Dosimeters that match the spectral sensitivity of photoresists to improve trace / space width variation

Abstract

To provide a radiometer probe for matching the spectral sensitivity of a dry-film resist.SOLUTION: The radiometer probe includes a light probe and a filter-diffuser assembly 200 connected to the light probe. The filter-diffuser assembly includes a filter housing 160 configured to receive an optical diffuser 135 positioned on a filter 150. The optical diffuser and the filter are separated by a spacer 140.SELECTED DRAWING: Figure 1B

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims priority from U.S. Application No. 16 / 446,506, filed June 19, 2019, which claims priority from U.S. Provisional Application No. 62 / 689,712, filed June 25, 2018, all of which are incorporated herein by reference.

[0002] (Technical field) The present embodiments generally relate to a dosimeter probe configured to match the spectral sensitivity of a dry film resist. Additionally, the present embodiments generally relate to calibrating the dosimeter probe to the sensitivity of a photoresist. [Background technology]

[0003] Photoresist compositions are used in microlithography processes to miniaturize electronic components, such as in the fabrication of flexible circuits, printed circuits, computer chips, and integrated circuits. Generally, in these processes, a thin film coating of a photoresist composition is first applied to a substrate material. The coated substrate is then baked to evaporate the solvent in the photoresist composition and fix the coating onto the substrate. The photoresist coated on the substrate is then imagewise exposed to radiation.

[0004] The radiation exposure causes a chemical transformation in the exposed areas of the coating surface. Visible light, ultraviolet (UV) light, electron beam, and X-ray radiant energy are radiation types commonly used today in microlithography processes. After this image-wise exposure, the coated substrate is treated with a developer to dissolve and remove either the radiation-exposed or unexposed areas of the photoresist.

[0005] The trend towards miniaturization of devices has led to the use of new photoresists sensitive to lower and lower wavelength radiation, and to the use of high performance multi-level systems to overcome the difficulties associated with such miniaturization. There are two types of photoresist compositions: negative-working and positive-working. When a negative-working photoresist composition is imagewise exposed to radiation, the areas of the resist composition exposed to radiation become less soluble in a developer solution (e.g., undergo a cross-linking reaction), while the unexposed areas of the photoresist coating remain relatively soluble in such a solution. Thus, treatment of the exposed negative-working resist with a developer solution causes removal of the unexposed areas of the photoresist coating, producing a negative image in the coating, thereby exposing the desired portions of the underlying substrate surface on which the photoresist composition was deposited.

[0006] Smaller dimensions of features formed using photoresist compositions can increase the susceptibility of the features to variations in the dimensions of the features formed. Thus, there is a need to reduce the variations in the features formed. Summary of the Invention

[0007] The following presents a simplified summary of one or more embodiments in order to provide a basic understanding of the present technology. This summary is not an extensive overview of all possible embodiments of the present technology, and is not intended to identify key or critical elements or to delineate the scope of any or all aspects of the present technology. Its sole purpose is to present some concepts of one or more embodiments in a simplified form as a prelude to the more detailed description that is presented later.

[0008] A dosimeter probe and associated method for matching the spectral response of a dry film resist is provided. The dosimeter probe includes an optical probe and a filter-diffuser assembly connected to the optical probe. The filter-diffuser assembly includes a filter housing configured to receive an optical diffuser disposed over the filter. The optical diffuser and the filter are separated by a spacer.

[0009] In some embodiments of the present disclosure, the optical probe is an international optical probe. Additionally, the optical diffuser may include a quartz cosine diffuser configured to attenuate the intensity of the exposure light within a targeted linear range. In some embodiments, the optical diffuser includes opaline glass, polytetrafluoroethylene (PTFE), or Spectralon that couples to a fiber and a spectrometer to collect the signal from a 180° field of view. In some embodiments of the present disclosure, the optical diffuser includes an upper side and an opposite lower side. The upper side of the optical diffuser may include an etched recess.

[0010] In some embodiments of the dosimeter probe, the optical diffuser is secured within the filter housing with an etched recess disposed opposite the filter and spacer. In some embodiments, the filter includes a metal coating on a first side and an insulating coating on an opposite second side. Additionally, the filter may include a metal coating on a first side and an insulating coating on an opposite second side. In some embodiments, the filter may be configured to target a linear range that includes at least one of the following transmission values: 100% at a wavelength of 365 nm, 40% at a wavelength of 405 nm, or 7% at a wavelength of 435 nm.

[0011] In some embodiments of the dosimeter probe, the filter may be disposed within the filter housing such that the insulating coating faces the optical diffuser and the spacer. In some embodiments, the spacer may include a Teflon shim configured to prevent interference caused by an air gap between the optical probe and the filter. In an alternative embodiment, the spacer may include a PTFE shim configured to prevent interference caused by an air gap between the optical probe and the filter. In some embodiments, the filter-diffuser assembly may be connected to the optical probe via threads using a thread-locking adhesive.

[0012] A method for calibrating a dosimeter probe may also be provided herein. The method includes using a dosimeter probe. The dosimeter probe may include an optical probe and a filter-diffuser assembly connected on the optical probe. The filter-diffuser assembly may include a filter housing configured to receive an optical diffuser disposed on the filter. Further, the optical diffuser and the filter may be separated by a spacer. The method may also include illuminating a light source. The light source may include an LED light source operating at 365 nm. The method may also include placing the dosimeter probe under the light source and measuring an irradiance. The irradiance may be compared to a stored gold standard irradiance. Based on the comparison, the method may also include calibrating the dosimeter probe based on a comparison of the measured irradiance to the stored gold standard irradiance.

[0013] To explain the manner in which the above and other advantages and features of the present disclosure are obtained, a more particular description of the above principles will be made by reference to specific embodiments illustrated in the accompanying drawings, which depict merely exemplary aspects of the disclosure and are therefore not to be considered as limiting its scope. These principles will be shown and explained with additional specificity and detail through the use of the following drawings, in which: [Brief description of the drawings]

[0014] [Figure 1A] FIG. 1A illustrates a dosimeter probe according to one embodiment of the present disclosure. [Figure 1B] FIG. 1B illustrates a filter-diffuser assembly of the dosimeter probe of FIG. 1 according to one embodiment of the present disclosure. [Figure 1C] FIG. 1C illustrates the filter-diffuser assembly of FIG. 1B before being coupled onto an optical probe according to one embodiment of the present disclosure. [Figure 1D] FIG. 1D illustrates a mechanical gasket secured to the filter-diffuser assembly of FIG. 1B according to one embodiment of the present disclosure. [Figure 1E] FIG. 1E illustrates a stainless steel (SST) weight secured to a dosimeter probe according to an embodiment of the present disclosure. [Diagram 2] FIG. 2 illustrates a process for determining the wavelength sensitivity of a dry film according to one embodiment of the present disclosure. [Diagram 3] FIG. 3 illustrates a calibration process according to one embodiment of the present disclosure for a dosimeter probe. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] The embodiments of the present invention are described with reference to the attached drawings, in which the same reference numerals are used to denote similar or equivalent elements throughout the drawings. The drawings are not drawn to scale and are provided only to illustrate the embodiments of the present invention. Several aspects of the embodiments of the present invention are described below with reference to the application of illustrative examples. It should be understood that numerous specific details, relationships and methods are shown to provide a thorough understanding of the embodiments of the present invention. However, those skilled in the art will readily recognize that the embodiments of the present invention can be implemented without one or more of the specific details or with other methods. In other instances, well-known structures or operations are not shown in detail to avoid obscuring the embodiments of the present invention. The embodiments of the present invention are not limited to the order of acts or events described, since some acts may occur in different orders and / or may occur simultaneously with other acts or events. Moreover, not all described acts or events are necessary to perform the method according to the embodiments of the present invention.

[0016] Dosimeters and their application to photoresists are commonly used in lithography with broadband sources. For example, a broadband source such as a typical mercury bulb may contain spectral peak outputs at 365 nm, 405 nm, and 435 nm. The intensity of these spectral peaks may vary from bulb to bulb and may vary with the age of the bulb. Thus, problems arise when engineers try to stabilize the dose that reaches the photoresist.

[0017] Some lithography processes may use narrow band or single band dosimeters. For example, a dosimeter probe may be configured to be sensitive only to i-line (365 nm) radiation. Because photoresist may be sensitive to wavelengths outside of i-line radiation, a dosimeter probe tuned to i-line radiation cannot properly calibrate the shutter times between machines.

[0018] When using dosimeter probes with broadband sources, the spectral sensitivity of the dosimeter probes can be narrower than the spectral radiation of the broadband source. However, the spectral sensitivity of dry film photoresists can be broader than the dosimeters used in lithography, so the use of these dosimeters in lithography with photoresists and broadband sources can produce undesired effects. Thus, variability can occur in the process that can prevent the manufacture of products within the desired tolerances. As a result, it is necessary to modify the dosimeter probes to match the sensitivity of the dry film resist. Furthermore, it is necessary to modify the dosimeter probes to reduce the variability between exposures with the same dose parameters.

[0019] An embodiment of the present disclosure provides a dosimeter probe, which includes an optical probe and a filter-diffuser assembly. The filter-diffuser assembly may include an optical diffuser, a filter, a spacer, and a filter housing. The dosimeter probe may be configured to match the sensitivity of the photoresist across many wavelengths. This provides a probe that is better matched to the sensitivity of the photoresist to enable dimensionally consistent results of the patterned photoresist.

[0020] 1A illustrates a dosimeter probe 100 as disclosed herein. As described above, the dosimeter probe 100 is configured to reduce variations in patterned photoresist that receive the same exposure dose. The dosimeter probe 100 may include an optical probe 130 and a filter-diffuser assembly 200. In some embodiments, the optical probe 130 may include an optical probe manufactured by International Light Technologies. In some embodiments, the filter-diffuser assembly 200 is configured to be coupled to the optical probe 130, as will be described in more detail below.

[0021] FIG. 1B illustrates a filter-diffuser assembly 200 as disclosed herein. The filter-diffuser assembly 200 may include a diffuser 135, a filter 150, a spacer 140, and a filter housing 160. In some embodiments, the optical diffuser 135 may include a quartz cosine diffuser. The cosine collector is an optical diffuser (e.g., opaline glass, polytetrafluoroethylene (PTFE), or Spectralon) that couples to a fiber and a spectrometer to collect light from a 180° field of view. The optical diffuser 135 may include an upper side and an opposite lower side. The upper side of the optical diffuser 135 may include an etched recess 136. Additionally, according to some embodiments, a seal ring 137 is configured to be disposed between the optical diffuser 135 and the optical probe 130. The optical diffuser 135 may be configured to attenuate the exposure intensity within a targeted linear range.

[0022] In some embodiments of the present disclosure, the filter 150 may be a thin film manufactured by Ocean Thin Films. In some embodiments, the filter 150 may have a metal coating on a first side and an insulating coating on an opposing second side. In some embodiments, the reactivity of the filter is configured by using one or more metal coatings on one side and one or more insulating coatings on the other side. However, other embodiments include using either one or more metal coatings and one or more insulating films on one or both sides of the filter, such that the sum of the reactivity of each metal coating and / or each insulating film results in the total desired reactivity of the filter. Additionally, the filter 150 may be configured to have a desired wavelength reactivity based on one or more wavelengths to which a particular photoresist is sensitive. For example, the filter may be configured to have 100% transmission at a wavelength of 365 nm, 40% transmission at 405 nm, or 7% transmission at 435 nm.

[0023] In some embodiments, when assembled into the filter-diffuser assembly 200, the insulating coating of the filter 150 may face outward with the metal coating facing the optical diffuser 135. The filter-diffuser assembly 200 may also include a filter housing 160. The filter 150 may be placed in the filter housing 160 with the insulating side down. The spacer 140 may be placed on the metal side of the filter 150. In some embodiments, the spacer 140 may include a Teflon shim. In other embodiments, the spacer 140 may include a PTFE shim or spacer. The spacer 140 may be introduced to prevent interference caused by an air gap between the optical probe 130 and the filter 150.

[0024] The light diffuser 135 may be fixed in the filter housing 160. Specifically, the light diffuser 135 may be fixed to the spacer 140. The light diffuser 135 is then fixed to the metal side of the filter 150 separated by the spacer 140. The light diffuser 135 may be fixed in the filter housing 160 such that the etched recess 136 and the seal ring 137 face up. In other words, the light diffuser 135 may be disposed in the filter housing 160 such that the underside contacts the spacer 140.

[0025] 1C, once the filter-diffuser assembly 200 is assembled, it may be connected to an optical probe (not shown) to create a dosimeter probe. The filter-diffuser assembly 200 may be secured to the optical probe 130 using a threaded adhesive 201. For example, LOCTITE® 242, a medium strength, medium viscosity thixotropic threaded adhesive, may be used to secure the two pieces together.

[0026] 1D, once the dosimeter probe 100 is assembled, a mechanical gasket 101 may be attached to the filter-diffuser assembly 200. The mechanical gasket 101 may be a loop of elastomer having a circular cross-section designed to be placed in a groove in the filter-diffuser assembly 200 and compressed to seal the interface between two or more portions when assembled.

[0027] 1E, a stainless steel (SST) weight 110 can be assembled to the dosimeter probe 100 at the optical probe 130. The SST weight 110 can have a number of openings. Additionally, the optical probe 130 can include a connection receiving element 102. A number of bolts can be used to pass through the openings 111 of the SST weight 110 into the connection receiving element 102 of the optical probe 130.

[0028] By using the filter-diffuser assembly 200, the dosimeter probe 100 allows for tighter absolute dose control for different bulbs and a given bulb life. This allows for better dimensional control in the patterned photoresist resulting in smaller variations in the dimensions of the final product. For example, circuit trace dimensions formed on a circuit board or flexure using a photoresist pattern with exposure using a dosimeter probe matched to the wavelength sensitivity of the photoresist used to form the circuit traces will produce circuit traces with lower variations across a batch. Thus, impedance characteristics and other property details are maintained within tighter ranges than when formed using other techniques. For example, exposure using a dosimeter probe matched to the wavelength sensitivity of the photoresist using techniques including those described herein is configured to pattern photoresist to form at least one set of structures with less than 12 μm of space between one structure and the next in the set. Furthermore, the use of exposure using a dosimeter probe matched to the wavelength sensitivity of the photoresist allows for the use of photoresist to pattern structures with only 10% or so variation in the feature or critical dimension of the structures formed using the photoresist.

[0029] FIG. 2 illustrates a process for determining wavelength sensitivity of a dry film according to one embodiment. The process for determining the wavelength sensitivity of a dry film, such as a photoresist, includes determining one or more spectral peaks of a radiation source used for exposure to the photoresist (202). For example, the process can use a broadband spectrometer to detect the peak power of the source. Once the peak power of the radiation source is known, a single wavelength radiation source, such as a single wavelength light emitting diode (LED), can be used to measure the sensitivity of one or more photoresists to each of the peak powers of the radiation source (203). For example, multiple samples of photoresist are exposed to different levels of the radiation source, with each sample spanning a range of dose levels. In various embodiments, this process is repeated at each peak power wavelength. The lowest dose level at which the photoresist is not fully developed is used to generate a dosimeter sensitivity profile at each peak power wavelength. For example, the sensitivity profile can be used to configure a filter for a filter-diffuser assembly, such as the one described herein (204).

[0030] A typical mercury bulb may have outputs at 365 nm, 405 nm, and 435 nm. The bulb life degrades faster at 365 nm than at 405 nm. If the exposure is only calibrated at the 365 nm peak, the photoresist will be overexposed as well as the bulb life. This is because the photoresist is more sensitive to 405 nm exposure. However, using a dosimeter probe that contains a filter configured with the sensitivity profile of the photoresist being exposed will provide more consistent results across the manufacturing process and across different exposure units.

[0031] FIG. 3 shows a process for calibrating a dosimeter probe for accurate radiation measurements when using custom filters. In the embodiments described herein, a conventional dosimeter probe is used as a calibration standard to ensure that the dosimeter probe is properly calibrated for the photoresist. Calibration can be performed using a single wavelength radiation source for each wavelength to be calibrated. Alternatively, the dosimeter probe is calibrated using a broadband radiation source, such as a mercury bulb. In step 210, a process is disclosed. A radiation source is used to generate at least one spectral peak output of a radiation source used in a lithography process. For example, an LED is used to generate an output at a wavelength that is tuned to at least one spectral peak output to which the photoresist will be exposed during the lithography process, such as an output at 365 nm. In step 215, a radiation source, such as an LED source, is powered on. In some embodiments, the LED source can be left powered on until the LED reaches an equilibrium temperature and provides a stable output. In step 220, a conventional dosimeter probe used as a calibration standard is placed under the LED source and the irradiance is recorded. In step 225, a dosimeter probe to be calibrated is placed under the LED source and the irradiance is recorded. In step 230, the irradiance of both the conventional dosimeter and the dosimeter probe are compared. The calibration factor of the dosimeter probe can be changed to match the conventional dosimeter or within the range of the conventional dosimeter. The process can be used to calibrate the dosimeter probe at one or more wavelengths. In some embodiments, the calibration process is performed in a test assembly. In other embodiments, the calibration process is performed at an exposure where the dosimeter probe will be used after calibration.

[0032] The above description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications of the disclosure will be readily apparent to those skilled in the art, and the general principles defined herein may be applied to other modifications without departing from the scope of the disclosure. Thus, the disclosure is not intended to be limited to the embodiments and designs set forth herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. 1. A process dosimeter probe for matching the spectral sensitivity of a dry film, comprising: An optical probe; a filter-diffuser assembly connected to the optical probe; The filter-diffuser assembly includes a filter housing configured to receive a light diffuser disposed in a filter; the optical diffuser and the filter are separated by a spacer such that the dosimeter probe is configured to expose a pattern onto the dry film resist to form at least one set of adjacent structures, the at least one set of adjacent structures having a gap between one structure of the set and an adjacent structure of the set that is less than 12 μm; the light diffuser includes a recess formed in the light diffuser; the light diffuser includes an upper side and an opposite lower side; an upper side of the light diffuser includes an etched recess; The dosimeter probe, wherein the optical diffuser is secured within the filter housing with the etched recess positioned opposite the filter and the spacer.

2. The dosimeter probe of claim 1 , wherein the optical diffuser comprises a quartz cosine diffuser configured to attenuate the intensity of the exposure light within a linear range of a target.

3. 10. The dosimeter probe of claim 1, wherein the optical diffuser comprises at least one of opaline glass, polytetrafluoroethylene (PTFE), or Spectralon coupled to a fiber and a spectrometer to collect a signal from a 180 degree field of view.

4. The dosimeter probe of claim 1 , wherein the filter includes a metallic coating on a first side and an insulating coating on an opposing second side.

5. 2. The dosimeter probe of claim 1, wherein the filter is configured to target a linear range that includes at least one of the following transmission values: 100% at a wavelength of 365 nm, 40% at a wavelength of 405 nm, or 7% at a wavelength of 435 nm.

6. The dosimeter probe of claim 1 , wherein the filter is disposed within the filter housing such that an insulating coating faces the optical diffuser and the spacer.

7. The dosimeter probe of claim 1 , wherein the spacer comprises a Teflon shim configured to prevent mechanical interference caused by an air gap between the optical probe and the filter.

8. The dosimeter probe of claim 1 , wherein the spacer comprises a PTFE shim configured to prevent mechanical interference caused by an air gap between the optical probe and the filter.

9. 10. The dosimeter probe of claim 1, wherein the filter-diffuser assembly is connected to the optical probe via threads using a thread lock adhesive.

10. 1. A method for calibrating a dosimeter probe, comprising: using a dosimeter probe including an optical probe and a filter-diffuser assembly connected to the optical probe; Irradiating a light source; positioning the dosimeter probe under the light source and measuring irradiance; comparing the measured irradiance with a reference irradiance; calibrating the dosimeter probe based on a comparison of the measured irradiance to the reference irradiance such that the dosimeter probe is configured to expose a pattern on a dry film resist to form at least one set of adjacent structures; the at least one set of adjacent structures having a gap between one structure and an adjacent structure of the set that is less than 12 μm; The filter-diffuser assembly includes a filter housing configured to receive a light diffuser disposed in a filter; the light diffuser and the filter are separated by a spacer; the light diffuser includes a recess formed in the light diffuser; the light diffuser includes an upper side and an opposite lower side; an upper side of the light diffuser includes an etched recess; The method of claim 1, wherein the light diffuser is secured within the filter housing with the etched recess positioned opposite the filter and the spacer.

11. The method of claim 10 , wherein the optical diffuser comprises a quartz cosine diffuser configured to attenuate the intensity of the exposure light within a target linear range.

12. 12. The method of claim 11, wherein the optical diffuser comprises at least one of opaline glass, polytetrafluoroethylene (PTFE), or Spectralon coupled to a fiber and a spectrometer to collect a signal from a 180 degree field of view.

13. The method of claim 10 , wherein the filter includes a metallic coating on a first side and an insulating coating on an opposing second side.

14. The method of claim 10 , wherein the filter includes a metallic coating on a first side.

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