A method for measuring wafer film thickness non-uniformity

Abstract

A wafer film thickness unevenness measurement method, the method comprising: a measurement region division module obtains a wafer to be measured, and excludes the edge region of the wafer to be measured, and then divides the effective measurement range of the wafer to be measured into T regions that are not connected to each other; a measured IF displacement difference acquisition module obtains a measured IF displacement difference curve of the wafer to be measured by means of linearly polarized light incident on the wafer to be measured; a theoretical IF displacement difference acquisition module regards the wafer to be measured as a uniform film, establishes a theoretical IF relationship model, and then obtains a theoretical IF displacement difference curve; an inversion calculation module inversely fits the measured and theoretical IF displacement difference curves, and obtains the thickness of the wafer film in each region of the T effective measurement regions; and a thickness unevenness evaluation module brings the thickness of the wafer film in each region of the wafer to be measured into a wafer film thickness unevenness model, and obtains the wafer film thickness unevenness evaluation result of the wafer to be measured. Effect: The wafer film thickness unevenness can be accurately measured.

Description

Technical Field

[0001] This invention relates to the field of semiconductor testing technology, and in particular to a method for measuring the non-uniformity of wafer thin film thickness. Background Technology

[0002] The primary purpose of wafer thin film thickness non-uniformity inspection is to ensure precise control of critical process parameters during chip manufacturing. Among the hundreds of processes in semiconductor manufacturing, thin film deposition is a fundamental step in building transistors, metal interconnects, and insulating layers. The thickness error of each thin film layer often needs to be controlled at the atomic scale. High-precision inspection methods can evaluate the performance of processes such as photolithography, etching, and metal deposition in real time, ensuring that the thickness of key materials such as oxide layers, silicon nitride, and polysilicon layers meets design requirements. This lays a solid physical foundation for subsequent pattern transfer and device manufacturing.

[0003] This testing is crucial for ensuring the electrical performance and reliability of devices. Even minute fluctuations in film thickness can cause significant changes in the physical properties of devices. For example, uneven metal layer thickness can directly lead to differences in conductivity, causing open circuit or short circuit risks; while thickness deviations in the gate stack or passivation layer can affect the switching speed and power consumption of transistors, and even lead to device failure. Especially in the fields of high-frequency communication and power devices, uneven thickness can also cause stress concentration, leading to mechanical failures such as cracking and delamination of the wafer during subsequent high-temperature or mechanical processing, seriously affecting the final product yield.

[0004] From a macro perspective of industrial economics and technological development, thickness uniformity testing is a core means of achieving consistency and yield management in large-scale mass production. In the mass production of integrated circuits, ensuring the performance consistency of each batch and even each chip is crucial for reducing manufacturing costs and enhancing market competitiveness. Through rigorous film thickness monitoring, manufacturers can effectively intercept defective products caused by process fluctuations, avoiding resource waste. Simultaneously, as process technologies evolve towards 3nm and even more advanced nodes, this testing technology also provides indispensable data support for new material research and development, process optimization, and compliance with international semiconductor manufacturing standards, driving the entire industry towards higher precision and higher efficiency.

[0005] Therefore, there is an urgent need to provide a high-precision method for measuring the non-uniformity of wafer thin film thickness. Summary of the Invention

[0006] The present invention provides a method for measuring the non-uniformity of wafer thin film thickness, which can accurately measure the non-uniformity of wafer thin film thickness.

[0007] To achieve the above objectives, the present invention provides a method for measuring the non-uniformity of wafer thin film thickness, which, as a key feature, includes the following steps:

[0008] Step 1: Construct a wafer thin film thickness non-uniformity measurement system. This system includes a measurement region division module, which is connected in parallel to a measured IF displacement difference acquisition module and a theoretical IF displacement difference acquisition module. These two modules are connected to the same inversion calculation module, which is also connected to a thickness non-uniformity evaluation module. The thickness non-uniformity evaluation module contains a built-in wafer thin film thickness non-uniformity model.

[0009] Step 2: The measurement area division module acquires the wafer to be tested, excludes the edge area of ​​the wafer to be tested, and then divides the effective measurement range of the wafer to be tested into T non-connected areas;

[0010] Step 3: The measured IF displacement difference acquisition module uses an IF displacement measuring device to incident linearly polarized light onto the wafer under test, and acquires the measured IF displacement difference at a fixed incident light wavelength. Different incident angles Measured IF displacement difference of the lower reflected beam The curve is obtained by denoising, smoothing and baseline correction of the IF displacement difference curve to obtain accurate displacement difference data.

[0011] Step 4: The theoretical IF displacement difference acquisition module treats the wafer under test as a uniform thin film, establishes a forward optical model, i.e., a theoretical IF relationship model, and then obtains the theoretical IF displacement difference. curve;

[0012] Step 5: The inversion calculation module will calculate the measured IF displacement difference. Curve and theoretical IF displacement difference The curve is inverted and fitted to obtain the thickness of the wafer thin film in each of the T effective measurement areas;

[0013] Step 6: The thickness non-uniformity evaluation module inputs the thickness of the wafer thin film in each region of the wafer under test into the wafer thin film thickness non-uniformity model to obtain the wafer thin film thickness non-uniformity evaluation result of the wafer under test.

[0014] Through the above design, this invention first avoids the influence of edge regions on the final result by excluding edge regions. Secondly, by dividing the effective measurement range of the wafer into T unconnected regions, the measured IF displacement difference of each measurement region is measured, and the theoretical IF displacement difference of each measurement region is calculated. Then, the film thickness information of each measurement region is fitted and input into the wafer film thickness non-uniformity model, ultimately obtaining the wafer film thickness non-uniformity evaluation result for the wafer under test.

[0015] The method provided by this invention utilizes the sub-picometer thickness resolution of IF displacement and the radially weighted edge enhancement characteristics to accurately capture minute thickness fluctuations at the wafer edge, achieving precise measurement of the thin film thickness in each measurement area of ​​the wafer under test, and significantly improving the measurement accuracy of wafer thin film thickness non-uniformity. Furthermore, this invention employs a fully non-contact, non-destructive testing process, eliminating the risk of wafer scratches and contamination, and can directly inspect product wafers. It is compatible with the entire process monitoring of semiconductor mass production, possessing strong practicality and safety.

[0016] The full name of the IF displacement is Imbert-Fedorov displacement.

[0017] Preferably, in step 3, when measuring using the IF displacement measuring device, the wafer thin film structure to be tested is the substrate-wafer thin film layer-dielectric layer; the wafer thin film layer is a wafer thin film layer deposited on the substrate.

[0018] Preferably, in step 4, the theoretical IF displacement difference of the wafer under test... The calculation expression is as follows:

[0019] (1);

[0020] (2);

[0021] (3);

[0022] (4);

[0023] (5);

[0024] (6);

[0025] In this context, the subscript TM indicates a TM-polarized wave, and the subscript TE indicates a TE-polarized wave. For spatial IF displacement, For IF angular displacement, Indicates the spread angle of the incident beam. Angle of incidence For the beam waist, Indicates the wavelength of the incident light. The theoretical IF displacement difference between TM and TE polarized waves. This represents the total IF shift of the TM-polarized wave. This represents the total IF shift of the TE-polarized wave. Indicates the IF displacement coefficient. It is the virtual part. Represents the reflection coefficient. This represents the imaginary part of the IF displacement coefficient. This represents the real part of the IF displacement coefficient. This indicates the transmission distance of the reflected light.

[0026] Preferably, the optical transmission coefficients of TM and TE polarized waves from different layers are preferred. The expression for calculating the reflection coefficient r is as follows:

[0027] (7);

[0028] (8);

[0029] (9);

[0030] (10);

[0031] in, , Indicates the basal layer. Indicates the wafer thin film layer. Indicates the dielectric layer. This represents the optical transmission coefficient of the TM-polarized wave in layer j. This represents the optical transmission coefficient of the TE-polarized wave in layer j. Let J be the dielectric constant of layer j. Let J be the incident angle of layer j. The reflection coefficient of the TE-polarized wave. The reflection coefficient of a TM polarized wave. It is the characteristic matrix of light in a wafer thin film. Representing matrices respectively The four elements in; The phase factor of the wafer thin film layer. The virtual part, The thickness of the wafer's thin film layer.

[0032] Preferably, in step 5, the evaluation function for the wafer thin film thickness of each of the T effective measurement regions obtained by inversion fitting is:

[0033] (11);

[0034] in, For the first Index of measurement areas, ; The number of incident angles. For the first An angle of incidence, ; Indicates the first The first one extracted from the curve of the relationship between the incident angle and the IF displacement difference in the measurement area. The IF displacement difference between the reference points; The first IF relationship calculated using the theoretical IF relation model Displacement difference between measurement areas; For the first Wafer thin film thickness in each measurement region;

[0035] The inversion calculation module evaluates the minimum value of the function. The corresponding theoretical wafer thin film thickness As the first The thickness output of the wafer thin film in each measurement area.

[0036] Preferably, the expression for the wafer thin film thickness non-uniformity model is:

[0037] (12);

[0038] (13);

[0039] in, Indicates the first The distance from the center point of each measurement region to the wafer center is given by R, where R is the wafer radius, h is the edge enhancement factor, m is the weighting exponent, and T is the total number of measurement regions. Let T be the average film thickness of the measurement areas. For radial weighting function, This is the output result of the wafer thin film thickness non-uniformity model.

[0040] Preferably, the size of the wafer under test is in the range of 4 to 12 inches; the substrate is made of silicon, silicon carbide (SiC), gallium nitride (GaN), or aluminum oxide. Or quartz crystal.

[0041] Preferably: the incident angle The angle range is 0° to 90°, and the incident light wavelength is... It is any fixed wavelength within the visible light range.

[0042] The beneficial effects of this invention are:

[0043] (1) This invention utilizes the subpicometer-level thickness resolution of IF displacement and the radial weighted edge enhancement characteristics to accurately capture minute thickness fluctuations at the wafer edge, thus solving the problem of seriously underestimating edge inhomogeneity in traditional methods;

[0044] (2) The present invention is a non-contact, non-destructive testing process with no risk of wafer scratches or contamination. It can directly test product wafers and is compatible with the entire process monitoring of semiconductor mass production. Attached Figure Description

[0045] Figure 1 This is a flowchart of the method of the present invention;

[0046] Figure 2 This is a block diagram of the wafer thin film thickness non-uniformity measurement system in the embodiment;

[0047] Figure 3 This is a diagram showing the division of the wafer thin film measurement area in the embodiment;

[0048] Figure 4 This is a schematic diagram of the IF displacement on the wafer surface in the embodiment;

[0049] Figure 5 This is a schematic diagram of the IF displacement measuring device in the embodiment;

[0050] Figure 6 This is a comparison chart of the incident angle-IF displacement difference curve obtained in the embodiment and the calculated curve. Detailed Implementation

[0051] The present invention will be further described in detail below with reference to the accompanying drawings and specific examples. The following embodiments or drawings are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0052] like Figure 1 As shown, a method for measuring the non-uniformity of wafer thin film thickness includes the following steps:

[0053] Step 1: Construct a wafer thin film thickness non-uniformity measurement system, such as... Figure 2 As shown, the wafer thin film thickness non-uniformity measurement system is equipped with a measurement region division module. The measurement region division module is connected in parallel to a measured IF displacement difference acquisition module and a theoretical IF displacement difference acquisition module. The measured IF displacement difference acquisition module and the theoretical IF displacement difference acquisition module are connected to the same inversion calculation module, which is also connected to a thickness non-uniformity evaluation module. The thickness non-uniformity evaluation module has a built-in wafer thin film thickness non-uniformity model.

[0054] Step 2: The measurement area division module acquires the wafer to be tested, excludes the edge areas of the wafer, and then divides the effective measurement range of the wafer into T non-contiguous regions, such as... Figure 3 As shown;

[0055] Step 3: The measured IF displacement difference acquisition module utilizes an IF displacement measuring device, such as... Figure 4 As shown, linearly polarized light is incident on the wafer under test to obtain the wafer under test at a fixed incident light wavelength. Different incident angles Measured IF displacement difference of the lower reflected beam The curve is obtained by denoising, smoothing and baseline correction of the IF displacement difference curve to obtain accurate displacement difference data.

[0056] Step 4: The theoretical IF displacement difference acquisition module treats the wafer under test as a uniform thin film, establishes a forward optical model, i.e., a theoretical IF relationship model, and then obtains the theoretical IF displacement difference. curve;

[0057] Step 5: The inversion calculation module will calculate the measured IF displacement difference. Curve and theoretical IF displacement difference The curve is inverted and fitted to obtain the thickness of the wafer thin film in each of the T effective measurement areas;

[0058] Step 6: The thickness non-uniformity evaluation module inputs the thickness of the wafer thin film in each region of the wafer under test into the wafer thin film thickness non-uniformity model to obtain the wafer thin film thickness non-uniformity evaluation result of the wafer under test.

[0059] In step 3, when measuring using the IF displacement measuring device, the wafer thin film structure to be tested is the substrate-wafer thin film layer-dielectric layer; the wafer thin film layer is a wafer thin film layer deposited on the substrate.

[0060] In step 4, the theoretical IF displacement difference of the wafer under test The calculation expression is as follows:

[0061] (1);

[0062] (2);

[0063] (3);

[0064] (4);

[0065] (5);

[0066] (6);

[0067] In this context, the subscript TM indicates a TM-polarized wave, and the subscript TE indicates a TE-polarized wave. For spatial IF displacement, For IF angular displacement, Indicates the spread angle of the incident beam. Angle of incidence For the beam waist, Indicates the wavelength of the incident light. The theoretical IF displacement difference between TM and TE polarized waves. This represents the total IF shift of the TM-polarized wave. This represents the total IF shift of the TE-polarized wave. Indicates the IF displacement coefficient. It is the virtual part. Represents the reflection coefficient. This represents the imaginary part of the IF displacement coefficient. This represents the real part of the IF displacement coefficient. This indicates the transmission distance of the reflected light.

[0068] Optical transfer coefficients of TM and TE polarized waves in different layers The expression for calculating the reflection coefficient r is as follows:

[0069] (7);

[0070] (8);

[0071] (9);

[0072] (10);

[0073] in, , Indicates the basal layer. Indicates the wafer thin film layer. Indicates the dielectric layer. This represents the optical transmission coefficient of the TM-polarized wave in layer j. This represents the optical transmission coefficient of the TE-polarized wave in layer j. Let J be the dielectric constant of layer j. Let J be the incident angle of layer j. The reflection coefficient of the TE-polarized wave. The reflection coefficient of the TM polarized wave. It is the characteristic matrix of light in a wafer thin film. Representing matrices respectively The four elements in; The phase factor of the wafer thin film layer. The virtual part, The thickness of the wafer's thin film layer.

[0074] In step 5, the evaluation function for the wafer thin film thickness in each of the T effective measurement regions is obtained through inversion fitting:

[0075] (11);

[0076] in, For the first Index of measurement areas, ; The number of incident angles. For the first An angle of incidence, ; Indicates the first The first one extracted from the curve of the relationship between the incident angle and the IF displacement difference in the measurement area. The IF displacement difference between the reference points; The first IF relationship calculated using the theoretical IF relation model Displacement difference between measurement areas; For the first Wafer thin film thickness in each measurement region;

[0077] The inversion calculation module evaluates the minimum value of the function. The corresponding theoretical wafer thin film thickness As the first The thickness output of the wafer thin film in each measurement area.

[0078] The expression for the wafer thin film thickness non-uniformity model is as follows:

[0079] (12);

[0080] (13);

[0081] in, Indicates the first The distance from the center point of each measurement region to the wafer center is given by R, where R is the wafer radius, h is the edge enhancement factor, m is the weighting exponent, and T is the total number of measurement regions. Let T be the average film thickness of the measurement areas. For radial weighting function, This is the output result of the wafer thin film thickness non-uniformity model.

[0082] The size of the wafer under test ranges from 4 to 12 inches; the substrate is made of silicon-based, silicon carbide (SiC), gallium nitride (GaN), or aluminum oxide. Or it could be quartz crystal.

[0083] The angle of incidence The angle range is 0° to 90°, and the incident light wavelength is... It is any fixed wavelength within the visible light range.

[0084] like Figure 5 As shown, the IF displacement measuring device is equipped with a laser, a half-wave plate, a first focusing lens, a first polarizer, a second focusing lens, a second polarizer, and a camera.

[0085] wherein the laser is configured to emit incident laser light of a fixed wavelength, the incident laser light sequentially passes through a 1 / 2 wave plate, a first focusing lens and a first polarizer to reach the wafer thin film, and is reflected by the wafer thin film to generate reflected light, and the reflected light sequentially passes through a second polarizer and a second focusing lens and then is captured by a camera.

[0086] In this embodiment, a structure model of wafer substrate - wafer thin film - medium is adopted. Specifically, the substrate is a silicon substrate, the medium is selected as air, the wafer thin film is silicon dioxide, the wafer size is 4 inches (101.6 mm), its optical constants are measured by an ellipsometer, the edge is excluded by 3 mm, the effective radius R is 47.8 mm, which is divided into 49 effective measurement areas, the incident wavelength is 632.8 nm, the incident angle range selected in the experiment is 30° to 90°, and the solution domain of the wafer thin film thickness d is (0, 200] nm. Taking area 20 as an example, the incident angle-IF displacement difference obtained under this area in the experiment is substituted into the evaluation function, and the thin film thickness d obtained when the evaluation function reaches the minimum value is 99.8 nm, and the average thickness of the 49 measurement areas is 100 nm. From Figure 6 it can be seen that the fitted theoretical IF displacement difference curve is almost consistent with the measured IF displacement difference curve obtained in the experiment. Then, the edge enhancement coefficient h is set to 2, and the weight index m is set to 2. The radial distance from the measurement point of each measurement area to the center of the wafer is calculated, and the weight is calculated according to formula (13). The central area, that is, t < 16 mm: average weight ≈ 1.1; the middle area, that is, 16 mm < t < 32 mm: average weight ≈ 1.8; the edge area, that is, t > 32 mm: average weight ≈ 2.7. Based on formula (12), =0.68, so the radial weighted non-uniformity RWU of the wafer to be measured is 0.68%.

[0087] The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and variations. Any modifications, equivalent substitutions, improvements and the like made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for measuring the non-uniformity of wafer thin film thickness, characterized in that, Includes the following steps: Step 1: Construct a wafer thin film thickness non-uniformity measurement system. This system includes a measurement region division module, which is connected in parallel to a measured IF displacement difference acquisition module and a theoretical IF displacement difference acquisition module. These two modules are connected to the same inversion calculation module, which is also connected to a thickness non-uniformity evaluation module. The thickness non-uniformity evaluation module contains a built-in wafer thin film thickness non-uniformity model. Step 2: The measurement area division module acquires the wafer to be tested, excludes the edge area of ​​the wafer to be tested, and then divides the effective measurement range of the wafer to be tested into T non-connected areas; Step 3: The measured IF displacement difference acquisition module uses an IF displacement measuring device to incident linearly polarized light onto the wafer under test, and acquires the measured IF displacement difference at a fixed incident light wavelength. Different incident angles Measured IF displacement difference of the lower reflected beam curve; Step 4: The theoretical IF displacement difference acquisition module treats the wafer under test as a uniform thin film, establishes a theoretical IF relationship model, and then obtains the theoretical IF displacement difference. curve; Step 5: The inversion calculation module will calculate the measured IF displacement difference. Curve and theoretical IF displacement difference The curve is inverted and fitted to obtain the thickness of the wafer thin film in each of the T effective measurement areas; Step 6: The thickness non-uniformity evaluation module inputs the thickness of the wafer thin film in each region of the wafer under test into the wafer thin film thickness non-uniformity model to obtain the wafer thin film thickness non-uniformity evaluation result of the wafer under test.

2. The method for measuring the non-uniformity of wafer thin film thickness according to claim 1, characterized in that: In step 3, when measuring using the IF displacement measuring device, the wafer thin film structure to be tested is the substrate-wafer thin film layer-dielectric layer; the wafer thin film layer is a wafer thin film layer deposited on the substrate.

3. The method for measuring the non-uniformity of wafer thin film thickness according to claim 1, characterized in that: In step 4, the theoretical IF displacement difference of the wafer under test The calculation expression is as follows: （1）； （2）； （3）； （4）； （5）； （6）； In this context, the subscript TM indicates a TM-polarized wave, and the subscript TE indicates a TE-polarized wave. For spatial IF displacement, For IF angular displacement, Indicates the spread angle of the incident beam. Angle of incidence For the beam waist, Indicates the wavelength of the incident light. The theoretical IF displacement difference between TM and TE polarized waves. This represents the total IF shift of the TM-polarized wave. This represents the total IF shift of the TE-polarized wave. Indicates the IF displacement coefficient. It is the virtual part. Represents the reflection coefficient. This represents the imaginary part of the IF displacement coefficient. This represents the real part of the IF displacement coefficient. This indicates the transmission distance of the reflected light.

4. The method for measuring the non-uniformity of wafer thin film thickness according to claim 2, characterized in that: Optical transfer coefficients of TM and TE polarized waves in different layers The expression for calculating the reflection coefficient r is as follows: （7）； （8）； （9）； （10）； in, , Indicates the basal layer. Indicates the wafer thin film layer. Indicates the dielectric layer. This represents the optical transmission coefficient of the TM-polarized wave in layer j. This represents the optical transmission coefficient of the TE-polarized wave in layer j. Let J be the dielectric constant of layer j. Let J be the incident angle of layer j. The reflection coefficient of the TE-polarized wave. The reflection coefficient of a TM polarized wave. It is the characteristic matrix of light in a wafer thin film. Representing matrices respectively The four elements in; The phase factor of the wafer thin film layer. The virtual part, The thickness of the wafer's thin film layer.

5. The method for measuring the non-uniformity of wafer thin film thickness according to claim 1, characterized in that: In step 5, the evaluation function for the wafer thin film thickness in each of the T effective measurement regions is obtained through inversion fitting: （11）； in, For the first Index of measurement areas, ; The number of incident angles. For the first An angle of incidence, ; Indicates the first The first one extracted from the curve of the relationship between the incident angle and the IF displacement difference in the measurement area. The IF displacement difference between the reference points; The first IF relationship calculated using the theoretical IF relation model Displacement difference between measurement areas; For the first Wafer thin film thickness in each measurement region; The inversion calculation module evaluates the minimum value of the function. The corresponding theoretical wafer thin film thickness As the first The thickness output of the wafer thin film in each measurement area.

6. The method for measuring the non-uniformity of wafer thin film thickness according to claim 1, characterized in that: The expression for the wafer thin film thickness non-uniformity model is as follows: （12）； （13）； in, Indicates the first The distance from the center point of each measurement region to the wafer center is given by R, where R is the wafer radius, h is the edge enhancement factor, m is the weighting exponent, and T is the total number of measurement regions. Let T be the average film thickness of the measurement areas. For radial weighting function, This is the output result of the wafer thin film thickness non-uniformity model.

7. The method for measuring the non-uniformity of wafer thin film thickness according to claim 2, characterized in that: The size of the wafer under test ranges from 4 to 12 inches; the substrate is made of silicon-based material, silicon carbide (SiC), gallium nitride (GaN), or aluminum oxide. Or quartz crystal.

8. The method for measuring the non-uniformity of wafer thin film thickness according to claim 1, characterized in that: The angle of incidence The angle range is 0° to 90°, and the incident light wavelength is... It is any fixed wavelength within the visible light range.

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