EP1549920A2 - Irradiation device for testing objects coated with light-sensitive paint - Google Patents

Abstract

The invention concerns an irradiation device for testing objects coated with light-sensitive paint, comprising a EUV radiation source, an optical system for filtering the radiation of the EUV radiation source, a chamber for receiving the object, as well as systems for intersecting the trajectory of the rays on the object. The invention also concerns a method for operating such a device. The invention aims at obtaining as quickly as possible an illumination at least partly simultaneous of several irradiation fields, with different doses, by using an inexpensive laboratory radiation source without resorting to complex optical systems. Therefor, the invention provides a device comprising a simplified and compact optical system, with closable diaphragm apertures located in front of the object to be irradiated and at least one control sensor placed on the trajectory of the rays and enabling the radiation dose to be measured.

Description

Device for test irradiation of objects coated with photosensitive paints

The invention relates to a device for test irradiation of objects coated with photosensitive paints with an EUV radiation source, an optical system for filtering the radiation from the EUV radiation source, a chamber for receiving the object and means for interrupting the beam path onto the object. The invention also relates to an operating method for such a device.

In semiconductor technology, lithography is a method for transferring circuit patterns of microelectronic components and integrated circuits to a silicon semiconductor wafer, the afer. For this purpose, a mask is first produced which contains the pattern in the form of transparency differences for the rays with which it is transferred to the wafer. The wafer surface is coated with a radiation-sensitive photoresist and exposed through the mask. Semiconductor structures are transferred to the photoresist using a so-called lithography scanner. In the subsequent development, depending on whether it is a positive or negative varnish, the exposed or the unexposed photoresist is detached and the wafer surface is exposed at these points.

The production of modern semiconductor elements, such as memory chips and CPUs, requires a resolution due to the decreasing structure size of the semiconductors, which necessitates the use of extremely short-wave radiation of approximately 13 nm with a quantum energy of approximately 92 eV (EUV radiation). The previously used radiation wavelengths of 248 nm (UV radiation), 193 nm (DUV radiation) or 157 nm (VUV radiation) are no longer sufficient to produce the structures that are becoming smaller. However, with decreasing structure size and wavelength, the requirements for the set varnishes, the so-called resist material, both in terms of sensitivity and line roughness.

The changed requirements for the coatings require an adaptation of their test systems, which are used before the series production of the wafers to determine the coating properties under different irradiation.

EUV radiation is extremely strongly absorbed by matter. It is therefore necessary that the EUV radiation is conducted under ultra high vacuum conditions. The source of the EUV radiation is a thermally emitting plasma. In contrast to the lasers previously used, plasma emits very broadband, so that in addition to the desired EUV radiation, DUV, VUV and UV radiation is also produced. It is therefore necessary to keep this radiation away from the paints with spectral filters.

A very stable EUV radiation source for researching EUV litography technology is the so-called EUV

Beam tubes on synchrotron storage rings that emit monochromatized EUV radiation. EUV radiation sources of this type emit very short radiation pulses (<1 ns) with repetition frequencies of a few MHz, so that these EUV sources are often referred to as quasi-cw sources. On EUV beam tubes on synchrotron storage rings, individual fields were sequentially irradiated with different radiation doses to test the varnish applied to plates in order to determine the influence of the radiation dose on the varnish. In addition, several fields coated with lacquer have already been exposed simultaneously on synchrotron storage rings, with a rapidly rotating diaphragm wheel arranged in front of the lacquer layer taking on the function of a gray wedge. The aperture openings arranged radially on the wheel are of different sizes, so that the individual fields are exposed to the radiation for different lengths during each revolution. reproducible Radiation conditions in the individual fields of the object are only possible with the aperture wheel because the EUV radiation source behaves quasi stationary due to the high repetition frequency and radiates very stably.

Finally, radiation tests on paints have already been carried out with low-power laboratory radiation sources for EUV radiation, only one single field on the object being irradiated. EUV laboratory radiation sources generate a dense and hot (> 200,000 ° C) plasma and emit the EUV radiation only in very short pulses (typically 100 ns) with very low repetition rates (typically 10 - 1000 Hz).

Based on this prior art, the object of the invention is to provide a device for test irradiation of objects coated with photosensitive paints, which, using an inexpensive radiation source, enables at least partially simultaneous irradiation of several radiation fields on the object with different doses in the shortest possible time , does not require complex and therefore costly optics in the beam path of the EUV radiation and in which a degradation of the optical elements in the beam path due to EUV radiation has no influence on the test result achieved.

This object is achieved in a device of the type mentioned in the introduction in that

- The EUV radiation source is a laboratory source for EUV radiation, the optical system at least one filter for suppressing unwanted spectral components of the radiation, in particular VIS, UV, DUV, VUV radiation, and at least one mirror for spectral filtering of the "in-band" - EUV area, the means for interrupting the beam path comprise a plurality of closable diaphragm openings, which enable the irradiation fields behind the diaphragm openings, radiation fields located on the object, to be timed and the at least one monitor detector is arranged in the direction of the beam path behind the optical system, which during the radiation dose of radiation.

The laboratory source for EUV radiation is, for example, a plasma-based low power source, e.g. an EUV lamp with a power of 100 W and a pulse frequency of 50 Hz according to the HCT (Hollow Cathode Triggered) principle. The laboratory source reliably provides the required EUV radiation over a long operating period.

The plasma from the laboratory source emits very broadband radiation, which in addition to the desired EUV radiation also contains DUV, VUV, UV and VIS radiation. In order to suppress these undesired spectral components of the radiation, the optical system preferably has a spectral filter. The filter can, for example, consist of a thin metal foil (e.g. a 150 nm thick zirconium foil on a support grid). The filter is preferably located at the outlet of the laboratory source. With this arrangement, the filter prevents contaminants from the laboratory source from entering the receiving chamber for the object to be irradiated and contaminating parts located there.

The optical system has the further task of ensuring that the radiation is carried out only with the "in-band" EUV radiation with a wavelength of 13.5 nm. A multilayer mirror is particularly suitable for filtering.

The components of the optical system ensure that practically only the desired EUV radiation hits the object. The compact optical system of the device according to the invention, in particular with only one filter and one mirror, enables a very short distance from the EUV laboratory source to the object to be irradiated with homogeneous irradiation of all irradiation fields. Due to the small distance, a large solid angle of the thermal emission of the plasma can also be used without an expensive condenser.

The diaphragm openings which can be closed according to the invention permit at least partially simultaneous irradiation of the radiation fields defined on the object through the diaphragm openings. All radiation fields are initially irradiated in parallel until individual aperture openings after reaching the target dose for the assigned

Radiation field are closed. This saves a considerable amount of time when testing the influence of the radiation dose on a photoresist.

The diaphragm openings are preferably arranged in a flat plate and have a diameter of 5 mm, for example. With 20 such apertures, the test duration for a photoresist can be reduced almost by a factor of 20 compared to individual irradiations with different radiation doses.

After a calibration has been carried out, the monitor detectors arranged behind the optical system allow an exact measurement of the radiation dose of the individual radiation fields. For example, several photodiodes (Schottky type) can be used as monitor detectors. The signals supplied by the diodes are preferably averaged in order to improve the measurement accuracy. In that the radiation dose is recorded continuously during the radiation, the radiation of the radiation fields can be carried out with precisely definable target values for the radiation dose. The monitor detectors are preferably arranged between the optical system and the closable openings; they are conveniently located as close as possible to the object to be irradiated. This arrangement of the monitor detectors makes the device insensitive to the degradation of the optical system.

As already mentioned at the beginning, the entire beam path must be guided to the object under vacuum conditions. The chamber for receiving the object is therefore designed and evacuated, for example, to a negative pressure of 10 ^{~ 6} mbar. It is separated from the discharge chamber of the laboratory source by a window with an opening for the passage of the radiation, the window in particular having a filter of the optical system, for example in the form of a metallic foil. This prevents contamination of the receiving chamber. The receiving chamber preferably has its own pump system and is separated from the laboratory source and preferably also the area for receiving the optical system when handling the object to be irradiated by means of a slide valve.

In order to achieve the most homogeneous radiation possible in the individual radiation fields, all are

Diaphragm openings arranged in one plane and the radiation fields generated by each diaphragm opening on the object do not overlap. The radiation fields are preferably arranged parallel to the plane of the diaphragm openings.

The object coated with photoresist is in particular a silicon wafer, for example a 6 inch wafer with a thickness of 650 μm and with 20 radiation fields defined by the aperture openings. There is a holder in the receiving chamber which receives the wafer in such a way that that the EUV radiation hits its photoresist coating.

In an expedient embodiment of the invention, the laboratory source emits radiation pulses of a duration of less than 1 μs, in particular 100 ns, with a repetition rate between 1 and 10,000 Hz, in particular 1-5000 Hz. The radiation from the laboratory source comes from a thermally emitting plasma, in particular from a laser-generated one or discharge-generated plasma or from an electron beam.

A thin metal foil, in particular a zirconium foil with a thickness of less than 200 nm but more than 100 nm is preferably arranged in the beam path as a filter for suppressing undesirable visible to VUV radiation. The film transmits up to 50% of the desired EUV radiation, while the unwanted radiation is suppressed by a factor> 1000.

Each mirror for spectral filtering of the "in-band" EUV range is preferably designed as a multilayer mirror, it being possible for the mirror to be designed as a plane mirror or as a curved mirror. The multilayer mirrors reflect up to 70% of the incident radiation in a narrow spectral band in the EUV range, while radiation which is not in this narrow band is almost completely absorbed by the multilayer mirror.

The diaphragm openings are preferably closed by means of a flat slide, which is in a to the plane of

Aperture openings are arranged parallel to the plane and has a contour that enables a successive opening or closing of the aperture openings. The contour is in particular stair-shaped, so that the diaphragm openings arranged in rows can be opened or closed line by line. The flat slide as a closure for all aperture openings provides with only a mechanical component is a very favorable solution in terms of design and control technology.

Further advantages and effects of the invention and its mode of operation result from the following description of an embodiment with reference to the figures.

Show it:

1 shows the spectrum of the radiation generated by the EUV radiation source. FIG. 2 shows a basic illustration of the invention

Device for test irradiation of objects coated with photosensitive lacquers, FIG. 3, one arranged in the device according to FIG

Diaphragm system with a flat slide valve Figure 4 shows an irradiation function with a variation of

50% with different exponents and FIG. 5 shows the film thickness of a coating application as a function of the dose of test radiation

The device for EUV test radiation is used to apply a photoresist (resist) for lithography in the area of EUV radiation. H. at a wavelength of 13.5 nm, with 20 different radiation doses in one operation. The removal of the photoresist after development and the sharpness of the structures depicted should be determined as a function of the dose.

The device for EUV test radiation consists of an EUV laboratory lamp (1) which generates radiation with a spectrum according to FIG. 1. The likewise horizontally oriented beam path (4) leaves the EUV laboratory lamp (1) via a horizontally oriented beam pipe (2) with an outlet opening (3). A jet pipe slide unit (5) is arranged at the outlet opening (3). The jet tube slide has a passage into which a 150 nm thick zirconium foil is inserted, which can be moved into the beam path (4) by means of the slide. The slide movable transversely to the axis of the beam path (4) allows the zirconium foil to be completely moved out of the cross section of the jet pipe (2), so that the outlet opening (3) is completely closed by the jet pipe slide, which is otherwise made of metal. A turbomolecular pump (6) is also arranged on the jet pipe (2) and generates a vacuum of approximately 10 ^"3 mbar in the EUV lamp (1) while maintaining a xenon atmosphere.

A hollow cylindrical angle piece (7), which receives a deflecting mirror (8), adjoins the jet tube slide unit (5). The deflecting mirror (8) is arranged in the interior of the angle piece in the outer region of the bend in such a way that the horizontally incident beam path (4) is deflected by 90 ° into a wafer chamber (9), designated overall by (9). A mirror recipient (11) carries and fixes the deflecting mirror (8). It is pointed out that the constructively favorable angle of incidence of the EUV radiation of 45 ° shown in the exemplary embodiment can be varied without further ado.

The angle chamber (7) is followed by the wafer chamber (9), which consists of a hollow cylindrical jet tube (12) and a receiving space (13) for the wafer coated with lacquer. The beam path (4) spreads from the deflecting mirror (8) through the beam pipe (12) in the direction of a diaphragm system (15). The surface of the wafer is oriented in the direction of the diaphragm system (15), so that the EUV radiation passing through the diaphragm system falls on the lacquer coating of the wafer. The closure of the

Aperture openings of the aperture system (15) are driven by a stepper motor (14). The side of the receiving space (13) a further turbo-molecular pump (17) is arranged, which kelstück mbar during the exposure for the maintenance of a pressure of 10 ^"6 in the winter (7) and the wafer chamber (9) provides.

In the direction of propagation of the beam path (4) of the EUV radiation to the side in the aperture system (15) there are three photodiodes (18) which can be seen in FIG. 3 and which record the radiation energy of the individual radiation pulses of the EUV lamp (1), the radiation energy being proportional to that charge generated in the photodiodes (18). The photodiodes are arranged as close as possible to the diaphragm openings in the diaphragm system, but in such a way that they are not covered by the motor-driven closure.

Finally, the device for EUV test radiation has a further slide (19), which is arranged between the angle piece (7) and the beam pipe (12) of the wafer chamber (9). If the slide (19) is closed, the wafer chamber is

(9) completely sealed off from the EUV lamp (1) and the interior of the elbow (7).

FIG. 3 illustrates the structure of the diaphragm system, designated overall by (15), which has a shadow mask (21) with 5 rows, each with 4 diaphragm openings (22). The EUV radiation passing through each aperture (22) defines a delimited radiation field on the lacquer layer (16) of the wafer. The distance between the wafer and the aperture system (15) and the distance between the aperture openings (22) is designed in such a way that the radiation fields do not overlap. As a result, the aperture system (15) produces twenty delimited radiation fields of approximately 5 mm in diameter on the surface of the wafer coated with photoresist.

A flat slide (24), which has a step-shaped contour (23) on the end face, is located on the side next to the shadow mask (21). The flat slide valve (24) is connected on the side opposite the contour (23) to the stepping motor (14) shown in FIG. By moving the flat slide

(24) in the direction of arrow (25), the diaphragm openings (22) can be mechanically closed line by line. The consequence of this is that the radiation fields defined by the individual aperture openings (22) are given individual radiation times.

During the irradiation of the coated wafer, the

Slide the slide tube slide unit (5) so that the beam path passes through the zirconium filter. The filter has two functions:

1. Retention of radiation with wavelengths greater than 20 nm. At wavelengths greater than 20 nm, the permeability of the zirconium filter is less than 10%. 2. Separation of the xenon atmosphere in the EUV lamp (1) from the area formed by the elbow (7) and the wafer chamber (9) into which no xenon gas should get. The zirconium filter is sufficiently stable to withstand the pressure difference between the EUV lamp (1) and the specified area.

The deflecting mirror (8) is a multilayer mirror with, for example, 40 layers of a silicon substrate with a period thickness of approximately 10 nm. This mirror reflects a wavelength of 13.5 +/- 0.2 nm at an angle of 45 ° into the beam tube (12) of the wafer chamber (9).

After the irradiation of the photoresist on the wafer has been completed, the slide (19) between the angle piece (7) and the wafer chamber is closed. As a result, the vacuum in the EUV lamp (1) and the angle piece (7) is maintained when the wafer chamber (9) is ventilated in order to open it, for example, to remove the irradiated wafer. The slide (19) not only enables shorter evacuation times for the wafer chamber (9) during the wafer handling, but also an effective protection of the sensitive optical system, which is formed by the zirconium foil in the beam tube slide unit (5) and the deflecting mirror (8) in the elbow.

The photodiodes (18) arranged in the beam mask (4) in the shadow mask (21) measure the radiation energy of the EUV radiation pulses by generating a charge proportional to the radiation energy in the photodiodes. The charge generated by the individual pulses is added up electronically and queried cyclically by a controller (not shown in the figure). If the query shows that a certain radiation dose (target value) has been reached, a control command for the stepper motor (14) is triggered, which moves the flat slide valve (24) in the direction of the arrow (25) in order to line by line the next aperture opening (22) to close. The setpoints, which must be reached depending on a target dose specified by the user (definition: a dose assumed by the user of the test system for the lacquer to be examined to be optimal) until the next aperture (22) is closed, form the bases of an irradiation function. The individual setpoints are calculated using the following formula:

If s ≠ 10 then:

RF \ RF s (F, Exp, Tar, Var) = Tar (\ + VB RF 10 ^Exp ) with VB = and RF = F - 10

100 otherwise: s (F, Exp, Tar, Var) = Tar

The following applies

The function value s is the setpoint that must be reached before the next aperture is closed. The parameter F stands for the currently closed field and lies in the value range from 1 to 20. Exp The parameter Exp is the exponent set by the user and has the values from 1 to 5.

Tar The Tar parameter is the target dose set by the user. Var The Var parameter is the variation range set by the user in percent in the range from 1 to 100.

For Tar: = 1.0 and Var: = 50, the characteristic curves shown in Fig. 4 result depending on the exponent Exp: = 1 to 5 for the setpoints s. It becomes clear that as the exponent Exp increases, the base density increases by the target dose Tar.

Irradiation with EUV radiation causes the lacquer film to be removed from the wafer after development. The relationship between dose and erosion after development is shown in the curve in Fig. 5 using the example of a specific paint. From a certain dose, the value for the remaining thickness of the paint film drops sharply. The minimum dose required for the irradiation of this lacquer (in the exemplary embodiment approximately 6 mJ / cm ² ) can be read off the x-axis. In this way, the EUV radiation sensitivity of a photoresist for wafers can be determined in one operation.

LIST OF REFERENCE NUMBERS

Claims

Claims: 1. Device for test irradiation of objects coated with photosensitive paints with an EUV radiation source, an optical system for filtering the Radiation from the EUV radiation source, a chamber for receiving the object and means for interrupting the beam path onto the object, characterized in that - the EUV radiation source is a laboratory source (1) for EUV radiation, the optical system at least one filter for suppression unwanted spectral components of the radiation and at least one mirror (8) for spectral filtering of the "in-band" EUV range, the means for interrupting the beam path comprise a plurality of closable diaphragm openings (22), which control the radiation behind the diaphragm openings allow radiation fields located on the object and the at least one monitor detector (18) is arranged in the direction of the beam path (4) behind the optical system, which detects the radiation dose during the radiation. 2. Device according to claim 1, characterized in that all diaphragm openings (22) are arranged in one plane (21) and the radiation fields generated by each diaphragm opening (22) on the object (16) do not overlap. 3. Device according to claim 1 or 2, characterized in that the object (16) is a wafer coated with photoresist and the chamber for receiving the object (9) has a holder for the wafer. 4. Device according to one of claims 1 to 3, characterized in that the radiation from the laboratory source (1) comes from a thermally emitting plasma. 5. The device and method according to one of claims 1 to 4, characterized in that a thin metal foil, in particular a zirconium foil with a thickness of less than 200 nm is arranged in the beam path (4) as a filter for suppressing undesirable visible to VUV radiation. 6. The device and method according to one of claims 1 to 5, characterized in that at least one mirror (8) for the spectral filtering of the "in-band" -EUV range is designed as a multilayer mirror. 7. Device according to one of claims 1-6, characterized in that each monitor detector (18) is at a distance from the object to be irradiated (16) which is less than half the distance between the laboratory source (1) and the object to be irradiated. 8. Device according to one of claims 1-7, characterized in that each aperture (22) is assigned a separate locking mechanism. 9. Device according to one of claims 2-7, characterized in that the diaphragm openings (22) can be closed with at least one flat slide (24). 10. The device according to claim 9, characterized in that the flat slide (24) is arranged displaceably in a plane parallel to the plane of the diaphragm openings (22) and has a contour (23) which a successive opening or closing of the diaphragm openings (22) allows. 11. The device according to claim 10, characterized in that the flat slide (23) has a stair-shaped contour (23) which enables a row-by-row opening or closing of the aperture openings (22) arranged in rows. 12. The method for operating a device according to any one of claims 1-11, characterized in that each aperture (22) is closed at the time when it is determined with the monitor detector (s) (18) that the radiation dose in which the Irradiation field associated with the aperture (22) corresponds to a desired value. 13. The method according to claim 12, characterized in that the signals of each monitor detector (18) are added up in a control and compared with the setpoints stored there for each aperture (22) and the control when the setpoint for a radiation field is reached Activates the closure (24) of the drive (14) assigned to the respective aperture. 14. The method according to claim 12, characterized in that the setpoints are generated automatically by the controller. 15. The method according to claim 12, characterized in that the setpoints are entered into the control by an operator. 16. The method according to claim 12, characterized in that the setpoints are generated by the controller based on an input of parameters by an operator. 17. The method according to claim 15, characterized in that the number of parameters to be entered by the operator is less than or equal to the number of radiation fields and at least one parameter for characterizing a typical dose for the photoresist to be tested, a parameter for determining the variation range in percent and a parameter for determining the dose curve are entered, the variation range being the range between the highest and lowest value based on the typical dose and the dose curve defines the change in dose between two successively closed radiation fields.