JP2007088463A - Method for forming a laminated polishing pad using laser ablation - Google Patents

Abstract

A method of forming a polishing pad for chemical mechanical polishing that is less cumbersome, time consuming, and can be produced cost-effectively.
An upper polishing pad is laminated to a sub-polishing pad to form a laminated pad, and the laminated pad is transferred to a laser ablation station including a laser, and a laser beam from the laser is modulated to modulate the upper polishing pad and A method is provided that includes modifying both the sub-polishing pads and inspecting the laser ablated laminated pad from a particular reference point without moving the laminated pad.
[Selection] Figure 1

Description

  The present invention relates to polishing pads used for chemical mechanical planarization (CMP), and more particularly to a method of forming a laminated polishing pad using laser ablation.

  In the fabrication of integrated circuits and other electronic devices, multiple layers of conductors, semiconductors and insulating materials are deposited on or removed from the surface of a semiconductor wafer. Thin layers of conductors, semiconductors and insulating materials can be deposited by a variety of deposition techniques. Common deposition techniques in modern processing include physical vapor deposition (PVD), also known as sputtering, chemical vapor deposition (CVD), plasma enhanced chemical vapor deposition (PECVD), and electrochemical plating (ECP).

  As the material layers are sequentially deposited and removed, the top surface of the substrate may become non-planar across its surface and require planarization. Flattening the surface or “polishing” the surface is a process of removing material from the wafer surface to form a substantially uniform plane. Planarization is useful for removing undesired surface topography as well as surface defects such as rough surfaces, agglomerated materials, crystal lattice damage, scratches and contaminated layers or materials. Planarization is also useful in forming features on a substrate by removing excess deposited material used to fill the feature, providing a uniform surface for the next level of metallization and processing. It is.

  Chemical mechanical planarization, or chemical mechanical polishing (CMP) is a common technique used to planarize substrates such as semiconductor wafers. In conventional CMP, a wafer carrier or polishing head is attached to a carrier assembly and placed in contact with a polishing pad in a CMP apparatus. The carrier assembly provides a controllable pressure to the substrate to press the wafer against the polishing pad. The pad is moved (eg, rotated) relative to the substrate by an external driving force. At the same time, a chemical composition (“slurry”) or other fluid medium is flowed over the substrate and between the wafer and the polishing pad. Thus, the wafer surface is polished in a manner that selectively removes material from the substrate surface by the chemical and mechanical action of the pad surface and slurry.

  Rutherford et al., US Pat. No. 6,007,407, discloses a polishing pad (“stacked pad”) for performing CMP, formed by stacking two separate layers. The upper polishing layer is attached to a lower layer or “subpad” formed from a material suitable to support the polishing layer. The subpad typically has a higher compressibility than the polishing layer and a lower stiffness than the polishing layer, and essentially serves as a support “cushion” for the polishing layer. Typically, the two layers are bonded with a pressure sensitive adhesive (“PSA”).

Unfortunately, the manufacture of laminated pads is somewhat cumbersome, time consuming and prohibitive because it requires multiple steps on multiple machines to form the various features of the pad. For example, the following is an overview of an exemplary method of forming a conventional stacked pad including radial and XY groove patterns and computer numerical control (“CNC”) holes.
A) Radial lathe Machine a radial groove in the upper pad.
2. Machine the cut-off groove in the upper pad.
3. Inspect the quality of the groove.
4). Move pad to XY lathe.
B) XY linear groove 5. Align the radial grooved pad with the YX table.
6). Machining the XY groove pattern.
7). Inspect the groove quality.
8). Transfer pad to subpad stack.
C) Subpad lamination 9. The upper polishing pad is laminated to the sub-polishing pad (“laminated pad”).
10. Align and cut the laminated pad.
11. Inspect alignment and cut quality.
12 Move the laminated pad to CNC hall operation.
D) CNC hall 13. The composite pad is aligned to confirm that the XY pattern matches the hole alignment structure.
14 Punch the CNC hall.
15. Inspect alignment and hole quality.
16. Move the pad to final inspection packaging and inventory control operations.

  As can be seen from the above, the conventional method requires a number of steps and machines, and thus additional time and expense, to produce a laminated polishing pad. Accordingly, what is needed is a method of forming a polishing pad for chemical mechanical polishing that is less cumbersome, takes less time, and can be manufactured cost effectively.

  One aspect of the present invention is a method of manufacturing a polishing pad for chemical mechanical polishing, wherein an upper polishing pad is stacked on a sub polishing pad to form a stacked pad, and the stacked pad is a laser including a laser. A method is provided that includes transferring to an ablation station, modulating the laser beam from the laser to modify both the upper polishing pad and the sub-polishing pad, and inspecting the laser ablated stacked pad.

  One aspect of the present invention is a method of manufacturing a composite polishing pad for chemical mechanical polishing, wherein an upper polishing pad is laminated on a sub polishing pad with an adhesive layer to form a laminated pad, Transfer to laser ablation station containing laser, modulate laser beam from laser to modify upper polishing pad, adhesive layer and sub-polishing pad from specific reference point, and laser ablation without moving laminate pad A method is provided that includes inspecting a laminated pad from a particular reference point.

  A method of manufacturing a laminated pad by pulsed laser ablation using energy modulation and focus control is provided. In order to provide an enormous combination of radial grooves, XY grooves and holes that can be machined with one machine tool, laminated pads can be attached to a table and lasers can be attached to an XY plotter. In addition, the method provides the ability to machine complex patterns (eg, integrated windows) without an alignment tool. Energy modulation and focus control allow the laser to cut or process laminated materials of various compositions. As the laser cuts through each individual layer, the energy is modulated and the laser is focused to meet the cutting requirements of the next layer in the stack. Advantageously, the entire machining and final pad cutting operation can be accomplished with one machine tool. In other words, the modulated pulsed laser can perform all machining steps, eliminating the need for work-specific machining equipment. Also, the reduction in process results in work consolidation and simplification. In addition, the present invention eliminates the alignment problem between the cutting machine tool and the machining machine tool by using one machine tool, eliminates or supports the subpad edge sealing, and eliminates the wear problem of the machine tool. It offers further advantages, including elimination, reduction of maintenance costs and spare parts, and elimination of manual errors by using CNC equipment.

  Referring to the drawings, FIG. 1 illustrates an exemplary method of forming the laminated pad of the present invention. In particular, a laminated polishing pad 10 is shown that includes a base layer 12 (“sub polishing pad”) and an upper polishing layer 14 (“upper polishing pad”). Base layer 12 may be made of, for example, a polymer impregnated felt (eg, Suba IV ™ from Rohm and Haas Electronic Materials CMP, Newark, Del.) Or a filled polymer sheet. Further, in an exemplary embodiment, the upper abrasive layer 14 may be a polymer impregnated felt, a microporous material, a filled polymer sheet (eg, IC1000 ™ from Rodel, Newark, Del.) Or an unfilled texture. Can be made of attached polymer.

  The polishing pad 10 also includes an adhesive layer 20 that bonds the base layer 12 to the polishing layer 14. In an exemplary embodiment, the adhesive layer 20 is an inexpensive and readily available thermoplastic or thermoset material. In particular, the adhesive layer 20 is a material selected from the following groups of adhesives: polyolefins, ethylene vinyl acetate, polyamides, polyesters, polyurethanes, polyvinyl chloride and epoxy resins. In addition, the adhesive layer 20 may be a pressure sensitive adhesive. In some cases, the polishing pad 10 can also include additional adhesive 22 attached to the exposed platen end of the base layer 12.

  In addition, the polishing pad 10 can include an opening (not shown) having a window secured therein. The window is permanently secured in the opening in one exemplary embodiment (“integrated window”), while in another embodiment, it is removably secured to the opening. The window is transparent to the wavelength of light used to perform optical in situ measurements of the substrate being planarized (eg, wafer W). Typical wavelengths are in the range of 190-3500 nm.

  In addition, the method of the present invention includes a laser 5 that outputs a laser beam 7 that is modulated to modify the various polishing layers of the laminated pad. In other words, the laser beam 7 can modify both the upper polishing pad and the sub-polishing pad. In addition, the laser beam can modify the adhesive layer. Preferably, the pad is modified using a specific reference point on the polishing pad. In addition, the modified pads can be inspected using specific reference points without moving the stacked pads.

  Note that the laser 5 can be moved in any direction (ie, x, y, or z plane) to accommodate as many designs or structures as desired. In the present invention, it is not necessary to move a support member (not shown), for example a table for supporting the polishing pad in the laser machining station, relative to the laser 5. Conversely, the laser 5 can be moved to achieve, for example, the desired removal of the selected abrasive layer or adhesive, independent of the movement of the support member. In addition, an inert gas may be supplied from a nozzle (not shown) to reduce oxygen at the cutting surface and reduce combustion or carbonization at the edge of the cutting surface. A laser beam may also be used with a high pressure water jet to reduce the heat that would be generated by conventional laser cutting. Thermal laser ablation is preferred.

In this embodiment, the laser 5 used for micromachining can be a pulsed excimer laser, YAG or CO ² laser with a relatively low duty cycle. In some cases, the laser 5 may be a continuous laser that is shuttered (ie, the pulse width (time) is very short compared to the time between pulses). A typical laser is Exitech's MicroAblator ™. Note that the excimer laser has a lower average power than other larger lasers, but the excimer laser has a very high peak power. The peak intensity and fluence of the laser is
Intensity (Watt / cm ² ) = Peak power (W) / Focal area (cm ² )
Fluence (Joule / cm ² ) = Laser pulse energy (J) / Focal area (cm ² )
And the peak power is
Peak output (W) = pulse energy (J) / pulse duration (s)
Sought by.

  Several key parameters should be considered during laser ablation. An important parameter is the selection of the wavelength of the minimum absorption depth. This should allow high energy deposition in small volumes for rapid and complete ablation. Another parameter is a short pulse duration to maximize peak power and minimize heat transfer to the surrounding work material. This combination reduces the response amplitude. Another parameter is the pulse repetition rate. If this speed is too low, energy not used for ablation leaves the ablation zone and allows cooling. Ablation is more efficient if the residual heat is retained by the high pulse repetition rate and the heat transfer time is limited. In addition, more incident energy is sent to the ablation and there is less loss to the surrounding work material and the environment. Yet another important parameter is beam quality. Beam quality is measured by lightness (energy), focusability and homogeneity. If the beam energy cannot be sent correctly and efficiently to the ablation region, it will not be used effectively. Furthermore, if the beam is not of a controlled size, the ablation area will be larger than desired and the sidewalls will be excessively tilted.

  In addition, special attention must be paid to the plume if the removal is by transpiration. A plume is a plasma-like material consisting of molecular fragments, neutral particles, free electrons and ions, and chemical reaction products. The plume is responsible for optical absorption and scattering of the incident beam and can condense and adhere to the surrounding work material and / or beam emitting optics. Usually, the ablation site is cleaned with a pressurized inert gas such as nitrogen or argon.

  Referring now to FIG. 2, a flowchart illustrating the method of the present invention is shown. In step S <b> 1, the upper polishing pad 14 is laminated on the sub polishing pad 12 using the adhesive 20 to form the laminated pad 10. Note that the laminated pad 10 may include additional adhesive 22. Next, in step S2, the laminated pad 10 is moved to the pulse laser machining station. In step S3, the laminated pad 10 is machined and cut using a specific reference point without moving the pad to another station. Here, the laminated pad 10 is subjected to laser ablation under modulation and focus control to create various features of the laminated polishing pad. For example, a CNC ablation can be formed in the laminated polishing pad using laser ablation. This method can also be used to groove a top polishing pad that includes a pad with a window in it. Other features of the present invention include laser ablating various upper polishing pads and sub-polishing pads to form a composite polishing pad, and laser ablating the edges of the sub-polishing pads to seal the sub-polishing pad. Laser ablation to flatten the polishing pad, and laser ablation to form a composite polishing pad having at least three polishing layers. Thermal laser ablation is preferred.

  Next, in step S4, the modified laminated polishing pad 10 is inspected for defects and scratches. Preferably, the inspection is performed using a specific reference point without moving the laminated polishing pad 10. Thereafter, in step S5, the modified laminated polishing pad 10 is moved to final inspection packaging and inventory management work.

  Accordingly, the present invention is a method of manufacturing a polishing pad for chemical mechanical polishing, wherein an upper polishing pad is stacked on a sub polishing pad to form a stacked pad, and the stacked pad includes a laser including a laser. A method comprising transferring to an ablation station is provided. In addition, the present invention includes modulating the laser beam from the laser to modify both the upper polishing pad and the sub-polishing pad, and inspecting the laser ablated laminated pad.

  Referring now to FIG. 3, a CMP apparatus 20 using the laser ablated polishing pad of the present invention is shown. The apparatus 20 includes a wafer carrier 22 for holding or pressing a semiconductor wafer 24 against a polishing platen 26. The polishing platen 26 includes the laminated polishing pad 10 of the present invention. As discussed above, the pad 10 has a lower layer 12 that faces the surface of the platen 26 and an upper polishing pad 14 that is used with a chemical polishing slurry to polish the wafer 24. Note that although not shown, means for supplying an abrasive fluid or slurry can be used with this apparatus. The platen 26 usually rotates about its central axis 27. In addition, the wafer carrier typically rotates about its central axis 28 and translates the surface of the platen 26 by the translation arm 30. It should be noted that although only one wafer carrier is shown in FIG. 3, the CMP apparatus may have two or more wafer carriers spaced circumferentially around the polishing platen. In addition, a transparent hole 32 is provided in the platen 26 and overlaps the window 4 of the laminated pad 10. Thus, the transparent hole 32 provides access to the surface of the wafer 24 through the window 4 for accurate end point detection during polishing of the wafer 24. That is, a laser spectrophotometer 34 is provided below the platen 26, and this laser spectrophotometer projects a laser beam 36 to accurately detect the end point during polishing of the wafer 24, and the transparent hole 32 and window. Pass through 4 and return.

FIG. 2 shows an embodiment of the inventive method for forming a laminated pad. It is a flowchart which shows the embodiment of the method of manufacturing the laminated pad of this invention. It is a figure which shows the CMP system which uses the polishing pad of this invention.

Claims (10)

A method of manufacturing a polishing pad for chemical mechanical polishing,
Laminating an upper polishing pad on a sub-polishing pad to form a laminated pad;
Transferring the laminated pad to a laser ablation station containing a laser;
Modulating the laser beam from the laser to modify both the upper polishing pad and the sub-polishing pad, and inspecting the laser ablated stacked pad.   The method of claim 1, further comprising laser ablating CNC holes in the polishing pad.   The method of claim 1, further comprising providing a groove in the upper polishing pad including a window therein.   The method of claim 1, further comprising laser ablating the various upper and lower polishing pads to form a composite polishing pad.   The method of claim 1, further comprising laser ablating an edge of the sub-polishing pad to seal the sub-polishing pad.   The method of claim 1, further comprising flattening the polishing pad. A method of manufacturing a composite polishing pad for chemical mechanical polishing,
Laminating the upper polishing pad to the sub-polishing pad by an adhesive layer to form a laminated pad;
Transferring the laminated pad to a laser ablation station containing a laser;
Modulating a laser beam from the laser to modify the upper polishing pad, the adhesive layer and the sub-polishing pad from a specific reference point, and the laser ablated laminated pad without moving the laminated pad A method comprising inspecting from a specific reference point.   The method of claim 7, further comprising laser ablating a CNC hole in the polishing pad.   The method of claim 7, further comprising laser ablating an edge of the sub-polishing pad to seal the sub-polishing pad.   The method of claim 7, further comprising laser ablating at least another adhesive layer in the polishing pad.

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