Method and system for cleaning a substrate having a contaminating element

Abstract

There is described a method of cleaning a substrate. The method generally has a step of irradiating, with a mid-infrared laser beam, a contaminating element resting against an area of the substrate, the mid-infrared laser beam having a central wavelength extending within a mid-infrared spectral band extending between 2.4 μm and 5 μm, the contaminating element having an absorption coefficient greater than an absorption coefficient of the substrate within the mid-infrared spectral band of the mid-infrared laser beam, wherein said irradiating removing the contaminating element from the area while maintaining an integrity of the area of the substrate.

Description

METHOD AND SYSTEM FOR CLEANING A SUBSTRATE HAVING A CONTAMINATING ELEMENT FIELD

[0001] The improvements generally relate to substrates used for electronic and / or photonic chips, and more specifically relate to the cleaning of such substrates.BACKGROUND

[0002] Foundries are factories that manufacture semiconductor devices like integrated circuits (ICs). These foundries typically specialize in complex and expensive manufacturing processes which can produce substrates containing a significant number of components before they are separated from one another using a singulating process, for instance. Although the manufacturing processes are mostly performed in a controlled environment, such as in clear or white rooms, there remains non-negligible chances of contaminating elements reaching the surfaces of the substrates. For example, semiconductor dust resulting from a previous manufacturing step may come to rest against an area of the substrate. The same may occur for epoxy residue, as epoxy-based adhesives are used frequently in semiconductor device manufacturing. In addition to these potential contaminant elements, undesirable grease or byproduct originating from some previous processing steps may often be found on some substrates. All of these contaminant elements need to be cleaned from the substrate before they are cleared for further processing steps. In some situations, the substrates are cleaned from their contaminating elements by hand by a skilled technician. These technician hours may be costly, especially since the typical foundry generally produces a significant number of such substrates on a daily basis. In some other situations, the amount and / position of contaminating elements may dissuade the skilled technician from initiating hand cleaning, and as a result the substrates may be discarded, which can be even more costly than hand cleaning. Other cleaning techniques, such as chemical cleaning techniques, plasma cleaning and ultrasonic cleaning techniques, can also be used in addition or in replacement of hand cleaning, but each of these techniques has its own set of drawbacks have limited efficiency in a production line. Although existing techniques for cleaning substrates in electronic foundries were satisfactory to a certain degree, there remains room for improvement.SUMMARY

[0003] Most standard laser sources used in laser cleaning applications operate in the ultraviolet region, the visible region or the near-infrared region of the electromagnetic spectrum. However, the typical materials used in substrates, e.g., glass materials or semiconductor materials, are known to have strong absorption coefficients in these regions of the electromagnetic spectrum. Accordingly, if contaminating elements were to be irradiated by such laser beams, the underlying substrate could be irreversibly damaged, too. The methods and systems disclosed herein aim at addressing at least some of the drawbacks associated with existing laser-cleaning processes using standard laser sources. Indeed, it is suggested to use a mid-infrared laser beam having a central wavelength extending within a mid-infrared spectral band extending between 2.4 pm and 5 pm. It was found that in the mid-infrared spectral band, materials of the typical substrates have a transparency window matching at least a portion of the mid-infrared spectral band. In addition, the most frequent contaminating elements, including liquid water, alcohol-based materials, organic contaminants, dust particles, isopropanol, methanol, polymer (e.g., acrylate), epoxies, all have strong absorption bands within the mid-infrared spectral band. Accordingly, it was found that by irradiating such a mid-infrared laser beam towards the contaminating elements resting against a substrate, the contaminating elements can be removed by ablation (or any other suitable removal mechanism) while maintaining the integrity of the underlying substrate. Mid-infrared laser beams are therefore uniquely situated to address the problem of a generalized cleaning solution for a wide range of contaminating elements resting against substrates at the foundry level, both front-end and back-end, for instance.

[0004] In accordance with a first aspect of the present disclosure, there is provided a method of cleaning a substrate, the method comprising: irradiation, with a mid-infrared laser beam, a contaminating element resting against an area of the substrate, the mid-infrared laser beam having a central wavelength extending within a mid-infrared spectral band extending between 2.4 pm and 5 pm, the contaminating element having an absorption coefficient greater than an absorption coefficient of the substrate within the mid-infrared spectral band of the midinfrared laser beam, wherein said irradiating removing the contaminating element from the area while maintaining an integrity of the area of the substrate.

[0005] Further in accordance with the first aspect of the present disclosure, the substrate can for example have a first ablation fluence and the contaminating element has a second ablation fluence, the mid-infrared laser beam having a given fluence below the first ablation fluence of the substrate and above the second ablation fluence of the contaminating element.

[0006] Still further in accordance with the first aspect of the present disclosure, the midinfrared laser beam can for example be a pulsed laser beam.

[0007] Still further in accordance with the first aspect of the present disclosure, the midinfrared laser beam can for example be emitted by a mid-infrared fiber laser source, the midinfrared fiber laser source being a fluoride glass fiber laser.

[0008] Still further in accordance with the first aspect of the present disclosure, said contaminating element can for example have a dimension above 500 nm, and preferably above 1 pm.

[0009] Still further in accordance with the first aspect of the present disclosure, said contaminating element can for example have an organic composition.

[0010] Still further in accordance with the first aspect of the present disclosure, the contaminating element can for example be one of: an epoxy residue, an organic grease residue, a high-OH-molecular link content material residue and water-based contaminant residue.

[0011] Still further in accordance with the first aspect of the present disclosure, said contaminating element can for example have an inorganic composition.

[0012] Still further in accordance with the first aspect of the present disclosure, the contaminating element can for example be one of a semiconductor dust residue, a glass residue, a solid polymer residue, a metallic residue, and an inorganic grease residue.

[0013] Still further in accordance with the first aspect of the present disclosure, the midinfrared laser beam can for example be a mid-infrared pulsed laser beam, the mid-infrared pulsed laser beam including pulses having a pulse duration in the nanosecond range.

[0014] Still further in accordance with the first aspect of the present disclosure, the method can for example further comprise, priorto said irradiating: capturing an image of the substrate; identifying, in the image, the contaminating element resting against the area of the substrate; and generating coordinates of at least one of the contaminating element and the area of the substrate; wherein said irradiation is performed based on said coordinates.

[0015] Still further in accordance with the first aspect of the present disclosure, the method can for example further comprise, between said capturing the image of the substrate and said irradiation, maintaining the area of the substrate dry.

[0016] Still further in accordance with the first aspect of the present disclosure, the method can for example further comprise determining irradiation pattern parameters based on one of: a size and shape of the contaminating element identified in the image.

[0017] Still further in accordance with the first aspect of the present disclosure, the substrate can for example have a characteristic feature, said capturing the image of the substrate including capturing an enlarged image of the characteristic feature of the substrate.

[0018] Still further in accordance with the first aspect of the present disclosure, the characteristic feature can for example be one of: a waveguide groove, and a coupling surface.

[0019] Still further in accordance with the first aspect of the present disclosure, the substrate can for example be one of a semiconductor substrate and a glass substrate.

[0020] In accordance with a second aspect of the present disclosure, there is provided a system for cleaning a substrate, the substrate having a contaminating element resting against an area of the substrate, the system comprising: a substrate support receiving the substrate; a mid-infrared laser source configured for emitting a mid-infrared laser beam towards the area of the substrate, the mid-infrared laser beam having a central wavelength extending within a mid-infrared spectral band extending between 2.4 pm and 5 pm; and a controller communicatively coupled to the mid-infrared laser source, the controller having a processor and a memory having stored thereon instructions that when executed by the processor perform the steps of: controlling the mid-infrared laser source for irradiating, with the midinfrared laser beam, the contaminating element resting against the area of the substrate, thecontaminating element having an absorption coefficient greater than an absorption coefficient of the substrate within the mid-infrared spectral band of the mid-infrared laser beam, wherein said irradiating removing the contaminating element from the area while maintaining an integrity of the area of the substrate.

[0021] Further in accordance with the second aspect of the present disclosure, the substrate can for example have a first ablation fluence and the contaminating element has a second ablation fluence, the mid-infrared laser beam having a given fluence below the first ablation fluence of the substrate and above the second ablation fluence of the contaminating element.

[0022] Further in accordance with the second aspect of the present disclosure, the midinfrared laser source can for example be a mid-infrared pulsed laser source emitting a midinfrared pulsed laser beam, the mid-infrared pulsed laser beam having pulses having a pulse duration ranging in the nanosecond range.

[0023] Further in accordance with the second aspect of the present disclosure, the system can for example further comprise a camera facing the area of the substrate and capturing an image thereof, the controller identifying, in the image, the contaminating element resting against the area of the substrate, and generating coordinates of at least one of the contaminating element and the area of the substrate, said irradiating including irradiating the contaminating element based on the coordinates.

[0024] Further in accordance with the second aspect of the present disclosure, mid-infrared laser source can for example be a fiber-based source having an output fiber outputting the mid-infrared laser source.

[0025] Further in accordance with the second aspect of the present disclosure, the output fiber of the mid-infrared laser source can for example be manipulable by a robot arm to direct the mid-infrared laser beam towards the area of the substrate.

[0026] Further in accordance with the second aspect of the present disclosure, the midinfrared laser source can for example be a mid-infrared fiber laser source provided in the form of a fluoride glass fiber laser.

[0027] All technical implementation details and advantages described with respect to a particular aspect of the present invention are self-evidently mutatis mutandis applicable for all other aspects of the present invention.

[0028] Many further features and combinations thereof concerning the present improvementswill appearto those skilled in the art following a reading of the instant disclosure.DESCRIPTION OF THE FIGURES

[0029] In the figures,

[0030] Fig. 1 is a schematic view of an example of a system for cleaning a substrate, in accordance with one or more embodiments;

[0031] Fig. 2A is a graph showing molecular absorption (a) varying as a function of wavelength for different substrate materials and for a contaminating element, in accordance with one or more embodiments;

[0032] Fig. 2B is a graph showing molecular absorption varying as a function of wavelength for different contaminating element materials, in accordance with one or more embodiments;

[0033] Fig. 3 is a flow chart of an exemplary method of cleaning a substrate, in accordance with one or more embodiments;

[0034] Fig. 4A is a top plan view of an example of a substrate having conducting pads against which rest contaminating elements, in accordance with one or more embodiments;

[0035] Fig. 4B is a top plan view of the substrate of Fig. 4A after irradiation of areas of the conducting pads using the mid-infrared laser beam, with brighter areas of the conducting pads being cleaned to remove the contaminating elements whereas darker areas of the conducting pads still have contaminating elements resting thereagainst, in accordance with one or more embodiments;

[0036] Fig. 4C is an enlarged view of the substrate of Fig. 4A, showing a junction between a brighter area free from contaminating elements and a darker area full of contaminating elements, within accordance with one or more embodiments;

[0037] Fig. 4D is a microscopic image of section 4D of Fig. 4C, in accordance with one or more embodiments;

[0038] Fig. 5A is a top plan view of an example of a substrate having tile array therein, showing a contaminating element having a dimension of about 50 pm resting against an area of the substrate overlapping with a portion of the tile array, in accordance with one or more embodiments;

[0039] Fig. 5B is a top plan view of the substrate of Fig. 5A after irradiation of the area of the substrate using the mid-infrared laser beam, showing that the integrity of the underlying tile array has been maintained, in accordance with one or more embodiments;

[0040] Fig. 6A is a top plan view of an example of a substrate having tile array therein, showing a contaminating element having a dimension of about 40 pm resting against an oxide area of the substrate spaced apart with the tile array, in accordance with one or more embodiments;

[0041] Fig. 6B is a top plan view of the substrate of Fig. 6A after irradiation of the oxide area of the substrate using the mid-infrared laser beam, showing that the integrity of the oxide area and adjacent tile array has been maintained, in accordance with one or more embodiments;

[0042] Fig. 7A is a top plan view of an example of a substrate having a waveguide taper therein, showing a contaminating element having a dimension of about 30 pm resting against over the waveguide of the substrate, in accordance with one or more embodiments;

[0043] Fig. 7B is a top plan view of the substrate of Fig. 7A after irradiation of the waveguide taper of the substrate using the mid-infrared laser beam, showing that the integrity of the underlying waveguide has been maintained, in accordance with one or more embodiments;

[0044] Fig. 8A is a top plan view of an example of a substrate having an edge, showing contaminating elements having a dimension of about 10 pm resting against the edge of the substrate, in accordance with one or more embodiments;

[0045] Fig. 8B is a top plan view of the substrate of Fig. 8A after irradiation of the edge of the substrate using the mid-infrared laser beam, showing that the integrity of the edge has been maintained, in accordance with one or more embodiments;

[0046] Fig. 8C is a top plan view of the substrate of Fig. 8B, showing yet another set of contaminating elements having a dimension of about 5 pm resting against the edge of the substrate, in accordance with one or more embodiments;

[0047] Fig. 8D is a top plan view of the substrate of Fig. 8C after irradiation of the edge of the substrate using the mid-infrared laser beam, showing that the integrity of the edge has been maintained while the other set of contaminating elements has been removed, in accordance with one or more embodiments;

[0048] Fig. 9 is a side elevation view of an example of a substrate having a series of waveguide grooves, shown with a contaminating element resting against one of the waveguide grooves, in accordance with one or more embodiments;

[0049] Fig. 10 is a side elevation view of an example of a substrate having an edge coupling surface, shown with a contaminating element resting against an edge coupling surface, in accordance with one or more embodiments; and

[0050] Fig. 11 is a schematic view of an example of a computing device of a controller, in accordance with one or more embodiments.DETAILED DESCRIPTION

[0051] Fig. 1 shows an example of a system 100 for cleaning a substrate 10 having one or more contaminating element(s) (hereinafter “the contaminating element”) resting against area(s) (hereinafter “the area”) of the substrate 10. As depicted, the system 100 has a substrate support 14 receiving the substrate 10, and a mid-infrared laser source configured for emitting a mid-infrared laser beam towards the area of the substrate 10 received on the substrate support 14. The mid-infrared laser beam typically has a central wavelength AMIR extending within a mid-infrared spectral band extending between 2.4 pm and 5 pm, preferably between 2.4 pm and 5 pm, and most preferably between 2.7 pm to 3.0 pm. As such, optical energy can be delivered to the area of the substrate 10 where laser cleaning is desirable toablate or otherwise remove the contaminating element from the area of the substrate 10. It is noted that the mid-infrared laser beam can be generated using a fiber laser source having a fiber segment made of a low phonon energy glass (e.g., fluoride glass) and having at least one laser-active doped region extending along the fiber segment. The mid-infrared laser source may be a mid-infrared pulsed laser source, a mid-infrared fiber laser source, or a combination of both. An example of such a fiber laser source is described in U.S. Patent No.10,084,287 B2, the contents of which are hereby incorporated by reference. For instance, the mid-infrared fiber pulsed laser source can be an ErZblan fiber laser, to name only one example. The system 100 can be used at any testing stages of the manufacture of the substrate 10. For instance, the system 100 can be used at a design stage where the substrate 10 is prototyped and corrected iteratively as desired, at a foundry stage where the substrate 10 is mass produced and / or at a packaging stage where the substrate 10 is integrated into a package, for instance.

[0052] Referring now to Fig. 2A, the contaminating element has an absorption coefficient acgreater than an absorption coefficient asof the substrate within the mid-infrared spectral band 20 of the mid-infrared laser beam. Put differently, the absorption coefficient QC(AMIR) of the contaminating element at the central wavelength AMIR is greater than the absorption coefficient QS(AMIR) of the substrate at that same central wavelength AMIR, i.e., QC(AMIR) > QS(AMIR). As depicted, the absorption coefficients QS(AMIR) of potential substrates, e.g., silicon dioxide (SiC>2) and silicon (Si), drop to low levels within the mid-infrared spectral band 20 whereas the absorption coefficient QC(AMIR) of an exemplary contaminant element having an organic composition has peaks within that same mid-infrared spectral band 20. It is known that a number of common contaminants are opaque in the mid-infrared spectral band 20 so they tend to absorb energy at a faster rate than the underlying substrate, which favors the ablation of the contaminating element while preserving the substrate thereunder. Fig. 2B shows example absorption peaks within the mid-infrared spectral band 20. More specifically, liquid water, methane, polymer (HDPE) and silicon dioxide (SiCh) all have strong absorption peaks within the mid-infrared spectral band 20 of the mid-infrared laser beam. As such, when the condition articulated above, irradiation of the area with the mid-infrared laser beam can lead to the removal of the contaminating element from the area of the substrate 10 while maintaining the integrity of the area of the underlying substrate 10.

[0053] In some embodiments, the contaminating element has an organic composition. For instance, the contaminating element can be an epoxy residue, an organic grease residue, a high-OH-molecular link content material (such as alcohol materials like isopropanol residue), a water-based contaminant residue, dust particles, polymer residues, epoxy residues, and the like. Some or all of these organic contaminating elements can be found in underfill materials or any other materials used in the assembly, processing and / or packaging of the substrate. In these cases, the strong absorption of the O-H, N-H and C-H molecular links (hydrogen-bonds) within the mid-infrared spectral band may lead to the ablation of the corresponding contaminating element. In some other embodiments, the contaminating element has an inorganic composition. For example, the contaminating element can be a semiconductor dust residue, an oxide residue, a glass residue, a solid polymer residue, a metallic residue, and an inorganic grease residue. For instance, the semiconductor dust residue can include silicon, SiGe, InP, SiN, SiC, etc. Some or all of these inorganic contaminating elements can come from previous chemical cleaning processes. Moreover, metallic residue and solid polymer residue can come from mechanical holders and grippers used for handling the substrates (e.g., wafers, dies). In these embodiments, the irradiation with the mid-infrared laser beam may still be able to ablate them for instance due to inhomogeneous or rough surfaces leading to total internal refraction of the mid-infrared laser beam within the contaminating element, or due to humidity surrounding the contaminating element, which can both cause heating, ablation and / or otherwise removal of the contaminating element upon irradiation with the midinfrared laser beam. Depending on the embodiment, the contaminating element can have a dimension above 500 nm, and preferably above 1 pm.

[0054] Referring back to Fig. 1 , the substrate 10 can include any type of components typically found in electronic chips and / or photonic chips. The substrate 10 can involve any type of glass, oxide or semiconductor material. For instance, the semiconductor material may include, but are not limited to, silicon, silicon nitride (SiN), silicon-on-insulator (SOI), silicon nitride (Si3N4), germanium (Ge), indium phosphide (InP), silicon carbide (SiC), gallium nitride (GaN), indium gallium arsenide (InGaAs), gallium arsenide (GaAs), lithium niobate (LiNbO3), indium antimonide (InSb), mercury cadmium telluride (MCT), indium arsenide (InAs), lead selenide (PbSe), lead sulfide (PbS), chalcogenide-based materials such as sulphide-based materials, selenide-based materials, telluride-based materials, any doped semiconductorincluding n-type doping, p-type doping, germanium doping, silicon doping, boron doping, arsenic doping, carbon doping, helium doping, antimony doping, and / or active laser material doping such as rare earth ion doping like erbium, ytterbium, quantum dot, gas. The oxide material may include, but are not limited to, silicon dioxide (SiCh), and the like. The glass material may include, but are not limited to, silica glass, laser-active ion doped glass, low phonon energy glass, and the like. The substrate 10 can also include crystalline materials such as CdSe, GaSe, TeO2, germanium, sapphire-based material, diamond-based materials, and the like.

[0055] As shown, the system 100 has a cleaning laser apparatus 110. In some embodiments, the system 100 can also incorporate a computer vision apparatus 130 incorporating a camera 132 imaging the substrate 10 in real time or quasi real time. A multiaxis movement stage 140 can optionally be used for moving the substrate 10 within a working zone as desired. The multi-axis movement stage 140 can be a translation stage and / or a rotation stage. In some embodiments, the cleaning laser apparatus 110 can be made integral to existing photonic testing apparatuses.

[0056] The system 100 can have a controller 150 which is communicatively coupled to the corrective laser apparatus 110, the computer vision apparatus 130 and / or the multi-axis moving stage 140, for instance. The controller 150 has a processor and a memory having stored thereon instructions that when executed by the processor perform preprogrammed instructions and / or method steps. To do so, the controller 150 generally incorporates hardware components provided in the form of a computing device and software components provided in the form of programs, algorithms and the like for performing the method steps. An example of the computing device is described below with reference to Fig. 11 .

[0057] Still referring to Fig. 1 , the corrective laser apparatus 110, the computer vision apparatus 130 and the multi-axis moving stage 140 can be fixedly or removably mounted to a frame 102. In this specific embodiment, the frame 102 is provided in the form of an optical bench or table. However, it is understood that, in some other embodiments, the corrective laser apparatus 110, the computer vision apparatus 130 and the multi-axis moving stage 140 can be mounted independently from one another at different locations of a foundry production line, for instance. In some embodiments, electronic probes and / or fiber probes may be in thepath of a mid-infrared laser beam of the corrective laser apparatus 110. In these embodiments, the corrective laser apparatus 110, a laser source thereof or an output thereof can be moved as desired above or below the substrate 10. Such movement can be generated using a scanning head involving two-axes or three-axes galvanometer scanner, a coarse gantry mechanism for movement within a centimeter squared, a fine gantry mechanism for movement within a relatively small area (e.g., 100 pm x 100 pm, 10 x 10 pm), a piezo micropositioner (e.g., a hexapod, a spatial light modulator (SLM)), an optical fiber cable with a microlens tip, a six degrees of freedom robotic arm, or any other motion apparatus with or without moving part(s) that can translate and / or deflect the mid-infrared laser beam, and / or any combination thereof. It is understood that the system 100 can have a galvometer of motorized elements to steer the mid-infrared laser beam towards areas of the substrates to be cleaned. These motorized elements can include, but are not limited to, fast shutter(s), salvo(S), beam shaping element(s), and / or digital technologies for preparing the mid-infrared laser beam for the irradiation of the area of the substrate. In some embodiments, the system 100 is provided with a contaminant exhaust system which draws the removed contaminants, or portions thereof, and convey them away from the substrate. In some embodiments, such a contaminant exhaust system has a channel having a first end proximate the substrate and a second end away from the substrate, and a gas flow circulator fluidly connected along the channel to actively suck air from the substrate. The contaminant exhaust system may help prevent redeposition of cleaned contaminants on the substrate after the irradiation step.

[0058] Fig. 3 is a flow chart of an exemplary method 300 of cleaning a substrate having a contaminating element, in accordance with an embodiment.

[0059] At step 302, the contaminating element is irradiated with a mid-infrared laser beam. The mid-infrared laser beam has a central wavelength extending within a mid-infrared spectral band which extends between about 2.4 pm and 5 pm. It is contemplated that the contaminating element has an absorption coefficient acgreater than an absorption coefficient asof the substrate within the mid-infrared spectral band of the mid-infrared laser beam. In other words, the absorption coefficient QC(AMIR) of the contaminating element at the central wavelength AMIR of the mid-infrared laser beam is greater than the absorption coefficient QS(AMIR) of the substrate at the central wavelength AMIR of the mid-infrared laser beam, i.e., QC(AMIR) > QS(AMIR).In some embodiments, the method 300 includes a step of controlling a given fluence of the mid-infrared laser beam relative to a first ablation fluence of the substrate and a second ablation fluence of the contaminating element. Indeed, the given fluence of the mid-infrared laser beam can be kept below the first ablation fluence of the substrate, and above the second ablation fluence of the contaminating element. When one or more of these conditions are respected, as shown at step 304, the contaminating element is removed from the area of the substrate while the integrity of the area of the substrate is maintained. By the maintaining the integrity of the area where irradiation occurs, it is intended that the irradiated area of the substrate remains more or less unaffected, thereby allowing the underlying components to function as designed, without any undesirable interference from the contaminating element.

[0060] In some embodiments, the method 300 includes a step 306 of capturing an image of the substrate, prior to the step 302 of irradiating. As depicted, the step 306 may be performed before the step 302 of irradiating to help guide the mid-infrared laser beam in the irradiation step. In these embodiments, the method 300 includes a further step 308 of identifying, in the captured image, the contaminating element resting against the area of the substrate. As such, coordinates of the contaminating element and / or of the area of the substrate can be generated. These coordinates may be used by a controller to aim the midinfrared laser beam where necessary. It is noted that the method 300 can include a step of capturing an image of the substrate, after the step 302 of irradiating. This post-irradiation image can be used to determine whether the contaminating element has been satisfactorily removed. If it has not been satisfactorily removed, yet another step 302 of irradiating may be performed, and so forth, until it is determined that the contaminating element has been satisfactorily removed. In other words, the step 302 of irradiating may be performed iteratively until the contaminating element has been removed. In some embodiments, a single irradiating step may be sufficient to remove a contaminating element. However, in some other elements, two or more irradiating steps may be required to remove a contaminating element in a satisfactory manner.

[0061] In these iterative steps, parameters with which the mid-infrared laser beam is operated may be modified to slightly increase the given fluence of the mid-infrared laser beam. The parameters of the mid-infrared laser beam may include, but are not limited to, pulseenergy, pulse duration, pulse repetition rate, scan speed, pitch, field of view, spot size, movement pattern, overlapping ratio, repetition of the movement pattern, and the like. It was found that the requirements on the fluence of the mid-infrared laser beam can be achieved by using pulses of a pulse duration in the nanosecond range. It is noted that in some embodiments upon identifying the contaminating element in the image, the controller may determine a size and type of the contaminating element, which may be linked to known reference parameters of the mid-infrared laser beam which may be stored in an accessible memory system. In these embodiments, upon identifying the size and / or type of contaminating element, proper parameters for the mid-infrared laser beam and / or for the irradiation pattern may be selected from a database associating sizes and types of contaminating element to corresponding mid-infrared laser beam parameters or irradiation pattern parameters.

[0062] The following paragraphs show experimental examples during which contaminating elements were removed from an area of a substrate while maintaining the integrity of the underlying substrate.

[0063] For instance, Fig. 4A shows a substrate having an elongated conducting pad. In this example, the conducting pads are made of gold. However, the conducting pads can be made of any conducting material including, but not limited to, silver, copper, doped semiconductor, graphene, and the like. In this example, the elongated conducting pad has contaminating elements resting thereagainst, as shown by its darker color relative to the brighter color of the circular conducting pad which has already been cleaned from contaminating elements. The contaminating element illustrated therein can come from an organic contaminating element such as underfill residue (e.g., epoxy residue). Fig. 4B shows the substrate of Fig. 4A after irradiation of areas of the elongated conducting pad using the mid-infrared laser beam. The dashed arrows show examples of irradiation patterns. However, any other suitable irradiation pattern could have been used in some other embodiments. As shown, these areas of the elongated conducting pad are not brighter, which indicates that the contaminating elements shown in Fig. 4A were removed satisfactorily. Figs. 4C and 4D are enlarged views of the substrate of Fig. 4A, showing a junction between a brighter area free from the contaminating elements and a darker area still bearing contaminating elements.

[0064] Fig. 5A shows another substrate having tile array therein. In this example, a contaminating element having a dimension of about 50 pm rests against an area of the substrate which overlaps with a portion of the tile array. In this case, the irradiation pattern parameters have been set to a movement pattern of a spiral having a final radius of 30 pm, a pitch of 5 pm (with the pitch defining an average radial distance extending between two consecutive circles of the spiral), a scanning speed of 5 mm / s, an overlapping ratio of 0% between consecutive irradiations of the mid-infrared laser beam, and the irradiation pattern has been repeated 5 times sequentially. Fig. 5B shows the substrate of Fig. 5A after irradiation of the area of the substrate using the mid-infrared laser beam. The dashed arrow shows an example irradiation pattern. However, any other suitable irradiation pattern could have been used in some other embodiments. Experimental results show that the integrity of the underlying tile array has been maintained while the undesirable contaminating element has been removed.

[0065] Fig. 6A shows another substrate having tile array therein. As depicted, a contaminating element having a dimension of about 40 pm rests against an oxide area of the substrate which is spaced apart with the tile array. In this example, the contaminating element is probably an inorganic dust residue. In this case, the irradiation pattern parameters have been set to a movement pattern of a spiral having a radius of 30 pm, a pitch of 5 pm, a scanning speed of 5 mm / s, an overlapping ratio of 0% between consecutive irradiations of the mid-infrared laser beam, and the irradiation pattern has been repeated 5 times sequentially. Fig. 6B depicts the substrate of Fig. 6A after irradiation of the oxide area of the substrate using the mid-infrared laser beam. The dashed arrow shows an example irradiation pattern. As shown, the integrity of both the oxide area and the adjacent tile array has been maintained while the contaminating element has been satisfactorily removed.

[0066] Fig. 7 A shows another substrate having a waveguide taper therein. As illustrated, a contaminating element having a dimension of about 30 pm rests against over the waveguide taper of the substrate in this example. In this example, the contaminating element is probably an organic alcohol residue. In this case, the irradiation pattern parameters have been set to a movement pattern of a spiral having a radius of 30 pm, a pitch of 5 pm, a scanning speed of 5 mm / s, an overlapping ratio of 0% between consecutive irradiations of the mid-infrared laserbeam, and the irradiation pattern has been repeated 5 times sequentially. Fig. 7B shows the substrate of Fig. 7A after irradiation of the waveguide taper of the substrate using the midinfrared laser beam, showing that the integrity of the underlying waveguide taper has been maintained. The dashed arrow shows an example irradiation pattern used to clean the contaminating element.

[0067] Fig. 8A shows another substrate having an edge against which contaminating elements rest. As shown, the contaminating elements have a dimension of about 10 pm. In this example, the contaminating element is a silicon residue. In this case, the irradiation pattern parameters have been set to a movement pattern of a spiral having a radius of 30 pm, a pitch of 5 pm, a scanning speed of 5 mm / s, an overlapping ratio of 0% between consecutive irradiations of the mid-infrared laser beam, and the irradiation pattern has been repeated 5 times sequentially. Fig. 8B is a top plan view of the substrate of Fig. 8A after irradiation of the edge of the substrate using the mid-infrared laser beam, showing that the integrity of the edge has been maintained. The dashed arrow shows an example irradiation pattern used to clean the contaminating element. In this example, this first irradiation step was not sufficient in cleaning a satisfactorily large area of the substrate. Accordingly, a further irradiation step has been performed. For instance, Fig. 8C shows the substrate of Fig. 8B after the first irradiation stem, showing yet another set of contaminating elements having a dimension of about 5 pm resting against the edge of the substrate. Fig. 8D depicts the substrate of Fig. 8C after irradiation of the edge of the substrate using the mid-infrared laser beam, showing that the integrity of the edge has been maintained while the other set of contaminating elements has been removed. The dashed arrow shows an example irradiation pattern used to clean the contaminating element in this second irradiation step. In this case, the irradiation pattern parameters have been set to a movement pattern of a spiral having a radius of 100 pm, a pitch of 5 pm, a scanning speed of 5 mm / s, an overlapping ratio of 0% between consecutive irradiations of the mid-infrared laser beam, and the irradiation pattern has been repeated 25 times sequentially.

[0068] The methods and systems described above are not limited to cleaning a substrate when its manufacturing is complete. In some embodiments, the methods and systems described herein may be used prior to important assembly and / or packaging steps whichrequire perfectly clean surfaces for optimal results. For instance, Fig. 9 shows an example application where a substrate 910 having a series of waveguide grooves 912 is to be assembled to a corresponding number of waveguides 914. For instance, in this embodiment, should the waveguide 914 (in this case an optical fiber) be inserted within one of the grooves 912 when a contaminating element 916 is present, the resulting performance of the component 900 may be detrimentally affected, as the presence of the contaminating element 916 may prevent the waveguide 914 from reaching the bottom of the waveguide groove 912 which in turn would reduce coupling efficiency. Accordingly, in this embodiment, it was found convenient to laser clean the entirety of the waveguide grooves 912 prior to the insertion of the waveguides 914 into the waveguide grooves 912. In this way, any coupling inefficiency may be prevented. In yet another example application, Fig. 10 shows a substrate 1010 having an edge coupler 1008 having an edge coupling surface 1012 which may be edge coupled to a waveguide 1014, e.g., an optical fiber. Here again, should a contaminating element 1016 rests against the edge coupling surface 1012 of the substrate 1010, inefficiencies in the coupling may be observed. Accordingly, it was found satisfactory to laser clean the entirety of the edge coupling surface 1012 of the substrate 1010 prior to the edge coupling of the waveguide 1014 against the edge coupling surface 1012. Alternatively or additionally, an edge coupling surface 1012 of the waveguide 1014 may be laser cleaned as well prior to the edge coupling. In this way, any coupling inefficiency may be prevented as well. It is intended that the methods and systems described herein may be used in some other applications to reduce the adverse effects of contaminating elements on substrates manufactured in foundries, for instance.

[0069] Referring now to Fig. 11 , the controller shown in Fig. 1 can be provided as a combination of hardware and software components. The hardware components can be implemented in the form of a computing device 1100, an example of which is described with reference to Fig. 11. The computing device 1100 can have a processor 1102, a memory 1104, and I / O interface 1106. Instructions 1108 for performing the methods disclosed herein, e.g., capturing image(s), identifying contaminating elements in the image(s), generating coordinates of the areas to be irradiated, instructing the laser cleaning system to irradiate the areas to be irradiated, can be stored on the memory 904 and accessible by the processor 1102.

[0070] The processor 1102 can be, for example, a general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field-programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), a programmable logic controller (PLC), or any combination thereof.

[0071] The memory 1104 can include a suitable combination of any type of computer-readable memory that is located either internally or externally such as, for example, randomaccess memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable readonly memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

[0072] Each I / O interface 1106 enables the computing device 1100 to interconnect with one or more input devices, such as mouse(s), keyboard(s), sensor(s), or with one or more output devices such as monitor(s), external memory system(s), accessible network(s).

[0073] Each I / O interface 1106 enables the controller to communicate with other components, to exchange data with other components, to access and connect to network resources, to server applications, and perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fibre optics, satellite, mobile, wireless (e.g., Wi-Fi, WiMAX), SS7 signalling network, fixed line, local area network, wide area network, and others, including any combination of these.

[0074] The computing device 1100 and any software application that can be run by the computing device 1100 are meant to be examples only. Other suitable embodiments of the controller can also be provided, as it will be apparent to the skilled reader.

[0075] As can be understood, the examples described above and illustrated are intended to be exemplary only. For instance, the applications where the methods and systems may be used may include, but are not limited to, waveguide groove cleaning, edge coupler cleaning, waveguide tip cleaning, mask cleaning, flip chip pad cleaning, conductive pad cleaning forinstance before indium phosphide (InP) laser hybrid bonding, and the like. In some embodiments, the systems and methods used herein can be used as an industrial grade solution implementable into a new foundry line. However, in some other embodiments, the systems and method used herein can be installed (e.g., retrofitted) to existing foundry processes. The scope is indicated by the appended claims.

Claims

1. WHAT IS CLAIMED IS:1 . A method of cleaning a substrate, the method comprising:irradiation, with a mid-infrared laser beam, a contaminating element resting against an area of the substrate, the mid-infrared laser beam having a central wavelength extending within a mid-infrared spectral band extending between 2.4 pm and 5 pm, the contaminating element having an absorption coefficient greater than an absorption coefficient of the substrate within the mid-infrared spectral band of the mid-infrared laser beam, wherein said irradiating removing the contaminating element from the area while maintaining an integrity of the area of the substrate.

2. The method of claim 1 wherein the substrate has a first ablation fluence and the contaminating element has a second ablation fluence, the mid-infrared laser beam having a given fluence below the first ablation fluence of the substrate and above the second ablation fluence of the contaminating element.

3. The method of claim 1 or 2 wherein the mid-infrared laser beam is a pulsed laser beam.

4. The method of any one of claims 1 to 3 wherein the mid-infrared laser beam is emitted by a mid-infrared fiber laser source, the mid-infrared fiber laser source being a fluoride glass fiber laser.

5. The method of any one of claims 1 to 4 wherein said contaminating element has a dimension above 500 nm, and preferably above 1 pm.

6. The method of any one of claims 1 to 5 wherein said contaminating element has an organic composition.

7. The method of claim 6 wherein the contaminating element is one of: an epoxy residue, an organic grease residue, a high-OH-molecular link content material residue and waterbased contaminant residue.

8. The method of any one of claims 1 to 7 wherein said contaminating element has an inorganic composition.

9. The method of claim 8 wherein the contaminating element is one of a semiconductor dust residue, a glass residue, a solid polymer residue, a metallic residue, and an inorganic grease residue.

10. The method of any one of claims 1 to 9 wherein the mid-infrared laser beam is a midinfrared pulsed laser beam, the mid-infrared pulsed laser beam including pulses having a pulse duration in the nanosecond range.

11. The method of any one of claims 1 to 10 further comprising, prior to said irradiating:capturing an image of the substrate;identifying, in the image, the contaminating element resting against the area of the substrate; andgenerating coordinates of at least one of the contaminating element and the area of the substrate;wherein said irradiation is performed based on said coordinates.

12. The method of claim 11 further comprising, between said capturing the image of the substrate and said irradiation, maintaining the area of the substrate dry.

13. The method of claim 11 or 12 further comprising determining irradiation pattern parameters based on one of: a size and shape of the contaminating element identified in the image.

14. The method of any one of claims 11 to 13 wherein the substrate has a characteristic feature, said capturing the image of the substrate including capturing an enlarged image of the characteristic feature of the substrate.

15. The method of claim 14 wherein the characteristic feature is one of: a waveguide groove, and a coupling surface.

16. The method of any one of claims 1 to 15 wherein the substrate is one of a semiconductor substrate and a glass substrate.

17. A system for cleaning a substrate, the substrate having a contaminating element resting against an area of the substrate, the system comprising:a substrate support receiving the substrate;a mid-infrared laser source configured for emitting a mid-infrared laser beam towards the area of the substrate, the mid-infrared laser beam having a central wavelength extending within a mid-infrared spectral band extending between 2.4 pm and 5 pm; anda controller communicatively coupled to the mid-infrared laser source, the controller having a processor and a memory having stored thereon instructions that when executed by the processor perform the steps of: controlling the mid-infrared laser source for irradiating, with the mid-infrared laser beam, the contaminating element resting against the area of the substrate, the contaminating element having an absorption coefficient greater than an absorption coefficient of the substrate within the mid-infrared spectral band of the mid-infrared laser beam, wherein said irradiating removing the contaminating element from the area while maintaining an integrity of the area of the substrate.

18. The system of claim 17 wherein the substrate has a first ablation fluence and the contaminating element has a second ablation fluence, the mid-infrared laser beam having a given fluence below the first ablation fluence of the substrate and above the second ablation fluence of the contaminating element.

19. The system of claim 17 or 18 wherein the mid-infrared laser source is a mid-infrared pulsed laser source emitting a mid-infrared pulsed laser beam, the mid-infrared pulsed laser beam having pulses having a pulse duration ranging in the nanosecond range.

20. The system of any one of claims 17 to 19 further comprising a camera facing the area of the substrate and capturing an image thereof, the controller identifying, in the image, the contaminating element resting against the area of the substrate, and generating coordinates of at least one of the contaminating element and the area of the substrate, said irradiating including irradiating the contaminating element based on the coordinates.

21. The system of any one of claims 17 to 20 wherein mid-infrared laser source is a fiberbased source having an output fiber outputting the mid-infrared laser source.

22. The system of claim 21 wherein the output fiber of the mid-infrared laser source is manipulable by a robot arm to direct the mid-infrared laser beam towards the area of the substrate.

23. The system of any one of claims 17 to 22 wherein the mid-infrared laser source is a mid-infrared fiber laser source provided in the form of a fluoride glass fiber laser.

Images