A method for focus monitoring for a semiconductor lithography process

Abstract

The application relates to the field of semiconductor photoetching technology, and discloses a focus monitoring method for a semiconductor photoetching process, which forms a focus monitoring mark on a mask plate, and monitors defocusing of different positions of a product wafer by using the focus monitoring mark. The application solves the problems of the prior art, such as the inability to monitor the difference of defocusing in a wafer, the inability to monitor defocusing without interrupting production, the increase of process cost and manufacturing cost of the mask plate caused by monitoring defocusing, and the like.

Description

Technical Field

[0001] This invention relates to the field of semiconductor lithography technology, specifically a focus monitoring method for semiconductor lithography processes. Background Technology

[0002] Photolithography patterning techniques below 20nm have reached their resolution limit, leading to defects due to defocusing. Maintaining optimal focus on exposure equipment is crucial, making a simple and convenient method for monitoring defocusing important. Current methods typically use photomask patterns to isolate defocusing, identifying changes in focus density (CD) and profile for assessment. However, this method cannot measure the degree of defocusing based on its location within the wafer. Using product wafers requires production interruption for evaluation. This method cannot measure differences in defocusing within the wafer, and the need to interrupt production for evaluation when using product wafers can lead to reduced throughput. The technology of this invention eliminates the need for production interruption for evaluation even when using product wafers, allowing for precise measurement of the degree of defocusing at all locations within the wafer.

[0003] Regarding defocus monitors, previous and current inventions have all utilized PSM (phase shift mask) technology. The implementation involves first adjusting one side of the overlay mark line (alignment unit) to phase 0° and the other side to phase 90°, then adjusting the quartz depth to create the mask (mark). The degree of mark switching varies depending on the severity of the defocus, thus allowing for measurement of the degree of defocus. This technology can measure the degree of defocus at different locations on the wafer. However, to form the focus monitor mark, additional processes are required during photomask fabrication. Adjusting the quartz depth has low reproducibility, leading to a high mask rejection rate. Therefore, the cost of mask fabrication is high, making it unusable in production environments. Summary of the Invention

[0004] To overcome the shortcomings of existing technologies, this invention provides a focus monitoring method for semiconductor photolithography processes, which solves the problems of existing technologies, such as the inability to monitor differences in defocus within the wafer, the inability to monitor defocus without interrupting production, and the significant increase in mask processing costs and manufacturing costs caused by monitoring defocus.

[0005] The technical solution adopted by the present invention to solve the above problems is:

[0006] A focus monitoring method for semiconductor photolithography processes involves forming focus monitoring marks on a photomask and using these marks to monitor defocusing at different locations on the product wafer.

[0007] As a preferred technical solution, the focus monitoring mark is placed within the groove of the mask plate.

[0008] As a preferred technical solution, each exposure area within the lane is equipped with two or more focus monitoring markers.

[0009] As a preferred technical solution, the focus monitoring mark is a pattern composed of several alignment units with the same line width.

[0010] As a preferred technical solution, several alignment units with the same line width are arranged at equal intervals.

[0011] As a preferred technical solution, the focus monitoring marker consists of at least five or more alignment units, which are within the resolution of the scanning lithography machine.

[0012] As a preferred technical solution, the focus monitoring markers are designed with different deviations and have the same or similar ADI CD values ​​in the same exposure dose.

[0013] As a preferred technical solution, the defocusing of different positions on the product wafer is monitored by calculating the CD value of the alignment unit.

[0014] As a preferred technical solution, the ADI CD difference of the focus monitoring marks with different deviations is calculated, and the direction of defocus is measured according to whether the calculated difference value is positive or negative.

[0015] As a preferred technical solution, the defocusing of different positions on the product wafer is monitored based on the characteristics of CD value changes.

[0016] Compared with the prior art, the present invention has the following advantages:

[0017] The focus monitoring mark of this invention uses a common mask manufacturing process to form the focus monitoring mark, allowing for the determination of the degree of defocus regardless of the wafer's location. It is inexpensive, avoiding significant increases in mask manufacturing costs and overall production costs. Furthermore, it allows for the monitoring of defocus without interrupting production, adapting to different wafer positions. Compared to previous technologies, it eliminates the need for special mask manufacturing processes, maintains the same mask price, and allows for the determination of defocus at all wafer points. It also provides more convenient and accurate monitoring of wafer defocus. This solves the problems of existing technologies, such as the inability to monitor defocus differences within the wafer, the inability to monitor defocus without interrupting production, and the significant increase in mask manufacturing costs associated with defocus monitoring. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the focus monitoring mark of the present invention;

[0019] Figure 2 One of the schematic diagrams showing the focus monitoring indicators corresponding to different Mask CD values;

[0020] Figure 3 The second illustration shows the focus monitoring indicators corresponding to different Mask CD values;

[0021] Figure 4 The third illustration shows the focus monitoring indicators corresponding to different Mask CD values;

[0022] Figure 5 for Figure 2 , Figure 4 A schematic diagram of the focal monitoring markers obtained after some areas overlap. Detailed Implementation

[0023] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the embodiments of the present invention are not limited thereto.

[0024] Example 1

[0025] like Figures 1 to 5 As shown, a focus monitoring method for semiconductor photolithography processes is described, in which focus monitoring marks are formed on a photomask, and the focus monitoring marks are used to monitor defocusing at different positions on the product wafer.

[0026] The focus monitoring mark of this invention uses a common mask fabrication process to form the focus monitoring mark, allowing for the determination of the degree of defocus regardless of the wafer's location. It is inexpensive and does not significantly increase the cost of mask fabrication or manufacturing. It also offers the advantage of monitoring defocus without interrupting production, depending on the wafer's position. Compared to previous technologies, it does not require a special mask fabrication process, maintains the same mask price, and can monitor the degree of defocus at all points on the wafer. This solves the problems of existing technologies, such as the inability to monitor differences in defocus within the wafer, the inability to monitor defocus without interrupting production, and the significant increase in mask fabrication and manufacturing costs associated with defocus monitoring.

[0027] As a preferred technical solution, the focus monitoring mark is placed within the groove of the mask plate.

[0028] As a preferred technical solution, each exposure area within the lane is equipped with two or more focus monitoring markers.

[0029] The setting of focus monitoring indicators in the above preferred technical solutions is beneficial for more accurate monitoring of defocusing.

[0030] As a preferred technical solution, the focus monitoring mark is a pattern composed of several alignment units with the same line width.

[0031] As a preferred technical solution, several alignment units with the same line width are arranged at equal intervals.

[0032] As a preferred technical solution, the focus monitoring marker consists of at least five or more alignment units, which are within the resolution of the scanning lithography machine.

[0033] The structure of the focus monitoring marker in the above preferred technical solutions is conducive to more accurate monitoring of defocusing.

[0034] As a preferred technical solution, the focus monitoring markers are designed with different deviations and have the same or similar ADI CD values ​​in the same exposure dose.

[0035] As a preferred technical solution, the defocusing of different positions on the product wafer is monitored by calculating the CD value of the alignment unit.

[0036] As a preferred technical solution, the ADI CD difference of the focus monitoring marks with different deviations is calculated, and the direction of defocus is measured according to whether the calculated difference value is positive or negative.

[0037] As a preferred technical solution, the defocusing of different positions on the product wafer is monitored based on the characteristics of CD value changes.

[0038] By employing the above-mentioned preferred technical solutions and utilizing CD values ​​(difference, variation characteristics, etc.), it is easier and more accurate to monitor the defocusing of product wafers.

[0039] Example 2

[0040] like Figures 1 to 5 As shown, as a further optimization of Embodiment 1, this embodiment also includes the following technical features based on Embodiment 1:

[0041] The focus monitoring mark of this invention uses a common mask, which is inexpensive, and has the advantage of being able to measure defocusing, depending on the position of the chip in the product. The focus monitoring mark of this invention is as follows: Figure 1 Line and space (effective line width and spacing) form a regular, repeating pattern. Generally, in patterns formed by lines and spaces, when exposure energy increases, out-of-focus areas occur, causing the line CD (critical dimension) to decrease; conversely, when exposure energy decreases, out-of-focus areas occur, causing the line CD to increase. For example... Figure 1 This indicates that the CD (disc change) characteristics are generally observed based on exposure dose and defocus.

[0042] like Figure 2 To reduce the mask bar size, at the same exposure dose fulcrum, the Wafer CD is compared to... Figure 1 You can see the result of the bar CD decreasing. As the mask CD gradually increases, with... Figure 2 -> Figure 3 -> Figure 4 The order shows that the average CD of the wafer increases. If the mask size within a mask is based on other repeating line and space graphics, then at the same exposure dose... Figure 5 Although the average CD values ​​are different, similar results can be obtained regarding CD variations. Figure 5 If the CD curves –U for L1 under dose (below L1 dose) and –O for L3 over dose (above L3 dose) overlap, we can obtain mutually symmetrical CD curves with opposite characteristics.

[0043] See the results of L3–L1, such as Figure 5You can see the positive and negative value ranges. In case the process margin range changes drastically due to the positive range, and a mask design is needed, you can use this to determine whether the difference in CD value is positive or negative, and whether the level of defocusing affects the process. Even if the CD value is positive, defocusing defects can be prevented in advance through process management.

[0044] This invention provides a method for measuring focus in a photolithography process. It includes a reticle and reticle stage (mask and mask workpiece stage), and a structure including a projection lens system, a wafer, and a wafer stage. To understand the focus, it does not perform focus splitting and does not use special masks such as alternative phase-shift masks (PSM masks), allowing observation of focus changes in a real product wafer.

[0045] Preferably, in the first item, the focus monitoring marker is located in the scribe lane within the mask, and is designed to be at least two or more per shot.

[0046] Preferably, the focus monitoring marker is a repetitive line and space graphic, consisting of at least five lines and a pitch (alignment unit, i.e., graphic size, which includes effective line width and space) within the resolution of a scanner. The focus monitoring marker is designed with different biases and has the same or similar ADI CD size at the same exposure dose.

[0047] Preferably, the ADI CD difference of different bias marks is calculated, and the sign of the calculated value is set to either plus or minus (positive or negative) to sense the direction of defocus.

[0048] The technology of this invention uses a standard mask manufacturing process to create a focus monitoring marker and monitor the focus value (CD). Regardless of the wafer's position, the degree of defocus can still be determined. Like previous technologies, this method eliminates the need for special mask manufacturing processes, maintains the same mask price, and allows for control of defocus at all points on the wafer.

[0049] This invention allows for the control of defocusing at all points on the wafer, enabling the prevention of defects. Therefore, improved yield can be expected. As with previous and current technologies, no special mask manufacturing is required, and mask prices will not increase.

[0050] As described above, the present invention can be implemented well.

[0051] All features disclosed in all embodiments of this specification, or steps in all methods or processes implied in the disclosure, may be combined and / or extended or replaced in any way, except for mutually exclusive features and / or steps.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Based on the technical essence of the present invention, any simple modifications, equivalent substitutions, and improvements made to the above embodiments within the spirit and principles of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for focus monitoring in semiconductor photolithography processes, characterized in that, Focus monitoring marks are formed on the photomask, and these marks are used to monitor defocusing at different locations on the product wafer. The focus monitoring marks are placed in the scribe lines of the photomask, and two or more focus monitoring marks are provided in each exposure area within the scribe lines; the focus monitoring marks are a pattern composed of several alignment units of the same line width, and the alignment units of the same line width are arranged at equal intervals; the focus monitoring marks are composed of at least five or more alignment units, and the alignment units are within the resolution of the scanning lithography machine. The two or more focus monitoring markers are designed with different deviations and have similar ADI CD values ​​in the same exposure dose; the ADI CD difference of the focus monitoring markers with different deviations is calculated, and the direction of defocus is measured according to whether the calculated difference value is positive or negative; the defocus of different positions of the product wafer is monitored according to the characteristics of ADI CD value change.

Images