TWI432915B - Method for monitoring photolithography process and monitor mark - Google Patents

Description

Method and monitoring mark for monitoring lithography process

The invention relates to a monitoring mark and blue control lithography process method which can be used for monitoring a lithography process, and more particularly to a method for monitoring a lithography process by measuring a linear end tightening size of a mark.

Generally, semiconductor devices are completed through hundreds of semiconductor processes, in which various circuit layouts on the wafer are defined by a plurality of photolithography processes. In the lithography process, a photoresist is applied on the surface of the semiconductor wafer, and then the circuit layout pattern of the reticle is mapped onto the photoresist by an exposure process, so that the chemical properties of the photoresist are The exposure is changed, and then the photoresist or the unexposed photoresist that is irradiated by the light source can be removed from the wafer by the photoresist to form a line layout corresponding to the mask. Usually, the lithography process is affected by the focus position of the lithography system. If the focus position is shifted, it will affect the accuracy of the exposed pattern and the critical dimension (CD), which will affect the score. Whether the circuit layout of the upper and lower layers can be joined as expected and the conductivity quality of the semiconductor device.

It can be seen from the above that if the focus position of the lithography process is deviated, the accuracy of the lithographic pattern formed on the wafer is considerably affected. Therefore, various process parameters of the lithography process machine must be periodically checked on the production line. package Including whether the focus position has a variation. At present, the method used by the industry to detect the focusing parameters of the machine is to make a simple geometric pattern similar to the alignment mark on the reticle, and to measure whether the machine is in the preferred focus position by measuring the lithographic size. However, the above-mentioned conventional marking pattern has less sensitivity to the change of the focus position due to the variation of the lithographic size variation, and can only test the single-point focusing situation, or the measuring machine mask must be made, which affects the overall process cost. In addition, the current method of managing the focus position of the machine does not have the function of monitoring the process conditions of the machine in real time, nor can it notify the problem or adjust the process parameters at any time according to the test result, so the quality of the product cannot be effectively grasped, and the overall capacity and cost are affected. .

The main object of the present invention is to provide a monitoring mark provided on a reticle and a method for monitoring the lithography process by using the monitoring mark to improve the conventional influence of the focus processing condition of the lithography process machine. Capacity and cost issues.

According to the scope of the present invention, there is provided a method of monitoring a lithography process, comprising providing a reticle comprising a monitor mark having at least one set of line-end monitor pattems; a lithography system capable of performing a lithography process to transfer a pattern on the reticle to a substrate; providing a process condition database including a linear end contraction of the linear end pattern after the lithography process (lire End shortening) one of the size and focus position of the lithography system Corresponding relationship; performing the lithography process to transfer the pattern on the reticle to the substrate, forming at least one lithography mark pattern corresponding to the monitoring mark, and the lithography mark pattern comprises a lithographic straight line pattern corresponding to the line pattern Measuring the lithography of the lithography mark pattern and tightening the size of the straight end to obtain a measurement result; and comparing the measurement result with the process condition database to monitor whether the focus position of the lithography process is deviated.

In accordance with the scope of the present invention, a monitoring mark for monitoring a lithography process having at least one set of straight end patterns is also disclosed. The linear pattern comprises at least ^one terminal and at least one linear pattern reference pattern, which reference pattern is provided based on a side of one end of a straight line pattern, and the reference line pattern having a distance from the end of the straight line pattern.

Please refer to FIG. 1 , which is a schematic diagram of a lithography process of the present invention. The lithography system 10 includes a stepper 12 having a light source 14, a reticle holder 16, an optical device 18, and a wafer holder 20. . In the lithography process, a photomask 22 including a product pattern is provided on the photomask holder 16, and at the same time, a target substrate such as the semiconductor wafer 24 is disposed on the wafer holder 20, and the stepper 12 is used. The light source 14 provides exposure energy to focus the product onto the photoresist material on the surface of the semiconductor wafer 24 to form a lithographic pattern on the photoresist material. Repeated exposure of different regions of the semiconductor wafer 24 by the stepper 12 to form a complex surface on the semiconductor wafer 24. After several lithographic product patterns, other semiconductor processes such as development and etching may be performed to pattern the surface material of the semiconductor wafer 24.

In order to monitor whether the lithography system 10 performs a lithography process at a good focus position setting, the present invention designs at least ^one monitoring mark on one side of the product pattern of the reticle 22 to provide a process condition for monitoring the lithography system 10 in real time. Yield function. Please refer to FIG. 2, which is a schematic diagram of a monitoring tag 30 for providing a real-time focus monitor (RTFM) function according to the present invention. The monitoring mark 30 includes a set of straight end monitoring patterns 32, wherein the straight end monitoring pattern 32 includes at least a straight line pattern 34 and a reference pattern 36 disposed on one side of one end 34a of the straight line pattern 34, and the reference pattern 36 preferably includes a vertical A reference straight line pattern (shown in FIG. 2) of one of the straight lines 34 has a line spacing D from the end 34a of the straight line pattern 34. In a preferred embodiment of the invention, the linear pattern 34 may have a line width W of about 0.15 to 0.30 microns and a line spacing D of about 0.5 microns.

Since the resolution limit of the general exposure machine causes the lithography pattern to have a 1ine-end shortening effect, the pattern formed by the monitor mark 30 of the present invention on the surface of the semiconductor wafer 24 after the lithography process. The end 34a is also tightened down by a size due to the linear end tightening effect. Please refer to FIG. 3, which is a schematic diagram of the lithography mark pattern 30' formed on the surface of the target substrate after the tampering process of the monitor mark 30 of the present invention. The lithography mark pattern 30' includes a lithography straight line pattern 34' and a lithography reference pattern 36', respectively corresponding to the straight line pattern 34 and the reference pattern 36 on the reticle 22, and the lithography mark pattern 3', and another line From D', Corresponding to the line spacing D of the original monitoring mark 30. Under the influence of the tightening effect at the end of the straight line, the end 34' is tightened such that the line pitch D' is larger than the original line pitch D, and the line pitch D' is the sum of the original line distance D and the straight line end tightening size S. Since the linear end tightening size S has a relatively high sensitivity to the in-focus position of the lithography system 10, if the focus position of the lithography system 10 is slightly deviated, the linear end tightening size S will be greatly varied, and the focus will be When the positional deviation is larger, the straight end end tightening size S is also larger. Therefore, the present invention utilizes this characteristic to monitor the process conditions of the lithography system 10 by measuring the straight end end tightening size S or the line pitch D'.

Please refer to FIG. 4, which is a graph showing the relationship between the line spacing D' of the RTFM monitor mark after exposure and the in-focus position of the lithography system, wherein the vertical axis represents the CD value of the line spacing D'. As shown in the figure, when the focus position is slightly mutated, the line pitch D' changes significantly, and the more the focus position shifts, the larger the CD value of the line pitch D'. Furthermore, since the relationship between the line spacing D' and the focus position of the lithography system is a concave arc-shaped curve, the lowest point of the arc-shaped curve can be regarded as the best focus position of the lithography system. At this time, the line spacing D' also has a minimum CD value, as indicated by the dotted circle in the figure.

As described above, the present invention utilizes a straight end pattern to have a relatively high sensitivity characteristic to the focus position of the lithography system, and applies it to the monitoring mark by measuring the CD value of the line end line distance after lithography. And according to the graph shown in Figure 4, it is possible to monitor whether the lithography system or the machine is performing the lithography process under the preferred focusing condition. For example, according to Figure 4, when the lithography system is in the best focus When the lithography process is performed at a position of 0.1 μm, the CD value of the lithographic line pitch D' of the lithography mark pattern formed on the target substrate should be about 0.93 μm. However, if the line distance D of the lithography mark pattern is measured after the lithography process, the result is greater than 0.93 μm, and it can be known that the focus position of the lithography system is deviated. Further, if the measured CD value of the line pitch D' is 0.98 μm, it can be seen from the graph of Fig. 4 that the in-focus position of the lithography system may be shifted to -0.3 or 0.45 μm. Therefore, a process condition database including the graph shown in FIG. 4 is provided before the lithography process, and the lithography mark pattern line pitch D' after each lithography process is measured, and the process condition database is further measured. By comparing, the focus of the lithography system can be grasped instantly. If the focus deviation occurs, the process parameters of the lithography system can be adjusted at any time to maintain good process conditions.

It should be noted that in other embodiments, the graph shown in FIG. 4 can also be used as the vertical axis coordinate of the linear end tightening dimension S shown in FIG. 3, and can also display the lithography mark pattern for focusing on the lithography system. The high sensitivity and relative relationship of positional variation.

Please refer to FIG. 5, which is a schematic diagram of a preferred embodiment of the monitoring mark of the present invention. The monitoring mark 40 of the present invention comprises a complex array of straight end monitoring patterns 42 (four groups are shown in FIG. 5), and each set of straight end monitoring patterns 42 includes a line pattern 44 and two reference patterns 46, 48, which are respectively disposed in the line pattern 44. One side of a straight end has a line spacing D from the straight line pattern 44. In addition, the linear patterns 44 of the respective sets of straight end monitoring patterns 42 are not parallel to each other, for example, each set of straight end monitoring patterns The angle between the linear pattern 44 of 42 and the horizontal axis is 0∘, 45∘, 90∘ and 135∘, respectively, and intersect at an intersection O, in a "meter" shape, wherein the intersection O is preferably about a straight line pattern 44. The middle point. Moreover, when monitoring the lithography process, the line spacing D' after the lithography of the four sets of linear end monitoring patterns 42 can be measured to monitor the lithography and focusing of the different angle patterns.

On the other hand, when the lithography system 10 is actually monitored by the monitoring mark 40 of the present invention, the monitoring mark 40 is integrated on the reticle containing the product pattern. Figure 6 is a schematic view of a reticle including the monitor mark 40 shown in Figure 5 of the present invention. As shown in Fig. 6, the mask 50 includes an exposure area 56 which is transferred to the target substrate in an exposure process of the lithography process. The exposed area 56 includes a plurality of product pattern areas 52 and at least one scribe line area 54, wherein the scribe line areas 54 are wrapped around the periphery of the product pattern area 52. A product pattern (not shown) is disposed in the product pattern area 52, and the main purpose of the lithography process is to transfer the product pattern to the target substrate. The monitoring mark 40 of the present invention is disposed in the scribe line region 54, adjacent to the product pattern region 52, and preferably located at a corner, a center point, and a midpoint of the exposed portion 56. Generally, the monitoring mark 40 is also It is disposed adjacent to the periphery of the corner of the product pattern area 52. In Fig. 6, when one exposure process of the lithography process is performed, the product pattern in the product pattern area 52 and the monitor mark 40 in the scribe line area 54 are simultaneously lithographically imaged to the target substrate, and a repeated exposure process is similarly performed. The exposed area 56 is lithographically drawn to different portions of the target substrate surface to complete a lithography process.

The method for monitoring the focus condition of the present invention is to measure the lithography mark pattern on the target substrate by using a scanning electron microscopy (SEM) or other instrument after performing a lithography process, for example, for example, by using a scanning electron microscopy (SEM) or other instrument. The CD values corresponding to the line spacing D' corresponding to the first group, the second group, the third group or the fourth group of linear end monitoring patterns 42a, 42b, 42c, 42d are respectively measured as needed, and then as shown in FIG. 4 Comparing the process condition database such as the graph and the CD value comparison and analysis of the linear end line distance D' after the lithography as described above, it can be known whether the focus deviation and the deviation are.

In the present embodiment, at least three monitor marks 40 are placed in different portions of the scribe lane region 54 in an exposure region 56 to monitor the focus plane deviation for the lithography process. The method comprises: after performing the lithography process or after one exposure process, respectively checking the lithography mark patterns corresponding to the at least three monitoring marks 40, and measuring the linear end tightening size S or the line spacing D′ of each lithography mark pattern, The comparison between the measurement result and the process condition database can be used to know whether the focus plane has a tilt deviation, and further know the deviation values in the horizontal and vertical directions.

7 is a schematic flow chart of a method for monitoring a lithography process of the present invention, comprising the following steps: Step 100: providing a reticle comprising at least one product pattern and at least one monitoring mark of the invention, as shown in FIG. Wherein the monitoring indicia of the present invention comprises at least one set of rectilinear end monitoring patterns, and in the preferred embodiment, comprising four sets of rectilinear end monitoring patterns as shown in Figure 5, and each set The straight line end monitoring patterns all have a straight line pattern and a reference pattern, and the reference pattern has a line spacing with the end of the line pattern; Step 102: providing a lithography system for performing a lithography process to turn the light in step 100 The mask pattern is transferred to a surface layer of a target substrate, such as a photoresist material, wherein the monitor mark of the present invention forms a corresponding lithography mark pattern on the surface layer after lithography; step 104: providing the lithography system a process condition database 116, which is related to the relative relationship between the line spacing D' (or the straight end dimension S) of the lithography mark pattern and the focus position of the lithography system, as shown in FIG. 4; Step 106: Optionally, according to the process condition database 116, set a minimum CD value 118 of the best focus position of the lithography process and a corresponding line pitch D' (or a straight end end size S); 108: performing a lithography process, transferring the monitoring mark on the reticle to the target substrate to obtain a lithography mark pattern; and step 110: measuring the straight end end size S of the lithography mark pattern or The CD value from D, to obtain a measurement result; Step 112: Compare the measurement result of step 110 with the process condition database 116 of step 104, or compare the measurement result with the line spacing D'/linear end Comparing the minimum CD value 118 of the compact size S, it is known whether the lithography system has a distance between the focus deviation and the deviation; and step 114: when the measurement result of the step 110 is greater than the line distance D'/the straight end end tightening size S When the minimum CD value is 118, it can be entered according to the process condition database 116. Line detection and adjustment of the process conditions of the lithography process.

According to the method of the present invention, a statistical process control (SPC) system may be additionally provided, and the comparison result of step 112 is immediately transmitted back to the SPC system, and if the focus position of the lithography process is found to be deviated. The SPC system can notify the relevant operator in step 114 to detect and adjust the lithography system according to the comparison result, so as to achieve the purpose of monitoring and adjusting the process parameters in real time, and maintaining the lithography system at a better focus position and the like. Under the conditions, improve product yield at the same time. On the other hand, the SPC system can also record the result of each step 112, or set the SPC system to perform focus plane deviation detection on the lithography process at a fixed period to provide periodic analysis of the performance of the lithography system.

In addition, when the process condition database 116 is provided in step 104, one of the standard process conditions of the lithography system of the present invention may be provided in advance, including the photoresist material of the lithography process, the exposure conditions, and the process parameters of the lithography system and related A process condition database 116 is established based on the standard process conditions, such as the focus position. In addition, the method for establishing the process condition database 116 is shown in FIG. 8 and includes the following steps: Step 200: providing at least one test substrate; Step 202: performing a lithography test process using the lithography system, including different focus positions And performing a plurality of lithography processes, repeatedly lithographically patterning the reticle of step 100 on the test substrate to form a plurality of test mark patterns; and step 204: measuring a line of each test mark pattern on the test substrate From D' or straight line The end tightening dimension S, the measured data and the corresponding in-focus position of the test processes are made into a graph as shown in FIG. 4 to establish a process condition database 116.

On the other hand, in addition to online mass production, the monitoring mark of the present invention can be used to monitor the focus position of the lithography system in real time, and the monitoring mark 40 of the present invention as shown in FIG. 5 can also be applied to the development of the test reticle, By setting at least three monitoring marks 40 and performing a test lithography process in the dicing area of the test reticle, it is possible to know whether the plane has a focus plane deviation, tilt, and optical system deformation during the lithography process. (lens aberration) or geometric curvature (curvature) variation, etc., to improve the mask design or machine settings.

Compared with the prior art, the present invention provides a high-sensitivity monitoring mark for the focus position by utilizing the sensitivity characteristics of the end of the straight line pattern relative to the focus position of the machine. In addition, the method for monitoring the lithography process of the present invention carefully sets the monitoring mark in the dicing area of the reticle, and simultaneously lithographically displays the monitoring mark and the product pattern of the present invention onto the target substrate during the exposure process, and After each batch of lithography process in mass production, by measuring the linear end line pitch or the straight end end of the monitoring mark of the present invention, it is immediately known whether the focus position of the machine is deviated, so that no downtime is required for testing. It can be monitored with the SPC system with the product, without affecting the process capacity, and can instantly master the results of the lithography process, improve the yield and reduce the process cost.

The above description is only a preferred embodiment of the present invention, and the patent application patent according to the present invention Equivalent changes and modifications made by the surrounding are intended to be within the scope of the present invention.

10‧‧‧ lithography system

12‧‧‧Stepper

14‧‧‧Light source

16‧‧‧Photomask holder

18‧‧‧Optical device

20‧‧‧ Wafer bearing

22‧‧‧Photomask

24‧‧‧Semiconductor wafer

30‧‧‧Monitor mark

32‧‧‧Line end monitoring pattern

34‧‧‧Line pattern

34a‧‧‧Line pattern end

36‧‧‧ reference pattern

30’‧‧‧ lithography mark pattern

34'‧‧‧ lithography straight line pattern

34a’‧‧‧ lithography straight line end

36'‧‧‧ lithography reference pattern

40‧‧‧Monitor mark

42‧‧‧Line end monitoring pattern

42a‧‧‧The first set of straight end monitoring patterns

42b‧‧‧Second set of linear end monitoring patterns

42c‧‧‧The third set of linear end monitoring patterns

42d‧‧‧Fourth set of linear end monitoring patterns

44‧‧‧Line pattern

46, 48‧‧‧ reference pattern

50‧‧‧Photomask

52‧‧‧Product pattern area

54‧‧‧Cut Road Area

56‧‧‧Exposure area

100~114‧‧‧ Method flow for monitoring lithography process

116‧‧‧Process Condition Database

118‧‧‧Minimum minimum end CD size after lithography

200~204‧‧‧ Method flow for establishing a process condition database

1 is a schematic view of a lithography system for performing a lithography process of the present invention.

Figure 2 is a schematic diagram of the RTFM monitoring flag of the present invention.

Fig. 3 is a schematic view showing the lithography mark pattern formed by the monitoring mark after the lithography process shown in Fig. 2.

Fig. 4 is a graph showing the relationship between the linear end line pitch of the RTFM monitor mark after exposure and the focus position of the corresponding lithography system.

Figure 5 is a schematic illustration of another embodiment of the RTFM monitoring tag of the present invention.

Figure 6 is a schematic view of a reticle including the monitoring mark shown in Figure 5 of the present invention.

FIG. 7 is a schematic flow chart of a method for monitoring a lithography process of the present invention.

Figure 8 is a schematic flow chart of establishing a process condition database according to the present invention.

100~114‧‧‧ Method flow for monitoring lithography process

116‧‧‧Process Condition Database

118‧‧‧Minimum minimum end CD size after lithography

Claims (4)

A monitoring mark for monitoring a lithography process, the monitoring mark comprising four sets of straight end patterns, each set of straight end patterns comprising a straight line pattern and two reference straight line patterns, wherein the two reference straight line patterns are respectively disposed at one end of the straight line pattern and Vertically adjacent to the line pattern, the reference line pattern has a line spacing from the end of the line pattern, wherein the line patterns of the four sets of line end patterns intersect at an intersection and are at an angle of 0° to a horizontal axis, respectively. 45°, 90° and 135°. The monitoring mark according to item 1 of the patent application, wherein the intersection point is a midpoint of one of the straight line patterns. The monitoring mark as described in claim 1 wherein the linear patterns are arranged in a "meter" shape. The monitoring mark as described in claim 1 is disposed in a scribe line area of a reticle, and the monitoring mark is transferred to a product pattern on the reticle through a lithography process. On the substrate.