Method and system for setting control limits in a semiconductor manufacturing process

Abstract

The application provides a method and system for setting control limits in a semiconductor manufacturing process, the method comprising: defining an upper specification limit (USL), a lower specification limit (LSL), a target value (Target) and a process capability index (Ppk) of a parameter to be monitored according to a set product technical requirement; obtaining a theoretical mean (mu) of the parameter to be monitored based on the target value (Target), and obtaining a theoretical standard deviation (sigma) of the parameter to be monitored based on the upper specification limit (USL), the lower specification limit (LSL) and the process capability index (Ppk); and obtaining control limits of a mean control chart, a range control chart and a standard deviation control chart of the parameter to be monitored based on the theoretical mean (mu) and the theoretical standard deviation (sigma) and in combination with the Shewhart control chart principle. In this way, the setting of the control limits is associated with the product technical requirement, is not dependent on manual experience, is more rigorous and reasonable, and is more in line with actual needs, thereby avoiding the situation that the control limits are too loose or too strict.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and in particular to a method and system for setting control limits during semiconductor manufacturing. Background Technology

[0002] Currently, when setting process control limits, the semiconductor manufacturing industry either relies on standard deviation (σ) or simply correlates with design tolerance (Tol). However, the actual process control is disconnected from product specifications, resulting in control limits that are either too tight or too loose, leading to situations where monitoring is either too strict or ineffective. Summary of the Invention

[0003] The purpose of this invention is to provide a method and system for setting control limits in semiconductor manufacturing processes, so as to solve the problem of the control limits being out of sync with the actual process.

[0004] To solve the above-mentioned technical problems, the present invention provides a method for setting control limits in a semiconductor manufacturing process, comprising:

[0005] Based on the set product technical requirements, define the upper limit of specifications (USL), lower limit of specifications (LSL), target value (Target), and process capability index (Ppk) of the parameters to be monitored.

[0006] The theoretical mean μ of the parameter to be monitored is obtained based on the target value Target, and the theoretical standard deviation σ of the parameter to be monitored is obtained based on the upper specification limit USL, the lower specification limit LSL and the process capability index Ppk.

[0007] Based on the theoretical mean μ and the theoretical standard deviation σ, and combined with the Shewhart control chart principle, the control limits of the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored are obtained.

[0008] Optionally, the theoretical mean μ is equal to the target value Target; the theoretical standard deviation σ = (USL - LSL) / (6 * Ppk).

[0009] Optionally, the control limit of the range control chart is Max(σ*d2±3*σ*d3, 0); where d2 and d3 are Shewhart control parameters.

[0010] Optionally, the control limit of the standard deviation control chart is Max(σ*c4±3*σ*c5, 0); where c4 and c5 are Shewhart control parameters.

[0011] Optionally, when the accumulated historical data reaches a preset threshold, the theoretical mean μ is replaced by the sample mean calculated based on the historical data, the theoretical standard deviation σ is replaced by the sample standard deviation, and the control limits of the range control chart and the standard deviation control chart are recalculated based on the updated parameters.

[0012] Optionally, the method for setting control limits during semiconductor manufacturing further includes:

[0013] Based on the theoretical mean μ and the theoretical standard deviation σ, the control limits of the mean control chart are obtained by combining the standard deviation shrinkage coefficient f.

[0014] Optionally, the standard deviation shrinkage coefficient f is determined based on the source of variation analysis; the control limit of the mean control chart is μ±3*σ*f.

[0015] Optionally, the variation source analysis uses the formula: σ² Total =σ² BetweenLot +σ² BetweenWafer +σ² WithinWafer ; where σ² Total For the total variance, σ² BetweenLot σ² represents the variance between different batches. BetweenWafer σ² represents the variance between different wafers. WithinWafer This represents the variance within the wafer.

[0016] Optionally, the process capability index Ppk is derived based on a set ppm requirement.

[0017] To address the aforementioned technical problems, the present invention also provides a system for setting control limits during semiconductor manufacturing, comprising: an acquisition module and an execution module;

[0018] The acquisition module is used to acquire the upper limit of the specification (USL), the lower limit of the specification (LSL), the target value (Target), and the process capability index (Ppk) of the parameter to be monitored.

[0019] The execution module calculates the control limits of the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored according to the control limit setting method in the semiconductor manufacturing process described above.

[0020] In summary, in the method and system for setting control limits in semiconductor manufacturing provided by this invention, the method for setting control limits in semiconductor manufacturing includes: defining the upper limit (USL), lower limit (LSL), target value (Target), and process capability index (Ppk) of the parameter to be monitored according to the set product technical requirements; obtaining the theoretical mean (μ) of the parameter to be monitored based on the target value (Target); obtaining the theoretical standard deviation (σ) of the parameter to be monitored based on the upper limit (USL), the lower limit (LSL), and the process capability index (Ppk); and obtaining the control limits of the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored based on the theoretical mean (μ) and the theoretical standard deviation (σ), combined with the Shewhart control chart principle.

[0021] This configuration links control limits to product technical requirements, eliminating reliance on human experience and basing them on Shewhart control parameters. This makes control limits more rigorous, reasonable, and aligned with actual needs, preventing overly lenient or stringent limits. Furthermore, because control limits are based on product technical requirements, the connection between control limits and initial quality requirements is enhanced, resolving the issue of control limits being disconnected from actual processes. Attached Figure Description

[0022] Those skilled in the art will understand that the accompanying drawings are provided to better understand the invention and do not constitute any limitation on the scope of the invention.

[0023] Figure 1 This is a flowchart illustrating the method for setting control limits during semiconductor manufacturing according to an embodiment of the present invention.

[0024] Figure 2 This is a schematic diagram of the Shewhart control parameter table according to an embodiment of the present invention. Detailed Implementation

[0025] To make the objectives, advantages, and features of this invention clearer, the 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 are not drawn to scale, and are only used to facilitate and clarify the explanation of the embodiments of this invention. Furthermore, the structures shown in the drawings are often part of the actual structures. In particular, different figures may emphasize different aspects and may sometimes use different scales.

[0026] As used in this invention, the singular forms “a,” “an,” “one,” and “the” include plural objects; the term “or” is generally used to mean “and / or”; the term “a number” is generally used to mean “at least one”; and the term “at least two” is generally used to mean “two or more”. Furthermore, the terms “first,” “second,” and “third” are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as “first,” “second,” or “third” may explicitly or implicitly include one or at least two of that feature; “one end” and “the other end,” and “proximal end” and “distal end” generally refer to two corresponding parts, which include not only endpoints. Furthermore, the terms "installed," "connected," and "attached," as used in this invention, and the term "set" on one element from another, should be interpreted broadly. They generally only indicate a connection, coupling, cooperation, or transmission relationship between the two elements, which can be direct or indirect through an intermediate element. They should not be construed as indicating or implying a spatial relationship between the two elements, meaning one element can be located inside, outside, above, below, or to one side of another element, unless otherwise explicitly stated. Those skilled in the art can understand the specific meaning of these terms in this invention based on the specific circumstances. Additionally, directional terms such as above, below, up, down, upward, downward, left, and right are used relative to exemplary embodiments as shown in the figures, with upward or upper directions pointing towards the top of the corresponding figure, and downward or lower directions pointing towards the bottom of the corresponding figure.

[0027] The purpose of this invention is to provide a method and system for setting control limits in semiconductor manufacturing processes, so as to solve the problem of the disconnect between control limits and actual processes. The following description refers to the accompanying drawings.

[0028] In existing semiconductor manufacturing processes, monitoring parameters often requires setting control limits. In some embodiments, the control limits are set as the target center value ± m * standard deviation, where m can be selected from 3 to 6. In other embodiments, the control limits are set as the target center value ± n * design tolerance, where n can be selected from 50% to 90%. The selection of m and n often relies on human experience, which can easily lead to a disconnect between actual process control and product specifications, resulting in control limits that are too tight or too loose, leading to overly strict or ineffective monitoring.

[0029] Therefore, please refer to Figure 1 This invention provides a method for setting control limits during semiconductor manufacturing, comprising:

[0030] Step S1: Based on the set product technical requirements, define the upper limit of specifications (USL), lower limit of specifications (LSL), target value (Target), and process capability index (Ppk) of the parameters to be monitored.

[0031] Step S2: Based on the target value Target, obtain the theoretical mean μ of the parameter to be monitored, and based on the upper specification limit USL, the lower specification limit LSL, and the process capability index Ppk, obtain the theoretical standard deviation σ of the parameter to be monitored.

[0032] Step S3: Based on the theoretical mean μ and the theoretical standard deviation σ, and in conjunction with the Shewhart control chart principle, obtain the control limits of the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored.

[0033] In step S1, the upper specification limit (USL), lower specification limit (LSL), target value (Target), and process capability index (Ppk) of a certain monitored parameter can be determined based on the quality level of the product's technical requirements. It's important to understand that the upper specification limit (USL) and lower specification limit (LSL) here are not control limits for subsequent monitoring, but rather the product's specification limits. The target value (Target) is the product's design value. The process capability index (Ppk) is an index used in Statistical Process Control (SPC) to measure process performance. The process capability index (Ppk) can be directly defined based on the quality level agreed upon by both the supplier and the buyer, or it can be inferred from a set ppm requirement. For example, based on the ppm requirement (parts per million defect rate), the process output "defect rate" can be calculated. Assuming no deviation between the process center and the specification center, the Ppk requirement can be derived. The process capability index (Ppk) can be selected as 1.00, 1.33, or 1.67, etc., and can be adjusted according to actual needs without adhering to these specific values.

[0034] In step S2, the theoretical mean μ and theoretical standard deviation σ are set based on the specification upper limit USL, specification lower limit LSL, target value Target, and process capability index Ppk obtained in step S1. The theoretical mean μ is the expected center of the parameter to be monitored, and subsequent control limits are extended outwards from this theoretical mean μ. In one embodiment, the theoretical mean μ is equal to the target value Target.

[0035] The theoretical standard deviation σ is the standard deviation of the data distribution for the ideal production process, calculated based on the parameters obtained in step S1. Here, it can be assumed that the data follows or approximately follows a normal distribution. In one embodiment, the theoretical standard deviation σ can be calculated using the following formula:

[0036] σ=(USL-LSL) / (6*Ppk)

[0037] In step S3, based on the theoretical mean μ and theoretical standard deviation σ, and using the Shewhart control chart principle, the control limits for the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored can be obtained, thus yielding the corresponding range control chart (R / MR chart) and standard deviation control chart (S chart). The Shewhart control parameters can be determined based on the sample size n, and can be referenced... Figure 2 It is determined by looking up a table.

[0038] In one embodiment, the control limits for the range control chart are Max(σ*d2±3*σ*d3, 0), where d2 and d3 are Shewhart control parameters. The control limits for the standard deviation control chart are Max(σ*c4±3*σ*c5, 0), where c4 and c5 are Shewhart control parameters.

[0039] The process of steps S1 to S3 above will be explained below with a specific example.

[0040] In one example, the specification upper limit (USL) obtained in step S1 is 200, the specification lower limit (LSL) is 100, the target value (Target) is 150, and the process capability index (Ppk) is 1.33.

[0041] In step S2, the theoretical mean μ = Target = 150; the theoretical standard deviation σ = (USL - LSL) / (6 * Ppk) = (200 - 100) / (6 * 1.33) = 12.5.

[0042] Step S3 substitutes the theoretical mean μ and theoretical standard deviation σ obtained in step S2 into the input, taking a sample size of n=9 as an example:

[0043] The upper limit of the range control is Max(σ*d2+3*σ*d3, 0)=Max(12.5*2.97+3*12.5*0.8078, 0)=67.4.

[0044] The lower limit of the range control is Max(σ*d2-3*σ*d3, 0)= Max(12.5*2.97-3*12.5*0.8078, 0)=6.83.

[0045] The upper limit of the standard deviation control is Max(σ*c4+3*σ*c5, 0)= Max(12.5*0.969+3*12.5*0.246, 0)=21.34.

[0046] The lower limit of standard deviation control is Max(σ*c4-3*σ*c5, 0)= Max(12.5*0.969-3*12.5*0.246, 0)=2.89.

[0047] Optionally, when the accumulated historical data reaches a preset threshold, the theoretical mean μ is replaced by the sample mean calculated based on the historical data, and the theoretical standard deviation σ is replaced by the sample standard deviation. The control limits of the range control chart and the standard deviation control chart are then recalculated based on the updated parameters. In some embodiments, as a certain parameter is continuously monitored, the acquired sample data accumulates. When this accumulated historical data reaches a preset threshold, the sample mean and sample standard deviation calculated based on this historical data can replace the theoretical mean μ and theoretical standard deviation σ used at the start of monitoring, thereby further improving the accuracy and reliability of the control limits.

[0048] Optionally, the method for setting control limits during semiconductor manufacturing further includes:

[0049] Step S4: Based on the theoretical mean μ and the theoretical standard deviation σ, the control limit of the mean control chart is obtained by combining the standard deviation shrinkage factor f. Step S4 is an optional step parallel to step S3, and is not necessarily performed after step S3. In some embodiments, the control limit of the mean control chart can also be set using the standard deviation shrinkage factor f, thereby obtaining the corresponding mean control chart (X Bar chart). The standard deviation shrinkage factor f is a coefficient used to shrink the theoretical standard deviation σ based on the specific analytical needs of the semiconductor manufacturing industry. In an example, the mean control limit of the parameter to be monitored is μ ± 3 * σ * f. The standard deviation shrinkage factor f can be set in various ways, such as directly setting it based on actual data statistics.

[0050] Preferably, the standard deviation shrinkage factor f can also be determined based on source of variation analysis (SOV). Source of variation analysis is a statistical analysis technique designed to identify, quantify, and compare the degree of influence of different factors on the fluctuation of a response variable. In semiconductor manufacturing, factors within a wafer, between wafers, and between lots can all affect parameter fluctuations.

[0051] Optionally, based on the specific analytical needs of the semiconductor manufacturing industry, the variation source analysis adopts the formula: σ² Total =σ² BetweenLot +σ² BetweenWafer +σ² WithinWafer ; where σ² Total For the total variance, σ² BetweenLot σ² represents the variance between different batches. BetweenWafer σ² represents the variance between different wafers. WithinWaferHere, represents the variance within the wafer; f is the standard deviation shrinkage coefficient, theoretically based on source variance analysis (SOV). In a demonstration example, the default value is tentatively set to 0.8 (default 𝜎). 2 Between (64%).

[0052] For example, in a specific demonstration, σ² BetweenLot +σ² BetweenWafer σ² Total If the mean is 64%, then the standard deviation contraction coefficient f = 0.8. In other words, the control limit for the mean control chart is ±3*σ*0.8, which represents a contraction compared to the default ±3*σ.

[0053] To address the aforementioned technical problems, the present invention also provides a system for setting control limits in a semiconductor manufacturing process, comprising: an acquisition module and an execution module; the acquisition module is used to acquire the upper limit of specifications (USL), the lower limit of specifications (LSL), the target value (Target), and the process capability index (Ppk) of the parameter to be monitored; the execution module calculates the control limits of the mean control chart, the range control chart, and the standard deviation control chart of the parameter to be monitored according to the method for setting control limits in a semiconductor manufacturing process as described above.

[0054] In summary, in the method and system for setting control limits in semiconductor manufacturing provided by this invention, the method for setting control limits in semiconductor manufacturing includes: defining the upper limit (USL), lower limit (LSL), target value (Target), and process capability index (Ppk) of the parameter to be monitored according to the set product technical requirements; obtaining the theoretical mean (μ) of the parameter to be monitored based on the target value (Target); obtaining the theoretical standard deviation (σ) of the parameter to be monitored based on the upper limit (USL), the lower limit (LSL), and the process capability index (Ppk); and obtaining the control limits of the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored based on the theoretical mean (μ) and the theoretical standard deviation (σ), combined with the Shewhart control chart principle.

[0055] This configuration links control limits to product technical requirements, eliminating reliance on human experience and basing them on Shewhart control parameters. This ensures control limits are more rigorous, reasonable, and aligned with actual needs, preventing overly lenient or stringent limits. Furthermore, because control limits are based on product technical requirements, the connection between control limits and initial quality requirements is enhanced. Customer product design requirements / subsequent process requirements (D1) are directly reflected in process control, indicating directions for process improvement and resolving the disconnect between control limits and actual processes.

[0056] It should be noted that the above embodiments can be combined with each other. The above description is only 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 present invention.

Claims

1. A method of setting a control limit in a semiconductor manufacturing process, characterized by, include: Define the upper limit of the specification (USL), the lower limit of the specification (LSL), the target value (Target), and the process capability index (Ppk) of the parameter to be monitored; The theoretical mean μ of the parameter to be monitored is obtained based on the target value Target, and the theoretical standard deviation σ of the parameter to be monitored is obtained based on the upper specification limit USL, the lower specification limit LSL and the process capability index Ppk. Based on the theoretical mean μ and the theoretical standard deviation σ, and combined with the Shewhart control chart principle, the control limits of the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored are obtained.

2. The method of setting a control limit in a semiconductor manufacturing process according to Claim 1, wherein The theoretical mean μ is equal to the target value Target; the theoretical standard deviation σ = (USL - LSL) / (6 * Ppk).

3. The method of setting a control limit in a semiconductor manufacturing process according to Claim 1, wherein The control limit of the range control chart is Max(σ*d2±3*σ*d3, 0); Where d2 and d3 are Shewhart control parameters.

4. The method of setting a control limit in a semiconductor manufacturing process according to Claim 1, wherein The control limit for the standard deviation control chart is Max(σ*c4±3*σ*c5, 0); C4 and C5 are Shewhart control parameters.

5. The method of setting a control limit for a semiconductor manufacturing process according to Claim 1, wherein, When the accumulated historical data reaches a preset threshold, the theoretical mean μ is replaced by the sample mean calculated based on the historical data, and the theoretical standard deviation σ is replaced by the sample standard deviation. The control limits of the range control chart and the control limits of the standard deviation control chart are then recalculated based on the updated parameters.

6. The method of setting a control limit in a semiconductor manufacturing process according to Claim 1, wherein The method for setting control limits during semiconductor manufacturing also includes: Based on the theoretical mean μ and the theoretical standard deviation σ, the control limits of the mean control chart are obtained by combining the standard deviation shrinkage coefficient f.

7. The method of setting a control limit for a semiconductor manufacturing process according to Claim 6, wherein, The standard deviation shrinkage coefficient f is determined based on the source of variation analysis; the control limit of the mean control chart is μ±3*σ*f.

8. The method of setting a control limit for a semiconductor manufacturing process according to Claim 7, wherein, The variation source analysis adopts the formula: σ² Total = σ² BetweenLot + σ² BetweenWafer + σ² WithinWafer ; wherein, σ² Total is the total variance, σ² BetweenLot is the variance between different batches, σ² BetweenWafer is the variance between different wafers, and σ² WithinWafer is the variance within a wafer.

9. The method of setting a control limit in a semiconductor manufacturing process according to Claim 1, wherein, The process capability index Ppk is derived based on the set ppm requirement.

10. A system for setting control limits in a semiconductor manufacturing process, characterized by include: Acquire module and execute module; The acquisition module is used to acquire the upper limit of the specification (USL), the lower limit of the specification (LSL), the target value (Target), and the process capability index (Ppk) of the parameter to be monitored. The execution module calculates the control limits of the mean control chart, range control chart, and standard deviation control chart of the parameter to be monitored using the method for setting control limits in the semiconductor manufacturing process according to any one of claims 1-9.

Images