Patent Application
20060131268
1. Field of the Invention
The present invention relates generally to substrate preparation and cleaning, and more particularly, to systems, apparatus, and methods for improving substrate preparation and/or cleaning operations.
2. Description of the Related Art
The fabrication of semiconductor devices involves numerous processing operations. These operations include, for example, dopant implants, gate oxide generation, inter-metal oxide depositions, metallization depositions, photolithography patterning, etching operations, chemical mechanical polishing (CMP), etc. Some processing operations may include removing of an entire layer of film/coating or a discrete portion of the film/coating from over the wafer surfaces. Other processing operations may include generating particulate contaminants, which can typically adhere to wafer surfaces. Generally, particulate contaminants consist of tiny bits of distinctly defined material having an affinity to adhere to the surfaces of the wafer. Examples of particulate contaminants can include organic and inorganic residues, such as silicon dust, silica, slurry residue, polymeric residue, metal flakes, atmospheric dust, plastic particles, and silicate particles, among others. Failure to remove a desired layer or the particulate contaminants from wafer surfaces can have detrimental effects on the performance of integrated circuit devices.
Cleaning wafer surfaces and removing the particulate contaminants and/or films or coatings can be achieved using non-contact laser cleaning techniques. In conventional laser cleaning systems, an Ultra Violet (UV) light beam is issued by a laser system and shined onto the wafer surface. The energy supplied by the UV light beam is then used to break the bond between the particulate contaminants/coatings/films and wafer surface. The particulate contaminants or portions of the coatings/films detached from wafer surfaces are then evaporated. In photoablation, one of such conventional non-contact cleaning techniques, UV light beams having 355 to 550 nanometer wavelengths and pulse durations of about seven (7) to ten (10) nanoseconds are implemented.
Several drawbacks can be associated with using the energy generated in the conventional laser cleaning systems. One of such limitations is the fairly difficult to control nature of the photoablation processes. By way of example, thermal processes cause the material of the particulate contaminants/film/coating to be evaporated layer by layer, starting from the very top surface of the particulate contaminants/film/coating. However, because thermal processes are hard to manage, the wafer surface defined directly underneath the location of the removed particulate contaminants/film/coating can be damaged. Additionally, the rather hard to control nature of the thermal processes can further damage the edges of the remaining film/coating surrounding the locally detached and removed portions. As such, thermal processes can be unsuitable for precise and discrete removal of the particulate contaminants or portions of films/coatings.
Yet another limitation associated with the conventional laser cleaning systems is the rather narrow range of UV light beam intensities (i.e., energy) supported by the typical laser systems suitable for removal of the particulate contaminants/films/coatings from the wafer surface. In particular, removing particulate contaminants/films/coatings strongly bonded to the wafer surfaces requires high UV light beam intensity laser pulses. However, again, implementing high intensity UV light beams can damage the wafer surface defined directly underneath the location of the detached particulate contaminant or the removed portion of film or coating.
Still another limitation is that the conventional laser systems are used in conjunction with custom gas recipes. However, to achieve effective cleaning, complicated and expensive gas recipes should be obtained and implemented.
Limitations associated with conventional laser cleaning systems can be understood by the four scanning electron microscopy (SEM) images associated with four stages of removing a silicon oxide film from over a silicon wafer, as depicted in
Accordingly, the nanosecond conventional laser cleaning systems can damage wafer surfaces being prepared. Such damages are disfavored as the condition of the wafer surfaces and the operation of the wafers can be adversely affected, ultimately lowering the process yield.
In view of the foregoing, there is a need for a system, apparatus, and method for preparing substrate surfaces capable of locally removing particulate contaminants, films, and coatings from over surfaces of the substrates without substantially damaging substrate surfaces.
Broadly speaking, the present invention fills these needs by providing a method, apparatus, and system capable of precise, discrete, and local removal of particulate contaminants, films, and coatings from over a surface of a substrate without substantially damaging the substrate surface. In one embodiment, high intensity ultra short laser beam pulses are implemented to locally remove the particulate contaminants, films, and coatings from over a surface. It should be appreciated that the present invention can be implemented in numerous ways, including as a process, an apparatus, a system, a device, or a method. Several inventive embodiments of the present invention are described below.
In one embodiment, a substrate preparation method is provided. The method includes providing a substrate to be prepared. The substrate has a first layer and a second layer. The first layer is configured to be removed from over the second layer. An energy frequency that is to be absorbed by the second layer while penetrating through the first layer transparently is determined. Energy that has the determined energy frequency is applied onto the first layer so as to disrupt a bond between the first layer and the second layer at a location of application of the energy. A portion of the first layer defined at the location of application of energy is removed.
In another embodiment, a substrate preparation apparatus is provided. The apparatus includes an energy source and a support component. The energy source is capable of emitting energy emitted in a femtosecond pulse duration onto a substrate to be prepared. The substrate has a first layer and a second layer wherein the first layer is configured to be removed from over the second layer. The energy is configured to have an energy frequency that is capable of being absorbed by the second layer while transparently penetrating through the first layer. The support component is configured to support the substrate to be prepared as energy is emitted onto the first layer of the substrate. The absorption of the energy by the second layer generates an energy wave that is capable of breaking a bond between the first layer and the second layer at a location of application of the energy so as to remove a portion of the first layer at the location of the application of the energy.
In yet another embodiment, another substrate preparation method is provided. An energy frequency that is configured to be absorbed by a substrate surface while transparently penetrating through a particulate contaminant adhered to the substrate surface is determined. Energy that has the determined energy frequency is applied onto the particulate contaminant so as to disrupt a bond between the particulate contaminant and the substrate surface.
The advantages of the present invention are numerous. Most notably, in contrast to the prior art, the embodiments of the present invention enable precise, discrete, and localized cleaning of substrate surfaces while substantially minimizing damages the substrate surface. Another advantage of the non-contact femtosecond laser system of the present invention is that the system can be implemented to prepare fragile materials. Yet another advantage of the present invention is that the non-contact femtosecond laser system of the present invention can be efficiently used to prepare substrate surfaces, thus maximizing throughput. Still another advantage of the non-contact laser system of the present invention is the capability of the system to perform dry-only cleaning of the substrate surfaces, thus enabling cleaning of materials that may be incompatible with wet chemistries. Yet another advantage of the present invention is that the localized, discrete, and precise removal capability of the present invention yields remaining films/coatings that have featureless featureless edges.
Other aspects and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.
The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, and like reference numerals designate like structural elements.
An invention that is capable of precisely and discretely removing particulate contaminants, films, and coatings from over surfaces of the substrate without substantially damaging substrate surfaces is provided. In one embodiment, high intensity ultra short laser beam pulses issued by a laser system is implemented to break a bond between the particulate contaminants/films/coatings and the substrate surface leading to the removal of the particulate contaminants, films, and coatings from over substrate surfaces. According to one example, an irradiation wavelength of the laser beam is selected such that the laser beam can be absorbed completely by the substrate while is absorbed minimally (if any) by the particulate contaminants/films/coatings being removed. In one example, the laser beam pulse duration can range between about one (1) femtosecond and 100,000 femtoseconds. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be understood, however, to one skilled in the art, that the present invention may be practiced without some or allof these specific details. In other instances, well known process operations have not been described in detail in order not to unnecessarily obscure the present invention.
The top component 105 houses a laser system 112 implementing an optic 114. A laser beam 116 issued by the laser system 112 is shined over a spot 101 on the substrate 106 so as to scan and ultimately strip the first layer 110, as the substrate 106 is translationally rotated in the rotation direction 107. Of course, one of ordinary skill in the art must appreciate that although in the illustrated embodiment the substrate 106 and stage 104 have been placed in the translational and rotation states, in another embodiment, the laser system 112 can be set on a scanning state so as to move in a scanning direction, thus scanning the entire surface of the substrate 106, as the stage 104 and the substrate 106 remain stationary while rotating. One of ordinary skill in the art must further appreciate that in a different embodiment, the substrate surface 106 can be scanned using the optics 114 while the laser system 112 remains stationary. For instance, an angle of the optics can be changed so as to shine the laser beam 116 at different spots on the substrate 106, scanning the entire substrate surface.
One of ordinary skill in the art must appreciate that the stage 104 can be rotated and moved translationally using any appropriate mechanism. Yet further, one of ordinary skill in the art must appreciate that while in the illustrated embodiment the substrate 106 is supported and rotated by the stage 104, in another embodiment, any appropriate mechanics and engineering can be implemented to support, rotate, and move the substrate translationally (e.g., edge carrier, edge drive rotation rollers, vacuum chuck, etc.). Furthermore, in another embodiment, the position of the laser beam on the substrate 106 can be raster scanned by a set of mirrors and/or lenses.
In accordance with one embodiment, the laser system 112 is a Ti:Sapphire femtosecond laser system, and is used to provide laser beams of a desired wavelength (e.g., 800 nanometers, etc.). In one example, the Ti-Sapphire laser is a Ti-Sapphire Newport Corporation (the Spectra-Physics, Ltd.), located in Mountain view, Calif.
As will be described in more detail below with respect to
As can be seen, in one instance, the exhausts 131 are fitted within respective pairs of seals 132 disposed in close proximity to exhausts 131. In this manner, advantageously, the seals 132 can prevent introduction of excess particulate contaminants into the chamber 103. In one embodiment, the gas introduced into the chamber 103 can be air or nitrogen. Of course, one of ordinary skill in the art must appreciate that any appropriate inert gas may be utilized to provide airflow within the chamber 103 and to expel released materials 115 from the chamber 103.
With continued reference to
As is described in more detail with respect to
In one example, absorption of the laser beam 116 by the second layer 108 results in a localized heating, causing a second layer active region 138 defined at an interface 111 of the first layer 110 and the second layer 108 to heat up locally. As can be seen, the second layer active region 138 is confided within a diameter of the spot 101. The second layer active region 138 is excited, heated up substantially rapidly, and expanded substantially rapidly. The heat can dissipate fast, causing the active region 138 to compress, giving rise to a stress wave 146 between the first layer 110 and the second layer 108 at the bond interface 111. In one example, a bipolar wave front 142 can be formed at the bond interface 111 when the stress wave reflects off a free surface (e.g., the interface between the first layer 110 and air, as confined within the diameter of the spot 101). In the event the energy of the stress wave 146 is greater than the tensile energy between the first layer 110 and the second layer 108 at the bond interface 111, the energy of the stress wave breaks the bond between the first layer 110 and the second layer 108 at the bond interface 111. As a consequence, the portion 136 of the first layer confided within the diameter of the spot 101 is detached and stripped off. According to one embodiment of the present invention, photospallation technique is implemented to break the forces between the contaminant particulates/films/coatings.
In one example, the pulse duration of the ultra short laser beam is configured to be shorter than a relaxation time of the material of the second layer 108. Thus, when the first layer is silicon oxide and the second layer is silicon, the pulse duration of the ultra short laser beam is about 70 femtoseconds. Additionally, the wavelength of the ultra short light beam is selected such that the laser beam 116 is absorbed by the silicon layer but not by the silicon oxide layer. In one example, the laser beam wavelength is about 800 nanometers. In one embodiment, the force created as a result of rapid expansion of the active region of the second layer is proportional to the power of the laser beam. By way of example, the shorter the laser beam pulse is, the faster the active region expands and thus the stronger the force breaking the bond between the particulate contaminants/films/coatings can be.
Precise, discrete, and localized removal capabilities associated with the high intensity femtosecond laser beam system can further be understood with respect to the localized removal of the portion 136 as illustrated in the exaggerated partial cross sectional view of
In the illustrated embodiment, removal of the portion 136 is achieved by removing the material in a removal direction 150, from a bottom surface 110bof the first layer 110 to a top surface 110a of the first layer 110. Ultimately, the material defined in the portion 136 is evaporated and thereafter removed from the chamber 103 by the airflow. In the illustrated embodiment, the remainder of the first layer 110 surrounding the removed portion 136′ is shown to have rather smooth edges. Of course, one of ordinary skill in the art must appreciate that localize removal capability of the present invention is substantially different than the prior art laser systems wherein the contaminants are removed layer by layer, starting from the top layer of the contaminant particulates toward the bottom layer of the contaminant.
The SEM images shown in
Although the diameters of the laser beams are about 5 microns, the energy density of the laser beam illustrated in
Furthermore, the removed portions of the first layer can produce particulate contaminants that can be deposited back on the removed portions of the first layer or a different location on the first layer. In the prior art with nanosecond laser beam systems, the deposited back contaminant particulates can be removed by increasing the energy of the laser beam. However, such increase in the laser beam energy can damage the portion of the second layer defined directly underneath the contaminant particulate. In the present invention, however, the deposited back contaminant particulates can be removed from over substrate using the high intensity ultra short laser beam pulses without substantially damaging the layer defined directly below the contaminant particulate.
Discrete removal of portions of the first layer 110 have been illustrated in the simplified top views of the substrate 106 depicted in
One of ordinary skill in the art must recognize and appreciate that the duration of the femtosecond laser beam pulse can range between approximately one (1) fs to 100,000 fs, a more preferred range of between approximately 30 fs to 150 fs, and the most preferred pulse duration of about 70 fs. In one embodiment, the 70 fs laser beam pulse duration is selected as the 70-femtosecond laser pulses can be easily obtained (e.g., coning the stagnation of the 70-femtosecond-laser beam pulse can be easily achieved due to the properties of the laser amplifier system and compression system). According to one embodiment, the irradiation wavelength depends on whether the discrete wavelength is easily obtainable and whether the discrete wavelength is absorbable by the second layer and not the first layer. One of ordinary skill in the art must appreciate that the irradiation wavelength can range between about 200 nanometers and 1500 nanometers, and most preferably approximately 800 nanometers. Yet further, one of ordinary skill in the art must appreciate that in one embodiment of the present invention, the absorption curve of silicon ranges between about 760 nm and 1160 nm. One of ordinary skill in the art must further recognize and appreciate that the high intensity ultra short laser beam pulse laser system of the present invention can be implemented to remove first layers having a thickness of approximately about one (1) nanometer and 10 microns, and more preferably between approximately one (1) nanometer and, five (5) microns and most preferably between approximately 50 nanometer and two (2) microns. One of ordinary skill in the art must appreciate that a size of the particulate contaminant being removed can range between approximately one (1) nanometer and 10,000 nanometers. In one exemplary embodiment wherein the first layer is an oxide layer, the thickness of the oxide layer being removed can be approximately 0.5 microns (i.e., 5000 Angstroms or 500 nanometers). Of course, one must note that in one embodiment, the layer being removed can have any suitable thickness so long as the coefficient of absorption of the layer being removed is very small.
In one example, an energy threshold of 0.05 J/cm2 maybe required for removal of 1 μm thick silicon oxide film using 800 nm irradiation wavelength. If the diameter of the spot is approximately five (5) μm, then 10 nJ per pulse is required to remove the material irradiated by the laser beam spot. The total area from which the film can be removed by one laser pulse depends only on the average power of the incoming beam and the threshold for film removal. According to one embodiment, if the threshold energy density of approximately 0.05 J/cm is implemented using a femtosecond laser system having a power of approximately 0.5 W, a removal speed of 10 cm2/s can be achieved. In such a scenario, in one embodiment, approximately one (1) minute may be needed to achieve complete coverage of the surface of a 12″ wafer at the energy densities above the threshold for film removal.
According to one embodiment of the present invention, the high intensity ultra short laser beam pulse laser system can be implemented to remove films/coatings in discrete locations. For instance, a specific layer of a substrate can be etched using the high intensity ultra short laser beam pluses in discrete locations without having to apply a photoresist material to mark the locations to be removed. In one example, the size of the laser beam spot being shined on the substrate layer to etch a feature can be approximately about 0.1 micron. In another example, the high intensity ultra short laser beam pulses can be implemented to remove material remaining on the beveled edge of the substrate. For instance, the high intensity femtosecond laser system can be implemented to remove material from over the beveled edge of the substrate ranging between approximately hundreds of microns and between tens of microns.
In another embodiment of the present invention, the femtosecond laser system can be integrated into a cleaning system implementing a proximity clean and dry system so as to clean the substrate surfaces. In such an embodiment, after the substrate surfaces have been cleaned and dried using the proximity head, high intensity ultra short laser beam pulse laser system can be implemented to remove edge polymer residues on the front side and/or backside surfaces of the substrate as well as the beveled edge of the substrate surface introduced during the prior processing operations (e.g., etch, lithography, deposition, etc.), etc. For additional information about the proximity vapor clean and dry system, reference can be made to an exemplary system described in the U.S. Pat. No. 6,488,040, issued on Dec. 3, 2002, having inventors John M. de Larios, Mike Ravkin, Glen Travis, Jim Keller, and Wilbur Krusell, and entitled “C
Although for ease of understanding and reference the description of
The femtosecond laser system of the present invention can further be implemented at the surface interface of SiC and Si wherein the wavelength of the laser beam can range between about 300 nanometers and 1000 nanometers; Si3N4 and Si wherein the wavelength of the laser beam can range between approximately 300 nanometers and 450 nanometers; SiC and Cu wherein the wavelength of the laser beam can range between approximately 500 nanometers and 1400 nanometers; and Si3N4 and Cu wherein the wavelength of the laser beam can range between about 500 nanometers and 1400 nanometers.
Proceeding to
Furthermore, depending on the application, the angle of the beams with the substrate surface can be controlled by the system control 118. Additionally, depending on the application, the size of the spot size can be minimized or the substrate coverage can be maximized using the system control 118. In another example, the system control 118 can be implemented to set the system for optimization for specific properties of the substrate layers and applications. According to one embodiment, to maximize throughput, the system control 118 may maximize the number of laser beams being shined onto the substrate.
According to one example, inspection and local removal of particulate contaminants of the apparatus 102″ can be implemented to clean the substrate backside. Specifically, the apparatus 102″ can be implemented to remove particulate contaminants and materials deposited around edges of scratches formed in the substrate backside. Once located, the particulate contaminants are ultimately evaporated and removed from over the substrate backside and into the chamber 103, which are ultimately, expelled using adequate flow of inert gases (e.g., nitrogen, argon, helium, a proprietary reactive gas mixture, etc.).
According to one embodiment of the present invention, the femtosecond laser system of the present invention in a clustered substrate processing system. For instance, after a substrate has been pre-processed in an etching chamber, a chemical vapor deposition system, a chemical mechanical polishing (CMP) system, etc., the substrate surfaces can be prepared in the femtosecond laser system of the present invention.
Yet further, in one exemplary implementation, the femtosecond laser system of the present invention can be implemented in a clustered substrate preparation apparatus that may be controlled in an automated way by a control station. For instance, the clustered substrate preparation apparatus may include a sender station, a femtosecond laser module, and a receiver station. Broadly stated, substrates initially placed in the sender station are delivered, one-at-a-time, to the femtosecond laser module. After being prepared, the substrates are then delivered to the receiver station for being stored temporarily. One of ordinary skill in the art must appreciate that in one embodiment, the clustered preparation apparatus can be implemented to carry out a plurality of different substrate preparation operations (e.g., cleaning, etching, etc.).
Although the foregoing invention has been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. For example, the embodiments of the present invention can be implemented to clean and prepare any substrate having varying sizes and shapes such as those employed in the manufacture of semiconductor devices, flat panel displays, hard drive discs, flat panel devices, and the like. Additionally, the present embodiments are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope and equivalents of the appended claims.
