Edge-exposure tool with an ultraviolet (UV) light emitting diode (LED)

Various embodiments of the present application are directed towards an edge-exposure tool with a light emitting diode (LED), as well as a method for edge exposure using a LED. In some embodiments, the edge-exposure tool comprises a process chamber, a workpiece table, a LED, and a controller. The workpiece table is in the process chamber and is configured to support a workpiece covered by a photosensitive layer. The LED is in the process chamber and is configured to emit radiation towards the workpiece. A controller is configured to control the LED to expose an edge portion of the photosensitive layer, but not a center portion of the photosensitive layer, to the radiation emitted by the LED. The edge portion of the photosensitive layer extends along an edge of the workpiece in a closed path to enclose the center portion of the photosensitive layer.

BACKGROUND

The integrated circuit (IC) manufacturing industry has experienced exponential growth over the last few decades. As ICs have evolved, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component that can be created) has decreased. Developments in the evolution of ICs include photolithography. Photolithography is a technology for transferring a geometric pattern from a photomask or photoreticle to a substrate.

DETAILED DESCRIPTION

According to a photolithography process, a photoresist layer is formed covering an front side of a wafer by a spin coating process. Radiation is generated and passed through a photomask or photoreticle to pattern the radiation. The photoresist layer is exposed to the patterned radiation, and is subsequently developed. The exposure chemically changes a portion of the photoresist layer upon which the patterned radiation impinges to transfer a pattern of the patterned radiation to the photoresist layer. Depending upon the type of photoresist (e.g., positive or negative) used for the photoresist layer, the development removes either the chemically changed portion of the photoresist layer, or a portion of the photoresist layer that was not chemically changed, thereby developing the pattern in the photoresist layer.

A challenge with the photolithography process is that the spin coating process forms the photoresist layer by dispensing a liquid photoresist onto a center of the wafer while the wafer is rotating about the center. Because the wafer is rotating, centrifugal force moves the liquid outward to an edge of the wafer. Ideally, the photoresist would evenly distribute over the wafer, such that the photoresist layer has a substantially uniform thickness. However, in reality, the photoresist builds up at the edge of the wafer, such that the photoresist layer has an increased thickness at the edge of the wafer relative to the center of the wafer. Further, the photoresist wraps around the edge of wafer to a back side of the wafer. The increased thickness of the photoresist layer may lead to, for example, exposure variation between the center of the wafer and the edge of the wafer, and/or may lead to poor control over critical dimensions of the pattern at the edge of the wafer. Further, the edge wrapping may lead to, for example, contamination of process tools used during the photolithography process and during subsequent processing.

A solution to the challenge is edge bead removal (EBR) in which an edge portion of the photoresist layer at or near the edge of the wafer, but not at a center portion of the photoresist layer, is removed. EBR comprises wafer edge exposure (WEE) in which the edge portion is exposed to radiation and subsequently developed to remove the edge portion from the front side of the wafer. A challenge with WEE is that the radiation is generated by a mercury-xenon lamp, which is costly to acquire, costly to operate, costly to maintain, and has a relatively short lifespan. Further, the mercury-xenon lamp is remote from a process tool in which the exposure is performed due to, inter alia, its large size and complexity, such that a radiation guide (e.g., a fiber optic cable) transfers radiation from the mercury-xenon lamp to the process tool. Further yet, the mercury-xenon lamp is unable to instantly turn on and off, such that a shutter gates radiation generated by the mercury-xenon lamp. The radiation guide and the shutter further add to the cost and complexity of the mercury-xenon lamp.

In view of the foregoing, various embodiments of the present application are directed towards an edge-exposure tool with a light emitting diode (LED), as well as a method for edge exposure using a LED. In some embodiments, the edge-exposure tool comprises a process chamber, a workpiece table, a LED, and a controller. The workpiece table is in the process chamber and is configured to support a workpiece covered by a photosensitive layer. The LED is in the process chamber and is configured to emit radiation towards the workpiece. A controller is configured to control the LED to expose an edge portion of the photosensitive layer, but not a center portion of the photosensitive layer, to the radiation emitted by the LED. The edge portion of the photosensitive layer extends along an edge of the workpiece in a closed path to enclose the center portion of the photosensitive layer.

By using the LED for edge exposure, costs are low. For example, the LED has a low acquisition cost, a low operating cost, and a low maintenance cost due its simplified structure relative to a mercury-xenon lamp. Further, the LED has a long lifespan relative to a mercury-xenon lamp. Further, the LED is in the process chamber, such that the LED does not depend on a costly and complex radiation guide. Further, the LED may be changed between an ON state and an OFF state nearly instantly, such that the LED does not depend on a costly and complex shutter. Further, the LED may be retrofitted into existing edge-exposure tools with minimal cost. For example, an open or close command for the shutter of a mercury-xenon lamp may be translated to an ON or OFF command for the LED with a low cost microcontroller.

With reference toFIG. 1, a cross-sectional view100of some embodiments of an LED-based edge-exposure tool102is provided. As illustrated, a process chamber104houses a workpiece table106and a LED housing108. In some embodiments, a temperature within the process chamber104, a pressure within process chamber104, gas concentrations within the process chamber104, or any combination of the foregoing may be controlled and/or varied relative to an ambient environment of the process chamber104. The workpiece table106is configured to support a workpiece110on a support surface106sof the workpiece table106. Further, the workpiece table106is configured to rotate the workpiece110about a central axis C of the workpiece table106that is at a center of the support surface106sand that is orthogonal to the support surface106s. Such rotation may, for example, be achieved by an electric motor or some other mechanical device associated with the workpiece table106.

The workpiece110is covered with a photosensitive layer112. The photosensitive layer112may, for example, be or comprise photoresist or some other suitable photosensitive material. In some embodiments, the photosensitive layer112has a non-uniform thickness T increasing from the central axis C to an edge of the workpiece110. As seen hereafter, this may, for example, be due to the process performed to form the photosensitive layer112. In some embodiments, the workpiece110has a planar top layout that is circular (not visible within the cross-sectional view100). In some embodiments, the workpiece110is or comprises a semiconductor substrate. The semiconductor substrate may be, for example, a bulk monocrystalline silicon substrate, a silicon-on-insulator (SOI) substrate, a germanium substrate, a group III-V substrate, or some other suitable semiconductor substrate. Further, the semiconductor substrate may be, for example, a 300 millimeter wafer, a 450 millimeter wafer, or some other suitable wafer. In some embodiments, the workpiece110further comprises one or more additional layers and/or structures arranged over and/or stacked on the semiconductor substrate. For example, the workpiece110may comprise a plurality of semiconductor devices overlying and partially defined by the semiconductor substrate. As another example, the workpiece110may comprise the semiconductor devices, and may further comprise a back-end-of-line (BEOL) metallization stack overlying and electrically coupled to the semiconductor devices. The semiconductor devices may be or comprise, for example, metal-oxide-semiconductor (MOS) devices or some other suitable semiconductor devices.

The LED housing108accommodates and protects an LED114. In some embodiments, the LED housing108has a high thermal conductivity so as to dissipate heat generated by the LED114. For example, the LED housing108may be copper, aluminum, or some other suitable material with a high thermal conductive. A “high” thermal conductivity may, for example, be a material with a thermal conductivity exceeding about 200 watts per meter-kelvin (W/m K), about 300 W/m K, or about 400 W/m K. Heat reduces a life span of the LED114, such that dissipating heat generated by the LED114with the LED housing108may enhance a lifespan of the LED114. In some embodiments, the LED housing108is to the side of the workpiece table106and/or overlies an edge portion112eof the photosensitive layer112.

The edge portion112eof the photosensitive layer112is a portion of the photosensitive layer112at or near a sidewall edge of the workpiece110and extends in a closed path (not visible within the cross-sectional view100) to completely enclose a center portion112cof the photosensitive layer112. For example, the edge portion112emay have a ring-shaped top layout or some other suitable closed-path top layout. The center portion112cmay, for example, have a circular top layout (not visible within the cross-sectional view100) or some other suitable top layout. Further, the edge portion112emay, for example, be a portion of the photosensitive layer112within a distance D of a sidewall edge of the workpiece110, where the distance D is about 2-4 millimeters, about 3.5-4.0 millimeters, about 0.5-3.0 millimeters, about 0.5-2.5 millimeters, about 0.5-1.0 millimeters, or less than about 2 millimeters.

The LED114is configured to generate and emit radiation116towards the edge portion112eof the photosensitive layer112. The LED114may be, for example, a laser LED or some other suitable LED. The radiation116may be or comprise, for example, ultraviolet (UV) radiation, some other radiation that invokes a chemical change in the photosensitive layer112, or some other radiation suitable for edge exposure. As used herein, the UV radiation may be or comprise, for example, radiation with wavelengths between about 10-400 nanometers, about 200-400 nanometers, about 10-121 nanometers, about 10-200 nanometers, or about 300-450 nanometers. In some embodiments, a LED lens118neighbors the LED114and/or adjoins the LED housing108. The LED lens118may, for example, focus the radiation116on the edge portion112eof the photosensitive layer112, and/or may, for example, collimate the radiation116in route to the edge portion112eof the photosensitive layer112.

An LED driver120drives the LED114. For example, the LED driver120applies a voltage across the LED114, and regulates the flow of current through the LED114, to drive the LED114. Further, the LED driver120changes the LED114between an ON state and an OFF state, and sets an intensity of the LED114. The intensity of the LED114is proportional to the drive current for the LED114, such that the LED driver120increases the drive current to increase intensity and reduces the drive current to decrease intensity. The drive current for a given intensity may, for example, be determined using a lookup table or a mathematical function describing the relationship between drive current and intensity. In some embodiments, the LED driver120drives the LED114based on instructions from a controller122. For example, the LED driver120may receive an ON command and an OFF command from the controller122, and may respectively turn the LED114to the ON state and the OFF state in response to the commands. As another example, the LED driver120may receive an intensity setting from the controller122, and may drive the LED114with a current to achieve the intensity in response to the intensity setting. The LED driver120may, for example, be implemented by an electronic circuit, and may or may not have a microcontroller and/or a microprocessor.

The controller122controls the LED driver120and coordinates operations of the edge-exposure tool102. In some embodiments, the controller122is or comprises one or more electronic memories and one or more electronic processors. The one or more electronic processors may, for example, execute processor executable instructions on the one or more electronic memories to carry out functions of the controller122(described hereafter). Further, in some embodiments, the controller122is or comprises a microcontroller, an application-specific integrated circuit (ASIC), some other suitable electronic device(s) and/or circuit(s), or any combination of the foregoing. As used herein, a term (e.g., device or circuit) with a suffix of “(s)” may, for example, be singular or plural.

During use of the edge-exposure tool102, the workpiece110is placed on the workpiece table106. The controller122controls the workpiece table106to rotate the workpiece110. Further, while the workpiece110is rotating, the controller122controls the LED driver120to expose the edge portion112eof the photosensitive layer112to the radiation116without exposing a remainder of the photosensitive layer112to the radiation116. Such exposure continues until the edge portion112eof the photosensitive layer112is entirely exposed. The exposure chemically changes the edge portion112eof the photosensitive layer112, whereby the edge portion112emay be removed. For example, a chemical developer may be applied to the photosensitive layer112to remove the edge portion112eof the photosensitive layer112without removing the remainder of the photosensitive layer112.

By using the LED114for edge exposure, costs are low. For example, the LED114has low acquisition costs, low setup costs, low operating costs, and low maintenance costs due to its simplified structure. Further, the LED114has a long lifespan. Further, the LED114is in the process chamber104, such that the LED114does not depend on a costly and complex radiation guide. Further, the LED114may be changed between an ON state and an OFF state nearly instantly, such that the LED114does not depend on a costly and complex shutter.

In some embodiments, the LED114is continuously ON during edge exposure. In some of such embodiments, the controller122instructs the LED driver120when to turn the LED114to the ON state and when to turn the LED114to the OFF state. In some embodiments, an ON/OFF state of the LED114is pulse width modulated during exposure. For example, the ON/OFF state of the LED114has a 50% duty cycle (i.e., the ON/OFF time ratio is 1:1). As another example, the ON/OFF state of the LED114has a 20% duty cycle (i.e., the ON/OFF time ratio is 1:4). The pulse width modulation of the ON/OFF state of the LED114keeps the temperature of the LED114low and enhances a lifespan of the LED114relative to continuous ON exposure. In some of such embodiments, the LED driver120implements the pulse width modulation, and the controller122instructs the LED driver120when to begin the pulse width modulation and when to end the pulse width modulation. In other embodiments, the controller122implements the pulse width modulation and instructs the LED driver120when to turn the LED114to the ON state and when to turn the LED114to the OFF state.

In some embodiments, an intensity of the LED114is limited during edge exposure. Limiting the intensity of the LED114reduces a temperature of the LED114, which enhances a lifespan of the LED114relative to full intensity exposure. For example, where the LED114is continuously ON during exposure, limiting an intensity of the LED114to about 60-70%, about 65-70%, or about 50-80% may increase the lifespan of the LED114by about 3-4 times, about 2-6 times, or about 3.0-3.5 times. As another example, where the ON/OFF state of the LED114is pulse width modulated with a 50% duty cycle, and the intensity of the LED114is limited to about 60-70%, about 65-70%, or about 50-80%, the lifespan of the LED114may be increased by about 6-7 times, about 5-8 times, or about 6.5-6.8 times.

In some embodiments, the edge-exposure tool102is used with multiple different photosensitive materials, each having different exposure intensities. For example, the edge-exposure tool102may perform edge exposure on a first workpiece covered by a first photosensitive material having a 50% exposure intensity, and may be further perform edge exposure on a second workpiece covered by a second photosensitive material having a 70% or 85% exposure intensity. Further, in some embodiments, the intensity of the LED114is varied depending upon a photosensitive material being exposed (e.g., a material of the photosensitive layer112). In some embodiments, the controller122monitors the photosensitive material and instructs the LED driver120what intensity to use during exposure. Further, in some embodiments, the controller122maintains a lookup table122ltindexed by photosensitive material and describing an exposure intensity for each photosensitive material.

By varying the intensity of the LED114based on photosensitive material, a lifespan of the LED114may be enhanced. For example, when the intensity of the LED114is varied based on photosensitive material, and an ON/OFF state of the LED114is pulse width modulated, the lifespan of the LED114may, for example, be increased by about 6-9 times, about 7-8 times, or about 7.5-8.0 times.

Some photosensitive materials have high exposure intensities relative to other photosensitive materials. Operating the LED114at a high exposure intensity causes the LED114to operate at a high temperature, which reduces the lifespan of the LED114faster than when the LED114is operating at a low exposure intensity and hence a low temperature. Further, without varying the intensity of the LED114based on photosensitive material, the LED114operates at the highest exposure intensity for possible photosensitive materials to ensure each of the possible photosensitive materials is sufficiently irradiated. This is regardless of whether a photosensitive material being irradiated actually depends upon such a high exposure intensity. Therefore, for photosensitive materials with a low exposure intensity, the lifespan of the LED114is needlessly reduced. Further, varying the intensity of the LED114based on photosensitive material enhances the lifespan of the LED114.

While the foregoing focused on using the LED114within the edge-exposure tool102, the LED114may be used with other types of exposure tools. For example, the LED114may be used in an exposure tool in which radiation generated by the LED114passes through a photoreticle or photomask to a photosensitive layer to transfer a pattern of the photoreticle or photomask to the photosensitive layer.

With reference toFIG. 2, a graph200of some embodiments of the output of the LED114ofFIG. 1is provided. As illustrated, during edge exposure, an ON/OFF state of the LED114is pulse width modulated. For example, the LED114alternates between an ON state and an OFF state. In some embodiments, an ON time Tonof the LED114at each cycle is the same as an OFF time Toffof the LED114at each cycle (i.e., a duty cycle of the pulse width modulation is about 50%). In some embodiments, the ON time Tonof the LED114is different than the OFF time Toffof the LED114. For example, a ratio between the ON time Tonand the OFF time Toffmay be about 1:4, about 2:5, about 1:6, or about 3:7. In some embodiments, the OFF time Toffof the LED114is zero (i.e., the duty cycle of the pulse width modulation is about 100%).

With reference toFIG. 3, a view300of some embodiments of the lookup table122ltofFIG. 1is provided. As illustrated, the lookup table122lthas exposure intensities for N different photosensitive materials, where N is an integer value greater than one. As noted above, in some embodiments of the edge-exposure tool102, the intensity of the LED114ofFIG. 1is varied depending on photosensitive material used during edge-exposure.

With reference toFIG. 4, a top layout view400of some embodiments of the workpiece110and the photosensitive layer112after edge exposure and development using the edge-exposure tool102ofFIG. 1is provided. As illustrated, the edge portion112eof the photosensitive layer112(seeFIG. 1) has been removed, thereby leaving the center portion112cof the photosensitive layer112and partially uncovering the workpiece110.

In some embodiments, the workpiece110includes a notch110nfor coarse alignment of the workpiece110to the workpiece table106ofFIG. 1. Further, in some embodiments, the edge exposure exposes alignment-mark portions of the photosensitive layer112and/or a workpiece-id portion of the photosensitive layer112so these portions of the photosensitive layer112are removed during development. The alignment-mark portions of the photosensitive layer112are surrounded by the center portion112cof the photosensitive layer112and cover alignment marks402on the workpiece110. The alignment marks402may, for example, be used for fine alignment of a photoreticle or photomask to the workpiece110during subsequent photolithography processes. The workpiece-id portion of the photosensitive layer112is also surrounded by the center portion112cof the photosensitive layer112and covers an identifier (ID)404of the workpiece110.

With reference toFIG. 5A, a cross-sectional view500A of some more detailed embodiments of the edge-exposure tool102ofFIG. 1is provided. As illustrated, a workpiece table motor assembly502is configured to rotate the workpiece table106. The workpiece table motor assembly502is controlled by the controller122and may be or comprise, for example, and electric motor or some other suitable mechanical device. Further, the LED housing108is supported by a mechanical arm504. In some embodiments, the LED housing108is connected to a second LED lens506by a mounting structure508, and/or is mounted to the mechanical arm504by the mounting structure508.

The second LED lens506may, for example, focus the radiation116towards the edge portion112eof the photosensitive layer112, and/or may, for example, collimate the radiation116in route to the edge portion112e. In some embodiments, the LED lens118collimates the radiation116, while the second LED lens506focuses the radiation116towards the edge portion110eof the photosensitive layer112, or vice versa. In other embodiments, the LED lens118is omitted and the second LED lens506collimates the radiation116, and/or focuses the radiation116towards the edge portion112eof the photosensitive layer112.

An imaging structure510is to the side of the workpiece table106, and comprises an image sensor510i. The image sensor510iis configured to sense incident radiation across a light-receiving surface of the image sensor510i. Further, the image sensor510iunderlies the edge portion110eof the workpiece110. The image sensor510imay be or comprise, for example, a charge-coupled device (CCD) image sensor, a complementary metal-oxide-semiconductor (CMOS) image sensor, or some other type of image sensor.

In some embodiments, the image sensor510iprovides feedback used to maintain a desired intensity of the LED114. For a given drive current, an intensity of the LED114may gradually decrease from the desired intensity. Therefore, the drive current may be gradually increased to compensate for the gradual decrease in intensity based on feedback from the image sensor510i. For example, if the desired intensity is X and the sensed intensity is Y, which is less than X, the drive current may be increased until X equals Y. The decrease in the intensity may, for example, be due to an increase in a temperature of the LED114and/or an increase in a total ON time of the LED114. For a given drive current, an intensity of the LED114may also gradually increase from the desired intensity. Therefore, the drive current may be gradually decreased to compensate for the gradual increase in intensity based on feedback from the image sensor510i. For example, if the desired intensity is X and the sensed intensity is Y, which is greater than X, the drive current may be decreased until X equals Y. The increase in the intensity may, for example, be due to a decrease in the temperature of the LED114. In some embodiments, the LED driver120monitors the image sensor510iand varies the drive current (as described above) to compensate for variations in the intensity of the LED114without involvement from the controller122. In other embodiments, the controller122monitors the image sensor510iand instructs the LED driver120to vary the drive current (as described above) to compensate for variations in the intensity of the LED114.

In some embodiments, the image sensor510iis employed to optically locate the edge of the workpiece110to enhance alignment of the LED housing108to the edge. For example, the image sensor510imay be moved to a location laterally spaced away from the workpiece110, and may then be moved gradually towards a center of the workpiece table106until the edge of the workpiece110is optically detected with the image sensor510i.

With reference toFIG. 5B, a top layout view500B of some more detailed embodiments of the edge-exposure tool102ofFIG. 5Ais provided. As illustrated, the edge portion112eof the photosensitive layer112extends laterally in a closed path to enclose the center portion112cof the photosensitive layer112. For example, the edge portion112eof the photosensitive layer112may have a ring-shaped top layout or some other suitable closed-path top layout. Further, the alignment-mark portions112amof the photosensitive layer112and the workpiece-id portion112idof the photosensitive layer112are surrounded by the center portion112cof the photosensitive layer112. Also illustrated, the mechanical arm504is connected to an arm motor assembly512. The arm motor assembly512is controlled by the controller122. The arm motor assembly512may, for example, rotate the mechanical arm504and/or telescope the mechanical arm504to move the LED housing108over the workpiece110.

With reference toFIG. 6, a cross-sectional view600of some other more detailed embodiments of the edge-exposure tool102ofFIG. 1is provided. As illustrated, the imaging structure510is omitted and the LED housing108further accommodates and protects a temperature sensor602. The temperature sensor602may, for example, be a thermistor or some other suitable temperature sensor.

In some embodiments, the drive current of the LED114is varied as a temperature of the LED114varies so as to maintain the LED114at a desired intensity. For example, for a given drive current, an intensity of the LED114may decrease as the temperature of the LED114increases. Therefore, the drive current may be increased as the temperature of the LED114increases to compensate for the decrease in intensity. As another example, for a given drive current, an intensity of the LED114may increase as the temperature of the LED114decreases. Therefore, the drive current may be decreased as the temperature of the LED114decreases to compensate for the rise in intensity. The temperature of the LED114may, for example, be monitored with the temperature sensor602and the extent of the increase or decrease in drive current may, for example, determined using a lookup table or a mathematical function describing the relationship between drive current and temperature for a fixed intensity. In some embodiments, the LED driver120monitors the temperature of the LED114and varies the drive current (as described above) to compensate for variations in the intensity of the LED114without involvement from the controller122. In others embodiments, the controller122monitors the temperature of the LED114and instructs the LED driver120to vary the drive current (as described above) to compensate for variations in the intensity of the LED114.

In some embodiments, current flowing through the LED114is increased as a total ON time of the LED114increases so as to maintain the LED114at a desired intensity. For example, for a given drive current, an intensity of the LED114may decrease as the total ON time of the LED114increases. Therefore, the drive current may be increased as the total ON time of the LED114increases to compensate for the decrease in intensity. The total ON time of the LED114may, for example, be tracked by a timer and stored in flash memory or some other nonvolatile memory. The extent of the increase in drive current may, for example, determined using a lookup table or a mathematical function describing the relationship between drive current and total ON time for a fixed intensity. In some embodiments, the LED driver120monitors the total ON time of the LED114and increases the drive current (as described above) to compensate for variations in the intensity of the LED114without involvement from the controller122. In others embodiments, the controller122monitors the total ON time of the LED114(as described above) and instructs the LED driver120to vary the drive current (as described above) to compensate for variations in the intensity of the LED114.

With reference toFIG. 7, a cross-sectional view700of some other more detailed embodiments of the edge-exposure tool102ofFIG. 1is provided. As illustrated,FIG. 7is a variant ofFIG. 5Athat further includes the temperature sensor602ofFIG. 6. The temperature sensor602and/or the image sensor510imay, for example, be employed (as described with regard toFIGS. 5A and 6) to maintain an intensity of the LED114at a desired level as total ON time increases and as temperature of the LED114varies.

With reference toFIG. 8, a cross-sectional view800of some other more detailed embodiments of the edge-exposure tool102ofFIG. 1is provided. As illustrated,FIG. 8is a variant ofFIG. 7in which the controller122ofFIG. 7is replaced with both an exposure controller122eand an LED controller122l. As well be explained hereafter, the embodiments ofFIG. 8illustrate how to retrofit an edge-exposure tool to use the LED114in place of a lamp, such as, for example, a mercury-xenon lamp or some other suitable lamp.

The exposure controller122econtrols the LED controller122las if it is controlling a lamp. The LED controller122lcontrols the LED driver120based on commands received from the exposure controller122eby translating the received commands into commands that can be interpreted by the LED driver120, and subsequently providing the translated commands to the LED driver120. For example, a lamp may not be able to instantly change between an ON state and an OFF state, such that a shutter may be used with the lamp to gate radiation generated by the lamp. Further, the degree to which the shutter is open may be used to control the intensity at which photosensitive material is irradiated by the lamp. Therefore, the LED controller122lmay receive a shutter open command, a shutter close command, an illuminance up command, an illuminance down command, or any combination of the foregoing from the exposure controller122e. The shutter open and close commands may respectively be translated to an ON command and an OFF command by the LED controller122lsince the LED114can instantly or near instantly change between an ON state and an OFF state. The illuminance up and down commands may respectively be translated to a power increase command and a power decrease command by the LED controller122lsince the intensity of the LED114varies with power. The power increase and decrease commands may, for example, be implemented by the LED driver120by respectively increasing and decreasing drive current flowing through the LED114.

In view of the foregoing, it should be appreciated that when retrofitting an edge-exposure tool to use the LED114in place of a lamp, the exposure controller122edoes not have to be modified, thereby saving time and money. The LED controller122lrepresents a virtual shutter (i.e., simulates a shutter), and translates commands for the virtual shutter to commands for the LED114, such that the exposure controller122emanages the differences between the lamp and the LED114. Further, while not shown, it should be appreciated that the temperature sensor602and/or the imaging structure510may be omitted in other embodiments, examples of which are illustrated respectively inFIGS. 5A and 6.

In some embodiments, each of the LED and exposure controllers122l,122eis or comprises one or more electronic memories and one or more electronic processors. The one or more electronic processors may, for example, execute processor executable instructions on the one or more electronic memories to carry out functions of the controller (e.g., the LED or exposure controller122l,122e). Further, in some embodiments, each of the LED and exposure controllers122l,122eis or comprises a microcontroller, an ASIC, some other suitable electronic device(s) and/or circuit(s), or any combination of the foregoing.

With reference toFIGS. 9A and 9BthroughFIGS. 15A and 15B, a series of views900A and900B through1500A and1500B of some embodiments of a method for a workpiece110using LED-based edge exposure is provided. Figures with a suffix of “A” are cross-sectional views. Figures with a suffix of “B” are top layout views of the workpiece110and correspond to like-numbered figures with a suffix of “A”.

As illustrated by the views900A,900B ofFIGS. 9A and 9B, a photosensitive layer112is deposited on a workpiece110. The photosensitive layer112comprises an edge portion112eand a center portion112c. The edge portion112eis a portion of the photosensitive layer112at or near a sidewall edge of the workpiece110and extends in a closed path to completely enclose the center portion112c. SeeFIG. 9B. Further, the edge portion112emay, for example, be a portion of the photosensitive layer112within a distance D of a sidewall edge of the workpiece110, where the distance D is about 2-4 millimeters, about 1.0-1.5 millimeters, about 3.5-4.0 millimeters, about 0.5-3.0 millimeters, about 0.5-2.5 millimeters, about 0.5-1.0 millimeters, or less than about 2 millimeters. In some embodiments, the photosensitive layer112further comprise alignment-mark portions112amand/or workpiece-id portion112idthat is/are surrounded by the center portion112c. SeeFIG. 9B. The alignment-mark portions112amoverlie alignment marks (not visible) of the workpiece110, and the workpiece-id portion112idoverlies an ID (not visible) of the workpiece110. The photosensitive layer112may, for example, be photoresist or some other suitable photosensitive material.

The workpiece110comprises a substrate110sand a target layer110toverlying the substrate110s. As seen hereafter, the target layer110tis a layer of the workpiece110to which a pattern is transferred by photolithography. The target layer110tmay be or comprise, for example, silicon oxide, silicon nitride, polysilicon, copper, aluminum copper, aluminum, titanium nitride, tantalum nitride, some other suitable material(s), or any combination of the foregoing. In some embodiments, the substrate110sis or comprises a semiconductor substrate. In some embodiments, the substrate110sfurther comprises one or more additional layers and/or structures arranged over and/or stacked on the semiconductor substrate.

In some embodiments, the depositing of the photosensitive layer112is performed using a spin-on-coating tool902. In some embodiments, a process for depositing the photosensitive layer112comprises arranging the workpiece110within a process chamber904of the spin-on-coating tool902, on a workpiece table906of the spin-on-coating tool902. In some embodiments, the workpiece110comprises a notch110nto facilitate alignment to the workpiece table906. The workpiece table906and the workpiece110are then rotated about a central axis C′ of the workpiece table906. Further, while the workpiece110is rotated, photosensitive material908in liquid form is deposited onto the workpiece110at or proximate the central axis C′. The photosensitive material908may, for example, be provided to the workpiece110from a photosensitive material source910through a nozzle912. Because the workpiece110is rotating, centrifugal force moves the photosensitive material908outward to an edge of the workpiece110, thereby defining the photosensitive layer112. Ideally, the photosensitive material908would evenly distribute over the workpiece110, such that the photosensitive layer112would have a thickness T that is uniform or substantially uniform from the central axis C′ to the edge of the workpiece110. However, in reality, the photosensitive material908builds up at the edge of the workpiece110, such that the thickness T of the photosensitive layer112increases from the central axis C′ to the edge of the workpiece110.

As illustrated by the views1000A,1000B ofFIGS. 10A and 10B, edge exposure is performed on the workpiece110using the edge-exposure tool102in any one ofFIGS. 1, 5A, 5B, and6-8. The edge exposure exposes the edge portion112eof the photosensitive layer112to radiation116from a LED114without exposing the center portion112cof the photosensitive layer112to the radiation116. The edge exposure chemically changes the edge portion112e, but not the center portion112c, thereby allowing the edge portion112eto be removed by a chemical developer without removing the center portion112c. The radiation116may be or comprise, for example, UV radiation or some other radiation suitable for edge exposure, and/or may have, for example, wavelengths between about 10-400 nanometers, about 200-400 nanometers, about 10-121 nanometers, about 10-200 nanometers, or about 300-450 nanometers.

By using the LED114for edge exposure, costs are low. For example, the LED114has a low acquisition cost, a low operating cost, and a low maintenance cost. Further, the LED114has a long lifespan. Further, the LED114is in the process chamber104, such that the LED114does not depend on a costly and complex radiation guide. Further, the LED114may be changed between an ON state and an OFF state nearly instantly, such that the LED114does not depend on a costly and complex shutter. Further, the LED114may be retrofitted into existing edge-exposure tools with minimal cost.

In some embodiments, a process form performing the edge exposure comprises arranging the workpiece110within a process chamber104of the edge-exposure tool102, on a workpiece table106of the edge-exposure tool102. The workpiece table106and the workpiece110are rotated about a central axis C of the workpiece table106, and the LED114is moved within the process chamber104to the edge portion112e. Thereafter, while the workpiece110is rotating, the LED114exposes the edge portion112eto the radiation116without exposing a remainder of the photosensitive layer112to the radiation116. Such exposure continues until the edge portion112eis entirely exposed. In some embodiments, the LED114is continuously ON during edge exposure. In some embodiments, an ON/OFF state of the LED114is pulse width modulated during exposure. The pulse width modulation of the ON/OFF state of the LED114keeps the temperature of the LED114low and enhances a lifespan of the LED114relative to continuous ON exposure. In some embodiments, an intensity of the LED114is limited during edge exposure. Limiting the intensity of the LED114reduces a temperature of the LED114, which enhances a lifespan of the LED114relative to full intensity exposure. In some embodiments, the intensity of the LED114is varied depending upon a type of photosensitive material being exposed. By varying the intensity of the LED114depending upon a photosensitive material type being exposed, the lifespan of the LED114may be enhanced.

Also illustrated by the views1000A,1000B ofFIGS. 10A and 10B, in some embodiments, additional exposure is performed on the workpiece110using the edge-exposure tool102in any one ofFIGS. 1, 5A, 5B, and 6-8. The additional exposure is performed in situ without moving the workpiece110from its location during edge exposure. The additional exposure exposes the alignment-mark portions112amof the photosensitive layer112and/or the workpiece-id portion112idof the photosensitive layer112to the radiation116from the LED114without exposing the center portion112cto the radiation116. As with the edge exposure, the additional exposure chemically changes the one or more exposed portions of the photosensitive layer112(e.g., the alignment-mark portions112am), but not the one or more unexposed portions of the photosensitive layer112(e.g., the center portion112c), thereby allowing the exposed portion(s) to be removed by a chemical developer without removing the unexposed portion(s).

In some embodiments, a process form performing the additional exposure comprises moving the LED114within the process chamber104to each portion of the photosensitive layer112(e.g., the workpiece-id portion112id) to be exposed to the radiation116. At each portion of the photosensitive layer112to be exposed to the radiation116, the LED114exposes the portion to the radiation116without exposing a remainder of the photosensitive layer112. In some embodiments, the exposure is performed while the workpiece110is stationary (e.g., not rotating). In other embodiments, the exposure is performed while the workpiece110is rotating about the central axis C. In such embodiments, the exposure is timed with the rotation of the workpiece110using notch110nof the workpiece110as a reference point so only the desired portion of the workpiece110is exposed to the radiation116. In some embodiments, the LED114is driven by the LED driver120in the same manner as during edge exposure.

As illustrated by the views1100A,1100B ofFIGS. 11A and 11B, the edge portion112eof the photosensitive layer112(seeFIGS. 10A and 10B) is removed from the workpiece110, while leaving the center portion112cof the photosensitive layer112. This, in turn, uncovers the target layer110talong the edge of the workpiece110. In embodiments in which the additional exposure ofFIGS. 10A and 10Bis performed, the alignment-mark portions112amof the photosensitive layer112(seeFIGS. 10A and 10B) and/or the workpiece-id portion112idof the photosensitive layer112(seeFIGS. 10A and 10B) is/are also removed. Removing the alignment-mark portions112amuncovers alignment marks402of the workpiece110. Removing the workpiece-id portion112iduncovers an ID404of the workpiece110.

In some embodiments, the removal is performed using a developer tool1102. In some embodiments, a process for performing the removal comprises arranging the workpiece110within a process chamber1104of the developer tool1102, on a workpiece table1106of the developer tool1102. In some embodiments, the notch110nof the workpiece110facilitates alignment of the workpiece110to the workpiece table1106. The workpiece table1106and the workpiece110are then rotated about a central axis C″ of the workpiece table1106. Further, while the workpiece110is rotated, a chemical developer1108in liquid form is deposited onto the workpiece110at or proximate the central axis C″. The chemical developer1108may, for example, be provided to the workpiece110from a developer source1110through a nozzle1112. Because the workpiece110is rotating, centrifugal force moves the chemical developer1108outward to an edge of the workpiece110. The chemical developer1108reacts with the one or more portions of the photosensitive layer112exposed to the radiation116ofFIGS. 10A and 10B, and removes the portion(s) of the photosensitive layer112.

As illustrated by the views1200A,1200B ofFIGS. 12A and 12B, the photosensitive layer112is exposed to patterned radiation1202. Pattern portions112pof the photosensitive layer112upon which the patterned radiation1202impinges undergo a chemical change, whereas a remainder of the photosensitive layer112remains unchanged, thereby transferring a pattern of the patterned radiation1202to the photosensitive layer112. In some embodiments, the workpiece110comprises a plurality of die regions110dand the photosensitive layer112is individually exposed to the patterned radiation1202at each of the die regions110d.

In some embodiments, the exposure is performed by a photolithography exposure tool1204. The photolithography exposure tool1204may be, for example, a scanner and/or a stepper. In some embodiments, a process for performing the exposure comprises arranging the workpiece110within a process chamber1206of the photolithography exposure tool1204, on a workpiece table1208of the photolithography exposure tool1204. Unpatterned radiation1210is then generated by a radiation source1212and passed through a photomask or photoreticle1214. The photomask or photoreticle1214imparts a pattern on the unpatterned radiation1210to generate the patterned radiation1202. The patterned radiation1202impinges on the photosensitive layer112and transfers the pattern to the photosensitive layer112. In some embodiments, the workpiece table1208and/or the photomask or photoreticle1214move laterally relative to one another to change the location at which the patterned radiation1202impinges on the photosensitive layer112.

As illustrated by the views1300A,1300B ofFIGS. 13A and 13B, the pattern portions112pof the photosensitive layer112(seeFIGS. 12A and 12B) are removed from the workpiece110, while leaving a remainder of the photosensitive layer112. The removal, in turn, uncovers some of the target layer110t. For example, in embodiments in which the workpiece110comprises the die regions110d, the removal partially uncovers the die regions110d.

In some embodiments, the removal is performed using the developer tool1102. In some embodiments, a process for performing the removal comprises arranging the workpiece110within the process chamber1104of the developer tool1102, on the workpiece table1106of the developer tool1102. The workpiece table1106and the workpiece110are then rotated about the central axis C″ of the workpiece table1106. Further, while the workpiece110is rotated, the chemical developer1108is deposited onto the workpiece110at or proximate the central axis C″. Because the workpiece110is rotating, centrifugal force moves the chemical developer1108outward to an edge of the workpiece110. The chemical developer1108reacts with the pattern portions112pof the photosensitive layer112exposed to the patterned radiation1202ofFIGS. 12A and 12B, and removes the pattern portions112p.

As illustrated by the views1400A,1400B ofFIGS. 14A and 14B, an etch is performed into the target layer110tof the workpiece110with the photosensitive layer112in place. During the etch, the photosensitive layer112serves as a mask and a pattern of the photosensitive layer112is transferred to the target layer110t. In some embodiments, an etchant of the etch has a first etch rate for the target layer110tand a second etch rate for the photosensitive layer112, where the first etch rate is substantially greater than the second etch rate. Due to the disparity between the first and second etch rates, the photosensitive layer112is minimally etched during the etch. In some embodiments, the substrate110sof the workpiece110serves as an etch stop for the etch. For example, an etchant used for the etch may have the first etch rate for the target layer110tand a third etch rate for the substrate110s, where the first etch rate is substantially greater than the third etch rate. Due to the disparity between the first and third etch rates, the substrate110sis minimally etched during the etch. As used above, “substantially greater” may, for example, be at least an order or magnitude greater, or may, for example, be about 5-50 times greater, about 5-20 times greater, or about 20-50 times greater.

In some embodiments, the etch is performed using an etch tool1402. The etch tool1402may, for example, be a plasma etch tool, a wet etch tool, or some other suitable etch tool. In some embodiments, a process for performing the etch comprises arranging the workpiece110within a process chamber1404of the etch tool1402, on a workpiece table1406of the etch tool1402. Further, plasma1408is generated by a plasma source1410and applied to the workpiece110with the photosensitive layer112in place.

As illustrated by the views1500A,1500B ofFIGS. 15A and 15B, the photosensitive layer112is removed. In some embodiments, the removal is performed by plasma ashing within a plasma ashing tool1502. In some embodiments, a process for performing the plasma ashing comprises arranging the workpiece110within a process chamber1504of the plasma ashing tool1502, on a workpiece table1506of the plasma ashing tool1502. Further, plasma1508is generated by a plasma source1510and applied to the photosensitive layer112.

With reference toFIG. 16, a flowchart1600of some embodiments of the method ofFIGS. 9A and 9BthroughFIGS. 15A and 15Bis provided.

At1602, a photosensitive layer is formed on a workpiece, where the workpiece comprises a substrate and a target layer covering the substrate. See, for example,FIGS. 9A and 9B.

At1604, an edge portion of the photosensitive layer is exposed to radiation to chemically change the edge portion, where the radiation is generated by a LED. See, for example,FIGS. 10A and 10B. In some embodiments, a workpiece-id portion of the photosensitive layer and/or alignment-mark portions of the photosensitive layer is/are also exposed to the radiation to chemical change these one or more portions. By using the LED for edge exposure, costs are low. For example, the LED has a low acquisition cost, a low operating cost, and a low maintenance cost. Further, the LED has a long lifespan and may be retrofitted into existing edge-exposure tools with minimal cost.

At1606, a chemical developer is applied to the photosensitive layer to remove the edge portion of the photosensitive layer. See, for example,FIGS. 11A and 11B.

At1608, the photosensitive layer is exposed to patterned radiation, where pattern portions of the photosensitive layer upon which the patterned radiation impinge undergo a chemical change. See, for example,FIGS. 12A and 12B.

At1610, a chemical developer is applied to the photosensitive layer to remove the pattern portions of the photosensitive layer. See, for example,FIGS. 13A and 13B.

At1612, an etch is performed into the target layer with the photosensitive layer in place to transfer a pattern of the photosensitive layer to the target layer. See, for example,FIGS. 14A and 14B.

At1614, plasma ashing is performed to remove the photosensitive layer. See, for example,FIGS. 15A and 15B.

In some embodiments, the exposure at1604ofFIG. 16may be repeated multiple times for different workpieces, each covered by a photosensitive layer. For example, the method ofFIG. 16may be repeated multiple times for the different workpieces, such that the exposure at1604may repeated multiple times for the different workpieces. Further, in some embodiments, the exposure intensity may be varied depending upon the photosensitive material of the photosensitive layer. The edge exposure may, for example, be performed within the edge-exposure tool102in any one ofFIGS. 1, 5A, 5B, and 6-8.

With reference toFIGS. 17 and 18, a series of cross-sectional views1700,1800illustrate the edge-exposure tool102performing edge exposure respectively on a first workpiece110′ and a second workpiece110″. The first workpiece110′ is covered by a first photosensitive layer112′ and, in some embodiments, comprises a first substrate110s′ and first target layer110t′ covering the first substrate110s′. The second workpiece110″ is covered by a second photosensitive layer112″ and, in some embodiments, comprises a second substrate110s″ and second target layer110t″ covering the second substrate110s″. The first and second substrates110s′,110s″ may, for example, each be as the substrate110sofFIGS. 9A and 9Bis described, and the first and second target layers110t′,110t″ may, for example, be each be as the target layer110tofFIGS. 9A and 9Bis described.

The first and second photosensitive layers112′,112″ comprise different photosensitive materials, each having a different exposure intensity. For example, the first photosensitive layer112′ may comprise a first photosensitive material having a first exposure intensity X, whereas the second photosensitive layer112″ may comprise a second photosensitive material having a second exposure intensity Y different than the first exposure intensity X. The exposure intensities X, Y may, for example, each be integer values between 0 and 100. During edge exposure, the controller122may, for example, lookup the first and second exposure intensities X, Y in a lookup table122ltby photosensitive material, and may set the LED driver120to drive the LED114so as to achieve the looked-up exposure intensity. In some embodiments, other parameters of the edge exposure may additionally and/or alternatively be varied by photoresist material. For example, where the ON/OFF state of the LED114is pulse width modulated, the duty cycle may be varied by photoresist material.

With reference toFIG. 19, a flowchart of some embodiments of a method for performing LED-based edge exposure atFIGS. 17 and 18is provided. The method may, for example, be performed at1604ofFIG. 16.

At1902, a workpiece covered by a photosensitive layer is received. See, for example,FIG. 17.

At1904, a photosensitive material of the photosensitive layer is determined. See, for example,FIG. 17. The photosensitive material may, for example, be automatically determined from a process control system using an identifier of the workpiece. The process control system may, for example, coordinate the manufacture of ICs in a semiconductor manufacturing facility.

At1906, an exposure intensity for the determined photosensitive material is determined. See, for example,FIG. 17. In some embodiments, the exposure intensity is automatically determined by looking up the exposure intensity in a lookup table by the determined photosensitive material.

At1908, an edge portion of the photosensitive layer is exposed to radiation to chemically change the edge portion, where the radiation is generated with the determined exposure intensity by a LED. See, for example,FIG. 17.

At1910, the acts at1902-1908are repeated for another workpiece covered by another photosensitive layer, where the other photosensitive layer has a different exposure intensity than the photosensitive layer. See, for example,FIG. 18.

By varying the exposure intensity of the LED based on photosensitive material, a lifespan of the LED may be enhanced. Some photosensitive materials have high exposure intensities relative to other photosensitive materials. Operating the LED at a high exposure intensity causes the LED to operate at a high temperature, which reduces the lifespan of the LED faster than when the LED is operating at a low exposure intensity and hence a low temperature. Further, without varying the intensity of the LED based on photosensitive material, the LED operates at the highest exposure intensity for possible photosensitive materials to ensure each of the possible photosensitive materials is sufficiently irradiated. This is regardless of whether a photosensitive material being irradiated actually depends upon such a high exposure intensity. Therefore, for photosensitive materials with a low exposure intensity, the lifespan of the LED is needlessly reduced. Further, varying the intensity of the LED based on photosensitive material enhances the lifespan of the LED.

In some embodiments, a method for edge exposure includes: receiving a workpiece covered by a photosensitive layer; and exposing an edge portion of the photosensitive layer, but not a center portion of the photosensitive layer, to radiation generated by a LED, wherein the edge portion of the photosensitive layer extends along an edge of the workpiece in a closed path to enclose the center portion of the photosensitive layer. In some embodiments, the method further includes applying a chemical developer to the photosensitive layer to remove the edge portion of the photosensitive layer without removing the center portion of the photosensitive layer. In some embodiments, the method further includes rotating the workpiece during the exposing. In some embodiments, the radiation includes UV radiation. In some embodiments, the exposing includes alternatingly changing the LED between an ON state and an OFF state. In some embodiments, the exposing includes: determining a photosensitive material of the photosensitive layer; determining an exposure intensity for the determined photosensitive material; and setting an intensity of the LED to the determined exposure intensity. In some embodiments, the edge portion of the photosensitive layer has a ring-shaped top layout, and wherein the center portion of the photosensitive layer has a circle-shaped top layout. In some embodiments, the method further includes exposing a workpiece-id portion of the photosensitive layer to the radiation without moving the workpiece from its location during the exposing of the edge portion and without exposing the center portion of the photosensitive layer, wherein the workpiece-id portion of the photosensitive layer is surrounded by the center portion of the photosensitive layer. In some embodiments, the method further includes exposing an alignment-mark portion of the photosensitive layer to the radiation without moving the workpiece from its location during the exposing of the edge portion and without exposing the center portion of the photosensitive layer, wherein the alignment-mark portion of the photosensitive layer is surrounded by the center portion of the photosensitive layer.

In some embodiments, an edge-exposure tool includes: a process chamber; a workpiece table in the process chamber, wherein the process chamber is configured to support a workpiece covered by a photosensitive layer; a LED in the process chamber, wherein the LED is configured to emit radiation towards the workpiece; and a controller configured to control the LED to expose an edge portion of the photosensitive layer, but not a center portion of the photosensitive layer, to the radiation emitted by the LED, wherein the edge portion of the photosensitive layer extends along an edge of the workpiece in a closed path to enclose the center portion of the photosensitive layer. In some embodiments, the radiation includes UV radiation. In some embodiments, the edge-exposure tool further includes a mechanical arm supporting the LED over the workpiece table, wherein the mechanical arm is configured to move the LED over the workpiece. In some embodiments, the edge-exposure tool further includes an LED driver electrically coupled between the controller and the LED, wherein the LED driver is configured to apply a voltage across the LED and to regulate a flow of current through the LED in response to commands from the controller. In some embodiments, the edge-exposure tool further includes an image sensor underlying the LED, wherein the image sensor is configured to measure an intensity of the LED, and wherein the LED driver is configured to regulate the flow of current based on the measured intensity. In some embodiments, the edge-exposure tool further includes: an LED housing in the process chamber, wherein the LED is in the LED housing; and a temperature sensor in the LED housing, wherein the temperature sensor is configured to measure a temperature of the LED, and wherein the LED driver is configured to regulate the flow of current based on the measured temperature. In some embodiments, the controller includes an exposure controller and an LED controller, and wherein the LED controller is configured to simulate a lamp and to translate commands received from the exposure controller for the lamp to commands for the LED.

In some embodiments, a method for edge exposure includes: arranging a wafer within a process chamber, wherein the wafer is covered by a photosensitive layer; exposing an edge portion of the photosensitive layer, but not a center portion of the photosensitive layer, to UV radiation generated by a LED, wherein the UV radiation chemically changes the edge portion of the photosensitive layer, wherein the edge portion of the photosensitive layer extends along an edge of the wafer in a closed path to encircle the center portion of the photosensitive layer, and wherein the LED is in the process chamber; and rotating the wafer during the exposing. In some embodiments, the exposing includes: alternatingly changing the LED between an ON state and an OFF state; determining a photosensitive material of the photosensitive layer; determining an exposure intensity for the determined photosensitive material; and setting an intensity of the LED to the determined exposure intensity. In some embodiments, the determining of the exposure intensity includes lookup up the exposure intensity in a lookup table by the determined photosensitive material. In some embodiments, the method further includes applying a chemical developer to the photosensitive layer to remove the edge portion of the photosensitive layer without removing the center portion of the photosensitive layer.