JP2975159B2 - Photolithography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to photolithography used in a semiconductor manufacturing process.

[0002]

2. Description of the Related Art In recent years, miniaturization of LSIs has been tremendous, and mass production of 4M bit DRAMs has already started. By the way, in a photolithography process for manufacturing a 4M LSI, a reduction projection exposure apparatus (stepper) using an i-line (365 nm) having a shorter wavelength instead of the conventional g-line (436 nm) is also used. , LS
In order to increase the density of I, use of a light source having a shorter wavelength than the i-line is being studied. This is because the minimum pattern size (resolution) R and the depth of focus D that can be exposed in the reduction projection exposure apparatus are given by the following equations. R = (k ₁ λ) / (NA) (1) D = (± k ₂ λ) / (NA) ² (2)

That is, as can be seen from equation (1), in order to increase the resolution R, either the wavelength λ is reduced, the NA called the numerical aperture of the reduction projection lens is increased, or k ₁ is reduced. Must be chosen. However, (2)
As can be seen from the equation, as the NA is increased, the depth of focus D
There is a problem that becomes shallow. Further, k ₁ can be slightly reduced by improving the process, but is 0.1 in the current technology.
It is said that about 6 is the limit. Therefore, NA
The influence on the depth of focus is smaller than when the value is increased, and reduction of the wavelength λ at which the resolution R can be reduced is being studied.

[0004]

On the other hand, if the wavelength becomes shorter in the ultraviolet region, the rate of change of the refractive index of the glass material of the projection lens with respect to the wavelength becomes larger, and the selection range of the glass material becomes narrower. Become. For this reason, the use of a lamp having a narrower half-width at half maximum of the radiated spectral line is being studied. However, in order to further reduce the half width of the light emitted from the lamp, the density of the enclosed mercury must be reduced, which not only reduces the light energy but also significantly increases the lighting current. And the reliability of the lamp to be used is poor in terms of the service life and structure.

The present invention has been made in view of the above circumstances, and it is an object of the present invention that the wavelength shorter than the i-line is about 313 nm, 302 nm, 297 nm, and 265 nm.
It is an object of the present invention to provide a novel photolithography that turns on a mercury lamp so as to efficiently emit one of ultraviolet rays selected from m and 254 nm, and uses the emitted light.

[0006]

Means for Solving the Problems In the photolithography of the present invention, a short arc type mercury lamp in which a pair of electrodes are arranged opposite to each other in a bulb and the mercury pressure at the time of lighting becomes 0.5 atm or less is pulsed. The lamp is turned on by electric current and has a wavelength of about 313 nm, 30
Ultraviolet rays of 2 nm, 297 nm, 265 nm, and 254 nm are radiated, and any ultraviolet ray selected from the radiated light is irradiated onto a resist surface on a semiconductor wafer through an original and a lens that transmits the ultraviolet rays.

[0007]

[Operation] Since a short arc type mercury lamp in which the mercury pressure at the time of lighting becomes 0.5 atm or less is lit by a pulse current, the Stall effect, which is a main factor for broadening the spectrum line, is suppressed, and the radiated wavelength is reduced. 313 nm, 302
Ultraviolet rays such as nm, 297 nm, 265 nm, and 254 nm have a narrow half width and a small decrease in energy. Moreover, even if a large current flows, the time is short, and the reliability of the mercury lamp increases.

[0008]

FIG. 1 is a diagram illustrating an example of an optical system used for photolithography according to the present invention.
At the time of lighting, mercury which becomes 0.5 atm or less is sealed, and the light is lit by the driving power supply 9 with a pulse current. 2 is a condenser mirror,
Reference numeral 3 denotes a plane mirror, 4 denotes an integrator, and 5 denotes a condenser lens group. In the case of the present invention, the achromatic lens is a combination of a quartz lens and a fluorite lens. In addition, the condenser mirror 2
If necessary, a band-pass filter made of an optical interference film may be inserted at an appropriate position in the optical path from the optical path to the condenser lens group 5. Reference numeral 6 denotes an original image called a reticle. This original image 6 is reduced by a reduction lens 7 and projected onto a photoresist layer 81 on a semiconductor wafer 8. That is, the photoresist layer 81 is irradiated with light emitted from the mercury lamp 1 through the original image 6. As the photoresist, for example, KTI895i for 313 nm, 302 nm, and 297 nm, Shp for 265 nm and 254 nm
Use of the SNR-248 is possible.

FIG. 2 shows an example of the mercury lamp 1. valve
Reference numeral 10 is made of quartz glass, has a bulging portion 11 on both sides, and has a thin tube portion 12 at the center. Tungsten electrodes 13, 13 are disposed in the bulging portions 11 on both sides so as to face each other, and a current introducing rod 15 made of molybdenum is connected to the outside thereof. A trigger wire 14 is arranged outside the bulb 10 so as to straddle between the electrodes 13 and 13, and metal bases 16 and 16 are arranged at both ends. ing. The distance between the electrodes is 20 mm, the inner diameter of the central thin tube portion 11 is 3 mm, and the length is 10 mm. And this mercury lamp 1
Has an outer tube (not shown), and is heated to 220 ° C. by a heating wire, and the pressure of mercury at the time of non-lighting at 220 ° C. is 15 Torr.

FIG. 3 is a circuit diagram for lighting the mercury lamp 1 used in the present invention. As shown in this figure, the lighting circuit includes a control circuit 900, a circuit breaker 901, a noise filter 902, a low frequency rectifier 903.
, Inrush current prevention semiconductor element 904, low frequency filter 9
05, main switching element 906, main transformer 907
, High-frequency rectifier 908, detection circuit 909, trigger power supply 910
, A main condenser 911 and a trigger coil 912.

Next, the operation of this circuit will be described.
When the circuit breaker 901 connected to the power supply is turned on, the current flows through the noise filter 902 and the low-frequency rectifier 903.
To charge the rectifying capacitor in the low-frequency filter 905. At this time, the inrush current preventing semiconductor element 904 is not turned on, and flows through a resistor (not shown) connected in parallel. When the capacitor of the low frequency filter 905 is charged to some extent, the control circuit 900
The switching regulator IC (not shown) is in an operation standby state. Here, when the charge start switch of the control circuit 900 is turned ON, the MOS-F
A drive signal is output to a main switching element 906 composed of elements such as ET, IGBT, and SIT to be driven. When the main switching element 906 is driven, the main transformer 907 operates to generate a high-frequency high voltage on the secondary side. This voltage is rectified and smoothed by the high-frequency rectifier 908 to charge the main capacitor 911. At this time, the state of charge of the main capacitor 911 is detected by the detection circuit 909, and this signal is compared with a reference value in the control circuit 900, amplified, and the drive signal of the main switching element 906 is adjusted. When the main capacitor 911 is charged to a certain voltage, the charging stops and enters the light emission standby state. When the flash start switch is turned on, the signal in the control circuit 900 causes the trigger power supply 910 to output the mercury lamp through the trigger coil 912. A trigger is applied to one trigger wire, and the mercury lamp 1 emits light.

The mercury lamp 1 was actually turned on by the drive power supply 9 described above, and its characteristics and the like were examined. The lighting conditions were a current pulse half width of 50 μs, a peak current of 500 A, and a lighting frequency of 50 Hz. As a result, as shown in FIG.
The half value width of 13 nm is about 1.0 nm, which can be reduced to 1/4 of that of a conventional mercury lamp for an i-line stepper. The peak value at 313 nm is also large,
In the output comparison of ± 0.5 nm, almost the same value could be obtained. In this embodiment, the FWHM of 313 nm light was about 100 μs.

According to the photolithography of the present invention, the photoresist 81 on the semiconductor wafer 8 is irradiated with pulse light from the mercury lamp 1 a plurality of times, and the exposure is performed while moving stepwise. That is, as an example, in the case of a conventional i-line mercury lamp, if the exposure time is 0.1 second with respect to an electric input of 2 kW, 2000 W × 0.1
Since the input energy is 200 J / sec, in order to correspond to this, in the case of the present invention, since one energy corresponds to about 40 J, it is only necessary to output five pulses in 0.1 sec. . That is, exposure is performed by repeating pulse emission at 50 Hz for 0.1 second, moving stepwise to the next exposure position at 0.5 second for 0.1 second, and pulse emission at 50 Hz for 0.1 second. That is, light is emitted as shown in FIG.

Therefore, k ₁ shown in the equation (1) is 0.6, N
When A is 0.6 and photolithography is performed at a wavelength of 313 nm, it is possible to down to 0.3 μm by design rules.
If the k ₁ reduction measure can be used together, photolithography that can be used sufficiently up to 256 Mbits, which is said to be a 3rd generation super LSI, can be obtained.

Although an example of the present invention has been described above, the present invention is not limited to this embodiment. For example, a conventional round mercury lamp can be used as a mercury lamp, and a shutter in an optical path is used. And the mercury lamp may be continuously pulsed.

[0016]

As described in detail above, the present invention provides
Since a short arc type mercury lamp in which the mercury pressure at the time of lighting becomes 0.5 atm or less is lit by a pulse current, the emission wavelength is about 313 nm, 302 nm, and 297 nm.
m, 265 nm, 254 nm ultraviolet light has a narrow half width and a small amount of energy reduction, so there is no problem of chromatic aberration despite using short wavelength ultraviolet light, and it can be applied to design rules up to 0.3 μm. It can be photolithography.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an example of an optical system used in the present invention.

FIG. 2 is a sectional view of an example of a mercury lamp used in the present invention.

FIG. 3 is an example of a drive power supply circuit diagram used in the present invention.

FIG. 4 is an explanatory diagram of a radiation wavelength intensity according to the present invention.

FIG. 5 is an explanatory diagram of pulse emission according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mercury lamp 2 Condensing mirror 3 Plane mirror 4 Integrator 5 Condenser lens group 6 Original picture 7 Reduction lens 8 Semiconductor wafer 9 Drive power supply

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-57-185663 (JP, A) JP-A-60-59733 (JP, A) JP-A-2-5395 (JP, A) (58) Field (Int.Cl. ⁶ , DB name) H01L 21/027 G03F 7/20 521

Claims (1)

(57) [Claims] 1. A short arc type mercury lamp in which a pair of electrodes are arranged opposite to each other in a bulb and a mercury pressure at the time of operation becomes 0.5 atm or less by a pulse current. Wavelength is about 313nm, 3
A photo-characteristic in which ultraviolet rays of 02 nm, 297 nm, 265 nm and 254 nm are emitted, and one of ultraviolet rays selected from the emitted light is irradiated on a resist surface on a semiconductor wafer through an original and a lens transmitting the ultraviolet rays. Lithography.