Overlay error measurement accuracy evaluation method

Abstract

The present invention provides an overlay error measurement accuracy evaluation method, comprising: setting an overlay mark; completing the photolithography and etching process of a front layer, and forming the front layer overlay mark on the front layer; completing the photolithography of the current layer for the first time, and measuring the overlay error of the current layer to the front layer; generating a compensation value based on the first overlay error measurement result, and generating a preset special compensation value in a special area; reworking the wafer, and performing a secondary exposure based on the generated compensation value; measuring the overlay error after the secondary exposure again, and performing a correlation analysis between the preset special compensation value and the measured special compensation value, or performing a correlation analysis between the actual measured overlay error after compensation and the predicted overlay error after compensation; and judging the measurement accuracy based on the correlation analysis result. The present invention is convenient and fast for evaluating the measurement method on the line; it is relatively flexible, and the wafer edge mark is prevented from being affected by other process steps by setting the special compensation value of the special area.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor integrated circuit manufacturing, and in particular relates to an overlay error measurement accuracy evaluation method. Background Art

[0002] Overlay (OVL) stability is crucial for mass production lithography processes and is key to improving process capabilities and expanding the process window. As the minimum linewidth of integrated circuit manufacturing processes continues to shrink, the requirements for overlay error in advanced node manufacturing processes are becoming increasingly stringent. Inaccurate measurement results can disrupt the overlay error control system, directly affecting lithography process stability and, in severe cases, even causing yield issues. Therefore, the ability to quickly evaluate overlay error measurement results is becoming increasingly important.

[0003] Currently, there are two main overlay error measurement methods in the industry: the earlier developed image-based overlay (IBO) and the more recently adopted diffraction-based overlay (DBO) method at advanced nodes. In addition to the influence of the process, the accuracy of both methods is also affected by the design of the overlay mark and the parameters of the measurement program.

[0004] Previously, the most commonly used method for evaluating overlay error measurement accuracy was CD-SEM after etching. While this method offers high accuracy, it requires the design of specific markers for measurement, which consumes a significant amount of mask area. Furthermore, CD-SEM measurement speeds are slow, and performing a large number of measurements consumes significant machine time, severely impacting wafer fab output. Etched wafers cannot be reprocessed for further evaluation, resulting in very high evaluation costs. Alternatively, the industry has used slicing to evaluate overlay error, but this method is destructive and can only be performed at specific points, making it impossible to collect large amounts of data for evaluation. Summary of the Invention

[0005] The purpose of the present invention is to provide a method for evaluating the accuracy of overlay error measurement, which can conveniently and quickly evaluate the online measurement method; it has great flexibility and can eliminate the influence of other process on the wafer edge mark by setting special compensation values ​​for special areas.

[0006] The present invention provides a method for evaluating overlay error measurement accuracy, comprising:

[0007] S1. Setting an overlay mark, wherein the overlay mark includes a matching previous layer overlay mark and a current layer overlay mark, and setting an overlay error measurement program;

[0008] S2. The wafer includes a front layer and a current layer. The photolithography and etching processes of the front layer are completed, and an overlay mark of the front layer is formed on the front layer.

[0009] S3, completing the photolithography process of the current layer for the first time, and measuring the overlay error of the current layer with respect to the previous layer using the measurement program;

[0010] S4. Generating an overlay error compensation value according to the first overlay error measurement result, specifically generating a common compensation value for a common area of ​​the layer and generating a preset special compensation value for a special area;

[0011] S5, reworking the wafer after the exposure in S3, and performing a second exposure according to the compensation value generated in S4;

[0012] S6. Using the measurement formula again to measure the overlay error after the second exposure, performing a correlation analysis between the preset special compensation value and the measured special compensation value, or performing a correlation analysis between the overlay error actually measured after compensation and the overlay error predicted after compensation;

[0013] S7. Determine the measurement accuracy based on the correlation analysis results.

[0014] Furthermore, the overlay mark includes at least one of a box mark, a line mark, and an advanced image measurement mark.

[0015] Furthermore, the measurement procedure includes: an image-based overlay error measurement method and a diffraction-based overlay error measurement method.

[0016] Furthermore, the wafer includes multiple shots, a portion of the shots are selected as special areas, and the remaining shots are selected as common areas.

[0017] Furthermore, the preset special compensation value is a compensation value set according to a certain gradient in different special areas based on the ordinary compensation value; the different preset special compensation values ​​that change according to a certain gradient are correspondingly distributed in different special areas.

[0018] Furthermore, the preset special compensation value includes at least one of the mask rotation Rx, Ry in the X / Y direction and the mask magnification Mx, My in the X / Y direction.

[0019] Furthermore, the preset special compensation values ​​may also include: X / Y direction translation transformation Tx, Ty, symmetric field rotation Rzs, asymmetric field rotation Rza, symmetric field magnification Ms, asymmetric field magnification Ma, scanning deflection α, scanning zoom β and at least one of other high-order exposure area internal compensation values.

[0020] Furthermore, when the slope K and the correlation coefficient R^2 of the fitting curve in the correlation analysis are both greater than 0.8, it is assessed that the measurement is accurate.

[0021] Furthermore, the front layer includes any one of a substrate layer, a dielectric layer or a functional layer in the wafer; and the current layer includes a photoresist layer or a layer having a function similar to that of a photoresist.

[0022] Furthermore, the linear fitting of the correlation analysis adopts the least square method to fit the curve by minimizing the sum of squares of errors from data points to the fitting curve; or adopts the spline interpolation method to fit by establishing a smooth curve between data points; or adopts the polynomial regression method to perform curve fitting.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present invention provides an overlay error measurement accuracy evaluation method, comprising: S1, setting an overlay mark and a measurement program; S2, a wafer including a front layer and a current layer, completing the photolithography and etching processes of the front layer, and forming the front layer overlay mark on the front layer; S3, completing the photolithography process of the current layer for the first time, and using the measurement program to measure the overlay error of the current layer relative to the front layer; S4, generating an overlay error compensation value based on the first overlay error measurement result, specifically generating an ordinary compensation value in the ordinary area of ​​the current layer and generating a preset special compensation value in the special area; S5, reworking the wafer after the exposure in S3, and performing a second exposure based on the compensation value generated in S4; S6, using the measurement program again to measure the overlay error after the second exposure, and performing a correlation analysis between the preset special compensation value and the special compensation value obtained by measurement, or performing a correlation analysis between the overlay error actually measured after compensation and the overlay error predicted after compensation; S7, judging the measurement accuracy based on the correlation analysis result. The method for evaluating the accuracy of photolithography overlay error measurement of the present invention can conveniently and quickly evaluate the online measurement method; it is highly flexible and can eliminate the influence of other process on the wafer edge mark by setting a special compensation value for a special area. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the process of the overlay error measurement accuracy evaluation method of the present invention.

[0026] Figure 2 Schematic diagram of the common area and special area of ​​the layer in step S4 of the overlay error measurement accuracy evaluation method of the present invention.

[0027] Figure 3 It is a predicted wafer overlay error map after setting a special compensation value in a special area in the overlay error measurement accuracy evaluation method of the present invention.

[0028] Figure 4 It is a schematic diagram of the correlation between the special compensation value preset after rework and the special compensation value obtained by measurement.

[0029] Figure 5 Schematic diagram of the correlation between the actual measured overlay error after compensation and the predicted overlay error after compensation. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are in a very simplified form and are not to exact scale, and are only used for the purpose of conveniently and clearly illustrating the embodiments of the present invention.

[0031] For ease of description, some embodiments of the present application may use spatially relative terms such as "above," "below," "top," "below," etc. to describe the relationship between one element or component and another (or other) elements or components as shown in the various figures of the embodiments. It should be understood that, in addition to the orientations described in the figures, the spatially relative terms are also intended to include different orientations of the device in use or operation. For example, if the device in the figures is turned over, the elements or components described as being "below" or "beneath" other elements or components will subsequently be positioned as being "above" or "above" other elements or components. The terms "first," "second," etc., hereinafter, are used to distinguish between similar elements and are not necessarily used to describe a specific order or chronological sequence. It is to be understood that, where appropriate, these terms used in this manner are interchangeable.

[0032] The embodiment of the present invention provides a method for evaluating the accuracy of overlay error measurement, such as Figure 1 Shown, including:

[0033] S1. Setting an overlay mark, wherein the overlay mark includes a matching previous layer overlay mark and a current layer overlay mark, and setting an overlay error measurement program;

[0034] S2. The wafer includes a front layer and a current layer. The photolithography and etching processes of the front layer are completed, and an overlay mark of the front layer is formed on the front layer.

[0035] S3, completing the photolithography process of the current layer for the first time, and measuring the overlay error of the current layer with respect to the previous layer using the measurement program;

[0036] S4. Generating an overlay error compensation value according to the first overlay error measurement result, specifically generating a common compensation value for a common area of ​​the layer and generating a preset special compensation value for a special area;

[0037] S5, reworking the wafer after the exposure in S3, and performing a second exposure according to the compensation value generated in S4;

[0038] S6. Using the measurement formula again to measure the overlay error after the second exposure, performing a correlation analysis between the preset special compensation value and the measured special compensation value, or performing a correlation analysis between the overlay error actually measured after compensation and the overlay error predicted after compensation;

[0039] S7. Determine the measurement accuracy based on the correlation analysis results.

[0040] The following describes in detail the steps of the overlay error measurement accuracy evaluation method according to an embodiment of the present invention.

[0041] Step S1, set the overlay mark, the overlay mark matches the process; the overlay mark includes the matching previous layer overlay mark and the current layer overlay mark, and set the overlay error measurement program. The overlay mark includes but is not limited to box mark (Box-in-Box), line mark (Bar-in-Bar, BIB), advanced image measurement mark (Advanced Image Metrology, AIM) and other suitable marks. The overlay mark also includes new overlay marks that will appear in the future with the development of technology. The measurement program includes but is not limited to image-based overlay error (Image-Based Overlay, IBO) measurement method and diffraction-based overlay error (Diffraction-Based Overlay, DBO) measurement method. In addition to the influence of the process, the design of the overlay mark and the parameters of the measurement program will affect the accuracy of the measurement results of the two methods. IBO is composed of an inner and outer layer structure, representing the previous layer and the current layer respectively, and its graphic feature is a grating structure using periodic lines and space. By acquiring images and obtaining the center positions of the previous layer and the current layer through calculation, the corresponding displacement deviation is obtained and decomposed into the X and Y directions.

[0042] S2. The wafer includes a front layer and a current layer. The photolithography and etching processes are performed on the front layer, and the front layer overlay mark is formed on the front layer. In one example, the front layer is, for example, a substrate layer, a dielectric layer, or any other functional layer in the wafer; the current layer is, for example, a photoresist layer or a layer having a photoresist-like function, or other suitable layer.

[0043] S3. Complete the photolithography process of the current layer for the first time, and use the measurement program to measure the overlay error of the current layer to the previous layer.

[0044] The overlay error at a point in a chip circuit diagram can be expressed as the relative displacement of corresponding points on two wafer layers in a coordinate system. Mathematical models can be used to decompose the overlay error vectors of multiple points into various geometric deformations within the wafer plane or within the exposure unit area. Some of these deformations can be compensated for by moving the projection lens or exposure stage. Quantifying these geometric deformations yields control parameters for compensation.

[0045] Measure overlay marks at several locations on the wafer. Based on the coordinates and vectors of each mark, a vector equation model is established to describe the overlay error of the wafer. A point in the Cartesian coordinate system has coordinates (x, y), and the overlay error measurement vector at that point is (x', y'). This can be expressed as a polynomial equation.

[0046] x'=f(x,y)=T x +M xx x+M xy y+Cx 2 +Dxy+…

[0047] y'=g(x,y)=T y +M yx x+M yy y+Ey 2 +Fxy+…

[0048] Among them, T*, M*, C*, E*, D, F… are degree of freedom coefficients that are independent of x and y. They are usually divided into low-order parameters and high-order parameters according to the order of the x and y degrees of freedom. Order 0 to 2 are low-order, and order 3 and above are high-order. The higher the order, the more accurate it is.

[0049] S4. Generate an overlay error compensation value according to the first overlay error measurement result. Specifically, generate a common compensation value for a common area of ​​the layer and generate a preset special compensation value for a special area. Figure 2 Schematic diagram of the common area and special area of ​​the layer in step S4 of the overlay error measurement accuracy evaluation method of the present invention. Figure 2 As shown, the wafer includes multiple shots. The area framed by the yellow line represents a shot. A portion of the shots are selected as special areas (e.g., the red dot area) for this example only; the specific number of areas is not limited. The remaining shots are designated as normal areas. Normal compensation values ​​are generated for normal areas, and special compensation values ​​are generated for special areas. The preset special compensation values ​​are based on the normal compensation values ​​and are set according to a certain gradient for different special areas. Different preset special compensation values ​​that vary according to a certain gradient are distributed in different special areas.

[0050] The preset special compensation value includes at least one of: X / Y reticle rotation Rx, Ry; and X / Y reticle magnification Mx, My. The preset special compensation value may also include at least one of: X / Y translation transformation Tx, Ty; symmetric field rotation Rzs; asymmetric field rotation Rza; symmetric field magnification Ms; asymmetric field magnification Ma; scan skew α; scan zoom β; and other high-order exposure area internal compensation values.

[0051] A wafer contains multiple shots (exposure units). Typically, a field may contain multiple shots, and the lithography machine exposes each shot one by one. Exposing the entire chip requires sequentially exposing multiple fields to cover the entire chip area. In photolithography, a field refers to the area on the photomask that is exposed. A photomask typically consists of one or more fields. The lithography machine processes one field during each exposure, then completes the exposure of the entire chip field by field.

[0052] S5, reworking the wafer after the exposure in S3, and performing a second exposure according to the compensation value generated in S4;

[0053] S6. Use the measurement program again to measure the overlay error after the second exposure, and perform a correlation analysis between the preset special compensation value and the measured special compensation value, or perform a correlation analysis between the overlay error actually measured after compensation and the overlay error predicted after compensation.

[0054] S7. Determine the measurement accuracy based on the correlation analysis results.

[0055] Figure 3 It is the predicted wafer overlay error map after setting the compensation value in a specific exposure area. The wafer is manufactured by stacking multiple circuit layers. Overlay alignment marks are set on the layers of the wafer. The photolithography process performs exposure by looking for the overlay alignment marks, so that the patterns of two adjacent layers of the wafer are aligned. When the photolithography equipment performs photolithography processing on the wafer layer after overlay error compensation according to the preset reference position, the overlay alignment marks of each layer of the wafer layer correspond to the overlay alignment marks of each previous layer of the wafer. In this case, the overlay error distribution map of each position on the wafer is as follows: Figure 3 As shown in the figure, the length of the arrow indicates the size of the overlay error. Figure 3 It can be seen that after the second exposure, the overlay error at each position on the wafer is relatively small.

[0056] Figure 4 This is a schematic diagram showing the correlation between the special compensation value measured after rework and secondary exposure and the preset special compensation value Rx. Figure 4As shown, the compensation value is explained using the mask rotation Rx in the X direction as an example. The preset special compensation value is the compensation amount set according to a certain gradient in different special areas based on the ordinary compensation value. Different special compensation values ​​that change according to a certain gradient are distributed in different special areas. The preset special compensation value Rx is used as the X-axis, and the measured special compensation value Rx' is used as the Y-axis. Different preset special compensation values ​​(such as 1, 2, 3, etc.) are distributed in different special areas. Rework, secondary exposure, and development are performed; measurement is performed, and Rx' of the special area shot is fitted using a data polynomial.

[0057] Draw a scatter plot and perform a linear fit between the preset special compensation value Rx and the measured special compensation value Rx' to obtain the slope K and correlation coefficient R^2 of the fitting curve. The measurement is considered accurate when both K and R^2 are greater than 0.8. Specifically, the measurement is considered accurate when 0.8 < R^2 < 1.

[0058] Figure 5 This is a schematic diagram showing the correlation between the actual measured overlay error and the predicted overlay error after rework and secondary exposure. Figure 5 As shown, the X-axis represents the predicted overlay error after compensation (the predicted measurement result), and the Y-axis represents the actual measured overlay error. A linear fit is performed to obtain the slope K and R^2 of the fitting curve. When K and R^2 are greater than 0.8, the measurement is considered accurate.

[0059] Linear fitting can be performed by using the least squares method to fit the curve by minimizing the sum of squares of errors from data points to the fitted curve, or by using the spline interpolation method to fit by establishing a smooth curve between data points, or by using polynomial regression method to fit the curve.

[0060] The method for evaluating the accuracy of photolithography overlay error measurement of the present invention can conveniently and quickly evaluate the online measurement method; it is highly flexible and can eliminate the influence of other process on the wafer edge mark by presetting the special compensation value of the special area.

[0061] In summary, the present invention provides a method for evaluating the accuracy of overlay error measurement, including: S1, setting an overlay mark and a measurement program; S2, the wafer includes a front layer and a current layer, completing the lithography and etching processes of the front layer, and forming the front layer overlay mark on the front layer; S3, completing the lithography process of the current layer for the first time, and using the measurement program to measure the overlay error of the current layer to the front layer; S4, generating an overlay error compensation value based on the first overlay error measurement result, specifically generating an ordinary compensation value in the ordinary area of ​​the current layer, and generating a preset special compensation value in the special area; S5, reworking the wafer after the exposure in S3, and performing a second exposure according to the compensation value generated in S4; S6, using the measurement program again to measure the overlay error after the second exposure, and performing a correlation analysis between the preset special compensation value and the special compensation value obtained by measurement, or performing a correlation analysis between the overlay error actually measured after compensation and the overlay error predicted after compensation; S7, judging the measurement accuracy based on the correlation analysis result. The method for evaluating the accuracy of photolithography overlay error measurement of the present invention can conveniently and quickly evaluate the online measurement method; it is highly flexible and can eliminate the influence of other process on the wafer edge mark by setting a special compensation value for a special area.

[0062] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Reference can be made to the common and similar parts between the various embodiments. The methods disclosed in the embodiments are described briefly because they correspond to the devices disclosed in the embodiments. For relevant details, refer to the method description.

[0063] The above description is only a description of the preferred embodiment of the present invention, and does not limit the scope of the rights of the present invention. Any person skilled in the art can make possible changes and modifications to the technical solution of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for evaluating overlay error measurement accuracy, characterized in that: include: S1. Setting an overlay mark, wherein the overlay mark includes a matching previous layer overlay mark and a current layer overlay mark, and setting an overlay error measurement program; S2. The wafer includes a front layer and a current layer. The photolithography and etching processes of the front layer are completed, and an overlay mark of the front layer is formed on the front layer. S3, completing the photolithography process of the current layer for the first time, and measuring the overlay error of the current layer with respect to the previous layer using the measurement program; S4. Generating an overlay error compensation value according to the first overlay error measurement result, specifically generating a common compensation value for a common area of ​​the layer and generating a preset special compensation value for a special area; S5, reworking the wafer after the exposure in S3, and performing a second exposure according to the compensation value generated in S4; S6. Using the measurement formula again to measure the overlay error after the second exposure, performing a correlation analysis between the preset special compensation value and the measured special compensation value, or performing a correlation analysis between the overlay error actually measured after compensation and the overlay error predicted after compensation; S7. Determine the accuracy of the measurement based on the correlation analysis results; The wafer includes multiple shots, a portion of the shots are selected as special areas, and the remaining shots are selected as common areas; The preset special compensation value is a compensation value set according to a certain gradient in different special areas based on the ordinary compensation value; the different preset special compensation values ​​that change according to a certain gradient are correspondingly distributed in different special areas.

2. The overlay error measurement accuracy evaluation method according to claim 1, wherein: The overlay mark includes at least one of a box mark, a line mark, and an advanced image measurement mark.

3. The overlay error measurement accuracy evaluation method according to claim 1, wherein: The measurement procedures include: an image-based overlay error measurement method and a diffraction-based overlay error measurement method.

4. The overlay error measurement accuracy evaluation method according to claim 1, wherein: The preset special compensation value includes at least one of the mask rotation Rx, Ry in the X / Y direction and the mask magnification Mx, My in the X / Y direction.

5. The overlay error measurement accuracy evaluation method according to claim 1, wherein: The preset special compensation values ​​may also include: X / Y direction translation transformation Tx, Ty, symmetric field rotation Rzs, asymmetric field rotation Rza, symmetric field magnification Ms, asymmetric field magnification Ma, scanning deflection α, scanning zoom β and at least one of other high-order exposure area internal compensation values.

6. The overlay error measurement accuracy evaluation method according to claim 1, wherein: When the slope K and the correlation coefficient R^2 of the fitting curve in the correlation analysis are both greater than 0.8, the measurement is evaluated as accurate.

7. The overlay error measurement accuracy evaluation method according to claim 6, wherein: The front layer includes any one of a substrate layer, a dielectric layer or a functional layer in the wafer; the current layer includes a photoresist layer or a layer having a function similar to photoresist.

8. The overlay error measurement accuracy evaluation method according to claim 1, wherein: The linear fitting of the correlation analysis adopts the least square method to fit the curve by minimizing the sum of squares of errors from data points to the fitting curve; or adopts the spline interpolation method to fit by establishing a smooth curve between data points; or adopts the polynomial regression method to fit the curve.

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