermally expand and deform, resulting in focal length shift. The light-transmitting heat-insulating unit isolates the optical module from the high-temperature area through heat-insulating materials (such as polytetrafluoroethylene or aerogel with low thermal conductivity), controls the temperature fluctuation within a preset range, suppresses the optical path shift caused by thermal expansion, ensures the stability of the spot position, and improves the acquisition accuracy of the reflected light intensity.

[0098] The above embodiments illustrate how to improve the acquisition accuracy of the reflected light intensity and the measurement accuracy of the real-time film thickness through structural improvements. The following further describes from the aspect of online correction how to improve the measurement accuracy of the real-time film thickness.

[0099] When performing real-time control of the film thickness during chemical mechanical polishing of the target wafer, it is necessary to obtain the reflected light intensity on the surface of the target wafer as accurately as possible, because this is the key input for controlling the film thickness based on the correspondence between the film thickness and the reflected light intensity. In practice, factors such as the polishing temperature, the concentration of the polishing liquid, and the surface roughness of the light-transmitting cover plate will affect the measurement of the reflected light intensity, so a series of operations are required to correct the reflected light intensity.

[0100] In a possible implementation, before performing real-time control of the film thickness of the target wafer during chemical mechanical polishing based on the correspondence relationship according to the reflected light intensity on the surface of the target wafer monitored in real time, it further includes:

[0101] Step ①: Obtain the reflected light intensity on the surface of the target wafer monitored in real time;

[0102] During the chemical mechanical polishing process, an optical sensing module is used to measure the reflected light intensity on the surface of the target wafer in real time. This is the basic data for subsequent film thickness control. Only by continuously obtaining the real-time value of the reflected light intensity can the film thickness situation of the current wafer be inferred according to the previously determined correspondence between the film thickness and the reflected light intensity.

[0103] Step ②: Obtain the polishing temperature, the concentration of the polishing liquid, and the surface roughness of the light-transmitting cover plate;

[0104] During the polishing process, the change in temperature will affect the physical and chemical properties of the polishing liquid, such as viscosity, chemical reaction rate, etc., and further affect the propagation and reflection of light in the polishing liquid. Polishing liquids with different concentrations have different characteristics such as light absorption and scattering, which will directly affect the measurement results of the reflected light intensity.

[0105] The roughness of the light-transmitting cover plate surface will cause light to scatter when passing through the cover plate, resulting in changes in the light intensity reaching the wafer surface and the light intensity reflected from the wafer surface, thereby affecting the measurement accuracy of the reflected light intensity.

[0106] Step ③: Based on the polishing temperature and the polishing liquid concentration, determine the first influence coefficient of the polishing liquid on the transmittance.

[0107] The temperature and concentration of the polishing liquid will jointly affect its light transmittance. Therefore, a relationship model can be established between the polishing temperature, the polishing liquid concentration, and the polishing liquid transmittance. According to this model, after obtaining the polishing temperature and the polishing liquid concentration in real time, a first influence coefficient can be determined, which reflects the degree of influence of the current state of the polishing liquid on the light transmittance. For example, if the polishing liquid concentration increases, it will cause an increase in light absorption and scattering in it, resulting in a decrease in transmittance, and the first influence coefficient will correspondingly reflect this change.

[0108] Step ④: Based on the polishing temperature and the roughness of the light-transmitting cover plate surface, determine the second influence coefficient of the light-transmitting cover plate on the transmittance.

[0109] The polishing temperature and the roughness of the light-transmitting cover plate surface will also affect the light transmittance of the light-transmitting cover plate. As the temperature changes, the material properties of the light-transmitting cover plate will change slightly, while the surface roughness will directly cause light scattering. By establishing a corresponding relationship model, according to the polishing temperature and the roughness of the light-transmitting cover plate surface obtained in real time, a second influence coefficient can be determined, which represents the degree of influence of the current state of the light-transmitting cover plate on the light transmittance.

[0110] Step ⑤: According to the first influence coefficient and the second influence coefficient, correct the reflected light intensity, and use the corrected reflected light intensity as the reflected light intensity of the target wafer surface.

[0111] After obtaining the first influence coefficient and the second influence coefficient, the reflected light intensity monitored in real time can be corrected. Since these two coefficients respectively reflect the influence of the polishing liquid and the light-transmitting cover plate on the light transmittance, and the change in the light transmittance will cause a deviation in the measured value of the reflected light intensity, so by multiplying the corresponding influence coefficients, the errors caused by these factors can be eliminated, and a more accurate reflected light intensity of the target wafer surface can be obtained. Using the corrected reflected light intensity for film thickness calculation and control can improve the accuracy and precision of film thickness control, thereby better ensuring the polishing quality of the wafer.

[0112] It should be noted that changes in the polishing temperature, the concentration of the polishing solution, and the state of the light-transmitting cover plate will directly affect the light propagation path and the reflection intensity. By correcting these factors in real time, the measurement errors caused by environmental fluctuations can be significantly reduced, and the reflected light intensity can more truly reflect the film thickness on the wafer surface. Traditional off-line calibration methods are difficult to cope with the rapidly changing environment during the CMP process (such as temperature gradients and fluctuations in the polishing solution composition). Real-time correction can dynamically compensate for these changes and ensure the timeliness and accuracy of the measurement data.

[0113] The following uses a comprehensive embodiment to illustrate the technical concept of the present invention. Exemplarily, during the manufacturing process of advanced processes, ILD / IMD uses an oxide layer to isolate different functional layers, so that there is no electrical conduction between layers and between metal wires. On the one hand, the ILD / IMD dielectric layer is relatively thick, so the grinding process has relatively high requirements for the grinding rate. On the other hand, the entire ILD / IMD CMP process is mainly to remove oxides, which is a grinding process that stops within a thin film. During the grinding process, a certain thickness of the thin film is removed without touching the interface between the two thin films. Therefore, precise monitoring of its stop point is one of its core requirements.

[0114] During the polishing process, there are many factors affecting the wafer planarization. To control the polishing rate, the in-plane uniformity after polishing, and the precise stop thickness, it is necessary to develop a real-time monitoring system for the non-metal film thickness and the ultra-thin metal film thickness. Figure 3 It is a schematic structural diagram of the film thickness real-time monitoring system provided by the embodiment of the present invention. Refer to Figure 3 , during the polishing process, the optical lens is placed inside the polishing platen and rotates with the rotation of the polishing platen. At the same time, the light emitted by the optical lens is emitted through the light-transmitting resin cover plate above the polishing pad. When the light contacts the non-metal film and the ultra-thin metal film on the wafer surface, a reflected light will be formed, and the reflected light is fed back by the optical lens to the controller to calculate the corresponding non-metal film thickness and ultra-thin metal film thickness. The computer will continuously calculate the non-metal film thickness and the ultra-thin metal film thickness, and depict the non-metal film and ultra-thin metal film thickness curves at that time. According to the depicted non-metal film and ultra-thin metal film thickness curves, the pressure of each pressure area of the polishing head is dynamically adjusted to achieve the purpose of improving the uniformity of the non-metal film on the wafer and the uniform removal of the ultra-thin metal film.

[0115] When the wafer moves above the optical lens, the trigger sensor will be automatically triggered, and at the same time, the spectrometer will collect the reflected light intensity R1 corresponding to the film thickness, and the sampling point frequency is 50 milliseconds. Each time, 300 sampling points (R1 - R300) are expected to be collected on the same wafer, and this process is a sampling cycle. Generally, 50 - 60 sampling cycles of optical parameter collection will be performed during equipment calibration, and these will be used as a set of calibration data. Different sets of optical parameters for different thickness film layers will be collected.

[0116] The calibration process of the non-metallic film thickness and ultra-thin metal film thickness real-time monitoring system is as follows: When starting to calibrate the device parameters, wafers with different film thicknesses need to be prepared. Taking the film thickness of silicon dioxide as an example, wafers with and thicknesses are required. These wafers are successively ground with DIW (deionized water). Since no abrasive is added, the thickness of the wafer remains unchanged during the grinding process. The light intensity values generated by each wafer are collected as shown in the following table.

[0117]

[0118]

[0119] Figure 4 is the relationship diagram between the reflected light intensity and the wafer thickness provided by the embodiments of the present invention. Referring to Figure 4 , the horizontal axis is the reflected light intensity of a certain film thickness, and the vertical axis is the film thickness on the wafer. Exemplarily, the reflected light intensity and the corresponding thickness are written into the calculation program, and the machine calibration process ends.

[0120] In some embodiments, a wafer with a film layer thickness of can be ground to and then stopped. When initially grinding, the reflected light intensity collected by the system is 11000, and when the thickness is , the reflected light intensity can be calculated as 1150 according to the formula written previously. The formula of the reflected light intensity and the film layer thickness written into the calculation program is only applicable when grinding stops at a certain thickness. During the grinding process, the reflected light intensity is still collected in real time, and one point is collected every 50 milliseconds. The reflected light intensity generated when the reflected light intensity reaches the pre-set thickness will be continuously collected. During the real-time collection process, a corresponding pie chart will be generated, and at the same time, the machine will automatically adjust the pressure of the polishing head.

[0121] In some embodiments, a CMP device is used to process wafers containing non-metallic thin films. It is required that the remaining thickness of the non-metallic film on the wafer surface is 2000 Å for the first processing and 150 Å for the second processing, the uniformity range (Range) of the non-metallic film surface after grinding is less than 200 Å, and the initial thickness of the non-metallic thin film on the wafer surface is 8000 Å. First, the first processing is carried out. The polishing head carries the wafer and rotates above the polishing pad, and a certain pressure is applied. In this case, a polishing head with five pressure zones is used. The initial pressure and pressure range division are shown in the following table.

[0122]

[0123] The grinding time is set to the maximum time (200 s), and the first grinding is carried out until the stop thickness is 2000 Å. During the grinding, the optical sensing module collects the real-time changes of the non-metallic thin film.Figure 5 It is a schematic diagram of the real-time change in the thickness of the non-metal film provided by an embodiment of the present invention; referring to Figure 5 , when the mechanical chemical polishing starts, the thickness of the non-metal thin film on the wafer surface is 8000 angstroms; during the overall polishing, the real-time thickness of the non-metal thin film changes; after the polishing ends, the thickness of the non-metal thin film is 2000 angstroms.

[0124] At the same time, when the non-metal thin film changes, the pressure in each area of the polishing head will also be slightly adjusted to ensure the uniformity of the non-metal thin film on the wafer. Figure 6 It is a schematic diagram of the real-time change in the pressure of the polishing head of the non-metal thin film control system provided by an embodiment of the present invention.

[0125] After the mechanical chemical polishing processes the wafer containing the non-metal thin film, we need to verify the thickness of the polished non-metal thin film by measuring it with a dedicated machine tool to ensure the accuracy of the stopping thickness of the non-metal thin film and the surface uniformity. Figure 7 It is a schematic diagram of the comparison between the feedback data and the measurement data of the CMP machine tool provided by an embodiment of the present invention; referring to Figure 7 , the comparison between the data measured by the measuring machine tool after polishing and the data measured by the non-metal film thickness real-time monitoring system. After the substrate with an 8000-angstrom non-metal thin film is processed by the CMP non-metal thin film monitoring system, the remaining thickness of the non-metal thin film is 2071 angstroms, and the required remaining thickness of the non-metal thin film is 2000 angstroms. The in-plane uniformity of the entire non-metal thin film is as Figure 7 shown, and the in-plane thickness range is 197 angstroms, meeting the production requirements.

[0126] In the embodiment of the present invention, by observing and adjusting the change in the non-metal film thickness in real time during the mechanical chemical polishing process, the number of manual measurements is reduced, the polishing accuracy is improved, and unnecessary waste of manpower and material resources is reduced. During the mechanical chemical polishing process, white light passes through the window on the polishing pad to measure the non-metal film thickness in real time, and at the same time, the topography of the wafer is continuously adjusted in real time by adjusting the pressure of the polishing head, so as to obtain a high-standard wafer planarization degree.

[0127] Figure 8 It is a schematic diagram of the structure of the real-time control device for the chemical mechanical polishing film thickness provided by an embodiment of the present invention. Referring to Figure 8 , the embodiment of the present invention provides a real-time control device 8 for the chemical mechanical polishing film thickness, which is applied to the film thickness monitoring device; the film thickness monitoring device includes an optical sensing module disposed in the vertical hole of the polishing disk, wherein the vertical hole penetrates the polishing disk and the polishing pad; the device includes:

[0128] A film thickness acquisition module 81, configured to obtain the film thicknesses of a plurality of thin film samples made of the same material; the film thicknesses of each thin film sample are different;

[0129] The reflected light intensity acquisition module 82 is configured to, for each thin film sample, control the optical sensing module to vertically irradiate the thin film sample with a preset light intensity and obtain the reflected light intensity of the thin film sample;

[0130] The correspondence determination module 83 is configured to determine the correspondence between the film thickness and the reflected light intensity based on the film thickness and the reflected light intensity of each thin film sample;

[0131] The real-time control module 84 is configured to, based on the correspondence, perform real-time control of the film thickness of the target wafer during chemical mechanical polishing according to the reflected light intensity of the surface of the target wafer monitored in real time.

[0132] In the present invention, by arranging an optical sensing module in the vertical hole of the polishing pad, the reflected light intensity of the wafer can be monitored in real time during the CMP process. By using the above optical sensing module, the correspondence between the film thickness and the reflected light intensity of samples with different thicknesses is obtained. Thus, during the CMP process, according to the correspondence and the reflected light intensity monitored in real time, the real-time film thickness can be determined, and real-time control of the film thickness of the target wafer during chemical mechanical polishing can be performed. It avoids the time waste caused by multiple downtime detections of the film thickness in the traditional method and improves the efficiency of chemical mechanical polishing.

[0133] An embodiment of the present invention provides a chemical mechanical polishing device, including a memory and a processor. The memory stores a computer program, and when the processor executes the computer program, the real-time control method for the film thickness of chemical mechanical polishing as described in any one of the above is implemented.

[0134] The above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for real-time control of film thickness in chemical mechanical polishing, characterized in that: Applicable to a film thickness monitoring device; the film thickness monitoring device comprises an optical sensor module arranged in a vertical hole of a polishing plate, wherein the vertical hole passes through the polishing plate and the polishing pad; the method comprises: Obtaining the film thickness of multiple thin film samples with the same material; the film thickness of each thin film sample is different; For each thin film sample, controlling the optical sensing module to vertically illuminate the thin film sample with a preset light intensity, and obtaining the reflected light intensity of the thin film sample; Based on the film thickness and reflected light intensity of each thin film sample, the corresponding relationship between the film thickness and the reflected light intensity is determined; Based on the corresponding relationship, the chemical mechanical polishing film thickness of the target wafer is controlled in real time according to the reflected light intensity of the target wafer surface monitored in real time.

2. The method for real-time control of film thickness during chemical mechanical polishing according to claim 1, characterized in that: Based on the corresponding relationship, according to the reflected light intensity of the target wafer surface monitored in real time, the chemical mechanical polishing film thickness of the target wafer is controlled in real time, including: During chemical mechanical polishing of the target wafer, the reflected light intensity of the target wafer surface is monitored in real time by the optical sensing module; Based on the corresponding relationship, the real-time remaining film thickness of the target wafer surface is determined according to the reflected light intensity of the target wafer surface monitored in real time; Based on the real-time remaining film thickness on the target wafer surface and the target remaining film thickness, the chemical mechanical polishing film thickness of the target wafer is controlled in real time.

3. The real-time control method for chemical mechanical polishing film thickness according to claim 1, characterized in that: The end of the vertical hole close to the polishing pad is also provided with a light-transmitting cover plate; The light-transmitting cover plate is used to isolate the optical sensing module from the polishing liquid.

4. The method for real-time control of film thickness during chemical mechanical polishing according to claim 3, characterized in that: Before performing real-time control of the film thickness of the target wafer by chemical mechanical polishing based on the corresponding relationship and according to the reflected light intensity of the target wafer surface monitored in real time, the method further includes: Acquire the reflected light intensity of the target wafer surface for real-time monitoring; Obtaining polishing temperature, polishing liquid concentration and surface roughness of the transparent cover plate; Determining a first influence coefficient of the polishing liquid on the transmittance based on the polishing temperature and the polishing liquid concentration; Determine a second influence coefficient of the light-transmitting cover plate on the transmittance based on the polishing temperature and the surface roughness of the light-transmitting cover plate; The reflected light intensity is corrected according to the first influence coefficient and the second influence coefficient, and the corrected reflected light intensity is used as the reflected light intensity of the target wafer surface.

5. The method for real-time control of film thickness during chemical mechanical polishing according to claim 3, characterized in that: The light-transmitting cover plate is a convex mirror; The highest point of the convex mirror is lower than the polishing pad.

6. The method for real-time control of film thickness during chemical mechanical polishing according to claim 3, characterized in that: A light-transmitting heat-insulating unit is also provided in the vertical hole between the light-transmitting cover plate and the optical sensing module.

7. The method for real-time control of film thickness during chemical mechanical polishing according to claim 1, characterized in that: For each thin film sample, controlling the optical sensing module to vertically irradiate the thin film sample with a preset light intensity, and obtaining the reflected light intensity of the thin film sample comprises: For each thin film sample, the thin film sample faces a polishing pad filled with deionized water; the polishing disk rotates to drive the polishing pad and the thin film sample to move relative to each other; During the relative movement between the polishing pad and the thin film sample, the optical sensing module is controlled to vertically irradiate the thin film sample with a preset light intensity, and the reflected light intensity of the thin film sample is obtained.

8. The method for real-time control of film thickness during chemical mechanical polishing according to claim 1, characterized in that: The method of determining the corresponding relationship between the film thickness and the reflected light intensity based on the film thickness and the reflected light intensity of each thin film sample includes: Based on the film thickness and reflected light intensity of each thin film sample, a linear fitting is performed to obtain a linear relationship between the film thickness and the reflected light intensity; The linear relationship is determined as the corresponding relationship between film thickness and reflected light intensity.

9. A chemical mechanical polishing film thickness real-time control device, characterized in that: Applicable to a film thickness monitoring device; the film thickness monitoring device comprises an optical sensor module arranged in a vertical hole of a polishing plate, wherein the vertical hole passes through the polishing plate and the polishing pad; the device comprises: A film thickness acquisition module is used to obtain the film thickness of multiple film samples with the same material; the film thickness of each film sample is different; A reflected light intensity acquisition module, for each thin film sample, controlling the optical sensing module to vertically illuminate the thin film sample with a preset light intensity, and obtaining the reflected light intensity of the thin film sample; A corresponding relationship determination module, used to determine the corresponding relationship between the film thickness and the reflected light intensity based on the film thickness and the reflected light intensity of each thin film sample; The real-time control module is used to perform real-time control on the chemical mechanical polishing film thickness of the target wafer based on the corresponding relationship and according to the reflected light intensity of the target wafer surface monitored in real time.

10. A chemical mechanical polishing device, characterized in that: The method comprises a memory and a processor, wherein the memory stores a computer program, and the processor implements the real-time control method for chemical mechanical polishing film thickness as claimed in any one of claims 1 to 8 when executing the computer program.

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