ENDPOINT WINDOW WITH CONTROLLED TEXTURE SURFACE
A chemical mechanical polishing pad window having a controlled texture surface comprising repeated patterned features. The window results in an improved endpoint detection and in situ rate monitoring by providing consistent values of the ISRMmax-min characteristic over the lifetime of a CMP pad. Also provided is a chemical mechanical polishing pad with the inventive window.
This application claims priority under 35 U.S.C. § 119 of U.S. Provisional Application Ser. No. 63/141,368, filed Jan. 25, 2021, entitled “ENDPOINT WINDOW WITH CONTROLLED TEXTURE SURFACE,” which is hereby incorporated by reference.
TECHNICAL FIELDThis disclosure generally relates to chemical mechanical planarization, and more specifically to an endpoint window with a controlled texture surface.
BACKGROUNDAn integrated circuit is typically formed on a substrate by the sequential deposition of conductive, semi-conductive, and/or insulative layers on a silicon wafer. A variety of fabrication processes require planarization of at least one of these layers on the substrate. For example, for certain applications (e.g., polishing of a metal layer to form vias, plugs, and lines in the trenches of a patterned layer), an overlying layer is planarized until the top surface of a patterned layer is exposed. In other applications (e.g., planarization of a dielectric layer for photolithography), an overlying layer is polished until a desired thickness remains over the underlying layer. Chemical mechanical planarization (CMP), which is sometimes alternatively referred to as chemical mechanical polishing, is one method of planarization. This planarization method typically involves a substrate being mounted on a carrier head. The exposed surface of the substrate is typically placed against a polishing pad on a rotating platen. The carrier head provides a controllable load (e.g., an applied force) on the substrate to push it against the rotating polishing pad. A polishing liquid, such as slurry with abrasive particles, can also be disposed on the surface of the polishing pad during polishing.
In some cases, a CMP pad may include a window to enable in situ monitoring of the polishing process. For example, a laser light may be passed through the window, reflected off of the material being removed via CMP, and the intensity of the reflected light may be used to determine when the etching process is complete. When a reflective material (e.g., a metal) is removed, the amount of light reflected from the wafer decreases. This decrease is observed by monitoring the intensity of the laser light returning through the window over time and can be used to detect the endpoint of an etching process (i.e., to determine when the reflective material is completely removed from the wafer's surface).
SUMMARYThis disclosure recognizes that reliable CMP endpoint detection requires a window with a finely tuned initial percent transmission to laser light and that this transmission should remain as stable as possible throughout the life of the pad. Previous windows for CMP pads fail to satisfy requirements for accurately and reliably monitoring polishing processes, resulting in process inefficiencies and decreased yields. Previous windows in CMP pads are susceptible to significant changes in transmission during use. For example, the diamond conditioner used as part of the CMP workflow may scratch and/or remove a portion of the window surface, thereby altering the transmission of light through the window. This disclosure recognizes that when the window is thinned after continued use and/or conditioning, the window is more likely to deform during use, resulting in undesired measurement variability, which may be quantified by an increased ISRMmax-min characteristic (see
This disclosure provides an improved window for endpoint detection and in situ rate monitoring. This unique CMP pad window provides a solution to problems of previous CMP pad window technologies including those described above. The CMP pad window described in this disclosure has a controlled texture surface comprising repeated patterned features, for example, a unique texture on at least one surface of the window. For example, a controlled texture surface comprising repeated patterned features (e.g. micropatterned texture) may be provided on the bottom surface of a CMP pad window to diffuse light passing therethrough. The repeating pattern provides a light diffusing texture. The repeated patterned features can be prepared using injection molding, laser cutting, and/or any other machining or surface patterning technique(s). The new CMP pad window provides reliable and reproducible removal rate monitoring and endpoint detection. This disclosure also includes new methods for preparing a surface texture on materials used for CMP pad windows. These methods facilitate more precise tuning of window texture and the transmission of light through the window, both of which are critical for providing reliable and improved performance. Methods may involve injection molding, machining (e.g., CNC machining with an appropriate diameter endmill bit, laser machining), and/or any other appropriate technique.
In an embodiment, a window for a chemical mechanical planarization (CMP) pad includes (e.g., is formed of) a material that is transmissive to light. A first surface of the window has repeated patterned texture or features. The first surface may correspond to (e.g., face the same direction as) a bottom surface of the CMP pad which does not contact a substrate being planarized during a CMP process using the CMP pad.
A measured ISRMmax-min characteristic of the window may be less than a threshold value (e.g., 1%, 0.5%, or 0.3%). The ISRMmax-min characteristic may be a difference between a maximum percent intensity and a minimum percent intensity measured across a surface of a wafer comprising a reflective material. The ISRMmax-min characteristic of the window may change by less than the threshold amount (e.g., 5%, 10%, 25%, or 50%) following use of the CMP pad for chemical mechanical planarization of one or more wafers for a period of time (e.g., at an end of a useful lifetime of the CMP pad).
The repeated patterned features are configured to diffuse light passing through the window. The repeated patterned features may include regularly spaced raised features. The window may have a width and length that is less than the width. The width and the length may characterize physical dimensions of the window (e.g., whether the window has a rectangular, rounded rectangular, ovular, or any other shape). As one example, the repeated patterned features may include a first set of regularly spaced raised features parallel to a direction of the width of the window and a second set of regularly spaced raised lines at an angle (e.g., in a range from 20° to 60°) relative to the first set of regularly spaced raised features. As another example, the repeated patterned features may include a crosshatch texture with a first set of regularly spaced features in the first surface at a first angle (e.g., 45°) relative to a direction of the width of the window and a second set of regularly spaced features in the first surface at a second angle (e.g., 90°) relative to the first set of lines, wherein the first angle is different than the second angle.
In another embodiment, a chemical mechanical planarization (CMP) pad includes a top surface which contacts a substrate being planarized during a CMP process using the CMP pad, a bottom surface opposite the top surface, and a window that allows light to pass between a top side associated with the top surface and a bottom side associated with the bottom surface. The window includes a material transmissive to the light. A first surface of the window has repeated patterned texture or features. The first surface may correspond to (e.g., face the same direction as) the bottom surface of the CMP pad which does not contact a substrate being planarized during a CMP process using the CMP pad.
A measured ISRMmax-min characteristic of the window may be less than a threshold value (e.g., 1%, 0.5%, or 0.3%). The ISRMmax-min characteristic may be a difference between a maximum percent intensity and a minimum percent intensity measured across a surface of a wafer comprising a reflective material. The ISRMmax-min characteristic of the window may change by less than the threshold amount (e.g., 5%, 10%, 25%, or 50%) following use of the CMP pad for chemical mechanical planarization of one or more wafers for a period of time (e.g., at an end of a useful lifetime of the CMP pad).
The repeated patterned texture or features are configured to diffuse light passing through the window. The repeated patterned texture may include regularly spaced raised features. The window may have a width and length that is less than the width. The width and the length may characterize physical dimensions of the window (e.g., whether the window has a rectangular, rounded rectangular, ovular, or any other shape). As one example, the repeated patterned features may include a first set of regularly spaced raised features parallel to a direction of the width of the window and a second set of regularly spaced raised lines at an angle (e.g., in a range from 20° to) 60° relative to the first set of regularly spaced raised features. As another example, the repeated patterned features may include a crosshatch texture with a first set of regularly spaced features in the first surface at a first angle (e.g., 45°) relative to a direction of the width of the window and a second set of regularly spaced features in the first surface at a second angle (e.g., 90°) relative to the first set of lines, wherein the first angle is different than the second angle.
To assist in understanding the present disclosure, reference is now made to the following description taken in conjunction with the accompanying drawings, in which:
It should be understood at the outset that, although example implementations of embodiments of the disclosure are illustrated below, the present disclosure may be implemented using any number of techniques, whether currently known or not. The present disclosure should in no way be limited to the example implementations, drawings, and techniques illustrated below. Additionally, the drawings are not necessarily drawn to scale.
Chemical Mechanical Planarization System with Endpoint Detection
An example polishing pad 200 is illustrated in
The window 202 is generally disposed in or over an aperture in the CMP pad 200. As illustrated in the side-view depiction of
The difference 154a between the maximum and minimum intensity along the surface of the wafer 104 is a relatively small value for the new window 202 described in this disclosure. For example, the difference 154a for windows 202 described in this disclosure may be less than a threshold value of about 1%, 0.5%, 0.1%, or the smaller (in units of percent light transmission). This difference 154a may be stable throughout the life cycle of the window 202 (see
Returning to
A slurry 108 may be provided on the surface of the polishing pad 200 before and/or during chemical mechanical planarization. The slurry 108 may be any appropriate slurry for planarization of the wafer type and/or layer material to be planarized (e.g., to remove a silicon oxide layer from the surface of the wafer 104). The slurry 108 generally includes a fluid and abrasive and/or chemically reactive particles. Any appropriate slurry 108 may be used. For example, the slurry 108 may react with one or more materials being removed from a surface being planarized. A conditioner 110 is a device which is configured to condition the surface of the polishing pad 200. The conditioner 110 generally contacts the surface of the polishing pad 200 and removes a portion of the top layer of the polishing pad 200 to improve its performance during chemical mechanical planarization. For example, the conditioner 110 may roughen the surface of the polishing pad 200.
As described in greater detail below, the uniquely textured window 202 described in this disclosure reduces or eliminates changes in the transmission of light through the window following contact with the slurry 108, the wafer 104, and/or the conditioner 110. For example, a bottom surface of the window 202 may have a repeated patterned feature, such as the repeating patterned textures illustrated in
Example Polishing Pad with Improved window
The CMP pad 200 may be formed of a thermoset material, such as a polyurethane, or any other appropriate material. The top surface 204 may include grooves or any other appropriate structure or pattern for facilitating CMP (see expanded view 210). For instance, grooves may facilitate the transport of polished material and/or any other products of the CMP process away from the surface 204 of the CMP pad 200 and the wafer 104 being planarized. The CMP pad 200 includes a window 202 on or in an aperture of the CMP pad 200. The window 202 may be formed of a thermoset or a thermoplastic material, such as a polyurethane, polyethylene terephthalate glycol, a cyclic olefin copolymer, or any other appropriate material (i.e., a material that is appropriately transmissive to light (see
An expanded top-side view 210 of the window 202 shows a top surface 220 of the window 202. The top surface 220 may have a unique texture, as described in greater detail with respect to
An expanded bottom-side view 212 of the window 202 shows a bottom surface 222 of the window 202. The bottom surface 222 may have a controlled texture comprising repeated patterned features for diffusing light passing through the window 202. For example, the bottom surface 222 may have a texture that includes repeated patterned features and optionally a roughened texture (see
In an example embodiment, the texture 304 through which light passes for in situ rate monitoring/endpoint detection includes a repeated pattern with regularly spaced features 306 (e.g., peaks of troughs/cups 352 of
An optional second set of features 310 may be at an angle 314 (e.g., 20° to) 90° relative to the first set of features 306. The second set of features 310 can be straight, curved, or any other appropriate shape or design, for example, as described with respect to
Still referring to
The patterned features shown in
The depth of machined and/or injection molded features (see
In some embodiments, separate pieces may be prepared, such that one piece includes the top surface 220 and another piece includes the bottom surface 222.
As also recognized herein, it is important to have a consistently low value of the ISRMmax-min characteristic that does not change significantly over the life of a CMP pad. This cannot be achieved by achieving the target transmission range alone but also requires further improved properties of the CMP window. For example, at least certain of the control windows shown in
The new window samples (samples 1-4 and A-D of
At step 704, a second surface 222 is prepared on the opposite face of the piece from step 702. If injection molding was used to prepare the first textured surface 220 at step 702, the second textured surface 222 may be prepared during the same injection molding process (e.g., using mold 502 of
At step 706, the window 202 from step 704 is disposed in or on an aperture in a CMP pad 200, such that light passing through the aperture also passes through the window 202. The window 202 may be attached to the CMP pad 200 using an adhesive (e.g., a pressure-sensitive adhesive) or without an adhesive (e.g., using ultrasonic welding or any other appropriate technique). For example, the window 202 may be attached with an adhesive or via welding to a top pad portion or a subpad portion of the CMP pad 200. In some embodiments, the window 202 is chemically bonded to the CMP pad 200 (e.g., in the presence of heat and/or appropriate adhesion promoters).
As an illustration of the attachment of the inventive window to the polishing pad, the following procedure may be used. A recess or pocket may be formed in the top pad using CNC or like method. The dimension of the recess will align with the dimension of the window to be installed. The dimensions of the recess are thus variable, but the recess does not extend the entire thickness of the top pad. In other words, the recess does not form an aperture through the top pad. A subpad is then laminated, or otherwise adhered to the top pad. A hole is then punched through the top pad and the sub pad at the recess, whereas the dimension of the hole is such that a ledge is formed by the remaining top pad material and the underlying subpad material. The window is then installed in the recess, on top of the hole, forming an optical detection port, or window, in the pad. This illustrates one embodiment of installing an inventive window into a polishing pad.
At step 804, a second window piece (e.g., piece 404 of
At step 806, the first piece with the first textured surface 220 is disposed on (e.g., attached to) the second piece with the second textured surface 222. The two pieces are generally combined such that the first surface 220 is exposed and faces a first direction (e.g., towards the top of the window 202) and the second surface 222 is exposed and faces a second direction opposite the first direction (e.g., towards the bottom of the window 202). The first and second pieces may be attached using an adhesive (e.g., a pressure-sensitive adhesive) or without an adhesive to form the window 202. In some cases, the first and second pieces may be chemically bonded to form window 202 (e.g., in the presence of heat and/or appropriate adhesion promoters).
At step 808, the window 202 from step 806 is disposed in or on an aperture in a CMP pad 200, such that light passing through the aperture also passes through the window 202. The window 202 may be attached to the CMP pad 200 using an adhesive (e.g., a pressure-sensitive adhesive) or without an adhesive (e.g., using ultrasonic welding or any other appropriate technique). For example, the window 202 may be attached with an adhesive or via welding to a top pad portion or a subpad portion of the CMP pad 200. In some embodiments, the window 202 is chemically bonded to the CMP pad 200 (e.g., in the presence of heat and/or appropriate adhesion promoters).
This example demonstrates the performance of the inventive windows compared to windows not having a controlled texture comprising repeated pattern features (a repeated patterned texture).
Four different windows were evaluated for performance using the change in the ISRMmax-min characteristic measured after a break-in period and again at the end of the pad life. The end of the pad life is defined as when the pad wear was such that 20% of the initial groove depth was remaining. The four windows were A) IC1010 pad with window, a hard thermoset polyurethane with a hardness of about 70 Shore D, commercially available from Rohm and Haas Electronic Materials; B) E6088 pad with a soft thermoplastic polyurethane having a hardness of about 55 Shore D, commercially available from CMC Materials Inc.; C) E6088 pad with an inventive window having controlled, repeated pattern texture from CNC machining, a thermoplastic polyurethane having a hardness of 75 Shore D; and D) E6088 pad having an inventive window with controlled, repeated pattern texture from injection molding, a thermoplastic polyurethane having a hardness of 75 Shore D. Windows A) and B) did not have a controlled texture surface comprising repeated patterned features.
All pads described above were given identical break-in period comprising 30 minutes of conditioning with deionized water, using an A2813 conditioner from 3M, at 5 lb. downforce. Following the break-in period, the ISRMmax-min characteristic was measured under identical conditions for each of the windows while polishing copper wafers, using a copper CMP polishing slurry, at 2.5 psi downforce and 80 rpm platen speed. The end-point detection was started about 20 seconds after the start of the polishing, and the record consisted of about 60 traces. The ISRMmax-min characteristic was calculated for the four windows and is shown below in the Table. A second ISRMmax-min characteristic measurement was taken on the same pads at the end of pad life. The ISRMmax-min characteristic was again calculated and is shown below in TABLE 1.
As can be seen in the Table above, the change in ISRMmax-min from the post break-in period to the end of pad life was dramatically different for the inventive windows when compared to the windows of commercial pads.
Modifications, additions, or omissions may be made to the systems, apparatuses, and methods described herein. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. The methods may include more, fewer, or other steps. Additionally, steps may be performed in any suitable order. Additionally, operations of the systems and apparatuses may be performed using any suitable logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set.
Herein, “or” is inclusive and not exclusive, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A or B” means “A, B, or both,” unless expressly indicated otherwise or indicated otherwise by context. Moreover, “and” is both joint and several, unless expressly indicated otherwise or indicated otherwise by context. Therefore, herein, “A and B” means “A and B, jointly or severally,” unless expressly indicated otherwise or indicated otherwise by context.
The scope of this disclosure encompasses all changes, substitutions, variations, alterations, and modifications to the example embodiments described or illustrated herein that a person having ordinary skill in the art would comprehend. The scope of this disclosure is not limited to the example embodiments described or illustrated herein. Moreover, although this disclosure describes and illustrates respective embodiments herein as including particular components, elements, feature, functions, operations, or steps, any of these embodiments may include any combination or permutation of any of the components, elements, features, functions, operations, or steps described or illustrated anywhere herein that a person having ordinary skill in the art would comprehend. Furthermore, reference in the appended claims to an apparatus or system or a component of an apparatus or system being adapted to, arranged to, capable of, configured to, enabled to, operable to, or operative to perform a particular function encompasses that apparatus, system, component, whether or not it or that particular function is activated, turned on, or unlocked, as long as that apparatus, system, or component is so adapted, arranged, capable, configured, enabled, operable, or operative. Additionally, although this disclosure describes or illustrates particular embodiments as providing particular advantages, particular embodiments may provide none, some, or all of these advantages.
The use of the terms “a” and “an” and “the” and similar referents in the context of describing the invention (especially in the context of the following claims) are to be construed to cover both the singular and the plural, unless otherwise indicated herein or clearly contradicted by context. The terms “comprising,” “having,” “including,” and “containing” are to be construed as open-ended terms (i.e., meaning “including, but not limited to,”) unless otherwise noted. Recitation of ranges of values herein are merely intended to serve as a shorthand method of referring individually to each separate value falling within the range, unless otherwise indicated herein, and each separate value is incorporated into the specification as if it were individually recited herein. The use of any and all examples, or exemplary language (e.g., “such as”) provided herein, is intended merely to better explain the disclosure and does not pose a limitation on the scope of claims.
Claims
1. A window for a chemical mechanical planarization (CMP) pad, the window comprising a material transmissive to light, wherein a first surface of the window has a controlled texture surface comprising repeated patterned features.
2. The window of claim 1, wherein the first surface corresponds to a bottom surface of the CMP pad which does not contact a substrate being planarized during a CMP process using the CMP pad.
3. The window of claim 1, wherein the repeated patterned features are configured to diffuse light passing through the window.
4. The window of claim 1, wherein the repeated patterned features comprise regularly spaced raised features.
5. The window of claim 4, wherein the repeated patterned features comprise a crosshatch pattern.
6. The window of claim 4, wherein the repeated patterned features comprise rounded ridges.
7. The window of claim 5, wherein the rounded ridges are randomly roughened.
8. The window of claim 2, wherein a second surface opposite the first surface corresponds to a top surface, the top surface is capable of contacting a substrate being planarized during a CMP process using the CMP pad, wherein the top surface has a roughened texture corresponding to an average surface roughness in a range from about 1 to about 50 micrometers.
9. The window of claim 1, wherein:
- the window has a width and length that is less than the width, wherein the width and the length characterize physical dimensions of the window; and
- the repeated patterned features comprise: a first set of regularly spaced raised features parallel to a direction of the width of the window; and a second set of regularly spaced raised lines at an angle relative to the first set of regularly spaced raised features.
10. The window of claim 1, wherein:
- the window has a width and length that is less than the width wherein the width and the length characterize physical dimensions of the window; and
- the repeated patterned features comprise a crosshatch texture comprising: a first set of regularly spaced features in the first surface at a first angle relative to a direction of the width of the window; and a second set of regularly spaced features in the first surface at a second angle relative to the first set of lines, wherein the first angle is different than the second angle.
11. A chemical mechanical planarization (CMP) pad comprising:
- a top surface which contacts a substrate being planarized during a CMP process using the CMP pad;
- a bottom surface opposite the top surface; and
- a window that allows light to pass between a top side of the CMP pad associated with the top surface and a bottom side of the CMP pad associated with the bottom surface, the window comprising a material transmissive to light, wherein a first surface of the window has repeated patterned features.
12. The CMP pad of claim 11, wherein the first surface of the window faces the same direction as the bottom surface of the CMP pad which does not contact the substrate being planarized during a CMP process using the CMP pad.
13. The CMP pad of claim 11, wherein the repeated patterned features are configured to diffuse light passing through the window.
14. The CMP pad of claim 11, wherein the repeated patterned features comprise regularly spaced raised features.
15. The CMP pad of claim 11, wherein the repeated patterned features comprise a crosshatch pattern.
16. The CMP pad of claim 11, wherein the repeated patterned features comprise rounded ridges.
17. The CMP pad of claim 16, wherein the rounded ridges are randomly roughened.
18. The CMP pad of claim 11, wherein a second surface opposite the first surface corresponds to a top surface, the top surface is capable of contacting a substrate being planarized during a CMP process using the CMP pad, wherein the top surface has a roughened texture corresponding to an average surface roughness in a range from about 1 to about 50 micrometers.
19. The CMP pad of claim 11, wherein:
- the window has a width and length that is less than the width, wherein the width and the length characterize physical dimensions of the window; and
- the repeated patterned features comprise: a first set of regularly spaced raised features parallel to a direction of the width of the window; and a second set of regularly spaced raised lines at an angle relative to the first set of regularly spaced raised features.
20. The CMP pad of claim 11, wherein:
- the window has a width and length that is less than the width wherein the width and the length characterize physical dimensions of the window; and
- the repeated patterned features comprise a crosshatch texture comprising: a first set of regularly spaced features in the first surface at a first angle relative to a direction of the width of the window; and a second set of regularly spaced features in the first surface at a second angle relative to the first set of lines, wherein the first angle is different than the second angle.
- a window as disclosed herein.
Type: Application
Filed: Jan 24, 2022
Publication Date: Jul 28, 2022
Inventors: Paul Andre LEFEVRE (Portland, OR), Dustin Miller (Beaverton, OR), Gary Snider (Oswego, IL), Carlos Barros (West Chicago, IL), Anthony Galto (Glen Ellyn, IL)
Application Number: 17/582,667