JPH0261511A - Apparatus for measuring cyclic surface structure - Google Patents

Abstract

PURPOSE:To measure the shape distribution of a surface structure having cyclicity within a short time with high accuracy by providing a plurality of photodiode arrays and a cycle calculation means. CONSTITUTION:A photodiode 9 calculates the angle of diffracted beam to the surface of a sample 8 based on what number is a photodiode detecting diffracted beam. A photodiode array 11 calculates the angle of reflected beam to the surface of the sample 8 based on which number is a photodiode detecting reflected beam. A data processing unit 16 inputs the photocurrents outputted from the arrays 9, 11 through a relay 15 to respectively integrate the same and respectively sets these integrated quantities to diffraction intensity and reflection intensity to further convert them to digital data to output the same to a personal computer 19. A cycle calculation means is constituted of the relay 15, the unit 16, the computer 19 and a control program for operating the computer 19 to calculate the cycle of a surface structure on the basis of the output signals of the arrays 9, 11.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an apparatus for automatically and non-destructively measuring the distribution state of a surface structure having periodicity that causes diffraction.
More specifically, the present invention relates to a device that can nondestructively measure the distribution state of the shape of a diffraction grating in the manufacturing process of a distributed feedback semiconductor laser in which the diffraction grating formed on the substrate significantly affects its oscillation characteristics. be.

(Prior art) Conventionally, the period A of a surface structure with periodicity (hereinafter referred to as a periodic surface structure) using diffraction of light is measured by returning the diffracted light or reflected light to the direction of the incident light and separating the diffracted light and the reflected light. The difference in angles of light δθ is determined using Bragg's equation: 2 A −5in(δθ) mmλ, (m−±1.±2. . . . ) (1). Here, λ is fllll+constant wavelength.

On the other hand, the depth of a periodic surface structure can be estimated using the diffraction intensity of light, but an example of determining the in-plane distribution of the diffraction intensity is a report by Fujitsu Laboratories (Detection et al., Institute of Electronics and Communication Engineers, 1986). There is a comprehensive national competition No. 931). In addition, a technique for observing the diffraction efficiency of a diffraction grating as well as reflected light and scattered light from a substrate has been reported by KDD Laboratories (Akiba et al., 1985 Society of Applied Physics General Meeting No. ip-2).

(Problem to be Solved by the Invention) However, in the conventional method of measuring the period of a periodic surface structure using diffraction of light, in order to find the angle of the diffracted light or reflected light, the reflected light or diffracted light is incident. Although it is necessary to accurately return the beam to the optical direction, this is impossible in principle and always causes an error corresponding to the n1 constant beam diameter. The error is converted into a period and becomes a number of angstroms. In a distributed feedback semiconductor laser in which the oscillation wavelength is determined by the period of the diffraction grating, this error cannot be ignored in terms of design. Furthermore, it is difficult to automatically measure the period using conventional methods. Therefore, no device has been reported to date that automatically measures the period distribution state of a diffraction grating.

In addition, with the technology reported by Fujitsu Laboratories mentioned above, aP
It takes a relatively long time for each measurement point to obtain the maximum value of the diffraction intensity by rotating the sample around the measurement point while constantly monitoring the position of the fixed point using visible light. Furthermore, this technique can only provide knowledge regarding diffraction intensity.

In addition, the technology reported by the KDD Research Institute mentioned above is
Since the diffraction patterns are only visually captured, the spatial resolution is significantly inferior.

In view of the above-mentioned problems, an object of the present invention is to provide a periodic surface structure measuring device that can measure the shape distribution of a periodic surface structure such as a diffraction grating fabricated on a substrate in a short time and with high precision. It is about providing.

(Means for Solving the Problem) In order to achieve the above object, the present invention has the following features in claim 1:
A laser beam is irradiated onto the surface of the object to be measured which has a periodic surface structure, and the angle of each of the diffracted light and reflected light from the surface of the object is determined by
In a measuring device for measuring a periodic surface structure for determining the shape of a surface structure of a fixed object, a plurality of light receivers each independently and simultaneously receive diffracted light and reflected light corresponding to the period of the surface structure of the object to be measured. An element array is provided, and period calculation means is provided for calculating the period of the surface structure based on the output signals of the plurality of light receiving element arrays.

Further, in claim 2, the surface of the object to be measured having a periodic surface structure is irradiated with a laser beam, and the angles of the diffracted light and reflected light from the surface of the object to be measured with respect to the surface of the object to be measured, respectively. In the periodic surface structure n1 constant device for determining the shape of the surface structure of the object to be measured, a plurality of devices each independently and simultaneously receive diffracted light and reflected light corresponding to the period of the surface structure of the a11 constant object. a light-receiving element array, and a period calculation means for calculating the period of the surface structure based on the output signals of the plurality of light-receiving element arrays, and two light-receiving element arrays that receive scattered light from the surface of the object to be measured. The light receiving element described above and a scattered light intensity calculation means for calculating the intensity of the scattered light based on the respective output signals of the two or more light receiving elements are provided.

(Function) According to claim 1 of the present invention, each of the diffracted light and the reflected light corresponding to the period of the surface structure of the object to be measured is independently and simultaneously received by the plurality of light receiving element arrays, and the period is calculated. The means calculates the period of the surface structure based on the output signals of the plurality of light receiving element arrays.

Further, according to claim 2, each of the diffracted light and the reflected light corresponding to the period of the surface structure of the 11 constant object is independently and simultaneously received by the plurality of light receiving element arrays, and the period calculation means calculates the The period of the surface structure is calculated based on the output signals of the plurality of light receiving element arrays. Furthermore, 2
Scattered light from the surface of the object to be measured is received by the plurality of light receiving elements, and the scattered light intensity calculating means calculates the amount of light scattered from the surface of the object to be measured.
The intensity of the scattered light is calculated based on the output signals of each of the plurality of light receiving elements.

(Example) As an example of the present invention, a substrate having a diffraction grating on the surface was used as a sample, and the period and depth of the diffraction grating (
A measuring device was constructed to measure the distribution of photoluminescence based on the diffraction intensity), the intensity of reflected light and scattered light, and the light absorption of the substrate.

FIG. 1 is an optical system layout diagram in one embodiment of the present invention, and FIG.
The figure is a ``1 constant processing system diagram'' in one embodiment of the present invention.
The figure is a control program chart in one embodiment of the present invention.

In FIG. 1, reference numeral 1 denotes an 11 constant light source, for example, a He-Cd laser device that emits a laser beam with a wavelength λ of 383.8 nm. A laser beam emitted from a measurement light source 1 is divided by a half mirror 2, and a portion reaches a photodiode 3, where it is monitored as a laser output 1ex. The remaining laser beam separated by the half mirror 2 passes through the mirror 4, slit 5, and lens 6, and then enters the sample 8, which is the object to be measured, placed on the X-Y-θ stage 7. The beam is irradiated at an angle α. Sample 8 is a 15 mm x 12 mm InP substrate with a diffraction grating formed on its surface by interference exposure method. A photodiode array 9 is arranged at a position where it can receive diffracted light from the surface of the sample 8 via a cylindrical lens 10. Further, depending on which photodiode in the photodiode array 9 receives the diffracted light, the angle of the diffracted light with respect to the surface of the sample 8, that is, the diffraction angle β can be calculated. A photodiode array 11 is arranged at a position where it can receive reflected light from the surface of the sample 8 via a cylindrical lens 12. Furthermore, depending on which photodiode in the photodiode array 11 receives the reflected light, the angle of the reflected light with respect to the surface of the sample 8, that is, the reflection angle α can be calculated.

The cylindrical lenses 10.12 are also called cylindrical lenses, and are lenses that condense incident light onto a straight line.

13. 13- is a photodiode that receives scattered light from the surface of the sample 8 and measures the scattering intensity 1 sca, and can be set at any angle with respect to the surface of the sample 8. Reference numeral 14 denotes a light receiving element made of lead sulfide (hereinafter referred to as PbS), which is arranged so that the photoluminescence light intensity 1 pL based on the light absorption of the sample 8 can be determined.

In FIG. 2, reference numeral 15 denotes a relay, which inputs the output signals of the photodiode arrays 9 and 11, and receives the output signals of the photodiode arrays 9 and 11 from the personal computer 19.
．． 11 output signals are switched and outputted to the data processing unit 16. The data processing unit 16 inputs the photocurrent outputted from the photodiode array 9゜11 via the relay 15, refines each of them, sets these integral amounts as a diffraction intensity 1 dir, a reflection intensity ef, and further Convert to digital data and use personal computer 19
Output to.

17 is a multi-channel digital multimeter for 10 channels (hereinafter simply referred to as a multimeter), which converts the outputs of the photodiodes 3, 13. Output to. Further, the lock-in amplifier 18 is a personal computer, 1
The operation of the lock-in amplifier 18 is controlled by a personal computer 19.

A stage controller 20 is connected to the personal computer 19 and the X-Y-θ stage 7, and controls the position and angle of the X-Y-θ stage based on commands from the personal computer 19.

Reference numeral 21 denotes an output system consisting of a display unit and a hard copy printer, which displays and prints data etc. calculated by the personal computer 19.

The period calculating means is constituted by a relay 15, a data processing unit 16, a personal computer 19, and a control program for operating the personal computer 19. Further, the scattered light intensity calculation means is constituted by a multimeter 17, a personal computer 19, and a control program for operating the personal computer 19.

Next, the operation of this embodiment will be explained based on the control program flowchart shown in FIG.

Before starting the measurement, the personal computer 19
data processing unit 16, stage controller 20,
The output system 21 and the like are initialized (SL), and the operator waits until measurement conditions are input and an instruction to start measurement is input (S2) (S3). The operator inputs the name of the sample 8, the size of the sample 8, the measurement interval of the sample 8 in the X direction and the Y direction, etc. into the personal computer 19 as the measurement conditions, and then inputs a measurement start command.

After receiving the measurement start command, the personal computer 19 moves the X-Y-θ stage 7 according to the size of the sample 8 and the measurement interval (S4), and performs the measurement (S5).
. In addition, at this time, the X-Y-θ stage 7 is configured to move the photodiode array 11 based on the following Bragg conditions.
is moved so that reflected light can be detected.

A−nλ/ (5Ina +sinβ) −(
2) In equation (2), α and β are the reflection angle and the diffraction angle, respectively, and λ is the wavelength of the 7illj constant light source 1. Depending on the value of n, the diffraction condition becomes n-th order.

Next, the personal computer 19 inputs data such as a diffraction intensity 1dir, a reflection intensity 1rer, a diffraction angle β, and a reflection angle α from the data processing unit 16, and further inputs the laser output Iex s scattering intensity 1sca and the photoluminescence intensity from the multimeter 17. A sense light intensity of 1 pL is input, and the period of the diffraction grating for each measurement point is calculated using the Bragg condition (S6).

In addition, each of the diffraction intensity 1dif', reflection intensity 1ref', scattering intensity 1sca, and photoluminescence light intensity 1pL has temporal fluctuations, so in order to eliminate these fluctuations, divide by the laser output 1ex, and distribute the It is treated as value data. That is, 1dif/lex is the value of diffraction intensity, Irer/Iex is the value of reflection intensity, l5ca/Ie
x is the value of scattering intensity, and IpL/lex is the value of photoluminescence light intensity. Furthermore, when creating the distribution map, each value is standardized.

Next, determine whether the final measurement point has been reached (S7)
, if the final measurement point has not been reached, the process moves to S4, moves the X-Y-θ stage, and then moves to S5. Execute the process of S8.

As a result of the determination in S7, if the final measurement point has been reached, a plurality of data inputted from the data processing unit 16 and the multimeter 17, values calculated from these data, etc. are stored in the memory provided in the personal computer 19. At the same time (S8), data is output to the output system 21 (S9
). Next, it is determined whether the measurement is completed (S10).

The end of the measurement is determined when the operator inputs a measurement end command, and when the measurement continuation command is input, the process shifts to Sl and the measurement can be continued.

In this example, the value for the period of sample 8 could be accurately determined in units of 1 angstrom. Furthermore, it takes less than 1 second to calculate the value of period A, and compared to the conventional method of calculating the angular difference between the diffracted light and the reflected light using a goniometer, this method significantly improves both accuracy and time. did it.

As an example of measurements performed in this example, FIG. 4 shows a periodic distribution diagram of a diffraction grating, and FIG. 5 shows a diffraction intensity distribution diagram. The measured sample was the InP substrate and plate of sample 8, and the measurement light source 1 was a II e-Cd laser (λ-363
．． 8nrA) was used. In FIG. 4, the period distribution is expressed every 2 angstroms, and period distributions of 2398 angstroms, 2400 angstroms, and 2402 angstroms are shown. Further, in FIG. 5, the diffraction intensity is expressed in 10 levels of shading.

Figure 6 shows the actual results obtained using a scanning electron microscope. The relationship between the depth of the diffraction grating of ipJ sample 8 and the diffraction intensity measured in this example is shown. In the figure, the horizontal axis represents the depth of the diffraction grating, and the vertical axis represents the diffraction intensity.

Furthermore, since the measured value includes an error in the n1 constant, the error is shown in error par in the figure.

As a result, it can be seen that the diffraction intensity has a linear relationship with the depth of the diffraction grating. Although the measurement limit of a scanning electron microscope is several tens of n111, the diffraction intensity measured by this measuring device is based on the element characteristics predicted in this example, that is, the linear relationship between the diffraction intensity and the depth of the diffraction grating. In this measurement device, the depth of the diffraction grating can be reduced to several n+m.
It is possible to set up to n1.

In this embodiment, H is used as the il'P1 constant light source 1.
Although an e-Cd laser (λ-383, 8na+) was used,
Highly accurate measurement data can be obtained by selecting and using lasers with various wavelengths λ depending on the period A of the sample 8.

In addition, in this embodiment, only two photodiodes are provided for receiving scattered light, but by providing a large number of photodiodes, it is possible to obtain scattered light intensities in multiple directions at the same time. Detailed shape analysis can be performed.

Further, by using the measuring device of the present invention, it becomes possible to quickly measure the distribution in the substrate plane regarding the period, depth, and shape of the periodic surface structure. Conventionally, the periodic distribution of a diffraction grating has only been optically measured at several points within the plane of a substrate, but this device measures the in-plane periodic distribution with spatial resolution down to the spot size of the incident light (approximately 50 μm). can. This is not possible with conventional technology and is positioned as a new technology.

(Effects of the Invention) As explained above, according to claim 1 of the present invention, the surface of the object to be measured having a periodic surface structure is irradiated with a laser beam, and the diffracted light from the surface of the 8111 object is emitted. al of the periodic surface structure to determine the shape of the surface structure of the object to be measured from the angle of each of the reflected light and the surface of the object to be measured.
In the LJ determination apparatus, a plurality of light receiving element arrays are provided which independently and simultaneously receive diffracted light and reflected light corresponding to the period of the surface structure of the object to be measured, and the method is based on the output signals of the plurality of light receiving element arrays. Since the period calculation means for calculating the period of the surface structure is provided, the optical comprehensive #111 determination of the periodic surface structure can be performed in a short time and non-destructively, thereby reducing the yield rate of the device manufacturing process. This method has advantages such as a remarkable improvement in performance and the ability to predict device characteristics. Furthermore, as long as it has a periodic structure that causes diffraction, it is possible to accurately observe the distribution state of the period of any r (1 constant object). Depth measurements can be made down to the atomic order, and further improvements can be expected to develop into a new type of microscope.

According to claim 2, the surface of the object to be measured having a periodic surface structure is irradiated with a laser beam, and each of the diffracted light and the reflected light from the surface of the object to be measured is reflected from the surface of the object to be measured. A periodic surface structure measuring device that determines the shape of the surface structure of the JIIJ constant object from an angle to the surface of the object, which independently and simultaneously receives diffracted light and reflected light corresponding to the period of the surface structure of the object. A plurality of light receiving element arrays are provided, and period calculation means is provided for calculating a period of the surface structure based on output signals of the plurality of light receiving element arrays, and the second method receives scattered light from the surface of the measurement target. The present invention includes two or more light receiving elements and a scattered light intensity calculation means for calculating the intensity of the scattered light based on the respective output signals of the two or more light receiving elements. Since the intensity of the scattered light can be obtained at the same time, the surface structure of the 71111 object can be analyzed and observed in more detail.

[Brief explanation of the drawing]

FIG. 1 is an optical system layout diagram in one embodiment of the present invention, and FIG.
The figure shows a measurement processing system diagram in one embodiment of the present invention, FIG. 3 shows a control program flowchart in one embodiment of the present invention, and FIG. 4 shows an example of measurement of periodic distribution of a diffraction grating in one embodiment of the present invention. FIG. 5 is a diagram showing an example of measurement of the diffraction intensity distribution according to an embodiment of the present invention, and FIG. 6 is a diagram showing the relationship between the diffraction intensity and the depth of the diffraction grating. 1...Measurement light source, 2...Half mirror 3, 13゜1
3″...Photodiode, 4...Mirror 5...
・Slit, 6... Lens, 7... X-Y-〇 stage, 8... Sample, 9, 11... Photodiode array, 10.12... Cylindrical lens, 14
...pbs. 15... Relay 16... Data processing unit, 1
7...Multi-channel digital multimeter, 1
8... Lock, in-amp, 19... Personal computer, 20... Stage controller, 21...
...Output system. Patent Applicant Nippon Telegraph and Telephone Corporation Agent Patent Attorney Yoshi 1) Takashi Sei Figure 3 Figure 4 Time J'l Goko's 1:! (nm)

Claims (2)

[Claims] (1) A laser beam is irradiated onto the surface of a measurement object having a periodic surface structure, and the angles of the diffracted light and reflected light from the surface of the measurement object with respect to the surface of the measurement object are determined. In a periodic surface structure measuring device for determining the shape of a surface structure of an object, a plurality of light receiving element arrays are provided that independently and simultaneously receive diffracted light and reflected light corresponding to the period of the surface structure of the object to be measured. A measuring device for a periodic surface structure, comprising a period calculation means for calculating a period of the surface structure based on the output signals of the plurality of light-receiving element arrays. (2) Two or more light-receiving elements that receive scattered light from the surface of the measurement target, and a scattered light intensity that calculates the intensity of the scattered light based on the output signals of each of the two or more light-receiving elements. 2. The periodic surface structure measuring device according to claim 1, further comprising calculation means.