Patent Application
20090311419
1. Field of the Invention
The embodiments described in the following relate to a method and an apparatus for developing a resist layer.
2. Description of the Related Art
The fabrication of highly integrated electrical circuits with small structural dimensions requires special structuring procedures. A common procedure is the so-called lithographic structuring method. This method comprises applying a thin layer of a radiation-sensitive photoresist on a surface of a semiconductor substrate disc, also referred to as wafer, optionally performing a pre-baking of the resist layer, and selectively exposing the same by means of electromagnetic radiation. The electromagnetic radiation may be transmitted through or reflected by a lithographic mask in order to image lithographic structures located on the mask onto the resist layer. Instead of using a lithographic mask, selectively exposing the resist layer may also be performed by directing an electron or ion beam onto the resist layer, which is referred to as “direct writing”. A baking process may be carried out following the exposure, also referred to as “post exposure bake”.
In a development process, structuring of the exposed resist layer is performed. This process comprises applying a developing liquid to the resist layer, referred to as developer in the following, whereby a soluble portion of the resist is dissolved out and removed, respectively. Thereafter, a rinsing liquid is applied to the wafer and the wafer is rotated in order to rinse off the developer and dissolved out resist components, and to spin-dry the wafer. The wafer may also be rotated during application of the developer in order to spread the developer over the complete resist layer. The developed and thus structured resist layer may serve as a mask in subsequent process steps like for example an etching process or an ion implanting process in order to selectively remove or impact on the underlying substrate material.
One main demand of the semiconductor industry is the continuous power enhancement provided by increasingly faster integrated circuits, which is interrelated to a miniaturization of the electronic structures. With the increase in circuit density and the decrease in feature size, however, lithography induced defects are becoming more and more significant. One issue is the elimination of so-called post-development defects, also referred to as “satellite” or “blob” defects. These defects are composed of resist material or fragments which are re-deposited on the wafer surface during the development process, and therefore affect subsequent process steps.
Conventional approaches for reducing post-development defects include extending the rinsing time of the rinsing step or carrying out an additional exposure of the resist. As a consequence, the lithographic process cycle is extended. Another approach is based on the application of tensides or rinse additives for defect suppression. These additional chemicals may, however, have an unclear impact on the lithographic process and on subsequent processes.
Various features of embodiments will become clear from the following description, taking in conjunction with the accompanying drawings. It is to be noted, however, that the accompanying drawings illustrate selected embodiments and are, therefore, not to be considered limiting of the scope of the invention. The present invention may admit other equally effective embodiments.
The embodiments described in the following relate to a method and an apparatus for developing an exposed resist layer formed on a surface of a semiconductor wafer, wherein the formation of post-development defects may be reduced or suppressed. The embodiments are based on the experience that dissolved out resist fragments do not only re-deposit but also accumulate together on the surface of a wafer to form a post-development defect pattern, which has a specific and recognizable structure. The accumulation of resist particles is related to a vibration of the wafer during the development process. A reason for a vibration is the rotation of the wafer, which is at least carried out during the rinsing and drying part of the development process.
One embodiment includes a method of developing a resist layer, the method comprising providing a substrate comprising an exposed resist layer formed on a surface of a substrate, applying a developer to the substrate to cause development of the resist layer, applying a rinsing liquid to the substrate, and rotating the substrate. The method further comprises suppressing a rotation-induced vibration of the substrate to suppress an agglomeration of a dissolved out resist components.
Another embodiment includes a method of developing a resist layer, the method comprising providing a substrate comprising an exposed resist layer formed on a surface of the substrate, applying a developer to the substrate to cause development of the resist layer, applying a rinsing liquid to the substrate, and rotating the substrate. The method further comprises applying a time-variant excitation vibration to the substrate. The excitation vibration superposes with a rotation-induced vibration of the substrate and excites the substrate to vibrate in a time-variant manner to suppress an agglomeration of dissolved out resist components.
Another embodiment includes an apparatus for developing an exposed resist layer formed on a surface of a substrate. The apparatus comprises a process chamber and a rotatable supporting device located in the process chamber for supporting the substrate. The apparatus further comprises a device for applying a developer to the substrate and a device for applying a rinsing liquid to the substrate. The apparatus furthermore comprises a vibration device being configured to apply an auxiliary vibration to the substrate which superposes with a rotation-induced vibration of the substrate.
Another embodiment includes an apparatus for developing an exposed resist layer formed on a surface of a substrate. The apparatus comprises a process chamber and a rotatable supporting device located in the process chamber for supporting the substrate. The apparatus further comprises a device for applying a developer to the substrate, a device for applying a rinsing liquid to the substrate, and a rotation device located in the process chamber. The rotation device is coupled to the supporting device and is configured to rotate the supporting device. The apparatus furthermore comprises a damping device being configured to absorb a vibration of the rotation device, thereby suppressing a rotation-induced vibration of the substrate.
Another embodiment includes an apparatus for developing an exposed resist layer formed on a surface of a substrate. The apparatus comprises a process chamber and a rotatable supporting device located in the process chamber. The supporting device comprises a supporting surface for supporting the substrate, wherein a diameter of the supporting surface exceeds 120 mm. The apparatus further comprises a device for applying a developer to the substrate and a device for applying a rinsing liquid to the substrate.
Another embodiment includes an apparatus for developing an exposed resist layer formed on a surface of a substrate. The apparatus comprises a process chamber and a rotatable supporting device located in the process chamber for supporting the substrate. The supporting device comprises a balance weight to rotate the substrate in a manner that a rotation-symmetric distribution of mass with respect to the rotation axis is provided, thereby suppressing a rotation-induced vibration of the substrate. The apparatus furthermore comprises a device for applying a developer to the substrate and a device for applying a rinsing liquid to the substrate.
For way of illustration,
The similar agglomeration of resist components in the defect patterns 120, 130 indicates a vibration of the wafers 101, 102 during the development process. This correlation makes use of the fact that the defect patterns 120, 130 have a geometric form comparable to Chladni figures. Chladni figures represent vibration modes in a mechanical surface and may for example be observed by vibrating a plate which is covered by sand. When the plate reaches resonance, the sand forms a pattern showing the nodal regions.
A further indication for a vibration-caused agglomeration of resist particles during rotation is the similar orientation of the defect patterns 120, 130 with respect to a notch 110 formed in the peripheral edge of the wafers 101, 102. The wafer notch 110, which is used for alignment purposes when processing the wafers 101, 102, may cause an unbalanced mass during rotation of the wafers 101, 102, and thus a vibration of the wafers 101, 102. In addition to this vibration fraction, a vibration of the wafers 101, 102 may for example be induced by devices applied for rotation of the wafers 101, 102.
The vibration of the wafers 101, 102 may cause a standing wave or a standing wave pattern on the wafers 101, 102, which is also present in the developing and rinsing liquid on the surface of the wafers 101, 102 during the development process. As a consequence, dissolved out resist fragments may flow to and accumulate at the nodes of the standing wave pattern, depending on the size of the particles and on the interface or surface flow of the liquid. The agglomeration of particles may further on be promoted by a charge separation caused by the movement of the particles (“diffuse double layer”), thereby lowering the activation energy for coagulation. In this connection, the aforesaid “vibration” of the wafer relates to all kinds of resonance or vibration modes which are e.g. substantially time-invariant or change in a way that an agglomeration of resist particles may take place.
The embodiments described in the following utilize the correlation between the formation of post-development defect patterns and the vibration of a wafer during rotation in a development process in order to reduce or eliminate formation of such defects. The embodiments are based on influencing or suppressing the rotation-induced vibration of the wafer in an active or passive manner.
The chuck 225 may be configured as a vacuum chuck which secures the wafer 100 on the chuck 225 by applying a vacuum or low pressure to the supporting surface of the chuck 225. For this purpose, the chuck 225 may be provided with through holes (not shown) which connect the supporting surface with a suction line 240. The suction line 240 may be arranged in the spindle 230 and may be further connected to a pumping device, for example a vacuum pump (not shown).
The apparatus 200 may further comprise a nozzle 280 for applying a developer 281 to the wafer 100 or to the resist layer 140 coating the surface of the wafer 100, respectively. The developer 281 may for example be an aqueous base solution. Various designs are conceivable for the nozzle 280 so that the developer 281 may be applied to the wafer surface in different ways, for example dispensed, dripped, sprayed etc. The nozzle 280 may further be connected to a supply line.
The apparatus 200 may further comprise a nozzle 290 for applying a rinsing liquid 291 to the wafer 100 or to the resist layer 140 arranged on the wafer surface, respectively. The rinsing liquid 291 may for example be de-ionized water. Similar to the nozzle 280, various configurations may be considered for the nozzle 290 so that the rinsing liquid 291 may be applied to the wafer surface in different ways, for example dispensed, dripped, sprayed etc. The nozzle 290 is as well further connected to a supply line.
In order to collect liquid being thrown from the wafer 100 during rotation, the apparatus 200 may comprise a cup 260. The cup 260 may comprise sidewalls which surround the wafer 100. The cup 260 may be connected to a drain 262 in order to remove collected liquid. The drain 262 may be further connected to a respective pumping device (not shown).
The apparatus 200 may furthermore comprise an inlet 270 being connected to a filter 271 and an outlet or exhaust 261 in order to create a fluid or air flow and to set a predefined atmosphere (temperature, pressure, humidity) in the process chamber 210 during a development process. The inlet 270 is further connected to a pumping device (not shown), so that a substantially uniform air flow (“laminar flow”) may be established towards the wafer surface via the filter 271, which is indicated by arrows 275. By means of the exhaust 261 which is connected to a respective pumping device (not shown), air may be evacuated from the process chamber 210. The exhaust 261 may be connected to the cup 260, as shown in
In a development process, the provided wafer 100, which has been coated with the resist layer 140 and exposed to a desired pattern of electromagnetic radiation, may be arranged on the chuck 225 in the process chamber 210. The wafer 100 may be secured to the chuck 225 by applying a low pressure to the supporting surface of the chuck 225. A predetermined atmosphere and air flow may be generated inside the process chamber 210 by means of the inlet 270, the filter 271 and the exhaust 261. Developer 281 may be applied to the wafer surface by means of the nozzle 280. In this way development of the resist layer 140 takes place, i.e. that developer soluble areas of the resist layer 140 are dissolved in the developer 281.
During application of the developer 281 to the wafer surface, the chuck 225 and thus the wafer 100 may be rotated in order to spread the developer 281 over the wafer surface and the resist layer 140, respectively, and to create a pool or puddle of the developer 281 on the surface. The puddle of developer 281 is allowed to remain on the wafer surface for a time sufficient to allow a complete development and thus structuring of the resist layer 140. For this purpose, the wafer 100 may further on be rotated. Alternatively, rotation of the wafer 100 may also be stopped and the wafer 100 may be left for a predetermined time, thereby developing the resist layer 140. This information is only considered to exemplify application of the developer 281 and development of the resist layer 140, and is therefore not limiting.
Subsequently, rinsing liquid 291 may be applied to the wafer surface by means of the nozzle 290, and the wafer 100 may be rotated in such a way (e.g. by increasing the rotation speed or by applying a high(er) rotation speed) that developer 280 and dissolved out resist components may be thrown off and removed from the wafer 100. After a pre-determined time, application of the rinsing liquid 291 to the wafer 100 may be terminated, and the wafer 100 may further on be rotated in order to be spin-dried.
The apparatus 200 makes it possible to suppress a vibration of the wafer 100 during rotation and thus to suppress an agglomeration of dissolved out resist components. A rotation-induced vibration may at least be suppressed in the rinsing part of the development process. In this way the formation of post-development defects on the wafer surface may be eliminated or reduced.
For this purpose, the apparatus 200 may comprise a piezoelectric vibrator 310 which may be mechanically coupled to the wafer 100 for example via the chuck 225. As shown in
The compensation vibration may be for example generated with a defined frequency and amplitude. In this way, provided that the rotation-induced vibration of the wafer 100 is substantially time-invariant, the wafer vibration may be compensated for or at least partially reduced so that an agglomeration of dissolved out resist fragments is suppressed. For the case that the rotation-induced vibration of the wafer 100 has a time-variant behavior, i.e. that for example the vibration frequency and/or the amplitude change with time, the frequency and/or the amplitude of the compensation vibration may be changed in a similar way over time in order to effectively compensate for or suppress the rotation-induced vibration. A time-variant behavior of the rotation-induced vibration of the wafer 100 may for example originate from the removal of liquid from the surface of the wafer 100 during rinsing and spin-drying. In either case, application of the compensation vibration to the wafer 100 by means of the piezoelectric vibrator 310 may eliminate or reduce the formation of post-development defects.
In addition to or instead of applying a compensation vibration, the apparatus 200 may further comprise a damped bearing 330 being arranged between the spin motor 250 and the spindle 230. By means of the damped bearing 330, a vibration of the spin motor 250 when operating the same and thus the transmittance of this vibration fraction to the wafer 100 may be absorbed, thereby also suppressing a rotation-induced vibration of the wafer 100.
A further embodiment for suppressing a rotation-induced vibration of a wafer in a development process includes providing a chuck having an enlarged supporting surface. For way of illustration,
The arrangement of the wafer 100 on the chuck 220 may result in a relatively large overhanging portion 105 of the wafer 100 in the form of an annulus which is not supported by the supporting surface of the chuck 220. The overhanging portion 105 for example may have a width of 90 mm, which is the case for the above-identified diameter values of the wafer 100 and of the chuck 220. The unsupported overhanging portion 105 may be another cause for a rotation-induced vibration of the wafer 100, or for an intensification of the same. In the latter case, the vibration may for example be primarily induced by an unbalance due to the wafer notch 110, or caused by a vibrating spin motor 250.
Accordingly, providing a chuck with a supporting surface exceeding the supporting surface of the chuck 220 (diameter 120 mm), indicated in
The following
The apparatus 201 depicted in
The apparatus 201 as well may comprise a damped bearing 330 between the spin motor 250 and the spindle 230. Additionally, a damped mounting 340 may be provided in order to attach the spin motor 250 in a damped manner. The damped mounting 340 may also serve for absorbing a vibration originating from the spin motor 250 and thus for suppressing a transmittance of the same to the wafer 100. In one embodiment, instead of providing both the damped bearing 330 and the damped mounting 340, only one of these damping elements 330, 340 may be used for absorbing a vibration of the spin motor 250.
The apparatus 202 shown in
A varying air flow introduced to the process chamber 210 via the inlet 270 and the filter 271 is indicated by the dashed arrows 350 in
An oscillating air flow exhausting from the process chamber 210 via the exhaust 261 is indicated in
The apparatus 203 depicted in
The oscillating low pressure is indicated by a dashed arrow in the suction line 240 of the apparatus 203.
In one embodiment, another approach for suppressing a rotation-induced vibration of a wafer in a development process is based on providing a rotation-symmetric distribution of mass with respect to the rotation axis. It is for example possible to provide a wafer having a peripheral edge, a notch being formed in the peripheral edge for alignment purposes and at least one balancing element. By means of the balancing element, an unbalance during rotation of the wafer due to the notch may at least be partially compensated to suppress the rotation—or unbalance-induced vibration.
For way of illustration,
As indicated in
The additional notches 411, 412, 413 may have a shape differing from the shape of the first notch 410. In this way, the alignment of the wafer 400 may further on be carried out by determining the position of the first notch 410 on the wafer 400, since the notch 410 may be distinguished from the additional notches 411, 412, 413.
The following
Another embodiment for providing a more rotation-symmetric distribution of mass with respect to a rotation axis is illustrated with respect to the plan view of a wafer 100 comprising a notch 110 shown in
In order to suppress an unbalance and thus a vibration during rotation caused by the notch 110 of the wafer 100, the total mass distribution of both the wafer 100 and the chuck 600 may be accounted for. Instead of providing a balancing element on the wafer 100, the chuck 600 may comprise an additional balance weight 610. In this way a more symmetric distribution of mass (mass of the wafer 100 plus mass of the chuck 600) with respect to the rotation axis may be provided. As illustrated in the side view of
Instead of reducing or suppressing a vibration of a wafer during rotation in an active or passive manner in a development process as described above, it is likewise possible to specifically excite the wafer to vibrate in a time-variant manner. In this way, an agglomeration of dissolved out resist components (which is based on a substantially time-invariant standing wave pattern) may be impeded and therefore also suppressed.
With respect to the apparatuses 200, 201, 202, 203 of
The devices and methods described in conjunction with the drawings are to be considered as examples and not limiting. The different embodiments are based on influencing a vibration of a wafer in a development process. The development process includes providing a wafer being coated with an exposed resist layer, applying a developer to the wafer, applying a rinsing liquid to the wafer, and rotating the wafer. The vibration of the wafer is induced by or occurs during rotation. By influencing the wafer vibration, the embodiments make it possible to suppress an agglomeration of dissolved out resist components and thus to suppress formation of post-development defects.
Apart from the described embodiments, further embodiments may be realized which comprise further modifications and combinations of the described devices and methods. It is e.g. possible to provide the apparatuses 200, 201, 202, 203 of
A potential example for a combination of different embodiments may be considered for generating an auxiliary vibration. It is e.g. possible to simultaneously use a piezoelectric vibrator and to vary the air flow introduced to and/or exhausted from a process chamber. Further combinations are for example actively generating a compensation vibration together with providing an enhanced rotation-symmetric distribution of mass with respect to a rotation axis.
Moreover, the detailed specification of the development process given with respect to the apparatus 200 of
The preceding description describes examples of embodiments of the invention. The features disclosed therein and the claims and the drawings can, therefore, be useful for realizing the invention in its various embodiments, both individually and in any combination. While the foregoing is directed to embodiments of the invention, other and further embodiments of this invention may be devised without departing from the basic scope of the invention, the scope of the present invention being determined by the claims that follow.
