GB2308667A

GB2308667A - Exposure equipment for a semiconductor device

Info

Publication number: GB2308667A
Application number: GB9626977A
Authority: GB
Inventors: Hee-Bom Kim; Chang-Nam Ahn
Original assignee: Hyundai Electronics Industries Co Ltd
Current assignee: SK Hynix Inc
Priority date: 1995-12-29
Filing date: 1996-12-27
Publication date: 1997-07-02
Also published as: JPH1022222A; DE19700049A1; GB9626977D0

Description

EXPOSURE EOUIPMENT Background of the Invention Field of the Invention The present invention relates to a semiconductor device, and more particularly to an exposure equipment of a semiconductor device having an aperture which is applied to a process of forming a pattern whose periodicity varies (hetero-periodicity) according to direction of the pattern.

Description of the Related Art In general, in a manufacture of a semiconductor device, the formation of a fine pattern is essentially required according to increase integration of the semiconductor devices. Factor for satisfying such requirements include wavelength according to an exposure equipment and limited resolution according to the characteristic of a lens. Limited resolution results from diffraction effect of light at a mask and a lens during projection of light. A method using off-axis illumination has been suggested for increasing resolution.

The name, "off-axis illumination," comes from light being incident upon a mask through an openings (hereinafter, called element light source) of aperture located away from a main axis of an exposure system providing a high resolution with respect to a pattern having a specific space periodicity. As the element light source for illumination employed using this principle, there are provided an annular aperture, a shrink aperture, a quadruple aperture, and a conventional aperture.

The above off-axis illumination method is efficient in increasing the resolution of a periodic pattern, as well as a process margins necessary for a semiconductor device manufacture, for example, allowed energy range or allowed defocus range.

To obtain the off-axis illumination, the element light source is arranged to be off from an optical axis. The annular, shrink, quadruple and conventional apertures used as an element light source for the off-axis illumination method, have a symmetric structure with respect to the control point regardless of direction and in consideration of the reduction of only the zero-th light among diffracted lights.

The period of a pattern exhibiting the maximum resolution is determined in accordance with a degree of distance of the element light source separated from the optical axis. Thus, a conventional off-axis input light is efficient on the formation of a pattern having one period.

In other words, since the conventional central-pointsymmetric element light sources are separated by the same distance with respect to the optical axis, the effect is available only for a pattern of a specific period.

However, as shown in FIG. 2A, there can be a case that the periodicity of a pattern used for manufacture of a semiconductor device differs in accordance with the direction thereof. Thus, the conventional central-pointsymmetric off-axis illumination in such a case incurs a problem of not obtaining the optimal resolution.

Summarv of the Invention To overcome the above problems, it is an object of the present invention to provide an exposure equipment having an aperture which can provide improved resolution regardless of the direction of a pattern, by calculating using equations a degree of an angled input of a light source exhibiting the maximum resolution according to periodicity of each direction of a mask and manufacturing an asymmetric element light source.

Accordingly, to achieve the above object, there is provided an exposure equipment includes: an off-axis input light source; and an aperture having element light sources to determine the proceeding path of light emitted from the off-axis input light source and designed to be asymmetric with respect to the control point according to directional period of a hetero-periodicity pattern.

Brief Description of the Drawings Further objects and advantages of the present invention will be apparent from the following description with reference being to the accompanying drawings wherein preferred embodiments of the present invention are clearly shown.

In the drawings: FIG. 1 is a graph for explaining principle of calculation of an off-axis degree of the input light according to the present invent ion; FIGS. 2A and 2B are diagrams showing an embodiment of an aperture design based on the off-axis degree of the input light according to the present invention; FIGS. 3A and 3B are diagrams showing the shapes of an aperture when an element light source is square; and FIGS. 4A-7 are diagrams showing an embodiment of an aperture according to the array and shape of the element light source.

Detailed Description of the Preferred Embodiment Referring to FIG. 1, an optimal off-axis degree of the input light corresponding to the period (P) of a pattern is obtained when phase difference of a position A and a position B is 1800, or in other words, when the distance between A and C the points of transmitted light on a mask 2 corresponds half the wavelength.

For instance, assuming that the angle made by light 3 input at an angle to an optical axis is i, since an equation of Sin(e)=(Distance between A and C)/P is generated, the optimal off-axis degree is shown in the following equation (1): Sin (#optimal)=(Light wavelength/2)/P (l) Accordingly, the optimmal off-axis degree of the input light can be represented by the following equation (2): Optimal Off-axis Degree of Input Light = Light Wavelength/(2 x Period of Pattern x Numeric Aperture (N/A) of lens).............. lens) (2) FIG. 2B is a diagram showing an aperture which is designed by obtaining an optimal off-axis degree of the input light in the above manner in case of a heteroperiodicity pattern as in FIG. 2A.

In the hetero-periodicity pattern as in FIG. 2A, the latitudinal period and the longitudinal period are 500nm and 600nm, respectively. When the wavelength of light projected from a light source and the N/A of the lens used in an exposure equipment used for formation of such a hetero-periodicity pattern, are 248nm and 0.5, respectively, the optimal off-axis degree of the input light is calculated from equation (2) and the values are 0.496 latitudinally and 0.413 longitudinally, as illustrated in FIG. 2B.

Thus, the element light source 11 is designed and manufactured as shown in FIG. 2B.

From the above-described embodiment and equation (2), when the N/A of a lens and the wavelength of the input light are fixed, it is assumed that the optimal off-axis degree is in a reverse proportion to the period of a pattern. That is, from FIGS. 2A and 2B, since an off-axis degree (0.496) of the horizontal axis having a short pattern period has a value greater than that (0.413) of the vertical axis having a long pattern period, the distance between the element light sources 11 along the horizontal axis is longer than that along the vertical axis in an aperture 30. In the meantime, the shape of the element light source 11 can be modified, i.e., a shape of square, diamond or arc can be used instead of the circular element light source as above.

FIGS. 3A and 3B show a case that the shape of the element light source 11 is square.

In the meantime, an array of the element light sources can also be differentiated while the shape of the element light itself can be modified into various shapes as suggested before. The array of the element light source 11 can be divided into the following shapes.

FIGS. 4A through 4C show the array of the element light source 11 to be square, and FIGS. 5A through 5C show the array of the element light source 11 to be a cross shape. Here, the shape of each arrayed element light source 11 can be variously changed into a circle, square and triangle as shown in each drawing.

When the wavelength of an incident light and N/A of a lens are fixed, it is inferred that the apertures shown in FIGS. 4A-4C and 5A-5C are applied to a pattern in which a period in a horizontal direction is longer than that in a vertical direction.

FIG. 6 shows an array where perpendicular and/or horizontal ratio of the square is fit to each directional period, and FIG. 7 shows an double annular array corresponding to two periods.

Referring to FIG. 7, the inner element light source with respect to the center corresponds a long period of a hetero-periodicity pattern and the outer light source with respect to the center corresponds a short period of the hetero-periodicity pattern.

As described above, the conventional off-axis input illumination which is symmetric with respect to the optical axis is highly effective to a particular period, not effective to a pattern having a different periodicity according to the direction. However, the asymmetric offaxis input illumination according to the present invention of which element light sources are designed asymmetrically to be appropriate to a period according to direction with respect to the hetero-periodicity pattern, thereby providing a high resolving power to all directions.

Therefore, it should be understood that the present invention is not limited to the particular embodiment disclosed herein as the best mode contemplated for carrying out the present Invent Ion, but rather that the present invention is not limited to the specific embodiments described in this specification except as defined in the appended claims.

Claims

What Is Claimed Is:

1. An exposure equipment comprising: an off-axis input light source; and an aperture having element light sources to determine proceeding path of light emitted from said off-axis input light source and designed to be asymmetric with respect to the starting point according to directional period of a hetero-periodicity pattern.

2. The exposure equipment as claimed in claim 1, wherein distance between said element light sources disposed in the horizontal and vertical directions in said aperture are determined from a degree of an off-axis input of the optimal light.

3. The exposure equipment as claimed in claim l, wherein said off-axis input degree of the optimal light equals to wavelength of light/(2 x period of pattern x numeric aperture of lens).

4. The exposure equipment as claimed in claim 1, wherein the shape of said element light source is either one of a circle, a square, an arc, or a cut square.

5. The exposure equipment as claimed in claim 1, wherein an array of said element light source is a rectangle or a cross shape.

6. The exposure equipment as claimed in claim 1, wherein an array of said element light source is a double annular shape.