Combined evaluation system for surface by light scattering method

Description: TECHNICAL FIELD [Detailed description of the invention]

【0001】

[Technical field to which the invention belongs]

The present invention relates to a surface composite evaluation system by a light scattering method, and more specifically, a surface by a light scattering method capable of simultaneously measuring and evaluating fine particles, scratches, and microroughness of an ultra-precision machined surface such as a silicon wafer. It is related to the composite evaluation system of.

【0002】

[Conventional technology]

The progress of high integration in VLSI is remarkable, and semiconductor memory DRAM with storage capacity of 1 to 4 gigabit is under development, so the design rule is about to enter the next generation 0.1 μm width. By the way, in the device wafer, metal contaminants, foreign substances (particles), and fine defects such as scratches are considered to be factors of device failure. That is, it is said that most of the defects of the semiconductor device are caused by foreign substances adhering to the silicon (Si) wafer, and the size is 1/5 to 1/5 of the pattern width in consideration of the yield and reliability in LSI manufacturing. Foreign matter (particles) of about / 3 becomes a problem. Therefore, control for a clean environment is also required more strictly, and when the pattern width is 0.1 μm, it is indispensable to detect and remove fine particles having a diameter of about 30 nm to 50 nm.

【0003】

However, although there are various particle size measuring machines (particle counters) that use scattered light, all of them detect the absolute amount of scattered light generated from fine particles, and due to the influence of noise (stray light), the fine particles that can be measured at present are The particle size is about 0.08 μm, and I can't find anything smaller than that. Further, in the conventional light scattering method, the particle size that can be detected in principle is about 30 nm due to the influence of the speckle pattern from the surface. When the particle size is 0.8 μm or less, the detected scattered light becomes extremely weak light. For example, when the particle size is 10 nm, the scattered light intensity from the particles is also 1 pW (10-).¹²It becomes extremely weak light of about W) and is detected as a photoelectron pulse train. Therefore, there is also a very weak light detection method such as a photo counting method, but it takes an enormous amount of time for measurement. Also, 10 stray lightsSince it is very difficult to suppress to about 12 W, scattered light from fine particles having a diameter of nanometer order is always below the stray light level, and the signal is buried in it, which makes measurement very difficult.

【0004】

Further, although the surface roughness can be measured by a fringe scanning interference microscope (Zygo) which is a three-dimensional surface structure analysis microscope, it is not possible to measure fine particles adhering to the surface. A scanning electron microscope is also used for microscopic observation of the surface, but there is a problem that the electron microscope is generally expensive and it takes too much measurement time to observe the surface of a large area. ..

【0005】

By the way, the present inventor has provided a particle size measuring device for ultrafine particles by a light scattering method for measuring the particle size of ultrafine particles on the order of nanometers adhering to the surface of a sample such as a silicon wafer as described in Japanese Patent No. 2747921. Already provided. That is, the particle size measuring device for ultrafine particles by this light scattering method is a laser light irradiating means for condensing laser light to a predetermined spot diameter and irradiating the sample surface, and the first focus of an elliptical mirror formed on the inner surface. And the second focal point are set to be located slightly outside the surface connecting the surrounding ridges, and the laser beam is placed in the vicinity including the first focal point at an equiangular position centered on the first focal point. An elliptical concentrator having an inlet / outlet for irradiating the light, and a moving device having a sample surface located in the vicinity including the first focal point of the elliptical concentrator and capable of moving the sample at a constant speed. A parabolic light condensing is formed on the inner surface of a parabolic mirror whose focus is aligned with the second focal point of the elliptical concentrator, and guides scattered light from ultrafine particles adhering to the sample surface focused on the focal point. A photoelectron multiplier, which is arranged at the other end of the parabolic condenser and detects the extremely weak scattered light guided by the parabolic condenser as a discrete pulsed signal in a single photoelectron state, is installed. A detector capable of cooling the photoelectron multiplying tube, and a signal processing means that integrates the signal of scattered light detected by the detector, converts it into a voltage, and calculates the particle size of ultrafine particles from the peak value voltage. It is composed of.

【0006】

The device described in the above-mentioned publication makes it possible to measure the particle size of nanometer-order ultrafine particles adhering to the surface of a sample such as a silicon wafer, but the surface of the silicon wafer is scratched by dicing or polishing. There were fine irregularities that could not be removed by polishing, and these could not be observed at the same time.

【0007】

[Problems to be Solved by the Invention]

Therefore, in view of the above situation, the present invention attempts to solve the problem by simultaneously measuring fine particles, scratches, and microroughness of sub-nanometer orders on an ultra-precision machined surface such as a silicon wafer in a short time by a light scattering method. It is possible to provide a composite evaluation system for a surface by a light scattering method, which is possible and has a relatively simple and inexpensive device structure.

【0008】

[Means for solving problems]

In order to solve the above-mentioned problems, the present invention has a convergent optical system that converges the laser light to a predetermined spot diameter and irradiates the sample surface at a predetermined incident angle, and the sample in the Y direction with respect to the irradiated laser light. A drive control system that scans in the X direction at a relatively constant speed at regular scanning intervals, a condensing optical system that condenses extremely weak total scattered light, and a single optical electronic state of the collected total scattered light. Fine particles on the sample surface based on a light detection system that detects as a pulsed signal and integrates the signal to convert it into a voltage, and the integrated voltage wave high value data and laser light irradiation position data obtained by the light detection system. Arithmetic processing to calculate and identify the particle size and position of the light, the groove width and length and position of the scratch, and the value and distribution of the microroughness according to the scattering model as Rayleigh scattering from the virtual fine particles arranged on the sample surface, respectively. A composite evaluation system for the surface by the light scattering method equipped with a system was constructed.

【0009】

Here, the present invention irradiates the sample surface driven by the drive control system at a constant scanning speed with the laser beam converged by the convergent optical system, and removes the positively reflected light from the sample surface. However, by detecting the extremely weak scattered light as a discrete pulsed signal in a single photoelectron state with the photomultiplier tube that constitutes the photodetection system, the effects of stray light, shot noise, and speckle due to external light are offset. The maximum detection sensitivity is 6 nm for the particle size of fine particles, 1 nm for the groove width of scratches, and 0.1 nm for the roughness value.

【0010】

Specifically, the integrated voltage wave height data is separated into a long wavelength component corresponding to the laser spot diameter and a short wavelength component sufficiently shorter than that, and the integrated voltage wave height data and the irradiation position data of the long wavelength component are separated. Based on this, the discontinuity of the detection signal of the long wavelength component in the Y direction is judged, and the particle size is calculated according to the particle scattering model in which virtual fine particles with different diameters are arranged in a discrete state on the sample surface, and the fine particles are calculated. Is measured.

【0011】

Further, the integrated voltage wave height data is separated into a long wavelength component corresponding to the laser spot diameter and a short wavelength component sufficiently shorter than that, and based on the integrated voltage wave height data and the irradiation position data of the long wavelength component, the integrated voltage wave height data is used. Judging the continuity of the detection signal of the long wavelength component in the Y direction, the particle size is calculated corresponding to the scratch scattering model in which a plurality of virtual fine particles are continuously arranged in a substantially linear shape on the sample surface, and the particles are calculated. The scratch is measured by converting the diameter into the groove width.

【0012】

Then, the integrated voltage wave height data is separated into a long wavelength component corresponding to the laser spot diameter and a short wavelength component sufficiently shorter than that, and based on the integrated voltage wave height data and the irradiation position data of the short wavelength component, the integrated voltage wave height data is used. The average particle size in each spot is calculated in correspondence with the roughness scattering model in which a plurality of virtual fine particles are spread on the sample surface and the particle size of the virtual fine particles is made uniform in the spot of the laser light, and the average particle size is averaged. Microroughness is measured in terms of roughness.

【0013】

Further, it is preferable that the scratch is measured based on the integrated voltage peak value data and the irradiation position data acquired for each of one or more different scanning directions, and the measurement results are combined.

【0014】

In addition, if the measurement results for fine particles, scratches, and microroughness measured by each scattering model are combined based on the common integrated voltage wave height data and irradiation position data and displayed two-dimensionally or three-dimensionally, the measurement range of the sample surface can be obtained. Is preferable because it can be visually evaluated.

【0015】

Further, since it is possible to change the penetration depth of the laser beam with respect to the sample surface by scanning the sample surface by changing the wavelength of the laser beam, it is also preferable to obtain information on the predetermined depth from the sample surface. ..

【0016】

The present invention simultaneously measures fine particles adhering to the sample surface, scratches formed on the surface during processing, and microroughness of the surface to evaluate the sample surface in a complex manner. explain. In the present invention, by scanning the sample surface at a constant scanning speed, even if external light wraps around and enters the condensing optical system, it is canceled out as a DC voltage component by the shining detection system and removed, so that it is true in the true sense. There is no noise as stray light. Therefore, since the obtained integrated voltage wave height data reflects only scattered light from fine particles, scratches, and microroughness (fine irregularities), it is different from the conventional method of extracting scattered light from fine particles buried in noise. Unlike, we were able to break the barrier of measurement limit with a particle size of 0.1 μm. Since the particle size of the fine particles on the sample surface and the groove width of the scratch are smaller than the laser spot diameter and are generated while the laser spot passes through, the signal waveform of the integrated voltage wave high value data of the scattered light caused by the fine particles and scratches is the laser. The pulse has a hem width corresponding to the spot diameter. The signal waveform of the integrated voltage wave high value data of the scattered light by scratch is the same waveform as that of fine particles, but if this signal waveform is continuous in the Y direction beyond the laser spot diameter, it is clear that it is fine particles. It can be determined that it is due to scratches. That is, if the signal waveform obtained by scanning in the X direction continues to be longer than the laser spot diameter even if it is scanned in the Y direction in a certain step, it can be regarded as a scratch. The groove width can be measured by the maximum peak value, and the scratch length can be measured from the scanning distance continuing in the Y direction.

【0017】

Further, on a surface without fine particles or scratches, if the number of irregularities due to surface roughness in the laser spot light differs for each spot, the scattered light intensity changes according to the scanning direction (X direction). That is, the microroughness is detected as a fluctuation component of the detection signal according to the surface roughness. This is a noise component in the measurement of fine particles and scratches, and this short wavelength component indicates the average roughness of the surface region corresponding to the laser spot diameter.

【0018】

Here, the waveforms of the detected voltage signals from the scattered light due to the fine particles and scratches and the surface roughness have a large difference, and the former is reflected as a long wavelength component of the detected voltage signal and the latter is reflected as a short wavelength component. That is, since the signal waveform due to the unevenness of the surface roughness is extracted as a change in the scattered light intensity when the laser spot is moved at regular intervals, the wavelength of the signal waveform due to the fine particles and scratches is due to the unevenness of the surface roughness. It is detected as being one order or more longer than the wavelength of the signal waveform. Therefore, the signal waveform of the integrated voltage wave high value data of the scattered light from the sample surface is separated into a long wavelength component having the same size as the laser spot diameter and a short wavelength component having a sufficiently short wavelength, and the data is processed. Here, as a means for separating the signal waveform of the integrated voltage wave high value data into a long wavelength component and a short wavelength component, a low-pass filter circuit, a high-pass filter circuit, or a band-pass filter circuit can be used in terms of hardware, but the same processing can be achieved. Can also be done with soft data processing.

【0019】

BEST MODE FOR CARRYING OUT THE INVENTION

First, a surface composite evaluation system by the light scattering method of the present invention will be described based on the configuration diagram shown in FIG. The basic configuration is the same as the device described in Japanese Patent No. 2747921 by the present inventor. In the figure, reference numeral 1 indicates a laser, 2 indicates a convergent optical system, 3 indicates a drive control system, 4 indicates a condensing optical system, 5 indicates an optical detection system, and 6 indicates an arithmetic processing system.

【0020】

The measuring device constituting the surface composite evaluation system by the light scattering method according to the present invention is a focusing optics that converges the laser beam generated by the laser 1 to a predetermined spot diameter and irradiates the sample surface A with a predetermined incident angle. System 2, drive control system 3 that scans sample A in the X direction at a relatively constant speed at regular scanning intervals in the Y direction with respect to the irradiation laser light, and a collection that collects extremely weak total scattered light. Obtained by the optical optical system 4, the optical detection system 5 that detects the collected all scattered light as a discrete pulsed signal in a single photoelectron state, integrates the signal, and converts it into a voltage, and the light detection system 5. Based on the integrated voltage wave height data and the irradiation position data of the laser beam, the particle size and position of the fine particles on the sample surface, the groove width and length and position of the scratch, and the value and distribution of the microroughness were arranged on the sample surface, respectively. It is equipped with an arithmetic processing system 6 that calculates and identifies in correspondence with a scattering model that is Rayleigh scattering from virtual fine particles.

【0021】

The drive control system 3 is composed of a 4-axis drive table in which a table rotation θ-axis table is added to the XYZ 3-axis. Further, the condensing optical system 4 is composed of an elliptical mirror 7 and a parabolic mirror 8, a laser spot is set on a sample surface A located near one focal point of the elliptical mirror 7, and the other of the elliptical mirror 7 is set. The focal point of the parabolic mirror 8 is located near the focal point of. Further, the photodetection system 5 uses a photomultiplier tube (PMT) 9 arranged so as to close the open end of the parabolic mirror 8 and a detection circuit connected to the photomultiplier tube (PMT) 9 to generate a voltage signal proportional to the scattered light intensity. It is composed of a signal control unit 10 that converts and obtains integrated voltage peak value data. The integrated voltage wave high value data obtained by the photodetection system 5 is data-processed by the arithmetic processing system 6 composed of a personal computer. Further, the drive control system 3 is driven by the arithmetic processing system 6 via the motor control unit 11, and the irradiation position data of the laser spot on the sample surface A is stored in the arithmetic processing system 6 together with the integrated voltage peak value data. To. Further, a CCD camera microscope 12 is attached for setting the position and focus adjustment of the laser spot in the optical system, and the CCD camera microscope 12 is controlled by the arithmetic processing system 6 via the CCD camera control unit 13.

【0022】

Next, the principle of measuring fine particles in the surface composite evaluation system by the light scattering method of the present invention will be described. In this embodiment, an argon laser having a wavelength of 488 nm was used as the laser light to irradiate the sample surface. In this case, the scattered light from the fine particles adhering to the sample surface, particularly the scattered light in the case of fine particles having a diameter of 100 nm or less, becomes Rayleigh scattered light, and the particle size is measured from the intensity thereof. Further, in the present embodiment, the laser spot diameter is 5 μm, and the spot light is scanned at 1 μm intervals.

【0023】

Generally, the scattered light intensity from the spherical particles by linearly polarized laser light, Mie scattered containing Bessel functions and a cylindrical function derived from the electromagnetic equations Maxwell obtained by turbulent type. Furthermore, the Rayleigh scattered light intensity is obtained as an approximate solution of Mie scattering. The total scattered light intensity of Rayleigh scattered light from microspherical particles is expressed by the following equation 1.

【0024】

[Number 1]

<img file="JP2002257518A_D0001.tif" />【0025】

Here, λ is the wavelength of the incident laser beam, n is the relative complex refractive index of the particle and the medium, and I₀Is the laser intensity, also d_PAs the particle diameter, α as the particle size parameter, α = πd_PDefined as / λ. As shown in Equation 1, since the total scattered light intensity is proportional to the sixth power of the particle size, it is the basic measurement principle of the present invention to measure the total scattered light intensity and then obtain the particle size.

【0026】

The scattered light intensity of particles on the order of nanometers (nm) makes the particles SiO.₂Even if an Ar laser beam with an output of 1 W and a wavelength of 488 nm is focused on a spot diameter of 5 μm and irradiated, it is 10^-12Very weak light below W. Therefore, because of the extremely weak light, the output signal from the photomultiplier tube (PMT) is taken out in the single photoelectron state (SPE) in which the photoelectron pulses are discrete. , It becomes difficult to detect the particle size on the order of nm. Therefore, in the present invention, this single photoelectron pulse is detected as an integrated voltage waveform through a simple CR detection circuit, and the diameter of the fine particles is measured (see the above-mentioned Japanese Patent No. 2747921). FIG. 2 shows how scattered light from the fine particles P adhering to the sample surface A is detected, (a) shows the relationship between the laser beam L and the fine particles P, (b) shows the laser spot S, and (c) shows the laser spot S. The intensity distribution of the laser beam is shown, (d) shows the photoelectron pulse detected by PMT, and (e) shows the integrated voltage waveform obtained through the CR detection circuit.

【0027】

When extremely weak scattered light from fine particles is detected by PMT, as shown in FIG. 3, the output current fluctuates due to shot noise due to irregular emission of photoelectrons from the PMT photoelectric surface. V in Figure 3_pIndicates the peak value of the detected voltage, V_ph(pp) indicates the peak width of shot noise fluctuation, V_ph(DC) indicates the direct current component of noise. In the present invention dealing with extremely weak light, the shot noise of PMT has a great influence on the measurement limit. The causes of optoelectronic flow in PMT are (1) stray light (background light) incident on the photoelectric surface, (2) incident scattered light detected from particles on the photoelectric surface, and (3) thermionic emission from the photoelectric surface. There are three types of dark current due to, but the measurement limit of the present invention depends on the dark current of (3). If the S / N due to shot noise of dark current is 10, the particle size of the fine particles at the detection limit is 8.5 nm, and if the S / N is 1, the particle size is about 6 nm, which is the theoretical detection of the present invention. It is the limit.

【0028】

The present invention scans a convergent laser beam on the surface of a sample to detect an integrated voltage wave height value from a photomultiplier tube that is proportional to the intensity of extremely weak scattered light generated from fine particles, scratches, and fine irregularities on the surface. The particle size and scratches of the fine particles are also measured by measuring the groove width on the order of nanometers and simultaneously measuring the microroughness on the order of submicrons.

【0029】

Fig. 4 (b) shows the integrated voltage peak value data of the scattered light obtained by scanning the sample in the surface state as shown in Fig. 4 (a) in the X direction. Sign p in the figure₁Is a large particle, p₂Is a small particle and S is a scratch. As shown in Fig. 4 (a), in the region where there are no fine particles or scratches on the sample surface, it is detected as the surface roughness due to the unevenness of the nm order, that is, the fluctuation component of the voltage signal according to the scattered light generated according to the microroughness. To. This is a noise component of S / N that affects the detection sensitivity of fine particles and scratches, and is a factor in reducing the detection resolution. That is, the scattered light intensity generated by the microroughness of the surface is proportional to the number of all irregularities existing in the laser spot light. For example, the roughness is 0.7 nm, which is about the same as the scattered light from fine particles with a particle size of about 15 nm, but the scattered light due to this microroughness is an S / N noise component that indicates detection sensitivity when measuring fine particles and scratches. This is an important factor in determining the detection resolution in fine particle and scratch measurement. However, the scattered light component that becomes noise in the measurement of fine particles and scratches can be regarded as due to the microroughness of the sample surface if the true stray light generated by the wraparound of external light can be removed. Can be measured.

【0030】

As shown in FIG. 4 (a), when the sample surface is irradiated with a convergent laser beam and scanned at a constant speed, fine particles as shown in FIG. 4 (b) are formed in the detection circuit of the photomultiplier tube (PMT). It is detected as an integrated voltage waveform according to the scattered light from the scratch. Stray light such as externally penetrating light into the optical system enters the PMT, but since these are taken out as DC voltage components, they can be canceled and the effect on detection sensitivity can be ignored. However, if the surface roughness, that is, the fine unevenness (microroughness) differs depending on the location, when the convergent spot light is scanned, the scattered light intensity from the unevenness in the spot light also fluctuates depending on the position, and the spot light is scanned. It is taken out as a change in light intensity for each interval (shift step). That is, as shown in FIG. 4 (b), it is detected in the form of fluctuation of the detection voltage according to the light intensity according to the change in the microroughness of the surface. As described above, this scattered light intensity is proportional to the number of all irregularities existing in the spot light, and the roughness is 0.7 nm, which is about the same as the scattered light by particles having a particle size of about 15 nm. This is the detection limit of the measurement method. However, as shown in Fig. 4 (b), the wavelength of the detection signal waveform from the particles corresponds to the laser spot diameter (D), so it is 1 compared to the wavelength of the fluctuation signal due to microroughness according to the scanning interval. There is a difference in order. Therefore, if the detection voltage signal wave is passed through a low-pass filter, only the fine particles and the scratch detection signal can be separated as shown in FIG. 5 (a). On the contrary, when it is passed through a high-pass filter circuit, as shown in Fig. 5 (b), the light intensity fluctuation signal due to microroughness can be extracted, and the microroughness of the surface, that is, the average surface roughness can be detected from this. it can.

【0031】

Further, as shown in FIG. 6, in the present invention, the surface information is taken in from the scattered light generated according to the surface state while scanning the laser spot light in the XY2 direction. That is, by synthesizing the detection signal components obtained by scanning in the X direction obtained at regular intervals in the Y direction, surface information on the surface to be measured can be obtained, and fine particles and scratches having a size of nm order can be measured. .. Furthermore, if the signal component by microroughness is extracted by filtering the wavelength component of the obtained detection signal, the average roughness of the sub-nano order can be detected.

【0032】

(Measurement of Fine Particles) Measuring fine particles adhering to the sample surface is described in Japanese Patent No. 2747921 described above, and is the same in the present invention. In measuring fine particles, standard fine particles (polystyrene latex particles: PSL) with known particle sizes were used to calibrate this fine particle measuring machine. That is, the average particle size and standard deviation are calculated by visually measuring the particle size from the PSL observation image obtained by a transmission electron microscope (TEM) in advance, and the surface of the Si wafer to which the same PSL is sprayed is applied. Calibration was performed by measuring with this measuring machine and comparing with the visual value. Calibration was performed using three types of PSL with an average particle size of 88 nm, 43 nm, and 37 nm. When the PSL with an average particle size of 37 nm sprayed on the Si wafer surface is measured with this measuring machine, the average particle size is 36 nm, the error is 2.7%, and the standard deviation is 3.2, which is accurate, and the sprayed PSL can be measured. I was able to confirm that it was there. It has also been confirmed that PSLs with average particle sizes of 43 nm and 88 nm can be measured with the same degree of accuracy.

【0033】

Using this measuring device, we attempted to measure fine particles on the surface of a clean Si wafer with no pattern. The measurement results are shown in FIG. 7 (a) as a particle distribution diagram and in FIG. 7 (b) as a histogram of the measured particle size. As shown in FIG. 7 (a), it was possible to show that particles having a diameter of about 24 to 32 nm, which have not been reported so far, are present in a clean Si wafer having no pattern. It was also shown that there are about 280 particles with an average particle size of about 28 nm in a 500 μm square and about 10 particles in a 100 μm square. However, although this absolute number differs depending on the type of Si wafer, the particle size also shows a normal distribution.

【0034】

(Measurement of Scratch) First, in the present embodiment, it is assumed that the shape of the scratch S formed on the sample surface A is linear as shown in FIG. In the case of a Si wafer, the cause of scratch formation on the surface is scratches during surface polishing such as polishing, which can be regarded as a straight line in the measurement range. Further, in this measuring device, the scattered light is converted into a voltage by the CR integrating circuit, and the unevenness cannot be distinguished. Therefore, the convex defect and the concave defect are approximated to the same scattered light intensity. Therefore, in the present invention, as shown in FIG. 9, the scratch is a virtual fine particle p having a diameter similar to the scratch width._sAre continuously arranged side by side on the sample surface, and the scratch groove is assumed to be a semicircle of approximate virtual fine particles.

【0035】

Therefore, the scratch measurement principle is basically the same as the above-mentioned fine particle measurement principle, and is an application of this. Therefore, the total scattered light intensity I from each virtual fine particle constituting the scratch_sIs represented by the above number 1. In this embodiment, the diameter of the virtual fine particles is d._sTherefore, the particle size parameter α in Equation 1 is πd._sThe same applies to the above except that it becomes / λ. However, since the intensity distribution in the laser spot is Gaussian distribution in Equation 1, the total scattered light intensity at the center of the laser spot (r = 0) is shown.

【0036】

Here, since scratch is defined as a series of virtual fine particles arranged in a straight line, the total scattered light intensity at the center of the laser spot is the magnitude when the groove width of the scratch is assumed to be the particle size. .. Number of single particles continuously present in the laser spot n_sIs D / d_sIf the light intensity ratio in the Gaussian distribution state with respect to the case where the light intensity in the laser spot is constant is t, the total scattered light intensity I actually generated from the scratch is_ssIs the number n of single particles that are continuously present in the laser spot in equation 1._sIt is expressed by multiplying by the light intensity ratio t, and becomes the following number 2.

【0037】

[Number 2]

<img file="JP2002257518A_D0002.tif" />【0038】

Therefore, the groove width of the scratch can be estimated by measuring the scattered light intensity. In this measuring device, the output result is shown as the particle size of a single fine particle, and the total scattered light intensity from the fine particle is converted into the particle size. Therefore, even when the scratch is measured, the result converted from the total scattered light intensity from the scratch into the particle size is output. Therefore, when determining the groove width of the scratch, the groove width of the scratch must be calculated from the total scattered light intensity output as this particle size. Dp the groove width of the scratch output as fine particles_sIf the actual scratch groove width is dp, then dp_sThe relationship between dp and dp is expressed by the following number 3.

【0039】

[Number 3]

<img file="JP2002257518A_D0003.tif" />【0040】

Here, k and a are constants, and k = 0.119 and a = 1.20. That is, the D / d existing within the spot diameter_sParticle size dp obtained from the total scattered light intensity from individual fine particles_sCan be calculated by substituting for equation 3. From this relational expression, dp_sIf the measurement limit of 6 nm for fine particles by this measuring device is selected, the dp will be about 1 nm.

【0041】

Using this measuring device, we attempted to measure scratches, which are concave elongated fine defects on the Si wafer surface. FIG. 11 shows a three-dimensional display of the scratch shape measurement results obtained by measuring the surface of a Si wafer with no pattern formed using this measuring device. The measurement was performed in the 2 × 2 mm region, and it is also shown that there are about 10 scratches with a groove width of 6 to 10 nm.

【0042】

(Measurement of microroughness) FIG. 6 shows a detection voltage signal obtained by two-dimensionally scanning a laser spot light. The signal from the surface region without particles or fine defects can be regarded as due to the unevenness of the surface, that is, the weakly scattered light according to the roughness. Therefore, if this scattered light is the sum of the scattered light generated from the unevenness in the spot light, the desired surface roughness can be considered as the average roughness in the spot. That is, as shown in FIG. 4A, one of the irregularities constituting an arbitrary roughness is considered as a single fine particle, and it is assumed that the convex portion exists uniformly in the entire laser spot, and these irregularities are assumed. It is considered that scattered light is emitted in proportion to the size and number of. Furthermore, if the spot light is scanned, it can be extracted as a detection voltage signal in which the scattered light intensity changes due to the difference in the number of irregularities for each spot according to the surface roughness, and the surface microroughness, that is, the average, can be extracted from this signal component. Roughness can be detected.

【0043】

However, as shown in FIGS. 4 (a) and 4 (b), if the wavelength l of the surface swell is very large with respect to the laser spot diameter D, the height difference h of this swell component is ignored and the laser Only minute height differences within the spot, i.e. average roughness, are detected. That is, the microroughness measurement principle is to measure the surface shape of a very minute region equipped with a high-pass filter that cuts wavelengths equal to or larger than the laser spot diameter and measures the roughness on a sub-nano order.

【0044】

Figure 12 shows a model for determining the scattered light intensity from minute irregularities. As shown in FIG. 12, the height is d in the spot of diameter D._rUnevenness is n_rIt is assumed that they are packed together and exist side by side. These convex parts have a particle size d_rThe scattered light generated from this single particle is regarded as a single particle of I_srThen, the whole grain n that is regarded as the microroughness existing in the spot._rScattered light intensity I generated from individuals_smIs represented by the following number 4.

【0045】

[Number 4]

<img file="JP2002257518A_D0004.tif" />【0046】

However, t_rIs the ratio (scattered light intensity ratio coefficient) when the intensity in the irradiation laser spot light is Gaussian distribution and when it is uniformly distributed, and is represented by the following number.

【0047】

[Number 5]

<img file="JP2002257518A_D0005.tif" />【0048】

Here, the number of single particles considered to be microroughness in the spot n_rIs the laser spot diameter D and its particle size d_rThan n_r= D²/ d_r²Is sought after. Therefore, the scattered light intensity I from the microroughness in the laser spot_smIs expressed as the next number 6 from the numbers 4 and 5.

【0049】

[Number 6]

<img file="JP2002257518A_D0006.tif" />【0050】

So, microroughness d_rTotal scattered light intensity in I_smAnd its particle size in scattered light intensity d_pFigure 13 shows the relationship with. Further, the microroughness is a value from peak to peak as shown in FIGS. 14 (a) and 14 (b), but the diameter of the fine particles is measured from the measured value from the center (reference line). Note that FIG. 14 (b) shows the detection signal after the smoothing process. Therefore, the measurable particle size for a sample of arbitrary microroughness is similar to the relationship in which the scale on the vertical axis is halved in FIG. Therefore, if the measurement limit of fine particles is 6 nm, the measurement limit of microroughness is about 0.1 nm.

【0051】

Next, the surfaces of Si wafers having different roughness were measured with this measuring device and a fringe scanning interference microscope (Zygo) to demonstrate the roughness measuring method by this measuring device. The results of the roughness measurement are shown in FIGS. 15 and 16. As shown in the figure, although there is a difference in the absolute value of the roughness, it can be shown that the surface roughness value by this measuring device correlates with the roughness value of the scanning white interferometer. We were able to demonstrate the effectiveness of the roughness measurement method using this measuring device.

【0052】

In addition, four Si wafers different from the above-mentioned Si wafers were measured with this measuring device and a scanning white interferometer, and a three-dimensional display of the surface state was attempted. The results measured by the scanning white interferometer are shown in FIGS. 17 (a) to 17 (d), and the results measured by this fine particle measuring machine are shown in FIGS. 18 (a) to 18 (d). In the present invention, the swell component having a wavelength sufficiently longer than the laser spot diameter is ignored, so that there is a clear difference between the results of FIGS. 17 and 18 due to the swell component, but in other microroughness. A sufficient correlation was found between the two.

【0053】

Finally, the procedure of data processing of the surface composite evaluation system by the light scattering method according to the present invention will be described with reference to FIG. First, the detection voltage signal obtained by scanning in the X direction is passed through a filter circuit to perform sorting by wavelength. The long wavelength component contains information on fine particles and scratches, and for each Y-direction scan, check whether the maximum peak value of the waveform corresponding to the particles is continuous above the laser spot diameter, and if it is discontinuous, the sample. It is estimated that it is a single fine particle attached to the surface, and the particle size of the fine particle is calculated from the peak value data. If it is continuous, it is presumed that it is a scratch formed on the sample surface, and the distance in the Y direction where the maximum value of the peak value data is continuous is calculated from the length of the scratch in the Y direction and the groove width of the scratch from the peak value. .. On the other hand, the microroughness is calculated from the short wavelength component extracted from the detected voltage signal. In addition, the position information on the sample surface is associated with each measurement result of the particle size, scratch length and groove width, and microroughness of the obtained fine particles, and the distribution is two-dimensional or three-dimensional. The measurement results can be displayed as shown in FIGS. 7 (a), 11 and 18.

【0054】

Further, in the present invention, the laser spot diameter is 5 μm and the scanning interval is 1 μm, which is a micron order that is very large compared to the particle size of fine particles, the groove width of scratches, and the order of microroughness. A maximum detection sensitivity of 6 nm in diameter, 1 nm in scratch groove width, and 0.1 nm in microroughness value can be achieved. Moreover, since they can be calculated simultaneously from one measured data, a complex evaluation of the sample surface can be performed.

【0055】

Further, although not described in detail in the present embodiment, the laser beam irradiated to the sample surface penetrates a predetermined depth from the sample surface according to the wavelength, so that the measurement result obtained in the present invention is the penetration depth. It is considered that the information of is integrated. Therefore, it is expected that information corresponding to the depth from the sample surface can be obtained by irradiating laser light of different wavelengths, and if they are comprehensively judged, more useful surface states can be observed. there is a possibility.

【0056】

[Effect of the invention]

According to the above-mentioned composite evaluation system for the surface by the light scattering method according to the present invention, the particle size and scratches of a single fine particle on an ultra-precision machined surface such as a Si wafer can be measured on the order of nanometers (nm), and micro. Roughness can be measured on the order of sub-nanometers, and they can be measured in the atmosphere at the same time, so the state of the sample surface can be evaluated in a complex manner. The detection sensitivity of a single particle is currently capable of detecting up to 19 nm, but in principle it is possible to detect up to 6 nm, the scratch groove width detection sensitivity is 1 nm, and the microroughness detection sensitivity is 0.1 nm. ..

【0057】

The present invention is a new measurement method in which Rayleigh scattered light from fine particles is detected while scanning by irradiating the surface of a sample with a focused laser beam, and the particle size is measured on the order of nanometers. That is, it is a new measurement method that detects extremely weak scattered light from fine particles as an integrated value of photoelectron pulses. As a result of theoretically demonstrating that it is possible to detect a particle size of 10 nm or less, which was impossible, and further measuring on a clean Si wafer with no pattern formed, a signal corresponding to a particle size of 19 nm was detected. ing. This means that the detection sensitivity is higher by one order or more compared to the measuring instrument using the conventional light scattering method.

【0058】

Further, by measuring the particle size of the Si wafer to which the standard fine particles (polystyrene latex particles: PSL) having a known particle size are attached by the measuring device according to the present invention and calibrating the particle size, the particle size is 100 nm or less. It has been confirmed that the characteristics with good linearity are obtained and the diameter of the standard fine particles is detected with relatively high accuracy by the measuring device according to the present invention, and its usefulness is also demonstrated. By comparing the measurement result of the microroughness by the measuring device according to the present invention with the measurement result by the fringe scanning interference microscope (Zygo), a correlation was observed between the two, and the measurement of the microroughness of the present invention was also relatively accurate. Was confirmed to be high, and its usefulness was also demonstrated.

【0059】

Further, as a result of attempting to measure fine particles on a clean Si wafer having no pattern formed by using the measuring device according to the present invention, fine particles having a diameter corresponding to about 24 to 32 nm, which has never been observed before, are detected. It was possible to show the state of fine particle adhesion distribution on the surface.

【0060】

Further, using the measuring device according to the present invention, an attempt was made to detect fine defects on the surface of the Si wafer, and scratches having a width of 10 nm or less and microroughness of about 0.5 nm could be detected. That is, it was possible to demonstrate that it is possible to simultaneously perform three types of measurements including not only fine particle measurement on the nanometer order but also elongated fine defects such as scratches and surface roughness on the sub-nanometer order.

[Simple explanation of drawings]

[Figure 1]

It is the schematic of the measuring apparatus which concerns on the composite evaluation system of the surface by the light scattering method of this invention.

[Figure 2]

It is explanatory drawing which shows the observation state at the time of irradiating the fine particle on the sample surface with a laser beam.

[Fig. 3]

It is explanatory drawing which shows the relationship between the shot noise by the irregular emission of the photoelectron from the PMT photoelectric surface, and the peak value of the detection voltage.

[Fig. 4]

(a) is a simplified cross-sectional view showing the state of the sample surface, and (b) is a graph showing the integrated voltage crest value data obtained by measuring the scattered light from the cross section.

[Fig. 5]

(a) shows a detection signal obtained by extracting a long wavelength component from the data of FIG. 4 (b), and (b) shows a detection signal obtained by extracting a short wavelength component from the data of FIG. 4 (b).

[Fig. 6]

It is explanatory drawing which shows the integrated voltage peak value data obtained by scanning the sample surface in X direction and Y direction.

[Fig. 7]

The results of measuring the fine particles adhering to the surface of the Si wafer are shown, (a) shows the distribution map of the detected fine particles, and (b) shows the histogram of the detected fine particles.

[Fig. 8]

It is a simplified perspective view which shows the shape of the scratch defined in this invention.

[Fig. 9]

It is a simplified perspective view which shows the measurement model of a scratch in this invention.

[Fig. 10]

It is explanatory drawing which shows the relationship between the virtual fine particle arranged in a straight line, and a laser spot.

[Fig. 11]

A three-dimensional display of the scratch shape measurement results on the Si wafer surface is shown.

[Fig. 12]

It is a simplified sectional view which shows the measurement model of the microroughness of this invention.

[Fig. 13]

It is a graph which shows the relationship between the surface roughness and the particle size of virtual fine particles in the measurement of microroughness.

[Fig. 14]

It is explanatory drawing which shows the difference in the measurement of microroughness and fine particle, (a) shows the detection signal, and (b) shows the detection signal after smoothing processing.

[Fig. 15]

It is a graph which shows the result of having measured the microroughness of the Si wafer surface by the measuring apparatus which concerns on this invention, and Zygo.

[Fig. 16]

It is a graph which shows the result of having measured the microroughness of the Si wafer surface different from the Si wafer of FIG. 15 by the measuring apparatus which concerns on this invention, and Zygo.

[Fig. 17]

This is a three-dimensional graph showing the results of measuring the microroughness of four Si wafers A, B, C, and D with Zygo.

[Fig. 18]

It is a graph which three-dimensionally displayed the result of having measured the microroughness of the Si wafers A, B, C, and D which are the same as FIG.

[Fig. 19]

It is a flowchart which showed the procedure of data processing in this invention.

[Explanation of symbols]

1 laser 2 Convergent optics 3 Drive control system 4 Condensing optical system 5 Light detection system 6 Arithmetic processing system 7 elliptical mirror 8 Parabolic mirror 9 Photomultiplier tube 10 Signal control unit 11 Motor control unit 12 CCD camera microscope 13 CCD camera control unit A Sample surface P, P₁, P₂ Fine particles p_s Virtual fine particles S scratch