JP2008139065A - Film evaluation apparatus and film evaluation method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a film evaluation apparatus for drastically reducing a measurement time, and improving an inspection throughput. <P>SOLUTION: A film evaluation apparatus comprises: an illumination optical system (20) for irradiating a film (a thin film) formed on a surface of a to-be-inspected object (a wafer 10) with a parallel light flux; a reflection optical system (30) for receiving a reflection light flux reflected by a front surface and a back surface of the film by the irradiation of the light flux; a data processing section (40) for obtaining information on an intensity distribution of the reflection light flux received by the reflection optical system; and a wavelength selecting section (a wavelength selecting unit 22) for selecting a wavelength of the illumination light flux so as to increase a change in the reflectivity of the reflection light flux relative to a fluctuation in a film thickness. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a film evaluation apparatus and a film evaluation method for evaluating the uniformity of the thickness of a thin film formed on, for example, a semiconductor wafer.

  In the semiconductor manufacturing process, there is a step of forming a photoresist film on a semiconductor wafer, and a film evaluation step for evaluating the film by measuring the uniformity of the photoresist film formed after this step is introduced.

  In this film evaluation process, for example, a thin film measuring apparatus using the ellipso optical principle has been proposed (Patent Document 1).

  However, in the measurement using the ellipso optical principle, a very small area is set as the measurement range, so when applied to measuring the uniformity of a thin film formed on the entire surface of a wafer having a large diameter in recent years, a huge number of measurement points are required. This requires a long time for measurement, and there is a problem that it is difficult to maintain the stability of measurement accuracy during this long measurement time.

  That is, the thin film can be measured locally with high accuracy, but there is a problem of complicating control of fluctuation factors such as external vibration noise and temperature management that can cause measurement errors during long-time measurement.

JP 2006-71381 A

  An object of this invention is to provide the film | membrane evaluation apparatus and film | membrane evaluation method which can shorten measurement time significantly and can improve the through-put property of a test | inspection.

  The film evaluation apparatus according to claim 1 of the present invention that achieves the above object includes an illumination optical system that irradiates a film formed on the surface of an object to be inspected with a parallel light beam, and a surface of the film that is irradiated with the light beam. And a reflection optical system that receives the reflected light beam reflected by the back surface, a data processing unit that acquires intensity distribution information of the reflected light beam received by the reflection optical system, and the reflected light beam And a wavelength selection unit that selects a wavelength of the illumination light beam having a large reflectance change.

  In the film evaluation apparatus according to claim 2 of the present invention, the wavelength selection unit is configured such that the thickness of the film is based on the thickness of the film, the refractive index of the film, and the incident angle of the light flux on the film. The wavelength of the luminous flux is selected so that the reflectance change of the reflected luminous flux is large with respect to fluctuations.

  The film evaluation apparatus according to claim 3 of the present invention is a reflected light beam in which the wavelength λ of the light beam having a large reflectance change of the reflected light beam with respect to the thickness variation of the film is reflected on the front surface and the back surface of the film. Is an odd multiple of ¼ of the wavelength λ of the luminous flux (λ × (1/4 to 3/4), λ × (3/4 to 5/4)...). It is characterized by satisfying.

  The film evaluation apparatus according to a fourth aspect of the present invention is characterized in that the reflective optical system includes a two-dimensional solid-state imaging device that receives the reflected light flux.

  The film evaluation apparatus according to claim 5 of the present invention irradiates the surface of the part to be inspected with a light beam having the same wavelength as the light beam applied to the film via the illumination optical system, and passes the reflection optical system. And receiving the surface-reflected light beam reflected from the surface of the inspected portion, and calibrating the intensity distribution information of the reflected light beam based on the intensity distribution information of the surface-reflected light beam obtained from the surface-reflected light beam by the data processing unit. Equipped with a calibration unit.

  In the film evaluation method according to claim 6 of the present invention, the film formed on the surface of the object to be inspected is irradiated with a light beam, the reflected light beam reflected on the front surface and the back surface of the film is received, and the film thickness is measured. A film evaluation method for evaluating a distribution, wherein a wavelength selection step for selecting a wavelength of the light beam having a large reflectance change of the reflected light beam with respect to a variation in thickness of the film, and a wavelength selected in the wavelength selection step An illumination process for irradiating the film with a light beam parallel to the film, a light receiving process for receiving a reflected light beam reflected by the light beam on the front and back surfaces of the film, and an intensity of the reflected light beam received in the light receiving process. And a data processing step for obtaining distribution information.

  According to the present invention, it is possible to greatly reduce the measurement time and improve the throughput of inspection.

  Hereinafter, an embodiment of a film evaluation apparatus and a film evaluation method of the present invention will be described with reference to FIGS.

  FIG. 1 is a schematic view of an entire apparatus showing an embodiment of a film evaluation apparatus of the present invention. FIG. 2 is an explanatory view of an optical path difference of reflected light reflected by the front and back surfaces of the film evaluated by the apparatus of FIG. 3 is an explanatory view of the interference effect of the reflected light reflected by the front and back surfaces of the film.

  Before describing the overall configuration of the film evaluation apparatus of this embodiment with reference to FIG. 1, the evaluation (measurement) principle will be described with reference to FIGS.

  As shown in FIG. 2, a thin film 11 made of a photoresist or the like is formed on the surface of the wafer 10. Of the illumination light beam incident on the thin film 11 at an angle θ, the film reflected light beam FR that reflects at the same angle θ as the incident angle θ on the surface of the thin film 11 and the thin film that passes through the thin film 11 and is reflected by the back surface of the thin film 11. There is an optical path difference f (t) corresponding to the total of the optical path ab and the optical path bc (ab + bc) between the surface 11 and the film reflected light beam BR that exits at the same angle θ as the incident angle θ.

  Here, if the thickness (film thickness) of the thin film 11 is t and the refractive index of the thin film 11 is n, the optical path difference f (t) can be expressed as optical path difference f (t) = 2 nt / cos (θ). I can do it. Therefore, if the incident angle θ of the illumination light beam to the thin film 11 is made constant, the refractive index n of the thin film 11 does not change, so the optical path difference changes with the film thickness t.

  Both light fluxes FR are caused by the phase difference (optical path difference f (t) / wavelength λ) between the film reflected light beam FR and the film reflected light beam BR generated by the optical path difference f (t) between the film reflected light beam FR and the film reflected light beam BR. And BR occur. When the film thickness t of the thin film 11 varies, the optical path difference (phase difference) changes (the interference effect changes), and the reflected light intensity changes (reflectance changes). Therefore, a brightness variation corresponding to the film thickness variation is captured on the wafer image obtained by photographing the reflected light (film reflected light beam).

  Here, the phase difference depends on the wavelength λ of the illumination light beam applied to the thin film 11 (phase difference = optical path difference f (t) / wavelength λ), and the reflected light intensity change (reflectance change) is repeated according to the phase difference. Therefore, it is possible to set the optimum film thickness fluctuation monitor sensitivity by appropriately switching the wavelength λ of the illumination light beam for the same film thickness t.

  The refraction of the thin film 11 is made in advance for the appropriate illumination wavelength (the wavelength that produces the optimum film thickness fluctuation monitor sensitivity), which is the wavelength λ of the illumination light beam that makes the greatest change in reflected light intensity (reflectance change) with respect to the film thickness fluctuation. It is possible to automatically select from the ratio n and the film thickness t.

  Further, the optical path difference f (t) is λ × 1/4, λ × 3/4, λ × 5/4, λ × 7/4, λ × 9/4... (Wavelength λ) of the wavelength λ of the illumination light beam. By automatically selecting the wavelength λ of the illumination light beam that is closest to the node of the odd-numbered multiple of one-fourth of the above, it is possible to set inspection conditions with good sensitivity.

  That is, for the appropriate illumination wavelength, the optical path difference f (t) is between odd multiples of ¼ of the wavelength λ of the illumination light beam (λ × (1/4 to 3/4), λ × (3/4 to It is also possible to select automatically by satisfying the relationship 5/4).

  FIG. 3 shows the intensity change of the interference light reflected on the surface of the thin film 11. The intensity change is small at an optical path difference that is an even multiple of ¼ of the wavelength λ of the illumination light beam, and is an odd multiple of ¼ of the wavelength λ. It shows that the intensity change is the largest due to the optical path difference.

  In the film evaluation apparatus of this embodiment, the optimum film thickness variation monitor sensitivity can be set by switching the wavelength λ of the illumination light beam. That is, as shown in FIG. 1, an inspection stage 12 on which a wafer 10 on which a thin film 11 (see FIG. 2) is formed is placed, and an illumination light beam having an appropriate illumination wavelength on the thin film 11 of the wafer 10 on the inspection stage 12. The illumination optical system 20 that irradiates the film, the reflection optical system 30 that receives the film-reflected light beam reflected from the front and back surfaces of the thin film 11 by irradiation of the illumination light beam of the illumination optical system 20, and the film received by the reflection optical system 30 And a data processing unit 40 that acquires intensity distribution information of the reflected light beam.

  The inspection stage 12 includes a rotary table 13, and a wafer 10 to be inspected that has been transferred by a wafer transfer mechanism (not shown) is placed on the rotary table 13. After the inspection, the inspected wafer 10 is unloaded from the turntable 13 by a wafer unloading device (not shown), and a new inspection target wafer 10 is placed on the turntable 13 by the wafer transfer mechanism.

  The illumination optical system 20 is selected by a mercury lamp 21 as an illumination light source, a wavelength selection unit 22 as a wavelength selection unit for selecting light of a predetermined wavelength from the light from the mercury lamp 21, and the wavelength selection unit 22. A bundle fiber 24 that guides the light (illumination light beam) having the wavelength to the concave mirror 23. The illumination light beam guided to the concave mirror 23 is reflected by the mirror surface to become a parallel light beam, and illuminates the entire thin film 11 formed on the wafer 10.

  The wavelength selection unit 22 includes a plurality of interference filters that transmit only a single wavelength from the emission line spectrum of the mercury lamp 21 therein. By selecting the interference filter, the wavelength selection unit 22 can select, for example, from the emission line spectrum of the mercury lamp 21. An illumination light beam having a single wavelength (appropriate illumination wavelength) such as g-line (436 nm) and j-line (313 nm) can be set. When inspecting the uniformity of the film thickness of the thin film 11 made of photoresist, it is selected from a wavelength band in which the photoresist is not exposed.

  The wavelength selection unit 22 selects an appropriate illumination wavelength, which is the wavelength λ of the illumination light beam having a large reflected light intensity change (reflectance change) with respect to the film thickness fluctuation of the thin film 11, so that even a slight thickness fluctuation can be detected. The data processing unit 40 can be regarded as a change in image luminance, and the film thickness variation monitor sensitivity can be improved.

  The reflective optical system 30 includes a concave mirror 31 that receives a film-reflected light beam (see FIG. 2) reflected by the front and back surfaces of the thin film 11.

  Note that the illumination optical system 20 and the reflection optical system 30 both measure the entire surface of the wafer 10 under the same conditions, and thus are configured by a telecentric optical system so that the illumination light beam and the reflected light beam are parallel to the optical axis. Is done.

  The data processing unit 40 receives a film reflected light beam reflected by the concave mirror 31 and shoots a wafer image, and includes a photographic optical system 41 including an imaging lens and a two-dimensional solid-state imaging device (CCD). And a computer 42 that performs image processing on the photographed wafer image, measures the uniformity of the film thickness (luminance) of the thin film 11 formed on the wafer 10, and creates a luminance dispersion value map.

  The imaging optical system 41 uses an imaging lens having a magnification capable of capturing the entire surface of the wafer 10 with a collective field of view, and a 1-inch CCD (1024 × 1024 pixels) two-dimensional solid-state imaging device that images a 300 mm wafer, for example, and has a size of 300 μm. / The entire surface of the wafer 10 can be photographed with an image resolution of pixels.

  The uniformity of the thickness of the entire thin film 11 formed on the wafer 10 can be measured from the output of the photographing optical system 41 (CCD output) with this image resolution.

  The concave mirror 23 and the concave mirror 31 are arranged so that the incident angle of the illumination light beam reflected by the concave mirror 23 with respect to the wafer 10 and the reflection angle of the film-reflected light beam received by the concave mirror 31 are the same angle with respect to the normal of the wafer 10. The concave mirror 31 is set so as to receive only regular reflection light.

  The computer 42 is connected to a display device 43 that displays a wafer image obtained by performing image processing on the output of the photographing optical system 41. The display device 43 displays the wafer image shown in FIGS. The dispersion value map of the image brightness shown in b) and (d) is displayed.

  Further, the computer 42 is equipped with a calibration unit 44 that calibrates the apparatus so as not to cause variations in wafer image brightness due to habits, illumination unevenness, image sensor sensitivity, and the like for each apparatus.

  The calibration unit 44 places the wafer 10 (bare silicon wafer) on which the thin film 11 is not formed on the inspection stage 12, and irradiates the illumination light beam having the same wavelength as that at the time of measurement via the illumination optical system 20. Calibration wafer image data (intensity distribution information of the surface reflected light beam of the wafer 10 on which the thin film 11 is not formed) obtained by receiving the reflected light beam with the reflection optical system 30 and photographing it is stored in the memory unit of the computer 42 in advance. When the wafer image data (intensity distribution information of the film reflected light beam reflected from the thin film 11) obtained by irradiating the thin film 11 on the wafer 10 with the illumination light beam and being photographed is input to the computer 42, this wafer. The image data is calibrated.

  The calibrated wafer image data is used for a measurement process for measuring the uniformity of the film thickness (luminance) of the thin film 11.

  The computer 42 is also connected with a keyboard 45 for inputting various information.

  FIG. 4 shows a wafer image photographed by the photographing optical system 41 of FIG. 1 and corrected by the calibration unit 44, and a graph representing the relationship between the image position of the wafer image and the image luminance after further measurement processing. .

  When there is no uneven application of the photoresist and the film thickness of the thin film 11 is uniform, a wafer image as shown in FIG. By measuring this wafer image, a straight line graph in which the image brightness does not change depending on the image position is obtained as shown in FIG.

  When uneven coating occurs and the film thickness of the thin film 11 varies, a wafer image having a radial abnormal contrast is obtained, for example, as shown in FIG. By performing measurement processing on this wafer image, a graph in which the image brightness decreases at a certain image position is obtained as shown in FIG.

  FIG. 5 is an image in which the brightness distribution state of the wafer image photographed by the photographing optical system 41 in FIG. 1 and corrected by the calibration unit 44 is divided into designated areas and displayed as the variance value of the brightness value of each pixel in the area. The brightness | luminance dispersion value map is shown.

  When there is no uneven application of the photoresist and the film thickness of the thin film 11 is uniform, a wafer image with uniform image brightness as shown in FIG. 5A is obtained as in FIG. When this is displayed as a variance value map, a variance value map in which the luminance value of each pixel is constant is obtained as shown in FIG.

  When uneven coating occurs and the film thickness of the thin film 11 varies, a wafer image having a radially abnormal contrast as shown in FIG. 5C is obtained as in FIG. 4C. When this is displayed as a variance value map, a variance value map is obtained in which the luminance values of the pixels in one area are different from the luminance values of the pixels in the other area, as shown in FIG.

  In addition to displaying the image brightness in a dispersion value map in this way, it is possible to perform defect inspection to determine whether or not a region other than a flat brightness distribution exists in the captured wafer image via a defect inspection image processing algorithm It is.

  FIG. 6 shows an example of simulating optimization of the wavelength of the illumination light beam. The refractive index n of the thin film 11 is 1.4, the incident angle and the reflection angle are both 15 degrees, and two illuminations having different illumination wavelengths are shown. A graph in the case of calculating a change in reflectance intensity with respect to a change in film thickness (film thickness t = 280 nm to 420 nm) by irradiation with a light beam (λ = 546 nm, 436 nm) is shown. The vertical axis in FIG. 5 represents the reflectance, and the horizontal axis represents the film thickness.

  When the optical film thickness (refractive index × geometric film thickness) is around 320 nm, the change in the reflectance with respect to the change in film thickness is small when the wavelength λ of the illumination light beam is 436 nm, whereas the change in film thickness occurs when the wavelength λ of the illumination light beam is 546 nm. On the other hand, the change in the film thickness can be detected with high sensitivity by selecting an illumination light beam having a wavelength λ of 546 nm.

  Further, when the phase obtained by dividing the optical path difference (2 nt / cos θ) by the wavelength λ is compared to 1.21 at the wavelength λ546 nm, it is 1.52 at the wavelength λ436 nm, and the illumination light beam having the wavelength λ546 nm is used. It can be predicted from the calculation (optical path difference / wavelength) that the sensitivity is higher.

  FIG. 7 shows another example of simulating optimization of the wavelength of the illumination light beam. The refractive index n of the thin film 11 is 1.4, the incident angle and the reflection angle are both 15 degrees, and the illumination wavelengths are different. The graph in the case of irradiating two illumination light beams (λ = 546 nm, 248 nm) and calculating the change in reflectance intensity with respect to the film thickness change (film thickness t = 220 nm to 340 nm) is shown. The vertical axis in FIG. 6 represents the reflectance, and the horizontal axis represents the film thickness (n × t).

  When the optical film thickness (refractive index × geometric film thickness) is around 300 nm, the change in the reflectance with respect to the change in film thickness is small when the wavelength λ of the illumination light beam is 248 nm, whereas the change in film thickness occurs when the wavelength λ of the illumination light beam is 546 nm. On the other hand, the change in the film thickness can be detected with high sensitivity by selecting an illumination light beam having a wavelength λ of 546 nm.

  In addition, when the phase obtained by dividing the optical path difference (2 nt / cos θ) by the wavelength λ is 1.14 at the wavelength λ546 nm, it is 2.50 at the wavelength λ248 nm, and the illumination light beam having the wavelength λ546 nm is used. It can be predicted from the calculation (optical path difference / wavelength) that the sensitivity is higher.

  FIG. 8 is a flowchart showing an embodiment of the film evaluation method of the present invention, which is performed using the above-described film evaluation apparatus.

  In step S100, the wavelength λ of the illumination light beam having a large reflectance change with respect to the film thickness change is obtained by the method described with reference to FIGS. 5 and 6, and the interference of the wavelength selection unit 22 is performed so that the illumination light beam of this wavelength is irradiated onto the thin film 11. Select a filter.

  A wafer 10 on which a thin film 11 to be inspected is previously formed is placed on the inspection stage 12.

  The illumination light beam having the wavelength selected in step S101 is irradiated onto the thin film 11 via the illumination optical system 20, while the film reflection light beam is received via the reflection optical system 30 in step S102.

  In step S103, the film reflected light beam is photographed by the photographing optical system 41, and data processing such as image processing of the CCD output of the photographing optical system 41 by the computer 42 is performed.

  The wafer image subjected to data processing in step S104 is displayed on the display device 43.

  According to the film evaluation apparatus and method of the present embodiment, in order to measure the thin film uniformity on the entire surface of the wafer, an inspection with a huge number of measurement points has been required so far, with only a short imaging time and image processing time. As a result, the inspection time and cost for confirming the uniformity of the thin film on the wafer can be significantly reduced, and the inspection throughput can be improved.

The present invention is not limited to the above-described embodiments, and can be applied to inspecting the uniformity of the film thickness of an oxide film (for example, SiO ₂ ) in addition to a thin film made of a photoresist. is there.

  Further, the wavelength selection unit 22 is configured to automatically perform wavelength selection, and information such as the refractive index n of the thin film 11 and the film thickness t of the thin film 11 is input to the computer 42 via the keyboard 45. Based on this, the optimum wavelength λ of the illumination light beam may be obtained by the computer 42, and this wavelength information may be output to the wavelength selection unit 22.

It is the schematic of the whole apparatus which shows one Embodiment of the film | membrane evaluation apparatus of this invention. It is explanatory drawing of the optical path difference of the reflected light reflected by the surface of a thin film evaluated by the apparatus of FIG. 1, and a back surface. It is explanatory drawing which shows the interference light intensity change of the reflected light reflected by the surface and back surface of a thin film evaluated with the apparatus of FIG. FIG. 4A shows a relationship between a wafer image photographed by the film evaluation apparatus of FIG. 1 and image brightness, FIG. 4A shows a uniform wafer image without uneven coating, and FIG. 4B shows no uneven coating. A graph showing the image brightness in relation to the image position, FIG. 6C shows a wafer image with uneven coating, FIG. 4D shows the image brightness of the image shown in FIG. It is a graph shown by the relationship of. FIG. 5 shows a wafer image photographed by the apparatus of FIG. 1 and an image in which this image is displayed as a dispersion value map. FIG. 5A shows a uniform wafer image without uneven application, and FIG. 5B shows no uneven application ( The image shown in a) is displayed as a dispersion value map, FIG. 8C is a wafer image with uneven coating, and FIG. 9D is the dispersion value map showing the image shown in FIG. It is an image. It is a graph which shows the relationship between the film thickness measured using two illumination lights ((lambda) = 546nm, 436nm) from which an illumination wavelength differs, and a reflectance. It is a graph which shows the relationship between the film thickness measured using two illumination light ((lambda) = 546nm, 248nm) from which an illumination wavelength differs similarly to FIG. 6, and a reflectance. It is a flowchart which shows one Embodiment of the film | membrane evaluation method of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Wafer 11 Thin film 20 Illumination optical system 22 Wavelength selection unit 23 Concave mirror 30 Reflective optical system 31 Concave mirror 40 Data processing unit 41 Shooting optical system 42 Computer 44 Calibration part

Claims (6)

An illumination optical system for irradiating a parallel light beam onto a film formed on the surface of the object to be inspected;
A reflective optical system that receives a reflected light beam reflected from the front and back surfaces of the film by irradiation of the light beam;
A data processing unit for acquiring intensity distribution information of the reflected light beam received by the reflective optical system;
A film evaluation apparatus comprising: a wavelength selection unit that selects a wavelength of the illumination light beam that has a large change in reflectance of the reflected light beam with respect to a change in thickness of the film. The film evaluation apparatus according to claim 1,
The wavelength selection unit has a large reflectance change of the reflected light beam with respect to a change in the film thickness based on the thickness of the film, the refractive index of the film, and the incident angle of the light beam on the film. A film evaluation apparatus for selecting a wavelength of a light beam. In the film evaluation apparatus according to claim 1 or 2,
The wavelength λ of the light beam, in which the reflectance change of the reflected light beam is large with respect to the thickness variation of the film, is an optical path difference of the reflected light beam reflected by the front surface and the back surface of the film is a quarter of the wavelength λ of the light beam. 1. A film evaluation apparatus characterized by satisfying a relationship of an odd multiple of 1 (λ × (1/4 to 3/4), λ × (3/4 to 5/4)...). In the film evaluation apparatus according to any one of claims 1 to 3,
The film evaluation apparatus, wherein the reflection optical system includes a two-dimensional solid-state imaging device that receives the reflected light flux. In the film evaluation apparatus according to any one of claims 1 to 4,
A surface-reflected light beam that irradiates the surface of the part to be inspected with a light beam having the same wavelength as the light beam that irradiates the film through the illumination optical system and reflects the surface of the part to be inspected through the reflective optical system. A film evaluation apparatus comprising: a calibration unit that receives light and calibrates the intensity distribution information of the reflected light beam based on the intensity distribution information of the surface reflected light beam obtained from the surface reflected light beam by the data processing unit. A film evaluation method for evaluating a thickness distribution of a film by irradiating a film formed on a surface of an object to be inspected with a light beam, receiving a reflected light beam reflected on the front and back surfaces of the film,
A wavelength selection step of selecting a wavelength of the luminous flux with a large change in reflectance of the reflected luminous flux with respect to a variation in thickness of the film;
An illumination step of irradiating the film with a light beam parallel to the film having the wavelength selected in the wavelength selection step;
A light receiving step of receiving a reflected light beam reflected on the front and back surfaces of the film by the light beam;
And a data processing step of obtaining intensity distribution information of the reflected light beam received in the light receiving step.

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