TWI774300B - An apparatus and a method for measuring rimmed roughness of a wafer - Google Patents

Abstract

An apparatus and a method for measuring rimmed roughness of a wafer are provided. The method comprises irradiating light at a rim of the wafer to generate scattering, scattered light being reflected and condensing on a photoelectric sensor; collecting scattered light signals at the rim of the wafer by the photoelectric sensor; applying Fourier Transformation to the scattered light signals to obtain rimmed roughness of the wafer. The method of the present invention is easy and convenient without additional operation to cut a sample, harmless to yield, and capable to measure the rimmed roughness of a whole rim of the wafer.

Description

Method and device for measuring edge roughness of wafer

The invention belongs to the technical field of integrated circuit manufacturing, and in particular relates to a method and device for measuring the edge roughness of a wafer.

Before the circuit is fabricated on the wafer, it is necessary to know whether the wafer is flat so that the subsequent layout can be confirmed. After the wafer is fabricated, the roughness data needs to be monitored to ensure the quality of the subsequent process. To detect the surface roughness of wafers, AFM (Atomic Force Microscope, atomic force microscope) is the most commonly used measurement, and usually each atomic force microscope samples 1 wafer per day. During measurement, a small sample is cut out from the wafer, usually only one location is sampled, and the size of the small sample must be less than 2cm×2cm, and the analysis range area of 100μm×100μm is measured under AFM, and a single measurement can only test the crystal. The roughness of the edge surface (upper slope) of the upper half of the circle. During AFM inspection, the wafer needs to be destroyed for analysis, which also makes it impossible to perform other experimental analysis on the sampled wafer. Conventional AFM measurements suffer from inefficiencies in manual operation, destructiveness, impact on yield, and detection of smaller areas that do not represent the edge of the entire wafer.

Therefore, there is an urgent need for a suitable method for measuring the edge roughness of a wafer.

The purpose of the present invention is to provide a method for measuring the edge roughness of a wafer, which is simple, fast, non-destructive, and capable of testing the edge roughness of the entire circumference of the wafer.

The present invention provides a method for measuring the edge roughness of a wafer, which includes: irradiating a light beam to the edge of the wafer to scatter, and the scattered light is reflected by mirrors arranged on the upper and lower sides of the wafer and then collected at the edge of the wafer. on the photoelectric sensor; the photoelectric sensor collects the scattered light signal of the edge of the wafer; and performs Fourier transform on the scattered light signal to obtain the edge roughness of the wafer.

Further, the edge roughness of the wafer is characterized by power spectral density.

Further, the photoelectric sensor includes: a photodiode or a charge coupled element.

Further, the light beam includes a first light beam irradiated from the peripheral side of the wafer to the edge of the wafer.

Further, the light beam further includes a second light beam irradiated to the edge of the wafer from above the wafer, and/or a third light beam irradiated from the bottom of the wafer to the edge of the wafer .

Further, the wavelength range of the light beam is: 1 nm to 100 nm.

The present invention also provides a device for measuring the edge roughness of a wafer, comprising: a radiation source, which is arranged at least on the peripheral side of the wafer; and a reflector, which is arranged on the upper and lower sides of the wafer ; Photoelectric sensor, the photoelectric sensor is arranged on the side of the edge of the wafer away from the center of the wafer; wherein, the beam emitted by the radiation source irradiates the edge of the wafer and scatters , the scattered light is concentrated on the photoelectric sensor after being reflected by the mirror.

Further, the mirrors disposed on the upper and lower sides of the wafer form a semi-ellipse or a semi-circle.

Further, the radiation source is arranged between the edge of the wafer and the photoelectric sensor.

Further, it also includes: a rotating unit, the rotating unit is used to drive the wafer to rotate.

Compared with the prior art, the present invention has the following beneficial effects: the present invention provides a method and device for measuring the edge roughness of a wafer, the measuring method includes: irradiating a light beam to the edge of the wafer to scatter, and the scattered The light is collected on the photoelectric sensor after being reflected by the mirrors arranged on the upper and lower sides of the wafer; the photoelectric sensor collects the scattered light signal from the edge of the wafer; A Fourier transform is performed to obtain the edge roughness of the wafer. The measuring method of the present invention is simple and fast, does not require additional operations for cutting samples, has no destructiveness and does not affect the yield, and can test the edge roughness of the entire circumference of the wafer.

B: Laser Box

B1: First beam

B2: Second beam

B3: Third beam

10: Wafer

A: The edge of the wafer

20: Reflector

30: Photoelectric sensor

S1, S2, S3: Steps

FIG. 1 is a schematic flowchart of a method for measuring edge roughness of a wafer according to an embodiment of the present invention.

FIG. 2 is a schematic diagram of an apparatus for measuring edge roughness of a wafer according to an embodiment of the present invention.

3A is a schematic diagram of an edge test position of a wafer according to an embodiment of the present invention.

FIG. 3B is a schematic diagram of scattered light signals of different edge roughness tests of wafers according to an embodiment of the present invention.

FIG. 4 is a schematic diagram of a PSD and frequency curve of an edge test of a wafer according to an embodiment of the present invention.

FIG. 5 is a schematic diagram of a straight line fitting between PSD and AFM Rq according to an embodiment of the present invention.

FIG. 6 is a schematic diagram of PSD corresponding to different polishing degrees according to an embodiment of the present invention.

Based on the above research, embodiments of the present invention provide a method and device for measuring edge roughness of a wafer. The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in a very simplified form and use inaccurate scales, and are only used to facilitate and clearly assist the purpose of explaining the embodiments of the present invention.

An embodiment of the present invention provides a method for measuring the edge roughness of a wafer. As shown in FIG. 1 , the method includes: irradiating a light beam to the edge of the wafer to scatter, and the scattered light is arranged on the upper and lower sides of the wafer. The mirrors on both sides are reflected and collected on the photoelectric sensor; the photoelectric sensor collects the scattered light signal at the edge of the wafer; Fourier transform is performed on the scattered light signal to obtain the edge roughness.

As shown in FIG. 2 , the wafer 10 can be fixed on the rotation unit by the electrostatic chuck, and the rotation unit drives the wafer 10 to rotate when the edge A of the wafer is collected. A radiation source, such as a laser source, is arranged on the side of the edge A of the wafer away from the center of the wafer. The radiation source emits a first beam B1 , and the mirrors 20 are distributed on the upper and lower sides of the wafer 10 , for example, the upper and lower mirrors 20 are symmetrical with respect to the plane of the wafer 10 . The upper and lower reflecting mirrors 20 may form a semi-elliptical shape or a semi-circular shape, for example. The photoelectric sensors 30 are distributed on the edge A of the wafer away from the center of the wafer. Exemplarily, the radiation source (not shown) that emits the first light beam B1 is distributed on the edge A of the wafer and the photoelectric sensors 30 between. Further, a radiation source may be arranged above and/or below the edge A of the wafer to emit the second beam B2 and/or the third beam B3. The photodetector 30 is, for example, a photodiode or a CCD (Charge Coupled Device). As the beam from the radiation source scans the edge A of the wafer, the photodetector 30 collects the scattered light from the edge A of the wafer.

The wavelength of the light beam is in the range of: 1 nm to 100 nm; alternatively in the range of 5 nm to 50 nm; or alternatively in the range of 10 nm to 20 nm.

As shown in FIG. 2, FIG. 3A and FIG. 3B, the arc length CD obtained by rotating 60° to 120° counterclockwise is based on the radius of the center O of the wafer 10 and the positioning hole (Notch) V of the wafer as the wafer. An example of the measured edge range of . In FIG. 3B , the abscissa is the distribution of the rotation angle from 60° to 120°, the ordinate is the collected scattered light signal of the wafer edge corresponding to the rotation angle, and the unit of the ordinate is mA. Figure 3B shows two curves of 0.25POR and 0.5POR, Production of record (POR), xPOR represents the degree of polishing, the smaller the coefficient x, the smaller the degree of polishing, and the rougher the edge of the corresponding wafer; the coefficient x The larger the value, the greater the degree of polishing, and the less rough (smooth) the edge of the corresponding wafer is. Exemplarily, 0.25 POR is 0.25 times the normal polishing time, and 0.5 POR is 0.5 times the normal polishing time. The edges of the wafers were polished to varying degrees and the edge roughness of the wafers was tested. In Fig. 3B, the curve of 0.25POR is rougher than the curve of 0.5POR, and the scattered light signal measured by the corresponding ordinate is also larger.

Power Spectra Density (PSD) versus frequency is shown in FIG. 4 . Specifically, the edge roughness of the wafer can be characterized by power spectral density (PSD). The contour of the edge surface of the wafer is inspected by laser during edge defect inspection, the power spectral density (PSD) is calculated from the contour of the edge surface, and the edge roughness is characterized using the PSD. Determining the edge roughness parameter includes determining a power spectral density of the edge roughness parameter based on the distribution of the scattered signals. Power Spectral Density (PSD) describes how the power of a continuous signal is distributed across frequency. In Figure 4, the abscissa represents the frequency, and the unit is: 1/rad. The ordinate is the power spectral density (PSD). The curve of 0.25POR is rougher than the curve of 0.5POR, and the corresponding power spectral density (PSD) measured on the ordinate is also larger.

The measurement method of the edge roughness of the wafer in this embodiment adopts power spectral density (PSD) to characterize the roughness, and the measurement method of atomic force microscope (Atomic Force Microscope, AFM) adopts AFM Rq (root mean square roughness) to characterize the roughness. Atomic Force Microscopy (AFM), the main principle is to use the atomic force between the needle tip and the test piece to cause the cantilever beam to produce fine displacement to measure the surface roughness (topography) of the sample. As shown in Figure 5, the power spectral density (PSD) and AFM Rq (root mean square roughness) are fitted to obtain a fitted straight line. The experimental data show that the power spectral density (PSD) and AFM Rq (root mean square roughness) are consistent and well correlated.

Power spectral density (PSD) can capture different wafer edge roughness. Test wafers with different roughnesses. As shown in FIG. 6 , the POR (Production of record, production record) polishes the edge of the wafer to different degrees and conducts the edge roughness test of the wafer. The abscissa in the figure represents the degree of polishing, xPOR, the smaller the coefficient x, the smaller the degree of polishing, and the rougher the edge of the corresponding wafer; the larger the coefficient x, the greater the degree of polishing, the less rough the edge of the corresponding wafer (smooth). In Figure 6, 0.25POR, 0.5POR, 0.75POR, 1POR and 1.5POR, the polishing degree gradually increases, and the corresponding edge roughness of the polished wafer gradually decreases. Compared with smooth surfaces, rough surfaces will have a stronger scattered light signal; correspondingly, the greater the roughness, the greater the power spectral density (PSD) value. The same batch of wafers was tested, and wafers numbered 01, 03, and 05 were recorded as 0.25 POR for polishing; wafers numbered 06, 08, and 10 were recorded as 0.5 POR for polishing; wafers numbered 11, 13, and 15 were recorded as 0.5 POR. The corresponding polish was recorded as 0.75POR; the corresponding polishes of the wafers numbered 16, 18 and 20 were recorded as 1POR; the corresponding polishes of the wafers numbered 21, 23 and 25 were recorded as 1.5POR. The method for measuring the edge roughness of the wafer in this embodiment uses power spectral density (PSD) to characterize the roughness, and the ordinate in the figure represents the measured value of the power spectral density (PSD). It can be seen from the figure that with the degree of polishing on the abscissa gradually increased, the measured The power spectral density (PSD) is getting smaller and smaller, that is, the edge roughness of the wafer is getting smaller and smaller, and the experimental data proves that the test method of this embodiment is effective.

Power Spectral Density (PSD) decomposes the measured surface structure into components for each spatial frequency, and obtains the value of the density of each component. The contour fluctuation of the edge surface of the wafer can be regarded as a complex vibration phenomenon formed by the superposition of harmonics of different frequencies and amplitudes. The power spectral density (PSD) function contains various frequency components, and its curve reflects the various spatial frequency components. weight distribution.

The present invention also provides a device for measuring the edge roughness of a wafer, as shown in FIG. 2 , comprising: a radiation source (not shown), the radiation source is disposed at least on the peripheral side of the wafer 10; a reflector 20, so The reflecting mirror 20 is arranged on the upper and lower sides of the wafer 10; the photoelectric sensor 30 is arranged on the side of the edge of the wafer 10 away from the center of the wafer; wherein , the light beam emitted by the radiation source irradiates the edge A of the wafer 10 to be scattered, and the scattered light is reflected by the mirror 20 and then collected on the photoelectric sensor 30 . Specifically, the mirrors 20 are disposed on the upper and lower sides of the wafer 10 . In this way, the light beam irradiated on the upper half edge surface (upper slope) of the wafer thickness direction can be reflected by the upper reflector and then concentrated on the photoelectric sensor; The light beam of the inclined plane) can be reflected by the lower reflector and collected on the photoelectric sensor 30; therefore, the edge roughness of the entire surface above and below the wafer edge can be tested. The mirrors 20 disposed on the upper and lower sides of the wafer 10 form a semi-ellipse or a semi-circle.

The radiation source is arranged between the edge of the wafer 10 and the photodetector 30 .

The measuring device further includes: a rotating unit, the wafer 10 can be fixed on the rotating unit by the electrostatic chuck, and the rotating unit drives the wafer 10 to rotate when the edge A of the wafer is collected, and can test the edge roughness of the entire circumference of the wafer. .

To sum up, the present invention provides a method and device for measuring the edge roughness of a wafer. The measuring method includes: irradiating a light beam to the edge of the wafer to scatter, and the scattered light is disposed on the wafer. The mirrors on the upper and lower sides of the wafer are reflected and collected on the photoelectric sensor; the photoelectric sensor collects the scattered light signal at the edge of the wafer; Fourier transform is performed on the scattered light signal to obtain the crystal. The edge roughness of the circle. The measuring method of the present invention is simple and fast, does not require additional operations for cutting samples, has no destructiveness and does not affect the yield, and can test the edge roughness of the entire circumference of the wafer.

The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments, and the same and similar parts between the various embodiments can be referred to each other. For the methods disclosed in the embodiments, since they correspond to the elements disclosed in the embodiments, the descriptions are relatively simple, and the related parts can be referred to the descriptions in the method section.

The above description is only a description of the preferred embodiments of the present invention, and does not limit the scope of the present invention. Any changes and modifications made by those of ordinary skill in the field of the present invention according to the above disclosure belong to the protection scope of the claims.

S1, S2, S3-steps

Claims (10)

A method for measuring edge roughness of a wafer, comprising: The light beam is irradiated to the edge of a wafer to be scattered, and the scattered light is reflected by a mirror arranged on the upper and lower sides of the wafer and then collected on a photoelectric sensor; The photoelectric detector collects the scattered light signal of the edge of the wafer; Fourier transform is performed on the scattered light signal to obtain the edge roughness of the wafer. The method for measuring the edge roughness of a wafer according to claim 1, wherein the edge roughness of the wafer is characterized by a power spectral density. The method for measuring the edge roughness of a wafer according to claim 1, wherein the photoelectric sensor comprises: a photodiode or a charge coupled element. The method for measuring edge roughness of a wafer according to claim 1, wherein the light beam includes a first light beam irradiated from the peripheral side of the wafer to the edge of the wafer. The method for measuring edge roughness of a wafer according to claim 4, wherein the light beam further comprises a second light beam irradiated from above the wafer to the edge of the wafer, and/or from below the wafer The third beam strikes the edge of the wafer. The method for measuring the edge roughness of a wafer according to claim 1, wherein the wavelength range of the light beam is: 1 nm to 100 nm. A device for measuring edge roughness of a wafer, comprising: a radiation source, the radiation source is disposed at least on the peripheral side of a wafer; a reflector, the reflector is disposed on the upper and lower sides of the wafer; and a photoelectric sensor, the photoelectric sensor is arranged on the side of the edge of the wafer away from the center of the wafer; Wherein, the light beam emitted by the radiation source irradiates the edge of the wafer to be scattered, and the scattered light is reflected by the mirror and then collected on the photoelectric sensor. The device for measuring the edge roughness of a wafer according to claim 7, wherein the mirrors disposed on the upper and lower sides of the wafer form a semi-ellipse or a semi-circle. The device for measuring the edge roughness of a wafer according to claim 7, wherein the radiation source is arranged between the edge of the wafer and the photoelectric sensor. The device for measuring edge roughness of a wafer according to claim 7, further comprising: a rotating unit, the rotating unit is used to drive the wafer to rotate.

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