Patent Description:
A spectroscopic measurement apparatus receives a spectral image of measurement target light generated in an object using a photodetector to acquire a spectrum of the measurement target light, and can analyze a composition of the object based on the spectrum, and can monitor phenomenon in the object. In the spectroscopic measurement apparatus, in some cases, it is required to acquire a spectrum of a high dynamic range (see Patent Document <NUM>).

For example, in a step of dry etching of an object by plasma processing, light due to a gas used for the etching is generated, and further, light due to a material of the etching object is also generated. A wavelength band of the light due to the gas may be different from a wavelength band of the light due to the material. Monitoring an intensity of the light due to the gas enables monitoring a state of the gas. Monitoring a temporal change in intensity of the light due to the material enables detection of etching end timing. The light due to the gas is of high intensity, whereas the light due to the material is often of low intensity.

With the development of miniaturization in semiconductor processes in recent years, openings formed by dry etching become small, and the intensity of the light generated due to the material (light for detection of etching end timing) is becoming weaker. In the step of dry etching of the object by plasma processing, it is important to monitor the state of the gas, and it is also important to detect the etching end timing. Therefore, it is necessary to acquire the spectrum of the measurement target light including both of the light of high intensity due to the gas and the light of low intensity due to the material using the spectroscopic measurement apparatus. In this case, a dynamic range of the spectrum of the measurement target light (ratio of maximum level and minimum level of light intensity of each wavelength) is large.

Further, in measuring a photoluminescence quantum yield of a sample using an integrating sphere, a spectrum of excitation light is measured in a state in which no sample is put in the integrating sphere, and further, a spectrum of the excitation light absorbed by the sample and a spectrum of light generated in the sample (for example, fluorescence) are measured at the same time in a state in which the sample is put in the integrating sphere. In order to accurately estimate the excitation light absorbed by the sample, in general, it is necessary to measure the spectrum of the excitation light and the spectrum of the generated light in a same exposure period.

At this time, since the excitation light intensity is extremely high compared with the generated light intensity, an exposure time has to be short for measuring the high excitation light intensity regardless of the necessity of measuring the low generated light intensity. Therefore, it is not possible to measure the generated light with a good S/N ratio. In a sample with low emission efficiency, although it is desired to increase the excitation light intensity, the photodetector is saturated with the excitation light having an intensity of a certain light amount or more, and thus, increasing the excitation light intensity is not easy.

Not limited to these examples, the dynamic range of the spectrum of the measurement target light may be large, and it may be desired to acquire the spectrum of the measurement target light at the same time.

Other examples of the prior art are illustrated in documents <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, <CIT> and <CIT>.

The dynamic range of the photodetector (the ratio of the maximum level and the minimum level of the light intensity detectable by the photodetector) has limitations. When the dynamic range of the spectrum of the measurement target light is larger than the dynamic range of the photodetector, the spectrum of the measurement target light fails to be acquired by receiving a spectral image by the photodetector at one time. That is, when a signal level output for light in a low-intensity wavelength band is set to a noise level or more, a signal level output for light in a high-intensity wavelength band is a saturation level or more. On the other hand, when the signal level output for light in the high-intensity wavelength band is set to the saturation level or less, the signal level output for light in the low-intensity wavelength band is the noise level or less.

It is considered that, with the use of two photodetectors having different exposure times, a spectrum of light of high intensity is acquired by the photodetector with short time exposure and a spectrum of light of low intensity is acquired by the photodetector with long time exposure. However, in this case, a wavelength axis or a spectrum acquisition operation may be different between the two photodetectors due to device difference or temperature difference. Therefore, it is desirable to use a single photodetector to obtain the spectrum of the measurement target light including both of the light of high intensity and the light of low intensity.

An object of an embodiment is to provide a spectroscopic measurement apparatus and a spectroscopic measurement method that can acquire a spectrum of light with a high dynamic range using one photodetector.

An embodiment is a spectroscopic measurement apparatus as defined in claim <NUM>. The spectroscopic measurement apparatus includes (<NUM>) an optical system for dispersing measurement target light to form a spectral image, (<NUM>) a photodetector including a light receiving surface on which a plurality of pixels are arranged respectively on a plurality of rows with the spectral image having a wavelength axis in a pixel arrangement direction of each of the plurality of rows being formed on the light receiving surface, and for receiving the spectral image for a first exposure time by a plurality of pixels arranged on one or a plurality of rows in a first region on the light receiving surface to output first spectrum data of the measurement target light, and receiving the spectral image for a second exposure time by a plurality of pixels arranged on one or a plurality of rows in a second region on the light receiving surface to output second spectrum data of the measurement target light, and (<NUM>) an analysis unit for obtaining a spectrum of the measurement target light based on the first spectrum data and the second spectrum data, and (<NUM>) the second exposure time is longer than the first exposure time, and when a wavelength band of the spectrum is divided into a saturation wavelength band including a wavelength band in which a value is at a saturation level or more in the second spectrum data and a non-saturation wavelength band other than the saturation wavelength band, the analysis unit obtains the spectrum of the measurement target light based on first partial spectrum data of the saturation wavelength band in the first spectrum data and second partial spectrum data of the non-saturation wavelength band in the second spectrum data.

An embodiment is a spectroscopic measurement method as defined in claim <NUM>. The spectroscopic measurement method includes (<NUM>) a light detection step of using a photodetector including a light receiving surface on which a plurality of pixels are arranged respectively on a plurality of rows, forming a spectral image of measurement target light having a wavelength axis in a pixel arrangement direction of each of the plurality of rows on the light receiving surface, receiving the spectral image for a first exposure time by a plurality of pixels arranged on one or a plurality of rows in a first region on the light receiving surface to output first spectrum data of the measurement target light, and receiving the spectral image for a second exposure time by a plurality of pixels arranged on one or a plurality of rows in a second region on the light receiving surface to output second spectrum data of the measurement target light, and (<NUM>) an analysis step of obtaining a spectrum of the measurement target light based on the first spectrum data and the second spectrum data, and (<NUM>) in the light detection step, the second exposure time is longer than the first exposure time, and in the analysis step, when a wavelength band of the spectrum is divided into a saturation wavelength band including a wavelength band in which a value is at a saturation level or more in the second spectrum data and a non-saturation wavelength band other than the saturation wavelength band, the spectrum of the measurement target light is obtained based on first partial spectrum data of the saturation wavelength band in the first spectrum data and second partial spectrum data of the non-saturation wavelength band in the second spectrum data.

According to the spectroscopic measurement apparatus and the spectroscopic measurement method of the embodiments, a spectrum of light of a high dynamic range can be acquired using one photodetector.

Hereinafter, embodiments of a spectroscopic measurement apparatus and a spectroscopic measurement method will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference signs, without redundant description. The present invention is not limited to these examples.

<FIG> is a diagram illustrating a configuration of a spectroscopic measurement apparatus <NUM>. The spectroscopic measurement apparatus <NUM> includes an optical system <NUM>, a photodetector <NUM>, an analysis unit <NUM>, a display unit <NUM>, and an input unit <NUM>, and acquires a spectrum of measurement target light reached from an object S. For example, the object S is an object of dry etching by plasma processing, and the measurement target light from the object S includes light due to a gas used for the etching, and light due to a material of the etching object. Further, for example, the object S is an object put in an integrating sphere for measuring a photoluminescence quantum yield, and the measurement target light from the object S includes excitation light and generated light (for example, fluorescence).

The optical system <NUM> guides the measurement target light from the object S to the light receiving surface of the photodetector <NUM>, and forms a spectral image of the measurement target light on the light receiving surface of the photodetector <NUM>. The optical system <NUM> may include an optical fiber for guiding the light. The optical system <NUM> disperses the measurement target light into wavelength components using a spectroscopic element such as a grating or a prism, and forms the spectral image on the light receiving surface of the photodetector <NUM>. The optical system <NUM> may include an optical element such as a lens and a mirror. Further, the optical system <NUM> may be a Czerny-Turner spectroscope, for example.

The photodetector <NUM> includes a light receiving surface on which a plurality of pixels are arranged respectively on a plurality of rows. On the light receiving surface, a spectral image having a wavelength axis in a pixel arrangement direction of each of the plurality of rows is formed. The photodetector <NUM> is a CCD image sensor or a CMOS image sensor formed on a semiconductor substrate, for example.

The photodetector <NUM> is preferably a photodetector that is thinned by grinding the rear surface (surface on the opposite side of the image sensor forming surface) of the semiconductor substrate and that can detect light with a high sensitivity in a wide wavelength band. Further, the CCD image sensor is preferable since it is of sensitivity higher than the CMOS image sensor. In addition, the CCD image sensor may be any of an interline CCD type, a frame transfer CCD type, and a full-frame transfer CCD type.

The light receiving surface of the photodetector <NUM> is divided into a first region and a second region. The photodetector <NUM> receives the spectral image for a first exposure time by a plurality of pixels arranged on one or a plurality of rows in the first region on the light receiving surface, and outputs first spectrum data of the measurement target light. Further, the photodetector <NUM> receives the spectral image for a second exposure time by a plurality of pixels arranged on one or a plurality of rows in the second region on the light receiving surface, and outputs second spectrum data of the measurement target light. The second exposure time is longer than the first exposure time.

The analysis unit <NUM> obtains the spectrum of the measurement target light based on the first spectrum data and the second spectrum data. The content of the analysis by the analysis unit <NUM> will be described later. The analysis unit <NUM> includes a storage unit storing input first spectrum data, second spectrum data, analysis results, and the like. Further, the analysis unit <NUM> may control the photodetector <NUM>.

The analysis unit <NUM> may be a computer or a tablet terminal including a processor such as a central processing unit (CPU) and a storage medium such as a random access memory (RAM) and a read only memory (ROM), for example, and in this case, it can be integrated with the display unit <NUM> and the input unit <NUM>. Further, the analysis unit <NUM> may be configured by a microcomputer or a field-programmable gate array (FPGA).

The display unit <NUM> displays the spectrum based on the first spectrum data and the second spectrum data input to the analysis unit <NUM>, and further, displays the analysis result by the analysis unit <NUM>. The input unit <NUM> is a keyboard, a mouse, and the like, for example, accepts an input instruction from an operator performing a spectroscopic measurement using the spectroscopic measurement apparatus <NUM>, and gives the input information (for example, measurement conditions, display conditions, and the like) to the analysis unit <NUM>. Further, the display unit <NUM> and the input unit <NUM> may be an integrated touch panel or the like.

<FIG> is a diagram showing an example of the spectral image. In this drawing, a wavelength axis extends in the horizontal direction, and an image for each wavelength extends in the vertical direction. In general, the spectral image has a vertically symmetrical shape with a certain center line (a dashed line in the drawing) extending in the horizontal direction as the axis of symmetry. Further, depending on the characteristics of the optical system <NUM>, the image for each wavelength has an arcuate shape in some cases.

<FIG> is a diagram schematically illustrating a configuration of the photodetector <NUM>. In the following, the description is made as the photodetector <NUM> is a CCD image sensor. The light receiving surface of the photodetector <NUM> is divided into the first region <NUM> and the second region <NUM> with the symmetry axis (the dashed line in <FIG>) of the spectral image to be formed as a boundary. In each of the first region <NUM> and the second region <NUM>, a plurality of pixels are arranged on one or a plurality of rows. Each pixel can generate and accumulate charges of an amount according to an intensity of received light. For example, each of the first region <NUM> and the second region <NUM> has <NUM> rows in the vertical direction, and <NUM> pixels are arranged in the horizontal direction in each row.

In the first region <NUM>, the charges generated and accumulated in each pixel are transferred to a horizontal shift register <NUM>, and the charges of one or more pixels in each column are added for each column in the horizontal shift register <NUM> (hereinafter, this operation is referred to as "vertical transfer"). After that, the charges added for each column in the horizontal shift register <NUM> are sequentially read from the horizontal shift register <NUM> (hereinafter, this operation is referred to as "horizontal transfer"). Then, a voltage value according to the amount of charges read from the horizontal shift register <NUM> is output from an amplifier <NUM>, and the voltage value is AD-converted by an AD converter into a digital value. Accordingly, the first spectrum data is acquired.

In the second region <NUM>, the charges generated and accumulated in each pixel are transferred to a horizontal shift register <NUM>, and the charges of one or more pixels in each column are added for each column in the horizontal shift register <NUM> (vertical transfer). After that, the charges added for each column in the horizontal shift register <NUM> are sequentially read from the horizontal shift register <NUM> (horizontal transfer). Then, a voltage value according to the amount of charges read from the horizontal shift register <NUM> is output from an amplifier <NUM>, and the voltage value is AD-converted by an AD converter into a digital value. Accordingly, the second spectrum data is acquired.

In the photodetector <NUM>, the second exposure time in the second region <NUM> is longer than the first exposure time in the first region <NUM>. The exposure time of each region can be set by an electronic shutter. The electronic shutter can be achieved by using an anti-blooming gate (ABG).

Preferably, the photodetector <NUM> synchronizes an output operation of the first spectrum data with an output operation of the second spectrum data. Further, preferably, the photodetector <NUM> has an output period of the second spectrum data at an integral multiple of an output period of the first spectrum data.

<FIG> is a timing chart illustrating a first operation example of the photodetector <NUM>. This drawing is a timing chart in the case in which a full-frame transfer type CCD image sensor is used. In this case, half of the charges accumulated during the vertical transfer period are transferred to the horizontal shift register in the vertical transfer, and the remaining half are transferred to the horizontal shift register in the next vertical transfer.

In the first operation example, the ABG is always in the off state, and the charges are continuously accumulated in both the first region <NUM> and the second region <NUM>. The output period of the second spectrum data from the second region <NUM> is five times the output period of the first spectrum data from the first region <NUM>. Therefore, the second exposure time in the second region <NUM> is about five times the first exposure time in the first region <NUM>. The analysis unit <NUM> may average a plurality (five, for example) of first spectrum data continuously output from the photodetector <NUM> and process the averaged first spectrum data.

<FIG> is a timing chart illustrating a second operation example of the photodetector <NUM>. This drawing is also a timing chart in the case in which a full-frame transfer type CCD image sensor is used.

In the second operation example, in the second region <NUM>, the ABG is always in the off state, and the charges are continuously accumulated. Therefore, in the second region <NUM>, the pulse phenomenon that occurs only for a moment can be measured. On the other hand, in the first region <NUM>, the ABG periodically repeats on/off. Therefore, in the first region <NUM>, the charges generated during the period when the ABG is in the on state are discarded, and the charges generated during the period when the ABG is in the off state are accumulated. In the first region <NUM>, the unread charges in the vertical transfer are discarded before the next vertical transfer.

In both of the first operation example and the second operation example, when the output operations of the first region <NUM> and the second region <NUM> are not synchronized, the signal instructing one output operation may be superimposed as noise on the signal instructing the other output operation. Therefore, when the output operations of the first region <NUM> and the second region <NUM> are performed at the same timing, preferably, the output operations of the first region <NUM> and the second region <NUM> are completely synchronized.

Further, in both of the first operation example and the second operation example, when the charge accumulation is saturated in a certain pixel, pixels in the vicinity of the pixel may be adversely affected. Therefore, it is also preferable to discard the charges exceeding a certain amount using the ABG.

<FIG> is a diagram showing an example of the first spectrum data. <FIG> is a diagram showing an example of the second spectrum data. The first spectrum data and the second spectrum data are acquired substantially at the same time by the photodetector <NUM>. The first spectrum data (<FIG>) is acquired in the first region <NUM> with a short exposure time, and is at the saturation level or less in all wavelength bands. On the other hand, the second spectrum data (<FIG>) is acquired in the second region <NUM> with a long exposure time, and is at the saturation level or more in a certain wavelength band.

The analysis unit <NUM> divides the entire wavelength band of the spectrum (approximately <NUM> to <NUM> in these drawings) into a saturation wavelength band (approximately <NUM> to <NUM>) including a wavelength band in which a value is at the saturation level or more in the second spectrum data and a non-saturation wavelength band (approximately <NUM> to <NUM>) other than the saturation wavelength band. In the saturation wavelength band, the first spectrum data is less than the saturation level even though the second spectrum data is at the saturation level or more. In the non-saturation wavelength band, the second spectrum data is less than the saturation level, and can have a S/N ratio better than that in the first spectrum data.

The analysis unit <NUM> obtains the spectrum of the measurement target light based on the first partial spectrum data of the saturation wavelength band in the first spectrum data and the second partial spectrum data of the non-saturation wavelength band in the second spectrum data.

The analysis unit <NUM> combines the first partial spectrum data in the saturation wavelength band in the first spectrum data and the second partial spectrum data in the non-saturation wavelength band in the second spectrum data as described below, and thus, one spectrum of the measurement light can be obtained.

The analysis unit <NUM> obtains a ratio of the integrated values of the first spectrum data and the second spectrum data in a wavelength band in which both of the first spectrum data and the second spectrum data are at the saturation level or less. Specifically, the analysis unit <NUM> first sets the values of the first spectrum data and the second spectrum data to zero in a wavelength band in which both or one of the first spectrum data and the second spectrum data is the saturation level or more.

<FIG> is a diagram showing an example in which the value in the predetermined wavelength band (wavelength band of the saturation level or more) is set to zero in the first spectrum data (<FIG>). <FIG> is a diagram showing an example in which the value in the predetermined wavelength band (wavelength band of the saturation level or more) is set to zero in the second spectrum data (<FIG>). The analysis unit <NUM> obtains the integrated values of the first spectrum data and the second spectrum data after setting the values in the predetermined wavelength band to zero, and obtains the ratio of these two integrated values. The ratio of the integrated values represents the intensity ratio of the output signals from the first region <NUM> and the second region <NUM>, and represents the ratio of the exposure times.

Further, the analysis unit <NUM> adjusts both or one of the first partial spectrum data and the second partial spectrum data using the ratio of the integrated values, and obtains the entire spectrum of the measurement target light based on the first partial spectrum data and the second partial spectrum data after the adjustment. In this adjustment, the first partial spectrum data may be multiplied by the integrated value ratio, or the second partial spectrum data may be divided by the integrated value ratio. For reducing the noise level, it is preferable to divide the second partial spectrum data by the integrated value ratio. <FIG> is a diagram showing the spectrum of the measurement target light obtained based on the first partial spectrum data and the second partial spectrum data after the adjustment.

The spectroscopic measurement method of the present embodiment performs measurement using the spectroscopic measurement apparatus of the present embodiment described above, and includes a light detection step of outputting the first spectrum data and the second spectrum data using the photodetector <NUM>, and an analysis step of obtaining the spectrum of the measurement target light based on the first spectrum data and the second spectrum data. The content of the light detection step is as described as the configuration and operation of the photodetector <NUM>. The content of the analysis step is as described as the analysis content of the analysis unit <NUM>.

<FIG> is a graph showing an example of the relationship between the exposure time in the first region and the dynamic range in an example and a comparative example. The dynamic range of the comparative example is a dynamic range in the case in which the spectrum of the measurement target light is acquired without division into the first region and the second region. The dynamic range of the example is larger than that of the comparative example. The dynamic range is expressed as a ratio of a maximum detectable level and a minimum detectable level. The maximum detectable level is a saturation charge amount of the horizontal shift register (for example, <NUM> ke-), and the minimum detectable level is a noise level. In the present embodiment, the second partial spectrum data is divided by the integrated value ratio (output signal intensity ratio), and thus, the minimum detectable level (noise level) in the second partial spectrum data becomes smaller, and the dynamic range becomes larger.

As described above, in the present embodiment, the spectrum of light having a high dynamic range can be acquired using one photodetector <NUM>. In addition, both of the light of high intensity and the light of low intensity can be measured substantially at the same time. Therefore, in a step of dry etching of an object by plasma processing, a spectrum of measurement target light including both of the light of high intensity due to a gas and the light of low intensity due to a material can be acquired, the state of the gas can be monitored, and the etching end timing can be detected. Further, in measuring a photoluminescence quantum yield of a sample using an integrating sphere, a spectrum of excitation light absorbed by the sample and a spectrum of light generated from the sample (for example, fluorescence) can be measured at the same time in a state in which the sample is put in the integrating sphere.

Further, the spectroscopic measurement apparatus and the spectroscopic measurement method of the present embodiment can measure both of the light of high intensity and the light of low intensity substantially at the same time, and further, can measure the light of high intensity and the light of low intensity at the different periods. In the latter case, the same measurement conditions can be set for the measurement of the light of high intensity and the measurement of the light of low intensity, and for example, an ND filter does not necessarily have to be inserted in the measurement of the light of high intensity. Examples of applications include a measurement of a spectrum of weak output light when a small current is applied to a light emitting diode (LED) and a measurement of a spectrum of bright output light when a rated current is applied to the LED. In such applications, the measurement of a high dynamic range of light can be performed with high wavelength accuracy.

The embodiments can be used as a spectroscopic measurement apparatus and a spectroscopic measurement method that can acquire a spectrum of light with a high dynamic range using one photodetector.

Claim 1:
A spectroscopic measurement apparatus (<NUM>) comprising:
an optical system (<NUM>) for dispersing measurement target light to form a spectral image;
a photodetector (<NUM>) including a light receiving surface on which a plurality of pixels are arranged respectively on a plurality of rows with the spectral image having a wavelength axis in a pixel arrangement direction of each of the plurality of rows being formed on the light receiving surface, and for receiving the spectral image for a first exposure time by a plurality of pixels arranged on one or a plurality of rows in a first region on the light receiving surface to output first spectrum data of the measurement target light, and receiving the spectral image for a second exposure time by a plurality of pixels arranged on one or a plurality of rows in a second region on the light receiving surface to output second spectrum data of the measurement target light; and
an analysis unit (<NUM>) for obtaining a spectrum of the measurement target light based on the first spectrum data and the second spectrum data, wherein
the second exposure time is longer than the first exposure time, and
when a wavelength band of the spectrum is divided into a saturation wavelength band including a wavelength band in which a value is at a saturation level or more in the second spectrum data and a non-saturation wavelength band other than the saturation wavelength band, the analysis unit (<NUM>) obtains the spectrum of the measurement target light based on first partial spectrum data of the saturation wavelength band in the first spectrum data and second partial spectrum data of the non-saturation wavelength band in the second spectrum data.