Apparatus for processing wafer-shaped articles

Abstract

Apparatus for processing wafer-shaped articles, the apparatus comprising: a support configured to support a wafer-shaped article; and a heating assembly comprising an array of LEDs configured to heat a wafer-shaped article supported by the support; wherein the LEDs are configured to emit light having a maximum intensity at a wavelength that is greater than or equal to 550nm and less than or equal to 980nm.

Description

[0001] APPARATUS FOR PROCESSING WAFER-SHAPED ARTICLES

[0002] Field of the Invention

[0003] The present invention relates to an apparatus for processing wafer-shaped articles.

[0004] Background

[0005] Semiconductor wafers may be subjected to various surface treatment processes, such as etching, cleaning, polishing and material deposition. To perform such processes, a wafer may be mounted on a rotatable chuck, so that various processes can be performed on a surface of the wafer.

[0006] For example, the surface of the wafer may be cleaned by applying a cleaning liquid or rinse liquid such as isopropyl alcohol or de-ionised water to the surface of the wafer. The surface of the wafer may then be dried by spinning the wafer using the rotatable chuck and heating the wafer to cause evaporation of the cleaning liquid or rinse liquid. Such a cleaning process is commonly referred to as a spin-clean process. Alternatively, an etching liquid may be applied to the surface of the wafer to etch the surface of the wafer.

[0007] An example of an apparatus that may be used for cleaning the surface of a wafer is described in US2017 / 0345681 A1 , the whole contents of which are incorporated herein by reference.

[0008] The apparatus described in in US2017 / 0345681 A1 includes a rotatable chuck on which a wafer is mountable, and a liquid dispenser for dispensing liquid on an upper surface of the wafer when the wafer is mounted on the rotatable chuck. The apparatus also includes an array of light emitting diode (LED) heating elements disposed below the wafer when the wafer is mounted in the rotatable chuck, and arranged to heat the wafer. After liquid is dispensed on the upper surface of the wafer, the array of LED heating elements is controlled to heat the lower surface of the wafer to heat the wafer and cause evaporation of the liquid.

[0009] During processing of a wafer, one or more flammable liquids may be dispensed onto a surface of the wafer. For example, as mentioned above, isopropyl alcohol may be dispensed onto an upper surface of a wafer to clean the upper surface of the wafer in a spin-clean process.

[0010] With such flammable liquids, there is potentially a risk of fire or explosion when the array of LED heating elements is controlled to heat the wafer to cause evaporation of the liquid. In particular, an electrical circuit is provided for supplying electrical power to the array of LED heating elements. If the flammable liquid comes into contact with the electrical circuit, there is a risk that the electrical circuit may cause the flammable liquid to catch fire or explode.

[0011] In order to reduce the risk of such fire or explosion, it is known to operate the array of LED heating elements in an inert atmosphere, for example an atmosphere of pure nitrogen. This is achieved by providing a gas supply mechanism that provides a supply of inert gas to the array of LED heating elements, for example to a space in which the array of LED heating elements is provided. The lack of oxygen in the inert atmosphere means that even if the flammable liquid comes into contact with the electrical circuit, a fire or explosion can be prevented.

[0012] Another example of an apparatus that may be used for cleaning the surface of a wafer is described in WO2022 / 069569, the whole contents of which are also incorporated herein by reference.

[0013] WO2022 / 069569 discloses that, surprisingly, operating LEDs of an array of LED heating elements such as that disclosed in US2017 / 0345681 A1 in an inert atmosphere was discovered to cause degradation in the light output of the LEDs over time. For example, the light output of the LEDs was found to fall to as low as 30% of the original light output of the LEDs after prolonged operation in an inert atmosphere. It was observed that significant decolouration of the LEDs also occurred after prolonged operation in the inert atmosphere.

[0014] Degradation in the light output of the LEDs occurs as a consequence of the LEDs being operated in an inert atmosphere that does not contain oxygen (or contains only a small amount of oxygen). For example, it was observed that operating the LEDs in a normal atmosphere (for example air) causes a drop of less than 10% of the light output of the LEDs over the whole operational lifetime of the LEDs. Therefore, the same degradation in the light output of the LEDs does not occur in air.

[0015] WO2022 / 069569 further discloses that the degradation in the light output of the LEDs can be reversed by operating the degraded LEDs in an environment that contains oxygen, for example air, for a period of time. While this is effective, it may mean that the apparatus cannot be fully used during this time. For example, it may not be possible to dispense any flammable liquids on the wafer while operating the degraded LEDs in the environment that contains oxygen. In addition, additional components are required to provide the second gas oxygen containing gas to the LEDs, which may increase the complexity and therefore expense of the apparatus.

[0016] The present invention has been devised in light of the above considerations.

[0017] Summary of the Invention

[0018] The exact process by which the degradation in the light output of the LEDs described in WO2022 / 069569 occurs was not fully understood, and was not considered to be essential to the disclosure of

[0019] WO2022 / 069569.

[0020] The present inventors have discovered that using commercially available blue LEDs which have a maximum intensity at a wavelength of approximately 455nm in such an inert atmosphere surprisingly causes a drop in the light output of the blue LEDs over time. For example, the light output of such blue LEDs has been observed to fall to as low as 30% of the original value after prolonged operation of the blue LEDs in the inert atmosphere, for example after an LED on-time of less than a week. A drop in the light output of the blue LEDs causes a corresponding drop in the heating of the wafer, and therefore a corresponding drop in the effectiveness of the drying of the wafer. In contrast, the present inventors have observed that operating such blue LEDs in a normal atmosphere (for example air) causes a drop of less than 10% of the light output of the blue LEDs over the whole lifetime of the blue LEDs, for example after more than 30000 hours on-time.

[0021] A change in colour of the blue LEDs that accompanies the drop in the light output of the blue LEDs during operation of the blue LEDs in the inert atmosphere has also been observed by the present inventors.

[0022] Without wishing to be bound by any particular theory, it is believed that degradation of a silicone lens of the commercially available blue LEDs occurs when the blue LEDs are operated in an inert atmosphere that does not contain oxygen (or contains only a small amount of oxygen). Commercially available LEDs typically include a lens for focussing and / or directing light generated by a chip or die or diode of the LED. For example, the lens may be a hemispherical lens positioned over the chip or die or diode. It is possible that a chemical reaction occurs in the lens driven by the light emitted by the blue LEDs. For example, it has been observed that the degradation occurs more quickly when the power level of the blue LEDs is higher.

[0023] This degradation also occurs when using white LEDs based on blue LEDs, which include a blue LED and a phosphor layer that converts the light from the blue LED into white light, and which also include such a silicone lens.

[0024] Surprisingly, the present inventors have discovered that when using higher wavelength (lower photonic energy) LEDs, such a drop in the light output of the LEDs over time does not occur, or is significantly reduced in magnitude. This discovery provides significant advantages, since the efficiency of the heating of the wafer by the LEDs can be maintained without having to perform the additional steps disclosed in WO2022 / 069569 of operating the LEDs in an environment that comprises oxygen, and without dispensing any flammable liquid, in order to safely restore the performance of the LEDs, which while effective can be time consuming and increase the complexity.

[0025] According to a first aspect of the present invention there is provided an apparatus for processing wafershaped articles, the apparatus comprising: a support configured to support a wafer-shaped article; and a heating assembly comprising an array of LEDs configured to heat a wafer-shaped article supported by the support; wherein the LEDs are configured to emit light having a maximum intensity at a wavelength that is greater than or equal to 550nm and less than or equal to 980nm.

[0026] Therefore, with the present invention, LEDs having a maximum intensity at a wavelength that is greater than or equal to 550nm and less than or equal to 980nm are used in the heating assembly. Such LEDs have a higher wavelength than the blue LEDs having a maximum intensity at a wavelength of approximately 455nm previously used described above. As mentioned above, surprisingly, the present inventors have discovered that when such higher wavelength LEDs are used in the heating assembly the light output of the LEDs is not significantly degraded when the LEDs are operated in an inert atmosphere. Therefore, the efficiency of the heating of the wafer-shaped article by the LEDs can be maintained without having to perform the additional steps disclosed in WO2022 / 069569 of operating the LEDs in an environment that comprises oxygen in order to safely restore the performance of the LEDs. Therefore, with the present invention the light output of the LEDs can be maintained over time without requiring additional time-consuming steps to restore the light output of the LEDs. Furthermore, a complexity and therefore cost of the apparatus may be reduced.

[0027] Another potential benefit of accommodating LEDs with light emission wavelength above 550nm is that at such low electromagnetic radiation energies the electron / hole pair generation in doped Silicon or Copper oxide layers could be mitigated or prevented thereby avoiding critical wafer stack materials from undergoing photo-corrosion. For example, the present inventors have observed that the risk photocorrosion of any Cu / CuO / Cu2O layers on a wafer being illuminated by the LEDs is reduced compared to using lower wavelength LEDs.

[0028] Furthermore, the present inventors have also observed that absorption of the light by the wafer is increased when using a higher wavelength than the previously used blue LEDs, which can increase the efficiency of the heating of the wafer by the LEDs. In particular, wall-plug efficiency of the LEDs is increased. A higher wall-plug efficiency may lead to less power dissipation, which may lead to lower thermal load into associated electronics or an associated heat sink. This may reduce cooling requirements for the apparatus, which may therefore reduce the complexity and cost of the apparatus.

[0029] Silicon wafers may be significantly transparent to light having a wavelength longer than 980nm. Therefore, an upper limit of the wavelength at which the LEDs have their maximum intensity in the present invention is less than or equal to 980nm, so that the light is absorbed by the wafer to heat the wafer.

[0030] The apparatus according to the first aspect of the present invention may have any one of the following optional features, or where compatible any combination of the following optional features.

[0031] The LEDs may be configured to emit light having a maximum intensity at a wavelength that is greater than 550nm.

[0032] The LEDs operate as heating elements, and may therefore be referred to as light-emitting heating elements, or LED heating elements.

[0033] Processing a wafer-shaped article may mean performing one or more steps on the wafer-shaped article, or handling or dealing with the wafer-shaped article, for example.

[0034] Processing the wafer-shaped article may mean cleaning the wafer-shaped article. For example, processing the wafer-shaped article may comprise dispensing a liquid onto a surface of the wafer-shaped article so as to clean the surface of the wafer-shaped article.

[0035] Cleaning the wafer-shaped article may mean removing one or more contaminants or dirt or debris or other substance from the wafer-shaped article, for example.

[0036] In addition, or alternatively, processing the wafer-shaped article may mean etching the wafer-shaped article. For example, processing the wafer-shaped article may comprise dispensing an etching liquid onto a surface of the wafer-shaped article so as to etch the surface of the wafer-shaped article.

[0037] The wafer-shaped article may be a wafer, for example a semiconductor wafer. The wafer-shaped article may be a silicon wafer.

[0038] The wafer-shaped article may have a predetermined diameter, for example 300mm.

[0039] The support may be a chuck.

[0040] The support may be rotatable. For example, the support may be a rotatable chuck or a rotary chuck.

[0041] The support may be configured to rotate the wafer-shaped article relative to an axis of rotation of the support that is substantially perpendicular to a surface of the wafer-shaped article, or around or about such an axis.

[0042] The support may include a mechanism adapted to receive the wafer-shaped article and hold the wafershaped article securely in place relative to the support (e.g. a clamp, screw, vacuum holder, plurality of gripping pins, etc.). For example, the support may comprise a plurality of rotatable gripping pin assemblies that extend from a surface of the support so as to surround a circumferential edge of the wafer-shaped article when the wafer-shaped article is received by the support. The rotatable gripping pin assemblies may be rotatable between a first configuration in which the rotatable gripping pin assemblies grip the wafer-shaped article and a second configuration in which the rotatable gripping pin assemblies do not grip the wafer-shaped article.

[0043] The support may be adapted to receive a wafer-shaped article of a predetermined size, e.g. a wafershaped article having a diameter of 300mm.

[0044] The support may include a motor for driving rotation of the support relative to the axis of rotation. Alternatively, the support may be caused to rotate by an external driving means, for example via magnetic induction.

[0045] The heating assembly comprises an array of LEDs configured to heat a wafer-shaped article supported by the support. In particularly, the array of LEDs is arranged to illuminate the wafer-shaped article with light emitted by the array of LEDs.

[0046] The LEDs heat the wafer by radiative heating using light.

[0047] The term “array” may merely mean a plurality of LEDs, and does not necessarily mean that the LEDs are arranged in any particular order.

[0048] The array of LEDs may be arranged to face towards the wafer-shaped article when the wafer-shaped article is received by the support.

[0049] The array of LEDs may be arranged to face towards a first surface of the wafer-shaped article, which is opposite a second surface of the wafer-shaped article on which processing (e.g. cleaning, deposition of material, etc.) is performed.

[0050] The LEDs may be disposed on a substantially plane surface (e.g. on a board, such as a circuit board).

[0051] The board may be arranged to be substantially parallel to the wafer-shaped article when the wafershaped article is received by the support. The LEDs may be substantially uniformly distributed over the plane surface, to illuminate the wafershaped article in a uniform manner, which may result in uniform heating of the wafer-shaped article.

[0052] The array of LEDs may be arranged to cover an area that is substantially the same as an area of the wafer-shaped article, or an area that is within 10% of an area of the wafer-shaped article.

[0053] All of the LEDs may be of the same type (e.g. they may all have the same characteristics).

[0054] The light emitted by the LEDs may be visible light. Alternatively, or in addition, the light emitted by the LEDs may be non-visible light, for example near intra-red (NIR) light.

[0055] Each of the LEDs may comprise a chip or die or diode of the LED that emits light, and a lens that focusses or directs the light emitted by the chip or die or diode. The lens may be a silicone lens. The lens may be a hemispherical lens that is positioned over the chip or die or diode. Of course, other shapes and / or materials for the lens are possible. Each of the LEDs may further comprise a case or housing that houses the chip or die or diode and the lens. The combination of the chip or die or diode, the lens and the case or housing may be referred to as an LED package, for example.

[0056] Where the support is rotatable, the heating assembly may be mounted relative to the support such that it does not rotate together with the support when the support is rotated. In other words, the array of LEDs may remain stationary when the support is rotated. This may facilitate providing electrical connections to the array of LEDs.

[0057] The LEDs may be arranged in the heating assembly on concentric circles (concentric about a centre of the heating assembly). Of course, other arrangements of the LEDs are also possible instead, such as different patterns of the LEDs.

[0058] The apparatus may comprise one or more reflectors and / or lenses and / or other optical components for focussing or directing the light emitted by the LEDs, for example so as to focus or direct the light onto one or more specific regions of the wafer-shaped article.

[0059] In each concentric circle the LEDs may be bunched into different groups. In other words, the LEDs in a respective concentric circle may not be evenly distributed around that concentric circle.

[0060] Each of the different groups may contain the same number of LEDs.

[0061] The different groups of LEDs may be independently controlled, for example by different power being supplied to different groups of the LEDs, and / or by different groups of the LEDs being operated at different times.

[0062] The maximum intensity of the light emitted by the LEDs is a peak intensity of the light emitted by the LEDs, for example a peak in intensity in an emission spectrum of the LED.

[0063] The LEDs may be configured to emit light having a maximum intensity at a wavelength that is greater than or equal to 650nm, or greater than or equal to 660nm.

[0064] The LEDs may be configured to emit light having a maximum intensity at a wavelength that is greater than 650nm, or greater than 660nm. The LEDs may be configured to emit light having a maximum intensity at a wavelength that is less than or equal to 920nm.

[0065] The LEDs may be configured to emit light having a maximum intensity at a wavelength that is greater than or equal to 650nm or greater than or equal to 660nm and less than or equal to 920nm.

[0066] The LEDs may be configured to emit red light or near infrared light.

[0067] The apparatus may comprise a liquid dispenser for dispensing a liquid onto a first surface of a wafershaped article supported by the support. For example, the liquid dispenser may comprise a rotatable dispensing arm having a dispensing nozzle. The liquid may be a flammable liquid, such as isopropyl alcohol.

[0068] The array of LEDs may be arranged to heat a second surface of the wafer-shaped article that is on an opposite side of the wafer-shaped article to the first surface of the wafer-shaped article.

[0069] The array of LEDs may be arranged to heat a lower or bottom surface of a wafer-shaped article supported by the support.

[0070] The array of LEDs may be separated from the wafer-shaped article by a plate that is transparent to the light emitted by the LEDs.

[0071] The plate may be made of quartz or sapphire.

[0072] The support may be configured to rotate a wafer-shaped article supported by the support.

[0073] The support may be a rotary support.

[0074] The heating assembly may be configured to remain stationary relative to the support.

[0075] The heating assembly may be configured to not rotate together with the support.

[0076] The support may comprise a rotatable chuck surrounding a stationary post, and the heating assembly may be mounted on the stationary post. The post being stationary means that the post does not rotate together with the rotatable chuck.

[0077] Each of the LEDs may comprise a housing or case. The housing or case may have a width of less than or equal to 4mm, for example less than or equal to 3.5mm.

[0078] In general, a size of the LED package, for example a size of the housing or case, is small enough to enable a plurality of the LEDs to be arranged in an array, and for there to be a sufficient number of the LEDs to enable control of the heating of the wafer-shaped article by the heating assembly.

[0079] The LEDs may have a power output of greater than or equal to 2W at maximum current, for example greater than or equal to 2.5W. However, the required power output will depend on the specific application so may be different to this.

[0080] The apparatus may further comprise a gas supply mechanism configured to supply a gas to the array of LEDs.

[0081] The LEDs may have a square shape or footprint. A gas supply mechanism means any arrangement for supplying gas to the array of light emitting heating elements, and may include for example one or more valves and one or more gas flow passages such as a pipe or tube.

[0082] At least part of the gas supply mechanism may be arranged in the stationary post described above. For example, the stationary post may include a gas pipe or tube inside the stationary post that extends along at least part of the stationary post.

[0083] The gas supply mechanism may be configured to supply a gas having an oxygen gas of less than 1% by volume to the array of LEDs.

[0084] Supplying a gas to the array of LEDs means providing the gas around the LEDs, and / or to the outsides of the LEDs.

[0085] For example, the array of LEDs may be contained in a chamber, volume, or space, and supplying the gas to the array of LEDs may comprise supplying the gas to the chamber, volume, or space containing the array of LEDs.

[0086] The gas may have an oxygen content of less than 0.5% by volume, or less than 0.1% by volume.

[0087] The gas may be an inert gas. Inert may mean that the gas is inert with respect to the processing liquid used in the processing of the wafer-shaped article. For example, the gas may be inert with respect to isopropyl alcohol.

[0088] The oxygen content of the gas may be insufficient for combustion. For example, the oxygen content of the gas may be insufficient for combustion of isopropyl alcohol.

[0089] The gas may comprise nitrogen or may be nitrogen, for example pure nitrogen, or any noble gas, e.g. argon.

[0090] The gas may comprise carbon dioxide or be carbon dioxide.

[0091] Alternatively, the gas may have an oxygen content of less than or equal to 10% by volume, or less than or equal to 9.5% by volume, or less than or equal to 2% by volume.

[0092] The gas may be a gas not reacting with flammable substances.

[0093] The heating assembly may be substantially enclosed in a chamber in the apparatus, and the gas supply mechanism may be configured to supply the gas to the chamber.

[0094] The invention includes the combination of the aspects and preferred features described except where such a combination is clearly impermissible or expressly avoided.

[0095] Summary of the Figures

[0096] Embodiments illustrating the principles of the invention will now be discussed with reference to the accompanying figures in which: Figure 1 is a schematic sectional view of an apparatus according to an embodiment of the present invention.

[0097] Figure 2 is an example of a heating assembly that can be used in embodiments of the present invention.

[0098] Figure 3 is a simplified schematic of an LED that can be used in embodiments of the present invention.

[0099] Detailed Description of the Invention

[0100] Aspects and embodiments of the present invention will now be discussed with reference to the accompanying figures. Further aspects and embodiments will be apparent to those skilled in the art. All documents mentioned in this text are incorporated herein by reference.

[0101] Fig. 1 is a schematic sectional view of an apparatus 1 for processing a wafer-shaped article according to an embodiment of the present invention. In Fig. 1 a semiconductor wafer 3 is mounted in the apparatus 1 for processing.

[0102] In this embodiment, the apparatus 1 is for cleaning a surface of the wafer 3. Cleaning is an example of processing of the wafer 3.

[0103] The apparatus 1 includes a rotatable chuck 5 which is adapted to receive the wafer 3. The rotatable chuck 5 includes a chuck body 7 which is rotatably mounted on a base 9, for example via one or more bearings. The chuck body 7 is rotatable relative to the base 9 about an axis of rotation indicated by reference numeral 11 . Rotation of the chuck body 7 relative to the base 9 may be driven, for example, by a motor (not shown), such as an electric motor, which may itself be controlled by a controller (not shown). For example, the chuck body 7 may be mounted on a rotor of an electric motor and a stator of the electric motor may be mounted on the base 9.

[0104] The chuck body 7 includes a set of gripping pins 13 which are adapted to receive the wafer 3 and to hold the wafer 3 securely in place. In this manner, when the wafer 3 is mounted on the rotatable chuck 5 via the gripping pins 13, the wafer 3 may be rotated by rotating the chuck body 7 relative to the base 9.

[0105] For example, the gripping pins 13 may each include a lateral cut out or recess in which an edge of the wafer 3 is received, so that the wafer 3 is supported from beneath by lower surfaces of the lateral cut outs or recesses. The gripping pins 13 may be movable, for example rotatable or translatable, between a gripping configuration in which the gripping pins 13 grip the wafer 3 and a non-gripping configuration in which the gripping pins 13 do not grip the wafer 3.

[0106] However, other suitable mechanisms may be used for holding the wafer 3 in place instead of the gripping pins 13 (e.g. clamp, screws, suction holder, etc.). Therefore, it is not essential for the gripping pins 13 to be provided. In Fig. 1 the wafer 3 is illustrated as being supported spaced apart from an upper surface of the chuck 5. This may be preferable to prevent or reduce transfer of contaminants between a lower surface of the wafer 3 and the upper surface of the chuck 5, but is not essential.

[0107] The chuck 5 includes a plate 15 mounted on the chuck body 7. The plate 15 is secured to the chuck body 7, for example via one or more screws or bolts, such that it rotates with the chuck body 7 relative to the base 9. As shown in Fig. 1 , the plate 15 is arranged such that it is substantially parallel to the wafer 3 when the wafer 3 is mounted in the chuck 5. The plate 15 is a transparent plate, for example made of quartz or sapphire. In particular, the plate is transparent to light, for example visible light.

[0108] The apparatus 1 further comprises a heating assembly 17. In this embodiment, the heating assembly 17 comprises an array of LEDs 19 arranged to illuminate the wafer 3 mounted in the chuck 5. The LEDs 19 heat the wafer 3 received by the chuck 5 by illuminating the wafer 3 with light emitted by the LEDs. In particular, the LEDs 19 heat the wafer by radiative heating.

[0109] In this embodiment, the heating assembly 17 is housed within a chamber, volume, or space 34 formed inside the chuck body 7 and covered by the transparent plate 15.

[0110] The LEDs 19 are arranged to emit light having a maximum intensity at a wavelength that is greater than or equal to 550nm and less than or equal to 980nm.

[0111] In this embodiment, the LEDs 19 are arranged to emit red light. Specifically, the LEDs 19 are arranged to emit red light having a peak wavelength of 660 nm or approximately 660nm, for example 660nm±1 Onm, or 660nm±5mm

[0112] The transparent plate 15 is substantially transparent to the wavelength of light emitted by the LEDs 19, i.e. all or a majority of light emitted by the LEDs 19 is transmitted by the transparent plate 15. Therefore, in this embodiment the transparent plate is transparent at least to light having a wavelength of 660nm.

[0113] The heating assembly 17 further comprises a plate 21 . The array of LEDs 19 is mounted on an upper surface of the plate 21 , which acts as a heat-sink for the array of LEDs 19 to dissipate heat generated by the LEDs 19. For example, the plate 21 may be made of a metal such as aluminium. A circuit board 23 including driving circuitry (not shown) for the LEDs 19 is provided on a lower surface of the plate 21. Interconnections between the array of LEDs 19 and the driving circuitry on the circuit board are made through the plate 21 .

[0114] The plate 21 is mounted on a stationary post 25, i.e. a post that does not rotate with the chuck body 7. The stationary post 25 is not connected to the chuck body 7, or is rotatably connected to the chuck body 7, such that it does not rotate with the chuck body 7. The plate 21 is substantially parallel to the transparent plate 15.

[0115] The array of LEDs 19 is arranged to face towards the wafer 3 when the wafer 3 is mounted in the rotatable chuck 5. In particular, the array of LEDs is arranged to face a lower surface of the wafer 3 when the wafer 3 is mounted in the rotatable chuck 5. As shown in Fig. 1 , when the wafer 3 is mounted in the rotatable chuck 5, the transparent plate 15 is located between the array of LEDs 19 and the wafer 3. Thus, light emitted by the array of LEDs 19 may be transmitted by the transparent plate 15 and impinge on the wafer 3 to heat the wafer 3. The transparent plate 15 may serve to protect the array of LEDs 19 from processes that are performed on the wafer 3 when the wafer 3 is mounted in the rotatable chuck 5. In particular, the transparent plate 15 may protect the array of LEDs from liquid dispensed on an upper surface of the wafer 3, as discussed below.

[0116] The array of LEDs 19 is arranged to illuminate a first surface 27 (a bottom or lower surface) of the wafer 3, which is opposite a second surface 29 (a top or upper surface) of the wafer 3. The second surface 29 of the wafer 3 is exposed, such that processes (e.g. etching, depositing of material, cleaning) may be performed on the second surface 29 of the wafer 3.

[0117] The array of LEDs 19 may be disposed substantially symmetrically about the axis of rotation 11 of the rotatable chuck 5. In this manner, the array of LEDs 19 may illuminate the wafer substantially symmetrically about the axis of rotation 11 .

[0118] The apparatus 1 further comprises a liquid dispenser for dispensing a liquid onto the second surface 29 of the wafer 3, for example for cleaning the second surface 29. In this embodiment, the liquid dispenser includes an arm 31 having a discharge nozzle 33. The arm 31 is supplied with process and / or rinse liquid that is discharged downwardly through the discharge nozzle 33 onto the second surface 29 of the wafer 3.

[0119] The arm 31 is a swing arm 31 that is pivotally mounted at an end of the arm 31 opposite to an end of the arm 31 at which the discharge nozzle 33 is located, so that the arm 31 can be rotated about the pivotal mounting to change a position of the discharge nozzle 33 relative to the second surface 29 of the wafer 3. In particular, by rotating the arm 31 about the pivotal mounting, a radial position of the discharge nozzle 33 relative to the second surface 29 of the wafer 3 can be changed, for example between a first position located at a centre of the second surface 29 of the wafer 3 and a second position located radially outside an outer circumferential edge of the wafer 3. The discharge nozzle 33 is moved in an arc over the second surface 29 of the wafer 3.

[0120] The configuration of the liquid dispenser described above, together with the rotation of the wafer 3 by the rotatable chuck 5, means that the liquid dispenser can be operated to dispense liquid over the entire second surface 29 of the wafer 3, by pivoting the arm 31 from the centre of the second surface 29 to the edge of the second surface 29 while the wafer 3 is rotated, if desired. Alternatively, the arm may be pivoted to a predetermined position at which the discharge nozzle 33 is adjacent to a centre of the wafer 3 and held stationary while liquid is dispensed from the discharge nozzle onto the second surface 29 of the wafer 3. The wafer is then distributed over the wafer due to the rotation of the wafer.

[0121] The liquid dispenser may be used to dispense a cleaning liquid such as water, for example deionised water, or isopropyl alcohol to the second surface 29 of the wafer 3 in order to clean the second surface 29 of the wafer 3.

[0122] Cleaning the second surface 29 of the wafer 3 may comprise removing one or more contaminants or dirt or debris or other substance from the second surface 29 of the wafer 3. Of course, in other embodiments other suitable liquid dispensers may be used instead of this specific liquid dispenser.

[0123] An example configuration of the heating assembly 17 in an embodiment of the present invention is illustrated in FIG. 2.

[0124] As shown in FIG. 2, the LEDs 19 are arranged on substantially concentric rings around a centre of the heating assembly 17. The arrangement of the LEDs 19 is rotationally symmetric around the centre of the heating assembly 17.

[0125] Within a given concentric ring, the LEDs 19 are bunched into discrete groups 35. In other words, the LEDs 19 in a given concentric ring are not evenly distributed around the concentric ring. The power to each of the groups 35 of LEDs 19 may be independently controlled.

[0126] In this example there are 20 concentric rings of LEDs 19, but of course in other embodiments the number of concentric rings may be different.

[0127] In FIG. 2, the heating assembly 17 is divided into four quadrants 37, which are joined together by connectors 39.

[0128] Of course, the heating assembly 17 may be different to that illustrated in FIG. 2. In particular, the arrangement of the LEDs in the heating assembly 17 is not essential to the present invention. For example, it is not essential for the LEDs 19 to be arranged in concentric rings, or for the LEDs in a given concentric ring to be bunched into groups.

[0129] As illustrated in FIG. 2 the array of LEDs 19 has a circular shape. The heating assembly 17 as a whole also has a circular shape.

[0130] A diameter of the heating assembly 17 may be the same as, or similar to, a diameter of the wafer 3.

[0131] The apparatus 1 of the present invention may be used to clean the second surface 29 of the wafer 3 by applying a cleaning liquid such as isopropyl alcohol to the second surface 29 of the wafer 3 using the liquid dispenser. The second surface 29 of the wafer 3 may then be dried by spinning the wafer 3 with the chuck body 7 and heating the wafer 3 with the LEDs 19 to cause evaporation of the cleaning liquid or rinse liquid. Such a cleaning process is commonly referred to as a spin-clean process.

[0132] During processing of the wafer 3 by the apparatus 1 , one or more flammable liquids may be dispensed on the second surface 29 of the wafer 3 by the discharge nozzle 33. For example, in spin-cleaning of the wafer 3 flammable isopropyl alcohol may be dispensed on the second surface 29 of the wafer 3.

[0133] As mentioned above, the transparent plate 15 is provided between the wafer 3 and the heating assembly 17 to protect the heating assembly 17 from coming into contact with such processing liquids. However, there is still a possibility that some of the processing liquid may infiltrate inside the chuck body 7, for example by infiltrating along a contact area between the transparent plate 15 and the chuck body 7, or through one or more mounting holes formed in the transparent plate 15. Therefore, there is still a possibility that some of the processing liquid could come into contact with the heating assembly 17 located inside the chuck body 7. As mentioned above, the heating assembly 17 includes a circuit board 23 including driving circuitry for the LEDs 19 provided on a lower surface of the plate 21. If flammable processing liquids come into contact with the circuit board 23, there is a potential risk of fire or explosion of the flammable liquid.

[0134] In order to remove or significantly reduce this risk, it is known to provide an inert atmosphere around the heating assembly 17, so that there is no risk, or significantly reduced risk, of fire or explosion if flammable processing liquids come into contact with the circuit board 23.

[0135] In particular, it is known to provide a supply of pure nitrogen gas (N2) to the space surrounding the heating assembly 17, so that the LEDs 19 and the circuit board 23 are surrounded by pure nitrogen gas. The absence of oxygen in the atmosphere around the LEDs 19 and the circuit board 23 removes the risk of fire or explosion if flammable processing liquids come into contact with the circuit board 23.

[0136] In particular, the heating assembly 17 is substantially enclosed in a chamber 34 formed by an internal surface of the chuck body 7 and the bottom surface of the transparent plate 15. Pure nitrogen gas can be supplied to the chamber 34 so that there is an inert atmosphere in the chamber 34 surrounding the heating assembly 17.

[0137] For example, a gas supply passage 41 may be provided in the stationary post 25 that has one or more outlets in the chamber 34, so that nitrogen gas can be supplied through the stationary post 25 to the chamber 34. However, a gas supply passage may instead be provided in a different location.

[0138] One or more gas outlets from the chamber 34 to outside of the chamber 34 may be provided, so that there is a flow of gas into the chamber and out of the one or more gas outlets.

[0139] Of course, a gas other than pure nitrogen gas can be supplied to the chamber 34. In particular, an important point is that the gas has a low oxygen content so that the risk of fire or explosion is reduced. Therefore, more generally, a gas having an oxygen content of less than 1% by volume may be supplied to the chamber 34.

[0140] The present inventors have discovered that using blue LEDs which have a maximum intensity at a wavelength of approximately 455nm as the LEDs in the arrangement described above in such an inert atmosphere surprisingly causes a drop in the light output of the blue LEDs over time. For example, the light output of such blue LEDs has been observed to fall to as low as 30% of the original value after prolonged operation of the blue LEDs in the inert atmosphere. A drop in the light output of the blue LEDs causes a corresponding drop in the heating of the wafer 3, and therefore a corresponding drop in the effectiveness of the drying of the wafer 3.

[0141] A change in colour of the blue LEDs that accompanies the drop in the light output of the blue LEDs during operation of the blue LEDs in the inert atmosphere has also been observed by the present inventors.

[0142] Without wishing to be bound by any particular theory, it is believed that the degradation in the light output of the blue LEDs occurs as a consequence of the blue LEDs being operated in an inert atmosphere that does not contain oxygen (or contains only a small amount of oxygen). More specifically, it is believed that degradation of a silicone lens of the blue LEDs, and blue LED based white LEDs, occurs when the blue LEDs are operated in an inert atmosphere that does not contain oxygen (or contains only a small amount of oxygen).

[0143] As shown in FIG. 3, an LED 43 that can be used as the LEDs 19 in the array of LEDs 19 comprises a substrate 45, a chip or die or diode 47 mounted on the substrate 45, and a lens 49 positioned over the chip or die or diode 47 on the substrate 45. The lens 49 may be a hemispherical lens, for example, and may be made of silicone.

[0144] Surprisingly, the present inventors have discovered that when using higher wavelength (lower photonic energy) LEDs, such a drop in the light output of the LEDs over time does not occur, or is significantly reduced in magnitude.

[0145] For example, the present inventors have discovered that when using red LEDs having a maximum intensity at a wavelength of 660nm there is no significant degradation in the light output of the red LEDs when the red LEDs are operated in an inert atmosphere that does not contain oxygen (or contains only a small amount of oxygen).

[0146] The same or similar beneficial effects can be achieved with other wavelengths that are greater than the wavelength at which the previously used blue LEDs have a maximum intensity, for example with LEDs having a maximum intensity at a wavelength of greater than or equal to 550nm.

[0147] The present inventors have also discovered that using LEDs having a maximum intensity at a wavelength above 550nm, for example above 650nm, can also provide other advantages. For example, the present inventors have observed that the photo-corrosion risk of any Cu / CuO / Cu2O layers on a wafer being illuminated by the LEDs is reduced compared to using lower wavelength LEDs.

[0148] Furthermore, the present inventors have also observed that absorption of the light by the wafer is increased when using a higher wavelength than the previously used blue LEDs, which can increase the efficiency of the heating of the wafer by the LEDs.

[0149] Silicon wafers may become significantly transparent to light having a wavelength of more than 980nm. Therefore, an upper limit of the wavelength at which the LEDs have their maximum intensity in embodiments of the present invention may be less than or equal to 980nm, or less than or equal to 920nm, for example, so that sufficient amounts of the light are absorbed by the wafer to heat the wafer.

[0150] As mentioned above, the LEDs 19 used in embodiments of the present invention may be red LEDs having a maximum intensity at a wavelength of 660nm.

[0151] Of course, other wavelength LEDs can be used instead.

[0152] Semiconductor wafer wet processing, specifically at back-end-of-line, is known to be capable of introducing unwanted and excessive losses to the exposed IC metal (Copper) and other metallic stack materials (Cobalt cap, Tantalum liner etc.) in ambient cleanroom lighting. Visible light possesses energy large enough to unlock the bandgap of Silicon or doped Silicon domains in the depleted zone of p / n junctions at the transistor level, thereby giving rise to electrical current in the IC circuitry. Such light- generated IC electricity would then be harvested by electrochemical processes involving the anodic dissolution of Copper or other wafer stack materials that are in direct contact with the aqueous cleaning electrolyte. Photo-corrosion could be avoided, or mitigated, by operating in visible light energy regime under the bandgap energy of photo-converting materials, in practice, above approximately twice the bandgap energy of those. For undoped Silicon, this translates to visible light wavelengths above 520nm. Therefore, wavelengths of 550nm or above as used in the present invention may not lead to such photocorrosion.

[0153] The LEDs 19 may have a power output of greater than or equal to 2W at maximum current, for example greater than or equal to 2.5W. For example, the LEDs 19 may have a power of approximately 2.6W at maximum current. Of course, in other applications different power LEDs may be used.

[0154] The LEDs 19 may have a width of less than or equal to 4mm, for example less than or equal to 3.5mm. In particular, a housing or case of the LED may have a width of less than or equal to 4mm, for example less than or equal to 3.5mm. Of course, other sizes of LEDs can also be used in the present invention.

[0155] The features disclosed in the foregoing description, or in the following claims, or in the accompanying drawings, expressed in their specific forms or in terms of a means for performing the disclosed function, or a method or process for obtaining the disclosed results, as appropriate, may, separately, or in any combination of such features, be utilised for realising the invention in diverse forms thereof.

[0156] While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention.

[0157] For the avoidance of any doubt, any theoretical explanations provided herein are provided for the purposes of improving the understanding of a reader. The inventors do not wish to be bound by any of these theoretical explanations.

[0158] Any section headings used herein are for organizational purposes only and are not to be construed as limiting the subject matter described.

[0159] Throughout this specification, including the claims which follow, unless the context requires otherwise, the word “comprise” and “include”, and variations such as “comprises”, “comprising”, and “including” will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

[0160] It must be noted that, as used in the specification and the appended claims, the singular forms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Ranges may be expressed herein as from “about” one particular value, and / or to “about” another particular value. When such a range is expressed, another embodiment includes from the one particular value and / or to the other particular value. Similarly, when values are expressed as approximations, by the use of the antecedent “about,” it will be understood that the particular value forms another embodiment. The term “about” in relation to a numerical value is optional and means for example + / - 10%.

Claims

Claims:1 . An apparatus for processing wafer-shaped articles, the apparatus comprising: a support configured to support a wafer-shaped article; and a heating assembly comprising an array of LEDs configured to heat a wafer-shaped article supported by the support; wherein the LEDs are configured to emit light having a maximum intensity at a wavelength that is greater than or equal to 550nm and less than or equal to 980nm.

2. The apparatus according to claim 1 , wherein the LEDs are configured to emit light having a maximum intensity at a wavelength that is greater than or equal to 650nm, or greater than or equal to 660nm.

3. The apparatus according to claim 1 or claim 2, wherein the LEDs are configured to emit light having a maximum intensity at a wavelength that is less than or equal to 920nm.

4. The apparatus according to any preceding claim, wherein the LEDs are configured to emit red light or near infrared light.

5. The apparatus according to any preceding claim, wherein the apparatus comprises a liquid dispenser for dispensing a liquid onto a first surface of a wafer-shaped article supported by the support.

6. The apparatus according to claim 5, wherein the array of LEDs is arranged to heat a second surface of the wafer-shaped article that is on an opposite side of the wafer-shaped article to the first surface of the wafer-shaped article.

7. The apparatus according to any preceding claim, wherein the array of LEDs is arranged to heat a lower surface of a wafer-shaped article supported by the support.

8. The apparatus according to any preceding claim, wherein the array of LEDs is separated from the wafer-shaped article by a plate that is transparent to the light emitted by the LEDs.

9. The apparatus according to claim 8, wherein the plate is made of quartz or sapphire.

10. The apparatus according to any preceding claim, wherein the support is configured to rotate a wafer-shaped article supported by the support.

11. The apparatus according to any preceding claim, wherein the support is a rotary support.

12. The apparatus according to claim 10 or claim 11 , wherein the heating assembly is configured to remain stationary relative to the support.

13. The apparatus according to any preceding claim, wherein the support comprises a rotatable chuck surrounding a stationary post, and wherein the heating assembly is mounted on the stationary post.

14. The apparatus according to any preceding claim, wherein the LEDs have a viewing angle of less than or equal to 120°, or less than or equal to 90°, or less than or equal to 60°.

15. The apparatus according to any preceding claim, wherein each of the LEDs comprises a lens.

16. The apparatus according to any preceding claim, wherein the apparatus further comprises a gas supply mechanism configured to supply a gas to the array of LEDs.

17. The apparatus according to claim 16, wherein the gas supply mechanism is configured to supply a gas having an oxygen content of less than 1% by volume to the array of LEDs.

18. The apparatus according to claim 16 or claim 17, wherein the heating assembly is substantially enclosed in a chamber in the apparatus, and wherein the gas supply mechanism is configured to supply the gas to the chamber.

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