GB2358955A

GB2358955A - Charged particle beam exposure apparatus and Method

Info

Publication number: GB2358955A
Application number: GB0027160A
Authority: GB
Inventors: Kazuto Ashihara; Yoshihisa Ooae
Original assignee: Advantest Corp
Current assignee: Advantest Corp
Priority date: 1999-11-19
Filing date: 2000-11-07
Publication date: 2001-08-08
Anticipated expiration: 2020-11-07
Also published as: GB2358955B; DE10057079A1; KR20010051744A; JP2001148340A; GB0027160D0; TW476979B; DE10057079C2

Abstract

A method and apparatus for charged beam exposure, in which contamination on the surface of the parts can be cleaned by introducing ozone of high concentration into at least a portion of a high vacuum chamber, this introduction of ozone occurring during exposure with the charged beam. The ozone is generated at a pressure lower than that of atmospheric pressure and therefore the method is substantially free from the danger of ozone leaking into the atmosphere. A charged particle beam EB is generated in the vacuum chamber 10 and the desired pattern is exposed on a sample W. During the pattern exposure, low pressure ozone is introduced into at least a portion of the vacuum chamber by an ozone supply mechanism 8 including, a second vacuum chamber lower in pressure than the atmosphere and an ionizer for ionizing the oxygen.

Description

2358955 CHARGED PARTICLE BEAM EXPOSURE APPARATUS AND METHOD

BACKGROUND OF THE INVENTION

The present invention relates to an exposure method and an exposure apparatus using a charged particle beam such as an electron beam or, in particular, to an exposure method and an exposure apparatus in which the beam drift due to the contamination accumulated in the apparatus is reduced thereby to maintain the accuracy of an exposure pattern for a long time.

With the increased degree of integration of integrated circuits, a technique capable of a higher degree of pattern exposure has been required. The limit of the pattern exposure technique is defined by the exposure technique. A higher degree of pattern exposure is difficult to realize with the conventional light exposure technique, and a new exposure technique is in demand. An exposure technique using a charged particle beam such as an electron beam can expose a much finer pattern than a light exposure technique and is being closely watched as the next- generation exposure technique.

The present invention, though applicable also to exposure using a charged particle beam other than an electron beam, will be explained with reference to electron beam exposure as an example. In the electron beam exposure apparatus, electrons are generated by an electron gun and are accelerated by an electric field thereby to generate an electron beam. The shape and direction of the electron beam are controlled by an electromagnetic lens or a deflector arranged in a lens barrel. The beam can be shaped by various methods. Normally, however, the electron beam is shaped into a rectangle by a rectangular first slit and further shaped into an exposure beam by a second slit or a blanking aperture array (BA. A) mask (generally called the transmission mask). The electron beam thus shaped is deflected by a deflector and radiated onto a sample such as a wafer or a reticle mask. These exposure patterns are connected thereby to expose a desired pattern. In electron beam exposure, it is possible to produce patterns less than 0.05 tm wide with a positioning accuracy of 0.02 um.

The electron beam exposure apparatus, however, poses a problem in that the position of radiation of the electron beam changes and the exposure pattern is deteriorated with time. This shift of the position of electron beam radiation is called the beam drift. The main cause of the beam drift is charge-up drift due to the electric field generated by the charge accumulated on the contamination of the electrostatic deflection electrode or the lower portion of the lens barrel arranged in proximity to the sample. The surface of the sample is normally coated with a resist film of an organic material, and the gas generated by the organic material due to irradiation by a high-energy electron beam, or the carbon component in the gas, attaches to the surfaces of the surrounding parts. As a result, contamination with a very high insulation property is generated on the surface of the parts. The charge of the reflected electrons and the secondary electrons are accumulated on the contamination thereby to generate an electric field. The radiated electron beam is deflected by this electric field so that the position of electron beam radiation is changed. This contamination is generated even on a portion far from the sample but the degree of contamination is reduced with the distance from the sample.

An increased beam drift makes normal exposure impossible, and therefore the contamination must be cleaned. Japanese Unexamined Patent Publication (Kokai) Nos. 61-20321 and 6-325709 disclose a method of cleaning 3 - the contamination in which the operation of the exposure apparatus is provisionally suspended, oxygen is introduced into the vacuum chamber in the exposure apparatus to generate a plasma, the surface of the parts is ashed into a gas by the plasma thus generated, and the gas is released outside thereby to remove the surface contamination. This method, however, requires the provisional suspension of the operation of the exposure apparatus for introducing oxygen thereinto. This not only extremely reduces the utilization rate of the apparatus but also deteriorates the plating on the surface of the parts.

Kokai No. 9-259811, on the other hand, discloses a method in which the contamination is cleaned by introducing ozone into at least a portion of the vacuum chamber of the electron beam exposure apparatus while at the same time performing the exposure. The ozone introduced into the vacuum chamber is activated by the electron beam for exposure and changes to the oxygen radical, which gasifies the contamination on the surface of the parts. This gas is discharged. The generation of the oxygen radical depends on the intensity of the electron beam. In view of the f act that the intensity of the electron beam for radiation is varied from one portion to another of the apparatus, a different amount of ozone is introduced into a different portion of the vacuum chamber.

Fig. 1 is a diagram showing an example configuration of a mechanism for supplying ozone to the electron beam exposure apparatus disclosed in Kokai No. 9-259811. oxygen is supplied from an oxygen cylinder 51 to an ozone generating unit (ozonizer) 52. The ozonizer 52, which is a device such as the Siemens ozone tube, is widely known and will not be described in detail. In any way, the ozonizer 52 generates ozone from the oxygen supplied thereto and produces a mixture (mixture gas) of oxygen and ozone. This mixture contains activated oxygen (oxygen radical). The concentration of ozone in the mixture is normally about 10%.

The ozone mixture is sent to a mass flow sensor MFS and introduced into a vacuum chamber in a column 10 of the electron beam exposure apparatus. An electron beam optical system for generating, shaping and deflecting the electron beam and a moving mechanism for holding and moving the sample are arranged in the vacuum chamber.

The interior of the vacuum chamber is maintained at a low pressure (vacuum) of about 1 x 1C Pascal (Pa) (1 x 10-' Torr). Thus, most of the gases in the vacuum chamber is the mixture of oxygen and ozone. AS the gases in the vacuum chamber are discharged by the vacuum pump P, the mixture is supplied from the MFS so that the interior of the vacuum chamber is maintained at a low pressure as described above. During the exposure, the electron beam bombards the ozone gas and generates the oxygen radical, which removes the contamination.

The mixture supplied from the ozonizer 52 to the MFS is partially introduced into the vacuum chamber through the MFS, while most portion of it is sent to an ozone processing unit 53 where it is processed to return it to oxygen and it is released into the atmosphere. In the mixture of oxygen and ozone supplied by the ozonizer 52, the particles bombard each other and are recombined and the ozone returns to oxygen molecules. Thus, the ozone concentration is reduced with time. It is therefore necessary to supply the MFS with the mixture immediately after it is generated in the ozonizer 52.

In the electron beam exposure apparatus, the electron beam is generated and a pattern is exposed by the electron beam, and therefore the interior of the vacuum chamber is desirably kept at as high a vacuum state as possible. In the electron beam exposure apparatus disclosed in Kokai No. 9-259811, ozone is introduced into the vacuum chamber in order to generate the oxygen radical even during the exposure.

Nevertheless, the amount of ozone thus introduced is desirably as small as possible to maintain the interior of the vacuum chamber in a high vacuum state. An excessively small amount of ozone introduced into the vacuum chamber, however, poses the problem that the contamination cannot be completely removed. The oxygen contained in the mixture introduced into the vacuum chamber does not substantially contribute to the generation of oxygen radical, and the generation of oxygen radical depends on the amount of ozone. By increasing the ozone concentration in the mixture, therefore, the amount of the oxygen radical generated can be increased while maintaining the interior of the vacuum chamber in high vacuum state. In the mixture of oxygen and ozone obtained from the conventional ozonizer described above, however, the ozone concentration is about 10% and decreases while being introduced from the ozonizer to the vacuum chamber. Therefore, the problem is that the ozone concentration of the mixture introduced into the vacuum chamber cannot be increased.

In Fig. 1, the mixture containing ozone generated in the ozonizer 52 is sent to the ozone processing unit 53 and to the MFS at the same time. For this purpose, the mixture is required to be placed under pressure. The high-concentration ozone is hazardous. Therefore, the mixture containing ozone from the ozonizer 52 is released into the atmosphere after being returned to oxygen in the ozone processing unit 53. The mixture containing the ozone generated in the ozonizer 52, however, may leak out into the atmosphere while being pressured and sent to the MFS and the ozone processing unit 53.

only a small portion of the mixture supplied to the MFS from the ozonizer 52 is introduced into the vacuum chamber through the MFS, and most of the mixture is sent to the ozone processing unit 53, where it is returned to oxygen and released into the atmosphere. In this way, only a small portion of the mixture containing the ozone 6 generated in the ozonizer 52 is actually used, and the greater proportion of the mixture is wasted. Specifically, as compared with the concentration of ozone actually introduced and used in the vacuum chamber, the amount of oxygen supplied and consumed as a material is so large that the oxygen material is costly.

SUMMARY OF THE INVENTION

The object of the present invention is to solve the aforementioned problems and provide a charged particle beam exposure method and apparatus in which the contamination on the surface of the parts can be removed by introducing ozone of high concentration into at least a portion of the vacuum chamber during exposure with a small amount of oxygen while minimizing the danger of ozone leaking out into the atmosphere.

In order to achieve the object described above, according to one aspect of the present invention, there are provided a charged particle beam exposure method and apparatus, in which the ozone generated under a reduced pressure is introduced into the vacuum chamber of the exposure apparatus.

Specifically, in the charged particle beam exposure method according to the invention, the low-pressure ozone is introduced into at least a portion of the vacuum chamber and a pattern is exposed on a sample by the charged particle beam. Thus, ozone is generated under a pressure lower than the atmospheric pressure.

According to another aspect of the invention, there is provided a charged particle beam exposure apparatus comprising a first vacuum chamber, a vacuum pump for evacuating the interior of the vacuum chamber, a charged particle beam optical system for generating a charged particle beam in the first vacuum chamber and exposing the desired pattern on a sample by the charged particle beam, and an ozone supply mechanism for introducing the low-pressure ozone into at least a portion of the vacuum chamber during the pattern exposure on the sample in the 7 charged particle beam optical system, wherein the ozone supply mechanism includes a second vacuum chamber with the interior thereof maintained under a pressure lower than the atmospheric pressure, and an ozonizer for ozonizing, in the second vacuum chamber, at least a portion of the oxygen supplied from a supply port, and wherein the ozone generated in the second vacuum chamber under low pressure is supplied to at-least a portion of the interior of the first vacuum chamber.

According to the invention, ozone is generated under a pressure lower than the atmospheric pressure and introduced into the first vacuum chamber of the apparatus. Under a reduced pressure, the mean free path of the particles is long and the chance of the particles bombarding each other is low. The ozone generated, therefore, is less likely to be extinguished than under normal pressure, thereby making it possible to generate a mixture containing a high concentration of ozone. This is also the case with the oxygen radical. Thus. the amount of ozone in the vacuum chamber can be increased without reducing the vacuum degree in the first vacuum chamber. The amount of oxygen radical generated in the first vacuum chamber depends on the amount of ozone, and therefore a strong cleaning effect can be obtained by generating a greater amount of oxygen radical without reducing the vacuum degree in the first vacuum chamber. Conversely, the vacuum degree can be improved in the case where the same cleaning ability is maintained by generating the same amount of oxygen radical.

The ozone generated is under a reduced pressure, and therefore the ozone concentration can be maintained for a long time. Further, under a reduced pressure, the flow rate increases in inverse proportion to the pressure. Therefore, the time required for ozone to reach the first vacuum chamber from the second chamber is shortened, thereby eliminating the problem of a reduced ozone concentration. In addition, the ozone generated under reduced pressure is less likely to leak out dangerously.

The pressure in the second vacuum chamber is maintained higher than the pressure in the first vacuum chamber. Specifically, conditions suitable for ozone generation are desirably selected.

In the case where the pressure in the second vacuum chamber is reduced by a second vacuum pump, a flow rate regulating valve for regulating the amount of the ozone and oxygen radical supplied to the first vacuum chamber from the second vacuum chamber is interposed between the second vacuum chamber and the first vacuum chamber thereby to control the introduction of ozone into the first vacuum chamber.

Alternatively, it is possible to connect the second vacuum chamber and the first vacuum chamber with a conduit and reduce the pressure in the second vacuum chamber using the vacuum pump for evacuating the first vacuum chamber. In that case, conditions such as the sectional area of the conduit and the amount of oxygen supplied are appropriately set to secure the desired pressure in the second vacuum chamber.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of the invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagram showing a configuration of an ozone generating unit of the conventional electron beam exposure apparatus in which ozone is introduced to at least a portion of a vacuum chamber during exposure; Fig. 2 is a diagram showing a configuration of an electron beam exposure apparatus according to a first embodiment of the invention; Fig. 3 is a diagram showing a configuration of an ozone generating unit according to the first embodiment; Figs. 4A and 4B are diagrams showing the difference of the ozone amount measurement between the prior art and - 9 the first embodiment; and Fig. 5 is a diagram showing a configuration of an electron beam exposure apparatus according to a second embodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig. 2 is a diagram showing a general configuration of an electron beam exposure apparatus according to a first embodiment of the invention. The electron beam exposure apparatus according to the first embodiment includes an improvement in the ozone generating unit of the electron beam exposure apparatus disclosed in Kokai No. 9-259811 described above. The other parts of the configuration are the same as the corresponding parts of the apparatus disclosed in Kokai No. 9259811.

First, a general configuration of the electron beam exposure apparatus according to the first embodiment will be briefly explained with reference to Fig. 2.

The electron beam exposure apparatus under consideration comprises a column 10 including a chamber 1 enclosing an electron gun 14, a chamber 2 enclosing a lens 36 for alignment and a first slit and a chamber 3 enclosing a deflector 5, a second slit or mask 20, a deflector 6, a round aperture 27 for a stop, a projection lens and a deflector 7, and a main chamber 4 enclosing a wafer W. The chamber 3 is f urther segmented into three chambers 3a, 3b, 3c. Stages 35a, 35b holding the wafer W and movable in X and Y directions are enclosed in the main chamber 4.

Reference character P2 designates a molecular turbo pump for evacuating the interior of the column, and character P3 a turbo molecular pump primarily for evacuating the interior of the chamber 4 larger in volume than the column. Character P1 designates an ion pump for maintaining a vacuum in the chamber 1 of the electron gun 14. The ion pump has an ability to maintain the vacuum of a certain degree to which the chamber 1 is evacuated by the turbo molecular pump P2. The ion pump, which is maintains a vacuum by ionizing a metal material such as titanium and adsorbing the gas, operates on the wellknown principle and, therefore, will not be explained.

The principle of exposure of the electron beam exposure apparatus is also widely known and will not be explained below. Instead, an explanation will be given about the introduction of ozone into the chambers.

In the electron beam exposure apparatus according to the first embodiment, ozone is introduced into the chambers during exposure. The electron beams bombard the ozone thus introduced, so that the ozone is separated into oxygen and active oxygen (oxygen radical). The oxygen radical reacts with the contamination, which about to attach or accumulate on the surface of the parts, and the contamination is evaporated as carbon monoxide or carbon dioxide and discharged by the vacuum pump. As a result, the beam drift described above is prevented.

Reference numeral 8 designates an ozone generating unit which is different from that of the apparatus disclosed in Kokai No. 9-259811. The mixture (gas) containing ozone generated in the ozone generating unit 8 is introduced into the chamber through a valve 9 adapted to open and close and mass flow sensors MFS1, MFS2, MFS3. The mixture from the MFS2 is supplied to the chamber 2 through the inlet 28, while the mixture from the MFS3 is supplied to the chamber 3 f rom the inlet 2 9. The cathode of the electron gun 14 is not when generating the electron beam, and is oxidized if supplied with ozone or oxygen. The chamber 1 encasing the electron gun 14, therefore, is isolated from the other chambers 2, 3, 4 in terms of vacuum by an orif ice OR1 arranged in the aperture apl. Also, a valve B1 is interposed between the turbo molecular pump P2 and the chamber 1 and is opened when a vacuum is produced. When a predetermined high degree of vacuum is reached, the valve Bl is closed to maintain a high vacuum in the chamber 1 by the ion pump is 11 - Pl. As a result, ozone is blocked from entering the chamber 1. The interior of the chamber 1 is maintained at higher vacuum than the interior of the other chambers 2, 3, 4.

The electron beam has a larger charge amount at the upper portion nearer to the electron gun where the oxygen radical is liable to be generated, while the problem of contamination is more serious in the'lower portion nearer to the wafer W. For this reason, ozone is increased in amount by reducing the vacuum degree in the lower portion. Specifically, ozone is supplied through different flow sensors MFS2, MFS3 into the chamber 2 and the lower chamber 3 thereby to reduce the flow rate in the flow sensor MFS2. Further, a second orifice OR2 is interposed between the chamber 2 and the chamber 3, and the ozone movement between the chambers 2 and 3 is limited by reducing the aperture ap2 of the orifice OR2. By reducing the opening degree of the valve B2, the interior of the chamber 2 is maintained in half vacuum, while the interior of the chambers 3 and 4 are kept in low vacuum. Specifically, the chamber 1 is kept at 1 x 10-4 to 1 x 10-3 Pa, the chamber 2 at 1 X 10-3 to 5 X 10-3 Pa and the chambers 3, 4 at 5 x 103 to 1 X 10-2 Pa.

Helium gas He is introduced into the mixture containing ozone being supplied to the valve 9 from the ozone generating unit 8. This is in order to remove the contamination attached to the hidden parts as the result of scattering the electron beam in a range not posing any exposure problem.

Fig. 3 is a diagram showing a configuration of the ozone generating unit 8 according to the first embodiment. As shown in Fig. 3, the ozone generating unit 8 includes an electrode 64 on the inside of a cylindrical case 62 and an rod-like electrode 63 held by insulating members 66, 67 at the center of the case 62. The member 67 is formed with a hole communicating with the right side thereof, and the interior of the case 62 is communicates with a conduit 71 connected to the valve 9 on the one hand and to the vacuum pump 68 on the other hand. The interior of the case 62 and the interior of the conduit 71 are evacuated (reduced in pressure) by the vacuum pump 68 to a pressure which is lower than the atmospheric pressure but higher than the pressure in the chamber 3. The vacuum pump 68 is connected to an ozone processing unit 69 whereby the ozone- contained in the gas discharged from the vacuum pump 68 is restored to oxygen and released into the atmosphere. The conduit 71 is connected to a helium gas cylinder 70 through the mass flow sensor MFS5, so that the mixture containing ozone is mixed further with the helium gas He and supplied to the valve 9. The f low rate in the valve 9 is variable. As described above, the interior of the case 62 and the interior of the conduit 71 are maintained at a higher pressure than the chamber 3. Thus, the mixture in the conduit 71 flows into the chamber 3 at a flow rate adjustable by the valve 9.

At the forward end of the case 62, a nozzle is connected to the mass flow sensor MFS4 through which the oxygen is supplied from the oxygen cylinder 61. A highfrequency signal of high voltage is applied between the electrodes 63 and 64 from an oscillator 65 thereby to cause discharge between the electrodes 63 and 64. The oxygen thus supplied is ozonized while passing between the electrodes 63 and 64. As described above, in the case 62 and the conduit 71, pressure is reduced by the vacuum pump 68 and therefore the ozone of high concentration is generated. This high concentration is maintained for a long time. This mixture contains also the oxygen radical as described above. The mixture containing the highconcentration ozone and the helium gas is introduced into the chambers 2 and 3 of Fig. 2 through the valves 9, the mass flow sensors MFS1 and MFS2 or MFS3.

The concentration of the ozone introduced into the 13 - chamber 3 was measured with a mass spectrometer when the invention was applied and when the invention was not applied and the result thereof is shown in Figs. 4A, 4B. The ozone is decomposed while being measured in the mass spectrometer, and therefore, the mass spectrometry is not considered a recommendable method but is employed for lack of a better method. Fig. 4A shows the amounts of oxygen, ozone and oxygen radical in the case where ozone is not introduced and in the case where ozone generated by the conventional method shown in Fig. 1 is introduced. Numeral 32 designates the oxygen whose molecular weight is 32, numeral 48 the ozone whose molecular weight is 48, and numeral 16 the oxygen radical whose molecular weight is 16. Fig. 4B shows the amounts of oxygen, ozone and oxygen radical with no ozone introduced and with ozone introduced according to the first embodiment. In the case where no ozone is introduced, the same result is obtained as in the prior art and its value is less than the detectable limit. As compared with the conventional method of generating and introducing ozone in which the amounts of ozone as well as oxygen and oxygen radical are increased, the ozone amount is increased about five times according to this embodiment. As described above, in spite of the fact that the measurement by the method using the mass spectrometer is not sufficiently accurate, it is certain that the amount of ozone has increased according to the invention.

Fig. 5 is a diagram showing a configuration of the electron beam exposure apparatus according to a second embodiment of the invention. The configuration of a right column 10, chambers 1 to 4, vacuum pumps P1 to P3 and orifices OR1, OR2 is the same as that of the first embodiment. The configuration of the ozone generating unit is also the same as that of the first embodiment except that DC power is applied from a high-voltage source 81 between the electrodes 63 and 64 to cause discharge instead of using the high-frequency signal 14 - source 65. A conduit 82 connected to a case 62 communicates with the chamber 3 through an inlet 29. AS the chamber is evacuated, therefore, the internal pressure of the conduit 82 and the case 62 is also reduced. The value is assumed by the pressure in the case 62 when the interior of the chamber 3 is vacuumized to 5 X 10-1 to 1 X 10-2 Pa depends on the sectional area and length of the conduit 82 and the amount of oxygen supplied. By setting these parameters appropriately, therefore, the desired pressure in the case 62 can be obtained.

It will be understood from the foregoing description that, according to this invention, there is provided a charged particle beam exposure apparatus, using an electron beam or the like, in which the contamination on the surface of the parts can be cleaned by introducing ozone of high concentration into at least a portion of a vacuum chamber with a small amount of oxygen consumption during exposure, thereby making it possible to alleviate the danger of ozone leaking out into the atmosphere.

- is -

Claims

1. A charged particle beam exposure method for exposing a pattern on a sample by a charged particle beam with low-pressure ozone introduced into at least a portion of a vacuum chamber, comprising the step of generating said ozone under a pressure lower than the atmospheric pressure.

2.

comprising:

of said vacuum chamber; A charged particle beam exposure apparatus a vacuum chamber; a vacuum pump for evacuating the interior a charged particle beam optical system for generating a charged particle beam in said vacuum chamber and exposing the desired pattern on a sample by said charged particle beam; and an ozone supply mechanism for introducing low-pressure ozone into at least a portion of the interior of said vacuum chamber during the pattern exposure on said sample in said charg 1 ed particle beam optical system; wherein said ozone supply mechanism includes a second vacuum chamber the. interior of which is lower in pressure than the atmosphere, and an ozonizer for ozonizing at least a portion of the oxygen supplied from a supply port in said second vacuum chamber; and wherein the ozone generated in said low pressure second vacuum chamber is supplied to at least a portion of the interior of said first vacuum chamber.

3. A charged particle beam exposure apparatus according to claim 2, wherein said ozone supply mechanism includes: a second vacuum pump for reducing the vacuum degree in said second vacuum chamber to below the vacuum degree in said first vacuum chamber, and a flow rate regulation valve interposed between said second vacuum chamber and said first vacuum chamber for regulating the amount of ozone supplied to said first vacuum chamber from said second vacuum chamber.

4. A charged particle beam exposure apparatus according to claim 2, further comprising a conduit for connecting said second vacuum chamber and said first vacuum chamber to each other, wherein said second vaicuum chamber is reduced in pressure by said vacuum pump.