Lithography system, sensor, converter element and method of manufacture

Abstract

charged particle beamlet lithography system for transferring a pattern to a surface of a target comprising a sensor for determining one or more characteristics of one or more charged particle beamlets. The sensor comprises a converter element for receiving charged particles and generating photons in response. The converter element comprises a surface for receiving one or more charged particle beamlets, the surface being provided with one or more cells for evaluating one or more individual beamlets. Each cell comprises a predetermined blocking pattern of one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface. The converter element surface is covered with a coating layer substantially permeable for said charged particles and substantially impermeable for ambient light. An electrically conductive layer is located between the coating layer and the blocking structures.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a charged particle lithography system, in particular to a maskless charged particle system, to a sensor therefore, in particular for determining charged particle beam properties, to a converter element therefore, as well as to a method of manufacturing the same.

2. Description of the Related Art

Charged-particle beamlet lithography systems make use of a plurality of charged particle beamlets to transfer a pattern onto the surface of a target. The beamlets may write the pattern by being scanned over the target surface while their trajectory may be controllably blocked so as to create a beamlet that can be turned on or off. Blocking may be established by electrostatic deflection of beamlets on a blocking surface. Additionally, or alternatively, the size and shape of the beamlets may be adapted along the trajectory. Deflection, shaping and/or size adaptation may be executed by one or more electron optical components like for example an aperture array, an array of electrostatic deflectors and/or beamlet blankers. In order to transfer a pattern onto the target surface, the controllable blocking of beamlets in combination with their movement over the target surface is performed in accordance with modulation information. An example of a multiple charged-particle beamlet lithography system is described in U.S. Pat. No. 6,958,804, which disclosure is herewith incorporated by reference in its entirety.

Such lithography systems can have very large numbers of beamlets, i.e. in the order of 10,000 or higher, for example 13,000. Future designs even envisage numbers in the order of 1,000,000 beamlets. It is a general aim for current electron beam lithography systems to be able to pattern a target surface in high-resolution, with some applications being capable of imaging patterns with a critical dimension of well below 100 nm feature sizes.

For such multiple beamlet, high-resolution lithography systems to be commercially viable it is important that the position of each one of the charged particle beamlets is precisely known and controlled. Additionally, knowledge and control of spot size and shape and intensity of the beamlets at the target surface are also of importance. Due to various circumstances, such as manufacturing tolerances and thermal drift, such beamlet characteristics may however deviate from their expected and desired characteristics, which may render these deviating beamlets invalid for accurate patterning.

Such deviations may include, among other things, a deviation in position, a deviation in spot size as exposed on the target surface and/or a deviation in beamlet intensity. Deviating beamlets may severely affect the quality of the pattern to be written. It is therefore desirable to detect these deviations so that corrective measures may be taken.

In conventional lithography systems, the position of each beamlet is determined by frequent measurement of the beamlet position. With knowledge of the beamlet position the beamlet can be shifted to the correct position. For accurate writing it is beneficial to determine the beamlet position within a distance in the order of a few nanometers.

Known beamlet position calibration methods generally comprise at least three steps: a measuring step in which the position of the beamlet is measured, a calculating step in which the measured position of the beamlet is compared to the desired expected position of that beamlet, and a compensation step in which the difference between the measured position and the desired position is compensated for. Compensation may be performed either in the software or in the hardware of the lithography system.

In advanced charged particle beamlet lithography systems, besides position control, beamlet spot size control may be of equal importance. Desired specifications for spot size measurements include determination of beamlet spot sizes in the range of 30 nm to 150 nm; accuracy of spot size measurements with 3 sigma value smaller than 5 nm; and a reproducibility of such spot size measurements within a single sensor with 3 sigma value smaller than 5 nm.

It is desirable to determine characteristics like beamlet position and/or beamlet spot size during operation of a lithography system to allow for early position and/or spot size calibration to improve the target surface patterning accuracy. In order to limit negative effects on throughput, i.e. the number of target surfaces that can be patterned within a predetermined period of time, it is desirable that the method of measuring the characteristics of the charged particle beamlets can be carried out within a limited period of time without sacrificing accuracy.

A sensor for measuring properties of a large number of charged-particle beamlets, in particular for charged particle beamlets used in a lithography system, is described in US published patent application 2007/057204 assigned to the present applicant, the content of which is herewith incorporated by reference in its entirety.

US 2007/057204 describes a sensor and method in which charged-particle beamlets are converted into light beams, using a converter element such as a fluorescent screen or a doped YAG material. Subsequently, the light beams are detected by an array of light sensitive detectors such as diodes, CCD or CMOS devices. A relatively fast measurement can be achieved by reading out a large number of light sensitive detectors in a single operation. Additionally the sensor structure, in particular the array of light detectors, enables a very small pitch of a multiplicity of beams to be measured without the necessity of unduly large structural measures in the region of the stage part of a lithography system.

However, in view of the continuously increasing demands of the industry regarding small dimensions without loss of throughput, there remains a need to provide even more accurate devices and techniques for measurement of beamlet properties in lithography systems, particularly in lithography machines comprising a large number of charged-particle beamlets that are designed to offer a high throughput.

BRIEF SUMMARY OF THE INVENTION

It is an object of the present invention to provide a more accurate sensor FIG. 4 shows parts of a charged particle beamlet lithography system.2Dchrome chromium.

The layers further comprise a third layer 105 comprising a third material. The third material serves the purpose of blocking charged particle beamlets. A suitable material for the third material is a material that blocks charged particles as well as ambient light while having a layer of limited thickness. A suitable material is tungsten, in which case a suitable thickness would lie within the range of 50 to 500 nm. Such thickness is thick enough to sufficiently block incoming charged particles. On the other hand, such thickness has a negligible influence on effects like defocus and edge roughness.

On top of the number of layers 103, 104, 105, a resist layer 107 is provided. As schematically shown in FIG. 3C, the resist layer 107 may be a single resist layer or, alternatively, a double resist layer comprising an upper layer 107a, and a lower layer 107b respectively. Further reference will be made to a single resist layer 107.

The resist layer 107 is then patterned in correspondence to a first predetermined pattern. After patterning, the resist layer 107 undergoes developing and etching steps in a fashion generally known in the art. The etching is performed until the third layer 105 is exposed. An exemplary end result of patterning, developing and etching the resist layer 107 is schematically shown in FIG. 3D.

After etching, the exposed third layer 105 is coated with a fourth layer 109, for example by means of evaporation, as is schematically shown in FIG. 3E. Generally, the fourth layer 109 is a metal layer. The fourth layer 109 may serve as an etch stopping layer and may improve etching quality. The layer 109 may comprise the same material as used in the second layer 104, for example chrome chromium.

After deposition of the fourth layer 109, the developed resist is removed by lift off such that the third layer 105 is exposed in accordance with a second predetermined pattern, as schematically shown in FIG. 3F. The second predetermined pattern is an inversion of the first predetermined pattern.

Subsequently, the exposed third layer 105 is etched in accordance with the second predetermined pattern until the second layer 104 is exposed. A schematic drawing of the converter element at this stage of the manufacturing process is shown in FIG. 3G.

Finally, as schematically shown in FIG. 3H, the fourth layer 109 as well as the second layer 104 in accordance with the second predetermined pattern are removed, the latter one until the first layer 103 is exposed. Removal may be performed by techniques known in the art, for example etching.

The resulting converter element is similar to the converter element described with reference to FIG. 2A. When the method of FIGS. 3A-3H would be used to manufacture the converter element of FIG. 2A, substrate 1 and layers 18, 20, and 21 in FIG. 2A correspond to substrate 101 and layers 105, 103, and 104 respectively.

The invention has been described by reference to certain embodiments discussed above. It will be recognized that these embodiments are susceptible to various modifications and alternative forms well known to those of skill in the art. Further modifications in addition to those described above may be made to the structures and techniques described herein without departing from the spirit and scope of the invention. Accordingly, although specific embodiments have been described, these are examples only and are not limiting upon the scope of the invention, which is defined in the accompanying claims.

Claims

1. charged particle beamlet lithography system for transferring a pattern to a surface of a target comprising a sensor for determining one or more characteristics of one or more charged particle beamlets, the sensor comprising a converter element for receiving charged particles and generating photons in response, the converter element comprising a surface for receiving one or more charged particle beamlets, the surface being provided with one or more cells for evaluating one or more individual beamlets, each cell comprising a predetermined blocking pattern of one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface, the surface being provided with a pattern comprising charged particle blocking regions and charged particle non-blocking regions, the charged particle blocking regions comprising one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface, wherein the converter element surface is covered with a coating layer substantially permeable for said charged particles and substantially impermeable for ambient light, and an electrically conductive layer is located between the coating layer converter element surface and the blocking structures, the electrically conductive layer being located underneath the blocking structures, the electrically conductive layer being located only within the blocking regions.

2. System according to claim 1, wherein the sensor is adapted for determining one or more characteristics of a plurality of charged particle beamlets for each of the beamlets in parallel by simultaneously generating a signal in response to receiving each of the plurality of charged particles beamlets.

3. System according to claim 1, wherein the conductive layer is substantially similar in shape and size as the dimensions of the blocking structures in a plane substantially parallel to the converter element surface.

4. System according to claim 1, wherein the conductive layer comprises chromium.

5. System according to claim 1, wherein the blocking structures comprise tungsten.

6. System according to claim 1, wherein the converter element comprises a scintillating material.

7. System according to claim 6, wherein the scintillating material comprises an yttrium aluminum garnet.

8. System according to claim 1, wherein the coating layer comprises titanium.

9. System according to claim 1, wherein the charged particle beamlets are electron beamlets.

10. System according to claim 1, wherein the sensor further comprises:

a photon receptor for receiving photons generated by said converter element; and

a control unit for receiving signals from the photon receptor and for determining one or more characteristics of one or more beamlets based on said signals.

11. System according to claim 1, further comprising:

a beamlet generator for generating a plurality of charged particle beamlets;

a modulation system for modulating the charged particle beamlets in accordance with a pattern to be transferred;

an electron-optical system for focusing the modulated beamlets onto the surface of the target;

a deflecting system for deflecting the focused beamlets over the surface of either the target or the sensor.

12. sensor for generating a signal in response to exposure thereof by a charged particle beam, the sensor comprising a converter element for receiving charged particles and generating photons in response, the converter element comprising a surface for receiving one or more charged particle beamlets, the surface being provided with one or more cells for evaluating one or more individual beamlets, each cell comprising a predetermined blocking pattern of one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface, the surface being provided with a pattern comprising charged particle blocking regions and charged particle non-blocking regions, the charged particle blocking regions comprising one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface, wherein said converter surface is covered with a coating layer substantially permeable for said charged particles and substantially impermeable for ambient light, and an electrically conductive layer is located between the coating layer converter element surface and the blocking structures, the electrically conductive layer being located underneath the blocking structures, the electrically conductive layer being located only within the blocking regions, and wherein the sensor further comprises a photon receptor associated with the converter element for generating a signal on the basis of photons generated by the converter element.

13. sensor according to claim 12, wherein the photon receptor is arranged for forming reception information based on photons generated by the converter element, the sensor further comprising a control unit for receiving the reception information from the photon receptor and determining a characteristic of the plurality of charged particle beams based on the reception information.

14. converter element for receiving charged particles and generating photons in response for use in a sensor for sensing a characteristic of a plurality of charged particles beamlets, the converter element comprising a surface for receiving one or more charged particle beamlets, the surface being provided with one or more cells for evaluating one or more individual beamlets, each cell comprising a predetermined blocking pattern of one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface, the surface being provided with a pattern comprising charged particle blocking regions and charged particle non-blocking regions, the charged particle blocking regions comprising one or more charged particle blocking structures forming multiple knife edges at transitions between blocking and non-blocking regions along a predetermined beamlet scan trajectory over the converter element surface, wherein the converter element surface is covered with a coating layer substantially permeable for charged particles and substantially impermeable for ambient light, and an electrically conductive layer is located between the coating layer converter element surface and the blocking structures, the electrically conductive layer being located underneath the blocking structures, the electrically conductive layer being located only within the blocking regions.

15. Method of manufacturing a converter element arranged for selectively converting impinging charged particles into photons, the method comprising:

providing a substrate comprising a conversion material for converting charged particles into photons;

subsequently coating the substrate with a first layer comprising an electrically conductive material, a second layer comprising an etch stop material and a third layer comprising a third material;

providing a resist layer on top of said third layer;

patterning, and developing the resist layer so as to form a first predetermined pattern, and etching the developed resist layer until the third layer is exposed;

coating the exposed third layer with a fourth layer comprising a further etch stop material;

lifting of the developed resist such that the third layer is exposed in accordance with a second predetermined pattern, the second predetermined pattern being an inversion of the first predetermined pattern;

etching the third layer in accordance with the second predetermined pattern until the second layer is exposed;

etching the fourth layer as well as the second layer in accordance with the second predetermined pattern until the first layer is exposed.

16. The method according to claim 15, wherein said first layer is substantially impermeable for ambient light and substantially permeable for charged particle beamlets.

17. The method according to claim 15, wherein the etch stop material of the second layer and the further etch stop material of the fourth layer are the same.

18. The method according to claim 15, wherein at least one of the etch stop material and the further etch stop material comprises chrome chromium.

19. The method according to claim 15, wherein the electrically conductive material of the first layer comprises at least one of titanium and aluminum.

20. The method according to claim 15, wherein the third layer material has a high selectivity to both wet and dry etching.

21. The method according to claim 15, wherein the third material comprises tungsten.

22. The method according to claim 15, wherein the conversion material of the substrate comprises a scintillating material.

23. The method according to claim 22, wherein the scintillating material comprises an yttrium aluminum garnet.

24. System according to claim 1, wherein the converter element surface is covered with a coating layer substantially permeable for said charged particles and substantially impermeable for ambient light, and the electrically conductive layer is located between the coating layer and the blocking structures.

25. System according to claim 24, wherein the coating layer comprises titanium.

26. sensor according to claim 12, wherein the electrically conductive layer comprises chromium.

27. sensor according to claim 12, wherein the blocking structures comprise tungsten.

28. sensor according to claim 12, wherein the converter element comprises a scintillating material.

29. sensor according to claim 28, wherein the scintillating material comprises an yttrium aluminum garnet.

30. sensor according to claim 12, wherein the converter element surface is covered with a coating layer substantially permeable for said charged particles and substantially impermeable for ambient light, and the electrically conductive layer is located between the coating layer and the blocking structures.

31. sensor according to claim 30, wherein the coating layer comprises titanium.

32. converter element according to claim 14, wherein the converter element comprises a scintillating material.

33. converter element according to claim 14, wherein the electrically conductive layer comprises chromium.

34. converter element according to claim 14, wherein said converter element surface is covered with a coating layer substantially permeable for said charged particles and substantially impermeable for ambient light, and the electrically conductive layer is located between the coating layer and the blocking structures.