JPH0474656B2 - - Google Patents

Description

[Detailed description of the invention]

[Purpose of the invention] (Field of industrial application) This invention forms a pattern on a substrate using a lens to be evaluated, and observes this pattern to determine astigmatism, curvature of field, and image quality of the lens to be evaluated. The present invention relates to a lens evaluation method for evaluating the performance of lenses, etc. (Prior Art) FIG. 3 is a process diagram showing this type of conventional lens evaluation method. In this method, a resist 2 is first applied onto a silicon substrate 1, as shown in FIG. 1A, and then, as shown in FIG. The pattern of the mask 4 is imaged on the resist 2, and then a resist pattern 2a is formed on the silicon substrate 1 by a development process, as shown in FIG.
In this case, a resist pattern including lines and spaces, contact holes, etc. is formed in the effective range of the lens. Such a sample,
Multiple lenses are fabricated with different imaging planes (optimal focus positions), and then observed using an optical microscope or electron microscope (hereinafter referred to as SEM), for example, images can be determined based on the degree of focus shift within the effective range of the lens. Surface curvature and inclination were evaluated, astigmatism was evaluated from the defocus of orthogonal patterns, and image quality was evaluated from the pattern shape. (Problems to be Solved by the Invention) The thickness of the resist 2 when producing the above-mentioned sample is often 1.0 [μm] or more, whereas the width of the lines and spaces is 1.0 [μm] or more.
[μm] or less may also be included, as well as
As shown in FIG. c, the sides of the resist pattern 2a are generally inclined, and the top profile and bottom profile are different. Therefore, when using an optical microscope, there is a problem that it becomes difficult to judge the resolution of resist patterns smaller than 0.8 [μm]. On the other hand, when using SEM, it is relatively easy to judge the resolution of such a resist pattern, but it requires a lot of effort and time to prepare and observe the sample, and in particular, there are problems in that multi-point observation is difficult. It was hot. Furthermore, when a plurality of types of samples are manufactured by shifting the focal point of the lens, there are cases in which the hem of the resist pattern 2a cannot be clearly identified, which makes it difficult to judge the resolution. Furthermore, in the case of a sample in which an image is extracted within the resist surface, such as a contact hole, it is difficult to judge the image simply by observing the resist pattern surface from the vertical direction. Therefore, we divided the above sample into
There is a method of cutting it and observing its cross section. In this way, it can be observed with an optical microscope or SEM,
Moreover, it is also possible to resolve resist patterns smaller than 0.8 [μm]. However, there were also problems in that it was difficult to cut the material so as to pass through the center of the contact hole, and a great deal of labor and time was required to produce a large number of samples. This invention was made to solve the above problems, and it facilitates the determination of resolution and non-resolution, as well as facilitates the evaluation of contact hole resolution.
Another object of the present invention is to provide a lens evaluation method that can significantly shorten the time required for sample production and observation. [Structure of the Invention] (Means for Solving the Problems) This invention forms a pattern on a substrate using a lens to be evaluated, and observes this pattern to determine astigmatism and image plane of the lens to be evaluated. In a lens evaluation method for evaluating performance such as curvature and image quality, first, a film to be etched is formed on the substrate, then a resist is applied on the film to be etched, and then the lens to be evaluated is forming an image of the mask on the resist film using the resist film, and forming a resist pattern corresponding to the mask by developing the resist film;
Next, the film to be etched is etched using this resist pattern as a mask material, and then the pattern of the film to be etched obtained by removing the resist is observed to evaluate the performance of the evaluation lens. It is said that (Function) In this invention, a resist pattern is formed on a film to be etched formed on a substrate, and then the bottom profile of the resist pattern is created by etching the film to be etched using this resist pattern as a mask material. Observe this bottom profile. In this case, since the etching film pattern has a slight step difference compared to the resist pattern, the entire pattern can be focused even under high magnification and low depth of focus in an optical microscope. It becomes easy to judge whether resolution is resolved or not, and it becomes easy to evaluate the resolution of contact holes.Moreover, since multi-point observation is possible, the time for sample production and observation can be significantly shortened. (Example) FIG. 1 is a process diagram for implementing this invention. Here, as shown in FIG. 1A, first, a silicon substrate 1 is prepared, a film to be etched 5 is formed on the surface thereof, and then a resist 2 is applied onto the film to be etched 5. Next, as shown in Figure b,
The pattern of the mask 4 is imaged on the resist 2 by irradiation with exposure light 3 from a lens to be evaluated (not shown), and then, as shown in FIG. resist pattern 2
form a. Next, as shown in FIG. 4D, etching is performed using the resist pattern 2a as a mask material to form an etched film pattern 5a corresponding to the bottom profile. Finally, as shown in FIG. 4E, by peeling off the resist pattern 2a, a lens evaluation sample in which only the film pattern 5a to be etched remains on the silicon substrate 1 is obtained. In this case, since the pattern 5a of the film to be etched is observed, it is desirable that the film to be etched 5 has the following properties. a; Silicon substrate 1 exposed by etching
The contrast between the etched film 5 and the remaining film to be etched 5 is large. b; The etching rate of the film to be etched 5 is much higher than that of the resist 2, that is, the etching selectivity is high. Further, it is desirable that the etching satisfies the following conditions. a; Even fine patterns such as contact holes can be etched. b; The method and conditions provide a high etching selectivity between the silicon substrate 1 and the film to be etched 5. In this example, in order to minimize the influence of flatness during exposure, a double-sided mirror wafer is used as the silicon substrate 1, and its surface is oxidized to form a silicon dioxide SiO ₂ film with a thickness of approximately 1000 Å. This is used as the film to be etched 5. As is well known, the etched surface of a silicon wafer and silicon dioxide SiO ₂ have a large contrast, so a pattern suitable for observation with a microscope can be obtained.
In addition, while a positive type resist is used as the resist 2, a dry etching method is used for etching, which is suitable for fine patterns. Dry Etching) method was adopted. In addition, more detailed conditions for CDE are exemplified as follows. Gas used and supply amount: CF ₄ = 400c.c./min O ₂ = 100c.c./min Output: 500W Pressure: 35Pa Resist 2 when etched under these conditions
When observed by SEM, the etching selectivity of the film to be etched 5 to
56.29, indicating a high selectivity with almost no regression of the resist below the measurement accuracy (435 Å). As a result, it is possible to form an etched film pattern 5a that accurately reflects the bottom profile of the resist pattern 2a. Thus, according to this example, since it is only necessary to observe the pattern of the etched film that has a high contrast with the underlying layer and has a step difference of about 1/10 compared to the resist, it is possible to use a high magnification and low focus in an optical microscope. Observations can be made even under deep conditions, thereby significantly reducing the labor and time required for evaluation. In addition, it has become possible to identify contact holes, etc. with limited resolution, especially in minute dimensions, using an optical microscope. This is also clear from the experimental results in Table 1.

【table】
Unit: Micron
That is, assume that the critical resolution of lines and spaces of the A lens observed by SEM is 0.80, and the critical resolution of contact holes is 1.00. Regarding this lens, the conventional evaluation method shown in Figure 3 shows that the line and space resolution is
0.80 and the contact hole resolution is 0.90, whereas in this example, the line and space resolution is 0.80 and the contact hole resolution is 0.80.
It was 1.00. This means that the method according to this embodiment can be evaluated more accurately than the conventional method. In addition, the same thing can be inferred from the observation results of the B lens, and furthermore, from this table, it is seen that in the conventional method, the error increases as the dimensions become smaller, but in this example, even in the micro dimensions, the error increases.
Measurement results similar to those of SEM were obtained. Furthermore, since the pattern can be easily distinguished in this embodiment, reading errors are reduced and measurement accuracy is improved. Table 2 shows the experimental results, in which the field curvature of one lens was measured multiple times.

〔Effect of the invention〕

As is clear from the above description, according to the present invention, a resist pattern is formed on a film to be etched formed on a substrate, and then the film to be etched is etched using this resist pattern as a mask material. A bottom profile of the resist pattern is created and this bottom profile is observed. In this case, since the etching film pattern has a slight step difference compared to the resist pattern, the entire pattern can be focused even under high magnification and low depth of focus using an optical microscope. In addition to making it easier to judge resolution and non-resolution, it also makes it easier to evaluate the resolution of contact holes.Furthermore, since multi-point observation is possible, the time required for sample production and observation can be significantly shortened. effective.

[Brief explanation of the drawing]

1A to 1E are process diagrams showing one embodiment of the present invention, FIG. 2 is an etching pattern obtained by the same embodiment, and FIGS. 3A to 3C are for explaining a conventional lens evaluation method. This is a process diagram. 1...Silicon substrate, 2...Resist, 2a...
...Resist pattern, 3...Exposure light, 4...Mask. 5... Film to be etched, 5a... Film pattern to be etched.

Claims (1)

[Claims] 1. Lens evaluation in which a pattern is formed on a substrate using a lens to be evaluated, and this pattern is observed to evaluate the performance of the lens to be evaluated, such as astigmatism, curvature of field, image quality, etc. In the method, first, a film to be etched is formed on the substrate, then a resist is applied on the film to be etched, and then an image of a mask is formed on the resist film using the lens to be evaluated. A resist pattern corresponding to the mask is formed by etching and development, and then the film to be etched is etched using this resist pattern as a mask material, and then the resist is removed. A lens evaluation method characterized in that the performance of the evaluation lens is evaluated by observing a pattern of a film to be etched. 2. The lens evaluation method according to claim 1, wherein a silicon wafer is used as the substrate, and the film to be etched is silicon dioxide obtained by oxidizing the surface of the silicon wafer.