Patent Application
20080152936
The present invention relates to methods for providing a high density relief structure in a recording stack of a master substrate, particularly a master substrate for making a stamper for the mass-fabrication of optical discs or a master substrate for creating a stamp for micro contact printing. Furthermore, the invention relates to a master substrate for creating a high-density relief structure, particularly a master substrate for making a stamper for the mass-fabrication of optical discs or a master substrate for creating a stamp for micro contact printing. The invention also relates to methods for making stampers, optical discs, stamps, and microprints, respectively.
Relief structures that are manufactured on the basis of optical processes can, for example, be used as a stamper for the mass replication of read-only memory (ROM) and pre-grooved write-once (R) and rewriteable (RE) discs. The manufacturing of such a stamper, as used in a replication process, is known as mastering.
In conventional mastering, a thin photosensitive layer, spincoated on a glass substrate, is illuminated with a modulated focused laser beam. The modulation of the laser beam causes that some parts of the master substrate are being exposed by UV light while the intermediate areas in between the pits to be formed remain unexposed. While the disc rotates, and the focused laser beam is gradually pulled to the outer side of the disc, a spiral of alternating illuminated areas remains. In a second step, the exposed areas are being dissolved in a so-called development process to end up with physical holes inside the photo-resist layer. Alkaline liquids such as NaOH and KOH are used to dissolve the exposed areas. The structured surface of the master substrate is subsequently covered with a thin Ni layer. In a galvanic process, this sputter-deposited Ni layer is further grown to a thick manageable Ni substrate comprising the inverse pit structure. This Ni substrate with protruding bumps is separated from the master substrate and is called the stamper.
Phase-transition mastering (PTM) is a relatively new method to make high-density ROM and RE/R stampers for mass-fabrication of optical discs. Phase-transition materials can be transformed from the initial unwritten state to a different state via laser-induced heating. Heating of the recording stack can, for example, cause mixing, melting, amorphisation, phase-separation, decomposition, etc. One of the two phases, the initial or the written state, dissolves faster in acids or alkaline development liquids than the other phase does. In this way, a written data pattern can be transformed to a high-density relief structure with protruding bumps or pits. The patterned substrate can be used as stamper for the mass-fabrication of high-density optical discs or as stamp for micro-contact printing.
One of the challenges encountered with PTM is getting a good pit shape. Since this method is based on heating, the shape will roughly be determined by the temperature profile in the recording stack. The problem lies in the fact that most materials have either a rather high absorption rate (most metals) or a rather low absorption rate (most dielectrics). Materials with a high absorption rate have a bad absorption profile. While the heat is penetrating the stack, the high absorption rate gives a rapid decrease in power flux and thus a rapid decrease in the temperatures that are reached. This makes it hard to get the needed pit depth. Materials with a low absorption rate would have a very good pit shape, but getting the needed temperatures would require very large write powers. This makes it impossible to directly write dielectrics with conventional recorders.
Until now, these problems were overcome by using a mask stack. A selectively etchable material is placed on an etchable dielectric material. Selectively etchable means that only the written or the unwritten stage is etchable. Unselectively etchable means that both the written and the unwritten stage are etchable. In such a stack with mask layer, the mask layer is very thin and the absorption profile is not an issue. During etching the written part of the mask layer will dissolve, forming a mask. The dielectric under the mask will only be etched where the mask layer was etched. Underetching is unavoidable and the dissolution time is very critical.
It is therefore an object of the present invention to provide methods and master substrates of the type mentioned at the beginning that provide a good pit shape in connection with PTM.
This object is solved by the features of the independent claims. Further developments and preferred embodiments of the invention are outlined in the dependent claims.
In accordance with a first aspect of the present invention, there is provided a method for providing a high density relief structure in a recording stack of a master substrate, particularly a master substrate for making a stamper for the mass-fabrication of optical discs or a master substrate for creating a stamp for micro contact printing, the method comprising the following steps:
The means for supporting heat induced phase transitions within the dielectric layer comprise a heat absorption rate that, during the writing process, ensures a temperature profile in the recording stack that finally leads to a good pit shape.
With a first general embodiment of the method in accordance with the invention the means for supporting heat induced phase transitions within the dielectric layer comprise at least one absorption layer arranged above and/or below the dielectric layer. Thereby, the problem with too low absorption of the dielectric layer is circumvented by heating through conduction. The absorption layer can be selectively or unselectively etchable.
With a second general embodiment of the method in accordance with the invention the means for supporting heat induced phase transitions within the dielectric layer comprise a dopant doped into the dielectric layer. Thereby, the dielectric layer itself is made more absorbing in the wavelength range defined by the dopant. Changing the doping concentration makes the absorption adjustable. This way the absorption can, for example, be made high enough to make writing with use of existing lasers possible, but low enough to get a good pit shape. It is clear that the first and second embodiments can be combined advantageously.
With a third general embodiment of the method in accordance with the invention the means for supporting heat induced phase transitions within the dielectric layer comprise nanocrystals grown within the dielectric layer during an annealing process. At room temperature, for example, a ZnS—SiO2 film contains tiny nanosized ZnS particles embedded in a SiO2 matrix. The size of the nanocrystals is temperature dependent: increasing the temperature initiates a growing in size of the nanocrystals. This leads to a blue-shift in the light absorption range of ZnS—SiO2. Scattering of blue light through the nano-composite material is assumed to be the main reason for this blue-shift. Preferred annealing temperatures vary between 600 and 900° C. For example the size of a ZnS—SiO2 nanocrystal is about 2 nm at room temperature, and it increases to about 7.5 nm at 700° C. and to up to 50 nm at 800° C. Therefore, heating, for example, a thin layer of sputter-deposited ZnS—SiO2 in an oven to 700° C. will cause a blue-shift, enabling the direct recording of marks. When such an annealing step is provided, at least in some cases additional absorption layers and/or doping are not necessary for recording marks in the ZnS—SiO2 with a 405 nm laser beam recorder.
In cases where an absorption layer is used, the absorption layer is preferably made of a material selected from the following group: Ni, Cu, GeSbTe, SnGeSb, InGeSbTe, silicide forming materials like Cu—Si or Ni—Si, material compositions like nucleation dominated phase change materials. The needed thickness of the absorption layer depends on many of the material properties, like absorption rate, thermal conductivity, specific heat etc. For example, a Ni layer comprising a thickness of about 10 nm leads to good results.
For all embodiments of the invention it is preferred that the dielectric layer is a ZnS—SiO2 layer. Also other dielectric materials, e.g. metal oxides such as Al2O3, Si3N4, ZrO2, are possible.
The etchant used in the etching process is preferably selected from the following group: acid solutions like HNO3, HCl, H2SO4 or alkaline liquids like KOH, NaOH.
If an absorption layer is used, during the etching process regions of the absorption layer where laser pulses were applied are removed together with regions of the absorption layer where no laser pulses were applied. Such a result is for example obtained, if the absorption layer is a Ni layer and HNO3 is used as the etchant.
However, it is also possible that during the etching process only the regions of the absorption layer are removed which are located above the regions of the dielectric layer which are removed. To achieve this, for example phase change materials in combination with alkaline and acid liquids can be used.
In accordance with a further development of the method in accordance with the invention, the step of providing a recording stack comprises providing a recording stack further comprising a mirror layer below the dielectric layer. Such a mirror layer improves the overall stack efficiency and makes the bottom surface of the pit smoother.
The mirror layer can, for example, be made from a material selected from the following group: Ag, Al, Si. In any case it is necessary that the mirror layer is resistant to the used etch liquid.
With some embodiments the step of providing a recording stack that comprises providing a recording stack comprising an absorption layer above the dielectric layer and a further absorption layer below the dielectric layer. Such a further lower absorption layer also provides heat from below, making it possible to improve the temperature profile in the upper dielectric layer. Like the upper absorption layer, the further absorption layer has to be made of a material that has a high absorption rate. The biggest difference with the upper absorption layer is the fact that the further absorption layer may not be etchable by the etchant used. Also the needed thickness of this layer depends on many of the material properties, like absorption rate, thermal conductivity, specific heat etc.
In this connection it may be advantageous, if the step of providing a recording stack comprises providing a recording stack further comprising a further dielectric layer below the further absorption layer. The lower dielectric layer provides heat isolation for the lower absorption layer and can consist of any dielectric mentioned. The thickness of the lower dielectric layer, together with its optical properties and the mirror layer provide a way to optimize the stack. Optimizing this thickness can control how the power is divided over the absorption layers. This gives great control over the pit shape.
With some embodiments of the method in accordance with the invention the step of providing a recording stack comprises providing a recording stack further comprising a covering layer. The covering layer is preferably as thin as possible, is present during writing, and is chemically removed via etching. Its function is to prevent the absorption layer to chemical degradation.
The covering layer preferably is made of an etchable dielectric or organic layer, such as photoresist.
With the second embodiment of the method in accordance with the invention, wherein the means for supporting heat induced phase transitions within the dielectric layer comprise a dopant doped into the dielectric layer, the dopant is preferably selected from the following group: N, Sb, Ge, In, Sn. However, also a different ratio ZnS—SiO2 is possible or a mixture of ZnS—SiO2 with other absorbing materials.
With the first general embodiment of the method in accordance with the invention, it is also possible that the step of providing a recording stack comprises providing a recording stack comprising a plurality of alternating dielectric layers and absorption layers. Also in this case the further developments discussed above, particularly in connection with the first general embodiment of the method in accordance with the invention, may be applied in the same or a similar manner. As regards the choice of the materials mentioned above, a highly preferred material for the plurality of dielectric layers is ZnS—SiO2, and a highly preferred material for the plurality of absorption layers is SnGeSb. It is to be noted that also this further development can, for example, also be used for making stampers for the mass fabrication of optical discs, for making optical discs, for making stamps for micro contact printing, and for making microprints. Such methods are discussed below and it is obvious for the person skilled in the art to further develop these methods accordingly. Therefore, also the corresponding feature combinations are disclosed herewith.
In the present context it is preferred that the plurality of alternating dielectric layers and absorption layers is formed by 2 to 20 dielectric layers and 2 to 20 absorption layers, preferably by 5 to 15 dielectric layers and 5 to 15 absorption layers, and most preferably by about 10 dielectric layers and 10 absorption layers.
If a plurality of alternating dielectric layers and absorption layers is provided, the dielectric layers preferably comprise a thickness between 0.5 and 20 nm, preferably between 1 and 10 nm, and most preferably of about 5 nm.
As regards the plurality of absorption layers, these absorption layers preferably comprise a thickness between 0.1 and 10 nm, preferably between 0.2 and 5 nm, and most preferably of about 1 nm.
In accordance with a second aspect of the present invention a master substrate for creating a high-density relief structure is provided, particularly a master substrate for making a stamper for the mass-fabrication of optical discs or a master substrate for creating a stamp for micro contact printing, wherein for forming the high-density relief structure there is provided a dielectric layer doped by a dopant enhancing its absorption properties for laser pulses. Thereby, as already mentioned in connection with the second embodiment of the method in accordance with the invention, the dielectric layer itself is made more absorbing in the wavelength range defined by the dopant. Changing the doping concentration makes the absorption adjustable, and the absorption can, for example, be made high enough to make writing with use of existing lasers possible, but low enough to get a good pit shape.
Also in this case the dopant preferably is selected from the following group: N, Sb, Ge, In, Sn. As already mentioned, also a different ratio ZnS—SiO2 is possible or a mixture of ZnS—SiO2 with other absorbing material.
In accordance with a further aspect of the invention, there is provided a master substrate for creating a high-density relief structure, particularly a master substrate for making a stamper for the mass-fabrication of optical discs or a master substrate for creating a stamp for micro contact printing, wherein for forming the high-density relief structure there is provided a dielectric layer containing nanocrystals grown by an annealing process. Thereby, as already mentioned in connection with the third embodiment of the method in accordance with the invention, a blue-shift in the light absorption range of ZnS—SiO2 can be obtained.
In accordance with a third aspect of the present invention, there is provided a method for providing a high density relief structure in a recording stack of a master substrate, particularly a master substrate for making a stamper for the mass-fabrication of optical discs or a master substrate for creating a stamp for micro contact printing, the method comprising the following steps:
This solution is based on the finding that there exist dielectric materials having a rather high absorption coefficient at the specified wavelength range. Therefore, at least in some cases, no additional absorption layer and no additional doping material is required to enable direct recording.
A preferred dielectric layer for writing with the specified wavelength range is a ZnS—SiO2 layer. ZnS—SiO2 at 257 nm wavelength comprises an absorption coefficient of about k=0.5. Another possibility to record ZnS—SiO2, particularly untreated ZnS—SiO2, is, for example, to use a wavelength of 266 nm, particularly in connection with the use of a LBR. Preferred write powers range between 0.5 and 1.5 mW.
When using ZnS—SiO2 for PTM mastering, the regions where no laser pulses were applied and which have not experienced a phase transition (the unrecorded areas) are removed by an etching process. Thus, the recorded material remains as a bump structure forming an inverse polarity structure compared to the case when the recorded material is removed. As a consequence of this inverse polarity there exists the risk of underetching the bump structure leading to problems, e.g. during separating the master substrate and a stamper grown thereon. In order to solve this problem of underetching, the ZnS component of the ZnS—SiO2 layer (14) preferably is present with less than 80% weight percentage. Thereby, the absorption of the PTM material can be lowered. While the default ratio is ZnS—SiO2=80%-20% weight percentage, it is preferred in this connection that the ratios are ZnS—SiO2=70%-30% and ZnS—SiO2=60%-40%, for example. With this solution the problem of underetching can be overcome or at least reduced.
A further possibility to avoid or at least reduce underetching as mentioned above is that the recording stack comprises at least one absorption layer. One or more absorption layers can be added to the recording stack to induce an extra heat flow from below. In this case, heat is generated in the absorption layer as well, in that way improving the bump shape. Possible absorption layers are for example SbTe, Si, Ag, Al, etc. When the ZnS—SiO2 layer is fully developed (etched up to the absorption layer), the absorption layer should be etch-resistant. After exposure, for example to HNO3, bumps with a taper-like profile remain.
It is also possible that after the etching process a coating is applied. For example, the developed master substrate can be covered with a silane film (or another spin-coated organic film) to fill the underetched regions. The capillary forces will make the polymer layer remain in the underetched parts of the bumps and improve in that way the bump.
Particularly to avoid or reduce underetching, embodiments are envisaged, wherein the etching process is stopped before an underetching of regions of the dielectric layer that shall not be removed occurs. If the etching process is well controlled, a predetermined depth can be obtained and underetching is prevented.
In accordance with a further embodiment the dielectric layer comprises a first surface arranged close to the laser during the application of the laser pulses and a second surface arranged afar from the laser during the application of the laser pulses, and wherein the etching process starts on the second surface of the dielectric layer. This technique can be referred to as “bump shape reversal” and it is one of the possibilities to obtain a proper bump shape. For example, before wet etching, a stamper is grown from the exposured PTM master. Then, the master substrate and the stamper are separated at the ZnS—SiO2-glass interface. Subsequently, the recorded PTM layer is developed. The resulting bump structure has the proper bump shape, directly suitable for replication or mother stamper growing.
In accordance with a fourth aspect of the present invention, there is provided a method for making a stamper for the mass-fabrication of optical discs, the method comprising the following steps:
In accordance with a fifth aspect of the present invention, there is provided a method for making an optical disc, the method comprising the following steps:
In accordance with a sixth aspect of the present invention, there is provided a method for making a stamp for micro contact printing, the method comprising the following steps:
In accordance with a seventh aspect of the present invention, there is provided a method for making a microprint, the method comprising the following steps:
In accordance with a eighth aspect of the present invention, there is provided a method for making a stamper for the mass-fabrication of optical discs, the method comprising the following steps:
In accordance with a ninth aspect of the present invention, there is provided a method for making an optical disc, the method comprising the following steps:
In accordance with a tenth aspect of the present invention, there is provided a method for making a stamp for micro contact printing, the method comprising the following steps:
In accordance with an eleventh aspect of the present invention, there is provided a method for making a microprint, the method comprising the following steps:
These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.
Furthermore, it is clear that the solutions in accordance with the fourth to eleventh aspects of the invention may be further developed corresponding to the embodiments and details disclosed in connection with the first to third aspects of the invention, and all combinations of the respective features shall be deemed to be disclosed hereby, even if presently not explicitly claimed with the appending claims.
a to 1c schematically show a first embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
ci schematically shows the making of a stamper and a stamp, respectively;
cii schematically shows the making of an optical disc;
ciii schematically shows the making of a microprint;
d and 1e show sectional analyses of the results of practical experiments made on the basis of a master substrate in accordance with
f and 1g show surface analyses of the results of practical experiments made on the basis of a master substrate in accordance with
a to 2c schematically show a second embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
a to 3c schematically show a third embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
a to 4c schematically show a fourth embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
a to 5c schematically show a fifth embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
d and 5e show surface analyses of the results of practical experiments made on the basis of a master substrate with a lower absorption layer;
a to 6c schematically show a sixth embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
a to 7c schematically show a seventh embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
d and 7e show sectional analyses of the results of practical experiments made on the basis of a master substrate in accordance with
f shows Differential Scanning Calorimeter measurements giving information about the phase transition of ZnS—SiO2;
g shows a comparison between calculated (simulated) and measured (via Atomic Force Microscopy) full width half maximum widths of marks recorded and etched in ZnS—SiO2;
a to 8c schematically show an eighth embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
d illustrates a targeted BD-ROM pit size, the intensity profile of a focused spot in a blue system (NA=0.85, 405 nm) and the intensity profile in a liquid immersion deep UV system (NA=1.2, 257 nm);
e shows a surface analysis of the result of a practical experiment made on the basis of a master substrate in accordance with
f shows a sectional analysis of the result of the practical experiment in accordance with
g shows a surface analysis of the result of a further practical experiment made on the basis of a master substrate in accordance with
h shows a sectional analysis of the result of the practical experiment in accordance with
a is a graph illustrating the growth of ZnS nanocrystals depending on the temperature;
b is a graph illustrating transmission spectra of nano-composite samples with a high ZnS content;
c to 9f schematically show a further embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention; and
a to 10h schematically show a marking mechanism in a dielectric layer of a master substrate, including a comparison of a conventional resist master (
a and 11b show a further embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention;
a to 12e show a further embodiment of a master substrate in accordance with the present invention during processing by a method in accordance with the invention and the respective measurement results;
a to 13d show a further embodiment of a method in accordance with the invention and the respective processing stages; and
a to 14e show a further embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention.
Throughout the drawings equal or similar reference numerals are assigned to equal or similar components which are explained only once in most cases to avoid repetitions.
a to 1c show a first embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
The recording stack 10 of the master substrate 12 comprises a dielectric layer 14 carrying an absorption layer 16. Under the dielectric layer 14 there is provided an optional mirror layer. The absorption layer 16 in this embodiment can be practically any material that has a high absorption rate and is unselectively etchable. Many metals (e.g. Ni, Cu, Ag, etc.) can be used as absorber. Crystalline phase change materials (e.g. GeSbTe, doped Sb2Te) that have a rather high melting temperature can also be used as absorber. A preferred material is Ni because of its availability and inertness to oxidation. The needed thickness of the absorption layer 16 depends on many of the material properties, like absorption rate, thermal conductivity, specific heat etc. For nickel, for example, 10 nm worked.
With the embodiment of
With the master substrate 12 of
First, the recording stack 10 shown in
Then, a heat induced phase transition is caused in the region 22 of the dielectric layer 14 where the pit 24 is to be formed by applying laser pulses. The result is shown in
Finally, the region 22 of the dielectric layer 14, which has experienced a phase transition, is removed by an etching process. As may be seen from
ci schematically shows the making of a stamper 40 and a stamp 42, respectively. The stamper 40 and the stamp 42, respectively, is formed on the basis of the high-density relief structure 24. To provide the metal layer, for example, a thin Ni layer is sputter-deposited on the high-density relief structure 24 formed in the recording stack of the master substrate 12. This Ni layer is subsequently electro-chemically grown to a thick manageable stamper 40 or stamp 42. The stamper 40 or the stamp 42 is separated from the master substrate 26 and further processed (cleaned, punched etc.).
cii schematically shows the making of an optical disc 50 on the basis of the stamper 40, as it is well known to the person skilled in the art.
ciii schematically shows the making of a microprint 52 on the basis of the stamp 42, as it is also well known by the person skilled in the art.
d shows a sectional analysis of the result of the following practical experiment. A pre-grooved BD-RE substrate with track pitch 320 nm was provided with a recording stack, comprising an 87 nm thick ZnS—SiO2 layer and a 10 nm Ni absorption layer. The pre-grooves were used for tracking. Continuous grooves were written in the pre-grooved stack by application of a continuous laser power (Pultsec, NA=0.85, 405 nm wavelength, continuous power of 3.4 mW). The Ni layer and written sections in the ZnS—SiO2 layer were etched with 1% HNO3 for 15 minutes. The peculiar shape indicates that the heated ZnS—SiO2 layer is partially etched. The measured depth profile indicates the presence of deep and shallow grooves. The shallow grooves are the left over of the pre-groove after sputter-deposition of the recording stack. The deep grooves are caused by selective etching of the written ZnS—SiO2 layer. After etching is performed, the final pit will be completely written in one material. This will rule out the possibility of underetching and will give smooth pit walls.
e shows a sectional analysis of the result of another practical experiment. A polycarbonate substrate was provided with a 200 nm thick ZnS—SiO2 layer and an absorption layer of Cu. A trace of 100 μm width was written with a Hitachi initializer (810 nm wavelength, 100 μm broad spot). After dissolution of the disc in HNO3, a step height of 190 nm resulted. This example shows that the process also works using a different absorption layer and different laser wavelength. The sample is less smooth. This is because the use of copper, which is highly susceptible to oxidation.
f shows an example of a bump structure written with the Pulstec. Again a 100 nm ZnS—SiO2 layer with 10 nm Ni top layer was used. A single tone of 14T length was written in the disc. The illuminated discs were treated with 1% HNO3 for 15 minutes. We clearly see an imprint of the pre-groove, the shallow groove that is present in both the bumps and the intermediate lands. The bumps/pits are rather wide because of the indirect heating effect. The wall angle is quite large. Also the obtained pit depth is almost the initial ZnS—SiO2 layer thickness steep.
g shows an example that the time can be varied to control the size of the written bumps. Three-dimensional AFM scans of a bump structure for three different dissolution times are shown, namely 5 (left image), 15 (middle image) and 25 minutes (right image) in 1% HNO3. This illustrates that also the crystalline state is dissolved in HNO3 but much slower than the unwritten amorphous phase. Apparently a dissolution time of 25 minutes is too long, 15 minutes seems to be optimum for these write conditions in combination with stack design.
a to 2c show a second embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
Also with this embodiment the recording stack 10 of the master substrate 12 comprises a dielectric layer 14 carrying an absorption layer 16, and under the dielectric layer 14 there is provided an optional mirror layer 32. However, with this embodiment the absorption layer 16 is a layer of which only the written phase is etchable by the etchant used to etch the dielectric layer 14. This adds some extra depth to the eventual pit 24, see
With the master substrate 12 of
First, the recording stack 10 shown in
Then, a heat induced phase transition is caused in the region 22 of the dielectric layer 14 where the pit 24 is to be formed by applying laser pulses. The result is shown in
Finally, the region 22 of the dielectric layer 14, which has experienced a phase transition, is removed by an etching process. As may be seen by comparing
In accordance with embodiment 2 it is for example also possible that the absorption layer 16 is replaced by a growth-dominated phase-change material (e.g. InGeSbTe, SnGeSb, etc.). The written mark 28 of the absorption layer 16 is etchable by the same etchant used to selectively etch region 22 of the dielectric layer 14. This potentially decreases the channel bit length through growth back. Also in this case the method in accordance with the invention can be carried out as described above.
a to 3c show a third embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
The recording stack 10 of the master substrate 12 also in this case comprises a dielectric layer 14 carrying an absorption layer 16, and under the dielectric layer 14 there is provided an optional mirror layer 32. However, with the third embodiment the absorption layer 16 is formed by a silicide forming layer like Cu—Si or Ni—Si. In embodiment 3 only the region 28, i.e. the written phase of the absorption layer 16 is dissolved, i.e. in the unwritten regions 30 both, the upper silicide forming layer 16a and the lower part 16b of the absorption layer 16 are not dissolved. An advantage of this is added pit depth.
With the master substrate of
a to 4c show a fourth embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
With embodiment 4 the recording stack 10 of the master substrate 12 is the same as described in connection with embodiment 3. However, in accordance with embodiment 4 both, the written phases 28, 22 and the topmost unwritten layer 16a are dissolved when the method described above in connection with embodiment 1 is applied. The result is shown in
a to 5c show a fifth embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
In accordance with embodiment 5 the upper absorption layer 16 and the dielectric layer 14 are as proposed in any of embodiments 1 to 4. However, there is added a further absorption layer 18 for providing heat also from below, making it possible to improve the temperature profile in the upper dielectric layer 14. Like the upper absorption layer 16, this layer 18 has to be made of a material that has a high absorption rate. The biggest difference with the upper absorption layer 16 is the fact that the further absorption layer 18 may not be etchable by the etchant used. The needed thickness of this layer 18 depends on many of the material properties, like absorption rate, thermal conductivity, specific heat etc. Furthermore, there is provided a further dielectric layer 36, which is arranged below the further absorption layer 18. The lower dielectric layer 36 provides heat isolation for the lower absorption layer 18 and can consist of any dielectric mentioned. The thickness of the lower dielectric layer 36, together with its optical properties and the mirror layer 32 provide a way to optimize the stack. Optimizing this thickness can control how the power is divided over the absorption layers. This gives great control over the pit shape.
With embodiment 5 the method in accordance with the invention can be applied as described above in connection with embodiment 1. The result is shown in
It is also possible to consider only the lower absorption layer 18 and omit the upper absorption layer 16. In this connection the following experiments were performed with a recording stack, comprising a 25 nm ZnS—SiO2 recording layer, a 25 nm phase-change absorption layer (InGeSbTe), a 10 nm ZnS—SiO2 interface layer and a 100 nm Ag layer (maybe provide a drawing of the stack). Laser-induced heating of the phase-change layer caused indirect heating of the ZnS—SiO2 top layer via diffusion. The phase-change layer was made crystalline prior to mastering. Continuous amorphous traces were written by applying a continuous laser power, amorphous marks were written by applying a pulsed write strategy. The write strategy contained short write pulses to allow for a sufficient cooling time in between the write pulses in order to melt-quench the phase-change film. The first write experiments were performed with an N-strategy. In such a write strategy, a 3T mark is written with three write pulses. The recorded disc was treated with NaOH developer (10%).
d shows AFM plots of grooves written with three different power settings (413 LBR, 25 nm ZnS—SiO2 film, 10 minutes with 10% NaOH), wherein the groove depth was 20 nm. The illuminated area remains as land plateaus after etching with NaOH. A higher write power leads to a wider land plateau (lands are light stripes) and a narrower groove in between the lands (grooves are the dark stripes).
e shows examples of written data. The unwritten ZnS—SiO2 phase dissolved in the alkaline liquid while the written areas remained at the surface. These recorded areas remain as bumps at the surface. The three panels represent three different recording powers. A pulsed write strategy was used to write these marks.
While the above embodiments 1 to 5 are related to the first general embodiment, embodiment 6 is related to the second general embodiment, wherein a dopant is used to enhance the absorption properties.
a to 6c show a sixth embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
With embodiment 6 the recording stack 10 of the master substrate 12 comprises a dielectric layer 14 which is doped by a suitable dopant 20 for enhancing the absorption properties. Under the dielectric layer 14 there is provided an optional mirror layer 32. The dopant is preferably selected from the following group: N, Sb, Ge, In, Sn. However, also a different ratio ZnS—SiO2 is possible or a mixture of ZnS—SiO2 with other absorbing material.
The dopant ensures that, even if no absorption layer is present, by applying laser pulses a heat induced phase transition is ensured in region 22 of the dielectric layer 14 (see
For example, doping ZnS—SiO2 with blue-absorbent phase change materials can be achieved with the following methods: A target with ZnS—SiO2 and GeSbSn mixed together can be prepared. The proportion of the absorbent material in the composition has to be sufficient for absorbing light at a 405 nm wavelength, but should also remain low enough to avoid any noise on the phase transition of ZnS—SiO2. A suitable composition was found to be around 15% (vol.) of GeSbSn and 80% (vol.) of ZnS—SiO2. As it is known as such in the art, the doping can also be performed using two separated targets of ZnS80—SiO2
a to 7c show a seventh embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
In accordance with embodiment 7 the recording stack 10 comprises a dielectric layer 14 made of ZnS—SiO2. Furthermore, there is provided an optional mirror layer 32 and an also optional covering layer 38. The covering layer 38 is preferably as thin as possible, is present during writing, and is chemically removed via etching. Its function is to prevent the absorption layer to chemical degradation, and not enhance the absorption properties.
With the master substrate of
First, a recording stack 10 comprising the dielectric layer 14 (and also the mirror layer 32 and the covering layer 38) is provided.
Then, a heat induced phase transition in region 22 of the dielectric layer 14 is caused where a pit 24 is to be formed by applying laser pulses having a wavelength of 257 nm.
Finally, the region 22 of the dielectric layer 14 which has experienced a phase transition is removed by an etching process.
d and 7e show sectional analyses of the results of practical experiments made on the basis of a master substrate in accordance with
As shown in
The phase-transition temperature of 800° C. is in agreement with recording experiments. Marks were written in a 50 nm ZnS—SiO2 layer at different recording powers and subsequently etched with HNO3. The mark widths were measured with AFM, these results are given in
a to 8c show an eighth embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
The recording stack 10 of the master substrate 12 comprises a substrate 90 which can, for example, be a glass substrate or a pre-grooved polycarbonate substrate. On the substrate 90 there is provided a mirror layer 32 for improving the reflection of the recording stack 10. The mirror layer 32 is optional and can be made out of metals like Ag, Al, Si, etc. As long as the layer below the dielectric layer 14 is unetchable by the used etchant, it can be used. This can be the substrate itself, but an added mirror layer 32 improves the overall stack efficiency and makes the bottom surface of the pit 24 smoother.
The recording stack 10 of the master substrate 12 comprises numerous pairs of ZnS—SiO2, a selectively etchable dielectric material, and SnGeSb absorption layers. These absorption layers can be selectively or unselectively etchable. In detail, the illustrated recording stack 10 comprises 10 pairs of 5 nm ZnS—SiO2 and 1 nm SnGeSb phase-change layer provided, i.e. 20 alternating dielectric 14, 54, 58, 62, 66, 70, 74, 78, 82, 86 and absorption layers 16, 56, 60, 64, 68, 72, 76, 80, 84, 88. The SnGeSb absorption layers are, for example, used to indirectly heat the ZnS—SiO2 dielectric layers when exposed to blue (405 nm) laser light (ZnS—SiO2 has hardly no absorption for 405 nm laser wavelength). The heat induces a phase-change in the ZnS—SiO2 dielectric layer. The ZnS—SiO2 layer exhibits selective etching upon laser-induced heating, thereby creating a relief structure after etching. The written state has a much lower etch rate when exposed to chemical reactants, like the acids mentioned above, than the initial unwritten state such that a bump structure remains after etching. If necessary, a covering layer can be used to prevent oxidation or material shifts due to melting (not shown in
With the master substrate 12 of
First, the recording stack 10 shown in
Then, heat induced phase transitions are caused in the regions 22 of the dielectric layers 14, 54, 58, 62, 66, 70, 74, 78, 82, 86 where the pit 24 (
Finally, the first absorption layer 16 and the regions 26 of the dielectric layers 14, 54, 58, 62, 66, 70, 74, 78, 82, 86, which have not experienced a phase transition, are removed together with the adjacent parts the absorption layers 16, 56, 60, 64, 68, 72, 76, 80, 84, 88 by an etching process. The result is shown in
With practical experiments, a recording stack that comprised 10 pairs of 5 nm ZnS—SiO2 and 1 nm SnGeSb phase-change layer provided a well-defined pit structure after etching. With one practical experiment, the recording stack was sputter-deposited on a glass substrate. Bumps and grooves were written with a laser beam recorder (first surface recording, NA=0.9, 405 nm wavelength). With another practical experiment, the recording stack was sputter-deposited on a pre-grooved polycarbonate substrate. This substrate was recorded on a Pulstec with an additional cover layer (second surface recordings, NA=0.85, 405 nm wavelength). The written discs were treated with HNO3 acid solution. The glass sample exposed with a LBR was directly etched. For the polycarbonate sample with recording stack, the cover layer was removed prior to etching. Recording powers ranged between 3 and 5 mW for both types of test samples illustrating that the thin absorption layers introduced indeed absorption in the recording stack. Laser induced heating of the recording stack caused partial crystallization of the as-deposited amorphous phase-change absorption layers. Written data tracks were clearly visible prior to etching. Such a detectable phase-change is of eminent importance if the material is used in combination with a 405 nm laser. In that case, only the top of the focused laser spot is used for writing, making the system very sensitive for power variations. A visually detectable phase change enables the use of the read back signal of the written marks to control the laser write power. This is better known as DRAW (=Direct Read After Write). This is illustrated in
A surface analysis and a sectional analysis of bumps written in the above mentioned stack that was sputter-deposited on the polycarbonate pre-grooved substrate (to enable writing with a Pulstec recorder) is given in
A surface analysis and a sectional analysis of bumps written in the above mentioned stack that was sputter-deposited on the glass substrate is given in
It is to be noted that equivalents and modifications not described above may also be employed without departing from the scope of the invention, which is defined in the accompanying claims.
This embodiment is directed to the growth control of the ZnS nanocrystal size by an annealing process. As already mentioned above, at room temperature, a ZnS—SiO2 film contains tiny nanosized ZnS particles embedded in a SiO2 matrix, wherein the size of the nanocrystals is temperature dependent: increasing the temperature initiates a growing in size of the nanocrystals. This leads to a blue-shift in the light absorption range of ZnS—SiO2. Scattering of blue light through the nano-composite material is assumed to be the main reason for this blue-shift. An annealing process initiates at least the following three effects inside sputtered as-deposited ZnS—SiO2:
1.) The size of the nanocrystals is about 2 nm at room temperature and increases up to 50 nm at 800° C. The size of the nanocrystals is responsible for light absorption at a specific wavelength: the smaller the nanocrystal size the smaller the wavelength absorbed. For that reason, it is possible to tune the light absorption spectrum with the growth of the nanocrystal size with temperature. As can be seen in
2.) A cubic to hexagonal (sphalerite to wurtzite) phase transition occurs between 700° C. and 800° C. in the ZnS nano-particles (see
3.) At 900° C., some parts of the ZnS molecules oxidize to ZnO and then react with SiO2 to form Zn2SiO4. Thus, the surfaces of the nanocrystals are passivated and stabilized against chemical attacks such as wet etching with acids. Thus, this step may also be responsible for the selective etching.
In summary, heating, for example, a thin layer of sputter-deposited ZnS—SiO2 in an oven to 700° C. will cause a blue-shift, enabling the direct recording of marks. When such an annealing step is provided, additional absorption layers or doping at least in some cases are not necessary for recording marks in the ZnS—SiO2, for example with a 405 nm laser beam recorder.
With the embodiment illustrated in
In the untreated condition shown in
d shows the master substrate 12 after it was heated in an oven to about 700° C. By this annealing process the size of the nanocrystals 34 in the ZnS—SiO2 layer increased to about 7.5 nm.
e shows the master substrate 12 after writing, i.e. after laser pulses having a wavelength of 405 nm were applied to a region 22 where a pit is to be formed.
f shows the master substrate 12 after etching. As may be seen, the material in the region 22 was removed and the pit 24 was formed.
a and 10b schematically show the marking mechanism in a dielectric layer 14 of a master substrate 12. The master substrate 12 comprises a recording layer 10 having a single dielectric layer 14 of ZnS—SiO2 deposited on a glass substrate 100.
c to 10h show a comparison of stamper growing with a conventional resist master (
i shows a SEM Scanning Electron Microscopy picture of bumps written in a Ni—ZnS—SiO2 stack (processing: 15 min @ 1% HNO3).
k shows the results of an AFM scan of a bump structure showing underetching features. An 80 nm ZnS—SiO2 layer sputter-deposited on a glass substrate was recorded with a 266 nm laser beam recorder (numerical aperture of 0.9). 17PP data with block pulses was random data recorded at a linear velocity of 2 m/s with powers from 75 to 115 ILV. The disc was treated for 50 s in 0.25% HNO3, revealing the embossed data pattern on the surface of the master. An AFM scan of the obtained bump structure is given in
l shows the results of an AFM scan of a stamper grown on the bump structure of
For example, the inverse polarity processing as described in relation to embodiment 10 in some cases might suffer from the problem of underetching. Possibly, this problem will also occur in connection with other embodiments. The following embodiments 11 to 15 particularly address the problem of underetching, in order to improve the shape of the written and developed structures after wet etching processes.
a and 11b show a eleventh embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
The recording layer stack 10 of the master substrate 12 comprises two dielectric layers 14 of ZnS—SiO2 enclosing an absorption layer 16. The recording layer stack 10 is arranged on a glass substrate 100. Possible absorption layer materials are SbTe, Si, Ag, Al, etc. When the dielectric layer 14 is to fully developed (up to the absorption layer), the absorption layer should be etch-resistant. Absorption layers 16 can be added to the recording stack 10 to induce an extra heat flow from below. Heat is generated in the absorption layer as well, in that way improving the bump shape. After exposure to HNO3 bumps with a taper-like profile remain.
a and 12b show a twelfth embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
a shows schematically the written and developed master substrate 12 comprising a single developed dielectric layer 14 deposited on a glass substrate 100. The master substrate 12 was fully developed and shows regions 114 of underetching. The developed master substrate 12 was covered with a silane film (or other spin-coated organic film) to fill the underetched regions. In
c and 12d show the results of an AFM analysis of a silane treatment of a master substrate 12. Silane was spin-coated on a 80 nm ZnS—SiO2 layer of a 12 cm glass master at a rotation speed of 200 rpm. The substrate was subsequently dried at 1500 rpm to remove the silane excess.
e shows the results of an AFM analysis of a stamper grown on a silane treated master substrate 12. A stamper was grown from the above discussed (
a to 13d show a thirteenth embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
In
e shows the results of an AFM analysis of a stamper grown from a not fully developed master substrate. The master substrate was a 80 nm ZnS—SiO2 master. The bumps were developed to a depth of 60 nm. The bumps are well shaped and the shape is well replicated in the stamper. The problem of underetching and the subsequent dovetail connections, as also discussed above, do not appear.
a to 14e show a fourteenth embodiment of a master substrate 12 in accordance with the present invention during processing by a method in accordance with the invention, wherein
a shows the master substrate 12 after the illumination process defining the written regions 22 and the unwritten regions 26 in the ZnS—SiO2 layer 14 on the glass substrate 100. In
According to a fifteenth embodiment of the invention, the bump shape may be optimized by lowering the absorption of the PTM material. This may be achieved by modifying the ZnS—SiO2 ratio. The default ratio is ZnS—SiO2=80%-20% weight percentage. The proposed ratios are ZnS—SiO2=70%-30% and ZnS—SiO2=60%-40% weight percentage.
It should be clear that the single features of the attached claims can be combined advantageously, even if the claims do not refer back to the respective other claims. Therefore, all possible combinations of the features of the claims shall be regarded as being disclosed herewith. The same applies to features mentioned only in the description.
| Number | Date | Country | Kind |
|---|---|---|---|
| 05100048.7 | Jan 2005 | EP | regional |
| 05102457.8 | Mar 2005 | EP | regional |
| 05106409.5 | Jul 2005 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/IB2006/050005 | 1/2/2006 | WO | 00 | 6/28/2007 |
