Method for monitoring a semiconductor process
By monitoring the thickness of the oxide layer formed by thermal oxidation in semiconductor processes, the problem of low accuracy and reliability of nitrogen ion implantation monitoring in existing technologies is solved, and high-precision and high-reliability monitoring of nitrogen ion implantation is achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- HUAHONG INTEGRATED CIRCUIT (CHENGDU) CO LTD
- Filing Date
- 2026-03-30
- Publication Date
- 2026-06-23
AI Technical Summary
Existing technologies using thermal wave methods to monitor nitrogen ion implantation have low accuracy and low reliability, and cannot effectively monitor leakage problems caused by lateral/longitudinal diffusion after P ion implantation.
By performing a thermal oxidation process after ion implantation in the monitored area, the thickness of the formed oxide layer is measured and compared with the expected film thickness range to determine the normality of the ion implantation dose.
This enables direct offline monitoring of nitrogen ion implantation, improving monitoring accuracy and reliability, and ensuring the stability and accuracy of the ion implantation equipment.
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Figure CN122270087A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of semiconductor technology, and in particular to a method for monitoring semiconductor processes. Background Technology
[0002] Phosphorus ion implantation is prone to lateral / vertical diffusion during annealing activation, which can lead to uncontrolled junction depth and increased leakage current. This phenomenon is more pronounced in shorter channels. Therefore, an nitrogen ion implantation process is introduced. After nitrogen ion implantation, nitrogen atoms combine with silicon holes, reducing the hole concentration required for phosphorus diffusion and thus suppressing phosphorus ion diffusion.
[0003] However, since nitrogen ions do not provide charge carriers, direct and quantitative process monitoring cannot be performed by measuring sheet resistance (Rs). Currently, indirect monitoring is performed by testing thermal waves (TW). However, because nitrogen is a lightweight ion, it causes less lattice damage, resulting in low sensitivity of thermal wave signals. Therefore, the monitoring accuracy of nitrogen ion implantation using thermal wave methods is low. Secondly, thermal waves are affected by unrelated and difficult-to-control factors such as the wafer itself and time, resulting in low reliability. Summary of the Invention
[0004] The purpose of this application is to provide a method for monitoring semiconductor processes, which solves the problems of low monitoring accuracy and low monitoring reliability of the existing technology using thermal wave method to monitor nitrogen ion implantation.
[0005] To address the aforementioned technical problems, this application provides a method for monitoring semiconductor processes, comprising:
[0006] A semiconductor substrate is provided, the semiconductor substrate including at least one monitoring region;
[0007] Ion implantation is performed on the monitored area;
[0008] A thermal oxidation process is performed on the monitored area;
[0009] Measure the thickness of the oxide layer formed by the thermal oxidation process;
[0010] The thickness of the oxide layer is used to determine whether the ion implantation dose is normal.
[0011] Furthermore, the implanted element for ion implantation is nitrogen.
[0012] Furthermore, the step of determining whether the ion implantation dose is normal based on the thickness of the oxide layer includes:
[0013] The thickness of the oxide layer is compared with the desired film thickness range;
[0014] If the thickness of the oxide layer is within the expected film thickness range, the ion implantation dose is considered normal; otherwise, the ion implantation dose is considered abnormal.
[0015] Furthermore, the desired film thickness range is set using a statistical process control method.
[0016] Furthermore, the target oxide layer thickness formed by the thermal oxidation process is 20 to 60 angstroms.
[0017] Furthermore, the step of setting the desired film thickness range using a statistical process control method includes:
[0018] When the ion implantation equipment is in a stable operating state, at least m sets of thickness data of the oxide layer measured by the method are continuously collected, where m≥25;
[0019] Calculate the mean μ and standard deviation σ of the thickness data of the oxide layer in the m groups;
[0020] μ+n*σ is used as the upper limit of the desired film thickness range, and μ-n*σ is used as the lower limit of the desired film thickness range, where 2≤n≤4.
[0021] Furthermore, the value of n is 3.
[0022] Furthermore, the semiconductor substrate is a monitoring chip specifically designed for process monitoring.
[0023] Furthermore, the step of measuring the thickness of the oxide layer formed by the thermal oxidation process includes:
[0024] Before performing the thermal oxidation process, the thickness of the natural oxide layer formed in the monitored area is measured;
[0025] After performing the thermal oxidation process, the total thickness of the oxide layer formed in the monitoring area is measured;
[0026] The thickness of the oxide layer formed by the thermal oxidation process is obtained by subtracting the thickness of the natural oxide layer from the total thickness of the oxide layer.
[0027] Furthermore, when applied to monitoring multiple ion implantation devices, it also includes:
[0028] When multiple ion implantation devices are in stable operation, at least m sets of oxide layer thickness data measured by the method are continuously collected, and the mean value of the thickness data is calculated, where m≥25;
[0029] Calculate the mean difference between any two ion implantation devices;
[0030] If the mean difference exceeds a preset value, a check is performed on the corresponding ion implantation device.
[0031] Compared with the prior art, the technical solution of this application has at least one of the following beneficial effects:
[0032] In the semiconductor process monitoring method provided in this application, the thickness of the oxide layer formed by thermal oxidation is strongly correlated with the nitrogen ion implantation dose. Ion implantation (with nitrogen as the implanted element) is performed in the monitoring area, followed by thermal oxidation. The thickness of the oxide layer formed by the thermal oxidation process is then measured. Based on the thickness of the oxide layer, the implantation dose is determined to be normal. The determination method compares the oxide layer thickness with a desired film thickness range. If the oxide layer thickness is within the desired film thickness range, the implantation dose is considered normal, and the ion implantation equipment continues to operate. Otherwise, the implantation dose is considered abnormal, and the ion implantation equipment is further inspected. This achieves offline direct monitoring of nitrogen ion implantation. Since the thickness of the oxide layer formed by thermal oxidation is strongly correlated with the nitrogen ion implantation dose, the monitoring accuracy is high. Furthermore, since the factors affecting the thickness of the oxide layer formed by thermal oxidation are relatively controllable, the reliability is high, solving the problems of low monitoring accuracy and low monitoring reliability in the prior art using thermal wave methods to monitor nitrogen ion implantation. Attached Figure Description
[0033] The accompanying drawings are provided to further illustrate the present application and form part of the specification. They are used together with the following detailed description to explain the present application, but do not constitute a limitation thereof. In the drawings:
[0034] Figure 1 This is a flowchart of a semiconductor process monitoring method in one embodiment of this application;
[0035] Figure 2 This is a top view of the distribution of monitoring points on the monitoring chip in one embodiment of this application;
[0036] Figure 3 This is a cross-sectional view of the oxide layer thickness measurement at a monitoring point in one embodiment of this application.
[0037] in, Figures 2-3 The specific reference numerals in the attached figures are as follows:
[0038] 1-Semiconductor substrate; C-Center point; 2-Natural oxide layer; 3-Oxide layer.
[0039] In the accompanying drawings, the same parts are referred to by the same reference numerals, and the drawings are not drawn to scale. Detailed Implementation
[0040] To make the technical solutions and advantages of the embodiments of this application clearer, the technical solutions of this application will be further described in detail below with reference to the accompanying drawings and embodiments. Although exemplary implementation methods of this application are shown in the accompanying drawings, it should be understood that this application can be implemented in various forms and should not be limited to the implementation methods described herein. Rather, these implementation methods are provided to enable a more thorough understanding of this application and to fully convey the scope of this application to those skilled in the art.
[0041] The present application is described in more detail below by way of example with reference to the accompanying drawings. The advantages and features of the present application will become clearer from the following description and claims. It should be noted that the drawings are in a very simplified form and are only used to facilitate and clarify the illustration of the embodiments of the present application. It is understood that the meanings of "on," "above," and "over" in the present application should be interpreted in the broadest sense, such that "on" not only means "on" something without any intervening feature or layer (i.e., directly on something), but also includes "on" something with an intervening feature or layer. In the embodiments of the present application, the terms "first," "second," etc., are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be noted that the technical solutions described in the embodiments of the present application can be arbitrarily combined without conflict.
[0042] As described in the background section, since nitrogen ions do not provide charge carriers, direct and quantitative process monitoring cannot be performed by measuring sheet resistance (Rs). Currently, indirect monitoring is performed by testing thermal waves. However, because nitrogen is a lightweight ion, it causes less lattice damage, resulting in low sensitivity of thermal wave signals. Therefore, the monitoring accuracy of nitrogen ion implantation using thermal wave methods is low. Secondly, thermal waves are affected by unrelated and difficult-to-control factors such as the wafer itself and time, resulting in low reliability.
[0043] To address the above problems, this application proposes an improved solution. Based on the strong correlation between the thickness of the oxide layer formed by the thermal oxidation process and the nitrogen ion implantation dose, ion implantation (with nitrogen as the implanted element) is performed in the monitored area, followed by thermal oxidation. The thickness of the oxide layer formed by the thermal oxidation process is then measured. Based on the thickness of the oxide layer, the implantation dose is determined to be normal. The determination method compares the oxide layer thickness with the expected film thickness range. If the oxide layer thickness is within the expected film thickness range, the implantation dose is considered normal, and the ion implantation equipment continues operation. Otherwise, the implantation dose is considered abnormal, and the ion implantation equipment is further inspected. This achieves offline direct monitoring of nitrogen ion implantation. Since the thickness of the oxide layer formed by the thermal oxidation process is strongly correlated with the nitrogen ion implantation dose, the monitoring accuracy is high. Furthermore, because the factors affecting the thickness of the oxide layer formed by the thermal oxidation process are relatively controllable, the reliability is high, solving the problems of low monitoring accuracy and low monitoring reliability in the prior art using thermal wave methods to monitor nitrogen ion implantation.
[0044] refer to Figure 1 As shown, Figure 1 This is a flowchart illustrating a semiconductor process monitoring method provided in an embodiment of the present invention; wherein the semiconductor process monitoring method may include the following steps:
[0045] Step S101: Provide a semiconductor substrate, wherein the semiconductor substrate includes at least one monitoring region;
[0046] Step S102: Perform ion implantation on the monitored area;
[0047] Step S103: Perform a thermal oxidation process on the monitored area;
[0048] Step S104: Measure the thickness of the oxide layer formed by the thermal oxidation process;
[0049] Step S105: Determine whether the ion implantation dose is normal based on the thickness of the oxide layer.
[0050] The semiconductor process monitoring method proposed in this application will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this application will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this application. Many specific details are set forth in the following description to provide a thorough understanding of this application; however, this application may also be implemented in other ways different from those described herein, and therefore this application is not limited to the specific embodiments disclosed below.
[0051] Example 1
[0052] like Figure 2 As shown, in step S101 above, a semiconductor substrate 1 is first provided. The semiconductor substrate 1 is a monitoring chip specifically used for process monitoring. A monitoring area is defined on the semiconductor substrate 1 using a radial multi-point sampling method. Specifically, a monitoring point (i.e., center point C) is set at the center position of the semiconductor substrate 1. Then, taking into account the edge exclusion, three concentric circles (i.e., inner circle, middle circle, and outer circle) concentric with the semiconductor substrate 1 are selected according to the principle of equal radial spacing. 8, 16, and 24 monitoring points are set at equal intervals on the inner circle, the middle circle, and the outer circle, respectively, for a total of 49 monitoring points.
[0053] In step S102 above, ion implantation is performed on the monitored area. In this embodiment, the implanting element is preferably nitrogen. Specifically, the semiconductor substrate 1 is fed into an ion implantation machine (denoted as Tool A), and nitrogen ion implantation is performed in all 49 monitored areas. The target dose of nitrogen ion implantation is determined according to the electrical requirements of the product device and the device process angle.
[0054] In step S103 above, a thermal oxidation process is performed on the monitoring area after implantation. The target oxide layer thickness of the thermal oxidation process is 20 to 60 angstroms, preferably 40 angstroms. Specifically, the semiconductor substrate 1 is thermally oxidized by an in-situ steam generation (ISSG) process. The formulation parameters of the ISSG process are fixed so that a silicon dioxide layer with a target thickness of 40 angstroms can be formed on the bare silicon surface under nitrogen-free ion implantation conditions.
[0055] like Figure 3 As shown, before performing the thermal oxidation process, a natural oxide layer 2 has been formed on the semiconductor substrate 1. After performing the thermal oxidation process, an oxide layer 3 formed by the thermal oxidation process is formed on the natural oxide layer 2. In step S104 above, the thickness of the oxide layer 3 formed by the thermal oxidation process is measured; specifically, before performing the thermal oxidation process, the thickness of the natural oxide layer 2 formed in the monitoring area is measured; after performing the thermal oxidation process, the total thickness of the oxide layer formed in the monitoring area is measured; the thickness of the oxide layer 3 formed by the thermal oxidation process is obtained by subtracting the thickness of the natural oxide layer 2 from the total thickness of the oxide layer.
[0056] In step S105 above, the ion implantation dose is determined to be normal based on the measured thickness of the oxide layer 3. Specifically, the measured thickness of the oxide layer 3 is compared with the expected film thickness range. If the thickness of the oxide layer 3 is within the expected film thickness range, the ion implantation dose is considered normal, and the ion implantation equipment continues to operate. Otherwise, the ion implantation dose is considered abnormal, and the ion implantation equipment and ion implantation formulation parameters are further checked. The expected film thickness range is set by a statistical process control method.
[0057] The step of setting the desired film thickness range using a statistical process control method includes: continuously collecting at least m sets of oxide layer thickness data measured by the method while the ion implantation equipment is in a stable operating state, where m ≥ 25; calculating the mean μ and standard deviation σ of the m sets of oxide layer thickness data; using μ + n*σ as the upper limit of the desired film thickness range and μ - n*σ as the lower limit of the desired film thickness range, where 2 ≤ n ≤ 4. In this embodiment, n is preferably 3.
[0058] Specifically, in this embodiment, when Tool A is in a stable operating state, at least 25 batches (1 monitoring piece per batch) of oxide layer thickness data measured by the method are continuously collected, resulting in a total of 25*49 sets of film thickness data; the average film thickness data of 49 monitoring points for each monitoring piece is taken to obtain 25 batch averages, and the mean μ and standard deviation σ of the 25 batch averages are calculated; the desired film thickness range is set to (μ-3σ, μ+3σ).
[0059] In subsequent mass production monitoring, for each batch of products, one monitoring wafer of the same specification is taken and subjected to the same nitrogen ion implantation process, the same ISSG process, and the oxide layer thickness formed by the thermal oxidation process at 49 monitoring points is measured. The average value X of the oxide layer thickness is calculated and compared with the set expected film thickness range (μ-3σ, μ+3σ).
[0060] If X is within the desired film thickness range, then the nitrogen ion implantation dose is considered normal and the ion implantation machine continues to operate.
[0061] If X > μ+3σ or X < μ-3σ, the nitrogen ion implantation dose is considered abnormal, and the ion implantation equipment and ion implantation formulation parameters are further checked. Furthermore, based on the inhibitory effect of nitrogen ion implantation on oxide layer formation, if X > μ+3σ, it is speculated that the nitrogen ion implantation dose may be too low; if X < μ-3σ, it is speculated that the nitrogen ion implantation dose may be too high.
[0062]
Example 2
[0063] This embodiment illustrates how the above method can be extended to monitor multiple ion implantation devices.
[0064] When three identical nitrogen ion implantation machines (referred to as Tool A, Tool B, and Tool C) are in stable operation, each machine is used for the same nitrogen implantation layer of the same product with the same target dose. At least 25 batches (one monitoring wafer per batch) of oxide layer thickness data measured by the above method are continuously collected. The mean values μ_A, μ_B, and μ_C of the corresponding 25 batches of the three nitrogen ion implantation machines are calculated according to the process described in Example 1.
[0065] Calculate the mean difference between any two nitrogen ion implanters. If the mean difference exceeds a preset value (e.g., 0.10 angstroms), then perform a check on the corresponding ion implanter.
[0066] This embodiment uses nitrogen as the specific monitoring object, based on nitrogen ion implantation to suppress the film thickness formation rate of silicon dioxide. Therefore, theoretically, other elements that can suppress the film thickness formation rate of silicon dioxide, such as carbon, can also use the monitoring method provided in this application.
[0067] In summary, the semiconductor process monitoring method provided in this application is based on the strong correlation between the thickness of the oxide layer formed by thermal oxidation and the nitrogen ion implantation dose. Ion implantation (with nitrogen as the implanted element) is performed in the monitoring area, followed by thermal oxidation. The thickness of the oxide layer formed by the thermal oxidation process is then measured. Based on the thickness of the oxide layer, the implantation dose is determined to be normal. The determination method compares the oxide layer thickness with the expected film thickness range. If the oxide layer thickness is within the expected film thickness range, the implantation dose is considered normal, and the ion implantation equipment continues to operate. Otherwise, the implantation dose is considered abnormal, and the ion implantation equipment is further inspected. This achieves offline direct monitoring of nitrogen ion implantation. Since the thickness of the oxide layer formed by thermal oxidation is strongly correlated with the nitrogen ion implantation dose, the monitoring accuracy is high. Furthermore, since the factors affecting the thickness of the oxide layer formed by thermal oxidation are relatively controllable, the reliability is high, solving the problems of low monitoring accuracy and low monitoring reliability in the prior art using thermal wave methods to monitor nitrogen ion implantation.
[0068] It should be noted that although preferred embodiments have been disclosed above in this application, these embodiments are not intended to limit this application. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of this application based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the technical solutions of this application. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of this application, without departing from the content of the technical solutions of this application, shall still fall within the scope of protection of the technical solutions of this application.
Claims
1. A method for monitoring semiconductor processes, characterized in that, include: A semiconductor substrate is provided, the semiconductor substrate including at least one monitoring region; Ion implantation is performed on the monitored area; A thermal oxidation process is performed on the monitored area; Measure the thickness of the oxide layer formed by the thermal oxidation process; The thickness of the oxide layer is used to determine whether the ion implantation dose is normal.
2. The method as described in claim 1, characterized in that, The implanted element is nitrogen.
3. The method as described in claim 1, characterized in that, The step of determining whether the ion implantation dose is normal based on the thickness of the oxide layer includes: The thickness of the oxide layer is compared with the desired film thickness range; If the thickness of the oxide layer is within the expected film thickness range, the ion implantation dose is considered normal; otherwise, the ion implantation dose is considered abnormal.
4. The method as described in claim 3, characterized in that, The desired film thickness range is set using a statistical process control method.
5. The method as described in claim 1, characterized in that, The target oxide layer thickness formed by the thermal oxidation process is 20 to 60 angstroms.
6. The method as described in claim 4, characterized in that, The step of setting the desired film thickness range using a statistical process control method includes: When the ion implantation equipment is in a stable operating state, at least m sets of thickness data of the oxide layer measured by the method are continuously collected, where m≥25; Calculate the mean μ and standard deviation σ of the thickness data of the oxide layer in the m groups; μ+n*σ is used as the upper limit of the desired film thickness range, and μ-n*σ is used as the lower limit of the desired film thickness range, where 2≤n≤4.
7. The method as described in claim 6, characterized in that, The value of n is 3.
8. The method as described in claim 1, characterized in that, The semiconductor substrate is a monitoring chip specifically designed for process monitoring.
9. The method as described in claim 1, characterized in that, The step of measuring the thickness of the oxide layer formed by the thermal oxidation process includes: Before performing the thermal oxidation process, the thickness of the natural oxide layer formed in the monitored area is measured; After performing the thermal oxidation process, the total thickness of the oxide layer formed in the monitoring area is measured; The thickness of the oxide layer formed by the thermal oxidation process is obtained by subtracting the thickness of the natural oxide layer from the total thickness of the oxide layer.
10. The method as described in claim 1, characterized in that, When used for monitoring multiple ion implantation devices, it also includes: When multiple ion implantation devices are in stable operation, at least m sets of oxide layer thickness data measured by the method are continuously collected, and the mean value of the thickness data is calculated, where m≥25; Calculate the mean difference between any two ion implantation devices; If the mean difference exceeds a preset value, a check is performed on the corresponding ion implantation device.