A method and device for measuring film stress

Abstract

The present invention discloses a method and device for measuring film stress, the method comprising: obtaining reflected sound waves in a certain direction on the surface of the measuring object before and after the film is formed, obtaining a deformation variable curve of the surface of the measuring object before and after the film is formed; and obtaining the stress of the film acting on the measuring object according to the deformation variable curve. The present invention uses acoustic wave technology to measure the stress generated by the film on the measuring object, and can accurately measure the stress of films of various thicknesses without being limited by the material of the film. It has the advantages of mature technology, high sensitivity, low cost, etc. The method is simple and easy to implement, and the measurement efficiency is improved.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor testing technology, and in particular to a method and device for measuring film stress on a wafer based on sonar technology. Background Art

[0002] During wafer production, it is often necessary to deposit thin films of various materials on the wafer surface. Films of different thicknesses have different effects on product performance. Since different film thicknesses will lead to different stresses on the wafer, it is of great significance to measure film stress.

[0003] At present, optical measurement is commonly used to measure stress on wafers after thin film deposition. However, since some thin films (such as metal films) have the property of absorbing light, it will have an adverse effect on the sensitivity and accuracy of the measurement. Therefore, the use of optical measurement is easily limited by the material of the film. In addition, the optical measurement method also has many problems such as complex algorithms, high measurement costs and immature technology. Summary of the invention

[0004] The purpose of the present invention is to overcome the above-mentioned defects in the prior art and to provide a method and device for measuring film stress.

[0005] To achieve the above object, the technical solution of the present invention is as follows:

[0006] The present invention provides a method for measuring film stress, comprising:

[0007] Acquiring reflected sound waves in a certain direction on the surface of the measurement object before and after the film is formed, and obtaining a deformation amount curve of the surface of the measurement object before and after the film is formed;

[0008] The stress exerted by the film on the measurement object is obtained according to the deformation curve.

[0009] Furthermore, the acquisition of reflected sound waves in a certain direction on the surface of the measurement object before and after the film is formed to obtain a deformation curve of the surface of the measurement object before and after the film is formed includes:

[0010] emitting a sound wave of a specific wavelength in a certain direction of the surface of the measurement object before and after the thin film is formed, and receiving a sound wave signal reflected from the surface of the measurement object before and after the thin film is formed;

[0011] calculating, according to the reflected sound wave signal, a first height curve and a second height curve of the surface of the measurement object before and after the film is formed;

[0012] Calculating a first height difference curve and a second height difference curve relative to a reference point according to the first height curve and the second height curve;

[0013] The height on the first height difference curve and the height at the corresponding position on the second height difference curve are calculated to obtain a deformation curve in a certain direction of the surface of the measurement object before and after the film is formed.

[0014] Further, obtaining the stress of the film acting on the measurement object according to the deformation variable curve includes:

[0015] According to the deformation variable curve, the corresponding curvature radius R is calculated;

[0016] Substitute the radius of curvature R into the following formula:

[0017]

[0018] The stress σ of the film acting on the measured object is obtained f ;

[0019] Among them, E s Represents the Young's modulus of the measured object, v s represents Poisson's ratio, t s Represents the thickness of the measured object, t f Represents the thickness of the film.

[0020] Furthermore, the certain direction includes the direction of any straight line from the center to the edge of the measurement object.

[0021] Further, the reference point includes a center point of the measurement object or a point on an edge along the certain direction.

[0022] Furthermore, the sound waves of the specific wavelength include ultrasonic waves.

[0023] Furthermore, the specific wavelength includes 850 nm.

[0024] The present invention also provides a thin film stress measuring device, comprising:

[0025] An acoustic wave transmitting module, used for transmitting an acoustic wave of a specific wavelength in a certain direction on the surface of the measurement object before and after the film is formed;

[0026] an acoustic wave detection module, used for receiving acoustic wave signals reflected from the surface of the measurement object before and after the film is formed;

[0027] A calculation module is used to calculate the deformation curve of the surface of the measurement object before and after the film is formed according to the reflected sound wave signal, so as to further calculate the stress of the film acting on the measurement object.

[0028] Further, the calculation module first calculates a first height curve and a second height curve of the surface of the measurement object before and after the film is formed according to the reflected sound wave signal, and then calculates a first height difference curve and a second height difference curve relative to a reference point according to the first height curve and the second height curve, and obtains a deformation variable curve in a certain direction of the surface of the measurement object before and after the film is formed by calculating the difference between the height on the first height difference curve and the height at the corresponding position on the second height difference curve, and then calculates the corresponding curvature radius R according to the deformation variable curve, and substitutes the curvature radius R into the following formula:

[0029]

[0030] The stress σ of the film acting on the measured object is obtained f ;

[0031] Among them, E s Represents the Young's modulus of the measured object, v s represents Poisson's ratio, t s Represents the thickness of the measured object, t f Represents the thickness of the film.

[0032] Furthermore, the acoustic wave transmitting module and the acoustic wave detecting module are respectively used to transmit ultrasonic waves of a specific wavelength and receive signals of the ultrasonic waves of a specific wavelength reflected from the surface of the measuring object before and after the film is formed by the transmitted ultrasonic waves of a specific wavelength; and / or, it also includes: a workbench for supporting the measuring object for stress measurement.

[0033] It can be seen from the above technical scheme that the present invention uses acoustic wave technology to measure the stress generated by the thin film on the measurement object (such as a wafer), which is not limited by the material of the thin film and can accurately measure the stress of thin films of various thicknesses. It has the advantages of mature technology, high sensitivity, and low cost. In addition, by measuring the actual deformation of the surface of the measurement object before and after the film is formed, and using the obtained deformation curve to calculate the corresponding radius of curvature, and further using a formula to deduce the stress of the film on the measurement object, it is only necessary to accurately judge the deformation (warping) distribution on the measurement object based on the acoustic wave measurement time and the distance between different materials. At the same time, it avoids the problem of insufficient measurement accuracy caused by the previous optical measurement method being easily affected by the material's light absorption characteristics. The method is simple and easy to implement, and improves the measurement efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The figure is a flow chart of a film stress measurement method according to a preferred embodiment of the present invention.

[0035] Figure 2 A preferred embodiment of the present invention Figure 1 Specific flow chart of step S1 in FIG.

[0036] Figure 3 A preferred embodiment of the present invention Figure 1 Specific flow chart of step S2 in FIG.

[0037] Figure 4 Schematic diagram of the state of the wafer undergoing stress deformation after thin film deposition.

[0038] Figure 5 The figure is a schematic structural diagram of a thin film stress measuring device according to a preferred embodiment of the present invention. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. Unless otherwise defined, the technical terms or scientific terms used herein should be understood by people with general skills in the field to which the present invention belongs. "Including" and similar words used in this article mean that the elements or objects appearing before the word include the elements or objects listed after the word and their equivalents, without excluding other elements or objects.

[0040] The core idea of ​​the present invention is to provide a method and device for measuring film stress.

[0041] A film stress measurement method of the present invention comprises:

[0042] Acquiring reflected sound waves in a certain direction on the surface of the measurement object before and after the film is formed, and obtaining a deformation amount curve of the surface of the measurement object before and after the film is formed;

[0043] The stress exerted by the film on the measurement object is obtained according to the deformation curve.

[0044] A thin film stress measuring device of the present invention comprises:

[0045] An acoustic wave transmitting module, used for transmitting an acoustic wave of a specific wavelength in a certain direction on the surface of the measurement object before and after the film is formed;

[0046] an acoustic wave detection module, used for receiving acoustic wave signals reflected from the surface of the measurement object before and after the film is formed;

[0047] A calculation module is used to calculate the deformation curve of the surface of the measurement object before and after the film is formed according to the reflected sound wave signal, so as to further calculate the stress of the film acting on the measurement object.

[0048] The present invention measures the stress generated by a thin film on a measurement object (such as a chip / wafer) by adopting acoustic wave technology. It only needs to measure the acoustic wave measurement time and the distance between different materials to accurately determine the deformation (warping) distribution on the measurement object. Therefore, the stress of thin films of various thicknesses can be accurately measured. At the same time, it avoids the problem of insufficient measurement accuracy caused by the susceptibility to the material's light absorption characteristics in previous optical measurement methods. It has the advantages of mature technology, simple method, high sensitivity, low cost, etc., and improves measurement efficiency.

[0049] The specific implementation modes of the present invention are further described in detail below in conjunction with the accompanying drawings.

[0050] refer to Figure 1 A film stress measurement method of the present invention comprises the following steps:

[0051] Step S1: Acquire the reflected sound waves in a certain direction on the surface of the measurement object before and after the film is formed, and obtain the deformation amount curve of the surface of the measurement object before and after the film is formed.

[0052] refer to Figure 2 In some embodiments, the method of step S1 specifically includes the following steps:

[0053] Step S11: emitting a sound wave of a specific wavelength in a certain direction of the surface of the measurement object before and after the thin film is formed, and receiving a sound wave signal reflected from the surface of the measurement object before and after the thin film is formed.

[0054] like Figure 5 As shown, the wafer 100 is taken as an example of the measurement object. First, the wafer 100 before thin film deposition is placed flat on the workbench 300 so that the wafer 100 is relatively fixed. Then, an acoustic wave transmitting module 500 is used to transmit acoustic waves of a specific wavelength to the surface of the wafer 100 before thin film deposition along a certain direction 400 on the surface of the wafer 100. And an acoustic wave detection module 600 is used to receive the acoustic wave signal reflected from the surface of the wafer 100.

[0055] The certain direction 400 may be a radial direction of any straight line from the center (center) to the edge of the wafer 100. Sound waves of a specific wavelength include ultrasonic waves.

[0056] For example, an ultrasonic transmitter (sound wave transmitting module 500 ) may be used to transmit ultrasonic waves from the center of the surface of the wafer 100 toward the edge, so as to use the ultrasonic waves to scan along the radial direction of the surface of the wafer 100 .

[0057] In some embodiments, the ultrasonic wavelength may be 850 nm.

[0058] According to λ=c / f, λ represents the wavelength (meter), c represents the speed of sound 340m / s, and f represents the frequency. When the frequency reaches 400MHz, the wavelength is 850nm.

[0059] Next, an ultrasonic detector (sound wave detection module 600) can be used to receive the ultrasonic signal reflected by the surface of the wafer 100 from the ultrasonic wave emitted in the radial direction on the surface of the wafer 100. In this way, the height (profile) information of the surface of the wafer 100 before the thin film deposition can be obtained.

[0060] The ultrasonic signal reflected on the surface of the wafer 100 before the thin film deposition and received by the ultrasonic detector will be output to the calculation module 700 for corresponding data processing.

[0061] Afterwards, a thin film 200 is deposited on the same surface of the wafer 100 .

[0062] like Figure 4 As shown, due to the difference in properties between the wafer 100 and the film 200, the wafer 100 may be warped. Films 200 of different thicknesses may cause different degrees of warping of the wafer 100. By emitting specific sound waves through an ultrasonic transmitter, the height information of the wafer 100 with films 200 of different thicknesses and materials on the surface can be detected. Figure 4 The thin film 200 deposited on the surface of the wafer 100 is shown in the figure, which generates a certain tensile stress on the wafer 100, causing the edge of the wafer 100 to bend upward. If Bow is used to represent the height difference between the edge and the center of the wafer 100, the height difference between the edge and the center of the wafer 100 after the deposition of the thin film 200 is represented by Post Bow. In fact, the wafer 100 before the deposition of the thin film 200 does not have an absolutely horizontal surface. Therefore, the height difference between the edge and the center of the wafer 100 before the deposition of the thin film 200 is not 0, and can be represented by Pre Bow.

[0063] For example, in the same manner as described above, the wafer 100 after the thin film 200 is deposited is placed flat on the workbench 300 again, so that the wafer 100 is relatively fixed. Then, an ultrasonic transmitter is used to emit ultrasonic waves, for example, with a wavelength of 850 nm, along the radial direction of the surface of the wafer 100 to the surface of the wafer 100 after the thin film 200 is deposited, and an ultrasonic scan is performed along the radial direction of the surface of the wafer 100. An ultrasonic detector is used to receive the ultrasonic signal reflected from the surface of the wafer 100. In this way, the height (profile) information of the surface of the wafer 100 after the thin film 200 is deposited can be obtained. The ultrasonic signal reflected from the surface of the wafer 100 after the thin film 200 is deposited and received by the ultrasonic detector will also be output to the calculation module 700 for corresponding data processing.

[0064] Step S12: Calculate a first height curve and a second height curve of the surface of the measurement object before and after the film is formed based on the reflected sound wave signal.

[0065] The calculation module 700 calculates and processes the ultrasonic signals reflected on the surface of the wafer 100 before and after the deposition of the thin film 200, and obtains a first height curve of the surface of the wafer 100 before the formation of the thin film 200 and a second height curve of the surface of the wafer 100 after the formation of the thin film 200.

[0066] Step S13: Calculate a first height difference curve and a second height difference curve relative to a reference point according to the first height curve and the second height curve.

[0067] against Figure 4 In the case of warping due to tensile stress, the center point of the wafer 100 can be used as the reference point (conversely, when the wafer 100 is in a warping state with a central bulge caused by compressive stress, a point on the edge of the wafer 100 along the scanning direction can be used as the reference point).

[0068] The calculation module 700 subtracts the height value of each point on the first height curve from the height value of the center of the wafer 100 as a reference point to obtain a first height difference curve (Pre Bow curve) relative to the center of the wafer 100. Similarly, the height value of each point on the second height curve is subtracted from the height value of the center of the wafer 100 as a reference point to obtain a second height difference curve (Post Bow curve) relative to the center of the wafer 100.

[0069] Step S14: calculating the difference between the height on the first height difference curve and the height at the corresponding position on the second height difference curve to obtain a deformation curve in a certain direction of the surface of the measured object before and after the film is formed.

[0070] Then, through the calculation module 700, the height on the second height difference curve is subtracted from the height at the corresponding position on the first height difference curve to obtain a deformation curve (Differ Bow curve) in the radial direction of the surface of the wafer 100 after the film 200 is formed relative to before the film 200 is formed, which is used to characterize the deformation change of the wafer 100 before and after coating.

[0071] Step S2: According to the deformation curve, the stress of the film acting on the measurement object is obtained.

[0072] refer to Figure 3 In some embodiments, the method of step S2 specifically includes the following steps:

[0073] Step S21: Calculate the corresponding curvature radius according to the deformation variable curve.

[0074] The calculation module 700 performs further calculations based on the obtained deformation variable curve to obtain a corresponding curvature radius R (which can be understood by referring to the existing mathematical calculation method for the curvature radius).

[0075] Step S22: Substitute the radius of curvature into the formula to obtain the stress of the film acting on the measurement object.

[0076] The calculation module 700 substitutes the obtained curvature radius R into the following formula for calculation:

[0077]

[0078] In the formula, E s represents the Young's modulus (the degree of resistance to elastic deformation) of the measurement object (wafer 100), v s represents Poisson's ratio (ratio of transverse strain to longitudinal strain), t s represents the thickness of the measurement object (wafer 100), t f represents the thickness of the film 200 (reference Figure 4 ).

[0079] Through the above calculation by the calculation module 700, the stress σ exerted by the film 200 on the wafer 100 can be obtained. f .

[0080] A thin film stress measurement device of the present invention is further described in detail below through specific implementation modes and in conjunction with the accompanying drawings.

[0081] refer to Figure 5 A thin film stress measuring device of the present invention can be used to implement a thin film stress measuring method of the present invention. The thin film stress measuring device includes: an acoustic wave emission module 500 , an acoustic wave detection module 600 , a calculation module 700 , and a workbench 300 .

[0082] The workbench 300 is used to support the measurement object (eg, the wafer 100 ) to perform stress measurement in the above method.

[0083] The acoustic wave transmitting module 500 is used to transmit the sound to the film 200 (reference Figure 4 ) is formed before and after the surface of the measurement object emits sound waves (such as ultrasonic waves) of a specific wavelength in a certain direction 400 (such as a radial direction).

[0084] The acoustic wave detection module 600 is used to receive acoustic wave signals (reflected ultrasonic wave signals) reflected from the surface of the measurement object before and after the film 200 is formed.

[0085] The calculation module 700 is used to calculate the deformation curve of the surface of the measurement object before and after the film 200 is formed according to the reflected sound wave signal, so as to further calculate the stress of the film 200 acting on the measurement object.

[0086] For example, the calculation module 700 may be a host computer. The host computer first calculates the first height curve and the second height curve of the surface of the wafer 100 before and after the film 200 is formed according to the reflected sound wave signal.

[0087] Then, a first height difference curve and a second height difference curve relative to the center point of the wafer 100 are calculated based on the first height curve and the second height curve.

[0088] Next, by calculating the difference between the height on the first height difference curve and the height at the corresponding position on the second height difference curve, a deformation curve in a certain direction 400 of the surface of the wafer 100 before and after the film 200 is formed is obtained.

[0089] Next, according to the deformation variable curve, the corresponding curvature radius R is calculated using conventional mathematical calculation methods, and the curvature radius R is substituted into the following formula:

[0090]

[0091] By calculation, the stress σ of the film 200 acting on the wafer 100 can be obtained. f .

[0092] Furthermore, the sound wave transmitting module 500 may be an ultrasonic wave transmitter, and the sound wave detecting module 600 may be an ultrasonic wave detector.

[0093] The present invention uses the sonar pulse principle and ultrasonic waves as the measurement source to achieve one-time non-contact full-aperture uniform sampling measurement of the surface of various wafers (chips). The method is simple, accurate, fast, and can measure repeatedly.

[0094] In summary, the present invention uses acoustic wave technology to measure the stress generated by the thin film 200 on the measurement object (such as a wafer / chip), and can accurately measure the stress of thin films 200 of various thicknesses without being limited by the material of the thin film 200. It has the advantages of mature technology, high sensitivity, and low cost. In addition, by measuring the actual deformation of the surface of the measurement object before and after the film 200 is formed, and using the acquired deformation curve to calculate the corresponding radius of curvature, and further using a formula to deduce the stress of the thin film 200 acting on the measurement object, it is only necessary to accurately judge the deformation (warping) distribution on the measurement object based on the acoustic wave measurement time and the distance between different materials. At the same time, it avoids the problem of insufficient measurement accuracy caused by the material's ability to absorb light that exists in previous optical measurement methods. The method is simple and easy to implement, and improves the measurement efficiency.

[0095] Although the embodiments of the present invention are described in detail above, it is obvious to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations are within the scope and spirit of the present invention as described in the claims. Moreover, the present invention described herein may have other embodiments and may be implemented or realized in a variety of ways.

Claims

1. A method for measuring film stress, characterized in that: include: Acquiring reflected sound waves in a certain direction on the surface of the measurement object before and after the film is formed, and obtaining a deformation amount curve of the surface of the measurement object before and after the film is formed; The stress exerted by the film on the measurement object is obtained according to the deformation curve.

2. The thin film stress measurement method according to claim 1, characterized in that: The step of acquiring reflected sound waves in a certain direction on the surface of the measurement object before and after the film is formed, and obtaining a deformation curve of the surface of the measurement object before and after the film is formed, comprises: emitting a sound wave of a specific wavelength in a certain direction of the surface of the measurement object before and after the thin film is formed, and receiving a sound wave signal reflected from the surface of the measurement object before and after the thin film is formed; calculating, according to the reflected sound wave signal, a first height curve and a second height curve of the surface of the measurement object before and after the film is formed; Calculating a first height difference curve and a second height difference curve relative to a reference point according to the first height curve and the second height curve; The height on the first height difference curve and the height at the corresponding position on the second height difference curve are calculated to obtain a deformation curve in a certain direction of the surface of the measurement object before and after the film is formed.

3. The thin film stress measurement method according to claim 1, characterized in that: The step of obtaining the stress of the film acting on the measurement object according to the deformation variable curve comprises: According to the deformation variable curve, the corresponding curvature radius R is calculated; Substitute the radius of curvature R into the following formula: The stress σ of the film acting on the measured object is obtained f ; Among them, E s Represents the Young's modulus of the measured object, v s represents Poisson's ratio, t s Represents the thickness of the measured object, t f Represents the thickness of the film.

4. The thin film stress measurement method according to claim 2, characterized in that: The certain direction includes the direction of any straight line from the center to the edge of the measurement object.

5. The thin film stress measurement method according to claim 4, characterized in that: The reference point includes a center point of the measurement object or a point on an edge along the certain direction.

6. The thin film stress measurement method according to claim 2, characterized in that: The sound waves of the specific wavelength include ultrasonic waves.

7. The thin film stress measurement method according to claim 2, characterized in that: The specific wavelength includes 850 nm.

8. A thin film stress measuring device, characterized in that: include: An acoustic wave transmitting module, used for transmitting an acoustic wave of a specific wavelength in a certain direction on the surface of the measurement object before and after the film is formed; an acoustic wave detection module, used for receiving acoustic wave signals reflected from the surface of the measurement object before and after the film is formed; A calculation module is used to calculate the deformation curve of the surface of the measurement object before and after the film is formed according to the reflected sound wave signal, so as to further calculate the stress of the film acting on the measurement object.

9. The thin film stress measuring device according to claim 8, characterized in that: The calculation module first calculates the first height curve and the second height curve of the surface of the measurement object before and after the film is formed according to the reflected sound wave signal, and then calculates the first height difference curve and the second height difference curve relative to the reference point according to the first height curve and the second height curve, and obtains the deformation variable curve in a certain direction of the surface of the measurement object before and after the film is formed by calculating the difference between the height on the first height difference curve and the height at the corresponding position on the second height difference curve, and then calculates the corresponding curvature radius R according to the deformation variable curve, and substitutes the curvature radius R into the following formula: The stress σ of the film acting on the measured object is obtained f ; Among them, E s Represents the Young's modulus of the measured object, v s represents Poisson's ratio, t s Represents the thickness of the measured object, t f Represents the thickness of the film.

10. The thin film stress measuring device according to claim 8, characterized in that: The acoustic wave transmitting module and the acoustic wave detecting module are respectively used to transmit ultrasonic waves of a specific wavelength and receive signals of the ultrasonic waves of the specific wavelength reflected from the surface of the measuring object before and after the film is formed by the transmitted ultrasonic waves of the specific wavelength; And / or, it also includes: a workbench, used for supporting the measurement object to perform stress measurement.

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