Method and system for characterizing surface roughness of a silicon wafer

Abstract

This invention provides a method and system for characterizing the surface roughness of silicon wafers. When characterizing the surface roughness of a wafer under test, the wafer is acquired, and a non-contact optical measurement method is used to obtain the surface optical feature signal values ​​of the wafer. Then, based on the surface optical feature signal values ​​and a set formula, the surface roughness value of the wafer is calculated. Thus, the surface roughness value can be obtained simply by acquiring the surface optical feature signal of the wafer. This solves the problems of low efficiency, difficulty in achieving full-wafer inspection, and susceptibility to vibration associated with traditional contact measurements. It provides a highly efficient, accurate, and online monitoring-suitable silicon wafer surface roughness characterization scheme. Specifically, the above method allows for non-contact optical measurement of the wafer, obtaining the roughness of the entire wafer in just 40 seconds.

Description

Technical Field

[0001] This invention relates to the field of measurement, and in particular to a method and system for characterizing the surface roughness of silicon wafers. Background Technology

[0002] With the development of semiconductor manufacturing processes and the continuous reduction in process dimensions, the requirements for the surface flatness of semiconductor substrate silicon wafers are also constantly increasing. To maintain the uniformity of surface flatness measurements, higher demands are placed on the accuracy and stability of surface flatness measurements. To ensure the accuracy and stability of surface flatness measurements, it is usually necessary to measure the surface roughness of the silicon wafer; only when the measurement results meet existing roughness standards can the wafer be shipped.

[0003] Currently, contact measurement methods such as atomic force microscopy are commonly used to characterize the roughness of silicon wafers. However, these methods have drawbacks such as long measurement time (generally, if only one point of 10μm×10μm in the center is measured, the measurement time is about 15 minutes, while if it is to be shipped as a product, 21 points need to be measured, and the measurement time is about five hours), small measurement range, and susceptibility to vibration. Summary of the Invention

[0004] The purpose of this invention is to provide a method and system for characterizing the surface roughness of silicon wafers, so as to solve the problems of long measurement time, small measurement range and susceptibility to dynamic vibration in existing silicon wafer surface roughness characterization methods.

[0005] To address the above problems, this invention provides a method for characterizing the surface roughness of a silicon wafer, comprising:

[0006] The test piece is acquired, and measurements are performed using a non-contact optical measurement method to obtain the surface optical feature signal values ​​of the test piece; and,

[0007] The surface roughness value of the test piece is calculated based on the surface optical characteristic signal value of the test piece and the set relationship.

[0008] Optionally, in the silicon wafer surface roughness characterization method, the defined relationship is:

[0009] Y=Ax 2 +Bx+C

[0010] Where x represents the surface optical feature signal value of the test piece, Y represents the surface roughness value of the test piece, and A, B and C are constants, with constants A=-0.0002±0.0001, B=0.0175±0.0001, and C=0.1318±0.0001.

[0011] Optionally, in the silicon wafer surface roughness characterization method, the non-contact optical measurement method includes a measurement method based on the principle of light scattering, and the surface optical characteristic signal value is the average haze value.

[0012] Optionally, in the silicon wafer surface roughness characterization method, before measuring the wafer to be tested, the characterization method further includes: cleaning the surface of the wafer to be tested to remove surface contaminants.

[0013] Optionally, in the silicon wafer surface roughness characterization method, the cleaning conditions for cleaning the surface of the wafer to be tested include: using SC-1 solution and SC-2 solution as cleaning solutions, cleaning temperature of 20-80℃, and cleaning time of 10-200 seconds.

[0014] Optionally, in the silicon wafer surface roughness characterization method, the characterization method further includes: performing metal contamination detection on the wafer to be tested before measurement using a non-contact optical measurement method to confirm whether the metal contamination level on the surface of the wafer to be tested is lower than a preset condition.

[0015] Optionally, in the silicon wafer surface roughness characterization method, the preset condition is: the number of particles with a size ≥1μm detected on the surface of the wafer to be tested is ≤200, and the surface metal content is less than or equal to 5E9 atoms / cm². 3 .

[0016] The present invention also provides a silicon wafer surface roughness characterization system, comprising:

[0017] Storage unit, used to store the defined relational formula;

[0018] A non-contact optical measurement unit is used to acquire surface optical feature signal values ​​of the sample under test.

[0019] The processing unit is used to, after receiving the surface optical feature signal from the non-contact optical measurement unit, retrieve the set relationship from the storage unit to perform calculations and output the surface roughness value of the test piece.

[0020] Optionally, in the aforementioned silicon wafer surface roughness characterization system, the defined relationship is:

[0021] Y=Ax 2 +Bx+C

[0022] Where x represents the surface optical feature signal value of the test piece, Y represents the surface roughness value of the test piece, and A, B and C are constants, with constants A=-0.0002±0.0001, B=0.0175±0.0001, and C=0.1318±0.0001.

[0023] Optionally, in the aforementioned silicon wafer surface roughness characterization system, the measurement method of the non-contact optical measurement unit includes: a measurement method based on the principle of light scattering, wherein the surface optical characteristic signal value is the average haze value.

[0024] In summary, the silicon wafer surface roughness characterization method and system provided by this invention, when characterizing the surface roughness of a wafer under test, involves acquiring the wafer under test, measuring it using a non-contact optical measurement method to obtain the surface optical feature signal value of the wafer under test; and calculating the surface roughness value of the wafer under test based on the surface optical feature signal value of the wafer under test and a set formula. Thus, the surface roughness value can be obtained simply by acquiring the surface optical feature signal of the wafer under test. This solves the problems of low efficiency, difficulty in achieving full-wafer inspection, and susceptibility to vibration associated with traditional contact measurement methods, providing a highly efficient, accurate, and online monitoring-suitable silicon wafer surface roughness characterization scheme. Specifically, the wafer under test can be inspected using a non-contact optical measurement method, and the roughness of the entire wafer can be obtained in just 40 seconds. Attached Figure Description

[0025] Figure 1 A flowchart of a silicon wafer surface roughness characterization method provided in an embodiment of the present invention;

[0026] Figure 2 This is a measurement result diagram of a standard silicon wafer measured using a surface light scattering instrument in an embodiment of the present invention;

[0027] Figure 3 This is a measurement result diagram of a standard silicon wafer measured using an atomic force microscope in an embodiment of the present invention;

[0028] Figure 4 This is a graph showing the particle data characterization results after cleaning the experimental piece in an embodiment of the present invention;

[0029] Figure 5 This is a graph showing the characterization results of the surface metal impurity concentration of the experimental piece after cleaning in an embodiment of the present invention.

[0030] Figure 6 This is a measurement result diagram of the experimental piece measured using a surface light scattering instrument in an embodiment of the present invention;

[0031] Figure 7 This is a measurement result diagram of the experimental piece measured using an atomic force microscope in an embodiment of the present invention;

[0032] Figure 8 This is a statistical result graph showing the calculated and measured values ​​of the surface roughness of each experimental piece in the embodiments of the present invention. Detailed Implementation

[0033] The silicon wafer surface roughness characterization method and system provided by the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the drawings are all in a very simplified form and use non-precise scales, only for the purpose of conveniently and clearly illustrating the embodiments of the present invention. Furthermore, the structures shown in the drawings are often part of the actual structure. In particular, different figures may have different focuses and sometimes use different scales. It should also be understood that, unless specifically stated or indicated, the terms "first," "second," "third," etc., in the specification are only used to distinguish the various components, elements, steps, etc., in the specification, and are not used to indicate the logical or sequential relationships between the various components, elements, steps, etc.

[0034] like Figure 1 As shown, this embodiment of the invention provides a surface roughness characterization method, including the following steps:

[0035] S1, For the test piece, a non-contact optical measurement method is used to measure and obtain the surface optical feature signal value of the test piece;

[0036] S2, the surface roughness value of the test piece is calculated based on the surface optical feature signal value of the test piece and the set relationship.

[0037] The characterization method provided in this invention allows for rapid measurement of the wafer under test using a non-contact optical method to obtain its optical characteristic signals, and then quickly calculates its surface roughness value according to the predefined formula. This solves the problems of low efficiency, difficulty in achieving full-wafer inspection, and susceptibility to vibration associated with traditional contact measurements, providing a highly efficient, accurate, and online-monitoring-suitable silicon wafer surface roughness characterization scheme.

[0038] The methods for measuring surface roughness include the following two:

[0039] Method 1 involves measuring the silicon wafer using a surface light scattering instrument. This instrument can measure the entire wafer quickly, requiring only 40 seconds. The measurement result is usually expressed as Average Haze. However, it requires a high level of cleanliness and strict control over metal impurities on the test or standard silicon wafer. Typically, the surface content of metals such as Cu and Fe on the test or standard silicon wafer is less than or equal to 5E9 atoms / cm². 3 As an example, the measurement results obtained using a surface light scattering meter are as follows: Figure 2 As shown;

[0040] Method two involves measurement using an atomic force microscope (AFM). This instrument can only measure a localized area of ​​the silicon wafer, typically only a 10μm × 10μm region at a time, with each region requiring 15 minutes of measurement. To reflect the overall condition of the wafer, usually 21 10μm × 10μm regions need to be measured, resulting in a total measurement time of 5 hours. However, this method does not have specific requirements for the cleanliness of the test or standard silicon wafers, so it is currently the commonly used method for measuring wafer roughness. Therefore, standards for wafer shipments are also based on the results of this method. As an example, the measurement results using an atomic force microscope are shown below. Figure 3 As shown;

[0041] Since a Localized Light Scattering (LLS) instrument analyzes the collected scattering signals through bidirectional reflectance distribution function analysis, the ratio of the collected scattering energy to the total reflected energy is defined as "Haze." Measuring the haze reflects surface roughness. The mean square roughness obtained by atomic force microscopy (AFM) is derived from the two-dimensional power spectral density of the surface roughness in the frequency domain. Based on this finding, in step S1 above, the non-contact optical measurement method employs a measurement method based on the principle of light scattering, specifically implemented using a Localized Light Scattering (LLS) instrument. Correspondingly, the surface optical characteristic signal value is the average haze value. In step S2 above, the set relationship is as follows:

[0042] Y=Ax 2 +Bx+C

[0043] Where x represents the surface optical characteristic signal value, Y represents the surface roughness value, and A, B and C are constants, with constants A=-0.0002±0.0001, B=0.0175±0.0001, and C=0.1318±0.0001.

[0044] Specifically, the surface optical feature signal value is the Average Haze value, and correspondingly, the surface roughness value is the root mean square roughness value. For the test piece, only a rapid measurement using LLS is needed to obtain its Average Haze value, and then the root mean square roughness value matching the AFM measurement result can be quickly calculated according to the above-mentioned set relationship.

[0045] Because surface light scattering instruments have high requirements for metal impurities, preferably, before measuring the test piece, the characterization method provided in this embodiment further includes: cleaning the surface of the test piece to remove surface contaminants, thereby avoiding metal contamination of subsequent measurement equipment. The cleaning conditions for the surface of the test piece include: using SC-1 and SC-2 solutions as cleaning solutions, a cleaning temperature of 20-40℃, and a cleaning time of 10-200 seconds.

[0046] Specifically, the steps for cleaning the surface of the test piece include:

[0047] Step 1 (SC-1 Cleaning): Use a mixed solution of ammonia (NH4OH), hydrogen peroxide (H2O2) and deionized water (DI water) (e.g., NH4OH:H2O2:DI water = 1:1:5 by volume) to treat for 10-200 seconds at a temperature of 20-80°C (preferably 20-40°C) to effectively remove organic contaminants and particles from the silicon wafer surface.

[0048] Step 2 (SC-2 cleaning): Use a mixed solution of hydrochloric acid (HCl), hydrogen peroxide (H2O2) and deionized water (DI water) (e.g., HCl:H2O2:DI water = 1:1:6 by volume) to treat for 10-200 seconds at a temperature of 20-80°C (preferably 20-40°C) to remove metal ion contaminants from the silicon wafer surface.

[0049] After cleaning, the silicon wafer surface must meet preset conditions. Preferably, these preset conditions are: the number of particles ≥1μm in size ≤200; and the concentration of key metallic impurities (such as Cu, Fe) on the surface ≤5×10⁻⁶. 9 atoms / cm³.

[0050] Further preferably, the characterization method further includes: performing metal contamination detection on the test piece before measurement using a non-contact optical measurement method to confirm whether the metal contamination level on the surface of the test piece is lower than a preset condition, thereby ensuring that no metal contamination will be caused to the measurement equipment subsequently.

[0051] Optional methods for detecting metal contamination include secondary ion mass spectrometry (SIMS) and inductively coupled plasma mass spectrometry (ICP-MS).

[0052] The following uses three experimental pieces with different roughnesses obtained from the same silicon ingot to verify our established relationship.

[0053] Each experimental piece was cleaned using SC-1 and SC-2 at a temperature of 25℃ for 60 seconds. The particle size characterization results for each experimental piece after cleaning are as follows: Figure 4 As shown, the characterization results of the surface metallic impurity concentration (taking Cu metallic impurities as an example) are as follows: Figure 5 As shown. From Figure 4 and Figure 5 It can be seen that the number of particles larger than 1 μm in each experimental piece is no more than 200, and the content of key metal impurities on the surface is less than or equal to 5 × 10⁻⁶. 9 atoms / cm³.

[0054] Subsequently, a surface light scattering instrument was used to measure each experimental piece, and the measurement results are as follows: Figure 6 As shown, the obtained measurement results are further analyzed to obtain the Average Haze value of each experimental piece, and the quantitative relationship Y=Ax established based on the aforementioned steps is calculated. 2 The mean square roughness value of each experimental piece is calculated using +Bx+C, and recorded as the calculated value. Simultaneously, as a reference standard, each experimental piece is measured using an atomic force microscope, and the measurement results are as follows: Figure 7 As shown, the obtained measurement results were further analyzed to directly obtain the mean square roughness value, which was recorded as the measured value. The statistical results of the calculated and measured surface roughness values ​​of each experimental piece are shown below. Figure 8 As shown in the figure, the calculated value (LLS Result) and the measured value (AFM Result) are in high agreement. This indicates that the characterization method provided in this embodiment of the invention establishes a quantitative relationship between surface optical measurement signals and surface roughness values ​​through data analysis. When measuring the surface roughness of the silicon wafer under test, the conversion of optical measurement signals into accurate surface roughness values ​​based on this quantitative relationship has extremely high accuracy and reliability.

[0055] In addition, embodiments of the present invention also provide a silicon wafer surface roughness characterization system, comprising:

[0056] A storage unit is used to store the defined relational expression as described in the characterization method provided in the embodiments of the present invention.

[0057] A non-contact optical measurement unit is used to measure silicon wafers using non-contact optical measurement methods to obtain surface optical feature signal values;

[0058] The processing unit is configured to, upon receiving the surface optical feature signal from the non-contact optical measurement unit, retrieve the set formula from the storage unit to perform calculations and output the surface roughness value of the silicon wafer.

[0059] It should be noted that non-contact optical measurements can also be performed using other rapid optical measurement devices based on principles such as light scattering, spectral reflection, or interference. When the non-contact optical measurement method changes, the set relationship can also be adjusted appropriately. As long as the measurement results based on the set relationship and the non-contact optical measurement method can obtain results applicable to existing roughness standards, it can be determined whether the silicon wafer product meets existing roughness standards, i.e., whether it meets actual shipping requirements.

[0060] In summary, the silicon wafer surface roughness characterization method and system provided in this invention, when characterizing the surface roughness of a wafer under test, involves acquiring the wafer under test, measuring it using a non-contact optical measurement method to obtain the surface optical feature signal value of the wafer under test; and calculating the surface roughness value of the wafer under test based on the surface optical feature signal value of the wafer under test and a set formula. Thus, the surface roughness value can be obtained simply by acquiring the surface optical feature signal of the wafer under test. This solves the problems of low efficiency, difficulty in achieving full-wafer inspection, and susceptibility to vibration associated with traditional contact measurement methods, providing a highly efficient, accurate, and online monitoring-suitable silicon wafer surface roughness characterization scheme. Specifically, the wafer under test can be inspected using a non-contact optical measurement method, and the roughness of the entire wafer can be obtained in just 40 seconds.

[0061] The above description is merely a description of preferred embodiments of the present invention and is not intended to limit the scope of the present invention in any way. Any changes or modifications made by those skilled in the art based on the above disclosure shall fall within the protection scope of the claims.

Claims

1. A method for characterizing surface roughness, characterized in that, include: The test piece is obtained and measured using a non-contact optical measurement method to obtain the surface optical feature signal values ​​of the test piece. as well as, The surface roughness value of the test piece is calculated based on the surface optical characteristic signal value of the test piece and the set relationship.

2. The method for characterizing the surface roughness of a silicon wafer as described in claim 1, characterized in that, The defined relation is: Y=Ax 2 +Bx+C Where x represents the surface optical feature signal value of the test piece, Y represents the surface roughness value of the test piece, and A, B and C are constants, with constants A=-0.0002±0.0001, B=0.0175±0.0001, and C=0.1318±0.0001.

3. The method for characterizing the surface roughness of a silicon wafer as described in claim 2, characterized in that, The non-contact optical measurement method includes a measurement method based on the principle of light scattering, wherein the surface optical characteristic signal value is the average haze value.

4. The method for characterizing the surface roughness of a silicon wafer as described in claim 1, characterized in that, Before measuring the test piece, the characterization method further includes cleaning the surface of the test piece to remove surface contaminants.

5. The method for characterizing the surface roughness of a silicon wafer as described in claim 4, characterized in that, The cleaning conditions for cleaning the surface of the test piece include: using SC-1 solution and SC-2 solution as cleaning solutions, cleaning temperature of 20-80℃, and cleaning time of 10-200 seconds.

6. The method for characterizing the surface roughness of a silicon wafer as described in claim 1, characterized in that, The characterization method further includes: performing metal contamination detection on the test piece before measurement using a non-contact optical measurement method to confirm whether the metal contamination level on the surface of the test piece is lower than a preset condition.

7. The method for characterizing the surface roughness of a silicon wafer as described in claim 6, characterized in that, The preset conditions are: the number of particles with a size ≥1μm detected on the surface of the test piece is ≤200, and the surface metal content is less than or equal to 5E9 atoms / cm². 3 .

8. A silicon wafer surface roughness characterization system, characterized in that, include: Storage unit, used to store the defined relational formula; A non-contact optical measurement unit is used to acquire surface optical feature signal values ​​of the sample under test. The processing unit is used to, after receiving the surface optical feature signal from the non-contact optical measurement unit, retrieve the set relationship from the storage unit to perform calculations and output the surface roughness value of the test piece.

9. The silicon wafer surface roughness characterization system as described in claim 8, characterized in that, The defined relation is: Y=Ax 2 +Bx+C Where x represents the surface optical feature signal value of the test piece, Y represents the surface roughness value of the test piece, and A, B and C are constants, with constants A=-0.0002±0.0001, B=0.0175±0.0001, and C=0.1318±0.0001.

10. The silicon wafer surface roughness characterization system as described in claim 8, characterized in that, The measurement method of the non-contact optical measurement unit includes: a measurement method based on the principle of light scattering, wherein the surface optical characteristic signal value is the average haze value.

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