JP4640057B2 - Spectrophotometer - Google Patents

Description

  The present invention relates to a spectrophotometer for performing material analysis in various fields such as semiconductors, optics, and electricity.

  In recent years, with the progress of semiconductor lithography (exposure technology), the irradiation laser has become shorter in wavelength, and the demand for measuring the transmittance and reflectance of optical materials in the deep ultraviolet wavelength region (for example, the region of wavelength 160 to 200 nm) has increased. Many spectrophotometers are used. Absorption due to oxygen gas in the air becomes an obstacle to measurement in the deep ultraviolet wavelength region, so absorption of nitrogen gas, etc. in advance throughout the optical path of the spectrophotometer, such as the light source unit, spectrometer unit, sample chamber unit, detector unit, etc. It is necessary to perform measurement after replacement with a non-gas (hereinafter, this operation is referred to as nitrogen purge) (for example, Patent Document 1). The following description is limited to the measurement in the deep ultraviolet wavelength region (hereinafter referred to as the deep ultraviolet region).

  FIG. 3 shows an example of the configuration of a conventional double beam spectrophotometer. First, the optical system will be described. The optical system includes a light source part L, a spectroscope part M, a sample chamber part N, and a detector part P. The light beam emitted from the light source 1 in the light source unit L is monochromatized by the spectroscope 2 in the spectroscope unit M. Next, the light beam is periodically switched in two directions alternately by an optical path selection mechanism 3 composed of a chopper or the like, and repeatedly passes through the sample chamber 4 or the control chamber 5 in the sample chamber N. . A sample to be analyzed is placed or enclosed in the sample chamber 4.

  An appropriate shape of the sample chamber 4 is selected according to the shape and dimensions of the sample. The shape of the control chamber 5 is usually the same as that of the sample chamber 4. When the sample is in a solvent, only the solvent is enclosed in the control chamber 5. When a sample such as a solid is directly installed in the sample chamber 4 without using a solvent, it is usually unnecessary to install anything in the control chamber 5. The light after passing is converted into an electrical signal by the detector 6. As the detector 6, a photomultiplier tube or the like is used. In addition, although a condensing lens, a mirror, etc. are used for said optical system as needed, since it is not directly related to this invention, illustration and description are abbreviate | omitted.

  The output of the detector 6 is amplified by an amplifier 7, taken out as a measurement output U, and used for spectrum display, quantitative calculation, and the like. Although not shown in FIG. 3, a signal synchronized with the operation of the optical path selection mechanism 3 is supplied to the amplifier 7, and the light beam signal passing through the sample chamber 4 and the light beam passing through the reference chamber 5 are supplied. The signals are electrically separated using the synchronization signal, and the difference between the two is taken out as the measurement output U. By taking out the difference between the two, it is possible to perform measurement while eliminating the influence of fluctuations unique to the apparatus, such as natural fluctuations of the light beam.

  The light source part L, the spectroscope part M, the sample chamber part N, and the detector part P are each unitized and continuously installed, and the optical path of the light beam is from the light source 1 to the detector 6 as a rule, only inside each unit. Pass through. Each unit has an airtight structure and can be replaced for each unit as needed. Each unit is provided with a pipe for purging nitrogen and a pipe for discharging nitrogen. In FIG. 3, only the purge pipe Z of the light source part L, the valve 8 and the discharge pipe E of the light source part L are shown as representative of the piping of each unit.

  Similar piping is separately provided for other units, and the unit can be purged individually or as a whole, if necessary, but is not shown in FIG. For example, the bulb 8 is opened in the light source part L, and nitrogen gas is introduced from the nitrogen gas inlet through the purge pipe Z. When the light source part L becomes atmospheric pressure or more, the gas exceeding atmospheric pressure is automatically released from the safety valve that forms part of the discharge pipe E. In the measurement, as a preparation, first, nitrogen purge is performed over the entire optical path of the spectrophotometer, such as the light source unit, the spectroscope, the sample chamber, and the detector unit, and then the measurement is started.

JP 2005-01099 A

  If the nitrogen purge is insufficient in the measurement in the deep ultraviolet region, absorption due to oxygen gas in the air causes noise and accurate information on the sample cannot be obtained, but the configuration of the conventional spectrophotometer shown in FIG. Therefore, it was sensuous to confirm whether the nitrogen purge was completed, and the reliability of the measurement was not guaranteed. That is, in the conventional apparatus, the measurer determines whether or not sufficient nitrogen purge has been performed by visually checking the data. For example, if the temporal fluctuation (flicker) of the energy value (corresponding to the measurement output U at that wavelength) becomes small at the wavelength of 175 nm, it is determined that the replacement is sufficiently completed.

  However, since this judgment method is a sensory method whose judgment criteria depend on the measurer, the reliability of the determination of nitrogen purge, which is very important for measurement, is determined by the measurer's sense and is not objective and incorrect. There was a problem that even a decision was overlooked. In addition, this method requires manpower, and has a problem from the viewpoint of unmanned and labor saving. The object of the present invention is to provide means for solving such problems.

  In order to solve the above-mentioned problems, the present invention provides a spectrophotometer equipped with a nitrogen purge means for an optical path for measuring in the deep ultraviolet region, and has means for automatically determining the completion of purge. Yes, the nitrogen purge completion is objectively determined. The present invention further includes measurement start signal generating means for automatically generating a sample measurement start signal based on an output signal from the determination means upon completion of nitrogen purge. The work of the measurement person always standing by the spectrophotometer and starting the measurement is omitted.

  Furthermore, the purge determination means in the present invention calculates the variation coefficient of the spectrophotometer output for a predetermined period starting from the nitrogen purge start time as the first operation, and if the variation coefficient is equal to or greater than a predetermined threshold, As a second operation, a variation coefficient for a predetermined period is calculated starting from the elapse of a predetermined time from the start of the nitrogen purge, and the same operation is repeated until the variation coefficient becomes equal to or less than the threshold value, thereby reducing the value to the threshold value or less. The determination is made automatically, and the determination is made more accurately and reliably.

  According to the present invention, since the determination of the completion of nitrogen purge can be objectively obtained, the reliability of measurement is improved, and the confirmation of completion of nitrogen purge is automatically performed unattended, thereby saving labor in analysis.

  The first feature of the spectrophotometer provided by the present invention is a spectrophotometer provided with means for purging nitrogen in the optical path for measuring in the deep ultraviolet region, and has means for automatically determining the completion of nitrogen purge. The second feature is that, following the completion of the nitrogen purge, a sample measurement start signal is automatically generated, and the configuration having these features is the best configuration.

  A description will be given below according to the illustrated embodiment. FIG. 1 shows the configuration of one embodiment of a double beam spectrophotometer according to the present invention. The optical system includes a light source unit LN, a spectroscope unit MN, a sample chamber unit NN, and a detector unit PN. The light beam emitted from the light source 1N in the light source unit LN is monochromatized by the spectroscope 2N in the spectroscope unit MN. Next, the light beam is periodically switched in two directions alternately by an optical path selection mechanism 3N composed of a chopper or the like, and repeatedly passes through the sample chamber 4N or the control chamber 5N in the sample chamber NN. .

  An analysis sample is installed or enclosed in the sample chamber 4N. An appropriate shape of the sample chamber 4N is selected according to the shape of the sample. The shape of the control chamber 5N is usually selected to be the same as that of the sample chamber 4N. When the sample is in a solvent, only the solvent is sealed in the control chamber 5N. When the sample is installed directly in the sample chamber 4N without a solvent, it is usually unnecessary to install anything in the control chamber 5N. The light after passing is converted into an electrical signal by the detector 6N. A photomultiplier tube or the like is used as the detector 6N. In addition, although a condensing lens, a mirror, etc. are used for said optical system, since it is not directly related to this invention, illustration and description are abbreviate | omitted.

  The output of the detector 6N is amplified by an amplifier 7N, taken out as a main measurement output UN, and used for spectrum display, quantitative calculation, and the like. Although not shown, a signal synchronized with the operation of the optical path selection mechanism 3N is supplied to the amplifier 7N, and the signal of the light beam passing through the sample chamber 4N and the signal of the light beam passing through the reference chamber 5N are synchronized with each other. The signals are electrically separated and the difference between the two is taken out as the actual measurement output UN. By taking out the difference between the two, it is possible to perform measurement while eliminating the influence of fluctuations unique to the apparatus, such as natural fluctuations of the light beam. The measurement output UN is a value corresponding to the output of the intensity of the monochromatic light beam, that is, the energy of the light beam.

  The light source unit LN, spectroscope unit MN, sample chamber unit NN, and detector unit PN are unitized and installed continuously, and the optical path of the light beam is basically in each unit from the light source 1N to the detector 6N. Only pass through. Each unit has an airtight structure and can be replaced for each unit as needed. Each unit is provided with a pipe for purging nitrogen and a pipe for discharging nitrogen. In FIG. 1, only the purge piping ZN of the light source unit LN and the discharge piping EN of the light source unit LN are shown as representative of the piping of each unit. Similar piping is provided individually for other units, and the unit can be purged individually or as a whole as necessary, but the description is omitted in FIG.

  In the actual measurement, as a preparation, first, a nitrogen purge is started over the entire optical path of the spectrophotometer, such as the light source unit LN, the spectroscope MN, the sample chamber NN, the detector unit PN, and the energy value (the actual measurement output at that wavelength) (Corresponding to UN). That is, after operating the optical system, the measurer gives a nitrogen purge start instruction from the button 21B to the CV calculator 21 and opens the valve 8N via the CV calculator 21 to start the nitrogen purge. From the start of the nitrogen purge, the verification output Q from the amplifier 7N is input to the CV calculator 21 and the energy value is verified to determine the completion of the nitrogen purge. The details of this test will be explained later in the next section. The test output Q is a difference signal between the light beam signal passing through the sample chamber 4N and the light beam signal passing through the control chamber 5N, as in the case of the main measurement output UN. On the other hand, the main measurement output UN is output outward during the main measurement.

  After the test is completed, the main measurement start signal R is output from the CV computing unit 21 to the amplifier 7N, and a message indicating the completion of nitrogen purge is displayed on the display unit 22 using the output. That is, the CV calculator 21 operates as a measurement start signal generating means. The main measurement output UN is output from the amplifier 7N by the main measurement start signal R, and the main measurement is started. Since the process after the start of the measurement is performed according to the general procedure of the spectrophotometer, description thereof is omitted.

  Hereinafter, the contents of the test performed through the CV calculator 21 will be described. As the first work of the energy value test, a total of 31 data are stored for the energy measurement values every 0.1 seconds from the start of the nitrogen purge to 3.0 seconds later. Next, CV values (coefficient of variation) are calculated for 31 data. If the CV value is less than 1%, the message “Nitrogen replacement is complete” is displayed on the display 22 and this measurement is performed. Is started. That is, if the nitrogen purge is insufficient, the amount of residual oxygen changes with time, so the energy measurement value also changes with time, and the CV value increases. However, when the nitrogen purge is completed, the absorption by the residual oxygen decreases, and the CV value Therefore, the CV value is an index for determining the completion of the nitrogen purge.

  When the CV value is 1% or more, as a second operation, a total of 31 pieces of data are stored for energy measurement values every 0.1 second from 0.1 second to 3.1 seconds after the start of nitrogen purge. . Next, as in the first operation, CV values are obtained for 31 pieces of data. If the CV value is less than 1%, the message “nitrogen replacement is complete” is displayed on the display 22 and the measurement is completed. Be started.

  When the CV value is 1% or more, as a third operation, the energy measurement values every 0.1 second from 0.2 second after the start of the nitrogen purge to 3.2 seconds after the start of the nitrogen purge, Data is stored. Next, as in the second operation, CV values are obtained for 31 data. If the CV value is less than 1%, the message “nitrogen replacement is complete” is displayed on the display 22 and the measurement is completed. Be started. Thereafter, when the CV value is 1% or more, the test is automatically repeated until the CV value is within 1%. Therefore, the measurer does not need any particular work from the start of the nitrogen purge to the completion of this measurement.

  FIG. 2 shows the flow of the verification described above as a flow chart. After starting the nitrogen purge, first, x = 0 is given as the initial time value, that is, 0.0 seconds of the first stage, and energy from x = 0 to x = 3.0, that is, 0.0 seconds to 3.0 seconds. A value is stored every 0.1 seconds. After storage is complete, a CV value is calculated and tested to see if the CV value is less than 1.0%. If the CV value is less than 1.0%, the message “nitrogen replacement is complete” is displayed and the measurement is started. If the CV value is 1.0% or more, 0.1 is added to x, and x = 0.1 to 3.1, that is, the energy value from 0.1 seconds to 3.1 seconds is 0.1. Stored every second. After storage is complete, a CV value is calculated and tested to see if the CV value is less than 1.0%. This repetition is automatically repeated until the CV value finally becomes less than 1.0%, and finally this measurement is started.

  The present invention is not limited to the above-described embodiments, and various modified embodiments can be given. For example, in FIG. 1, after the nitrogen purge is completed, a message is displayed and the main measurement is automatically started. However, automatic progress is interrupted until the message is displayed, and the measurer confirms the message and starts the main measurement. You may make it do. As for other operations, the embodiment of FIG. 1 shows an example, and the automation or manualization of each stage of the operation can be freely configured for convenience of measurement. The configuration of the optical path and the nitrogen purge pipe is only an example. The parameters such as the CV value itself representing the time and variation, the threshold value of the CV value, and the number of data described in FIG. 2 are also examples, and the present invention is not limited to the parameter values. The present invention includes all of these.

  The present invention can be applied to a spectrophotometer for performing material analysis in various fields such as semiconductors, optics, and electricity.

It is a figure which shows the structure of one Example of this invention. It is a flowchart which shows the flow of the test | inspection of one Example of this invention. It is a figure which shows one example of a structure of the conventional spectrophotometer.

Explanation of symbols

1, 1N light source 2, 2N spectrometer 3, 3N optical path selection mechanism 4, 4N sample chamber 5, 5N control chamber 6, 6N detector 7, 7N amplifier 8, 8N valve 21 CV calculator 21B button 22 indicator E, EN Discharge piping L, LN Light source M, MN Spectrometer N, NN Sample chamber P, PN Detector Q Verification output R Main measurement start signal U Measurement output UN Main measurement output Z, ZN Purge piping

Claims (2)

In a spectrophotometer equipped with a nitrogen purge means for purging nitrogen in an optical path for measurement in the deep ultraviolet wavelength region , fluctuation in spectrophotometer output over a predetermined period starting from the start point of nitrogen purge as the first operation If the coefficient of variation is equal to or greater than a predetermined threshold, the coefficient of variation of the predetermined period is calculated starting from a predetermined time after the nitrogen purge start time as the second work, If the variation coefficient is equal to or greater than the threshold, the variation coefficient for the predetermined period is calculated as a third work starting from a predetermined time after the start of the second work, and the variation coefficient is equal to or greater than the threshold. For example, by repeating the same operation until the coefficient of variation becomes less than the threshold value, it is automatically determined that the threshold value has been reached. Spectrophotometer comprising the automatically determining purge judgment means the completion of the nitrogen purge. In a spectrophotometer equipped with a nitrogen purge means for purging nitrogen in the optical path for measurement in the deep ultraviolet wavelength region, the spectrophotometer is equipped with a purge determination means for automatically determining the completion of the nitrogen purge, and the purge determination means nitrogen 2. The spectrophotometer according to claim 1, further comprising a measurement start signal generating means for automatically generating a measurement start signal for the sample based on the purge completion output signal.

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