Chemical mechanical polishing method

Abstract

The present application relates to a kind of chemical mechanical polishing methods, comprising the following steps: providing a chemical mechanical polishing device and a wafer formed with metal layer;Metal layer on the surface of wafer is chemically mechanically polished using chemical mechanical polishing device, the whole process of chemical mechanical polishing to metal layer is divided into first stage and second stage;First stage grinds metal layer to predetermined thickness;Second stage continues to grind the remaining metal layer until the metal layer on the surface of wafer is completely removed;In first stage, intermediate transition stage is added, intermediate transition stage controls the polishing pad of the polishing head away from the polishing wafer, and the polishing pad is cooled and trimmed.The present application inserts intermediate transition stage in the process of polishing to cool and trim the polishing pad, effectively avoids the influence of heat and grinding by-product generated by mechanical grinding on chemical action in polishing, reduces the probability of metal residue existing on the surface of wafer after polishing, improves the production efficiency and product quality of wafer.

Description

Technical Field

[0001] This invention belongs to the field of semiconductor manufacturing technology, and in particular relates to a chemical mechanical polishing method. Background Technology

[0002] Chemical mechanical polishing (CMP) is a key step in wafer manufacturing. It combines mechanical friction with chemical etching. During CMP, the chemical reagents in the polishing slurry oxidize the substrate material being polished, forming a soft oxide film. The oxide film is then removed by mechanical friction. Through repeated oxidation-film formation and mechanical removal processes, effective polishing is achieved.

[0003] The chemical mechanical polishing (CMP) process for removing the metal layer on a wafer typically involves two steps. The first step is to grind away most of the metal layer on the wafer surface using a polishing slurry corresponding to the metal layer. The second step uses the same polishing slurry as the first step, but at a reduced polishing rate to finely polish the metal layer in contact with the barrier layer. The polishing is then stopped on the barrier layer using optical endpoint detection technology.

[0004] However, the chemical reaction between the polishing slurry and the metal layer on the wafer surface in the chemical mechanical polishing (CMP) process for removing metal layers is a complex oxide generation process. If the heat generated by mechanical friction and the byproducts remaining on the polishing pad surface cannot be dissipated in time, they will affect the chemical reaction, leading to passivation of the metal surface and the formation of a protective layer. This disrupts the balance between chemical reaction and mechanical removal, affects the accuracy of endpoint detection, and leaves metal residue on the wafer surface after polishing, impacting wafer production efficiency and product quality. Summary of the Invention

[0005] The purpose of this invention is to solve one of the above-mentioned technical problems and provide a chemical mechanical grinding method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A chemical mechanical polishing method for polishing a metal layer on a wafer surface includes the following steps:

[0008] A chemical mechanical polishing apparatus and a wafer having a metal layer formed thereon are provided; the chemical mechanical polishing apparatus includes a stage, a polishing pad fixed on the stage, and a polishing head for holding the wafer.

[0009] The metal layer on the wafer surface is chemically mechanically polished using a chemical mechanical polishing device. The entire process of chemical mechanical polishing of the metal layer is divided into the first stage and the second stage.

[0010] The first stage involves grinding the metal layer on the wafer surface to a predetermined thickness; the second stage continues grinding the remaining metal layer until the metal layer on the wafer surface is completely removed.

[0011] An intermediate transition stage is added to the first stage. During the intermediate transition stage, the grinding head is kept away from the grinding pad, and the grinding pad is cooled and trimmed.

[0012] In some embodiments of the present invention, the method for cooling the abrasive pad specifically includes the following steps:

[0013] Coolant is supplied to the grinding pad, and the grinding pad is rinsed with coolant.

[0014] In some embodiments of the present invention, the flow rate of the coolant is 1L / min-2L / min.

[0015] In some embodiments of the present invention, the chemical mechanical polishing apparatus further includes a dresser; the method for dressing the polishing pad specifically includes the following steps:

[0016] Use a dresser to dress the grinding pad and remove grinding byproducts from its surface.

[0017] In some embodiments of the present invention, the method of adding an intermediate transition stage in the first stage specifically includes the following steps:

[0018] Determine the critical time T1 and the duration T2 of the intermediate transition phase;

[0019] When the first stage reaches the critical time T1, the chemical mechanical polishing device is controlled to switch to the intermediate transition stage to cool and trim the polishing pad. After the intermediate transition stage lasts for time T2, the chemical mechanical polishing device is controlled to switch back to the first stage to continue coarse polishing of the metal layer on the wafer surface.

[0020] In some embodiments of the present invention, the method for determining the critical time T1 specifically includes the following steps:

[0021] Chemical mechanical polishing (CMP) was performed on multiple simulated wafers with metal layers formed on their surfaces. The polishing speed of each simulated wafer in the first stage of CMP was calculated, and the time point at which the polishing speed of each simulated wafer in the first stage of CMP was determined. Based on the time point at which the polishing speed of the multiple simulated wafers changed during the first stage of polishing, the critical time T1 was determined.

[0022] In some embodiments of the present invention, the method for determining the duration T2 of the intermediate transition phase specifically includes the following steps:

[0023] The duration T2 of the intermediate transition stage is determined based on the grinding pad temperature and the surface condition of the grinding pad during the intermediate transition stage; the surface condition of the grinding pad is used to determine the grinding rate of the grinding pad on the wafer.

[0024] In some embodiments of the present invention, the total duration of the first stage is preset. Starting from the start of the first stage grinding, when the grinding time of the first stage reaches 40%-50% of the total duration, the intermediate transition stage is started; the duration T2 of the intermediate transition stage is 10S-20S.

[0025] In some embodiments of the present invention, in the first and second stages, the pressure of the grinding head on the wafer in the chemical mechanical polishing apparatus is 1 ps i-3 ps i, the pressure of the retaining ring on the edge of the grinding head on the wafer is 5 ps i-9 ps i, the flow rate of the polishing fluid is 100 ml / min-400 ml / min, and the rotation speed of the bearing stage is 60 rpm-120 rpm.

[0026] In some embodiments of the present invention, during the intermediate transition stage, the pressure of the grinding head on the wafer in the chemical mechanical polishing apparatus is 0 ps i-1 ps i, the pressure of the retaining ring on the edge of the grinding head on the wafer is 4 ps i-7 ps i, the flow rate of the polishing fluid is 0 ml / min-100 ml / min, and the rotation speed of the bearing stage is 80 rpm-100 rpm.

[0027] The beneficial effects of this invention are as follows:

[0028] This invention divides the entire process of chemical mechanical polishing (CMP) of the metal layer on the wafer surface into a first stage and a second stage, and inserts an intermediate transition stage in the first stage to cool and trim the polishing pad used for polishing the wafer. This reduces the temperature of the polishing pad and removes residual polishing byproducts from the surface of the polishing pad, effectively preventing the heat generated by the mechanical friction between the polishing pad and the wafer from affecting the chemical interaction between the polishing slurry and the metal layer. It also improves the impact of polishing byproducts on the pH value of the polishing slurry, thereby preventing the formation of a protective layer on the surface of the metal layer that disrupts the balance between chemical and mechanical removal. This reduces the probability of metal residue on the wafer surface after polishing and improves wafer production efficiency and product quality. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 The flowchart of the chemical mechanical grinding method provided by the present invention;

[0031] Figure 2 This is a schematic diagram showing the relationship between metal layer thickness and time during the first stage of grinding without the intermediate transition stage.

[0032] Figure 3This diagram illustrates the relationship between metal layer thickness and time during the first stage of grinding, which incorporates an intermediate transition phase.

[0033] Figure 4 A diagram showing the comparison of process time before and after adding the intermediate transition stage;

[0034] Figure 5 This is a diagram showing the comparison of grinding effects before and after adding the intermediate transition stage;

[0035] (a) is a schematic diagram of the grinding effect before the intermediate transition stage is added, and (b) is a schematic diagram of the grinding effect after the intermediate transition stage is added. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of this application clearer, the application is described and illustrated below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application. All other embodiments obtained by those skilled in the art based on the embodiments provided in this application without inventive effort are within the scope of protection of this application.

[0037] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations according to this application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion, for example, a process, method, system, product, or apparatus that comprises a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or apparatus.

[0038] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0039] The technical solution of the present invention will be described in detail below with reference to specific embodiments and accompanying drawings.

[0040] As attached Figure 1-5 As shown, in an illustrative embodiment of a chemical mechanical polishing method of the present invention, the method is used to polish a metal layer on the surface of a wafer, and the method includes the following steps.

[0041] A chemical mechanical polishing (CMP) apparatus is provided, comprising at least a support platform, a polishing pad, and a polishing head. The polishing pad is fixed to the support platform, and the support platform rotates the polishing pad during wafer polishing. The polishing head holds the wafer to be polished; during polishing, the polishing head presses down, bringing the wafer close to the polishing pad and applying appropriate pressure to generate friction between the wafer and the polishing pad. When polishing stops, the polishing head lifts, moving the wafer away from the polishing pad. In this embodiment, the CMP apparatus further includes a polishing slurry supply module and a control module. The polishing slurry supply module supplies polishing slurry to the polishing area and typically consists of a polishing slurry storage tank, pipes, nozzles, etc. The polishing slurry provides the medium required for chemical etching and mechanical removal, while also helping to remove debris and heat generated during polishing. The control module controls the overall operation of the CMP apparatus and monitors the CMP process, and typically includes a control system, sensors, a display, etc. The control module needs to monitor the wafer's processing status in real time, adjust the pressure of the polishing head and the rotation speed of the support platform, and control the supply and cleaning process of the polishing slurry.

[0042] Provide a wafer with a metal layer formed thereon, wherein the metal forming the metal layer includes, but is not limited to, one of Cu, W, and Al.

[0043] The chemical mechanical polishing apparatus is used to perform chemical mechanical polishing on the metal layer on the wafer surface, and the entire process of chemical mechanical polishing on the metal layer is divided into a first stage and a second stage.

[0044] The first stage uses a high grinding rate to coarsely grind the metal layer to grind the metal layer on the wafer surface to a predetermined thickness. During the grinding process, the thickness of the metal layer is determined by electrical endpoint detection technology. The second stage uses the same grinding fluid as the first stage, but reduces the grinding rate to finely grind the remaining metal layer in contact with the barrier layer until the metal layer on the wafer surface is completely removed. During the grinding process, optical endpoint detection technology is used to stop the grinding on the barrier layer.

[0045] An intermediate transition stage is added to the first stage. During the intermediate transition stage, the polishing head is controlled to move the wafer away from the polishing pad, and the polishing pad is cooled and trimmed.

[0046] The effects of chemical mechanical polishing on the metal layer on the wafer surface before and after the intermediate transition stage are shown in the attached figure. Figure 2-5 As shown.

[0047] Among them, judging from the grinding effect of the first stage, the attached Figure 2 This is a schematic diagram showing the relationship between metal layer thickness and time during the first stage of grinding without the intermediate transition stage. (See attached diagram) Figure 3 This is a schematic diagram illustrating the relationship between metal layer thickness and time during the first stage of grinding, which includes an intermediate transition phase. (See attached diagram.) Figure 2-3 It can be seen that before the intermediate transition stage is added, there are time points in the first stage grinding process of each wafer where the grinding speed changes significantly. When the total duration of the first stage is preset, the thickness of the remaining metal layer of each wafer after the first stage grinding is different, and the thickness of the metal layer on the surface of some wafers cannot reach the predetermined thickness. After the intermediate transition stage is added, the grinding speed of each wafer in the first stage grinding process becomes more similar and more stable. When the total duration of the first stage is preset, the thickness of the remaining metal layer of each wafer after the first stage grinding is basically the same and can all reach the predetermined thickness.

[0048] Judging from the grinding time of the first and second stages, Figure 4 A diagram showing the comparison of process time before and after adding the intermediate transition stage is attached. Figure 4 In the process, wafers numbered 1-9 are polished using a process without intermediate transition stages, while wafers numbered 11-25 are polished using a process with intermediate transition stages. The endpoint detection time refers to the duration of electrical endpoint detection, i.e., the duration of the first stage. The total time refers to the total duration of the first and second stages, as specified in the appendix. Figure 4 It can be seen that before the intermediate transition stage is added, the duration of the first stage of each wafer varies greatly in order to grind the metal layer to the predetermined thickness, which leads to the instability of the total duration of the first and second stages. After the intermediate transition stage is added, the duration of the first stage of each wafer is more stable, which in turn makes the total duration of the first and second stages tend to be stable.

[0049] Judging from the overall grinding effect of the first and second stages, Figure 5 This is a comparative illustration of the grinding effect before and after adding the intermediate transition stage. (a) shows the grinding effect before adding the intermediate transition stage, and (b) shows the grinding effect after adding the intermediate transition stage. (See attached diagram.) Figure 5 It can be seen that before the intermediate transition stage is added, there are still metal residues at the edge of the wafer, but after the intermediate transition stage is added, there are basically no metal residues at the edge of the wafer.

[0050] In some embodiments of the present invention, the method for cooling the abrasive pad specifically includes the following steps.

[0051] High-pressure coolant is supplied to the polishing pad via pipes and high-pressure nozzles, and the polishing pad is then rinsed with the high-pressure coolant to reduce its temperature. This prevents the heat generated by the mechanical friction between the polishing pad and the wafer from affecting the chemical interaction between the polishing fluid and the metal layer, thereby preventing the formation of a protective layer on the metal layer surface that disrupts the balance between chemical and mechanical removal. This avoids metal residue on the wafer surface after polishing, which would negatively impact wafer production efficiency and product quality. In this embodiment, high-pressure water is used as the coolant.

[0052] In some embodiments of the present invention, the flow rate of the coolant is 1L / min-2L / min.

[0053] In some embodiments of the present invention, the chemical mechanical polishing apparatus further includes a dresser; the method for dressing the polishing pad specifically includes the following steps.

[0054] The grinding pad is trimmed using a trimmer to remove grinding byproducts from its surface and to mitigate the impact of these byproducts on the pH of the grinding fluid.

[0055] In some embodiments of the present invention, the method of adding an intermediate transition stage in the first stage specifically includes the following steps.

[0056] Determine the critical time T1 and the duration T2 of the intermediate transition phase.

[0057] When the first stage reaches the critical time T1, the chemical mechanical polishing device is controlled to switch to the intermediate transition stage. The polishing head is raised, and the pressure between the polishing head and the wafer, the pressure of the outer edge of the polishing head on the wafer, the flow rate of the polishing fluid and the rotation speed of the stage are adjusted. The polishing pad is cooled and adjusted. After the intermediate transition stage lasts for time T2, the chemical mechanical polishing device is controlled to switch back to the first stage to continue polishing the metal layer on the wafer surface.

[0058] In some embodiments of the present invention, the method for determining the critical time T1 specifically includes the following steps.

[0059] Chemical mechanical polishing was performed on multiple simulated wafers with metal layers formed on their surfaces, and the thickness of the metal layers was measured in real time. The relationship between time and metal layer thickness during the polishing process is shown in the attached figure. Figure 2 As shown, based on the metal layer thickness during the grinding process and the grinding speed of the first stage of chemical mechanical grinding of each simulated wafer, the time point at which the grinding speed of the first stage of chemical mechanical grinding of each simulated wafer changes is determined, and the minimum value of the time point at which the grinding speed changes during the first stage of grinding of each simulated wafer is taken as the critical time T1.

[0060] In some embodiments of the present invention, the method for determining the duration T2 of the intermediate transition phase specifically includes the following steps.

[0061] The duration T2 of the intermediate transition stage is determined based on the polishing pad temperature and surface condition during this stage. The polishing pad surface condition is used to determine the polishing rate of the wafer. The polishing rate refers to the amount of material removed from the wafer surface by the polishing pad per unit time under a certain pressure. The polishing rate can be calculated by measuring the thickness change of the wafer before and after polishing, combined with polishing time and pressure. The polishing rate helps to understand the performance of the polishing pad and the machinability of the wafer material, thereby optimizing polishing process parameters and improving polishing efficiency and quality.

[0062] In some embodiments of the present invention, the total duration of the first stage is preset before mechanical and chemical polishing of the wafer. When the polishing time of the first stage reaches 40%-50% of the total duration, the intermediate transition stage is started. The duration T2 of the intermediate transition stage is 10S-20S.

[0063] In some embodiments of the present invention, in the first and second stages, the pressure of the grinding head on the wafer in the chemical mechanical polishing apparatus is 1 ps i-3 ps i, the pressure of the retaining ring on the edge of the grinding head on the wafer is 5 ps i-9 ps i, the flow rate of the polishing fluid is 100 ml / min-400 ml / min, and the rotation speed of the bearing stage is 60 rpm-120 rpm.

[0064] In some embodiments of the present invention, during the intermediate transition stage, the pressure of the grinding head on the wafer in the chemical mechanical polishing apparatus is 0 ps i-1 ps i, the pressure of the retaining ring on the edge of the grinding head on the wafer is 4 ps i-7 ps i, the flow rate of the polishing fluid is 0 ml / min-100 ml / min, and the rotation speed of the bearing stage is 80 rpm-100 rpm.

[0065] In some embodiments of the present invention, the grinding head is a grinding head with a zoned pressure function. The grinding head is divided into five or seven pressure zones. During the chemical mechanical polishing process, the pressure of each pressure zone on the wafer can be the same or different, but the pressure of each pressure zone on the wafer in each polishing stage needs to be controlled within the corresponding pressure range.

[0066] Finally, it should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. The same or similar parts between the various embodiments can be referred to each other.

[0067] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them; although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications can still be made to the specific implementation of the present invention or equivalent substitutions can be made to some technical features without departing from the spirit of the technical solutions of the present invention, and all such modifications and substitutions should be covered within the scope of the technical solutions claimed in the present invention.

Claims

1. A chemical mechanical polishing method for polishing a metal layer on a wafer surface, characterized in that, Includes the following steps: A chemical mechanical polishing (CMP) apparatus and a wafer having a metal layer formed thereon are provided; the CMP apparatus includes a stage, a polishing pad fixed on the stage, and a polishing head for fixing the wafer; The metal layer on the wafer surface is chemically and mechanically polished using the chemical mechanical polishing apparatus, and the entire process of chemical mechanical polishing of the metal layer is divided into a first stage and a second stage. The first stage involves grinding the metal layer on the wafer surface to a predetermined thickness; the second stage continues grinding the remaining metal layer until the metal layer on the wafer surface is completely removed. An intermediate transition stage is added to the first stage, in which the grinding head is controlled to move away from the grinding pad, and the grinding pad is cooled and trimmed; The method of adding an intermediate transition stage in the first stage specifically includes the following steps: Determine the critical time T1 and the duration T2 of the intermediate transition phase; When the first stage reaches the critical time T1, the chemical mechanical polishing device is controlled to switch to the intermediate transition stage to cool and adjust the polishing pad. After the intermediate transition stage lasts for a time T2, the chemical mechanical polishing device is controlled to switch back to the first stage to continue polishing the metal layer on the wafer surface. The method for determining the critical time T1 specifically includes the following steps: Chemical mechanical polishing (CMP) is performed on multiple simulated wafers with metal layers formed on their surfaces. The polishing speed of each simulated wafer in the first stage of CMP is calculated, and the time point at which the polishing speed of each simulated wafer changes in the first stage of CMP is determined. Based on the time point at which the polishing speed changes in the first stage of CMP on multiple simulated wafers, the critical time T1 is determined. The method for determining the duration T2 of the intermediate transition phase specifically includes the following steps: The duration T2 of the intermediate transition stage is determined based on the polishing pad temperature and polishing pad surface condition during the intermediate transition stage; the polishing pad surface condition is used to determine the polishing rate of the polishing pad on the wafer.

2. The chemical mechanical grinding method according to claim 1, characterized in that, The method for cooling the abrasive pad specifically includes the following steps: Coolant is supplied to the polishing pad, and the polishing pad is rinsed with the coolant.

3. The chemical mechanical grinding method according to claim 2, characterized in that, The flow rate of the coolant is 1L / min-2L / min.

4. The chemical mechanical grinding method according to any one of claims 1-3, characterized in that, The chemical mechanical polishing apparatus further includes a dresser; the method for dressing the polishing pad specifically includes the following steps: The dressing tool is used to dress the abrasive pad and remove abrasive byproducts from the surface of the abrasive pad.

5. The chemical mechanical grinding method according to claim 1, characterized in that, The total duration of the first stage is preset. Starting from the start of the first stage grinding, when the grinding time of the first stage reaches 40%-50% of the total duration, the intermediate transition stage is started; the duration T2 of the intermediate transition stage is 10S-20S.

6. The chemical mechanical grinding method according to claim 1, characterized in that, In the first and second stages, the pressure of the grinding head on the wafer in the chemical mechanical polishing apparatus is 1psi-3psi, the pressure of the bearing ring on the edge of the grinding head on the wafer is 5psi-9psi, the flow rate of the polishing fluid is 100ml / min-400ml / min, and the rotation speed of the stage is 60rpm-120rpm.

7. The chemical mechanical grinding method according to claim 1 or 6, characterized in that, During the intermediate transition stage, the pressure of the polishing head on the wafer in the chemical mechanical polishing apparatus is 0psi-1psi, the pressure of the bearing ring on the edge of the polishing head on the wafer is 4psi-7psi, the polishing fluid flow rate is 0ml / min-100ml / min, and the stage rotation speed is 80rpm-100rpm.

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