JP3203381B2 - X-ray exposure equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an X-ray exposure apparatus using laser-excited plasma as an X-ray source.

[0002]

2. Description of the Related Art An X-ray exposure apparatus using laser-excited plasma as an X-ray source has attracted attention, and is expected to be applied to, for example, an exposure apparatus used in a semiconductor integrated circuit manufacturing process. Also, in the case of observing, as a resist image, a transmission pattern of X-rays applied to a sample with a so-called X-ray microscope, application of an exposure apparatus using laser-excited plasma as an X-ray source has been considered.

Conventionally, when a laser-excited plasma is used as an X-ray source, a target object is irradiated with a laser beam intensity that maximizes the conversion efficiency from irradiation laser energy to X-ray energy, or such a target object is irradiated with the laser beam. An X-ray source irradiated with laser without any consideration was used.

Here, in an X-ray exposure apparatus in which the X-ray source can be regarded as a point light source, there is a limit on the exposure resolution due to the fact that the X-ray source as the light source has a finite size. It is called "blur (δ _P )"). This is shown in FIG.
Explaining by using X, the image of the edge portion of the object to be exposed
A semi-shadow blur δ _P determined by the relative positional relationship between the source, the object to be exposed, and the image and the diameter D of the X-ray source occurs.

Moreover, other factors, as shown in FIG. 2 (A), for example, blur due to diffraction (hereinafter "diffraction blur ([delta] _f)"
It has been conventionally known that such influences on the resolution of X-ray exposure.

[0006] Therefore, in order to perform high-resolution X-ray exposure, the penumbra blur must be much lower than the resolution determined by diffraction blur or the like (that is, the resolution determined by the penumbra blur is worse). Is not allowed.

[0007]

However, the conventional X-ray exposure apparatus does not perform the excitation laser beam irradiation in consideration of the above-mentioned relationship between the resolution and the energy density of the excitation laser beam. Was not enough.

On the other hand, in the X-ray exposure apparatus, it is necessary to increase the size of the X-ray source in order to increase the X-ray energy density on the object to be exposed. It needs to be considered.

The present invention has been made in view of the above problems, and the resolution determined by penumbra of an X-ray exposure apparatus is equal to or higher than the resolution determined by other factors. Alternatively, an object of the present invention is to provide an excitation laser beam irradiation condition in which the resolution determined by penumbra becomes the highest (that is, the highest), and to further downsize the laser-excited plasma generator.

[0010]

According to the present invention, there is provided a pulsed laser excited plasma X-ray source for generating X-rays by converging a pulsed laser beam on a target object.
An X-ray exposure apparatus for forming a transmission X-ray pattern of an object to be exposed on a surface to be transferred by X-ray irradiation from the X-ray source,
The X-ray source has a finite size, so that the penumbra of the image of the object to be exposed on the surface to be transferred is minimized or less than or equal to the resolution limited by other factors. And exciting the target object with an appropriate laser beam irradiation intensity.

Here, in the case of contact exposure, the required X-ray energy density is P _E [J / cm ³ ], the wavelength of the X-ray is λ (a typical value when the spectrum width is wide), and the wavelength λ of the X-ray is λ. Is the absorption coefficient of the resist to α [cm ⁻¹ ], the distance between the object to be exposed and the surface to be transferred is h, and the excitation laser pulse time width is τ.
_P , the energy conversion efficiency per solid angle from the excitation laser light to the wavelength of the exposure X-ray or the X-ray in the wavelength range per solid angle is η (I), and the excitation laser intensity is I [w / cm ² ],

[0012]

(Equation 3) What is necessary is just to excite the target object with the laser beam irradiation intensity satisfying the following condition.

In the contact type exposure, if the penumbra of the image of the object to be exposed on the surface to be transferred does not fall below the resolution limited by other factors,

[0014]

(Equation 4) The target object is excited with the laser beam irradiation intensity satisfying the following condition.

Further, these X-ray exposure apparatuses use a mask pattern of an integrated circuit as the object to be exposed,
Applied to semiconductor integrated circuit manufacturing equipment.

These X-ray exposure apparatuses use a biological sample as the object to be exposed, and form a transfer image of the biological sample on a resist surface, thereby obtaining a contact-type transfer type replica. Applied as a microscope.

[0017]

SUMMARY OF THE INVENTION It is an object of the present invention to irradiate an optimum excitation laser beam intensity in an X-ray exposure apparatus so that the influence of penumbra is reduced and the resolution determined by other factors is not impaired. An object of the present invention is to obtain an apparatus for performing exposure by generating X-rays. Hereinafter, the operation of the present invention will be described in consideration of the effects of penumbra and diffraction blur on the resolution of the X-ray exposure apparatus.

First, the energy density absorbed by the resist required for X-ray exposure is P _E [J / cm
³ ], the energy of the excitation laser is E _L
[J], the absorption coefficient of the transfer surface (for example, resist) is α
[Cm ⁻¹ ], and the conversion efficiency per solid angle from laser light energy to X-ray energy in a specific wavelength or wavelength range is η [sr ⁻¹ ] (where η is the laser light intensity I [w on the target object). / Cm ² ], the following “η
(I) ”).

Although the following discussion can be applied to a general X-ray exposure system using an X-ray optical element, in order to facilitate understanding, a contact-type exposure (strictly The case of proximity exposure will be discussed.

Assuming that the distance from the plasma (the target object generating the plasma) to the object to be exposed is d [cm] and the distance from the object to be exposed to the transfer surface is h [cm], the required energy E of the excitation laser is _L is

[0021]

(Equation 5) Given by (∵d >> h)

On the other hand, assuming that the diameter D of the X-ray source formed on the target object is equal to the focused diameter of the irradiation laser light beam,

[0023]

(Equation 6) Given by Here, τ _P is the pulse time width of the irradiation pulse laser beam.

In this case, the penumbra δ _P due to the finite size D of the X-ray source is:

(Equation 7) Given by

Then, by substituting equation (2) into equation (3),

(Equation 8) Becomes

Here, substituting equation (1) for E _L in equation (4) gives:

(Equation 9) Becomes

From the equation (5), the penumbra δ _P does not depend on the distance d between the plasma and the object to be exposed, and depends on the laser light intensity I on the target of the X-ray source and the conversion into X-rays. It can be seen that it depends only on the efficiency η (I). Therefore, in the present invention, attention has been paid to the fact that when the target (type, etc.) is determined, the penumbra blur δ _P is determined by a change in the laser beam intensity I.

On the other hand, there is diffraction blur as a resolution limit determined by other factors. However, in order to simplify the discussion, the contact type exposure described here will be described.

Assuming that the X-ray wavelength is λ, the diffraction blur δ _f is

(Equation 10) Given by

Therefore, in order for penumbra blur δ _P to be equal to diffraction blur δ _f ,

[Equation 11] Needs to be satisfied.

Therefore, by irradiating the target with the excitation laser intensity that satisfies the expression (7), the exposure can be performed with the minimum laser energy without deteriorating the resolution. It becomes possible.

If the resolution determined by penumbra is
If you want higher resolution than determined by diffraction blur,

[0033]

(Equation 12) It is good.

If the above expression (8) is satisfied, the effect of penumbra blurring on the resolution of the entire apparatus can be made smaller than the effect of diffraction blurring. Also, under conditions where the resolution determined by penumbra is always lower (ie worse) than the resolution determined by diffraction, by irradiating with a laser intensity that minimizes penumbra, the overall resolution determined by penumbra and diffraction blur is reduced. Can be the best.

This optimum (maximizing the overall resolution)
The laser irradiation condition is a case where the penumbra (δ _P ) obtained by the equation (5) is minimized. This can be obtained by differentiating the equation (7) with respect to the laser intensity I.

(Equation 13) What is necessary is just to find the laser intensity I satisfying the following.

Exposure at a laser intensity I that satisfies the expression (9) allows an optimum resolution to be obtained for the entire apparatus.

Incidentally, actually,

[Equation 14] The laser intensity may be such that

If an X-ray absorbing object or an X-ray absorbing medium other than the object to be exposed exists in the X-ray optical path, letting the transmittance thereof be T, the following equations (7) and (8) are obtained. T on the right side of each equation
Divided by Hereinafter, the present invention will be described in more detail through examples.

[0039]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an embodiment of the present invention applied to an X-ray microscope for obtaining a contact transfer type replica. In this apparatus, a pulse laser beam 1 is condensed by a lens 2 and is irradiated on a target object 3. Then, a sample chamber 8 in which the biological sample 4 is placed below the focal point on the target object 3 is arranged.

The biological sample 4 comprises a resist 5 and an X-ray transmitting film 6
, And a medium (such as water), and the inside of the sample chamber 8 is sealed with an O-ring 7.

In this embodiment, yttrium is used as an example of the target object 3. FIG. 3 shows the laser light intensity dependence of the conversion efficiency of the yttrium into the “water window” region to X-rays.

Next, in this embodiment, the distance between the biological sample 4 and the resist 5 was 1 μm, and the average wavelength λ of the irradiated X-rays.
Is λ {28} (peak wavelength of the spectrum of the X-ray generated from yttrium), the diffraction blur δ _f becomes δ _f
≒ 0.05 μm.

When the thickness of the water layer in the sample chamber 8 is 1 μm and the resist 5 is exposed to 1 KJ / cm ³ ,
FIG. 4 shows the laser intensity dependence of penumbra blur δ _P calculated by equation (5). Here, the dependence of the conversion efficiency to X-rays on the laser intensity (FIG. 3) is approximated by a quadratic equation.

As is clear from FIG. 4, first, the penumbra decreases as the laser intensity increases. Then, when the laser intensity becomes about 5 × 10 ¹² w / cm ² ,
The same degree as the diffraction blur [delta] _f. When the laser intensity is further increased, penumbra is further reduced to about 5 × 10 ¹³ w / c
smallest in m ^2.

When the laser intensity is further increased, the penumbra begins to increase again. This is because the conversion efficiency η (I) to X-rays sharply decreases at the place where the laser intensity I is large.

FIG. 4 shows that the penumbra blur δ _P in the present embodiment.
But comparable to the diffraction blur [delta] _f or laser intensity becomes less it is understood that the range of approximately ^{5 × 10 12 ~6 × 10 13} w / cm 2.

Therefore, by using the X-rays generated as a result of irradiating the laser beam within the range of the laser intensity, the exposure can be performed in an optimal resolution state. It is possible to obtain a more accurate replica than before.

Also, as described above, in this embodiment, penumbra does not depend on the distance between the plasma and the resist, so that there is an advantage that the excitation laser device can be downsized.
That is, under the conditions shown in the above embodiment, the laser intensity is about 5 × 1
At ¹² w / cm ² , 1 KJ / cm ³ exposure can be performed with a penumbra blur of 0.05 μm. At this time, when the distance between the plasma and the resist is 1.0 cm, the laser energy is about 5 J Necessary, if the distance between the plasma and the resist is 0.5 cm, the laser energy is about 1 J
No problem. Moreover, in this case, both the exposure amount and the penumbra are 1.0c.
Same as m. FIG. 5 shows these relationships.

[0049]

As described above, according to the present invention, since the effects of laser beam intensity and penumbra blur, which have not been taken into account in the past, are taken into account, exposure by X-ray irradiation under optimum resolution is performed. Work can be done.

Further, by irradiating the target object with the laser beam intensity given by the formulas (8) and (9), it is possible to minimize the penumbra, or to at least make it equal to or less than the diffraction blur. When applied to various types of exposure apparatuses, high-resolution pattern transfer and the like can be performed.

Further, as described above, since the penumbra does not depend on the distance between the plasma and the resist, there is an advantage that the size of the excitation laser device can be reduced.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a contact X-ray microscope to which an embodiment of the present invention is applied.

FIG. 2 is an explanatory diagram showing a state of diffraction blur and penumbra blur in X-ray exposure.

FIG. 3 is a diagram showing a conversion efficiency of laser light energy to y-ray in a “water window” region in yttrium according to one embodiment of the present invention.

FIG. 4 is a diagram showing the relationship between penumbra and laser intensity according to one embodiment of the present invention.

FIG. 5 shows the relationship between laser energy and plasma-resist distance required to perform 1 KJ / cm ³ exposure at 0.05 μm penumbra in the X-ray exposure apparatus according to one embodiment of the present invention. FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Pulse laser beam 2 Lens 3 Target object 4 Sample 5 Substrate with resist 6 Substrate with X-ray transmissive film 7 0-ring 8 Sample chamber 9 X-ray 10 Window 11 Vacuum container

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-100310 (JP, A) JP-A-2-100297 (JP, A) JP-A-63-219125 (JP, A) JP-A-2-100 109299 (JP, A) Abstracts of the 51st Annual Meeting of the Japan Society of Applied Physics, Fall 1990 1990 Volume 2 499 (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 7/20 503 H05G 1/02 H05H 1/30 JICST file (JOIS)

Claims (5)

(57) [Claims] 1. A transmission X-ray pattern of an object to be exposed by irradiating X-rays from a pulsed laser-excited plasma X-ray source for generating X-rays by converging a pulsed laser beam onto a target object. X-ray exposure apparatus for forming an image on a surface to be transferred, wherein a semi-shadow blur of an image of the object to be exposed on the surface to be transferred due to the finite size of the X-ray source is limited by diffraction blur. Increase the size of the X-ray source until it is as large as the resolution.
X-ray exposure apparatus characterized by exciting the target object by listening to the laser light irradiation intensity. 2. An X-ray energy density required for contact-type exposure is P _E [J / cm ³ ], an X-ray wavelength is λ (a typical value when the spectrum width is wide), and an X-ray wavelength λ is used. Is the absorption coefficient of the resist to α [cm ⁻¹ ], the distance between the object to be exposed and the surface to be transferred is h, and the excitation laser pulse time width is τ.
_P , when the energy conversion efficiency per solid angle from the excitation laser beam to the wavelength of the exposure X-ray or X-ray in the wavelength range per solid angle is η (I), and the erection laser intensity is I [w / cm ² ], ] An X-ray exposure apparatus, wherein the target object is excited with a laser beam irradiation intensity satisfying the following condition. 3. In a contact type exposure, when a penumbra of an image of an object to be exposed on a surface to be transferred does not fall below a resolution limited by other factors, an excitation laser pulse time width is set.
ΤP, the wavelength or wavelength range of the exposure X-ray from the excitation laser beam.
The energy conversion efficiency per solid angle to X-ray is η
(I) If the erection laser intensity is I [w / cm ² ]
, (Equation 2) An X-ray exposure apparatus that excites the target object with a laser beam irradiation intensity that satisfies the following. 4. The method according to claim 2, wherein a mask pattern of an integrated circuit is used as the object to be exposed.
X-ray exposure apparatus of the mounting. 5. A method of using a biological sample as the object to be exposed, and forming a transferred image of the biological sample on a resist surface.
The X-ray exposure apparatus according to claim 2 or 3, wherein: