Patent ID: 12233505

Like reference symbols in the various drawings indicate like elements.

DETAILED DESCRIPTION

Friction-based monitoring of chemical mechanical polishing has been proposed. For example, a sensor include a flexible plate, e.g., a leaf spring, on which a piece of polishing pad is mounted. The sensor can measure the strain on a flexible plate to generate a signal representative of the friction from the substrate. However, such sensor can be bulky. For example, the vertical length of the plate may present form factor problems given the space available in the platen. Moreover, installation of the sensor in the polishing pad can be cumbersome. However, a capacitive sensor can take up less space, can generate a signal representative from which a direction of friction can be determined, and/or can be integrated into a polishing pad for ease of installation. In addition, a capacitive sensor can provide increased precision and accuracy in friction measurements. Contacts for the sensor can be placed on the bottom of the polishing pad, such that electrical connection to other circuitry can be performed easily.

FIGS.1A and1Billustrate an example of a polishing apparatus100. The polishing apparatus100includes a rotatable disk-shaped platen120on which a polishing pad110is situated. The platen is operable to rotate about an axis125. For example, a motor121can turn a drive shaft124to rotate the platen120.

The polishing pad110can be a two-layer polishing pad with an outer polishing layer112and a softer backing layer114. The polishing layer112can be formed to have a plurality of plateaus116separated by grooves118(seeFIG.2). The grooves118in the polishing surface of the polishing layer112can serve to carry a polishing liquid.

The polishing apparatus100can include a port130to dispense the polishing liquid132, such as slurry, onto the polishing pad110.

The polishing apparatus can also include a polishing pad conditioner170to abrade the polishing pad110to maintain the polishing pad110in a consistent abrasive state. In addition, conditioning improves consistency of friction between the substrate and the polishing pad. The polishing pad conditioner170can include a conditioner head172that permits the conditioner head172to sweep radially over the polishing pad110as the platen120rotates. The conditioner head172can hold a conditioner disk176, e.g., a metal disk having abrasives, e.g., diamond grit, on the lower surface. The conditioning process tends to wear away the polishing pad110over time, until the polishing pad110needs to be replaced.

The polishing apparatus100includes at least one carrier head140. The carrier head140is operable to hold a substrate10against the polishing pad110. The carrier head140can have independent control of the polishing parameters, for example pressure, associated with each respective substrate.

In particular, the carrier head140can include a retaining ring142to retain the substrate10below a flexible membrane144. The carrier head140also includes a plurality of independently controllable pressurizable chambers146defined by the membrane, and which can apply independently controllable pressures to associated zones on the flexible membrane144and thus on the substrate10. Although only three chambers146are illustrated inFIG.1for ease of illustration, there could be one or two chambers, or four or more chambers, e.g., five chambers.

The carrier head140is suspended from a support structure150, e.g., a carousel or a track, and is connected by a drive shaft152to a carrier head rotation motor154so that the carrier head can rotate about an axis155. Optionally the carrier head140can oscillate laterally, e.g., on sliders on the carousel150or track; or by rotational oscillation of the carousel itself. In operation, the platen is rotated about its central axis125, and the carrier head is rotated about its central axis155and translated laterally across the top surface of the polishing pad.

While only one carrier head140is shown, more carrier heads can be provided to hold additional substrates so that the surface area of polishing pad110may be used efficiently.

The polishing apparatus100also includes an in-situ monitoring system200. In particular, the in-situ monitoring system200generates a time-varying sequence of values that depend on the friction of the surface of layer on the substrate10that is being polished. The in-situ monitoring system200includes a sensor202which generates a signal that depends on the frictional coefficient of a localized, discrete area of the substrate10. Due to relative motion between the substrate10and the sensor202, measurements can be taken at different locations on the substrate10.

The CMP apparatus100can also include a position sensor180, such as an optical interrupter, to sense when the sensor202is beneath the substrate10. For example, the optical interrupter180could be mounted at a fixed point opposite the carrier head140. A flag182is attached to the periphery of the platen. The point of attachment and length of flag182is selected so that it interrupts the optical signal of sensor180while the sensor202sweeps beneath substrate10. Alternatively or in addition, the CMP apparatus100can include an encoder to determine the angular position of platen.

If needed, sense circuitry250can be used to receive an analog signal, e.g., a voltage or current level, from the sensor202, e.g., on wires252. The sense circuitry250can be located in a recess in the platen120, or could be located outside the platen120and be coupled to sensor202through a rotary electrical union129. In some implementations, the drive and sense circuitry receives multiple analog signals from the sensor202, and converts those analog signals into a serial digital signal.

A controller190, such as a general purpose programmable digital computer, receives the signal from the sensing circuitry250or directly from the sensor202. The controller190can include a processor, memory, and I/O devices, as well as an output device e.g., a monitor, and an input device, e.g., a keyboard. The signals can pass from the sensor202to the controller190through the rotary electrical union129. Alternatively, the sense circuitry250could communicate with the controller190by a wireless signal.

The controller190can be configured to convert the signals from the sensor202into a series of values indicative of the coefficient of friction of the substrate10. As such, some functionality of the controller190can be considered part of the in-situ monitoring system200.

Since the sensor202sweeps beneath the substrate with each rotation of the platen, information on the friction is accumulated in-situ and on a continuous real-time basis (once per platen rotation). The controller190can be programmed to sample measurements when the substrate generally overlies the sensor202(as determined by the position sensor180). As polishing progresses, the coefficient of friction of the surface of the substrate changes, and the sampled signals can vary with time. The time varying sampled signals may be referred to as traces. The measurements from the monitoring systems can be displayed on the output device during polishing to permit the operator of the device to visually monitor the progress of the polishing operation.

In operation, the CMP apparatus100can use the in-situ monitoring system200to determine when the bulk of the filler layer has been removed and/or to determine when the underlying stop layer has been substantially exposed. In particular, when an underlying layer is exposed, there should be a sudden change in the coefficient of friction. This change can be detected, e.g., by detecting changes in slope of the trace, or by detecting that the amplitude or slope of the trace passes a threshold value. Detection of exposure of the underlying layer can trigger the polishing endpoint and halt polishing.

The controller190may also be connected to the pressure mechanisms that control the pressure applied by carrier head140, to carrier head rotation motor174to control the carrier head rotation rate, to the platen rotation motor121to control the platen rotation rate, or to slurry distribution system130to control the slurry composition supplied to the polishing pad. In addition, the computer190can be programmed to divide the measurements from the sensor202from each sweep beneath the substrate into a plurality of sampling zones194, to calculate the radial position of each sampling zone, and to sort the amplitude measurements into radial ranges. After sorting the measurements into radial ranges, information on the film thickness can be fed in real-time into a closed-loop controller to periodically or continuously modify the polishing pressure profile applied by a carrier head in order to provide improved polishing uniformity.

Now referring toFIGS.2and3, the sensor202can includes a pad portion210having a top surface212configured to contact the substrate, and at least one pair of capacitive sensors220positioned below and on opposite sides of the pad portion210. The sensor202can include a lower body240, which can be a printed circuit board, and a polymer body230. Gaps between the lower body240and the polymer body230define the spaces between opposite electrodes of the capacitive sensors220.

The pad portion210includes a substrate contacting portion214, the upper surface of which provides the top surface212to contact the polishing pad. The substrate contacting portion214can have a lateral cross-section (seeFIG.3) which is square, circular, or some other suitable shape. The substrate contacting portion214can have a width W of about 0.2-0.5 mm, and a height H of about 0.2-1 mm. The height H of the upper portion214can be greater than the width W of the substrate contacting portion214.

The pad portion210can optionally also include a lower portion216that extends laterally outward on all sides of the substrate contacting portion214; the lower portion216that has a lateral dimension that is greater than the lateral dimension of the substrate contacting portion214. The lower portion216can extend entirely across the capacitive sensors220, and can extend entirely across the polymer portion240. The lower portion216, if present, can have a height less than the height of the upper portion, e.g., about 0.1-0.5 mm.

In some implementations, the lower portion216extends to and contacts the remainder of the polishing pad110. The lower portion216can be secured to the polishing layer112, e.g., with an adhesive. Alternatively, the lower portion216can be integrally joined to the remainder of the polishing pad110, i.e., without an adhesive, seam or similar discontinuity.

In some implementations, there is a gap between the side edges of the lower portion216and the polishing pad110.

In general, the substrate contacting portion214is formed of a material that does not adversely impact the polishing process, e.g., it should be chemically compatible with the polishing environment and sufficiently soft as to avoid scratching or damaging the substrate. The pad portion210can be the same material as the polishing layer112of the polishing pad110, e.g., a polyurethane. Alternatively, the pad portion210can be a different material than the polishing layer112, e.g., an acrylate.

The pad portion210can be supported on the polymer body230. The bottom surface of the pad portion210can be secured to the top surface of the polymer body230, e.g., by an adhesive or by fabricating the pad portion210directly on the polymer body230.

A plurality of projections232extend from the bottom of a main body234of the polymer body230to contact the lower body240, e.g., the printed circuit board. Recesses between the projections232define gaps236between the polymer body230and the lower body240. The polymer body230can be secured to the lower body240, e.g., by adhesive. The gaps236can partially underlie the substrate contacting portion214. For example, the width of the projection232can be less than the width W of the substrate contacting portion214. Alternatively, the gaps236can be laterally spaced so that they do not directly underlie the substrate contacting portion214. For example, the width of the projection232can be greater than the width W of the substrate contacting portion214.

The polymer body230can be silicone material, e.g., polydimethylsiloxane (PDMS). The polymer body230can be formed by a molding process, e.g., injection molding into the form having the projections232extending from a main body234.

The interior horizontal surfaces of the recesses can be coated with a conductive material to form electrodes238. The sidewall surfaces of the recesses (i.e., the sides of the projections) need not be coated.

As noted above, the lower body240can be a printed circuit board. Electrodes242are formed on a top surface of the lower body240, and conductive contacts244can be formed on the bottom surface of the lower body240. In addition, the lower body240can include conductive lead lines246, e.g., extending through the thickness of the lower body, to electrically connect each electrode242with a corresponding conductive contact244.

In some implementations, electrical contacts254can be formed on the top surface of the platen120(seeFIG.1A). These electrical contacts254are connected by the wires252to the sense circuitry250and/or controller190. Thus, when the polishing pad110is installed on the platen120, each conductive contact244makes an electrical connection to a corresponding electrical contact254. This permits the electrical connection of the sensor202to other components, e.g., the sense circuitry250and/or controller190, to be made quickly and easily. When the polymer body230is secured to the lower body240, each electrode238on the polymer body230is aligned with a corresponding electrode242on the lower body240with a gap236between. A set of two electrodes238,242with a gap236therebetween provides a capacitive pressure sensor220. In brief, if the space between the electrodes238,242changes, this will result in a change in capacitance and thus a change in a signal sensed by circuitry coupled to the sensor220, e.g., through the conductive contact244.

In a rest state, e.g., when not being compressed by pressure from a substrate, the gap236can have a height of 10 to 50 microns. The electrodes238,242can have a lateral dimension of 0.5 to 1 mm. The electrodes238,242and the gap238can be square, circular, or another suitable lateral cross-sectional shape.

A pair of capacitive pressure sensors220a,220bpositioned on opposing sides of a midline of the substrate contacting portion214can provide a shear sensor. In particular, frictional drag on the substrate contacting portion214from the substrate will tend to apply a torque on the pad portion210. This will cause a differential in pressure on the two sensors220a,220b. For example, if the substrate10is moving rightward across the polishing pad110, friction on the pad portion210will tend to increase pressure on the right-hand capacitive pressure sensor220a, and reduce pressure on the left-hand capacitive pressure sensor220b. Conversely, if the substrate10is moving leftward across the polishing pad110, friction on the pad portion210will tend to reduce pressure on the right-hand capacitive pressure sensor220a, and increase pressure on the left-hand capacitive pressure sensor220b.

To detect the amount of shear, and thus measure the friction between the substrate and the substrate contacting portion214, a differential between the signals from the two sensors220a,220bcan be calculated. For example, the signal from the right-hand capacitive pressure sensor220acan be subtracted from the signal from the left-hand capacitive pressure sensor220b.

As shown inFIG.3, in some implementations, the sensor202includes two pairs of capacitive pressure sensors220(i.e., four capacitive pressure sensors). The two sensors of each pair are positioned on opposing sides of a midline of the upper portion214. In addition, the two pairs can be arranged to measure shear along perpendicular axes. With this configuration, the in-situ monitoring system200can generate a measurement indicative of a total frictional force, e.g., as a square root of the sum of the squares of the shear measured in the two perpendicular directions. This calculation can be performed by the controller190. In some implementations, the sensor202includes three or more pairs of capacitive pressure sensors220, with each pair of capacitive pressure sensors220including two capacitive pressure sensors on opposite sides of the pad portion210. For example, althoughFIG.3illustrates empty spots diagonally above and below the pad portion210, these spots could be occupied by additional capacitive pressure sensors.

Different substrate layers have different coefficients of friction between the deposited layers and the substrate contacting portion214. This difference in coefficients of friction means that different deposited layers will generate different amounts of frictional force, and thus different amounts of shear on the sensor202. If the coefficient of friction increases, the shear will increase. Similarly, if the coefficient of friction decreases, the shear will decrease. When deposited layer16has been polished down to expose the patterned layer14, the shear will change to reflect the different coefficient of friction between the material of the deposited layer14and the polishing pad110. Consequently, a computing device, such as the controller190, can be used to determine the polishing endpoint by monitoring the changes in shear, and thus friction, detected by the in-situ monitoring system.

Referring toFIG.4, the controller can be used to control the polishing system100. An implementation of a computer program for chemical mechanical polishing begins with the initiation of a chemical mechanical polishing process on the substrate10(410). During the polishing process, the computer90receives input from the sensors202(420). Input from the individual capacitive sensors220can be received simultaneously or serially, an can be received continuously or periodically. The controller190(or the circuitry250) receives the signals from the capacitive sensors220and determines the shear experienced by the sensor202(430). The controller190monitors the signal for changes in shear. When a change in shear indicates a desired polishing endpoint, the controller190ends the polishing process (440).

In some implementation, the controller190detects changes in the slope of the shear data to determine a polishing endpoint. The controller190can also monitor for shear signal smoothing to determine a polishing endpoint. Alternatively, the controller190consults a database containing pre-determined endpoint shear values based on the deposited layers used in order to determine the occurrence of an endpoint.

As noted above, the controller190can sort the measurements from the sensor202into radial ranges. The polishing parameters can then be adjusted based on the measurements, e.g., to provide improved uniformity. When the measurements indicate that an underlying layer has become exposed in a particular range, the polishing parameters can be adjusted to reduce the polishing rate in that range. Machine parameters that are independently controllable for the different radial ranges of the substrate, can then be controlled based on the measurements for the respective radial ranges.

In particular, the measurements may then be used for real-time closed loop control of the pressure applied by the carrier head140. For example, if the controller190detects that the friction is changing in one radial zone, e.g., at the edge of the substrate, this can indicate that the underlying layer is being exposed, e.g., the underlying layer is being exposed first at the edge of the substrate. In response, the controller190can cause the carrier head140to reduce the pressure applied at the edges of the substrate. In contrast, if the controller190has not detected a change in friction in another radial range, e.g., a center portion of the substrate, this can indicate that the underlying layer is not yet exposed. The controller190can cause the carrier head140to maintain the pressure applied at the center of the substrate.

Referring toFIG.1B, the in-situ monitoring system can include multiple sensors202. For example, the in-situ monitoring system can include multiple sensors202placed at substantially the same distance from but at equal angular intervals around the axis of rotation of the platen. As another example, there can be sensors202positioned at different radial positions on the polishing pad110. For example, the sensors202can be arranged in 3×3 grid. Increasing the number of sensors permits an increase in the sampling rate from the substrate10.

To fabricate the sensor202, the lower body240can be fabricated, e.g., as a printed circuit board having the electrodes242. The polymer body230can be fabricated by injection molding. The electrodes238can be deposited in the recesses between the projections232, e.g., by a sputtering process. The polymer body230is aligned and secured to the lower body240to form the capacitive sensors220.

The assembly of the polymer body230and lower body240can then be placed into an aperture in the backing layer114. Then the polishing layer112can be fabricated on top of the assembly and the backing layer. For example, the polishing layer112can be fabricated by a 3D printing process, e.g., by ejection and curing of droplets of pad precursor material. This permits the pad portion210and the remainder of the polishing layer112to be fabricated together as one continuous piece, i.e., without an adhesive, seam or similar discontinuity.

Alternatively, the polishing layer112could be fabricated separately, and then placed on the assembly and the backing layer114, and secured, e.g., by adhesive.

Alternatively, the pad portion210can be secured to the assembly of the polymer body230and lower body240separately. Thereafter, the sensor202can be installed in the polishing pad110, e.g., by being inserted into an aperture in the polishing pad110and secured, e.g., by adhesive.

The monitoring system can be used in a variety of polishing systems. Either the polishing pad, or the carrier head, or both can move to provide relative motion between the polishing surface and the substrate. The polishing pad can be a standard (e.g., polyurethane with or without fillers) rough pad, a soft pad, or a fixed-abrasive pad.

The functional operations described in this specification, e.g., for the controller and/or sense circuitry, can be implemented in digital electronic circuitry, or in computer software, firmware, or hardware, including the structural means disclosed in this specification and structural equivalents thereof, or in combinations of them. Embodiments can be implemented as one or more computer program products, i.e., one or more computer programs tangibly embodied in an information carrier, e.g., in a non-transitory machine readable storage medium or in a propagated signal, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple processors or computers. A computer program (also known as a program, software, software application, or code) can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a standalone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program does not necessarily correspond to a file. A program can be stored in a portion of a file that holds other programs or data, in a single file dedicated to the program in question, or in multiple coordinated files (e.g., files that store one or more modules, sub programs, or portions of code). A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

The processes and logic flows described in this specification can be performed by one or more programmable processors executing one or more computer programs to perform functions by operating on input data and generating output. The processes and logic flows can also be performed by, and apparatus can also be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application specific integrated circuit).

A number of embodiments have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of this disclosure. For example:The top surface of the polymer body need not be coplanar with the top surface of the backing layer.AlthoughFIG.2illustrates the polishing pad as having two layers, the polishing pad could be a single layer pad. A recess could be formed in the back surface of the polishing pad and the sensor inserted into the recess.The polishing pad could be built up around the sensor by a 3D printing process. For example, the assembly of the polymer body and lower body could be placed on a print stage, and the lower portion of the polishing pad could be fabricated around the assembly, e.g., by selectively ejecting droplets of precursor material into areas around but not on the assembly. This can build layers until the top of the pad material is coplanar with the top of the assembly. After this point, droplets of precursor material could be ejected across both the previously formed layers and the assembly, thus forming the pad portion and the upper portion of the remainder of the polishing pad.The technique of fabrication of the polishing pad by 3D printing around the assembly can be used for a single-layer pad, in which case the same material can be used throughout the pad, or for a multi-layer pad, in which case a different precursor or different curing technique can be used to form the lower portion (and thus the backing layer) of the polishing pad around the assembly.

Accordingly, other embodiments are within the scope of the following claims.