Patent Application
20060105274
This Utility Patent Application claims priority to German Patent Application No. DE 10 2004 052 267.7, filed on Oct. 27, 2004, which is incorporated herein by reference.
One embodiment of the present invention relates to a method for forming a lithography mask, and in particular a method for forming a lithography mask on a semiconductor material region. In one case, the present invention relates to a method for improving the uniformity of sub-50-nanometer structures through thermal aftertreatment of a chemically amplified resist with the aid of a thermal stepper.
The processing of semiconductor structures in many cases involves lithography processes and in particular photolithography processes which are based on the application and formation of so-called photolithography masks that serve as patterning mask for a semiconductor material region lying below the photolithography mask. In order to form such photolithography masks on semiconductor material regions, firstly a material that forms the basis of the photolithography mask to be formed is applied on the surface region of the semiconductor material region, exposed in accordance with structure data present and subsequently developed. After the exposure operation, by means of which the spatial-geometrical structure data are transferred into the material region for the photolithography mask, in many cases a thermal aftertreatment step also takes place, by means of which the structure information transferred by radiation is correspondingly converted into chemical information.
In this case, it is essential to comply with specific temporal relations between the irradiation operation and the thermal aftertreatment step. In known production methods for photolithography masks on surfaces of semiconductor material regions, it is not possible to ensure an identical temporal sequence between irradiation operation and thermal aftertreatment operation for different regions on a semiconductor material region, which is also referred to as a wafer.
One embodiment of the invention is a method for producing a photolithography mask in which it is possible to ensure the temporal coordination of the individual process steps for all of the regions of the processed semiconductor material region.
A method according to one embodiment of the invention for forming a photolithography mask on a semiconductor material region including (a) providing a semiconductor material region having a surface region, (b) forming a resist material region having a surface region on the surface region of the semiconductor material region or on a processing partial region thereof, (c) controlling irradiation of the resist material region and thereby formation of a patterned irradiated resist material region at least on or in the processing partial region, (d) thermally aftertreating of the patterned irradiated resist material region at least on or in the processing partial region, and (e) developing of the thermally aftertreated resist material region at least on or in the processing partial region and thereby formation of a patterned resist material region as mask structure on the surface region of the semiconductor material region or on or in a processing partial region thereof.
In one embodiment step (c) is carried out, with regard to the semiconductor material region formed with the resist material region, spatially section-by-section, to be precise with first spatial sections of the semiconductor material region. Step (d) is carried out, with regard to the semiconductor material region formed with the exposed resist material region, likewise spatially section-by-section, to be precise with second spatial sections of the semiconductor material region, the first spatial sections of the material region formed with the exposed resist material region thereby also being correspondingly thermally aftertreated. According to one embodiment of the invention, the respective time period from the end of the exposure of the respective first spatial section of the semiconductor material region until the beginning of the thermal aftertreatment of the respective first section of the semiconductor material region is chosen to be identical or approximately identical for each of the first spatial sections. What is thereby achieved is that all of the first sections of the semiconductor material region and, consequently, the processing partial region of the semiconductor material region are subjected to identical temporal conditions with regard to the resist material, in contrast to the prior art, in which, on account of the so-called first-last die delays, there are time period differences between the exposure and the thermal aftertreatment, which may then also become apparent in material differences or differences in the properties of the differently treated first spatial sections.
The accompanying drawings are included to provide a further understanding of the present invention and are incorporated in and constitute a part of this specification. The drawings illustrate the embodiments of the present invention and together with the description serve to explain the principles of the invention. Other embodiments of the present invention and many of the intended advantages of the present invention will be readily appreciated as they become better understood by reference to the following detailed description. The elements of the drawings are not necessarily to scale relative to each other. Like reference numerals designate corresponding similar parts.
In the following Detailed Description, reference is made to the accompanying drawings, which form a part hereof, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. In this regard, directional terminology, such as “top,” “bottom,” “front,” “back,” “leading,” “trailing,” etc., is used with reference to the orientation of the Figure(s) being described. Because components of embodiments of the present invention can be positioned in a number of different orientations, the directional terminology is used for purposes of illustration and is in no way limiting. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. The following detailed description, therefore, is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims.
Structurally and/or functionally similar or equivalent structures or method steps are designated by the same reference symbols below. A detailed description of the structural elements or method steps is not repeated on every occasion when they occur.
One embodiment of the present invention forms temporal intervals between the end of the exposure operation and the beginning of the thermal aftertreatment operation to be approximately identical for all of the first spatial sections of the semiconductor material region and thus for all of the sections of the treatment partial region, in order to be able to make the processing results for all of the sections comparable or identical.
One embodiment of the invention proposes a method for forming a lithography mask on a semiconductor material region, having the following steps:
In one embodiment of the method according to the invention, it is provided that the first sections of the semiconductor material region and/or the second sections of the semiconductor material region are chosen such that they cover the processing partial region of the semiconductor material region.
As an alternative or in addition, it is conceivable for the first sections of the semiconductor material region and/or the second sections of the semiconductor material region to be chosen such that a first section of the semiconductor material region corresponds to precisely one second section of the semiconductor material region, in one case it is essentially identical thereto.
Furthermore, as an alternative or in addition, it is conceivable for each first section of the semiconductor material region and/or each second section of the semiconductor material region to correspond to a die.
In one case, each first section of the semiconductor material region and/or each second section of the semiconductor material region correspond(s) to an, in one case contiguous, group of dies.
In accordance with one embodiment of the method according to the invention, it is provided that in steps (c) and (d), the first sections of the semiconductor material region are processed individually and/or in groups of first sections of the semiconductor material region in a temporal sequence that is fixed for both steps (c) and (d).
In this case, it may be provided that in step (e), the first sections of the semiconductor material region are processed individually and/or in groups of first sections of the semiconductor material region in the temporal sequence that is fixed for steps (c) and (d).
It is also conceivable that, as an alternative or in addition, in step (c), processing parameters or the totality of all processing parameters for the first sections of the semiconductor material region are identical or approximately identical or are chosen to be identical or approximately identical, in one case with regard to a type of radiation, radiation intensity, radiation energy, radiation power, wavelengths or wavelength ranges, frequencies or frequency ranges, radiation duration, radiation profile, instant for the beginning of the irradiation and/or instant for the end of the irradiation.
It is furthermore possible that, as an alternative or in addition thereto, in step (d), processing parameters or the totality of all processing parameters for the first sections of the semiconductor material region are identical or approximately identical or are chosen to be identical or approximately identical, in one case with regard to the type or the devices, intensity, energy, power, with regard to wavelengths or wavelength ranges, frequencies, or frequency ranges, duration, profile, instant for the beginning of the thermal treatment and/or instant for the end of the thermal treatment.
In step (d), a radiation may be used for heating.
In step (d), an infrared radiation may be used for heating.
In this case, it is possible that in step (d), an arrangement with or comprising infrared diodes is used as heat source, in one case for the local or section-by-section thermal treatment of the first sections of the semiconductor material region or of groups of first sections of the semiconductor material region by irradiation.
Furthermore, as an alternative or in addition, it may be provided that a first or irradiation device is used in step (c), that a second or thermal treatment device is used in step (d), and that the first device and the second device (W1, W2) are coupled to one another—in one case fixedly—geometrically and/or temporally.
In this case, scanning devices, scan devices or stepper devices may be used as first device and/or as second device.
In one case, the first device and the second device are provided in a common treatment unit.
In one embodiment of the method, in step (b), resist material region (31) is formed with or from a chemically amplified resist material or CAR material.
One embodiment of the invention relates to methods for improving the uniformity of sub-50 nm structures through thermal aftertreatment of a chemically amplified resist with the aid of a thermal stepper.
The production of microchips is based on the microlithographic process of structure transfer. This step defines the minimum structure dimensions of the individual circuit elements, the packing density and thus the space requirement of the chips. It is an aim of all chip manufacturers' endeavors to be able to realize ever smaller structures, that is, circuits, on the chip. The smallest structures that are customary at the present time in DRAM memory fabrication lie in the feature size range of 90 to 110 nm.
In photolithography, the so-called chemically amplified resists (chemical amplification resists, CAR) are used to a greater extent for various optical lithography technologies (248 nm, 193 nm, 157 nm and 13 nm). See Solid State Technology, Vol. 39, No. 7, pp. 164-173, (1996). In this case, the resists may work according to the principle of acid-catalyzed cleavage. By way of example, in the case of positively working resists, a polar carboxylic acid group is formed here from a nonpolar chemical group, for example a tert-butyl carboxylate group, in the presence of a photolytically produced acid (photo acid). In a subsequent development step, the exposed resist film is treated with aqueous alkaline developer solutions, the carboxylic acid-rich, polar regions being removed by development and the unexposed resist regions remaining. Corresponding acid-catalyzed crosslinking reactions are effected in the case of negative systems.
These acid-catalyzed cleavage processes or crosslinking processes generally take place at temperatures in the range of 80 to 160° C. This means that in the lithography process heating steps are necessary, the so-called PEB or post exposure bake, that is to say a heating step effected after the exposure.
For this post exposure bake, use is made of so-called hotplates, in principle simple electrical precision heating plates which, however, guarantee a very exact temperature adjustment and distribution over the heating area (typical tolerance fluctuations over the heating area <1° C.). The substrates to be processed (silicon wafer or else a mask blank) are placed onto the heating area of the hotplates by means of an automated mechanism and are thus heated by direct mechanical contact. It is likewise possible for the substrates to be heated contactlessly by way of a very thin air cushion (<1 mm) between hotplate and substrate in the case of so-called proximity hotplates. This method using hotplates is used globally on an industrial scale as the only method for processing both the chemically amplified resists and the non-amplified resists.
As a result of the increasing reduction of the feature sizes, in particular with dimensions ranging below 50 nm, an effect becomes apparent here which may be referred to as first/last die effect or first/last die delay. In modern exposure devices, the entire Si wafer is no longer exposed, but rather only individual fields comprising one or more chips, the so-called die. As a result of the successive exposure of the individual fields—in one case in a stepper or scanner—a time difference now arises between the first and last exposure fields on the wafer. Thus, for example, in the case of a 256 Mbit chip on a 300 mm wafer there are approximately 250 exposure fields, that is to say that with a cycle of for example, 500 ms the delay between first and last dies adds up to a good two minutes. In the case of high-resolution patterning (for example, in 157 nm lithography), this time difference may become apparent adversely in the structure dimension obtained, since it is not taken into account during the PEB on a hotplate by means of the heat treatment of the entire wafer all at once. While in the exposed regions a high acid diffusibility influences the desirable protective group cleavage, a time-dependent lateral diffusion (typical average diffusion lengths lie in the range of 10 nm-30 nm) into the nominally unexposed regions is undesirable, because this ultimately leads, depending on the time period between exposure and PEB (the so-called post exposure delay), to the alteration of the feature sizes on the wafer. (See W. Hinsberg et al., “Extendibility of Chemically Amplified Resists: Another Brick Wall?”, Pro. SPIE Vol. 5039 (2003), page 1.) The result is an inadequate uniformity—from a production engineering standpoint—of the structures over the entire wafer.
The neutralization of acid by aminic contaminants from the air, which are only able to be monitored in a complicated manner, likewise plays a part in the first/last die effect. The resulting effects are likewise time-dependent.
One embodiment of the present invention is intended to present a method by means of which the first/last die delay can be avoided. This is done by virtue of the fact that the PEB is no longer effected by means of a conventional hotplate, but rather by means of a thermal stepper subsequent to the exposure.
One embodiment of the invention solves the problem by virtue of the fact that the individual dies are in each case thermally treated (subjected to heat treatment) at an identical temporal interval relative to their preceding exposure. This is achieved by virtue of the fact that the exposed wafer is no longer subjected to heat treatment as an entire wafer, but rather with the aid of a stepper-like device which can selectively subject an exposure field to heat treatment by means of thermal radiation. This thermal stepper is adapted to the die-to-die exposure cycle of the exposure device.
In one embodiment of the invention, the first/last die delay is completely avoided as a result of the selective heat treatment and the adapted cycle with respect to the exposure device. The temporal interval between exposure and PEB is identical for each exposed field.
In one embodiment of the invention, such a thermal stepper can be linked directly to an exposure device, or be integrated in a clustered track, analogously to the tracks used hitherto. Through the use of a plurality of stations, the total throughput of an exposure device is not affected.
In one embodiment of the invention, by virtue of the heat treatment by means of thermal radiation, it is no longer necessary to heat the entire wafer. Only the actually required region of the wafer (namely the exposed photoresist) is subjected to heat treatment. By way of the associated lower overall heat capacity and more effective heating of the resist, this discloses the possibility of possibly shortening PEB times (times of approximately 60-90 seconds have typically been used hitherto).
In one embodiment of the invention, the use of thermal radiation affords the possibility of carrying out the PEB in vacuo. In this case, with lithography techniques such as for example, E-beam or EUV (extreme UV), both of which take place in vacuo, the PEB could likewise be carried out in vacuo as it were in situ after the exposure. In this case, the exposed resist no longer comes into contact with air and thus with amines prior to the PEB.
In one embodiment of the invention the wafer is no longer subjected to heat treatment as a whole, rather each individual exposure field is subjected to heat treatment selectively and in a manner adapted to the exposure cycle of these fields. As a result, the time period between exposure and PEB is identical for each field and CD (critical dimension) fluctuations from field to field are completely avoided as a result. The uniformity over the entire wafer is thereby considerably improved.
The thermal stepper is realized with the aid of a clocked IR diode array.
In this variant, the clocked IR diode array used in example 1 is replaced by radiant heating with a variable diaphragm. The radiant heating consists for example, of electrical heating elements. A quartz radiator—in one case without a UV component—may also be used. The diaphragm system is realized in such a way that a cooled individual diaphragm is arranged above each die, said individual diaphragm being folded upward, by way of example. These diaphragms are opened and closed again in accordance with the exposure cycle. In principle, each die is then heated analogously to
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Although specific embodiments have been illustrated and described herein, it will be appreciated by those of ordinary skill in the art that a variety of alternate and/or equivalent implementations may be substituted for the specific embodiments shown and described without departing from the scope of the present invention. This application is intended to cover any adaptations or variations of the specific embodiments discussed herein. Therefore, it is intended that this invention be limited only by the claims and the equivalents thereof.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2004 052 267.7 | Oct 2004 | DE | national |
