Chemical Mechanical Polishing with Changes in the Die Base

Abstract

A method for processing a substrate includes selectively dispensing a processing fluid onto the substrate on a die-by-die basis and chemically mechanically polishing the substrate after dispensing the processing fluid, where the processing fluid modifies the polishing rate of the chemical mechanical polishing in one or more selected dies to which the processing fluid is applied compared to one or more remaining dies to which the processing fluid is not applied.

Description

Technical Field

[0001] The present disclosure relates to chemical mechanical polishing, and more particularly to die-by-die variations in polishing.

Background Art

[0002] Integrated circuits are typically formed on a substrate by sequentially depositing conductive, semiconductive, or insulating layers on a silicon wafer. In various manufacturing processes, planarization of the layers on the substrate is required. For example, one manufacturing step includes depositing a fill layer on an uneven surface of a lower layer and planarizing the fill layer. In some applications, the fill layer is planarized until the upper surface of the lower layer is exposed. In other applications, the fill layer is planarized until a specific thickness remains on the lower layer.

[0003] Chemical mechanical polishing (CMP) is one of the generally recognized planarization methods. In this planarization method, it is usually necessary to attach the substrate to a carrier head. The exposed surface of the substrate is usually placed against a rotating polishing pad. The carrier head applies a controllable load to the substrate to press the substrate against the polishing pad. A polishing fluid, such as a slurry containing polishing particles, is usually supplied to the surface of the polishing pad.

[0004] One problem in CMP is that variations in slurry distribution, the condition of the polishing pad, the relative speed between the polishing pad and the substrate, the initial thickness of the substrate layer, and the load applied to the substrate can cause variations in the material removal rate across the entire substrate.

Summary of the Invention

[0005] In one aspect, a method of processing a substrate includes selectively dispensing a processing fluid onto the substrate die-by-die and chemically mechanically polishing the substrate after dispensing the processing fluid. The processing fluid changes the polishing rate of chemical mechanical polishing in one or more selected dies to which the processing fluid is applied compared to one or more remaining dies to which the processing fluid is not applied.

[0006] In another aspect, the system includes a processing station including a dispenser that supplies a processing fluid onto the substrate die-by-die, a chemical mechanical polishing station, and a substrate transfer robot that transfers the substrate from the processing station to the chemical mechanical polishing station. The processing fluid is a material that changes the polishing rate of one or more selected dies to which the processing fluid is applied, in comparison to one or more remaining dies to which the processing fluid is not applied in subsequent chemical mechanical polishing.

[0007] One or more of the following advantages may be provided by embodiments, but are not limited thereto.

[0008] The amount of material removed can be varied die-by-die, improving the uniformity of polishing.

[0009] Details of one or more embodiments are set forth in the accompanying drawings and the following description. Other features, objects, and advantages will be apparent from the description and drawings, and from the claims.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Modes for Carrying Out the Invention

[0011] Like reference numerals in the various drawings indicate like elements.

[0012] When a substrate containing a plurality of dies is polished using a chemical mechanical polishing process, in some cases, the substrate material may be removed at different rates at different locations on the surface. When the polishing process ends when some dies are properly polished, other dies may be over-polished or under-polished and become unusable.

[0013] One approach to compensating for non-uniform polishing is to use a carrier head with a plurality of independently controllable concentric pressurizable chambers. This can compensate for radial non-uniformities, but cannot compensate for angular (circumferential) non-uniformities, also known as asymmetric polishing. Carrier heads with angled and distributed chambers have been proposed, but such carrier heads may not provide the resolution necessary to address die-to-die variations in polishing rate.

[0014] However, a method for improving the uniformity of polishing for each die is to perform one or more preliminary processing steps. The processing steps are performed for each die prior to the polishing step and change the effectiveness of subsequent polishing operations. For example, the processing step can provide a protective coating to reduce the polishing rate on the die or modify the surface of the die to increase the polishing rate (without necessarily removing material).

[0015] FIG. 1 shows an example of a chemical mechanical polishing system 5 that includes both a polishing station 20 and a preprocessing station 100. In some embodiments, the chemical mechanical polishing system 5 includes an in-line metrology system for measuring the thickness of one or more die layers on the substrate 10.

[0016] The polishing station 20 includes a rotatable disk-shaped platen 24 on which a polishing pad 30 is disposed. The platen 24 is operable to rotate about an axis 25. For example, a motor 22 can rotate a drive shaft 28 to rotate the platen 24. The polishing pad 30 may be a two-layer polishing pad having an outer polishing layer 34 and a softer backing layer 32.

[0017] The polishing station 20 can include a supply port 42, for example, at an end of a slurry supply arm, to dispense a polishing liquid 44, such as a polishing slurry, onto the polishing pad 30. The polishing station 20 can also include a conditioner system with a conditioning disk for maintaining a consistent roughness from substrate to substrate by wearing the polishing pad.

[0018] The carrier head 70 is operable to hold the substrate 10 against the polishing pad 30. The carrier head 70 is suspended from a support structure 72, such as a carousel or a track, and is connected by a drive shaft 74 to a carrier head rotation motor 76 so that the carrier head can rotate about an axis 71. Optionally, the carrier head 70 can vibrate laterally on a slider on the carousel, for example, by movement along a track or by rotational vibrations of the carousel itself.

[0019] The carrier head 70 can include a flexible membrane 80 having a substrate mounting surface that contacts the back surface of the substrate 10, and a plurality of pressurizable chambers 82 that apply different pressures to different zones on the substrate 10, such as different radial zones. The carrier head 70 can include a retaining ring 84 for holding the substrate. During operation, the platen rotates about its central axis 25, the carrier head rotates about its central axis 71, and translates laterally across the upper surface of the polishing pad 30.

[0020] In some embodiments, the polishing apparatus includes an in-situ monitor system, such as an optical monitor system or an eddy current monitor system, that can be used to monitor the thickness of a layer being polished on the substrate.

[0021] The processing station 100 includes a dispenser 102 for selectively supplying a processing fluid 104 onto a selected die on a substrate. In some embodiments, the processing station 100 includes a support 106. The substrate support 106 may be a CMP carrier head, a chuck stage with the substrate facing up or down, or a fixture with lift pins or contact pins for holding the substrate. The substrate can be held facing up, facing down, or at another angle (such as vertical).

[0022] The dispenser may include one or more nozzles for supplying the processing fluid to the selected die. The nozzles can move in the X-Y directions or along a specified operation path. Since the nozzles can adjust their height and spread angle, they can reliably cover the selected die while minimizing the chemical overflow onto other dies. The chemicals of the processing fluid can also be supplied by a foam or other material that is saturated with the chemicals and arranged in contact with the selected die.

[0023] In some embodiments, an actuator 103 is connected to the dispenser 102 or the support 106 to control their relative positions. The actuator 103 can include a pair of linear actuators for moving the dispenser 102 or the support 106 in two orthogonal directions. Possible dispenser mechanisms include droplet ejection (e.g., piezoelectrically driven), spin-on, spray-on, and screen printing.

[0024] As will be further described below, the chemical properties of the fluid vary depending on the type of process. In some embodiments, depending on the dispensing mechanism, the processing station 100 includes a mask 140 for controlling the area of the surface of the substrate to which the processing fluid 104 is applied. The mask 140 can be used, for example, to correct for consistent non-uniformities from an upstream process when the specific die requiring processing is the same between substrates. The mask 140 can be held at a constant height relative to the substrate surface during the dispensing process, allowing only specific areas on the substrate to be processed. In some embodiments, a vertical actuator 142 can adjust the distance between the upper surface of the substrate 10 and the mask 140.

[0025] In the case of screen printing, the mask 140 can be held in contact with the substrate surface, and the dispenser can include a roller or blade for spreading the processing fluid over the entire substrate 10. In the case of droplet ejection, the dispenser 102 can be moved laterally across the substrate by an actuator 103 while controlling the ejection so that the processing fluid is dispensed only onto the selected die, but the mask 140 can be used to prevent ejection onto other areas on the substrate 10. In the case of spin-on printing, the processing fluid can flow from the dispenser while the support 106 is rotating.

[0026] Depending on the processing technique, the processing station 100 can also include an energy source 120 for curing the processing fluid. For example, the energy source can be a UV light source or an array of UV light sources for curing fluids such as crosslinkable polymers. Alternatively, the energy source can be a heater, such as an IR lamp or an array of IR lamps, that provides a heat treatment after the fluid is applied. In some embodiments, the energy source is scanned across the entire substrate, for example, by an actuator, and is controllably modulated to process specific areas corresponding to the selected die.

[0027] Depending on the processing technology, the processing station 100 can also include a substrate surface cleaning device 130. The surface cleaning device 130 can include a fluid source and an outlet 132 arranged to flow fluid 134 over the entire surface of the substrate 10. In some embodiments, the fluid is a gas, such as filtered air, N2, or an inert gas. For example, if surface treatment is performed between two CMP steps, gas can be used to blow excess water and / or polishing fluid from selected dies before applying the surface treatment fluid. In some embodiments, for removing a processing fluid, such as for removing an etchant, the fluid is a liquid, such as deionized water. In some embodiments, for example, if the processing fluid is a photoresist, the fluid is a developer for removing the exposed or unexposed portions of the processing fluid. The substrate surface cleaning device 130 can also include a vacuum source for sucking excess processing fluid. Thus, the substrate surface cleaning device can include a chemical or gas supply nozzle, an array of chemical or gas supply nozzles, a vacuum nozzle, or an array of vacuum nozzles.

[0028] The polishing station 20 and the processing station 100 can be integrated into a single tool. In this case, during operation, the substrate 10 to be polished can be transferred from a cassette to the processing station 100, for example, via a factory interface module, before being polished at the polishing station 20. Next, the substrate is transferred to the polishing station 20, polished, and then returned to the same or a different cassette via the factory interface module. In some embodiments, the substrate 10 is transferred from the processing station 100 to the polishing station 20 while remaining within the same carrier head 70, for example, by the movement of a carrier head along a track or the rotation of a carousel. In such embodiments, the substrate remains in a face-up or face-down position for both processing and polishing. In some embodiments, the substrate 10 is transferred from the processing station 100 to the polishing station 20 by a separate robot. For example, the substrate can be processed at an in-line processing station and then lifted by a robot and inserted into the loading station of the polishing system. In such embodiments, the substrate can be inverted by the robot from a face-up orientation to a face-down orientation during transfer, or the substrate can remain in a face-up or face-down position for both processing and polishing.

[0029] In some embodiments, the polishing station 20 and the processing station 100 are independent of each other and are arranged in proximity to each other, for example, within the same cleaning chamber.

[0030] The polishing apparatus 5 can be controlled by a control system 90, for example, a controller such as a programmed computer or a microcontroller. For example, the control system can control motors or actuators for controlling various parameters of the polishing station 20, such as the position and rotational speed of the carrier head, the rotational speed of the platen, the flow rate of the polishing liquid, etc. Similarly, the control system 90 can control various parameters of the processing station 100, such as the actuator 103 for controlling the relative position of the substrate 10 and the dispenser 102, and the valve for controlling the timing of dispensing the processing fluid 104, so as to controllably dispense the processing fluid to a selected location. Further, the control system 90 can control the operation of a robot or other transfer mechanism for transferring the substrate from the processing station 100 to the polishing station 20.

[0031] Referring to FIG. 2, the substrate 10 includes a plurality of dies 12. The dies 12 can be separated by scribe lines 14. At least one die 12a needs to be polished more or less compared to other dies. This can be due to non-uniformities in the incoming substrate, such as the layer on die 12a being thicker or thinner compared to other dies, or the inherent non-uniform polishing rate by the polishing station 20, or a combination thereof.

[0032] The dispenser of the processing station applies the processing fluid onto the region 16 of the substrate corresponding to the selected die 12a and is used to adjust the subsequent polishing rate of the selected die 12a at the polishing station. Each region 16 can completely overlap with the corresponding selected die 12a. The processing fluid is not applied to the remaining dies, i.e., at least one of the dies 12.

[0033] Referring to FIG. 3, the method of operating the polishing apparatus by the control system can optionally include obtaining data indicating which die (also known as the selected die) on the substrate requires processing (202). The data can also indicate whether the polishing rate increases or decreases due to the processing.

[0034] For example, in a feed-forward technique, the thickness of the layer being polished can be measured at each position of a plurality of dies on the substrate. The measurement can be performed in an in-line or independent measurement station. Based on the thickness measurement, the controller can determine the dies having a layer thickness that varies beyond a threshold value from a default thickness value or the average thickness of the dies. The controller can save data indicating that these dies have been selected for processing.

[0035] As another example, in a feedback technique, the thickness of the layer after polishing can be measured at each position of a plurality of dies on the substrate. The measurement can be performed in an in-line or independent measurement station. The controller can determine the dies having a layer thickness that varies beyond a threshold value from a default thickness value or the average thickness of the dies. The controller can then save data indicating that the corresponding dies on subsequent substrates have been selected for processing.

[0036] As yet another example, the data indicating which die on the substrate requires processing can be received by user input, for example, based on prior experimental measurements.

[0037] The substrate is loaded into the processing station, and the selected die is processed with a processing fluid (204). This processing locally increases or decreases the material removal amount of a specific die in a subsequent CMP polishing process.

[0038] In some embodiments, the control system controls the operation of the dispenser to selectively dispense the processing fluid to the die selected based on the data. For example, a droplet ejection printer can be controlled in conjunction with the movement of the printer by an actuator to supply the processing fluid only onto the selected die.

[0039] As yet another example, data indicating which dies on a substrate require processing is not stored by the controller, but the selection of which dies to process is controlled by the physical configuration of the processing station, such as the position of the apertures in the mask. The mask design can be based on prior experimental measurements.

[0040] In some embodiments, the processing includes forming a protective film on the selected die. The protective film can be a layer of an organic material such as a crosslinkable polymer or a layer of an inorganic material such as water glass. The protective film can be thinner than the layer to be polished, for example, 10% or less, such as 5% or less, such as 2.5% or less of the thickness of the layer to be polished.

[0041] The protective film can also be removed in a subsequent polishing process, in which case time not spent polishing the layer is consumed. The time required for the polishing process to remove the protective film varies depending on the physical properties of the protective film, such as thickness, molecular weight, degree of crosslinking, etc. Some embodiments indicate that the thickness of the protective film, or the degree of curing (by exposure time or intensity of the energy source), is controlled by a control system according to data that scales according to the difference between the layer thickness of the selected die's layer and a default thin or average thickness value.

[0042] In some embodiments, the processing includes a "destructive" process that damages the layer to be polished on the selected die to make the polishing process more effective, i.e., to achieve a higher polishing rate. The destructive process can include the formation of microcracks or surface damage and surface corrosion by ultrasonic processing nozzles or kinetic energy, or by the supply of a chemical etching solution. This destructive process can occur without actually reducing the thickness of the layer on the selected die. The thickness of the vulnerable part of the layer can vary depending on the output of the ultrasonic processing, the flow rate of the chemical, the processing time, etc.

[0043] In some embodiments, the process includes forming a surface monolayer on the selected die. The surface monolayer can change the hydrophilicity of the surface and affect the interaction between the polishing fluid and the surface of the layer on the selected die. The initial removal rate of the selected die can be higher or lower than that of the die without treatment until the surface monolayer is completely removed, for example, depending on the degree of hydrophilicity or hydrophobicity.

[0044] In some embodiments, the process includes forming a surface layer of a different material on the layer of the selected die. For example, applying a specific oxidizing agent can oxidize the surface of the metal layer (such as a Cu or W layer) of the selected die into different states that may have a higher or lower removal rate with a given CMP polishing fluid. The surface of a specific die can also be treated with an inhibitor or accelerator to change the initial CMP removal rate in the next step.

[0045] Overall, for any of the above techniques, the processing conditions can depend on the removal amount delta required for each die. The removal amount delta can be determined from CMP upstream processes such as the etching depth of each die, post-CMP die measurement information obtained from previous wafers polished in the same CMP process, in-situ measurement information from CMP (such as the remaining film thickness obtained for each die on the current wafer), or a combination of these information. Once the removal amount delta for a specific die is determined, the processing conditions such as processing time, chemical flow rate, temperature, UV intensity, curing time, etc. can be determined accordingly.

[0046] After the treatment, the substrate undergoes a chemical mechanical polishing process (206) at a polishing station.

[0047] The above techniques describe the treatment before the CMP polishing step, but the treatment can also be applied during the CMP polishing process, for example, by removing the substrate from the polishing station, before continuing with the CMP polishing. Further, this treatment can be performed After prior to polishing at a subsequent polishing station, buffing station, or rework station.

[0048] Although FIG. 2 shows the processing applied to individual dies, the processing can also be applied to a specific area of the substrate so as to cover multiple dies. For example, the processing can be applied to a specific radius of a circle, a cone, or other shapes. This processing can also be applied to specific features of interest within the die.

[0049] The hardware for performing the CMP pre-treatment can be installed in the wafer polishing unload / loading area or in the path between two CMP polishing chambers. The unique advantage of mounting such CMP pre-treatment hardware with dual heads for each polishing chamber system is that while one wafer is being processed before entering the polishing chamber, another wafer is being polished inside the chamber, so that the execution of the CMP pre-treatment for the CMP throughput is minimized.

[0050] As used herein, the term "substrate" can include, for example, a product substrate (e.g., including multiple memory or processor dies), a test substrate, a bare substrate, and a gate substrate. The substrate can be at various stages of integrated circuit manufacturing. For example, the substrate can be a bare wafer or can include one or more deposited and / or patterned layers. The term "substrate" can include circular disks or rectangular sheets.

[0051] The above polishing apparatus and method can be applied to various polishing systems. The polishing pad, the carrier head, or both can move to provide relative motion between the polishing surface and the substrate. For example, the platen may orbit rather than rotate. The polishing pad may be a circular (or other shaped) pad fixed to the platen. Some aspects of the endpoint detection system can be applied to a linear polishing system, such as when the polishing pad is a continuous belt or an open reel belt that moves linearly. The polishing layer may be a standard (e.g., polyurethane with or without fillers) abrasive, a soft material, or a fixed abrasive material. The term relative position is used. That is, it should be understood that the polishing surface and the substrate can be held in a vertical or other direction.

[0052] The various systems and processes described herein, or control of some of them, can be implemented in a computer program product that is stored on one or more non-transitory machine-readable storage media and includes instructions executable on one or more processing devices. The systems described herein, or portions thereof, can be implemented as an apparatus, method, or electronic system that includes one or more processing devices and memory for storing executable instructions for performing the operations described herein.

[0053] Although this specification contains many details of particular embodiments, these should not be construed as limiting the scope of the invention or the scope of the claims, but rather as descriptions of features that may be specific to particular embodiments of a particular invention. The particular features described herein in the context of separate embodiments can also be implemented in combination in a single embodiment. Conversely, the various features described in the context of a single embodiment can also be implemented separately in multiple embodiments or in any suitable sub-combination. Furthermore, although features have been described above as functioning in a particular combination and may initially have been claimed as such, in some cases one or more features from the claimed combination can be excised and the claimed combination may be directed to a sub-combination or a variation of a sub-combination.

[0054] Similarly, although operations are shown in the drawings in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in a sequential order, or that all of the illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Furthermore, the separation of the various system modules and components in the embodiments described above should not be understood as requiring such separation in all embodiments, and it should be understood that the program components and systems described may generally be integrated into a single software product or packaged into multiple software products.

[0055] Particular embodiments of the subject matter have been described. Accordingly, other embodiments are within the scope of the following claims.

Claims

1. A method for processing a substrate, comprising: selectively dispensing a processing fluid onto the substrate die by die; after dispensing the processing fluid, chemically mechanically polishing the substrate using a polishing liquid; wherein the processing fluid changes the polishing rate of the chemical mechanical polishing in one or more selected dies to which the processing fluid is applied as compared to one or more remaining dies to which the processing fluid is not applied.

2. The method according to claim 1, wherein selectively dispensing the processing fluid includes one or more of drop-on-demand printing, spin-on coating, spray-on, or screen printing.

3. The method according to claim 2, wherein selectively dispensing includes flowing the processing fluid through a mask.

4. The method according to claim 2, wherein selectively dispensing includes selectively ejecting droplets of the processing fluid onto the substrate.

5. The method according to claim 2, wherein selectively dispensing includes disposing the processing fluid across all the dies on the substrate and curing the processing fluid in the one or more selected dies.

6. The method according to claim 1, further comprising curing the processing fluid before chemically mechanically polishing the substrate.

7. The method according to claim 1, including forming a protective film with the processing fluid that reduces the polishing rate in the selected dies as compared to the remaining dies.

8. The method according to claim 1, wherein the processing fluid damages the layer to be polished so as to increase the polishing rate in the selected dies as compared to the remaining dies.

9. The method according to claim 1, wherein the processing fluid forms a single layer that adjusts the hydrophilicity of the selected dies as compared to the remaining dies.

10. The method according to claim 1, including measuring the thickness of a layer at a plurality of positions corresponding to a plurality of dies on the substrate and determining the selected dies based on the thickness.

11. A system, comprising: A processing station including a dispenser for supplying a processing fluid onto a substrate for each die, wherein the processing fluid changes a polishing rate at one or more selected dies to which the processing fluid is applied compared to one or more remaining dies to which the processing fluid is not applied in a subsequent chemical mechanical polishing, the processing station, A chemical mechanical polishing station including a supply port for dispensing a polishing liquid, A substrate transfer robot for transferring the substrate from the processing station to the chemical mechanical polishing station A system comprising.

12. The system according to claim 11, wherein the dispenser comprises one or more of a drop ejection printer, a spin-on coater, a spray-on coater, or a screen printer.

13. The system according to claim 11, wherein the processing station includes a mask arranged to prevent the processing fluid from being applied to the remaining dies.

14. The system according to claim 11, wherein the processing station includes an energy source for curing the processing fluid.

15. The system according to claim 14, further comprising a control system configured to be coupled to the energy source and selectively activate the energy source so that the processing fluid is cured at the selected die.

16. The system according to claim 11, wherein the dispenser comprises a transducer that applies acoustic energy to the processing fluid and causes ultrasonic treatment of a layer on the substrate at the selected die.

17. The system according to claim 11, further comprising a control system configured to acquire data indicating the selected die and control the dispenser to apply the processing fluid at the selected die.

18. The system according to claim 17, wherein the control system is configured to receive a plurality of thickness measurements for a plurality of positions corresponding to a plurality of dies on the substrate and determine the selected die based on the plurality of thickness measurements.

19. The system according to claim 18, comprising an in-line or stand-alone measurement system for providing the plurality of thickness measurements on the substrate.

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