JP4208532B2 - Method for measuring the transmittance of an optical element - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an apparatus and method for measuring the transmittance of a test object, and more particularly to an apparatus and method for measuring the transmittance of a test object with respect to pulsed laser light. The present invention is suitable, for example, for an apparatus and a method for measuring the transmittance of a test object with respect to excimer laser light.
[0002]
[Prior art]
In a lithography process for manufacturing a semiconductor element, an exposure apparatus that exposes a pattern image on a reticle onto a wafer via a projection optical system is used. In recent years, miniaturization of the line width of semiconductor integrated circuits has been increasingly demanded. For this reason, the exposure wavelength of the exposure light source has been shortened. For example, an exposure apparatus that employs a KrF excimer laser with a wavelength of 248 nm as an exposure apparatus light source has already been developed, and an ArF excimer laser with a wavelength of 193 nm and an F ₂ laser with a wavelength of 157 nm are also used.
[0003]
With these shorter wavelengths, optical materials that can be used for projection systems and illumination systems are limited to quartz glass and calcium fluoride (CaF ₂ ) crystals. Both are required to have a high initial transmittance for each exposure wavelength, and at the same time, there is no deterioration in transmittance upon irradiation with excimer laser light. The initial transmittance of the optical member is measured by a spectroscope. On the other hand, since the transmittance of the optical member is deteriorated by the excimer laser light irradiation, this deterioration amount is actually irradiated with the excimer laser light to obtain the transmittance at a predetermined illuminance, and the difference from the initial transmittance is evaluated.
In particular, in order to guarantee the transmittance performance of the exposure apparatus, the transmittance and the transmittance deterioration amount for each illuminance are equivalent to the illuminance of 0.1 to 30 mJ / cm ² of the excimer laser corresponding to each part of the projection system and the illumination system. It is essential to evaluate
[0004]
Conventionally, there is an apparatus shown in FIG. 2 as an optical element transmittance measuring apparatus for excimer laser light. Such an apparatus irradiates an optical element to be evaluated with an excimer laser beam having an exposure wavelength and directly measures the transmittance. The laser light from the ArF excimer laser light source 1 is guided into the N ₂ purged chamber 2, is shaped into a desired uniform beam diameter through the aperture stop 3 and the uniform optical system 4, and is adjusted by the illuminance adjusting optical system 5. The desired illuminance is adjusted. The laser light then passes through the CaF ₂ beam splitter 6a, and the reflected light is received by the detector 21a composed of a photodiode for monitoring the laser light quantity after passing through the ND 7a. On the other hand, the laser beam that has passed through the beam splitter 6a passes through the optical element sample (test object Φ30 thickness 30 mm) 10 mounted on the stage 20, passes through the ND 7b through the CaF ₂ beam splitter 6b, and then the detector 21b. Is received. 8 is a stopper. Control of the stage 20 and outputs from the detectors 21 a and 21 b are processed by the controller 22.
[0005]
Now, laser light from an ArF excimer laser oscillates at a frequency of 500 Hz and energy of 15 mJ, and irradiates the object 10 with an illuminance of 30 mJ / cm ² . The outputs A0 and B0 of the detectors 21a and 21b when the optical element sample 10 is retracted from the laser optical axis by the stage 20 are measured, and the controller 22 calculates (B0 / A0). Next, the test object 10 is moved on the laser optical axis by the stage 20, the outputs As and Bs of the detectors 21a and 21b at this time are measured, and the controller 22 calculates (Bs / As). Next, the controller 22 calculates the transmittance of the test object 10 by calculating (Bs / As) / (B0 / A0) from these.
[0006]
[Problems to be solved by the invention]
FIG. 3 shows the result of measuring the CaF ₂ crystal as the optical element sample (test object) 10 with such a configuration. In the figure, the horizontal axis represents the number of irradiation pulses, and the vertical axis represents the measured transmittance value.
[0007]
Here, there was a problem that the initial transmittance obtained from the measuring device shown in FIG. 2 did not match the transmittance measured by a separate spectrometer. That is, the initial transmittance obtained from the above measuring instrument was 90.51%, whereas the transmittance measured with a spectroscope before irradiation was 91.31%, and the initial measured transmittance was reliable. It turns out that there is no sex. At the same time, since the initial illuminance at the time of irradiation with a predetermined illuminance of 30 mJ / cm ² is not correct, the deterioration amount at the time of irradiation of illuminance of 30 mJ / cm ² cannot be accurately evaluated.
[0008]
Hereinafter, the result of the present inventors diligently examining this cause will be described with reference to FIGS. 5 and 6. In the case of a pulsed laser beam such as an excimer laser, the energy fluctuation of one pulse is about 10%, so that averaging is necessary. Here, when data of several M to several hundred M pulses is captured, the pulse interval to be captured is thinned out due to the limitation of the processing speed of the control system. Here, the output of 100 pulses out of 1000 pulses is monitored, and the average value is 1 data.
[0009]
FIG. 5 schematically shows the transmittance for each data. As described above, the amount calculated as the initial transmittance is the averaged transmittance T at the time of 1000 pulse irradiation. Here, when irradiation is performed at an illuminance of 30 mJ / cm ² , the transmittance change occurs at an initial number of about 100 pulses like CaF ₂ . For this reason, the initial transmittance is calculated to be low due to averaging. That is, as shown in FIG. 6, the transmittance deteriorates for each irradiation pulse within one data at the time of initial 1000 pulse irradiation. If this is averaged, even if it is the transmittance | permeability which a spectroscope will show between 1-100 pulses, in order to take the average with the transmittance | permeability which deteriorated after that, it shows in FIG. The initial transmittance T using the apparatus is calculated to be low.
[0010]
Therefore, an exemplary embodiment of the present invention is to provide a transmittance measuring apparatus and method capable of accurately measuring an initial transmittance and accurately measuring a transmittance deterioration amount at a predetermined illuminance (here, 30 mJ / cm ² ). With a purpose.
[0012]
[Means for Solving the Problems]
The transmittance measuring method according to one aspect of the present invention includes a state in which the test object is retracted from the optical axis of the laser beam and a test object is disposed on the optical axis of the laser beam. And measuring the transmittance of the test object with respect to the laser beam with a predetermined illuminance using each measurement result, and the transmittance deterioration amount of the test object with respect to the laser beam with the predetermined illuminance The laser light of the test object is obtained by using a light quantity measurement result of the laser light in a state where the laser light is irradiated on the test object with an illuminance smaller than the predetermined illuminance. the initial transmission and the first transmittance calculating step of calculating, after the first transmittance calculating step, the light amount measurement result of the laser beam in a state in which the laser beam is irradiated to the test object at the predetermined illuminance for Using, the second transmittance calculating step of calculating a transparently rate against the laser beam of the test object, the initial transmission and the second transmission rate calculated by the first transmittance calculating step And evaluating a transmittance deterioration amount of the test object with respect to the laser light having the predetermined illuminance based on a difference from the transmittance calculated in the calculating step .
[0015]
Further objects or other features of the present invention will become apparent from the preferred embodiments described with reference to the accompanying drawings.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a block diagram of a transmittance measuring apparatus according to the first embodiment of the present invention. The laser light from the ArF excimer laser light source 1 is guided into the N ₂ purged chamber 2, is shaped into a desired uniform beam diameter through the aperture stop 3 and the uniform optical system 4, and is adjusted by the illuminance adjusting optical system 5. The desired illuminance is adjusted. The laser light then passes through the CaF ₂ beam splitter 6a, and the reflected light is received by the detector 21a composed of a photodiode for monitoring the laser light quantity after passing through the ND 7a. On the other hand, the laser beam that has passed through the beam splitter 6a passes through the optical element sample (test object Φ30 thickness 30 mm) 10 mounted on the stage 20, passes through the ND 7b through the CaF ₂ beam splitter 6b, and then the detector 21b. Is received. 8 is a stopper. Control of the stage 20 and the stage 23 described later and outputs from the detectors 21a and 21b are processed by the controller 22.
[0017]
The outputs A0 and B0 of the detectors 21a and 21b when the optical element sample 10 is retracted from the laser optical axis by the stage 20 are measured, and the controller 22 calculates (B0 / A0). Next, the test object 10 is moved on the laser optical axis by the stage 20, the outputs As and Bs of the detectors 21a and 21b at this time are measured, and the controller 22 calculates (Bs / As). Next, the controller 22 calculates the transmittance of the test object 10 by calculating (Bs / As) / (B0 / A0) from these. Further, as described above, in order to cope with the energy fluctuation of one pulse of pulsed light, the output of 100 pulses out of 1000 pulses is averaged and used as one data.
[0018]
Now, laser light from an ArF excimer laser is oscillated at a frequency of 500 Hz and energy of 15 mJ, and set to irradiate an optical element sample (test object) with an illuminance of 30 mJ / cm ² . Here, a neutral density filter ND1 (transmittance 10%) and 12 neutral density filter ND2 (transmittance 50%) shown in 11 are arranged on the stage 23. The stage 23 can move, for example, in the vertical direction of the paper surface shown in FIG. 1, and either one of ND1 and ND2 can be arranged on the optical axis, or neither can be arranged on the optical axis. . Go on the laser optical axis during initial irradiation, and sets the illuminance of the laser light when the ND1 to 3 mJ / cm ^2, to set the illuminance of the laser light when the ND2 to 15 mJ / cm ^2. Furthermore, when ND1 and ND2 are retracted from the laser optical axis, the illuminance of the laser light is set to 30 mJ / cm ² . Thus, the stage 23 can variably adjust the illuminance of the laser light.
[0019]
ND1 and ND2 may be mounted on a turret that moves in place of the stage 23 that moves linearly. In this case, when the turret rotates, only ND1 is arranged on the optical axis at a certain rotational position, only ND2 is arranged on the optical axis at another position, and both retreat from the optical axis at another position. The description regarding the stage 23 also applies to the stage 24 described later with reference to FIG.
[0020]
The transmittance measurement results according to this embodiment are shown in FIG. The initial transmittance of 91.34% obtained when the illuminance was 3 mJ / cm ² substantially coincided with the transmittance of 91.33% measured with a spectroscope. This is because, as described above, CaF ₂ deteriorates at an initial number of about 100 pulses, so that the illuminance is reduced to one and the deterioration at the time of 1000 pulse irradiation matches the deterioration at the time of 100 pulse irradiation. Further, illuminance 15 mJ / cm ^2, and, from the transmittance when irradiated with laser light intensity 30 mJ / cm ^2, it was possible to calculate the respective deterioration amount. In the configuration shown in FIG. 1, the illuminance adjusting optical system 5 can finely adjust the illuminance of the laser light, but cannot adjust it to an arbitrary illuminance.
[0021]
The illuminance set in the measurement of the initial transmittance is not limited to 1/10 of the desired illuminance as in this embodiment. However, in the case where the desired illuminance is 30 mJ / cm ² and the test object is CaF _2, a configuration in which the first 1000 pulses can be equated with the first 100 pulses is preferable. . In other words, the illuminance set in the measurement of the initial transmittance depends on the type of test object (for example, quartz glass or calcium fluoride) and the type of laser used (for example, ArF excimer laser, F ₂ excimer laser). Etc.) and desired illuminance (for example, illuminance required by the exposure apparatus). However, the illuminance set in the measurement of the initial transmittance is smaller than the desired illuminance in order to measure the initial transmittance without any deterioration of the test object.
[0022]
The adjustment of illuminance is not limited to that using ND as in the first embodiment. For example, in the second embodiment, by using the controller 22 and changing the output energy of the laser light source 1 to 1 to 15 mJ, the illumination intensity to the optical element sample is set to 2 to 30 mJ / cm 2. It is possible.
[0023]
FIG. 7 shows a third embodiment of the present invention. Aperture stops 15 and 16 are arranged on the stage 24 instead of the above-described ND. By changing the diameters of the aperture stops 15 and 16, it is possible to set the illumination intensity to the optical element sample 10 to 3 and 15 mJ / cm ² .
[0024]
Hereinafter, with reference to FIG. 8, an exposure apparatus 100 according to one aspect of the present invention will be described. The exposure apparatus 200 includes an illuminating device 110 that illuminates a mask or a reticle (a term used interchangeably in the present application) 120 on which a circuit pattern is formed, a stage 145 that supports a plate, and an illuminated mask pattern. A projection optical system 130 that projects the diffracted light generated by The exposure apparatus 100 is a projection exposure apparatus that exposes a circuit pattern formed on the mask 320 to the plate 340 by, for example, a step-and-repeat method or a step-and-scan method. Such an exposure apparatus is suitable for a lithography process of submicron or quarter micron or less. Here, in the “step and scan method”, the wafer is continuously scanned with respect to the mask to expose the mask pattern onto the wafer, and after the exposure of one shot is completed, the wafer is stepped to expose the next shot. This is an exposure method for moving to an area. The “step-and-repeat method” is an exposure method in which the wafer is moved stepwise for each batch exposure of shots of the wafer and the next shot is moved to the exposure region.
[0025]
The illumination device 110 illuminates the mask 120 on which a transfer circuit pattern is formed, and includes a light source unit 112 and an illumination optical system 114.
[0026]
The light source unit 112 is a light source that emits illumination light, and is, for example, the same light source as the laser light source 1 used in the above-described transmittance measuring device. For example, an ArF excimer laser with a wavelength of about 248 nm or F _{2 with a} wavelength of about 157 nm. Excimer laser. The illumination optical system 114 is an optical system that illuminates the mask 120 and includes a lens, a mirror, a light integrator, a stop, and the like. For example, a condenser lens, a fly-eye lens, an aperture stop, a condenser lens, a slit, and an imaging optical system are arranged in this order. The illumination optical system 114 can be used regardless of on-axis light or off-axis light. The light integrator includes an integrator configured by stacking a fly-eye lens and two sets of cylindrical lens array (or lenticular lens) plates, but may be replaced with an optical rod or a diffractive element. As an optical member such as a lens of the illumination optical system 114, an optical element manufactured from a test object whose transmittance measured by the transmittance measuring device of the present invention is a predetermined value or more can be used.
[0027]
The mask 120 forms a circuit pattern (or image) to be transferred, and is supported and driven by a mask stage (not shown). The diffracted light emitted from the mask 120 passes through the projection optical system 130 and is projected onto the plate 140. The plate 140 is an object to be processed such as a wafer or a liquid crystal substrate, and is coated with a photoresist. In the case of a scanner, the pattern of the mask 120 is transferred onto the plate 140 by scanning the mask 120 and the plate 140. In the case of a stepper, exposure is performed with the mask 120 and the plate 140 being stationary.
[0028]
The projection optical system 130 includes an optical system composed only of a plurality of lens elements, an optical system (catadioptric optical system) having a plurality of lens elements and at least one concave mirror, a plurality of lens elements, and at least one kinoform. An optical system having a diffractive optical element such as an all-mirror optical system can be used. When correction of chromatic aberration is required, a plurality of lens elements made of glass materials having different dispersion values (Abbe values) can be used, or the diffractive optical element can be configured to generate dispersion in the opposite manner to the lens element. To do. As an optical member such as a lens of the projection optical system 130, an optical element manufactured from a subject whose transmittance measured by the transmittance measuring device of the present invention is a predetermined value or more can be used.
[0029]
The stage 145 supports the plate 140. Since any structure known in the art can be applied to the stage 145, detailed description of the structure and operation is omitted here. For example, the stage 145 can move the plate 140 in the XY directions using a linear motor.
[0030]
In the exposure, the light beam emitted from the light source unit 112 irradiates the mask 120 with, for example, Kohler illumination by the illumination optical system 114. The light that passes through the mask 120 and reflects the mask pattern is imaged on the plate 140 by the projection optical system 130. The illumination optical system 114 and the projection optical system 130 used by the exposure apparatus 100 include the optical elements measured by the transmittance measuring device of the present invention and transmit ultraviolet light, far infrared light, and vacuum ultraviolet light with high transmittance. Therefore, it is possible to provide a device (semiconductor element, LCD element, imaging element (CCD, etc.), thin film magnetic head, etc.) with high throughput and high economic efficiency.
[0031]
Next, an embodiment of a device manufacturing method using the above-described exposure apparatus 100 will be described with reference to FIGS. FIG. 9 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like). Here, the manufacture of a semiconductor chip will be described as an example. In step 1 (circuit design), the device circuit is designed. In step 2 (mask production), a mask on which the designed circuit pattern is formed is produced. In step 3 (wafer manufacture), a wafer is manufactured using a material such as silicon. Step 4 (wafer process) is called a pre-process, and an actual circuit is formed on the wafer by lithography using the mask and wafer. Step 5 (assembly) is called a post-process, and is a process for forming a semiconductor chip using the wafer created in step 4, and includes processes such as an assembly process (dicing and bonding) and a packaging process (chip encapsulation). . In step 6 (inspection), inspections such as an operation confirmation test and a durability test of the semiconductor device created in step 5 are performed. Through these steps, the semiconductor device is completed and shipped (step 7).
[0032]
FIG. 10 is a detailed flowchart of the wafer process in Step 4. In step 11 (oxidation), the wafer surface is oxidized. In step 12 (CVD), an insulating film is formed on the surface of the wafer. In step 13 (electrode formation), an electrode is formed on the wafer by vapor deposition or the like. In step 14 (ion implantation), ions are implanted into the wafer. In step 15 (resist process), a photosensitive agent is applied to the wafer. Step 16 (exposure) uses the exposure apparatus 100 to expose a circuit pattern on the mask onto the wafer. In step 17 (development), the exposed wafer is developed. In step 18 (etching), portions other than the developed resist image are removed. In step 19 (resist stripping), the resist that has become unnecessary after the etching is removed. By repeatedly performing these steps, multiple circuit patterns are formed on the wafer.
[0033]
【The invention's effect】
As described above, the present invention calculates the transmittance by setting the initial irradiation illuminance of the laser light to a low value in the measurement of the transmittance of the optical element with respect to the excimer laser light, and then setting the desired illuminance to calculate the transmittance. Thus, the transmittance at each illuminance can be accurately calculated. It is also possible to calculate the transmittance deterioration amount from the transmittance with respect to the desired laser light illuminance.
[Brief description of the drawings]
FIG. 1 is a block diagram of a transmittance measuring apparatus according to a first embodiment of the present invention.
FIG. 2 is a block diagram of a conventional transmittance measuring device.
3 is a graph showing a measurement result of transmittance of a test object obtained by the transmittance measuring apparatus shown in FIG. 2;
4 is a graph showing a measurement result of transmittance of a test object obtained by the transmittance measuring apparatus shown in FIG. 1. FIG.
FIG. 5 is a diagram schematically showing a problem of the transmittance measuring apparatus shown in FIG.
6 is a diagram schematically showing a problem of the transmittance measuring apparatus shown in FIG. 2. FIG.
FIG. 7 is a block diagram of a transmittance measuring apparatus according to a third embodiment of the present invention.
FIG. 8 is a schematic side view showing a part of an exposure apparatus having a dividing means according to one aspect of the present invention.
FIG. 9 is a flowchart for explaining how to fabricate devices (ie, semiconductor chips such as IC and LSI, LCDs, CCDs, and the like).
FIG. 10 is a detailed flowchart of the wafer process in Step 4 shown in FIG. 9;
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ArF excimer laser light source 2 Chamber 3, 15, 16 Aperture stop 4 Uniform optical system 5 Illuminance adjustment optical system 6 Beam splitter 7, 11, 12 ND
8 Stopper 10 Optical element sample (test object)
21a, 21b Detector 22 Controller 20, 23, 24 Stage

Claims (4)

Measure the light amount of the laser light in a state where the test object is retracted from the optical axis of the laser light and the test object is disposed on the optical axis of the laser light, and using each measurement result, A method for measuring the transmittance of the test object with respect to the laser light with a predetermined illuminance, and evaluating the transmittance deterioration amount of the test object with respect to the laser light with the predetermined illuminance ,
First, the initial transmittance of the test object with respect to the laser light is calculated using a light amount measurement result of the laser light in a state where the test object is irradiated with the laser light with an illuminance smaller than the predetermined illuminance . 1 transmittance calculation step;
After the first transmittance calculation step, using the measurement result of the laser light in a state where the laser light is irradiated on the test object at the predetermined illuminance, the laser light of the test object is measured. a second transmittance calculating step of calculating a that transparently rate,
Based on the difference between the initial transmittance calculated in the first transmittance calculation step and the transmittance calculated in the second transmittance calculation step, the test object with respect to the laser light with the predetermined illuminance And a step of evaluating the transmittance deterioration amount . It said first transmittance calculation step The method of claim 1, wherein the use of neutral density filters to regulate the intensity of the laser beam to a smaller illumination intensity than the predetermined illuminance. It said first transmittance calculation step The method of claim 1, wherein the controlling the output of the laser light intensity of the laser beam to adjust to a smaller illumination intensity than the predetermined illuminance. It said first transmittance calculation step The method of claim 1, wherein adjusting the diameter of the aperture stop to adjust the illuminance of the laser light to a smaller illumination intensity than the predetermined illuminance.

Images