DE102016206210A1 - Projection exposure system with sensor unit for particle detection - Google Patents

Abstract

The invention relates to a projection exposure apparatus (100) for semiconductor lithography with a device for detecting particles in the system. The device contains a sensor unit (2) for receiving particles and an evaluation unit (3) for detecting the particles received by the sensor unit (2). The evaluation unit (3) is connected to the sensor unit (2) during operation of the projection exposure apparatus (100) and is suitable for determining the arrival or presence of particles from an electrical state variable.

Description

The invention relates to a projection exposure apparatus for semiconductor lithography, in particular an EUV projection exposure apparatus, by means of which structures of phase masks, so-called reticles, on semiconductor wafers for the production of semiconductor components are mapped in a known manner. To illuminate the reticle, a plasma using tin droplets is used in such systems. This tin particles regularly get to components of the system and thereby affect their function. For example, it can lead to tin deposits on the collector mirror of the light source or on optical elements of the lighting system. Such deposits often lead to damage to the coatings of the components as well as to a reduction in reflectivity. Likewise, especially in systems in which no pellicle, so no film-like particle barrier is used, the risk that particles reach the reticle, resulting in image defects, but also to damage and in extreme cases, the failure of this relatively complex to be manufactured component can.

Beyond contamination with tin particles, there is a risk that particulates will be generated by abrasion, especially in the environment of mechanically actuated components, and deposit on the optical components in the environment, which may result in similar problems as described above practically throughout the projection exposure apparatus.

A detection of particles is currently carried out only by tracking the use of samples or test wafers, which are used in the system at a suitable location and removed again for evaluation after a certain period of operation. A rapid response to the increased occurrence of damaging particles, such as in the case of a mechanical bearing that begins to "eat" is thus not possible in the prior art.

The object of the present invention is to provide possibilities for the rapid detection of the occurrence of contaminating particles in a projection exposure apparatus for semiconductor lithography.

This object is achieved by a device having the features of independent claim 1. The subclaims relate to advantageous developments and variants of the invention.

A projection exposure apparatus according to the invention for semiconductor lithography, for example an EUV projection exposure apparatus, comprises a device for detecting particles in the system. The device contains a sensor unit for receiving particles and an evaluation unit for detecting the particles received by the sensor unit. The evaluation unit is connected to the sensor unit during operation of the projection exposure apparatus and is suitable for determining the arrival or presence of particles from an electrical state variable.

Due to the fact that the evaluation unit is connected to the sensor unit during the operation of the projection exposure apparatus, monitoring of the particle volume is achieved in real time, which was previously not possible according to the prior art. Thus, in particular in cases in which the particle volume exceeds a predetermined critical threshold, the system can be switched off to protect against unacceptable damage to components. In addition, the real-time monitoring referred to allows conclusions to be drawn from the coincidence of system events with increased particle volume on upcoming problems. If, for example, the actuation of a mechanical actuator correlates with an increased emission of particles, it may be concluded that an associated mechanical bearing has increased friction coefficients and abrasion occurs. The bearing in question can then be replaced before it reaches a critical state, that is, fails or represents a danger to the function of the adjacent optical components by further enhancing the particle emission.

The sensor unit shows a receiving area on which particles can accumulate. This receiving area can be positioned in particular in the facility where the increased emergence of particles is problematic, for example in the area of the reticle, the intermediate focus of the illumination system or on a frame of a mirror. However, the receiving area does not necessarily have to be positioned at the places of interest mentioned above. It may also be sufficient for certain applications, for example, to maintain the required vacuum to arrange the Absaugmündungen of vacuum pumps in the areas of interest and detached to mount the receiving area of the Absaugmündungen in the respective suction. In this case, there may be advantages in terms of the accessibility of the sensor unit, for example for maintenance or cleaning purposes.

The sensor unit may, for example, be arranged in the region of a field facet mirror in an illumination system, in particular on that side of the field facet mirror which faces the incident electromagnetic radiation used for imaging in the system, the so-called useful radiation. It is advantageous if the sensor unit is indeed in the range of the EUV illumination, but not in the useful range. This area is typically referred to as overbeam area. The useful range is understood to be that region on the facet mirror which is achieved by electromagnetic radiation involved in the imaging. As a rule, however, the illuminated area on the facet mirror is larger than the useful area. This arrangement of the sensor unit has the advantage that the sensor unit provides realistic information about the particle loading of the field facet mirror. In addition, the sensor unit can be cleaned in such an arrangement, if necessary, by means of cleaning heads already present for cleaning the Feldfacettenspiegels anyway. Furthermore, in this variant - if necessary - an exchange of the sensor unit by the adjacently arranged in the housing of the lighting system service opening of the lighting system can be made. Advantageous distances of the sensor unit from the surface of the mirror facets of the field facet mirror are in the range of 5-500 mm, preferably in the range of 5-100 mm.

Alternatively or additionally, the sensor unit may be arranged on a field facet mirror in a lighting system. For this purpose, in particular free surfaces on the already existing mirror support of the field facet mirror can be used advantageously and there remains the possibility, the previously mentioned above not in real time readable samples - the so-called witness samples - in the usual places for them as additional measures for particle monitoring in System. This variant also shows the advantages already mentioned in the introduction of realistic particle measurement and cleaning by the cleaning heads provided for the field facet mirror.

Another possible arrangement of the sensor unit may be on a pupil facet mirror or G-mirror in a lighting system. The G mirror, which is also commonly referred to as a grazing incidence mirror, is located geometrically in an illumination system of a projection exposure apparatus directly at the transition to the holding device for a reticle to be imaged, the so-called reticle stage. Particles on the reticle are generally extremely critical, since they are imaged on a semiconductor substrate to be exposed, the so-called wafer, 1: 1. Particle protection of the reticles is thus desired. Placing a sensor unit between the G-mirror and the reticle stage, it can also be used as an alarm sensor for a possible contamination of the reticle. The additional use of a valve between the illumination system and the reticle, which closes when triggered by the sensor unit in cooperation with the evaluation when exceeding a critical number of detected particles alarm, represents a useful variant of the invention.

It is also advantageous if the sensor unit is arranged in an area which is achieved during operation of the projection exposure apparatus by the electromagnetic radiation used for the exposure. Also in this case, an arrangement of the sensor unit in the overjet area is advantageous. The general advantage of the placement in the EUV beam path is that the particles from the light source almost exclusively follow the gas flow in the mini-environment, which is almost congruent with the beam path. Thus, a very high coverage can be achieved.

Although most of the particles follow the beam path, this is not the case for everyone. Some particles suffer collision processes that lead to deviating particle trajectories. For this reason, an arrangement of the sensor unit in a range that is not reached during operation of the projection exposure of the electromagnetic radiation used for exposure, makes sense.

In an advantageous embodiment of the invention, the sensor unit can be arranged on a support structure of a lighting system. In this way, it is comparatively easy to obtain information about the particle distribution within the illumination system, in particular because particles from the light source have an angular distribution predetermined by the intermediate focus shaping when entering the mini-environment of the illumination system formed by the support structure. Taking into account the o. G. Shock processes, there is a significant probability that the particles reach the support structure.

The electrical state variable may in particular be an electrical resistance. Since electrical resistances of circuits are easily measurable, an easily evaluable sensor can be realized in this way.

Alternatively, the electrical state variable may be a capacitance.

For example, a sensor unit may have at least one current path with an interruption element. In that case, in which a particle precipitates in the interruption area, can then easily on the basis of the then existing change of the respective electrical state quantity are determined by the impact of particles on the sensor unit. Thus, for example, in those cases in which a short circuit is produced by the impact of an electrically conductive particle, the particle can be detected by a sharply decreasing electrical resistance in the interruption region.

A particularly effective detection of particles can be achieved in that the interruption region has conductor structures which mesh with one another like a comb and are electrically insulated from one another. In this case, the structures forming the teeth of the combs or the spacing of the teeth may have widths in the range from 60 nm to 1000 nm, in particular from 60 nm to 100 nm. By appropriate dimensioning of the combs, a certain selectivity with regard to the detectable particle size can be achieved.

A spatially resolved detection of particles can be achieved in particular by a plurality of interruption areas being arranged flat on the sensor unit.

By virtue of the fact that the interruption regions are each electrically contacted individually, a simple spatially resolved measurement can take place on the surface of the sensor unit by means of the unique addressing of the interruption regions on the surface of the sensor unit.

Also conceivable is a parallel electrical contacting of the interruption areas.

In a further embodiment of the invention, the interruption region may be covered by an electrically insulating layer. In this case, if a conductive particle, such as a tin particle, does not generate a short circuit in the interruption region, however, at the moment of impact, the electrical properties of the interruption region would nevertheless change, at least for a short time. If a preferably constant bias voltage were applied to such an arrangement, then a small tunnel current would flow, the magnitude of which would also change briefly when the particle strikes. In this way, it becomes possible to measure a plurality of impinging particles with a single interruption area without the interruption area - unlike the case described above - being consumed by the occurrence of an electrical short circuit triggered by the particle. A measurement of the capacitance of the capacitor formed by the last described arrangement would allow a particle detection even when non-conductive particles, depending on the particle size, the dielectric constant of the particles, the electrode geometry or other parameters of the device.

The electrical state variable may in particular also be a signal form of an electrical signal. This variant is used in particular when the sensor unit contains a so-called delay-line detector. Such a detector usually has a closed, meandering conductor which is either applied to a substrate or realized using strained wires. A charged particle impinging on the conductor triggers an electrical pulse in the direction of both conductor ends, on the basis of which the location of the impact can be determined. Also, such a detector can detect a plurality of successive events. Uncharged particles can be detected by applying an electrical pulse to the conductor in conjunction with a transit time measurement. A detailed description of an exemplary delay line detector, which is also known by its inventor under the name "Schmidt Böcking detector", can be found in the European patent application EP 1 124 129 A2 whose content is hereby incorporated in full.

In an advantageous embodiment of the invention, the sensor unit can be designed to be movable. Such a movable sensor unit can be used in particular during exposure pauses for measuring particle concentrations in the beam path of the system. During operation of the system, the sensor unit can be swung out of the beam path.

A cyclical cleaning of the sensor unit in particular without the need for removal or replacement can be achieved by providing the sensor unit with a voltage source, by which a current can be generated, which, due to the heat generated by it, to detach particles deposited on the sensor unit leads. In many cases, it may be sufficient to reach the melting temperature of tin, which is about 231 ° C, so that a tin particle liquefies and thus easier to remove. It is also conceivable to produce temperatures that lead to the vaporization of a tin particle.

In addition, an effective cleaning of a sensor unit can also be achieved in that it is arranged in an area which is reached by an already existing in the system cleaning head. This may be the case in particular when a sensor unit is mounted in the over-beam area already mentioned above.

It is also conceivable to use already developed sensor units after their use in the manner of the known witness samples for the detection of contamination.

In an advantageous embodiment of the invention, at least one valve for at least partially closing off a partial volume of the projection exposure apparatus can be present in relation to a further component of the projection exposure apparatus, wherein the valve can be activated by means of the evaluation unit. In this case, a targeted foreclosure of the other component of the system can be triggered with increased particle volumes. The further component may in particular be a light source, a reticle holder or a wafer holder.

The invention will be explained by way of example with reference to the drawing. It shows:

1 a schematic representation of an EUV projection exposure apparatus with various embodiments of the invention;

2 a variant of the invention;

3 a first embodiment of a sensor unit according to the invention;

4 a further embodiment of a sensor unit according to the invention; and

5 A third embodiment of a sensor unit according to the invention.

1 shows an example of the basic structure of an EUV projection exposure system 100 for microlithography, in which the invention can find application. A in a schematically indicated support structure 101 arranged lighting system 102 the projection exposure system 100 points next to a light source 103 an illumination optics 104 for illuminating an object field 105 in an object plane 106 on. One is illuminated in the object plane 106 arranged reticle 107 that of a schematically represented Retikelhalter 108 is held. A merely schematically illustrated projection optics 109 which are the mirrors 122 . 123 . 124 . 125 . 126 and 127 includes, serves to image the object field 105 in a picture field 110 in an image plane 111 , A structure is shown on the reticle 107 on a photosensitive layer in the area of the image field 110 in the picture plane 111 arranged wafers 112 , by a wafer holder also shown in detail 113 is held. The light source 103 can useful radiation 114 especially in the range between 5 nm and 30 nm.

One from the light source 103 generated useful radiation 114 is by means of one in the light source 103 integrated collector aligned so that they are in the area of a Zwischenfokusebene 115 undergoes an intermediate focus before moving to a field facet mirror 116 meets. After the field facet mirror 116 becomes the useful radiation 114 from a pupil facet mirror 117 reflected. With the aid of the pupil facet mirror 117 and an optical assembly 118 with mirrors 119 . 120 and 121 become field facets of the field facet mirror 116 in the object field 105 displayed.

Well recognizable in the figure, the two are each by means of a holder 1 . 1' on the supporting structure 101 arranged sensor units 2 , Here is the first sensor unit 2 arranged in an area which is in operation of the projection exposure apparatus 100 is not reached by the electromagnetic radiation used for exposure. By not indicated in the figure arrows is indicated that the sensor unit 2 is designed to be movable. By this mobility can be achieved in particular that the sensor unit 2 is moved into areas which during operation of the projection exposure system 100 be passed by the useful radiation. This can be done in particular during exposure pauses, preferably when the light source is activated. During operation of the system, the sensor unit 2 be removed from the field of useful radiation. The second sensor unit 2 in contrast, in the area of the field facet mirror 116 located and is also located in the light path of the useful radiation of the projection exposure system 100 , but preferably as already mentioned in the overexposed area. In this way, the particle load of the field facet mirror 116 by means of the signal line 4 with the sensor unit 2 connected evaluation unit 3 be reliably determined in real time and when a critical particle load occurs emergency measures, such as a shutdown of the light source 103 , be initiated. Alternatively or additionally, at least one of the valves also recognizable in the figure 200 . 201 . 204 or 206 , which via the control lines 202 . 203 . 205 or 207 with the evaluation unit 3 are connected, closed to the interior of the lighting system 102 or the reticle 107 to protect against contamination.

In addition, in the area of the Zwischenfokusbene 115 another on a holder 1'' arranged sensor unit 2 arranged. This positioning of the sensor unit 2 is particularly advantageous because at the designated point the particles in the case of increased particle ejection of the light source 103 enter the lighting system. In this way, an early detection of particles can be guaranteed and also a closing in particular of the valve 200 be initiated.

Also recognizable in the figure are the other two sensor units 2 pointing to the pupil facet mirror 117 or the G-mirror 121 are arranged. In contrast to the field facet mirror 116 arranged sensor unit 2 are these two sensor units 2 but arranged outside of the range reached by the useful radiation. Especially in the case where the on the G-mirror 121 arranged sensor unit 2 detects an increased particle volume, closing, for example, the valve 201 be initiated.

2 shows a variant of the invention, in which sensor units 2 on clear areas between field faceted blocks 5 on a base body 6 a field facet mirror 116.2 are arranged. Omitted in the illustration shown are the signal connections to a in the 2 also not shown evaluation. As already mentioned above, this variant offers the possibility of a particularly space-saving arrangement of the sensor units 2 ,

The following are in the 3 to 5 exemplary embodiments of the sensor unit 2 shown.

In 3 is an example of a possible embodiment of a sensor unit according to the invention 2.3 shown. The sensor unit 2.3 shows a current path with interruption region, the comb-like interlocking conductor structures 7 which is on an insulating substrate 8th arranged and electrically isolated from each other. With the ladder structures 7 connected is formed as an ohmmeter evaluation 3.3 through which an electrical short circuit can be detected.

Such a short circuit is, for example, by the tin particles also indicated in the figure 9 created.

4 shows a variant in which said interruption areas flat on a sensor unit 2.4 are arranged. The respective contact can be done individually or in parallel. In the case of a single contact, a spatially resolved measurement is possible.

If you put the in 3 and 4 While structures shown with an insulating cover layer, so incident particles cause usually no change in resistance of the interruption region more, however, can also be made of the electrical properties of the capacitor thus created a determination of the particle size at the location of the sensor unit.

In 5 is schematically illustrated an embodiment of the invention, wherein by means of a sensor unit 2.5 a delay line detector 10 is realized. A closed, meander-shaped ladder 11 is doing with a schematically indicated evaluation 3.5 connected, by means of which the duration of an electrical pulse in the closed conductor 11 can be determined. In this case, the evaluation unit 3.5 be formed passive or active. A passive evaluation unit registers electrical pulses, which depend on the impact of a charged, indicated in the figure particle 9 originate. An active evaluation unit itself generates electrical pulses and determines from the signal response of the system, ie in particular from the transit time of the pulses in the conductor 11 or the occurrence of reflections o. Ä. The presence or possibly the location of particles 9 on the ladder 11 , By means of an active evaluation unit, in particular, uncharged particles can also be detected.

LIST OF REFERENCE NUMBERS

1, 1 ', 1' '

holder

2, 2.3, 2.4, 2.5

sensor unit

3, 3.3, 3.5

evaluation

4

signal line

5

Field facet block

6

body

7

Comb-like ladder structures

8th

Insulating substrate

9

tin particles

10

Delay Line Detector

11

ladder

100

Projection exposure system

101

supporting structure

102

lighting system

103

light source

104

illumination optics

105

object field

106

object level

107

reticle

108

reticle

109

projection optics

110

field

111

image plane

112

wafer

113

wafer holder

114

effective radiation

115

Between the focal plane

116, 116.2

Field facet mirror

117

Pupil facet mirror

118

module

119-120

mirror

121

G levels

122-127

mirror

200, 201, 204, 206

Valve

202, 203, 205, 207

control line

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• EP 1124129 A2 [0023]

Claims (22)

Projection exposure apparatus ( 100 ) for semiconductor lithography, comprising - a device for detecting particles in the system with - a sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) for receiving particles - an evaluation unit ( 3 . 3.3 . 3.5 ) for the detection of the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) received particles, characterized in that the evaluation unit ( 3 . 3.3 . 3.5 ) during operation of the projection exposure apparatus ( 100 ) with the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) and is adapted to determine the arrival or presence of particles from an electrical state variable. Projection exposure apparatus ( 100 ) according to claim 1, characterized in that it is an EUV projection exposure apparatus ( 100 ). Projection exposure apparatus ( 100 ) according to claim 2, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) in the region of a field facet mirror ( 116 . 116.2 ) in a lighting system ( 102 ) is arranged. Projection exposure apparatus ( 100 ) according to claim 2, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) on a field facet mirror ( 116 . 116.2 ) in a lighting system ( 102 ) is arranged. Projection exposure apparatus ( 100 ) according to claim 2, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) on a G-mirror ( 121 ) in a lighting system ( 102 ) is arranged. Projection exposure apparatus ( 100 ) according to one of the preceding claims, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) is arranged in an area which, during operation of the projection exposure apparatus ( 100 ) is achieved by the electromagnetic radiation used for the exposure. Projection exposure apparatus ( 100 ) according to one of the preceding claims 1-5, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) is arranged in an area which, during operation of the projection exposure apparatus ( 100 ) is not reached by the electromagnetic radiation used for the exposure. Projection exposure apparatus ( 100 ) according to claim 2, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) on a supporting structure ( 101 ) of a lighting system ( 102 ) is arranged. Projection exposure apparatus ( 100 ) according to one of the preceding claims, characterized in that the electrical state variable is an electrical resistance. Projection exposure apparatus ( 100 ) according to one of claims 1 to 8, characterized in that it is the capacity of the electrical state quantity. Projection exposure apparatus ( 100 ) according to claim 9 or 10, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) has at least one current path with an interruption region. Projection exposure apparatus ( 100 ) according to claim 11, characterized in that the interruption area conductor structures ( 7 ), which comb-like engage in each other and are electrically isolated from each other. Projection exposure apparatus ( 100 ) according to claim 11 or 12, characterized in that a plurality of interruption areas flat on the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) is arranged. Projection exposure apparatus ( 100 ) according to claim 13, characterized in that the interruption areas are each electrically contacted individually. Projection exposure apparatus ( 100 ) according to claim 13, characterized in that the interruption areas are electrically contacted in parallel. Projection exposure apparatus ( 100 ) according to one of claims 11, 12 or 13, characterized in that the interruption region is covered by an electrically insulating layer. Projection exposure apparatus ( 100 ) according to one of claims 1 to 16, characterized in that the electrical quantity of state is a signal form of an electrical signal. Projection exposure apparatus ( 100 ) according to claim 17, characterized in that the means of the sensor unit ( 2.5 ) and the evaluation unit ( 3.5 ) a delay line detector ( 10 ) is formed. Projection exposure apparatus ( 100 ) according to one of the preceding claims, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) is designed to be movable. Projection exposure apparatus ( 100 ) according to one of the preceding claims, characterized in that the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) is provided with a voltage source, through which a current can be generated, which for detachment from on the sensor unit ( 2 . 2.3 . 2.4 . 2.5 ) leads deposited particles. Projection exposure apparatus ( 100 ) according to one of the preceding claims, characterized in that at least one valve ( 200 . 201 . 204 . 206 ) for at least partially closing off a partial volume of the projection exposure apparatus ( 100 ) is present in relation to a further component of the projection exposure apparatus, the valve ( 200 . 201 . 204 . 206 ) by means of the evaluation unit ( 3 . 3.3 . 3.5 ) is controllable. Projection exposure apparatus ( 100 ) according to claim 21, characterized in that the further component is a light source ( 103 ), a reticle holder ( 108 ) or a wafer holder ( 113 ).

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