KR20180081460A - Apparatus and method for contamination identification - Google Patents

Abstract

Provided are a method and an apparatus for identifying contaminants on a substrate. Identifying contaminants removed from a substrate can be useful for identifying and eliminating the contaminants, removing the same, and minimizing potential damage to the substrate by adjusting an eliminating method. Moreover, the method for identifying contaminants can provide liberation of contaminant molecules from a surface of the substrate by considering various types of geometrical structures and substrate materials, sample preparation, and chemical analysis of contaminants.

Description

[0001] APPARATUS AND METHOD FOR CONTAMINATION IDENTIFICATION [0002]

The present invention relates to a contamination identification apparatus and method useful for cleaning a surface, and more particularly to a contamination identification apparatus and method useful for cleaning surfaces of components typically used in the semiconductor industry, optics, and the like. The disclosed contamination identification apparatus and method can be applied to extend the useful life of a photomask reticle.

Electromagnetic radiation has been used for a long time for surface cleaning. Examples of these processes include removal of surface contaminants, removal of a thin layer of material coating such as paint, or removal of oil from a metal work surface. Some early examples used flash lamp radiation sources. These systems may have limited application due to the maximum achievable output.

Lasers are increasingly being used in these types of processes due to their high maximum power achievable, high energy stability and wavelength selectivity. These features enable high localization, improved material selectivity, and depth control of the cleaning effect. The cleaning process of the laser surface can be broadly classified into surface contamination layer removal and particulate removal. Removal of the surface contaminant layer is generally accomplished by laser cutting. Particle removal involves total removal of contaminants.

Under both categories, the cleaning process can be useful because it provides higher maximum power through the use of pulsed laser radiation. In particular, short pulsed radiation can provide improved processing. Short pulse radiation has been shown to reduce heat affected zone in laser cutting. This allows for finer control of the removal depth as well as improved localization of deflection removal. In addition, short pulsed radiation may increase the rate of heat buildup in the particles and / or the substrate to improve particulate removal, thereby increasing the acceleration that results in particle removal.

Substrate damage can be a problem for both the fusing process and the particulate removal process, and several techniques have been developed to minimize these effects. In the case of a fusing process, the selection of the wavelengths that increase the absorption of the contaminants can reduce fluence requirements and thus reduce substrate damage. In addition, when multiple pulses are used to completely remove contaminants, the required fluence can be reduced. However, substrates with high absorptivity at selected wavelengths tend to soften with contaminants even with wavelength selection and multiple pulse removal processes. In this case, the ability to terminate the removal process at the substrate interface is limited. Since the absorption cross section for the contaminants is reduced relative to the substrate, the problem is greatly increased for smaller size contaminants.

Like the erosion removal process, the particulate removal process may also cause substrate damage to the substrate with high absorption at sensitive substrates and processing wavelengths. This problem becomes large when small particles are removed due to the increased adhesion between the particles and the substrate and the self-focusing of the laser underneath the particles. In the case of particle cleaning processes, apparatus and methods developed to reduce the risk of damage to the substrate include controlling the environment above the contaminated surface. Examples of microparticle laser processes that enable reduction of fluence levels include wet laser cleaning, vapor laser cleaning, and increased humidity cleaning. The combination of lasers and other cleaning processes (including etching, organic solvents, and ultrasonics) has been shown to increase the cleaning effect and reduce the risk of substrate damage. However, with the exception of the dry laser cleaning process, all of the aforementioned particulate removal processes require access to the environment above the substrate surface. This may be impractical for some systems.

An alternative dry laser particulate cleaning process has been developed. Laser acoustic wave cleaning and laser shockwave cleaning are dry laser cleaning methods that are also evaluated for particulate cleaning. Laser acoustic wave cleaning involves direct excitation to the substrate, and as discussed above, there is a high probability of substrate damage, especially for small particles. The laser shockwave cleaning improves removal of particulates and has been shown to focus the laser on the substrate surface and reduce the risk of substrate damage by relying on the shock wave interaction with the microparticles. If this technique is applied to the removal of small particles, the difficulties will also increase. In addition, shock waves can damage other sensitive features on or near the substrate surface. This is especially the case when there is a sensitive material on the substrate surface, as it requires a relatively high laser intensity to be focused on the substrate for shock wave generation.

Even the latest dry laser technology can have limitations when access to the environment on the surface is impractical (eg, closed systems). Because the particles are entirely removed from the surface, the removal process moves the particles only to another location on the substrate for the closed system. Typically, these techniques utilize additional control devices and methods that completely remove particles from the substrate being cleaned. These methods include the use of directional airflow, reduced pressure (vacuum) or gravity, which requires an open approach to the environment, mostly on the surface of the substrate.

Semiconductor manufacturing is one of the major industrial sectors that use surface cleaning processes, including laser cleaning methods. Most of the required cleaning processes have strict tolerances on the level at which substrate damage is tolerated. In addition, due to the characteristics of small-sized products, it is necessary to remove very small particles to avoid product malfunction. Cleaning is a problem in multiple wafer processing stages and involves the removal of extended contaminant layers (e.g., resist removal) and particulate contaminants.

Surface cleaning is also a requirement for optical instruments (e.g., photomasks) used in the wafer fabrication process. Particularly for photomasks, accumulation of contaminants is observed during normal use of the mask in the wafer printing process. These masks are exposed to deep ultraviolet (DUV) radiation during typical processing used to print mask patterns on wafers. Exposure to this radiation causes the growth of contaminants in the form of small particles that absorb the illumination radiation. This growth is commonly referred to as haze.

As the size of the particles increases, they block more light that is transmitted through the photomask, creating a problem of haze in the wafer printing process. Ultimately, the haze contamination absorbs a sufficient amount of light to cause defects in the image of the photomask printed on the wafer. Before the haze contamination reaches this level, the photomask surface must be cleaned. This cleaning requirement results in reducing the usable life of the photomask because the process currently used to remove haze degrades the absorbent film on the mask. In the case of a partially absorbent film, current cleaning methods result in a reduction in the thickness of the film, thus affecting the transmittance and phase characteristics of the film. Changes in phase and / or transmittance will change the size and shape of the printed features on the wafer beyond acceptable tolerances, thereby reducing reticle life. Once the usable life of the photomask is exceeded, a duplicate set of photomasks must be made to continue manufacturing. The replica set is also needed for use during cleaning of contaminated photomasks. Since the cleaning process is typically performed at another facility, several days may be required as a requirement before cleaning and validating the mask. The smaller the size of the features required for semiconductor fabrication, the smaller the size of haze growth that results in printing defects. This increased sensitivity to haze growth means that newer photomasks need to be cleaned more frequently and have a shorter usable life.

In addition, most of the contaminants on the semiconductor substrate, as well as the composition and sources of haze, are often difficult to discern. To this end, it would be advantageous to develop tools and methods that not only eliminate contaminants, but also allow the user to identify the physical and chemical properties of contaminants. This can be achieved by collecting it for analysis as the contaminants are removed from the substrate. The collection and subsequent analysis of the pollutants helps to identify the sources of pollutants. This information can then be used to mitigate or even eliminate contamination problems in the semiconductor manufacturing process, saving both process time and manufacturing costs.

Identifying the chemical or basic composition of the particles on the surface of the substrate is limited by the technique and resolution of the instrument used for the analysis. Contaminants can be too small and can be distributed thinly as individual particles or as a film along the surface, and many chemical analytical techniques do not have a solution for detecting or identifying chemical components. For example, if the reticle used in photolithography is exposed to multiple washes with various chemical compositions, it is not possible to detect contaminants that remain after each wash, either chemically or by particle inspection. Through the passage of time and through continuous exposure to both molecular contaminants in energy and ambient air, these residual molecules tend to bind or grow on the surface. These molecules are approximately nanometers, often in the order of microns, and can not be detected by standard chemical analysis tools. However, these molecules are present up to 10 nanometers and grow to a size observable by particle inspection equipment. As these molecules grow, especially when they grow into sufficiently large defects that the molecules can be decomposed on the wafer, they interfere with the fabrication capabilities of the wafer. In this case, identifying the composition of the molecules on the reticle allows the manufacturer to determine the source of the contamination.

The application of alternative cleaning methods to remove haze contamination on the photomask surface is hampered by the use of pellicles attached to the photomask surface (s). The pellicle consists of a bonded frame bonded to the surface of the photomask and a thin membrane stretched over the pellicle frame. Externally generated particles use pellicles to prevent them from seating on the surface of a photomask that can affect the printing process. Ultimately, the externally generated particles settle on the membrane on the mask surface, which has a considerably reduced impact on the printing process. Except for the small filter valve on the pellicle frame to allow pressure equalization, the top surface of the photomask is effectively sealed from the local environment by pellicle attachment.

In the currently accepted haze removal method, it is necessary for the wafer manufacturer to return the contaminated photomask to the mask manufacturer or a third party again. Here, the pellicle frame is removed from the photomask, the mask is cleaned, the defect is inspected, the new pellicle is attached to the photomask, and in many cases, before the mask is returned to the wafer manufacturer, Inspect. This typically takes several days to complete, additional processing increases the cost of the photomask, and degrades the quality of the photomask due to the cleaning process. Also, since the adhesive is usually removed from the pellicle and falls on the printable area of the photomask, there is a possibility that the mask may be damaged to such an extent that the mask can not be used by the haze removing process.

Current efforts to improve the problems associated with haze growth on photomasks focus on the processes that can be performed before the pellicle is added, due to the difficulty associated with pellicle cleaning all the time. These efforts are primarily focused on the use of surface agents and alternative chemicals in the cleaning process. The latter changes the species of haze pollutants, but does not eliminate their growth. Both areas show a decrease in growth rate at best and can not eliminate the requirement for cleaning. More recently, it has been shown that the growth rate of haze formation on a photomask is reduced when an inert environment is used. When this method is applied, it is necessary to control all the environments in which the photomask is exposed, including all process equipment. Like other processes under development, the process has the potential to reduce growth rates, but it does not eliminate the requirements and adverse effects of cleaning.

The present invention provides a contamination identification apparatus and method useful for cleaning a surface, and more particularly, to provide a contamination identification apparatus and method useful for cleaning surfaces of parts typically used in the semiconductor industry, optical equipment, and the like .

In one aspect of the present invention, a method of cleaning a surface of a substrate is provided. The method includes sending a laser toward a substrate having contaminant particulates disposed thereon, causing a temperature rise in the substrate, and transferring thermal energy from the substrate to the particulates to decompose the particulates. The laser has a wavelength substantially equal to the local maximum absorption spectrum of the substrate.

In another aspect of the present invention, a method is provided for increasing the usable life of a photomask substrate. The method includes the steps of sending electromagnetic radiation through a protective material towards a substrate having contaminant particulates disposed thereon, generating a temperature rise in the substrate, and transferring thermal energy from the substrate to the particulates to decompose the particulates . The radiation has a wavelength substantially the same as the local maximum absorption spectrum of the substrate.

In a further aspect of the present invention, a method of cleaning a surface of a substrate at least partially enclosed within a pellicle is provided. The method includes the steps of sending a laser through a pellicle membrane to a substrate having a layer of contaminating particulate disposed thereon, generating a temperature rise in the substrate, and transferring thermal energy from the substrate to the particulate layer to form at least a portion of the particulate layer . The laser has a wavelength substantially equal to the local maximum absorption spectrum of the substrate.

In yet another aspect of the present invention, a non-destructive method for the liberation and analysis of surface contaminants is provided. This method is performed with the substrate under atmospheric conditions to enable in-situ detection and analysis of the substrate having at least one portion that is incompatible with vacuum. The method focuses on liberating molecules from the substrate and then forming airborne molecular contamination (AMC) in the air where more precise detection or analysis is possible. The method consists of an electromagnetic radiation source which collides on the substrate to liberate surface contaminants. The liberated AMC is then delivered to the metrology system for detection or analysis. Alternatively, the liberated contaminants may accumulate on the secondary collection substrate for internal analysis or to concentrate the contaminants for delivery to an external metrology system. Partial local vacuum can be used to aid in the collection of liberated molecules or particles from the surface.

Accordingly, in order that the detailed description of the invention may be better understood and its present contribution to the art may be better appreciated, a more particular description of certain embodiments of the invention has been set forth in somewhat broader order. Of course, further embodiments of the invention described below form the subject of the claims appended hereto.

In this respect, before describing in detail one or more embodiments of the invention, it is to be understood that the invention is not limited in its application to the arrangement and arrangement of parts described in the following description or illustrated in the drawings. The invention is capable of other embodiments in addition to those described and may be practiced or carried out in various ways. It is also to be understood that the phraseology and terminology used in the present description and in the abstract is for the purpose of description and should not be regarded as limiting.

As such, those skilled in the art will recognize that the concepts underlying the present disclosure may be readily utilized as a basis for designing other structures, methods, and systems for accomplishing several objects of the present invention. It is important, therefore, that the claims be regarded as including equivalents as long as they do not depart from the spirit and scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS A number of drawings are provided to illustrate various embodiments of the present invention.

1A is a schematic diagram showing laser excitation and surface contaminants.
1B is a schematic view showing the substrate surface for showing the removal of contaminants. According to certain embodiments of the present invention, multiple species may be removed from the mask, which species may be in the form of gases, liquids, solids, and the like.
2 is a view showing a surface of a photomask having a thin film absorber on top, including a film and contaminants on the substrate.
Figure 3 shows a quartz absorption spectrum of the electromagnetic spectrum from the deep ultraviolet region to the far infrared region.
4 is a view showing a surface of a photomask having a thin film absorber including a pellicle attached to a surface thereof. According to certain embodiments of the present invention, there may be contaminants on the film and / or substrate.
5A is a schematic view showing a photomask having a pellicle showing a laser beam focused on a surface through a pellicle.
5B is a schematic diagram showing the beam spot size on the mask versus the pellicle generated by the focusing.
Figure 5c is a schematic view of a photomask with a pellicle, showing a laser beam focused on the surface through the pellicle and a side view of the beam spot on the pellicle.
6A is a cross-sectional view showing the gaussian beam energy distribution and the corresponding temperature profile generated.
6B is a cross-sectional view showing the top-hat beam energy distribution and the generated corresponding temperature profile. According to certain embodiments of the present invention, Gaussian, flat top and / or top hat energy distributions may be used.
7 is a view showing a photomask having a cooling plate contacting the lower portion of the mask. According to a particular embodiment of the invention, the point of contact may be, for example, water (or other liquid or gas) flow through a cooling plate or electrical contact for thermoelectric cooling.
Fig. 8 is a view showing forced air-cooling of a region on the photomask. Fig. According to a particular embodiment of the invention, the airflow is sent to the pellicle frame.
Figure 9A is a diagram showing a single pass of a laser beam across a surface to minimize local heat accumulation. Between the spots, a single row or column is shown with large lateral spacing.
Figure 9B is a diagram showing two passes of a laser beam across the surface to minimize local heat accumulation. Between the pulse sets, a single row with two sets of beam spots is shown superimposed with large gaps.
9C is a diagram showing multiple laser passes over an area of a substrate to achieve complete cleaning of a section of the substrate.
9D is a diagram showing a second dimensional surface cleaning.
9E is a diagram showing the use of discontinuous pulses on the surface
10 is a diagram showing the use of a laser pulse pattern to control the position of the residual material.
11A is a diagram showing the use of gravity to control the position of the residue material.
11B is a view showing the use of gravity to control the position of the residual material.
Figure 12 is a schematic diagram showing a contaminated substrate surface with a thermocouple or infrared temperature monitoring device.
Figure 13 is a schematic view showing a contaminated substrate surface with imaging, microscopy, spectroscopy or combination systems for contaminant analysis.
14 is a schematic view showing a contaminated substrate surface with an imaging system and an imaging system in which laser beam transmission is a common path;
15 is a system diagram showing robot load and X / Y / Z stage movement of a substrate with respect to a laser beam.
16A is a block diagram illustrating a typical wafer fabrication process using a photomask wet cleaning process.
16B is a block diagram illustrating the flow of a wafer fabrication process including use of laser photomask cleaning without pellicle removal.
16C is a block diagram illustrating the flow of a wafer fabrication process including the use of laser photomask cleaning without the use of additional mask sets during the cleaning process.

The present invention will now be described with reference to the drawings, in which like reference numerals refer to like parts throughout. According to certain embodiments of the present invention, a laser surface cleaning method is provided in which the risk of substrate damage is reduced.

1A shows the case where the excitation energy 2 is emitted from the energy source such as the laser 1 and directed toward the surface of the substrate 4 so that the contaminant fine particles (for example, (3) or a heat transfer to the contaminant layer. However, it is also possible to use energy sources other than lasers (e.g., generators or lamps and other devices capable of irradiating energy along the electromagnetic spectrum, including x-rays, microwaves, infrared rays, near- . In addition, the surface can be the surface of any material (e.g., the surface of a silicon wafer). The temperature rise of the resulting contaminant typically results in heat-based removal, including, but not limited to, sublimation or evaporation material 6 and decomposition material 5, the effect of which is illustrated in FIG. The pollutant fine particles 3 can also be found on the photomask as shown in Fig. 2 showing the substrate 4 and the pollutant particulates 3 on the thin film absorber 7.

According to certain embodiments of the present invention, the method reduces the risk of substrate damage because the temperature typically used to bring about surface cleaning is lower than the thermal damage level of substrate (4) material (s) (4) . The risk of substrate damage is also typically reduced relative to other technologies because in some cases a relatively long pulse width is often available that reduces the potential for multiple photon absorption processes.

The above-described exemplary method provides a reduced overall reduction of small contaminants / particles since there is little dependence on particle size. This method may be particularly advantageous for applications where the environment above the contaminated substrate is nearly or completely closed. In this case, the method may also include sending a beam through a material disposed against a surface that is part of the substrate environment enclosure. For example, the method of the present invention can be used to clean haze contaminants from the surface of a pellicleized photomask.

It has been suggested that degradation of pollutant species can be an advantage in the cleaning process of the laser surface. However, before the embodiment of the present invention was developed, there was no disclosure of a process for bringing a heat-based surface cleaning using laser heating of a substrate.

According to a particular embodiment of the invention, the method comprises the steps of selecting a laser wavelength substantially coinciding with a strong absorption of the substrate, and setting the laser energy and pulse width to achieve the desired cleaning effect. The increased absorption at the substrate allows, in some cases, lower laser energy for the cleaning process. Therefore, as the laser is sent to the surface or reflected off the surface, the likelihood of damage to adjacent materials that can interact with the laser is reduced. Although not a requirement, in accordance with certain embodiments of the present invention, a wavelength that is highly absorbed by contaminants or contaminants is selected because it can enhance the desired heat removal effect. The use of multiple laser wavelengths and / or laser energy can be used in a cleaning process, especially if the substrate is composed of one or more materials. Multiple laser energies may typically be used for the same part, if a change in properties of the material or material occurs during the first step of the desired cleaning process. For example, multiple wavelengths can be generated by using multiple laser sources, a single tunable laser source, or both. Multiple energies can be used by controlling the output energy of the laser source (s) using internal or external control of the laser (s).

A practical example

The following is an example of a method according to one embodiment of the present invention applied to the surface cleaning of haze contaminants from a photomask substrate used in a wafer manufacturing process. This example can be used in all the further embodiments of the method according to the invention described above.

Certain embodiments of the present invention are applicable to surface cleaning of wafers (e.g., silicon wafers). The type of haze growth has also been observed for these substrates and can be problematic in some cases without removing it before printing the wafer. It has been proposed to use environmental controls to control haze growth on silicon wafers. However, certain embodiments of the present invention are intended to mitigate haze or to remove other forms of contaminants, such as on a surface such as a silicon wafer. More specifically, in accordance with certain embodiments of the present invention, it is possible to remove haze by exciting the silicon wafer substrate with a laser below the thermal damage threshold.

The method according to certain embodiments of the present invention can clean the contaminated precursor material because such methods typically do not rely on direct absorption of the material disposed on the substrate. In this manner, the method according to certain embodiments of the present invention can serve as a surface preparation technique to reduce the rate of contaminant formation. For example, photomask haze growth can be reduced by applying the method according to the present invention prior to use in a wafer manufacturing process and removing or repositioning haze growth precursor materials (e.g., acid residues, water, etc.) or nucleation sites have. Other techniques may be used with the present invention to further mitigate regrowth or modification of the haze after processing the reticle with the present invention. For example, surface treatment before, during, after, or after pellicization or environmental control can increase reticle life by reducing haze regrowth or modification rates.

When applying the method according to certain embodiments of the present invention to a substrate made of multiple materials, it may be necessary to consider material parameters as well as beam parameters, including excitation wavelength selection. The basis of the cleaning process is particularly preferably such that all contaminated areas of the substrate do not exceed the thermal damage threshold of the substrate and reach a temperature substantially close to the temperature typically required for removal. In particular, if there is a significant discrepancy between absorbing materials, thermal damage may be caused to other materials by the laser energy typically required to bring one of the materials to the processing temperature. The local fluence of the beam can be controlled based on the exposed material.

According to a particular embodiment of the invention, it is possible to improve thermal equilibrium between materials with significantly different absorption constants using lasers of longer pulse width, including even continuous wave (CW) lasers. However, the use of such a long pulse width laser may result in the maximum thermal increase in the system, and may not be useful if the material adjacent to the substrate surface has a thermal damage threshold below the process temperature.

According to a particular embodiment of the present invention, a laser wavelength that is significantly absorbed in all materials on the substrate is selected. For example, the same laser energy can be used to bring the desired process temperature below the damage threshold of any substrate material. Taking into account the thermal properties (including diffusivity), one can take advantage of the advantages of heat transfer between different materials. This can in some cases achieve removal on the entire substrate with the use of a reduced process fluence, especially when it is preferentially done with respect to an absorbent material having a low heat energy flow from a high absorbent material.

Control of the beam parameters is particularly preferred in embodiments of the present invention involving the cleaning of haze contaminants on the photomask surface. For example, due to the physical structure of a typical photomask, the choice of wavelength is highly desirable. Referring to Fig. 2, the photomask usually consists of a quartz substrate 4 having a thin absorbing film 7 on a critical surface. For metal films, there is an important absorption coefficient for most producible laser wavelengths. However, in the case of a quartz substrate, generally, there is a limited wavelength range in which the substrate has a considerable absorption power and a laser source can be used normally. Given the thermal properties of the metal layer versus quartz, certain processes according to embodiments of the present invention may utilize wavelengths that are highly absorbed by the quartz substrate material, since heat transfer between materials occurs preferentially from quartz to metal layer to be.

The above discussion generally applies to the case of a partially absorbing photomask film. In general, the film usually contains a metal component, and quartz has a relatively low thermal diffusivity, so that heat flow to the photomask with the partial absorption film preferentially occurs from quartz to film. However, unlike pure metal films, these films may have wavelength regions that do not absorb significantly. This has the potential to increase the range of wavelengths that can be used to preferentially excite the quartz section of the substrate. For a partially absorbent film, in addition to heat flow, changes in heat inducing materials (e.g., oxidation, annealing, etc.) must be considered. The phase and transmission characteristics of these materials are important in their function and can be changed through heat treatment. If the thermal performance of the material adversely affects film performance, it may be necessary to limit the maximum temperature of the removal process. It may be necessary to control process uniformity by pulse shaping or pulse superimposition in order for the thermal change of the material to produce a beneficial effect.

A specific example of an exemplary method according to the present invention is to remove ammonium sulfate from the surface of the photomask. With respect to temperature and other areas, ammonium sulphate is expected to decompose at temperatures above 280 ° C. The lowest thermal damage point of a typical photomask typically becomes the melting / reflow point (i.e., about 1600 ° C) for a base quartz substrate. Thus, there is a potential process in which decontamination / cleaning can occur at a temperature below the level that damages the substrate material.

It is important to note that only the process temperature requirements are typically determined by the exact species removed from the photomask. It is advantageous to have considerable absorption capacity in the contaminant, but this is not a requirement. As discussed above, due to the potential differences in the material absorption properties, the relative absorption of the substrate material in general must be considered. Particularly, since the quartz substrate has heat flow preferentially compared to the absorbing film, it is preferable that the quartz substrate has a considerable absorbing power at the process wavelength.

The quartz substrate used for the photomask is designed to have a high transmittance, typically in the deep ultraviolet (DUV) wavelength range, particularly as shown in the quartz absorption spectrum in FIG. This is typically achieved by using a synthetically formed substrate having a very low impurity level. Except for relatively weak absorption at wavelengths around 3 micrometers, these materials typically have high transmittance in the infrared region as well. The predominant absorption for these substrates generally occurs at wavelengths below 0.2 μm or above 8 μm. The shorter wavelengths are not in the particularly preferred wavelength range, because they are usually absorbed by the air, and have higher photon energies and produce more multiphoton processes.

According to a particular embodiment of the invention, it is particularly preferred to select a quartz absorption at a wavelength in excess of 8 탆, for example around 9 탆. This typically results in high absorption in the quartz substrate without high environmental absorption. In particular, when the photomask has a metal film layer (e.g., chromium), the wavelength has an additional advantage because the reflectance of the metal film increases as the wavelength increases in this region. This typically reduces the light that can be absorbed by the film and generally improves the bias of thermal excitation to quartz. In addition, this wavelength may also provide advantages for photomasks with partial absorbent film coatings (i.e., MoSi), due to the relatively high absorption coefficient for the quartz. In general, due to the high quartz absorption as compared to quartz and the high thermal diffusivity of the partial absorber, the temperature of the membrane material reaching a constant fluence must be similar to the temperature for quartz. This is expected even if the partial absorption film has a relatively high absorption coefficient in the wavelength range.

The process just described for use in accordance with certain embodiments of the present invention typically increases the usable life of the photomask by replacing the current cleaning process used to remove haze from the photomask surface. Unlike conventional chemical cleaning processes used for cleaning haze, the laser removal process according to certain embodiments of the present invention generally does not reduce the absorber thickness and / or linewidth of the absorber film. Since material loss is the result of this process, there is a limit to the number of conventional "cleaning processes " that can be performed before the photomask is no longer usable. This is so in the case of a photomask with a partially absorbing film, especially because the loss of material results in a phase loss and increases the transmittance through the film. By design, the performance of the partial absorbing film photomask depends greatly on the phase and transmittance of the film. It is possible to use an unlimited number of cleaning cycles together with the laser cleaning process according to the present invention.

It has been found that using a temperature below the critical range may result in a change in the material of the partial absorbent film. For example, a partially absorbed MoSi film is required to operate the cleaning process below the first temperature, since it is annealed at a first temperature and the phase delay of the light transmitted through the film through the film is affected by the annealing effect, . Otherwise, the lifetime of the partial absorption membrane photomask is reduced, as is the nominal wet "cleaning process" that is currently used for haze removal. However, the process temperature of the present invention can be finely controlled by adjusting the energy provided to the surface (e.g., control pulse duration, pulse amplitude, CW energy, etc.), thereby avoiding the critical temperature tolerance of the film .

However, it may be advantageous to operate the cleaning process from above the annealing temperature, if the phase delay of the light transmitted through the film due to the annealing effect of the film is increased and loss of transmissivity is minimized or absent. A standard wet "cleaning process" is essential for the production of photomasks and may result in low phase retardation that is not tolerated by the partially absorbent film prior to use. Further, in addition to the use of the present invention, a wet cleaning treatment may be required. For example, if a non-haze related defect is present or visible on the photomask, a wet cleaning process may be required. When a material change occurs in the partial absorption film during the cleaning process of the present invention, it is possible to restore the lost phase delay by the wet cleaning treatment to prolong the lifetime of the photomask. Thermal deformation to the partial absorbent film can also prolong the life of the photomask reticle by using the method of the present invention to recover the lost phase during the wet cleaning process itself (without requiring haze cleaning) .

One of the reasons for using an aggressive wet cleaning process is the fact that adhesive residues are left by removal of the pellicle frame from the photomask. Wet scrubbing processes generally affect the adhesive residues and result in contamination of the working area of the mask, since it is generally difficult for the adhesive to concentrate. However, during the laser cleaning process described herein, some may be focused away from the adhesive residues and leave them unaffected. Due to the controlled removal of the pellicle frame and most of the adhesive after the laser cleaning process according to embodiments of the present invention, attachment of the following pellicle is possible without wet cleaning requirements (aggressive or vice versa). This is especially true when the laser cleaning process according to one embodiment of the present invention is combined with the use of an alternative bonding method or the use of a multi-part pellicle that does not require exposure of the adhesive for pellicle exchange.

The method according to certain embodiments of the present invention is applicable to haze cleaning of photomasks, and there is no need to remove the pellicle. These laser cleaning methods are typically performed through the pellicle film material without affecting the properties of the pellicle film shown in FIG. 4, which shows the pellicle 8, the pellicle frame 9, and the substrate pellicle adhesive 10.

In this case, absorption of the pellicle film 8 at the process wavelength and energy density (fluence) at the surface of the substrate 4 are typically considered. Like the substrate 4 and the substrate coating 7, the cleaning process generally does not result in a temperature rise of the pellicle film above the damage threshold. However, depending on the pellicle film, there may be substantial absorption of the pellicle film in the vicinity of the absorption peak near 9 mu m with respect to the quartz substrate. However, since the pellicle membrane is located above the substrate surface, it is still possible to operate in an important pellicle membrane absorption region.

5A is a schematic view showing the excitation energy through a focusing lens 11 which produces a converging beam 12 on a substrate film coating 7 disposed on the surface of a substrate 4 through a pellicle film to remove contaminant particles 3. [ (2). Wavelength and convergence properties allow focusing at various heights and can reduce the relative temperature rise in the pellicle membrane (8). The temperature rise of any material is proportional to the fluence applied to the surface;

ΔT to F Equation 1

Where DELTA T is the temperature change in the material and F is the absorbed laser fluence.

For constant intensity or beam pulse energy, fluence is inversely proportional to the square of the beam spot radius.

F to E / r ² Equation 2

Where F is fluence, E is energy, and r is the radius of the beam on the substrate surface.

Figure 5b shows the spot beam size on the pellicle. The ratio of the beam radius at the pellicle (pellicle beam 14) to the beam radius on the mask surface 4 (mask beam 13) is typically increased by focusing the beam through the pellicle. Therefore, the relative fluence on the pellicle film can be reduced as compared with the photomask substrate surface. 5c is a side view showing convergence at surface 4 at the point of non-converging energy versus mask beam 13 at the entry point (pellicle beam 14) of the pellicle 9. FIG.

In addition to wavelength considerations, using a process that results in a large temperature rise (e.g., a long pulse length or a high repetition rate) in the system can be limited by the damage threshold of the pellicle film. This is typically below process temperature requirements for many photomask haze components.

Pulse shaping

The pulse width of the laser, the pulse shape over time, and the spatial distribution can be used to improve the cleaning process according to certain embodiments of the present invention, or to increase the safe operating range for the process. A shorter pulse width can be used to minimize the overall heat input to the system (substrate and contaminants). By maintaining the process temperature for an extended period of time using a longer pulse width, the completeness of the heat removal process can be improved. The temperature rise in the contaminant species can be controlled using an aged pulse shape. Using a long temperature rise can lead to an initial result (e.g., melting) followed by a secondary result (e.g., decomposition). The shorter the rise time, in some cases, the vaporization of contaminants can be improved while limiting the cracking process. Also, a combination of short and long aged pulse shapes may be used to optimize the removal process. In addition, by using multiple pulses to lower the desired beam energy for complete cleaning, the risk of substrate damage can be further reduced.

The spatial distribution of the laser beam can be used to increase the process window. For example, FIG. 6A shows a typical Gaussian spatial distribution 15 that can result in a temperature gradient in the substrate 16, while FIG. 6B shows a flat top or top Represents the spatial distribution (17). The spatial distribution can be used to increase the process window. For example, by having a flat top or top hat spatial distribution, a uniform temperature rise in the beam spot is possible, while a Gaussian distribution typically results in a temperature gradient in the beam spot. In order to avoid the risk of substrate damage, the maximum energy of the beam is typically limited by the peak of the Gaussian distribution. As discussed above, if more than one material is present on the substrate, a longer pulse width may be used to enable thermal equilibrium between the substrate materials.

Thermal management

Since certain embodiments of the present invention include a thermal-based process, it is often desirable to manage the overall temperature of the system to avoid damage to thermally sensitive or easily contaminated materials. This is particularly the case when the photomask haze is cleaned without removing the pellicle. Pellicle membranes typically have low thermal damage thresholds. Thus, it is often useful to avoid accumulation of the overall system temperature which can be transmitted to and / or damaged by the pellicle material. This includes the pellicle frame and the enclosed environment between the mask surface and the pellicle membrane.

Temperature management of the system can be achieved by several methods. The following examples illustrate some representative methods of sample cooling, and it should be understood that other methods may also be present. One way to manage the temperature of the system is to use contact cooling. The photomask can be placed in contact with the plate 17 serving as a heat sink for drawing heat generated on the front face of the mask to the rear of the mask, for example, as shown in Fig. 7, and the heat exchange pipe 18 , 19). This reduces heat transfer to the mask surface, the pellicle film, and the adhesive top environment between the pellicle frame and the mask surface. Cooling can be accomplished in a variety of ways, including flowing water or other cooling fluids or gases onto the mask and / or pellicle, and thermo-cooling or laser-induced cooling of some or all of the mask and / or pellicle.

Another possible way to control temperature is to use forced convection cooling. Filtered and / or cooled gas or liquid flows are typically directed onto a portion of the mask, pellicle membrane, frame and / or adhesive region to directly reduce the heat buildup of these materials shown in FIG. The temperature can be controlled using the top flow 22, side flow 23, or bottom flow 24 of the coolant. This not only reduces the risk of damage to the pellicle membrane, but also typically reduces the risk of causing pollutant emissions from the pellicle frame and pellicle membrane adhesives. In addition to the hardware control of system thermal accumulation, heat accumulation can be reduced by allowing increased process times. Allowing the system to apply a slower pulse rate or allowing a delay between a series of pulses allows the temperature of the entire system to eliminate injected heat without rising beyond the threshold level.

In addition, the pulse-to-pulse heat accumulation can be advantageously controlled and can vary depending on the thermal properties of the contaminants, substrate and / or adjacent materials. Generally, pulse-to-pulse heat accumulation can be controlled by reducing the number of laser pulses touching the surface per unit time. This temperature accumulation may be controlled by increasing the distance between the laser adjacent pulses. It may be particularly desirable for the material (e.g., pellicle film material) to have a large transverse displacement between adjacent pulses particularly sensitive to pulse-to-pulse heat accumulation. In this case, the process typically includes positioning the laser beam at approximately the same position in multiple times to obtain complete cleaning of the target surface. For example, a first series of laser pulses 13 is exposed to the surface 4 by a relatively large lateral separation, as shown in Fig. 9a. The second pass over the same area places an additional series of laser pulses 13 that are slightly shifted relative to the first spot set, as shown in Figure 9b. This process continues until the entire area is exposed to the laser pulse 13, as shown in Fig. 9B. According to certain embodiments of the present invention, overlap in the second direction may be used to fully expose the substrate surface 4 shown in Figure 9D. According to certain embodiments of the present invention, this process is repeated, or the overlap between passes is increased, particularly if it is desired that multiple pulses are included in the cleaning process, especially for complete removal. Changing the position of the beam relative to the surface as shown can be accomplished by moving the beam and / or moving the substrate. In addition, when pulses are applied in a more systematically distributed manner across the mask, the possibility of heat accumulation on the mask can be further reduced, as shown in Figure 9E.

Residue control

According to certain embodiments of the present invention, a laser cleaning method can produce a residue material on the photomask surface in accordance with the decomposition products of the contaminants. There may be a reason to still need to control the position or concentration of the residue even though the residue no longer affects the use of the substrate material (i.e., even if the substrate is effectively cleaned). Conventional methods for controlling the formation of residues, such as, for example, applying a directional airflow or stream, or creating a reduced pressure on a substrate to be cleaned, may be used in accordance with certain embodiments of the present invention. However, for closed systems such as, for example, pellicleized photomasks, it is typically not desirable to use such environmental controls. As such, an alternative method for controlling the location of the residue material is used in a closed system according to certain embodiments of the present invention. For example, according to a particular embodiment of the invention, the pattern of laser pulses is controlled. 10 shows an embodiment in which the pattern of laser pulses 13 is directed to a circular or increasing square pattern 25, 26 whose diameter starts increasing from the center of the surface of the substrate 4, The residual material is preferably moved toward the edge of the substrate, as shown in Fig. Another method in accordance with certain embodiments of the present invention for controlling residues is to use gravity. The placement of the photomask with the surface facing downward is shown in an inclined position 28 as shown in Figure 11a or Figure 11b, each of which remains on the side of the pellicle film, or photomask, Water can be deposited preferentially. In another method in conjunction with certain embodiments of the present invention, the reticle can be rotated (i.e., turned) to move the residual material away from the mask center and / or into the inactive area on the reticle. Also, in accordance with certain embodiments of the present invention, when reducing the temperature of a region, pellicle, or pellicle frame of a photomask, residues are preferably deposited on these surfaces, as shown in Figure 8, This is because it is generated through the transition from the gas phase to the liquid or solid. For example, these cooling methods include, but are not limited to, flow of water, other fluids or gases, thermal-electric cooling, or laser induced cooling in and / or around the desired deposition area.

Mitigation and modification of haze growth

By using the present invention in conjunction with surface preparation or environmental control techniques, the reticle life can be extended. Some of these techniques require treatment prior to pellicle mounting, while other techniques can be performed with post-pellicariization. For example, the surface treatment method with the present invention before pelletization can increase the time between the cleaning processes. This may be important when there is a limit on the number of rinses possible by the inventive method prior to further rinsing (e.g., wet rinsing). In one embodiment of the method according to the present invention, a seed crystal or other nucleation material is placed under the pellicle in the inactive region of the reticle. These parent crystals can serve as desirable growth sites for haze. This can effectively reduce the concentration of the residue and precursor material available in the active area of the photomask and reduce the growth rate in these areas. Another embodiment of this method is to coat the surface of the mask with a substance that reacts with and / or neutralizes the residue and precursor material liberated by the cleaning process of the present invention. This may also reduce the haze growth rate in the active region on the mask by limiting the available reactive species.

In addition, post-pellicle techniques can be used in combination with the present invention. For example, environmental control or manipulation both inside and outside the pellicle can be used in combination with the cleaning process of the present invention. One embodiment includes the step of exchanging the environment under the pellicle with a non-reactive gas after the cleaning process. This can be done without removing the pellicle by gas exchange through a filtered vent on the pellicle frame. It may be further advantageous to maintain an inert environment outside the pellicle in conjunction with the present invention to mitigate haze re-growth or modification. These combined processes can extend the time between cleaning processes by the method of the present invention and can be important when using a limited number of cleaning processes.

Additional post-pellicles, and environmental control embodiments of the present invention, will introduce or exchange with the environment a material that empties the environment under the pellicle and reacts or neutralizes haze residues and / or precursors. This process can be performed before, during, or after the cleaning process. In all cases, the haze residues and / or precursor species liberated during the cleaning process will react with the introduced / exchanged material to produce non-haze forming species.

Additional post-pellicleization techniques may be used in conjunction with the present invention to mitigate haze regrowth or modification. These techniques utilize the thermal effects of the present invention to inhibit haze growth and modification by altering the surface metrology and / or substrate composition. For example, operating at or near quartz reflow temperature can lead to changes in the material state or morphology of the quartz substrate. It is believed that this can reduce or eliminate the active area, causing nucleation of crystalline haze growth, thereby reducing the rate of haze growth or modification. Alternative embodiments can combine the surface preparation or environmental control method with a combination of thermal effects of the method according to the present invention to modify or remove the activation / nucleation sites. The precursor material can be activated by heat treatment or react with the surface under thermal excitation to reduce haze growth and modification.

Instrumentation

In combination with instrumentation, the method according to certain embodiments of the present invention may be used to monitor critical process parameters and / or assess the progress or completion of the cleaning process. For example, a temperature measurement of a locally generated substrate material in combination with a cleaning process may be utilized. To determine the risk of temperature-related damage, the temperature measurement can be evaluated before applying the cleaning process. In addition, these temperatures can be monitored during the cleaning process to confirm process control and / or reduce the risk of material damage. For example, in accordance with certain embodiments of the present invention, the temperature of the substrate and / or absorber film is monitored during the process, and when accumulation of too much temperature is detected, the control of the applied energy is fed back to maintain the desired process, The ability to turn off. 12, multiple methods of monitoring existing temperatures are shown and include, for example, contact of a thermocouple 30 and the like, and contactless techniques such as non-contact infrared camera 29, for example.

According to certain embodiments of the present invention, as shown in Figure 13, the instrumentation may be used to analyze contaminants for the properties of the material before, during, and / or after the removal process. Ideal processing parameters can be set through the identification of contaminants prior to performing the cleaning process. This makes it possible to use the minimum process temperature, thereby reducing the risk of substrate damage. Monitoring of contaminants during the process can also be used to assess the completion of the cleaning process based on the strength of the measurement signal as the cleaning process proceeds. Also, monitoring for other materials during the process can be used to signal when the process produces different contaminants and / or causes undesirable changes in the substrate material. This information can be used to control the process and / or reduce the risk of substrate damage and / or poor cleaning results.

There are several methods available to determine the chemical or elemental composition of the particles on the surface. Such methods include, but are not limited to, spectroscopy, mass spectrometry, electrochemical analysis, thermal analysis, separation, hybrid techniques (including one or more techniques), and microscopy. In one embodiment of the apparatus discussed herein, spectroscopy, mass spectrometry, or a hybrid of the two is used. When reference is made herein to metrology techniques, it should be understood that the various subsets of these techniques are broadly included. For example, the techniques included in the spectroscopic method include Fourier Transform Infrared Spectroscopy (FTIR), infrared spectroscopy, Raman spectroscopy, laser induced fracture spectroscopy, electron paramagnetic resonance spectroscopy (EPR) Energy spectroscopy (EDS or EDX), electron energy loss spectroscopy (X-ray photoelectron spectroscopy, energy dispersive X-ray spectroscopy, Loss Spectroscopy, EELS) and fluorescence analysis. In order to identify the chemical composition of the particles on the substrate, EDX, Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), Raman spectroscopy, FTIR and liquid chromatography Liquid Chromatography-Mass Spectrometry (LC-MS).

Liquid chromatography is a separation process for separating fine particles from a solvent containing a sample mixture using an absorber. The solvent and sample mixture are dispersed across the absorber at different rates depending on the compound. This allows the compound to be separated at different regions of the absorber. Liquid chromatography along with mass spectrometry can be used to more accurately identify molecules.

Mass spectrometry is a chemical analytical technique that can determine the exact chemical composition by ionizing particles and classifying them into masses and building spectra based on mass and ionic charge. Mass spectrometry techniques are destructive. Common techniques include quadrupole mass filters and TOF-SIMS.

A Quadrupole Mass Filter (QMF) ionizes particles using an ion source and then accelerates ions in the beam using an ion accelerator. The ion path is centered on and extends along four parallel rods used to generate pulsating electromagnetic waves. The rods operate as two sets with 180 ° phase difference. This causes radial displacement of these ions along the beam in a vibrating manner as ions move axially along the rod. The ions are not accelerated axially along the beam. At the end of the rod is a detector that identifies the radial position of the ions. The radial position of the ions on the detector is based on the mass to charge ratio as they pass through the quadrupole. One advantage of QMF is that it is relatively inexpensive compared to other mass spectrometers. There are some disadvantages when using a quadrupole mass filter. Quadrupole mass filters have limited resolution and must adjust the peak-to-mass response, and these filters are not suitable for pulse ionization.

Propagation Time Secondary ion mass spectrometry (TOF-SIMS) is a technique for pouring primary beam ions onto the surface of a substrate. Secondary ions are collected and collected by the detector. Based on the time of impact from the primary ion beam and the time at which the secondary ion is detected, the mass spectrum of the compound can be discerned. This is the most precise method available with a resolution of one billionth of a percent. However, there are some limitations. TOF-SIMS should be performed in a vacuum to avoid contamination from the ambient atmosphere. This method is also destructive, and the liberated ions are often part of the base material of the substrate as well as particles that settle on top of the substrate. In the case of some applications such as photolithography, this damages the pattern on the reticle and makes the reticle useless. The method is largely qualitative, and the results can often vary depending on the operator of the equipment.

Raman spectroscopy uses monochromatic light (one wavelength) to pour photons into molecules. Energy is exchanged between incident photons and molecules, resulting in changes in the energy and wavelength of the emerging photons. This phenomenon is known as scattering. Different molecules have different energy exchange with the photons, resulting in changes in the spectrum and the spectrum used to identify the molecules. The latest and most advanced Raman technology is surface-enhanced Raman spectroscopy (SERS). This technique can detect single molecules. This technique typically requires silver or gold colloids or substrates. Often, the sample is prepared as a plasmon surface composed of nanostructures of silver / gold on a porous silicon wafer. Samples are expensive and can be time consuming.

There are many advantages when using standard Raman spectroscopy. Raman can be used in solids and liquids, does not require sample preparation, and does not interfere with analysis and is not destructive. This technique can identify chemicals with very high confidence, and analysis of this method is very fast. Raman analysis is available at relatively small sample sizes (<1 um), and minerals are more readily detected by Raman than IR spectroscopy. One of Raman's greatest strengths is its ability to perform this type of analysis under standard atmospheric conditions.

Fourier Transform Infrared (FTIR) spectroscopy is a technique that relies on the vibration response of chemical bonds when a compound is exposed to a range of IR spectra. Depending on the technique, the infrared spectrum emitted or absorbed during exposure to the IR spectrum is observed for solids, liquids or gases and is used to identify compounds. FTIR has advantages over Raman in that there are few interference problems such as fluorescence. However, FTIR inherently requires minimum thickness, uniformity and dilution.

Further, according to a specific embodiment of the present invention, the measurement can be used to analyze the material properties of the substrate 4 and / or materials on or adjacent to the substrate before, during, and / or after the removal process, Or monitoring. For example, a measurement of the material properties of the partial absorber film on the substrate can be used to calculate the phase delay of the material before processing. This can be used to determine the process temperature for cleaning to induce an appropriate phase delay in the absorber film. The instrumentation can also be used to monitor the phase during processing, feed back information to the process, or stop the process if it is outside the process limits. The material characterization of the substrate can be used to accurately determine the energy required to induce a desired surface material or morphological change. In addition, the material properties of the pellicle membrane can be monitored to determine if adverse effects occur in the pellicle material. This information can be used to limit the process temperature prior to machining or to stop the process if damage occurs. For example, one or more ellipsometers or cameras 31 may be used to measure the material response of the pellicle film, absorber film, and substrate surface. This data can then be used to calculate the properties of the desired material, including film thickness, transmittance and phase.

Alternative measurements to monitor the presence and amount of surface contaminants can be used before, during, and / or after the cleaning process according to certain embodiments of the present invention. For example, measurements can be used to detect the presence of contaminants in accordance with a particular embodiment of the present invention to determine whether to apply a laser pulse to a region of the measured substrate. Next, using this information, the number of pulses applied to the entire substrate can be minimized, thereby reducing not only the total cleaning process time but also the total heat energy applied to the system.

Measurements measuring transverse size / dimension, location, number, density, and / or height (thickness) of contaminants or contaminants can also be utilized in accordance with certain embodiments of the present invention in combination with a cleaning process. Using these measurements, for example, the efficiency and completion of the process can be verified by measurements before and / or after the cleaning process. During the process, these measurements can be used to evaluate the field efficiency of the process. For example, if multiple laser pulses are used for complete removal, the detection of residual contaminants can be used to evaluate the number of pulses required for removal and the need for additional pulses. In this case, according to a particular embodiment of the invention, the metrology is designed to look at the area to be cleaned during the cleaning process. This is typically done by imaging the area exposed by the laser and may include the use of the same optics as used for laser delivery, as shown in Fig. The imaging lens 32 permits detailed monitoring of the pollutant particles 3 through the partial reflection mirror 29, allowing simultaneous monitoring and cleaning.

There are multiple methods according to embodiments of the present invention for the detection of particles and the evaluation of particle dimensions. These methods include, for example, measurement of intensity of reflected and transmitted light, imaging, low angle scattered light detection, interferometer, scanning electron beam, scanning tunneling microscopy, near-field microscopy, atomic force microscopy and the like. Multiple methods may be combined to provide additional information in accordance with certain embodiments of the present invention.

In the case of photomasks, for example, multiple measurements can be included in a laser cleaning process according to certain embodiments of the present invention. For example, identifying the presence of certain contaminants (e. G., Ammonium sulphate) on a photomask defines the decomposition temperature requirements and often allows selection of laser energy high enough to perform just the cleaning process.

According to a particular embodiment of the invention, the transmitted light intensity is measured and the result compared to the structure programmed for the absorptive film on the photomask surface. Next, contaminants are identified using mismatches between the programmed features and the detected features. Further, the printing characteristics of the photomask are evaluated using spatial imaging measurement according to a specific embodiment of the present invention. This method is typically used to assess the impact of contamination on the performance of the photomask. This measurement can also be used to detect in-situ damage to the absorber layer caused by the cleaning process. This is particularly suitable for a partial absorption film in which the thickness of the film has a direct relationship with the performance of the photomask. According to certain embodiments of the present invention, the combination of scattered light detection and transmitted light detection improves the identification of contaminants by detecting typically smooth surfaces and other irregular surface topography of the photomask and photomask film.

Also, the properties of the material adjacent to the surface being cleaned are monitored using metrology in accordance with certain embodiments of the present invention. For example, the temperature of the pellicle membrane on the photomask can be monitored to reduce the risk of damage to the pellicle membrane. By using the permeability characteristics of the pellicle membrane, it is also possible to verify the effect of the cleaning process during or after the cleaning process. In addition, the detection of particulates within the pellicle membrane can be accomplished prior to performing the cleaning process and / or detecting the loss of these particles during the process, and / or preventing the risk of pellicle and / or substrate material damage Can be used to determine if the energy used in the hazard process should be limited.

As will be appreciated by those skilled in the art in practicing one or more embodiments of the present invention, the examples of metrology discussed above do not include all of the present invention. Rather, these examples merely illustrate the use of metrology within some of the methods according to the present invention.

Identification of contaminants

As described above, a photomask substrate typically comprises a base substrate that is transparent to radiation used in a lithographic exposure process, and an optical film that partially or completely absorbs exposure radiation. Since the optical properties of these substrates are critical to their performance, the surfaces should be free of chemical contamination as much as possible. It is also important to ensure that these surfaces are free from contamination due to the energy and wavelength of the exposure radiation. This radiation can lead to deterioration of residual surface contamination and, in some cases, to the formation of gradual defects (haze) which affect the performance of the photomask.

Much effort is put into the photomask cleaning process to minimize surface contamination. However, there is always a certain level of residual contamination, which may vary from photomask to photomask. In addition to residual surface contaminants, there may also be environmental accumulation of contaminants. Changes in the surface contaminants of photomasks used in wafer fabrication can change the performance and lifetime of the photomask at the time of production. Therefore, it is advantageous not only to be able to detect the presence and level of surface contaminants, but also to be able to analyze its chemical composition.

Identification of contaminants removed from photomasks or other contaminated substrates can be useful to identify and remove contaminants, reduce them, and adjust the removal process to minimize the possibility of damage to the substrate. Identification of the contaminants includes glass of molecules at the surface of the contaminated substrate, which describes the various geometries and chemical analysis of the substrate material, sample preparation, and contaminants.

Now, a number of methods of performing such identification will be described with respect to FIG. 17, and in each method, the surface of the contaminated substrate 4 is irradiated, for example, with a laser (31), resulting in a photon induced chemical reaction in which molecules are cleaved or generated by transfer of momentum from the molecular photon to the molecule, or by thermal bond breakage between the contaminant and the substrate surface by the photon, Or molecules liberated by heat cutting or generation due to heat generated from the substrate. In one embodiment, when contaminants are liberated, the temperature of the photomask is kept below the critical temperature to prevent damage to the photomask. In all methods, the molecules enter the vapor phase close to the substrate surface. It is possible to create a pressure difference near the surface of the substrate 4 to move the liberated molecules away from the substrate, and then the molecules are collected or collected for analysis. Those skilled in the art will recognize that it is advantageous to create a pressure differential in the local area of the substrate, specifically in the area where the laser is irradiated to the substrate. In one embodiment, a cylindrical tube 38 surrounding the energy source 31 and extending to the surface of the substrate 4 is provided. The sensors 39 on the substrate can be employed to identify contaminants by providing inputs to the gas analysis tool 40. Alternatively, a pressure difference is created in the cylindrical tube 38, for example by means of a vacuum pump 41, which can be used to draw any freely floating molecules into the analysis tool or collection device 43. The detection or chemical analysis method may vary depending on whether the molecules to be identified and the contaminants 3 are drawn directly to the analysis tool 40 or accumulated by the collection device 43.

The glass of the molecule from the surface of the contaminated substrate can be performed using a number of methods including thermal evaporation, pyrolysis, or other methods of photodissociation that release physical momentum transfer, photolytic bond cleavage, or surface contaminants. A preferred embodiment uses a laser. The laser wavelength may vary depending on the substrate material and the contaminants to be analyzed. At certain wavelengths, the material can be transparent, which means that as the photon passes through the substrate, it does not significantly affect the substrate. At other wavelengths, the substrate and / or contaminants can act as a part or complete black body that absorbs some or all of the photons and energy from the energy source. This results in a temperature rise of the substrate and / or contaminants. At sufficiently high energy, photon density, and at the appropriate wavelength, this can lead to glass of contaminants from the substrate surface. In a preferred embodiment, the electromagnetic wave has a wavelength substantially equal to the local maximum absorption spectrum of the photomask.

In the contamination identification method described herein, molecular contaminants (AMC) in the air can be analyzed either as the pollutants are liberated directly from the contaminated substrate or after they have been stored in the collection device 43. For AMC released to the atmosphere above the contaminated substrate, the device may employ any type of sensor 39 and weather analysis tool 40. Alternatively, the AMC liberated from the contaminated substrate can be accumulated in the collection vessel 44 or on the collection substrate 45. The AMC liberated from the contaminated substrate can be trapped in the collection vessel 44 or condensed on the surface of the collection substrate 45 in a concentrated state. The collection device 43 can collect AMCs from individual contaminated substrates or from multiple contaminated substrate samples prior to performing the analysis, or in the case of the collection substrate 45 using a multisurface analysis method.

In one embodiment, the collection substrate 45 may be a cold plate at a temperature below 0 DEG C to further ensure condensation of gaseous contaminants. For example, the collection substrate may be cooled to a desired temperature by cooling or in liquid N ₂ to -190 ℃ Peltier (Peltier) cooling unit. At this time, a pressure difference may be generated to increase the condensation and accumulation probability of the AMC by pulling the AMC from the environment above the contaminated substrate 4 towards the cold collecting substrate.

In another embodiment, the collection vessel 44 may be a closed volume having an inlet and an outlet port. The interior of this volume is cooled down below 0 ° C to ensure more condensation of meteorological contaminants. At this time, a pressure difference may be generated to pull the AMC from the environment above the contaminated substrate 4 through the inlet port into the enclosed volume to increase the condensation and accumulation potential of the AMC.

When cooling the collecting device, it is very important to understand that all of the condensable gases in the inlet created by the pressure difference are condensed on the collecting substrate 45 or in the collecting container 44. [ This includes any atmospheric moisture, due to the moisture in the environment surrounding the collecting device 43. For this reason, it is desirable to place the contaminated substrate surface and collecting device 43 in an environment with reduced humidity from this point onward, which is referred to as a drying environment.

The drying environment can be achieved by replacing the air around the contaminated substrate and the collection device with a dry gas, preferably a dry inert gas, such as nitrogen, argon or helium. By measuring the dew point which should be kept below -10 ° C, the degree of drying of the environment can be monitored. This minimizes the amount of moisture from the atmosphere that is condensed on the collection substrate or in the collection vessel and improves the signal to noise ratio of the measurements performed on the contaminants during identification and quantification.

It should also be appreciated by those skilled in the art that the proximity of the cooling collector to the contaminated substrate surface is important. The closer the collection device is to the contaminated substrate surface, the more AMC is accumulated by the collection device. This is important when handling small amounts of pollutants.

After the AMC has accumulated in the collection device, these materials can then be analyzed using measurements such as mass spectrometry. In addition, AMC can be re-volatilized and analyzed in the atmosphere using a variety of gaseous spectrometers.

Methods used for the analysis include, but are not limited to, spectroscopy, mass spectrometry, electrochemical analysis, thermal analysis, separation, hybrid techniques (including one or more techniques), and microscopy. In the case of photomask substrates, some analytical techniques have more advantages such as spectroscopy, mass spectrometry, separation and hybrid techniques.

The design of the contamination identification device according to aspects of the present invention may also vary depending on the geometry. Some applications may be on a flat substrate surface. In such applications, a stationary energy source and collection tube may be employed to surround the activated surface and the energy source. Other applications may have geometric constraints, which can utilize adjustable focusing optics and stretchable collection tubes. If the contaminated substrate contains different materials, the apparatus may utilize energy sources of various wavelengths. In a preferred embodiment, various geometries and multi-material substrates are considered.

The application of the method of the present invention for the analysis of the surface contaminants of the photomask depends on the production conditions of the photomask. In the initial production of the photomask, the entire substrate surface is exposed to the atmosphere. In this stage of photomask production, an electromagnetic radiation source may be applied to the entire photomask. The radiation can expose the entire photomask at one time, or the radiation source can be focused toward the substrate surface, and the surface and radiation source can be scanned with respect to each other. The liberated AMC contaminants can be drawn from the atmosphere just above the contaminated substrate, and can be analyzed directly, for example, by a measurement tool such as a mass spectrometer. Alternatively, the AMC can be collected by the acquisition device for later analysis.

It is advantageous for certain embodiments of the present invention to analyze AMC when it is generated directly on top of the photomask substrate. For example, in one aspect of the present disclosure, the presence, relative amount and identification of contaminants are determined as the laser is first applied to the substrate. The level of contamination can then be compared to the collection average level of the photomask or an acceptable nominal value of contamination. The level of contamination and the type of contamination can be used to determine if the reticle is clean enough to be used in production. Photomasks can be roughened in use or sent to another cleaning process to further reduce surface contamination. By identifying the contaminants, the production process of the entire photomask can be controlled to remove the contaminants and improve the overall production quality. The disclosed processes can be applied to the photomask twice, thereby determining the level and identification of the contamination. This measure can be compared to previous levels and used in the process of the present invention to determine if the cleaning process reduces surface contaminants. The cleaning process and the contamination identification process can be repeatedly used until a desired level of surface contamination is reached.

This method has advantages over other direct measurement techniques. The disclosed process is not limited to a single analytical technique. Gas and substrate samples can be easily prepared and many powerful analytical tools can be used. The way to liberate AMC is nondestructive and does not make photomask and other products useless. The disclosed method does not require a vacuum chamber to perform the analysis. Most analytical techniques are limited by sample size. The process of the present invention is a per-energizing-pulse local process, which is limited by the process region. However, in the case of integrating a high-precision stage in a continuous pulse and a moving contaminated sample substrate, the sample size is not particularly limited.

In yet another aspect of the present invention, electromagnetic radiation used to detect the presence, level and identification of AMC can be used to aid surface cleaning of the photomask. In this case, as radiation is applied to the surface, it is expected that the level of contamination will decrease. Repeated exposure of some parts or the entire photomask surface combined with monitoring of the level of contamination liberated can be used to determine if the photomask is clean enough to be used in production.

In the latter half of photomask production, a pellicle is added to the top surface of the photomask substrate. The pellicle is made of a hollow rectangular frame with a fluoropolymer thin film (pellicle) over the top and adhered to one side of the substrate. When the pellicle is present, the photomask is incompatible with the vacuum system. For example, applying a vacuum to the photomask liberates the volatile material from the pellicle frame and the adhesive that further contaminates the photomask surface. When the process of the present invention is applied, it can be applied to a region on the upper surface of the photomask outside the pellicle frame, or to the rear side of the photomask not containing the pellicle. Alternatively, the electromagnetic radiation may be applied through the pellicle. However, only species of AMC that can penetrate the pellicle membrane are detected and identified. The method of the present invention can be applied to a photomask immediately after the photomask is produced or for some time after it is used in production. The level of surface contamination can be determined prior to use in production, by level measurement and identification of AMC immediately after application of the pellicle. By analyzing the level of surface contamination after the photomask has been used in the production phase, the level and type of environmental contamination that is exposed while the photomask is being used in production can be determined. This allows the manufacturer to early detect and identify the build up of surface contaminants prior to failure of the reticle during production, allowing the process to be controlled to prevent further contamination.

Because of the low level of contamination typically on the photomask, it may be advantageous to collect free contaminants from a single photomask. The accumulation of the material liberated from the photomask can improve the ability to measure and identify the presence and level of contaminants. In addition, chemical analysis of surface contaminants typically requires only a larger sample volume and detection. Depending on the level of contamination, collecting free AMCs from a multiple photomask substrate onto a single acquisition substrate to accumulate large amounts of residual surface contaminants can be very useful in identifying contaminants and locating contamination sources.

Those skilled in the art will recognize that on-site or remote analysis of contaminants on the substrate is possible by the contamination identification apparatus and methods disclosed herein. This analysis can be destructive or non-destructive and can be used for chemical analysis, weather or surface analysis methods. Multiple analysis types can be used simultaneously for more accurate identification or self-calibration. It will be appreciated by those skilled in the art that the collected sample can have a much higher concentration than the contaminated substrate surface, allowing low level contaminant detection. Chemical analysis can be performed on multiple contaminated substrate surfaces and monitored over time, and chemical analysis can be performed on multiple contaminated substrates with various materials and geometries.

Device

A particular method according to embodiments of the present invention is included in an apparatus used to perform a cleaning process of the laser surface. An example of such a device is shown in FIG. 15, and is configured for substrate material handling with a robot end effector and platform 34 that accurately positions the substrate material with respect to at least one axis of movement that positions a substrate sample proportional to the laser beam And further includes a robot 35. For example, the apparatus may comprise one or more of the aforementioned measurements and / or may comprise a method of controlling the temperature of the substrate and / or adjacent material during the cleaning process. The apparatus may also include metrology for use in registering the substrate with the laser beam in accordance with the staging system. The metrology may include a computer-controlled visual recognition system. The apparatus may also utilize computer control of laser, motion and / or metrology and may provide software-based recipe control of the cleaning process. Laser control may include, for example, controlling the amount of energy applied during the cleaning process, as well as when applying a laser pulse.

Wafer fabrication process

The method and / or apparatus according to certain embodiments of the present invention may be utilized as part of a novel wafer fabrication process that involves removal of haze formation from a pellicleized photomask surface. Typically, the photomask is taken out of the wafer printing process when the level of haze is sufficient to adversely affect the wafer printing process. The time before the photomask is taken out is typically determined by direct detection of high levels of haze contaminants, or based on a predetermined duration and / or usage level in the wafer process. Typically, a photomask is sent to another facility to remove the pellicle, clean the photomask, and attach another pellicle to the photomask. These other equipment (e.g., a mask shop) maintains the equipment necessary to accomplish this task and to perform repairs and additional inspections of photomasks that are not needed in the wafer fabrication facility. Typically a photomask replica set is used for the time required to clean the photomask and attach the new pellicle. These additional photomasks add significant cost to the overall wafer printing process because of the high material and installation and evaluation costs.

A novel wafer fabrication method according to a particular embodiment of the present invention includes an apparatus utilizing one or more of the methods described above for cleaning the photomask surface of a haze. A typical wafer fabrication process according to one embodiment of the present invention shows the use of a wet cleaning process to remove contaminants in the photomask, as shown in Figure 16a. Also, within the scope of particular embodiments of the present invention, alternative methods utilize one or more of the laser cleaning methods described above to perform cleaning operations in the wafer fabrication facility, without pellicle removal, as shown in the flowchart of Figure 16b have. This can minimize or eliminate additional pellicle cost and / or deterioration of the photomask film produced by current wet cleaning processes.

According to a particular embodiment of the present invention, in the novel wafer fabrication process, there is no need to use additional masks or mask sets for product fabrication while the original mask set is cleaned. In this manufacturing process, the original photomask (s) are immediately put back into production, following the cleaning process, as shown in the flow chart of Fig. 16C. This not only shortens the installation time required to use a duplicate mask set, but also has the potential to eliminate duplicate mask sets. Verifying the cleaning process using inspection metrology can be advantageously used before returning the photomask to production. Such measurements may be provided by, for example, devices or by additional devices in the manufacture of wafers or other equipment. Nevertheless, the entire process time for removing the haze of the photomask during the measurement is shortened.

Many features and advantages of the invention will be apparent from the detailed description, and the appended claims are intended to cover all such features and advantages of the invention that fall within the true spirit and scope of the invention. Furthermore, it is not desired to limit the invention to the exact construction and operation shown and described, since various modifications and variations will readily occur to those skilled in the art, and accordingly, all suitable modifications and equivalents may be deemed to be within the scope of the present invention.

Claims (37)

Emitting an electromagnetic wave having a wavelength equal to a local maximum absorption spectrum of the photomask toward a photomask having contaminant particles on the upper side;
Generating a temperature rise in the photomask;
Transferring thermal energy from the photomask to the contaminant to free molecules of the contaminant from the surface of the photomask;
Generating a pressure difference on the photomask to move the released contaminant molecules away from the photomask;
Collecting the released contaminant molecules; And
And analyzing the composition of the contaminant. The method according to claim 1,
Wherein the electromagnetic wave is laser light. 3. The method of claim 2,
Wherein the laser wavelength is greater than or equal to 8 micrometers. The method according to claim 1,
Wherein the photomask comprises at least one thin film layer. 5. The method of claim 4,
The thin film layer is patterned,
Wherein the photomask includes void areas under portions of the exposed photomask. The method according to claim 1,
Further comprising: maintaining a temperature of the photomask below a threshold temperature to prevent damage to the photomask. The method according to claim 1,
Wherein the photomask comprises two or more materials,
Wherein the laser wavelength is substantially equal to a local maximum absorption spectrum of the photomask. The method according to claim 1,
Wherein the pressure difference is localized within less than the entire area of the photomask. 9. The method of claim 8,
Wherein the pressure difference is localized to a region where the laser is applied to the photomask. The method according to claim 1,
Wherein the pressure difference is generated in a collection tube surrounding a source of electromagnetic waves for the photomask. The method according to claim 1,
The step of collecting the released contaminant molecules comprises:
Cooling the collection substrate below 0 ° C; And
And using the pressure difference to direct the released contaminant molecules to the collection substrate. 12. The method of claim 11,
Wherein the photomask and the collection substrate are in a drying environment at atmospheric pressure. The method according to claim 1,
Wherein the step of analyzing the composition of the contaminant is a spectroscopic method. The method according to claim 1,
Wherein analyzing the composition of the contaminant is performed using mass spectrometry. The method according to claim 1,
Wherein analyzing the composition of the contaminant determines the level and type of the contaminant. The method according to claim 1,
The step of analyzing the composition of the pollutant may include:
Comparing the level and type of the contaminant to a benchmark for a photomask. &Lt; Desc / Clms Page number 21 &gt; Sending an electromagnetic wave having a wavelength equal to a local maximum absorption spectrum of the substrate toward a substrate having fine particles of contaminants on the upper side in an atmospheric pressure drying environment;
Generating a temperature rise in the substrate;
Transferring thermal energy from the substrate to the contaminant to free molecules of the contaminant from the surface of the substrate; And
And collecting the released contaminant molecules in a cooling collection device. 18. The method of claim 17,
Further comprising: maintaining a temperature of the substrate below a threshold temperature to prevent damage to the substrate. 18. The method of claim 17,
Wherein the cooling collection device comprises a cooling plate. 18. The method of claim 17,
Wherein the cooling collection device is cooled to below &lt; RTI ID = 0.0 &gt; 0 C. &lt; / RTI &gt; 18. The method of claim 17,
Wherein the cooling collection device is installed adjacent to the substrate surface. 18. The method of claim 17,
Wherein the cooling collection device comprises a cooled enclosed volume having an inlet port and an outlet port. 23. The method of claim 22,
Wherein a pressure differential is created between the cooling shut-off volume and the drying environment such that the released contaminant molecules travel through the inlet port into the cooling shut-off volume. 18. The method of claim 17,
Wherein the drying environment has a dew point of less than -10 占 폚. 18. The method of claim 17,
Wherein the drying environment is an inert gas environment. 26. The method of claim 25,
Wherein the inert gas is nitrogen. Sending an electromagnetic wave having a wavelength equal to a local maximum absorption spectrum of the substrate toward a substrate having contaminants on the upper side in an atmospheric pressure drying environment;
Generating a temperature rise in the substrate; And
And transferring thermal energy from the substrate to the contaminants to decompose the contaminants. 28. The method of claim 27,
Wherein the electromagnetic wave is laser light. 28. The method of claim 27,
Wherein the laser wavelength is 8 micrometers or more. 28. The method of claim 27,
Wherein the substrate comprises at least one thin film layer. 31. The method of claim 30,
The thin film layer is patterned,
Wherein the substrate comprises void areas beneath respective portions of the exposed photomask. 28. The method of claim 27,
Further comprising: maintaining a temperature of the substrate below a threshold temperature to prevent damage to the substrate. 28. The method of claim 27,
Wherein the substrate comprises at least two materials,
Wherein the laser wavelength is equal to a local maximum absorption spectrum value of the substrate. 28. The method of claim 27,
Wherein the drying environment has a dew point of less than -10 占 폚. 28. The method of claim 27,
Wherein the drying environment is an inert gas environment. 36. The method of claim 35,
Wherein the inert gas is nitrogen. 28. The method of claim 27,
Wherein the substrate is placed in a drying environment at atmospheric pressure before surface cleaning begins.

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