JP2012132854A - Analyzer and analytic method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem of a conventional analyzer using Raman scattering in which effective data may not be obtained when a sample is oscillated on a random cycle.SOLUTION: An analyzer for analyzing a sample by irradiating a face of the sample with a laser beam and measuring Raman scattering light, comprises: an object lens for condensing the laser beam; a plate body disposed between the object lens and the sample and having two openings; a detecting device for detecting reflected light of the laser beam from the sample and intensity data of the Raman scattering light at the same time; a storage device for storing detection results in time series; and an operational device for integrating intensity data of Raman scattering light measured when intensity data of the reflected light stored as a detection result has a prescribed or larger value.

Description

  The present invention relates to an apparatus and method for analyzing a sample by measuring Raman scattering, and more particularly to a technique for reducing the influence of an analysis position shift caused by vibration of a sample.

  In a conventional optical microscope using Raman scattering, laser light is focused on a minute spot of about 1 μm, irradiated on the sample surface, and the material of the sample is analyzed by measuring Raman scattered light. Analysis using Raman scattering is excellent in spatial resolution, and is used for evaluation of crystallinity of a minute region of a semiconductor device.

  In such an analysis apparatus using Raman scattering, the condensing part of the laser beam is fixed, so that the analysis surface moves when the stage or the sample body is vibrated according to the measurement conditions. For this reason, not only the portion to be analyzed but also the Raman scattered light from the surrounding portion is measured together, resulting in average data, not local data, and appropriate analysis cannot be performed.

  For example, a cryos stage that performs measurement while controlling the temperature of a sample is accompanied by a large vibration. Since the sample fixed on the cryos stage vibrates with an amplitude of several tens of μm on the cryos stage, the obtained Raman scattering data becomes average data of a region having a width of several tens of μm.

  Therefore, although it is not an analysis device using Raman scattering, a disk having an opening crossing at least one of the observation optical system and illumination optical system of a microscope is rotated in synchronization with the vibration period of the sample, and the analysis surface is opened. In some cases, image blurring is reduced by taking an image at a timing immediately below the image and acquiring only reflected light from a certain position of the sample (see, for example, Patent Document 1).

JP 2003-84208 A

  The above method may also be applied to analyzers using Raman scattering. However, it is effective when the sample has a fixed period of vibration, but there is a problem that only average data can be obtained when the sample has a random period of vibration.

  The present invention has been made to solve the above-described problems, and in an analyzer using Raman scattering, effective data can be obtained even when a sample is accompanied by random-period vibration. Is.

  The analyzer according to the present invention is an analyzer that irradiates a sample surface with laser light and analyzes the sample by measuring Raman scattered light, and includes an objective lens that collects the laser light, the objective lens, and the sample. , A plate-like body having two openings, a detection device that simultaneously detects intensity data of reflected light and Raman scattered light from the sample of the laser light, and stores the detection results in time series And a computing device that integrates the intensity data of the Raman scattered light measured when the intensity data of the reflected light is greater than or equal to a predetermined value from the stored detection result. .

  According to the present invention, it is possible to prevent measurement of Raman scattered light other than a portion to be analyzed on a sample on a cryostage accompanied by random-period vibration. Therefore, effective data can be obtained and appropriate analysis can be performed even when the sample is accompanied by vibration of a random period.

It is a block diagram which shows the optical system of the analyzer which concerns on Embodiment 1 of this invention. It is a flowchart which shows the analysis process which concerns on Embodiment 1 of this invention. It is sectional drawing of the silicon pn diode as a sample. It is a schematic diagram which shows the positional relationship of a sample and a plate-shaped object in case reflected light intensity becomes the maximum. It is a schematic diagram which shows the case where an analysis position and a mark are obstructed by a plate-like body and laser light cannot be irradiated.

Embodiment 1 FIG.
Next, embodiments of the present invention will be described with reference to the drawings. In the following description of the drawings, the same or similar reference numerals are used for the same or similar parts. However, the drawings are schematic and ratios of dimensions and the like are different from actual ones. Therefore, specific dimensions and the like should be determined in consideration of the following description, and it is natural that the relationship and ratio of the dimensions may be different between the drawings.

  1 is a block diagram showing an optical system of an analyzer according to Embodiment 1 of the present invention. In the figure, a laser beam 1a emitted from a laser light source 1 that irradiates a laser beam reflects Raman scattered light and reflected light (hereinafter also referred to as Raman scattered light / reflected light) 1b from a sample 14 described later at substantially right angles. Then, it passes through a beam splitter 2 provided for separation from the irradiated laser 1a, the transmitted light is condensed by the objective lens 3, and the plate-like body provided with openings 4a and 4b at predetermined positions. 4 and the sample 14 is irradiated.

The Raman scattered light / reflected light 1 b from the sample 14 passes through the openings 4 a and 4 b of the plate-like body 4, is then reflected at a substantially right angle by the beam splitter 2, and is collected by the condenser lens 5. The condensed Raman scattered light / reflected light 1 c is split by the spectroscope 6, and each light is detected by the multichannel detector 7. Each data related to the Raman scattered light and the reflected light detected by the multi-channel detector 7 is recorded in time series in the calculation device 8 having a storage device, and a predetermined calculation is performed based on the recorded data.
In the present embodiment, the beam splitter 2 is configured to reflect the Raman scattered light / reflected light 1b at a right angle. However, the beam splitter 2 is configured to reflect at an acute angle depending on the position of the condenser lens 5, the position of the spectroscope 6, and the like. Or a configuration that reflects at an obtuse angle.

As described above, the plate-like body 4 is provided with openings 4a and 4b at predetermined positions, but the other portions are coated with a coating that absorbs the wavelength of laser light, such as carbon black. Yes. The shape of the plate-like body 4 is substantially circular, and the size may be about 10 mm in diameter. Since the sizes of the openings 4a and 4b are restricted by the alignment operation described later, the diameter is in the range of 5 μm to 10 μm, and the distance between the openings 4a and 4b is adjusted to the measurement target. The opening 4a is at the center of the plate-like body 4 and is arranged coaxially with the laser optical axis.
Here, the shape of the plate-like body 4 is a substantially circular plate shape, but it is not necessary to be particularly circular. For example, the shape may be a quadrangle, a hexagon, an octagon, or the like. If the structure has the opening, the shape need not be specified and is a design matter.

  The spectroscope 6 is parallel to an incident slit 9 on which the Raman scattered light / reflected light 1c collected by the condenser lens 5 is incident, a collimator mirror 10 that converts the light that has passed through the focal position and diffused into parallel light of a predetermined width, and parallel. A diffraction grating 11 that splits light based on a wavelength, a condensing mirror 12 that condenses parallel light from the diffraction grating 11 again, and an exit slit 13 that emits the condensed light.

The multi-channel detector 7 is a multi-pixel detector such as a CCD camera or an InGaAs detector. The multi-pixel detector can detect Raman scattered light / reflected light 1c at different pixels. That is, the Raman scattered light / reflected light 1c can be detected simultaneously. In the present invention, it is essential to simultaneously detect Raman scattered light and reflected light. For example, by using a spectroscope 6 having a reverse dispersion of 40 cm ⁻¹ / mm and a multi-channel detector 7 having a 1024 pixel and an element size of 26 μm × 26 μm, a theoretical ^value of 1040 cm ⁻¹ is obtained. When a frequency band can be secured and a semiconductor device is targeted, Raman scattered light and reflected light can be detected simultaneously.

  The calculation device 8 has a storage device, and simultaneously records the intensity data of the Raman scattered light and the reflected light detected by the multichannel detector 7 in time series. Further, the calculation device 8 extracts the time when the intensity exceeds a predetermined threshold from the recorded time-series data of the reflected light, and extracts the Raman scattering intensity detected at the same time as that time. Have a calculation function to integrate. The storage device does not necessarily have to be included in the computing device 8 and may be an external device.

Next, an analysis method according to Embodiment 1 of the present invention will be described. FIG. 2 is a flowchart showing an analysis process according to Embodiment 1 of the present invention. This flow will be described with reference to an example in which the crystallinity evaluation of the buffer layer at the pn junction interface of the silicon pn diode shown in FIG. FIG. 3 is a cross-sectional view of a silicon pn diode, which has a front electrode 16 and a back electrode 17 on the front and back surfaces, respectively. Here, the front electrode 16 is made of Al and the back electrode 17 is made of Au, and the thickness of the buffer layer 20 at the pn junction interface between the n ⁻ layer 18 and the p ⁺ substrate 19 for crystallinity evaluation is 10 μm.

  In FIG. 2, a sample is attached to the center of the cryostage as the first step. Next, as a 2nd step, the plate-like body is fixed. Here, first, an operation of determining a structure serving as a mark whose relative positional relationship with the buffer layer 20 is determined is performed. The position of the mark needs to have a higher reflectance than the surroundings. In the sample given as an example, the surface electrode 16 made of Al is used as a mark. The distance between the buffer layer 20 as the analysis position and the surface electrode 16 serving as a mark is uniquely determined from the device structure.

  Therefore, the plate-like body 4 provided with the opening 4a and the opening 4b having the same interval as the distance between the buffer layer 20 as the analysis position and the surface electrode 16 serving as the mark is provided between the objective lens 3 and the sample 14. Provided. The distance between the plate-like body 4 and the sample 14 is desirably set to 1 mm or less in order to reduce light diffraction. This setting is carried out by providing a holder that can change the position three-dimensionally between the objective lens 3 and the sample 14, inserting the plate 4 into the holder, and adjusting the position of the plate with a micrometer. it can. At this time, the horizontal position adjustment is performed so that the optical axis of the laser and the center of the plate-like body are coaxial.

  Next, as a 3rd step, the surface of the sample 14 and the plate-like body 4 are aligned with a micrometer attached to the stage. This operation may be performed by simple adjustment to confirm that Al marks as the surface electrode 16 are approximately present directly under the opening of the plate-like body 4 through the opening with an optical microscope.

  Next, as a 4th step, the stage is moved with a micrometer of the sample stage to finely adjust the sample surface. At this time, the sample 14 is irradiated with laser light (step 4-1). The sample 14 generates reflected laser light and Raman scattered light having a wavelength specific to the sample. When the sample 14 is irradiated with laser light and the intensity of the reflected light is measured (step 4-2) and it is determined that the intensity is not maximum (no flow in the figure), the sample position is changed so that the intensity becomes maximum. (Step 4-3). The 4th process is repeated until the strength reaches a maximum. When it is determined that the intensity is maximum (the flow of yes in the figure), the process proceeds to the next process (5th process). FIG. 4 shows the positional relationship between the sample and the plate-like body when the reflected light intensity is substantially maximum. In the figure, the buffer layer 20 serving as an analysis position and the surface electrode 16 serving as a mark are located almost immediately below the opening of the plate-like body.

  Here, the determination of whether or not the reflected light intensity is substantially maximum can be easily obtained by, for example, a method of detecting a peak value. The position where the sample position is moved and the reflected light intensity starts to decrease is determined to be almost maximum. In addition, the maximum value of the reflected light intensity is stored in advance in a separate storage device, the sample position is moved, and when the difference from the stored maximum value is minimum, the reflected light intensity is determined to be almost maximum. May be.

  Next, as a 5th process, the cryostage is turned on. From this point, the sample 14 starts to vibrate. The positional relationship between the sample 14 and the plate-like body 4 is changed, and as shown in the schematic diagram of FIG. 5, the buffer layer 20 as the analysis position and the surface electrode 16 serving as a mark are blocked by the plate-like body 4, and the laser beam is emitted. There are cases where irradiation is impossible.

  Next, as a 6th step, the reflected light and the Raman scattered light are separated by the spectroscope 6 and detected by the multichannel detector 7. Since the detector is multichannel, the light intensity data of reflected light and Raman scattered light can be detected simultaneously. The reflected light intensity varies depending on the positional relationship between the sample and the plate-like body 4.

Next, as the 7th step, the light intensities of the reflected light and the Raman scattered light are recorded in time series.
Finally, as the 8th step, the light intensity data of the Raman scattered light from the buffer layer 20 is accumulated by integrating the light intensity data of the Raman scattered light obtained at the timing when the light intensity data of the reflected light exceeds a predetermined threshold value. Can be regarded as a result of pseudo integration.

That is, when the light intensity data of the reflected light exceeds a predetermined threshold, the laser light is appropriately irradiated to the analysis position, and by integrating the light intensity data of the Raman scattered light during this period, Only the light intensity data of the Raman scattered light from the analysis position can be appropriately obtained.
Here, in setting the predetermined threshold value, it is necessary to consider the influence of Raman scattered light not only from the part to be analyzed but also from the peripheral part. The threshold can be lowered if the influence of the Raman scattered light from the surrounding portion is small, and the threshold needs to be increased if the influence is large. Thus, it is obvious that the threshold value can be easily set by those skilled in the art in consideration of the measurement sensitivity and the influence from the surroundings.

1 laser light source, 1a laser light, 1b Raman scattered light / reflected light, 1c Raman scattered light / reflected light, 2 beam splitter, 3 objective lens, 4 plate, 4a opening, 4b opening, 5 condenser lens, 6 Spectrometer, 7 Detector, 8 Measuring device, 9 Entrance slit, 10 Collimator mirror, 11 Diffraction grating, 12 Condensing mirror, 13 Exit slit, 14 Sample, 15 Cryostage, 16 Front electrode, 17 Back electrode, 18 n ^- layer, 19 ^{p +} substrate, 20 a buffer layer

Claims (3)

  In an analyzer that irradiates a sample surface with laser light and analyzes the sample by measuring Raman scattered light, an objective lens that condenses the laser light, provided between the objective lens and the sample, A plate-like body having an opening, a detection device that simultaneously detects intensity data of reflected light and Raman scattered light from the sample of the laser light, a storage device that stores the detection results in time series, and a storage device And an arithmetic unit that integrates the intensity data of the Raman scattered light measured when the intensity data of the reflected light is equal to or greater than a predetermined value based on the detection result.   2. The analyzer according to claim 1, wherein the sample is a semiconductor, and an interval between two openings of the plate-like body is equal to an interval between a metal electrode of the semiconductor and an analysis position.   An analysis method for irradiating a sample surface with laser light and analyzing the sample by measuring Raman scattered light, the step of condensing the laser light with an objective lens, and providing between the objective lens and the sample A step of branching the laser light by the plate-like body having two openings, a step of simultaneously detecting intensity data of reflected light and Raman scattered light from the sample of the laser light, and A step of storing in series, and a step of integrating the intensity data of the Raman scattered light measured when the intensity data of the reflected light exceeds a predetermined value from the stored detection result. Analysis method.

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