KR100791680B1 - Method for exposing in a stepper - Google Patents

Abstract

An exposure method of a stepper is provided to guarantee a focus margin and reduce a decrease of an exposure latitude by performing an exposure process under at least three exposure conditions determined based upon exposure energy of an optimum condition, a focus of an optimum condition, a maximum focus and a minimum focus. Focus and exposure energy of an optimum condition is calculated with respect to a semiconductor substrate coated with photoresist, and a maximum focus and a minimum focus capable of being exposed are calculated(S300). A reticle image is exposed in a first exposure condition in which the exposure energy and focus of the optimum condition is varied. The reticle image is exposed in the focus of the optimum condition and at exposure energy varied from the exposure energy of the optimum condition by a predetermined value. The reticle image is exposed in a second exposure condition in which the exposure energy and focus of the optimum condition is varied. The first exposure condition can be exposure energy corresponding to 20 % of the exposure energy of the optimum condition and the maximum focus.

Description

Exposure method of stepper {METHOD FOR EXPOSING IN A STEPPER}

1 is a view for explaining a conventional single exposure method,

2 is a view for explaining a conventional dual exposure method,

3 is a flowchart illustrating an exposure process of a stepper according to an exemplary embodiment of the present invention.

FIG. 4 is a diagram for describing a process of performing an exposure process based on an exposure condition which is the last step of FIG. 3.

5 is a graph for explaining the difference in the stepper exposure process between the present invention and the prior art.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stepper exposure method, and more particularly, to a stepper exposure method capable of securing a focus margin and reducing a reduction in exposure margin.

In general, the exposure method of the photolithography process is largely divided into a contact method and a projection method, which are rarely used in the manufacture of semiconductor devices at present, but in some cases when the alignment margin is large. Also used. In addition, a projection method is a method of transferring a pattern formed on a mask onto an exposed substrate, that is, a wafer using light, and is classified into a stepper method and an aligner method.

Since the stepper method is limited by the effective inner diameter of the projection lens when performing a single exposure operation, the reticle pattern is repeatedly exposed while moving the stage. Through-put While this is deteriorated, there is an advantage that the alignment is improved. The reticle is a pattern of an opaque metal such as chromium is mainly formed on the surface of the quartz plate. The aligner method basically improves throughput by transferring patterns by simultaneously scanning a uniform optical path with a mask and plate size of 1: 1, but the degree of alignment is lower than that of the stepper method in the wide area, that is, in terms of wide area alignment. have. Therefore, at present, a stepper is mainly used in the exposure process for manufacturing a highly integrated semiconductor element.

On the other hand, as the integration of semiconductor devices increases, photography process engineers monitor the dose and focus of the light of stepper equipment more frequently and tune processes using simulation tools to advance the processor with reduced photoprocessing margins. We are working to ensure reduced photo process margins using Resolution Enhancement Technology (RET) technology.

Conventional photo process margin securing methods include a single exposure method and a dual exposure method.

First, as shown in FIG. 1, as shown in FIG. 1, an optimum exposure condition is found by an ED-Tree (Energy Defocus) method, and then an exposure process is performed through the reticle image 10 as an exposure condition. A predetermined photosensitive film pattern is formed on the coated semiconductor substrate.

Herein, a process of finding an optimal exposure condition by using the ED-Tree method will be described. First, a photosensitive film pattern is formed by dividing an exposure energy and a focus value differently for each region of a semiconductor substrate coated with a photoresist. After that, the CD of the photosensitive film pattern is measured with an electron microscope (SEM) to calculate the exposure energy and the focus under the optimum conditions.

As such, the calculated optimal conditions are used to determine the reticle image to be used in the exposure process.

In FIG. 1, when the optimum condition is an exposure energy of 24mj / cm 2 and the focus is 0 μm, exposure is performed using one reticle image 10 under such an optimum condition.

As described above, since the exposure energy and the focus of all the reticle images 10 are determined to be the same value, the single exposure method facilitates the management of the exposure energy and the focus. In addition, even if the CD tolerance range is managed at ± 30 nm, the effect of lowering the yield has been overcome by maintaining the CD uniformity of the edge portion of the semiconductor substrate with only the capability of the stepper itself without any change in the overall film quality.

However, with the recent entry into the era of ultra-high density semiconductor devices, the conventional single exposure method as described above maintains the CD uniformity of the edge of the semiconductor substrate only with the capability of the stepper itself, even if managed within the CD tolerance range of ± 15 nm. It is difficult to secure the margin of the photo process because it becomes difficult.

For this reason, there is a dual exposure method to secure a second photo process margin.

In the dual exposure method, as shown in FIG. 2, the exposure is performed using the first reticle image 20 under an exposure condition in which the focus is changed by a predetermined value in the + direction and the exposure energy is reduced by 1/2 among the optimal conditions. Then, the exposure is performed by using the reticle image 22 under an exposure condition in which the focus is changed by a predetermined value in the − direction and the exposure energy is reduced by 1/2. Here, the first and second reticle images 20 and 22 are the same reticle image.

That is, in FIG. 2, when the exposure energy of the optimum condition is 24mj / cm 2 and the focus value is 0 μm, the exposure process is performed on the first reticle image 20 under the condition of the exposure energy of 12mj / cm 2 and the focus of −3 μm. After the exposure, the exposure process is performed on the second reticle image 20 under conditions of an exposure energy of 12mj / cm 2 and a focus of +3 μm.

In the case of the dual exposure technology, the focus margin (DOF) is increased, but the exposure margin (EL: Exposure Latitude) is reduced due to a problem that it is difficult to apply to the actual process.

SUMMARY OF THE INVENTION An object of the present invention is to solve such problems of the prior art, and by reducing the exposure margin by performing an exposure process based on at least three or more exposure conditions set on the basis of optimal exposure energy, focus, maximum focus, and minimum focus. In addition, the present invention provides a stepper exposure method capable of reducing the focus margin and securing a focus margin.

In order to achieve the above object, the present invention provides a stepper exposure method, comprising: a first step of calculating a focus and exposure energy of optimal conditions for a semiconductor substrate coated with a photoresist, and calculating a maximum focus and a minimum focus that can be exposed; And a second step of exposing the reticle image to a first exposure condition with a change in focus and exposure energy of the optimum condition; and a reticle with an exposure energy that is constant changed from the focus energy of the optimum condition and the exposure energy of the optimum condition. A third step of exposing the image, and a fourth step of exposing the reticle image under a second exposure condition in which the exposure energy and focus of the optimal condition are changed.

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Here, the first exposure condition is an exposure energy corresponding to 20% of the exposure energy of the optimal condition and the maximum focus value, and the second exposure condition is 20% of the exposure energy of the optimal condition and the minimum focus. Value.

In the third step, the reticle image is exposed using only 60% of the exposure energy under the optimum conditions.

 Detailed technical configuration of the present invention will be described in detail below with reference to the accompanying drawings.

3 is a flowchart illustrating an exposure process of a stepper according to a preferred embodiment of the present invention, FIG. 4 is a view for explaining a process of performing an exposure process based on an exposure condition which is the last step of FIG. It is a graph for explaining the difference in the stepper exposure process between the present invention and the prior art.

Referring to FIG. 3, in step S300, prior to arranging all the exposure steps of the stepper, the exposure energy and the focus margin are evaluated for all regions of the semiconductor substrate to which the photoresist is applied. In more detail, the photoresist-coated wafer is equally divided into unit regions, and the semiconductor substrate is subjected to a conventional developing process after the exposure is performed while splitting exposure energy and focus to each unit region. To be processed. After the processing of the developing step is completed, the focus margin and exposure energy margin in each region of the semiconductor substrate are evaluated using an electron microscope (SEM). That is, in step S300, the exposure energy and the focus of the optimum condition are calculated, and the maximum and minimum focus that can be exposed are calculated.

Then, in step S302, three exposure conditions are set based on the calculated exposure energy and focus, maximum focus, and minimum focus of the optimum conditions. That is, 20% of the optimal exposure energy and the maximum focus are set to the first exposure condition, 60% of the optimal exposure energy and the focus of the optimal condition are set to the second exposure condition, and 20% and the minimum of the optimal exposure energy are set. The focus is set to the third exposure condition.

Then, in step S304, the exposure process is performed based on the first, second, and third exposure conditions set through the above process. That is, as shown in FIG. 4, the exposure process is performed on the reticle image 400 using the first exposure condition, and then the exposure process is performed on the reticle image 400 using the second exposure condition. The desired pattern is formed on the semiconductor substrate by performing the exposure process after performing the exposure process on the reticle image 400 using the three exposure conditions.

That is, in the exposure process using the first exposure conditions, only 20% of the exposure energy of the optimal exposure energy is supplied, the stepper equipment is adjusted to the maximum focus, the exposure process is performed on the reticle image, and the second exposure condition is used. In the exposure process, only 60% of the exposure energy of the optimal condition is supplied, the stepper equipment is adjusted to the focus of the optimal condition, and the exposure process is performed on the reticle image. The photoresist pattern is formed on the semiconductor substrate by supplying only 20% of the exposure energy, and adjusting the stepper equipment to the minimum focus, and then performing an exposure process on the reticle image.

According to the present invention, by performing the exposure process based on the first, second and third exposure conditions set based on the exposure energy, focus, maximum focus and minimum focus of the optimum conditions, as shown in FIG. Compared to the single method, the reduction in the exposure margin is smaller and stable focus margin can be obtained.

That is, as shown in FIG. 5, even if the applied focus margin of the present invention increases, the decrease in the exposure margin decreases, whereas in the conventional dual method, the decrease in the exposure margin increases when the focus margin increases by a certain amount or more. have.

The present invention is not limited to the above-described specific preferred embodiments, and various modifications can be made by any person having ordinary skill in the art without departing from the gist of the present invention claimed in the claims. Of course, such changes will fall within the scope of the claims.

As described above, the present invention performs the exposure process based on at least three or more exposure conditions set based on the optimum exposure energy, focus, maximum focus, and minimum focus, thereby reducing the reduction in the exposure margin and the focus margin. It can be secured to form a fine pattern effectively.

Claims (5)

delete As a stepper exposure method, A first step of calculating a focus and exposure energy of optimal conditions for the semiconductor substrate coated with the photoresist, and calculating a maximum focus and a minimum focus that can be exposed; A second step of exposing the reticle image to a first exposure condition in which the exposure energy and focus of the optimum condition are changed; Exposing the reticle image with exposure energy that is constant from the focus of the optimal condition and the exposure energy of the optimal condition; A fourth step of exposing the reticle image to a second exposure condition in which the exposure energy and focus of the optimum condition are changed; Stepper exposure method comprising a. The method of claim 2, The first exposure conditions, And exposure energy corresponding to 20% of the exposure energy under the optimum conditions and the maximum focus. The method of claim 2, The second exposure condition is, 20% of the exposure energy of the optimum condition and the minimum focus. The method of claim 2, The third step is to expose the reticle image using only 60% of the exposure energy of the optimum conditions stepper exposure method.

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