JPH04233717A - X-ray exposing device - Google Patents

Abstract

PURPOSE:To reduce the amount of consumption of helium, of the X-ray exposing device with which an exposing operation is conducted in a helium-reduced state. CONSTITUTION:A circulation path 115, to be used to circulate the gas in an exposing chamber, is provided outside the exposing chamber, and a pump 14 which circulates gas, a cooler with which gas is cooled down to liquid nitrogen temperature or lower and the impurities in the gas are trapped, and a heater 117 to be used to heat up the gas cooled by the aforesaid cooler and reintroduced into the above-mentioned exposing chamber, are provided outside the exposing chamber.

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 that performs exposure using X-rays.

0002

[Prior Art] Conventionally, exposure methods using X-rays include:
Exposure in air, exposure in helium atmosphere, exposure in vacuum, etc. are being considered. In atmospheric exposure, X-rays are significantly attenuated by oxygen and nitrogen in the atmosphere, resulting in a low throughput. Furthermore, in vacuum exposure, heat diffusion is very slow, so the temperature of the irradiated area of the mask or wafer increases, and there is a risk that the transferred pattern will be misaligned. In recent years, for these reasons, exposure in a helium atmosphere, which absorbs little X-rays, has attracted attention.

[0003] In general exposure in a helium atmosphere, helium is introduced into the exposure chamber from a helium cylinder and evacuated during the exposure, and a large amount of expensive helium is consumed. In order to reduce the amount of helium consumed, a method has been proposed in which the exposure chamber is combined with a circulation system for reintroducing the helium exhausted from the exposure chamber into the exposure chamber.

0004

[Problems to be Solved by the Invention] Exposure in a helium atmosphere is a method in which helium is introduced into the exposure chamber from a helium cylinder and exhausted during exposure, which consumes a large amount of expensive helium. Another problem is that the manufacturing cost is high.

[0005] In an exposure chamber combined with a circulation system, the helium exhausted from the exposure chamber is
Because it is a method of reintroducing it directly into the exposure chamber,
If exposure is continued for a long time, the purity of helium in the exposure chamber decreases, causing a problem in that the X-ray intensity on the resist surface coated on the wafer becomes non-uniform. This means that the absorption rate of X-rays is 3 compared to helium.
This is due to atmospheric components containing oxygen and nitrogen, which are twice as large, mixed in as impurities.

[0006] Usually, in various exposure apparatuses including X-ray exposure,
Since the amount of exposure is controlled by time, non-uniform X-ray intensity on the resist surface means that the amount of exposure changes, resulting in large variations between each wafer in the devices being manufactured. Yield also decreases.

The present invention has been made in view of the problems of the prior art described above, and provides an X-ray exposure apparatus that can reduce the amount of helium consumed and does not reduce the yield of manufactured elements. The purpose is to realize the following.

[0008]

[Means for Solving the Problems] The X-ray exposure apparatus of the present invention uses X-rays as exposure light, and the inside of the chamber is kept in a reduced pressure helium state during exposure. The exposure chamber is provided with a circulation path for circulating gas inside the exposure chamber, and the circulation path includes a pump for circulating the gas and a trap for trapping impurities in the gas by cooling the gas to a temperature below liquid nitrogen temperature. and a heater for heating the gas cooled by the cooler and reintroducing it into the exposure chamber.

In this case, a temperature sensor is provided to detect the temperature of the gas cooled by the cooler, and a heater is controlled according to the detected value of the temperature sensor to control the temperature of the gas reintroduced into the exposure chamber. A temperature controller that makes the temperature equal to the temperature inside the chamber may be provided, and each of the pump, cooler, and heater provided in the circulation path
They may be provided in the above order in the gas flow direction.

0010

[Operation] As the gas in the exposure chamber is circulated through the circulation path, it is cooled down to liquid nitrogen temperature by the cooler, so the main impurities contained in the gas, such as nitrogen and oxygen, are condensed and trapped. Ru. Thereafter, the gas reintroduced into the exposure chamber is heated by the heater, so the atmosphere density within the exposure chamber does not change significantly. This makes it possible to recycle helium without reducing helium purity.

[0011]

Embodiments Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

X-rays 101 generated by an X-ray source (not shown)
is a mirror 103 housed in a mirror chamber 102
The light is reflected from the convex surface of the light beam, is magnified, and enters the exposure chamber 105 through the beryllium window 104. Here, the interior of the mirror chamber 102 is maintained at a high vacuum of 10<-7 >Torr or less, and the interior of the exposure chamber 105 is kept in a reduced pressure helium atmosphere. The X-rays incident on the exposure chamber 105 expose the resist on the wafer 110 through an X-ray transmission type X-ray mask 108 supported by a mask holder (not shown).

The exposure chamber 105 includes a helium inlet 106 for creating a reduced pressure helium atmosphere inside, an exhaust port 111, and an oxygen sensor 113 for detecting the internal atmosphere.
, a temperature sensor 119, a wafer chuck 109 for fixing the wafer 110, a leak gas inlet 107 for introducing leak gas such as air or nitrogen during maintenance and inspection, etc.
A circulation path 115 is provided for recycling helium. Circulation path 1 provided outside the exposure chamber 105
Reference numeral 15 is for circulating gas within the exposure chamber 105. Further, the oxygen sensor 113 is connected to the exposure chamber 1.
It is provided to detect helium purity from the oxygen concentration in 05.

The circulation path 115 includes a pump 114, a cooler 112, a temperature sensor 116, and
A heater 117 is provided. The temperature of the heater 117 is controlled by a temperature controller 118 which inputs the detection signal of the temperature sensor 116, and the helium flowing out from the exposure chamber 105 is reintroduced into the exposure chamber 105 after passing through these devices in order. Ru.

In order to maintain the exposure chamber 105 in a reduced pressure helium atmosphere, the exhaust port 111 is opened and the exposure chamber 105 is
After evacuating the inside of the exposure chamber 105, helium is introduced from the helium inlet 106 until the inside of the exposure chamber 105 reaches a predetermined pressure, and then the exhaust port 111 is closed. In this state, helium in the exposure chamber 105 is circulated by the circulation path 115 as follows.

Helium in the exposure chamber 105 is drawn into a circulation path 115 by a pump 114 . pump 1
The helium that has passed through 15 is then transferred to a cooler 11 installed
2, it is cooled and impurities are removed. The temperature of the cooled helium is detected by a temperature sensor 116. A temperature regulator 118 controls the temperature of a heater 117 provided next in accordance with the detection result of the temperature sensor 116, so that the temperature of helium is approximately the same as the temperature inside the exposure chamber 105.

By configuring the circulation path 115 as described above, impurities are removed from the helium reintroduced into the exposure chamber 105 from the heater 117 and the temperature is adjusted, making it possible to use helium effectively. becomes.

The gas is cooled by a cooler 112 to condense and trap impurity components other than helium. Although various molecules begin to condense at temperatures below their respective boiling points, impurities can be more reliably removed by cooling them to below their melting points, which is preferable. For example, when removing water molecules, the cooling temperature may be set to 0° C. or lower, but in order to remove organic matter, oxygen, nitrogen, etc., it is necessary to set the cooling temperature to lower than the liquid nitrogen temperature. In this low temperature region, impurities other than hydrogen and neon are removed. Although hydrogen and neon are difficult to remove, the risk of them being mixed in as impurities is very small, and even if hydrogen or neon is mixed in, the exposure unevenness caused by this can be almost ignored, so there is no problem. .

Since the helium cooled by the cooler is raised to a desired temperature by the heater 117 and changes in its density are suppressed, unevenness in the amount of exposure is further reduced.

As a means for the cooler 112, for example, a liquid nitrogen trap is insufficient for removing oxygen and nitrogen, and considering the actual cooling temperature, it is necessary to use a liquid helium trap, a refrigerator, etc. be. Furthermore, as the heater 117 that increases the temperature of the cooled gas,
For extremely low-temperature gases, a general heater can be used; for gases such as helium, which have high thermal conductivity and small heat capacity, after bringing the temperature to around room temperature with a heater, the temperature in the constant-temperature water bath must be Sufficient temperature control can be achieved just by circulating it. In addition, by applying feedback to these mechanisms using the temperature sensor 116 and temperature controller 118, the desired temperature can be adjusted by ±0.1°C.
It becomes possible to perform the following temperature control.

Next, the operation of this embodiment will be explained in detail by citing specific numerical values.

0.2 using the X-ray exposure apparatus shown in FIG.
A first experiment was conducted in which a test pattern with a line width of 5 μm was printed. As the cooler 112, a combination of a liquid nitrogen trap 202 and a liquid helium trap 203 as shown in the schematic cross-sectional view of FIG. 2 is used.
A combination of a sheath heater and a constant temperature water tank was used.

Liquid nitrogen is introduced through the liquid nitrogen inlet 202A, and liquid helium is introduced through the liquid helium inlet 203A. The vaporized gas generated by cooling the gas in the circulation path 115 is discharged through the vaporized gas exhaust ports 202B and 2.
From 03B, each is discharged.

As for the experimental procedure, first, the exposure chamber 1
Wafer 11 coated with chemically amplified negative resist inside 05
0 and the X-ray mask 108, the inside of the exposure chamber 105 is evacuated to a high vacuum of about 10-7 Torr, and then a helium with a purity of 99.999 is supplied from the helium inlet 106.
% helium and the pressure inside the exposure chamber 105 is 150T.
It was introduced until it became orr. In this state, the resist coated on the wafer 110 was exposed to the X-rays 101 magnified by the mirror 103 and incident through the beryllium window 104.

During the exposure operation, the oxygen concentration in the exposure chamber 105 was monitored by the zirconia type oxygen sensor 113 attached to the exposure chamber 105, and it was found that the oxygen concentration in the exposure chamber 105 was always 7p.
pm or less, and the temperature of the helium introduced from the circulation path 115 is controlled by feedback based on the detection result of the temperature sensor 116 (it is heated to about 23°C ± 20°C by a sheath heater and then passed through a constant temperature water bath). As a result, the temperature was maintained within the range of 23°C±0.1°C.

In this exposure experiment in which helium purity and temperature fluctuations were suppressed within the above ranges, the defect rate was 1% or less, and good exposure could be performed. Note that the defect rate referred to here refers to the line width of the baked pattern on the resist.
± of the line width of the X-ray absorber pattern drawn on the mask
This refers to the percentage of items that are not within 10%.

After this, we investigated the relationship between the purity of helium and the accuracy of the baked pattern, and found that the line width of the baked pattern widened as the helium purity decreased, and the impurity concentration was 0.1.
It has been found that the defect rate begins to increase above %.

Next, as a second experiment, X shown in FIG.
Using a line exposure device, helium purity was measured assuming actual exposure conditions.

FIGS. 3A and 3B are a top sectional view and a side sectional view showing the configuration of the cooler 112 provided in the helium circulation path 115, respectively.

The refrigerator 303 utilizes the adiabatic expansion of helium and has a cooling capacity of 45W at 80K.
On the top surface of the refrigerator 303 is a vacuum chamber 302 and
A circulation path 115 sandwiched between the two is placed. Further, as the heater 117, a combination of a sheath heater and a constant temperature water bath was used, as in the first experiment.

First, the inside of the exposure chamber 105 is heated to 10-7T.
The vacuum was evacuated to a high vacuum level of about 100.degree. A needle valve is provided between the exposure chamber 105 and the pump 114, and the amount of gas flowing into the circulation path 115 is set to 14SLM (Standard Liter p
er Minutes).

Purity measurement was performed by using a zirconia type oxygen sensor 113 to monitor the oxygen concentration. It is assumed that normal exposure operations are performed 40 times per hour in the exposure chamber 105, and when the oxygen concentration is checked after 24 hours, it is suppressed to 5 ppm or less, and the oxygen is reintroduced into the exposure chamber 105. The temperature of helium was 23°C ± 0.0°C as in the first experimental example.
The temperature range was 1°C. By controlling the atmosphere in the exposure chamber 105 as described above, the wafer 110
The variation in exposure amount on the resist surface was 1% or less. In addition, when the oxygen concentration during steady operation was monitored using a comparison exposure chamber with only a temperature control mechanism in the circulation system, it was 21 ppm after 24 hours of operation.

In the embodiments described above, the exposure chamber 105 has been described as one in which helium is circulated with the exhaust port 111 closed, but the helium inlet 10
A steady state may be established by slowly exhausting air from the exhaust port 111 while introducing helium little by little from 6.

[0035] In addition, although it has been described that a liquid helium trap or a refrigerator is used as the cooler 112, and a combination of a sheath heater and a constant temperature water bath is used as the heater 117, other types may be used. There is no particular limitation as long as the temperature can be lowered or raised to a desired temperature. Further, the combination of the temperature sensor and the temperature raising mechanism is not limited to one stage, but may be stacked in several stages depending on the temperature of helium and temperature control accuracy.

[0036] Furthermore, although the explanation has been made assuming that the pump, cooler, and heater are provided in order in the direction of gas flow in the circulation path, by arranging them in this order, it is also possible to trap impurities generated by the pump. This is because it becomes possible. If the impurities generated by the pump are of a negligible level, the position of the pump is not particularly limited.

[0037]

[Effects of the Invention] Since the present invention is constructed as described above, it produces the following effects.

[0038] In the first aspect, since helium can be reused without reducing helium purity, the amount of helium consumed can be reduced;
This has the effect of lowering manufacturing costs.

[0039] In addition to the above-mentioned effects, the second aspect of the present invention has the effect that even better exposure can be performed because the temperature of the gas reintroduced into the exposure chamber can be precisely controlled. be.

In the third aspect of the present invention, since impurities generated by the pump are also trapped, there is an effect that the purity of helium in the exposure chamber can be further improved.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of an embodiment of the present invention.

2 is a schematic cross-sectional view showing a first configuration example of the cooler 112 in FIG. 1. FIG.

3(a) is a top sectional view showing a second configuration example of the cooler 112 in FIG. 1, and FIG. 3(b) is a side sectional view thereof.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 101 Temperature sensor 117 Heater 118 Temperature controller 202 Liquid nitrogen trap 202A Liquid nitrogen inlet 202B, 203B Vaporized gas outlet 203
Liquid helium trap 203A Liquid helium inlet 302 Vacuum chamber 303 Freezer

Claims (3)

[Claims] 1. In an X-ray exposure apparatus in which X-rays are used as exposure light and the inside of the chamber is kept in a reduced pressure helium state during exposure, a circulation path for circulating gas inside the exposure chamber is provided outside the exposure chamber. The circulation path is provided with a pump for circulating the gas, a cooler for cooling the gas to below the liquid nitrogen temperature and trapping impurities in the gas, and a gas cooler that is cooled by the cooler. An X-ray exposure apparatus characterized by comprising: a heater for heating the exposed gas and then reintroducing the heated gas into the exposure chamber. 2. The X-ray exposure apparatus according to claim 1, further comprising a temperature sensor for detecting the temperature of the gas cooled by the cooler, and controlling a heater according to the detected value of the temperature sensor for exposure. An X-ray exposure apparatus comprising: a temperature controller that makes the temperature of gas reintroduced into the chamber equal to the temperature inside the exposure chamber. 3. In the X-ray exposure apparatus according to claim 1 or 2, the pump, the cooler, and the heater provided in the circulation path are provided in the above order in the gas flow direction. Characteristics of X-ray exposure equipment.