HK1191104A - Anti-dust pellicle component for euv - Google Patents

Description

Pellicle for EUV

Technical Field

The present invention relates to a pellicle for EUV (extreme Ultra violet), and more particularly, to a pellicle for EUV having high intensity while suppressing as much as possible a reduction in incident EUV light.

Background

With the progress of high integration and miniaturization of semiconductor devices, the fabrication of patterns of about 45nm is now in practical use. For the formation of the pattern, a conventional technique for improving the excimer light technique, that is, a technique such as ArF immersion and double exposure, is possible. However, it is difficult to apply an exposure technique for excimer light to the next generation of finer patterns of 32nm or less. Therefore, an EUV exposure technique using EUV light having a significantly shorter wavelength than excimer light and a dominant wavelength of 13.5nm is inevitably selected.

Although practical application of the EUV exposure technology has been advanced, many technical problems to be solved are associated with light sources, resists, pellicle assemblies, and the like. For example, there are various problems to be solved with respect to a pellicle for preventing dust from adhering to a photomask while suppressing a reduction in manufacturing efficiency, and these problems become a significant obstacle in practical use of a pellicle for EUV.

In particular, there is a problem that the EUV light transmittance is high and the change with time due to oxidation or the like does not occur, and there is no way to develop a material for a chemically stable transmission film suitable for a pellicle.

The conventional dust-proof pellicle for EUV has various problems, particularly, the organic material is opaque to EUV light and has poor decomposition. Although there is no material having complete transparency to a wavelength band of EUV light, a thin film made of silicon is known as a relatively transparent material (patent document 1, non-patent document 1).

In view of reducing the attenuation of EUV light, the thinner the silicon thin film is, the better the film is. However, these silicon thin films are extremely thin films of the order of nanometers, such as those composed of silicon having a thickness of 20nm and rubidium having a thickness of 15nm, and are extremely brittle, and thus cannot be used alone as a pellicle for EUV.

Thus, when the pellicle film made of silicon is used as a pellicle film of an EUV pellicle, it is proposed that the pellicle film made of silicon be integrated with a honeycomb-shaped structure as a reinforcing structure for an ultrathin film while having an opening for passing EUV light.

For example, a pellicle for EUV using soi (silicon On insulator) having a lattice structure as a honeycomb for reinforcing a pellicle for EUV has been proposed (patent document 2).

As the mesh structure for reinforcing the EUV pellicle, a lattice structure, a plate-like body having an opening of any shape, such as a circular shape or a polygonal shape, may be used depending on the purpose, in addition to the honeycomb shape, i.e., any shape may be used as long as it meets the purpose. The strength is determined by the distance between the grids, the width of the grid edges, and the height of the grid edges, and the strength is increased as the distance is narrower, the width of the grid edges is larger, and the edges are higher.

Since the structure of the mesh is partially opaque to EUV light, the aperture ratio of the mesh structure is to be increased in order to minimize attenuation of EUV light by the EUV pellicle. However, as described above, in order to improve the strength of the EUV pellicle, the aperture ratio of the mesh structure is decreased.

Generally, EUV light emitted from a light source in a stepper is imaged on a wafer by an optical system of the stepper to draw a desired pattern, but if the decrease in light due to the EUV pellicle on the optical path is large, a complementary technique such as increasing the light emission intensity of the light source, the reflectance of a mirror, or the sensitivity of a resist applied on the wafer is necessary. Thus, the reduction of light by the EUV pellicle affects the entire components of the EUV optical system, and is avoided as much as possible.

In this case, the factors for reducing the EUV light incident on the EUV pellicle assembly are attenuation due to light absorption by the EUV pellicle and the aperture ratio of the mesh structure. The aperture ratio of the mesh structure is determined by factors such as the width of the edges of the mesh constituting the mesh structure, the pitch of the mesh, and the height of the mesh.

Here, the reason why the height of the grid has an influence on the aperture ratio of the grid structure is that, in the EUV stepper, the light is incident on the EUV pellicle at an inclination of 4 ° to 6 ° with respect to the vertical direction of the pellicle surface, and thus the method of forming the shadow due to the height of the grid is changed.

In view of the above, a configuration is used in which the strength of the EUV pellicle can be improved without reducing the amount of light reaching the mask as much as possible.

[ Prior art documents ]

[ patent document ]

[ patent document 1 ] specification of Mi national patent No. 6,623,893

[ patent document 2 ] Japanese patent application laid-open No. 2010-256434

[ non-patent literature ]

[ non-patent document 1 ] Shroff et al, "EUV pellicle development for Mask Defect Control," emulsifying Lithographics technologies X, Proc of SPIE Vol.6151p.1-10(2006)

As a result of intensive studies on a method for solving the problem of (1) suppressing a decrease in strength of the EUV pellicle and (2) suppressing a decrease in exposure amount during patterning by increasing the aperture ratio of a mesh-shaped structure for reinforcing the EUV pellicle, the present inventors have found that, by setting the longitudinal cross-sectional shape of the mesh-shaped structure to a shape in which the tip is thinner as the distance from the EUV pellicle is larger, the transmittance of the EUV pellicle can be improved without decreasing the strength of the EUV pellicle, and have obtained the present invention.

It is therefore an object of the present invention to provide a pellicle for EUV having high intensity while reducing the reduction of incident EUV light.

Disclosure of Invention

The object of the present invention can be achieved by providing a pellicle for EUV having an EUV transparent pellicle reinforced by a mesh-shaped structure, wherein the longitudinal cross-sectional shape (cross-sectional shape in the height direction) of the mesh-shaped structure is tapered as it is farther from the front end of the EUV transparent pellicle.

In the present invention, the angle of the inclination angle of the tapered shape is preferably in the range of x (1 ± 0.3) the incident angle of the illumination light to the EUV transmissive film (claim 2), and more preferably in the range of ± 2 ° the incident angle of the illumination light to the EUV transmissive film (claim 3).

[ Effect of the invention ]

According to the present invention, it is possible to increase the light transmittance of the EUV pellicle while suppressing a decrease in the strength of the EUV pellicle.

Drawings

FIG. 1 is a view showing a honeycomb reinforcing structure in a pellicle for EUV according to the present invention.

FIG. 2 is a view showing a lattice-shaped reinforcing structure in the pellicle for EUV according to the present invention.

FIG. 3 is a drawing showing a basic unit of a honeycomb in the pellicle for EUV according to the present invention.

FIG. 4 is a diagram showing a basic unit of a lattice in the pellicle for EUV according to the present invention.

FIG. 5 is an explanatory diagram illustrating a decrease in the amount of incident light when a conventional dust-proof pellicle for EUV is used.

FIG. 6 is a view illustrating a reduction in the amount of incident light when the pellicle for EUV according to the present invention is used.

FIG. 7 is a longitudinal sectional view (in the height direction) of the pellicle for EUV according to the present invention.

Detailed Description

The present invention will be described in detail below, but the present invention is not limited to these.

The pellicle for EUV having an EUV transparent film reinforced by a mesh-shaped structure is characterized in that the longitudinal cross-sectional shape (cross-sectional shape in the height direction) of the mesh-shaped structure is tapered as it is farther from the tip of the EUV transparent film.

An EUV pellicle for EUV in an EUV scanner is integrated with an EUV mask for drawing a lithography pattern to form an EUV reticle. The EUV light exposure is designed such that EUV light from an EUV light source is first irradiated to one end of the EUV reticle, and the irradiation is actually repeated by moving the EUV reticle repeatedly, so that irradiation from the one end to the opposite end on the EUV reticle is repeated, and then the EUV light is returned to the one end and return exposure is performed again, so that an exposure cycle is repeated, and one single-pass irradiation of the EUV light to the wafer by the movement of the EUV reticle is repeated, so that the number of times of exposure necessary to satisfy the exposure amount is completed.

One reciprocation of the EUV reticle is to complete a single pass of the EUV from the one end to the opposite end, and then the EUV reticle is returned to the initial position in preparation for starting the next exposure. The EUV reticle is reciprocated.

In a scanner operating as an on-site production machine, productivity is high, and the number of exposures per unit time is required to be large, that is, the reciprocating motion of the EUV reticle is required to be swiftly performed.

In this way, if the time for reciprocating the EUV reticle is shortened, the acceleration applied to the EUV reticle is 6G to 10G, and in order to withstand such a large acceleration, it is necessary to design the EUV pellicle.

In order to improve the strength of the EUV pellicle, the strength of the grid-shaped structure of the strength reinforcement member of the EUV pellicle, which is an EUV transmissive pellicle, may be increased. Specifically, the width and height of the grid-shaped structure may be increased, and the pitch of the grid may be further narrowed (see fig. 1 to 4). However, this method reduces the aperture ratio of the grid, and as a result, the amount of EUV light transmitted through the EUV pellicle is reduced. Therefore, the EUV pellicle is designed to obtain more transmitted light while maintaining the necessary intensity.

In the EUV exposure machine, EUV illumination light emitted from an EUV light source is irradiated onto an EUV mask. According to the pattern information of the EUV mask, the EUV mask reflects the light and images the wafer. At this time, the beam of EUV illumination light irradiated on the EUV mask is irradiated at an incident angle of 4 ° to 6 ° with respect to a perpendicular line on the EUV mask, and the beam of light reflected on the EUV mask is reflected at a reflection angle of 4 ° to 6 °.

As described above, when the illumination light is incident and reflected, the incident and reflected light passes through the EUV pellicle, and the incident and reflected light has an angle, and the EUV light also reaches the side surface of the grid of the EUV pellicle. Due to the incidence to this side, the effective exposure is reduced. Thus, if the longitudinal section (height direction) of the reinforcing structure is tapered, the transmittance can be improved without substantially reducing the strength of the pellicle assembly (fig. 6).

Although the transmittance can be theoretically improved to the maximum extent by making the angle of the inclination angle (θ) (see fig. 7) of the longitudinal section of the reinforcing structure equal to the angle of incidence of the illumination light on the EUV transmissive film, a sufficient improvement in the transmittance can be expected if the angle of incidence of the illumination light on the EUV transmissive film is in the range of x (1 ± 0.3). In the present invention, it is particularly preferable from the viewpoint of practicality that the angle of the inclination angle is designed to be within a range of ± 2 ° of the incident angle of the illumination light to the EUV transmissive film.

The incident angle in the present invention is an incident angle of light on the EUV mask plane (treated as being parallel to the EUV transmissive film plane), and the inclination angle (θ) is an angle formed by an inclination of a tapered shape at the tip of the reinforcing structure and a perpendicular line to the EUV transmissive film surface.

Fig. 5 and 6 are a longitudinal sectional view of a conventional EUV pellicle and a longitudinal sectional view of an EUV pellicle according to the present invention. The beam 4 of EUV light is incident on the grid 2 reinforcing the EUV transmissive film 1 at a substantially constant angle. Due to this incident angle, only light in a range narrower than the openings a 'and B' of the grid reaches the EUV mask 3. Here, the irradiation site B becomes wider in the case where the longitudinal section is a tapered shape as compared with the irradiation site a (conventional EUV pellicle; see fig. 5) in the case where the longitudinal section of the grid 2 is rectangular (EUV pellicle of the present invention; see fig. 6).

In an actual EUV exposure apparatus, since the EUV mask is irradiated with illumination light at a certain spread angle, a difference in angle in the reverse direction occurs in the forward direction of a light flux at a certain angle, but the above-described representative light flux may be used for the expression.

The shape of the grid-shaped structure in the pellicle for EUV of the present invention may be any shape, such as a honeycomb shape, a lattice shape, or other shapes, as long as the shape satisfies the target values of the intensity of the pellicle and the transmittance of EUV light, and the shape is preferably a shape in which a plane is buried in a single shape. In the present invention, a honeycomb shape is preferable as the shape having excellent transmittance and strength.

As shown in fig. 7, in the EUV pellicle according to the present invention, the grid-shaped structure is opened toward the light source of the exposure apparatus, and the vertical cross-sectional shape (the height-direction cross-sectional shape) of the grid-shaped structure needs to be tapered toward the tip of the EUV transmissive film.

The mesh-shaped structure is manufactured by a known technique such as a photolithography technique in which the transmittance of a resist is adjusted, a technique using a speed difference in the depth direction in an rie (reactive Ion etching) technique, or an mems (micro Electro mechanical systems) technique.

The present invention will be described in further detail with reference to examples and comparative examples, but the present invention is not limited to these examples.

[ example 1 ]

A silicon substrate having a diameter of 200mm and a thickness of 725 μm is formed on a mounting substrate made of a silicon single Crystal (NPC) having substantially few Crystal defects, such as COP (coefficient of performance Crystal)100nm thin film, thermal oxide film (SiO) with thickness of 150nm₂) An SOI (silicon On insulator) substrate is formed by attaching. The SOI substrate was used to produce a pellicle film for EUV as follows.

After the mounting substrate of the SOI substrate was thinned to 50 μm, a honeycomb structure pattern was etched on the mounting substrate side, and a honeycomb structure having a curve was fabricated at each internal angle of 6 corners of a honeycomb unit by drie (deep Reactive Ion etching).

The pitch in the honeycomb structure was 200 μm, the width of the honeycomb side was 25 μm, and the height of the honeycomb side was 75 μm.

Then, HF treatment was performed to remove the BOX (Buried oxide) film, thereby obtaining a pellicle film for EUV. The inclination angle of the vertical cross section of the supporting honeycomb of the EUV pellicle is 1 °.

[ example 2 ]

The pellicle for EUV was produced in the same manner as in example 1. The inclination angle of the vertical cross section of the supporting honeycomb of the EUV pellicle was 3.5 °.

[ example 3 ]

The pellicle for EUV was produced in the same manner as in example 1. The inclination angle of the vertical cross section of the supporting honeycomb of the EUV pellicle was 4.5 °.

[ example 4 ]

A dust-proof pellicle for EUV was produced in the same manner as in example 1, except that the drie (deep Reactive Ion etching) etching was changed to a normal RIE technique, and the etching depth and etching rate were changed to form a honeycomb having a longitudinal cross section with a narrow tip. The inclination angle of the vertical cross section of the supporting honeycomb of the EUV pellicle is 6 °.

[ example 5 ]

The pellicle for EUV was produced in the same manner as in example 4. The inclination angle of the vertical cross section of the supporting honeycomb of the EUV pellicle was 7.5 °.

[ example 6 ]

The pellicle for EUV was produced in the same manner as in example 1. The inclination angle of the vertical cross section of the supporting honeycomb of the EUV pellicle was 8.5 °.

An aluminum alloy frame having a length of 150mm, a width of 125mm and a thickness of 1.5mm was bonded to the 6 types of EUV pellicle water glass cut out in the same size, and the frame was used as an EUV pellicle.

< EUV transmittance measurement experiment >

The 6 types of EUV pellicle units thus obtained were mounted on an EUV transmittance measuring apparatus, and EUV light was irradiated by vacuum suction with incident light at an angle of 6 ° (the incident angle to the EUV pellicle was 6 °), and the transmittance of the EUV pellicle unit was measured. The results are shown in Table 1.

< vibration experiment >

The frames of the 6 kinds of EUV pellicle assemblies were fixed to a transparent acrylic resin case for vibration experiments with double-sided tape. Next, an acrylic resin box to which a frame of the pellicle for EUV was fixed was attached to a vibration table of a vibration testing machine, and vacuum evacuation was performed in the acrylic resin box using a rotary vacuum pump to apply sinusoidal vibration to the vibration table.

The acceleration of breakage of the dust-proof pellicle for EUV was measured by vibrating the pellicle while increasing the acceleration of the sinusoidal vibration. The results are shown in Table 1.

[ TABLE 1 ]

	Inclination angle (degree)	Transmittance (%)	Acceleration of fracture (G)
				Example 1	1	80.2	25
Example 2	3.5	80.3	25
				Example 3	4.5	82.2	28
Example 4	6	82.5	26
				Example 5	7.5	83.3	25
Example 6	8.5	83.8	20

[ comparative example ]

A honeycomb having a vertical cross section with an inclination angle of zero (the vertical cross section of the honeycomb is rectangular; see FIG. 5) was produced in the same manner as in example 1, and after a pellicle for EUV was produced in the same manner as in example 1, the transmittance was measured and a vibration test was performed. As a result, the transmittance was 79.8% and the breaking acceleration was 26G.

The pellicle assemblies for EUV of the present invention of examples 1 to 6 were compared with comparative examples, and although the breaking acceleration was the same as that in the case of the conventional pellicle assemblies for EUV, the improvement in transmittance was observed.

As is clear from the above results, the EUV pellicle according to the present invention can provide an EUV pellicle with improved transmittance, although the strength is hardly reduced, because the angle of the inclination angle of the vertical cross section of the lattice-shaped structure is appropriate.

[ possibility of Industrial utilization ]

The pellicle for EUV of the present invention has a higher aperture ratio and superior strength than conventional pellicle assemblies, and has a structure in the form of an EUV pellicle reinforcing grid, and therefore is less likely to be damaged even in the case of an extremely thin pellicle used for EUV exposure, and is effective for pattern formation in semiconductor devices and the like, and therefore the present invention is extremely useful in industry.

[ description of symbols ]

1 EUV transparent film

2 grid

3 EUV mask

Beam of 4 EUV light

A, B irradiated part

Openings of A ', B' grids

Claims (3)

1. A pellicle for EUV having an EUV transparent film reinforced by a mesh-shaped structure, wherein the longitudinal cross-sectional shape of the mesh-shaped structure is such that the tip of the structure becomes thinner as it becomes farther from the EUV transparent film.

2. The pellicle of claim 1, wherein the angle of the inclination angle of the shape with the tapered tip is in the range of x (1 ± 0.3) the angle of incidence of the illumination light on the EUV transparent film.

3. The pellicle of claim 2, wherein the angle of the inclination angle is within ± 2 ° of the incident angle of the illumination light to the EUV transmissive pellicle.