Ion implantation angle calibration method

Abstract

This application provides an ion implantation angle calibration method for calibrating the angle of a target stage device in an ion implanter at different energy levels. The method includes: selecting multiple wafers and performing ion implantation on the corresponding wafers at different ion implantation angles; performing thermography on all ion-implanted wafers to obtain multiple data sets composed of ion implantation angles and thermography values; fitting a Gaussian function to all data sets with the ion implantation angle as the abscissa and the thermography value as the ordinate to obtain a Gaussian fitting curve; obtaining the angle calibration value based on the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve, and calibrating the angle of the target stage device. The calibration method of this application is applicable to the angle calibration of target stage devices in ion implanters at different energy levels.

Description

Technical Field

[0001] This application relates to the field of semiconductor manufacturing, and in particular to an ion implantation angle calibration method. Background Technology

[0002] Ion implantation is a crucial process for altering the electrical properties of semiconductor wafers. The accuracy of the ion implantation angle is critical to chip performance. Deviations in the ion implantation angle can cause deviations in the ion concentration at the target depth, which can be fatal to wafer acceptance testing (WAT). Therefore, to ensure the accuracy of the ion implantation angle, the platen of the ion implanter must be accurately calibrated along the x-axis, y-axis, and rotation angle reference points.

[0003] The V-curve measurement method is typically used to calibrate the ion implantation angle. Specifically, this method involves using multiple wafers and performing ion implantation processes at different angles. Because different ion implantation angles result in variations in the thermal wave (TW) measurement values ​​used to detect lattice damage, an ion implantation angle-thermal wave value curve is obtained. Then, a parabolic fitting method is used to confirm the x / y axes of the platen device and the reference points for the rotation angle.

[0004] However, while the parabolic fitting method has a good fitting effect for high-current, low-energy models, it often cannot fit medium-current, high-energy models well, thus significantly reducing the calibration accuracy of the ion implantation angle for medium-current, high-energy models. Summary of the Invention

[0005] The technical problem to be solved by this application is to provide an ion implantation angle calibration method, which is applicable to the angle calibration of the target stage device of ion implanters in different energy ranges.

[0006] To address the aforementioned technical problems, this application provides an ion implantation angle calibration method for calibrating the angle of the target stage device of an ion implanter at different energy levels. The method includes: selecting multiple wafers and performing ion implantation on the corresponding wafers using different ion implantation angles; performing thermal wave measurements on all ion-implanted wafers to obtain multiple data sets composed of ion implantation angles and thermal wave values; performing Gaussian function fitting based on all data sets with the ion implantation angle as the abscissa and the thermal wave value as the ordinate to obtain a Gaussian fitting curve; obtaining the angle calibration value based on the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve, and calibrating the angle of the target stage device.

[0007] In this embodiment of the application, the relationship of the Gaussian fitting curve is as follows:

[0008] Where X is the ion implantation angle; Y is the thermal wave value; a is a parameter related to the peak height of the Gaussian distribution; b is the ion implantation angle located in the middle of the Gaussian distribution; c is a parameter related to the half-width at half-maximum of the Gaussian distribution; and d is the thermal wave compensation parameter for Gaussian fitting.

[0009] In this embodiment, the initial value of 'a' is the difference between the maximum and minimum thermal wave values ​​in the data set; the initial value of 'b' is the ion implantation angle corresponding to the minimum thermal wave value in the data set; the initial value of 'c' is the difference between the ion implantation angle corresponding to the maximum and minimum thermal wave values ​​in the data set; and the initial value of 'd' is any value between the maximum and minimum thermal wave values ​​in the data set.

[0010] In this embodiment of the application, the least squares method or gradient descent method is used to fit all data sets, the initial value of a, the initial value of b, the initial value of c, and the initial value of d to obtain the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve.

[0011] In this embodiment, the geometric center of the wafer surface is taken as the origin, the straight line passing through the origin and parallel to the horizontal plane is taken as the x-axis, and the straight line passing through the origin and perpendicular to the x-axis is taken as the y-axis; when ion implantation is performed on the corresponding wafer using several ion implantation angles with the x-axis as the axis of symmetry, the obtained angle calibration value is the angle calibration value of the target stage device in the y-axis direction.

[0012] In this embodiment of the application, when ion implantation is performed on the corresponding wafer using several ion implantation angles with the y-axis as the axis of symmetry, the obtained angle calibration value is the angle calibration value of the target stage device in the x-axis direction.

[0013] In this embodiment, the wafer includes a notch mark, and the rotation angle of the notch mark relative to the center of the circle is the rotation angle of the target stage device; when ion implantation is performed on the corresponding wafer using different rotation angles, the obtained angle calibration value is the rotation angle calibration value of the target stage device.

[0014] In this embodiment, the angle calibration value of the target stage device in the x-axis or y-axis direction is equal to the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve.

[0015] In this embodiment, the rotation angle calibration value of the target stage device is equal to the absolute value of the difference between the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve and 180°.

[0016] In the embodiments of this application, when performing thermal wave measurements, there are at least three measurement points on each wafer, and the ratio of the variance to the mean of the measurement data obtained on the same wafer does not exceed 0.2.

[0017] In this embodiment of the application, if the ratio of the variance to the mean of the measurement data obtained on the same wafer exceeds 0.2, the measurement point is reselected.

[0018] In this embodiment of the application, the wafer is silicon. <100> And the crystal orientation error does not exceed 1°.

[0019] Compared with the prior art, the technical solution of this application takes into account the characteristic that the implanted ion depth conforms to the Gaussian distribution in the wafer, and proposes a method for ion implantation angle calibration based on Gaussian fitting function. It can fit the ion implantation angle-thermal wave value curve with high accuracy and is suitable for calibrating the x-axis / y-axis and rotation angle of the platen device of ion implanters in different energy ranges. Attached Figure Description

[0020] The following accompanying drawings describe in detail the exemplary embodiments disclosed in this application. The same reference numerals denote similar structures in several views of the drawings. Those skilled in the art will understand that these embodiments are non-limiting and exemplary, and the drawings are for illustrative purposes only and are not intended to limit the scope of this application. Other embodiments may similarly fulfill the inventive intent of this application. It should be understood that the drawings are not drawn to scale. Wherein:

[0021] Figure 1 This is a schematic diagram of ions incident on the wafer surface;

[0022] Figure 2 The distribution of the five incident angles with the x-axis as the axis of symmetry;

[0023] Figure 3 The ion implantation angle-thermal wave value curve is obtained by fitting a parabolic function.

[0024] Figure 4 The platen rotation angle-thermal wave value curve is obtained by fitting a parabolic function.

[0025] Figure 5 This is a flowchart of the ion implantation angle calibration method according to an embodiment of this application;

[0026] Figure 6 This is a scatter plot of data obtained in Example 1 with the ion implantation angle as the abscissa and the thermal wave value as the ordinate.

[0027] Figure 7 This is a comparison chart of Gaussian fitting and parabolic fitting in Example 1;

[0028] Figure 8 This is a scatter plot of data obtained in Example 2, with the ion implantation angle as the abscissa and the thermal wave value as the ordinate.

[0029] Figure 9 This is a comparison chart of Gaussian fitting and parabolic fitting in Example 2. Detailed Implementation

[0030] The following description provides specific application scenarios and requirements for this application, intended to enable those skilled in the art to make and use the content of this application. Various partial modifications to the disclosed embodiments will be apparent to those skilled in the art, and the general principles defined herein can be applied to other embodiments and applications without departing from the spirit and scope of this application. Therefore, this application is not limited to the embodiments shown, but rather to the widest scope consistent with the claims.

[0031] To improve the accuracy of ion implantation angles, precise calibration of the platen device along the x / y axes and at the rotation angle reference point is required. (Reference) Figure 1 The x / y axis and rotation angle are now defined to represent the Si on the ion-implanted wafer surface. <100> The geometric center is the origin O, the x-axis is a straight line passing through the origin O and parallel to the horizontal plane, and the y-axis is a straight line passing through the origin O and perpendicular to the x-axis. The Si surface of the wafer... <100> The notch is also provided, and the rotation angle of the notch relative to the center O is the rotation angle of the target stage of the ion implanter. Figure 1 In this context, θ is the angle between the ion beam direction and the y-axis direction, and A is the ion beam injection surface.

[0032] Currently, when calibrating the x / y axis and rotation angle reference angle of the platen device, ion implantation is performed on multiple wafers using a series of different ion implantation angles to obtain thermal wave values ​​at different ion implantation angles. Then, the ion implantation angle-thermal wave value curve is obtained through parabolic fitting. Based on the ion implantation angle-thermal wave value curve, it is determined whether the x / y axis reference angle and platen rotation angle of ion implantation have drifted.

[0033] Taking x-axis / y-axis angle calibration as an example, the calibration method for current medium-current high-energy lasers is explained. Ten wafers are selected, and five incident angles with the x-axis as the axis of symmetry are chosen: 1°, 0.5°, 0°, -0.5°, and -1°. Figure 2The distribution of five incident angles with the x-axis as the axis of symmetry is shown, with each incident angle corresponding to a set of angular coordinates. For example, (-1°, 0°), where -1° represents the angle between the projection of the ion beam incident direction onto the plane formed by the x-axis and the wafer normal, and 0° represents the angle between the projection of the ion beam incident direction onto the plane formed by the y-axis and the wafer normal, and the normal. Five more incident angles with the y-axis as the axis of symmetry are selected: 1°, 0.5°, 0°, -0.5°, and -1°. After ion implantation and thermoelectric wave measurement, a parabolic function is used to fit a curve with the ion implantation angle as the abscissa and the thermoelectric wave value as the ordinate. The angle corresponding to the lowest point of the curve is the axial reference zero point. The platen rotation angle calibration method is similar, but the selected angle differs. With a certain tilt angle, for example, rotation angles of 178°, 179°, 180°, 181°, and 182° are selected for ion implantation. The ion implantation angle-thermal wave value curve obtained by fitting a parabolic function is shown below. Figure 3 As shown, the platen rotation angle-thermal wave value curve is as follows: Figure 4 As shown.

[0034] refer to Figure 3 and Figure 4 When calibrating the target stage of a medium-current high-energy ion implanter, the ion implantation angle-thermal wave value curve and platen rotation angle-thermal wave value obtained by parabolic fitting method often have a large deviation from the measured data points. Therefore, when the angle corresponding to the lowest point of the curve is used as the reference zero point for calibration, there will be a large error, which reduces the calibration accuracy of the ion implantation angle.

[0035] Based on this, the present application provides an ion implantation angle calibration method, which uses a Gaussian fitting method to calibrate and calculate the ion implantation angle, and can meet the accuracy requirements of ion implantation angle calibration for ion beams of different energy ranges.

[0036] refer to Figure 5 The ion implantation angle calibration method of this application embodiment can be used not only for angle calibration of high-current, low-energy ion implanters, but also for angle calibration of medium-current, high-energy ion implanters. The method may include:

[0037] Step S1: Select multiple wafers and perform ion implantation on the corresponding wafers using different ion implantation angles;

[0038] Step S2: Perform thermal wave measurements on all ion-implanted wafers to obtain multiple data sets consisting of ion implantation angle and thermal wave value;

[0039] Step S3: Using the ion implantation angle as the abscissa and the thermal wave value as the ordinate, perform Gaussian function fitting based on all data sets to obtain a Gaussian fitting curve;

[0040] Step S4: Obtain the angle calibration value based on the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve, and perform angle calibration on the target stage device.

[0041] The wafer used for ion implantation is silicon. <100> Furthermore, the crystal orientation error does not exceed 1° to improve calibration accuracy. The different ion implantation angles selected are related to the angle to be calibrated. For example, to calibrate the angle of platen in the y-axis direction, several ion implantation angles with the x-axis as the axis of symmetry are used; to calibrate the angle of platen in the x-axis direction, several ion implantation angles with the y-axis as the axis of symmetry are used; to calibrate the rotation angle of platen, the angles of platen in the x-axis and y-axis directions are fixed, while the rotation angle of the notch mark on the wafer relative to the center is changed.

[0042] Each wafer is assigned to one specific ion implantation angle for the ion implantation process. For example, if five incident angles with the x-axis as the axis of symmetry are selected, five wafers should be selected accordingly. The selected ion implantation angles should have a certain gradient, generally not exceeding 1°. As an example, 1°, 0.5°, 0°, -0.5°, and -1° with the x-axis as the axis of symmetry can be selected. When performing ion implantation on wafers, in addition to the desired angle, other parameters such as the type and concentration of dopant ions and the implantation energy must be kept consistent.

[0043] After ion implantation, thermography is performed on all ion-implanted wafers, so that each ion implantation angle corresponds to a thermography value, obtaining several data sets consisting of the ion implantation angle and the corresponding thermography value. These data sets are used for subsequent Gaussian function fitting. During thermography measurement, there are at least two measurement points on each wafer. In some embodiments, the ratio of the variance to the mean of the measurement data obtained on the same wafer does not exceed 0.2. If the ratio exceeds 0.2, the measurement points are reselected to improve calibration accuracy. In some embodiments, a scatter plot or histogram can be obtained by plotting the ion implantation angle on the x-axis and the thermography value on the y-axis.

[0044] Unlike the current parabolic fitting method, this embodiment uses a Gaussian function with the ion implantation angle as the abscissa and the thermal wave value as the ordinate to fit all data sets with a Gaussian function, obtaining a Gaussian fitting curve. The relationship of the Gaussian fitting curve is as follows:

[0045]

[0046] In the Gaussian fitting curve equation, X represents the ion implantation angle, and Y represents the thermowave value at ion implantation angle X. 'a' is a parameter related to the peak height of the Gaussian distribution, with an initial value of 'a' being the difference between the maximum and minimum thermowave values ​​in the data set. 'b' is the ion implantation angle located at the middle position of the Gaussian distribution, with an initial value of 'b' corresponding to the minimum thermowave value in the data set. 'c' is a parameter related to the half-width at half-maximum (WHM) of the Gaussian distribution, with an initial value of 'c' being the difference between the ion implantation angles corresponding to the maximum and minimum thermowave values ​​in the data set. 'd' is the thermowave compensation parameter for the Gaussian fitting, with an initial value of any value between the maximum and minimum thermowave values ​​in the data set.

[0047] The angle calibration value is obtained based on the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve, and the target stage device is then calibrated. In this embodiment, the least squares method or gradient descent method can be used to fit all data sets, the initial values ​​of a, b, c, and d, achieving a fitting accuracy of 0.000001, thus obtaining the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve. If the ion implantation angle used in the ion implantation process is symmetrical about the x-axis, the obtained angle calibration value is the y-axis angle calibration value of the target stage device, and the target stage device is calibrated in the y-axis direction. Similarly, if the ion implantation angle used in the ion implantation process is symmetrical about the x-axis, the obtained angle calibration value is the y-axis angle calibration value of the target stage device, and the target stage device is calibrated in the y-axis direction. If the ion implantation angle used in the ion implantation process is symmetrical about the y-axis, the obtained angle calibration value is the y-axis angle calibration value of the target stage device, and the target stage device is calibrated in the x-axis direction. If the rotation angle of the target stage device is changed during the ion implantation process, the obtained angle calibration value is the rotation angle calibration value of the target stage device, and the target stage device is calibrated in the rotation angle. The angle calibration value of the target stage device in the x-axis or y-axis direction is equal to the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve. The rotation angle calibration value of the target stage device is equal to the absolute value of the difference between the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve and 180°.

[0048] Example 1

[0049] Since the calibration methods for the x-axis and y-axis angles of the target stage are similar, this embodiment uses the y-axis angle calibration as an example. Five wafers were selected, boron was used as the dopant ions, and the implantation energy was 700 keV. Five ion implantation angles (1°, 0.5°, 0°, -0.5°, and -1°) with the x-axis as the axis of symmetry were selected for the ion implantation process. Afterwards, thermal wave values ​​were measured, resulting in five sets of data as shown in Table 1. The ion implantation angle was plotted on the x-axis, and the thermal wave value on the y-axis, as shown in Table 1. Figure 6 The data scatter plot shown.

[0050] Table 1. Measurement results of thermal wave values

[0051] -1° 622 -0.5° 581 0° 534 0.5° 580 1° 624

[0052] The Gaussian function fitting method is used, where X represents the ion implantation angle and Y is the corresponding thermal wave value. The fitting formula is as follows:

[0053]

[0054] Based on five sets of data, the difference between the maximum and minimum thermal wave values ​​is 44, which is used as the initial value of 'a' in the fitting formula. The difference between the ion implantation angle corresponding to the maximum thermal wave value and the ion implantation angle corresponding to the minimum thermal wave value is calculated to be 1, and this is used as the initial value of 'c' in the fitting formula. The ion implantation angle corresponding to the minimum thermal wave value, 0°, is used as the initial value of 'b'. In this embodiment, 624 is selected as the initial value of 'd'.

[0055] Five sets of data were fitted using the gradient descent method with a fitting accuracy of 0.000001, yielding a corresponding b value of 0.001631. This 0.001631° represents the Y-axis angle calibration value for the platen device. Parabolic fitting was then performed on the same five sets of data using the same fitting accuracy. The resulting fitting comparison graph can be found in [reference needed]. Figure 7 .Depend on Figure 7 It is evident that the Gaussian function fitting method in this application embodiment is more suitable for the y-axis angle calibration of the target stage device.

[0056] Example 2

[0057] Five wafers were selected, and boron was used as the dopant ion. The implantation energy was 700 keV. Ion implantation was performed at five rotation angles (178°, 179°, 180°, 181°, and 182°) of the platen at a 35° ion implantation angle. Thermometer values ​​were then measured, resulting in five sets of data as shown in Table 2. The ion implantation angle was plotted on the x-axis, and the thermometer value on the y-axis. Figure 8 The data scatter plot shown.

[0058] Table 2. Thermal wave value measurement results

[0059] 178° 657 179° 608 180° 584 181° 633 182° 658

[0060] The Gaussian function fitting method is used, where X represents the ion implantation angle and Y is the corresponding thermal wave value. The fitting formula is as follows:

[0061]

[0062] Based on five sets of data, the difference between the maximum and minimum thermal wave values ​​is 74, which is used as the initial value of 'a' in the fitting formula. The difference between the ion implantation angle corresponding to the maximum thermal wave value and the ion implantation angle corresponding to the minimum thermal wave value is calculated to be 2, and this is used as the initial value of 'c' in the fitting formula. The ion implantation angle corresponding to the minimum thermal wave value, 180°, is used as the initial value of 'b'. In this embodiment, 658 is selected as the initial value of 'd'.

[0063] Five sets of data were fitted using gradient descent with a fitting accuracy of 0.000001, yielding a b value of 179.7866. Therefore, the required rotation angle of the platen device is 0.2134° (180° - 179.7866°). Parabolic fitting was then performed on the five sets of data using the same fitting accuracy. The resulting fitting comparison graph can be found in [reference needed]. Figure 9 .Depend on Figure 9 It is evident that the Gaussian function fitting method of this application embodiment is more suitable for the rotation angle calibration of the target stage device.

[0064] In summary, the method for calculating ion implantation angle calibration based on Gaussian fitting function proposed in this application takes into account the characteristic that the implanted ion depth conforms to a Gaussian distribution in the wafer, and can accurately fit the ion implantation angle-thermal wave value curve. It is suitable for the x-axis / y-axis and rotation angle calibration of platen devices of ion implanters with different energy ranges.

[0065] After reading this application, those skilled in the art will understand that the foregoing application content is presented by way of example only and is not restrictive. Although not explicitly stated herein, those skilled in the art will understand that this application is intended to encompass various reasonable changes, improvements, and modifications to the embodiments. These changes, improvements, and modifications are all within the spirit and scope of the exemplary embodiments of this application. It should be understood that the terms "comprising," "including," "including," or "comprises," when used in this application, specify the presence of the described features, integrals, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components, and / or groups thereof.

[0066] Furthermore, this application specification describes exemplary embodiments by referring to idealized exemplary cross-sectional views and / or plan views and / or perspective views. Therefore, differences from the illustrated shapes are foreseeable due to factors such as manufacturing techniques and / or tolerances. Thus, exemplary embodiments should not be construed as limited to the shapes of the regions shown herein, but should include deviations in shape caused, for example, by manufacturing processes. For instance, etched areas shown as rectangular typically have circular or curved features. Therefore, the regions shown in the figures are substantially schematic, and their shapes are not intended to illustrate the actual shape of the regions of the device, nor are they intended to limit the scope of the exemplary embodiments.

Claims

1. A method of ion implantation angle calibration, characterized by, The method for calibrating the angle of the target stage device for ion implanters at different energy levels includes: Multiple wafers were selected, and ion implantation was performed on the corresponding wafers using different ion implantation angles; Thermal measurements were performed on all ion-implanted wafers to obtain multiple data sets consisting of ion implantation angle and thermal wave value; Using the ion implantation angle as the abscissa and the thermal wave value as the ordinate, Gaussian function fitting is performed on all data sets to obtain a Gaussian fitting curve. An angle calibration value is obtained based on the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve, and the target stage device is then calibrated at the angle. The relationship of the Gaussian fitting curve is as follows: ； Where X is the ion implantation angle; Y is the thermowave value; a is a parameter related to the peak height of the Gaussian distribution, and the initial value of a is the difference between the maximum and minimum thermowave values ​​in the data set; b is the ion implantation angle located at the middle position of the Gaussian distribution, and the initial value of b is the ion implantation angle corresponding to the minimum thermowave value in the data set; c is a parameter related to the half-width at half-maximum (WHM) of the Gaussian distribution, and the initial value of c is the difference between the ion implantation angle corresponding to the maximum and minimum thermowave values ​​in the data set; d is the thermowave compensation parameter for Gaussian fitting, and the initial value of d is any value between the maximum and minimum thermowave values ​​in the data set.

2. The ion implantation angle calibration method of claim 1, wherein, The least squares method or gradient descent method is used to fit all data sets, the initial values ​​of a, b, c, and d to obtain the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve.

3. The ion implantation angle calibration method of claim 1, wherein, With the geometric center of the wafer surface as the origin, a straight line passing through the origin and parallel to the horizontal plane as the x-axis, and a straight line passing through the origin and perpendicular to the x-axis as the y-axis; when ion implantation is performed on the corresponding wafer using several ion implantation angles with the x-axis as the axis of symmetry, the obtained angle calibration value is the angle calibration value of the target stage device in the y-axis direction.

4. The ion implantation angle calibration method of claim 3, wherein, When ion implantation is performed on the corresponding wafer using several ion implantation angles with the y-axis as the axis of symmetry, the obtained angle calibration value is the angle calibration value of the target stage device in the x-axis direction.

5. The ion implantation angle calibration method of claim 3, wherein, The wafer includes a notch mark, and the rotation angle of the notch mark relative to the center of the circle is the rotation angle of the target stage device; when ion implantation is performed on the corresponding wafer using different rotation angles, the obtained angle calibration value is the rotation angle calibration value of the target stage device.

6. The ion implantation angle calibration method of claim 3, wherein, The angle calibration value of the target stage device in the x-axis or y-axis direction is equal to the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve.

7. The ion implantation angle calibration method of claim 5, wherein, The rotation angle calibration value of the target stage device is equal to the absolute value of the difference between the ion implantation angle corresponding to the lowest point in the Gaussian fitting curve and 180°.

8. The ion implantation angle calibration method of claim 1, wherein, When performing thermal wave measurements, there are at least three measurement points on each wafer, and the ratio of the variance to the mean of the measurement data obtained on the same wafer does not exceed 0.

2.

9. The ion implantation angle calibration method of claim 8, wherein, If the ratio of the variance to the mean of the measurement data obtained on the same wafer exceeds 0.2, then the measurement point is reselected.

10. The ion implantation angle calibration method according to claim 1, characterized in that, The wafer is silicon. <100> And the crystal orientation error does not exceed 1°.

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