Photomask for forming a resist pattern and manufacturing method thereof, and resist-pattern forming method using the photomask

Abstract

A method includes; a step of setting square mask cells in rows and columns on a transparent mask-substrate surface by demarcating by orthogonal lines of equal intervals, each of which has one side having a length smaller than a resolution limit of an optical system; a step of setting the resist thicknesses corresponding to the mask cells; a step of assigning normalized light-intensities respectively to the mask cells as transmission intensities, corresponding to the film thicknesses and having three or more different values; a step of setting each of the mask cells a light-transmission area and a shade-area and determining a transmission-light intensity by an transmission area ratio; a step of providing shade films on the shade areas of the mask substrate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1C are schematic views illustrating a photomask;

FIGS. 2A-2C are views illustrating a procedure of arranging a mask pattern;

FIGS. 3A and 3B are views illustrating a resist pattern where positive resist-1 is used;

FIG. 4 shows a characteristic for explaining a relationship between a space width of mask pattern and a remaining-resist-film thickness;

FIG. 5 is a view showing a mask-pattern arrangement when the positive resist-2 is used;

FIGS. 6A and 6B are views for explaining a resist pattern form when the positive resist-2 is used;

FIG. 7 is a view showing a dependence of a resist-film thickness upon a space width;

FIGS. 8A and 8B are views for explaining a lens form and a contour map of resist form, respectively;

FIG. 9 is a contour map showing a resist-film thickness in once exposure;

FIGS. 10A and 10B are views showing a distribution of intensity in once exposure and an average intensity in double-exposure;

FIG. 11 is a view showing a relationship, in double-exposure, between a shift amount of photomask and a square sum over the differences between a target resist-film thickness and a formed-resist-film thickness;

FIG. 12 is a contour map showing a resist-film thickness obtained by exposure and development where quadruple-exposure is done;

FIG. 13 is a contour map of resist-film thickness of a lens outer peripheral region where the rate of change is great;

FIGS. 14A-14D are views showing preparatory cell intensities provided to the first, second, third and fourth mask substrates;

FIGS. 15A-15D are views showing preparatory cell intensities after unified the first, second, third and fourth mask substrates;

FIGS. 16A and 16B are views showing an intensity in once exposure and an average intensity in double-exposure using two photomasks;

FIGS. 17A and 17B are contour maps showing a resist-film thickness distribution obtained as a result of quadruple-exposure using the first to fourth photomasks and a contour map showing a difference between a target form and an obtained form;

FIGS. 18A-18I are schematic views for explaining the correction of the mask for intensity of light;

FIGS. 19A-19D are views showing a result of correction of the mask pattern;

FIGS. 20A and 20B are views showing a result of quadruple-exposure by using a corrected photomask;

FIGS. 21A and 21B are views showing a result of forming a resist pattern by arranging the same form of mask patterns in four locations within one exposure field;

FIG. 22 is a typical view showing a form of test pattern A; and

FIG. 23 is a view for explaining double-exposure.

Claims

1. A method of fabricating a photomask for forming a resist pattern by exposing a resist layer provided on an underlying layer to light transmitting through the photomask so that a resist pattern can be formed changing in film thickness on the overlying layer by performing development, the method comprising: a step of providing a transparent mask substrate;a step of setting a plurality of square mask cells in rows and columns on a surface of the mask substrate by demarcating the surface by a plurality of straight lines orthogonal to each other at an equal interval, each of which has one side having a length provided smaller than a length of a resolution limit of an optical system of an exposure equipment for which the photomask is used;a step of setting the resist layer with film thicknesses in positions respectively corresponding to the mask cells;a step of assigning normalized light intensities respectively to the mask cells as intensities of transmission light thereof, corresponding to the film thicknesses and having three or more different values in which a maximum intensity of the transmission light is taken 1;a step of setting each of the mask cells with any one or both of a light-transmission area and a shade area and determining a light intensity of the transmission light by an area ratio of the light-transmission area to the mask cell;a step of providing shade films on the shade areas of the mask substrate.

2. A method of fabricating a photomask for forming a resist pattern by exposing a resist layer provided on an underlying layer to light transmitting through the photomask so that a resist pattern can be formed changing in film thickness on the overlying layer by performing development, the method comprising: a step of providing, in a position where to use the photomask, a virtual mask plane having a coordinate origin in a position corresponding to an on-resist reference point set on the resist layer;a step of setting a plurality of square cells in rows and columns by demarcating the mask plane with a plurality of straight lines orthogonal to each other at an equal interval, each of which has one side having a length provided smaller than a length of a resolution limit of an optical system of an exposure equipment for which the photomask is used;a step of setting four subcells by drawing virtual divisional lines in row and column directions and dividing each of the cells into two equal parts with respect to the row and column directions;a step of setting film thickness of the resist layer for positions corresponding to each of the subcells;a step of setting one of normalized light intensities of light transmitting through the subcells as a subcell intensity, the subcell intensity corresponding to the film thickness, the normalized light intensities having three or more different values in which a maximum value of the light transmitting through the subcells is normalized to 1;a step of setting each of the subcells with a preparatory cell intensity having a set of f our values and having an average value giving the subcell intensity;a step of providing first to fourth transparent mask substrates;a step of setting mask cells corresponding to the cells in rows and columns by demarcating with a plurality of straight lines orthogonal to each other at an equal interval, on a surface of each of the first to fourth mask substrates;a step of setting sub-mask-cells corresponding to the subcells by a plurality of virtual divisional lines drawn in row and column directions and setting an on-mask reference point, on the surface of each of the first to fourth mask substrates;a step of aligning the on-mask reference point of the first mask substrate with the coordinate origin;a step of aligning the on-mask reference point of the second mask substrate with a position shifted a distance of ½ times the one-side length of the mask cell in a row direction from the coordinate origin;a step of aligning the on-mask reference point of the third mask substrate with a position shifted a distance of ½ times the one-side length of the mask cell in a column direction from the coordinate origin;a step of aligning the on-mask reference point of the fourth mask substrate with a position shifted a distance of ½ times the one-side length of the cell in the row and column directions from the coordinate origin;a step of providing the sub-mask-cells of the first to fourth mask substrates with preparatory cell intensities corresponding to the subcells, in greater order;a step of selecting one of the preparatory cell intensities of the sub-mask-cells belonging to each of the mask cells of the first to fourth mask substrates;a step of setting any one or both of a light-transmission area and a shade area to each of the mask cells of the first to fourth mask substrates, and defining the cell intensity with a light intensity through each of the mask cells to a corresponding area of the resist layer; anda step of forming a shade film over the shade areas of each of the first to fourth mask substrates, thereby obtaining first to fourth photomasks.

3. A method of fabricating a photomask for forming a resist pattern by exposing a resist layer provided on an underlying layer to light transmitting through the photomask so that a resist pattern can be formed changing in film thickness on the overlying layer by performing development, the method comprising: a step of providing, in a position where to use the photomask, a virtual mask plane having a coordinate origin in a position corresponding to an on-resist reference point set on the resist layer;a step of setting a plurality of square cells in rows and columns by demarcating the mask plane with a plurality of straight lines orthogonal to each other at an equal interval, each of which has one side having a length provided smaller than a length of a resolution limit of an optical system of an exposure equipment for which the photomask is used;a step of setting n2 subcells by drawing virtual divisional lines in row and column directions and dividing each of the cells into n (n: integer of 2 or greater) equal parts with respect to the row and column directions;a step of setting film thickness of the resist layer for positions corresponding to each of the subcells;a step of setting one of normalized light intensities of light transmitting through the subcells as a subcell intensity, the subcell intensity corresponding to the film thickness, the normalized light intensities having three or more different values in which a maximum value of the light transmitting through the subcells is normalized to 1;a step of setting each of the subcells with a preparatory cell intensity having a set of n2 values and having an average value giving the subcell intensity;a step of providing first to n2-th mask substrates;a step of setting mask cells corresponding to the cells by a plurality of virtual grid lines drawn in row and column directions mutually orthogonal, and setting sub-mask-cells corresponding to the subcells by a plurality of virtual divisional lines drawn in the row and column directions, and setting an on-mask reference point, on the surface of each of the first to n2-th mask substrates;a step of setting the mask cells by shifting the column-directional position in increments/decrements of P/n from 0 to P/n×(n−1) (P: one-side length of the mask cell), shifting the row-directional position in increments/decrements of P/n from 0 to P/n×(n−1) relative to the column-directional position, with each position of which the on-mask reference point of each of the first to n2-th mask substrates is aligned;a step of providing the sub-mask-cells of the first to n2-th mask substrates with preparatory cell intensities corresponding to the subcells, in greater order;a step of selecting, as a cell intensity, one of the preparatory cell intensities of the sub-mask-cells belonging to each of the mask cells;a step of setting any one or both of a light-transmission area and a shade area to each of the mask cells, and defining the cell intensity with a light intensity to a corresponding area of the resist layer through each of the mask cells by means of an area ratio of the light-transmission area to the mask cell; anda step of forming a shade film over the shade areas of each of the first to n2-th mask substrates, thereby obtaining first to n2-th photomasks.

4. A method according to claim 1, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure to light and development on the resist layer by use of a test mask having, on a transparent mask substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell in which the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the mask cells, the area ratio required to reduce the resist layer to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing an exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

5. A method according to claim 2, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure to light and development on the resist layer by use of a test mask having, on a transparent mask substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell in which the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the mask cells, the area ratio required to reduce the resist layer to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing an exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

6. A method according to claim 3, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure to light and development on the resist layer by use of a test mask having, on a transparent mask substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell in which the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the mask cells, the area ratio required to reduce the resist layer to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing an exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

7. A method according to claim 1, wherein, in the case, of the mask cells, the mask cells arranged successively in the column direction have the shade areas, the shade areas are continuously provided connected in order in the column direction while in the case, of the mask cells, the mask cells arranged successively in the row direction have the light-transmission and shade areas, the shade areas are provided non-connected in order in the row direction.

8. A method according to claim 2, wherein, in the case, of the mask cells, the mask cells arranged successively in the column direction have the shade areas, the shade areas are continuously provided connected in order in the column direction while in the case, of the mask cells, the mask cells arranged successively in the row direction have the light-transmission and shade areas, the shade areas are provided non-connected in order in the row direction.

9. A method according to claim 3, wherein, in the case, of the mask cells, the mask cells arranged successively in the column direction have the shade areas, the shade areas are continuously provided connected in order in the column direction while in the case, of the mask cells, the mask cells arranged successively in the row direction have the light-transmission and shade areas, the shade areas are provided non-connected in order in the row direction.

10. A method according to claim 4, wherein, in the case, of the mask cells, the mask cells arranged successively in the column direction have the shade areas, the shade areas are continuously provided connected in order in the column direction while in the case, of the mask cells, the mask cells arranged successively in the row direction have the light-transmission and shade areas, the shade areas are provided non-connected in order in the row direction.

11. A method according to claim 7, wherein, each of the mask cells, set with both of light-transmission and shade areas, is divided into two parts by a virtual divisional line drawn in the column direction, to set the light-transmission area on one side of the virtual divisional line and the shade area on other side thereof, thereby setting the light-transmission areas in the mask cells on same side with respect to the virtual divisional line.

12. A method according to claim 8, wherein, each of the mask cells, set with both of light-transmission and shade areas, is divided into two parts by a virtual divisional line drawn in the column direction, to set the light-transmission area on one side of the virtual divisional line and the shade area on other side thereof, thereby setting the light-transmission areas in the mask cells on same side with respect to the virtual divisional line.

13. A method according to claim 9, wherein, each of the mask cells, set with both of light-transmission and shade areas, is divided into two parts by a virtual divisional line drawn in the column direction, to set the light-transmission area on one side of the virtual divisional line and the shade area on other side thereof, thereby setting the light-transmission areas in the mask cells on same side with respect to the virtual divisional line.

14. A method according to claim 10, wherein, each of the mask cells, set with both of light-transmission and shade areas, is divided into two parts by a virtual divisional line drawn in the column direction, to set the light-transmission area on one side of the virtual divisional line and the shade area on other side thereof, thereby setting the light-transmission areas in the mask cells on same side with respect to the virtual divisional line.

15. A method according to claim 1, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure and development on the resist by use of a test mask having, on a transparent substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell wherein the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the resist cells, the area ratio required to reduce the resist to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by virtue of the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

16. A method according to claim 2, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure and development on the resist by use of a test mask having, on a transparent substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell wherein the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the resist cells, the area ratio required to reduce the resist to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by virtue of the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

17. A method according to claim 3, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure and development on the resist by use of a test mask having, on a transparent substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell wherein the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the resist cells, the area ratio required to reduce the resist to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by virtue of the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

18. A method according to claim 4, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure and development on the resist by use of a test mask having, on a transparent substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell wherein the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the resist cells, the area ratio required to reduce the resist to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by virtue of the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

19. A method according to claim 7, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure and development on the resist by use of a test mask having, on a transparent substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell wherein the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the resist cells, the area ratio required to reduce the resist to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by virtue of the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.

20. A method according to claim 11, further comprising, in setting any one or both of a light-transmission area and a shade area in each of the mask cells: a step of obtaining a relationship between an area ratio of the light-transmission area to the mask cell and a resist-film thickness by performing exposure and development on the resist by use of a test mask having, on a transparent substrate, a test pattern having a shade film over the shade areas set with a spacing serving as a light-transmission area in a stripe form at a pitch equal to the one-side length of the mask cell wherein the light-transmission and shade areas are changed in width in order,a step of obtaining, for each of the resist cells, the area ratio required to reduce the resist to a target film thickness,a step of setting the mask cells on a transparent mask substrate, setting any one or both of the light-transmission and shade areas in the mask cell, and providing a cell intensity with an intensity of light transmitting through each of the mask cells by virtue of the area ratio of the light-transmission area to the mask cell,a step of obtaining a temporary photomask by forming a shade film over the shade areas of the mask substrate,a step of measuring a resist-film thickness by performing exposure by use of the temporary photomask,a step of changing the area ratio on each of the mask cells by use of a comparison result of between a resist-film thickness and a target film thickness.