EP2559054A1 - Lithography method with combined optimisation of radiated energy and design geometry - Google Patents

Lithography method with combined optimisation of radiated energy and design geometry

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Publication number
EP2559054A1
EP2559054A1 EP11714291A EP11714291A EP2559054A1 EP 2559054 A1 EP2559054 A1 EP 2559054A1 EP 11714291 A EP11714291 A EP 11714291A EP 11714291 A EP11714291 A EP 11714291A EP 2559054 A1 EP2559054 A1 EP 2559054A1
Authority
EP
European Patent Office
Prior art keywords
dose
radiated
pattern
adjustment
lithography
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Ceased
Application number
EP11714291A
Other languages
German (de)
French (fr)
Inventor
Serdar Manakli
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Original Assignee
Commissariat a lEnergie Atomique CEA
Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Publication date
Application filed by Commissariat a lEnergie Atomique CEA, Commissariat a lEnergie Atomique et aux Energies Alternatives CEA filed Critical Commissariat a lEnergie Atomique CEA
Publication of EP2559054A1 publication Critical patent/EP2559054A1/en
Ceased legal-status Critical Current

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Classifications

    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
    • H01J37/317—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/70—Microphotolithographic exposure; Apparatus therefor
    • G03F7/70483—Information management; Active and passive control; Testing; Wafer monitoring, e.g. pattern monitoring
    • G03F7/7055—Exposure light control in all parts of the microlithographic apparatus, e.g. pulse length control or light interruption
    • G03F7/70558—Dose control, i.e. achievement of a desired dose
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y40/00—Manufacture or treatment of nanostructures
    • G—PHYSICS
    • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
    • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
    • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
    • G03F7/20—Exposure; Apparatus therefor
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01J—ELECTRIC DISCHARGE TUBES OR DISCHARGE LAMPS
    • H01J37/00—Discharge tubes with provision for introducing objects or material to be exposed to the discharge, e.g. for the purpose of examination or processing thereof
    • H01J37/30—Electron-beam or ion-beam tubes for localised treatment of objects
    • H01J37/317—Electron-beam or ion-beam tubes for localised treatment of objects for changing properties of the objects or for applying thin layers thereon, e.g. for ion implantation
    • H01J37/3174—Particle-beam lithography, e.g. electron beam lithography

Definitions

  • the present invention applies to the field of electronic lithography.
  • the costs of equipment and developments for a new generation of technology are consequently increasing in very high proportions.
  • Today, the critical dimensions accessible in photolithography are greater than or equal to 65 nm.
  • the 32-45 nm generation is under development and there is no viable solution for technology nodes below 22 nm.
  • the present invention solves this problem by providing a method of combined optimization of the energy of the applied electronic radiation and the area of application which makes it possible to reduce in significant proportions the necessary increase in the radiation dose and therefore the times. exposure.
  • the invention provides a method of radiation lithography of at least one pattern to be etched on a resinated support comprising a step of calculating modulation of at least one radiated dose and a step of calculating at least one adjustment to be made to said pattern to be etched in at least one direction of the medium, said method being characterized in that said adjustment is a function of the energy latitude of the process at the point where the radiated dose is received and in that the modulation of the dose radiated is modified according to said at least one adjustment of said at least one pattern.
  • the modulation calculation step of at least one radiated dose is performed by convolution of said pattern with a function of distributing said radiated dose on said support.
  • said radiated dose is calculated before modulation under stress that the average radiated dose is substantially at a level of the sensitivity threshold of the resin chosen as a parameter.
  • the sensitivity threshold level parameter of the resin is chosen substantially equal to 0.5.
  • the energy latitude (EL) of the process at the point where the radiated dose is received is calculated as belonging to the group consisting of the slope of the tangent at this point to the curve of the doses received, the contrast of the radiated doses and the slope of dose.
  • the adjustment to be made to the pattern centered on one of the reception points of a dose radiated in the at least one direction is calculated as being equal to the distance oriented on the sensitivity threshold line of the resin at 0.5. the process between the intersection of said threshold line with the tangent of slope EL to the curve of the doses received at said reception point and secondly the radiation dose curve.
  • the calculation steps for modulation of the radiated dose and adjustment of the pattern to be etched are repeated for as long as the dose variation radiated on a reception point of a modulation calculation to the previous one remains greater than a predetermined threshold value.
  • the modulation calculation step of at least one radiated dose is performed using a parameter table.
  • the doses radiated in the middle of the pattern before adjustment are all substantially equal to a normal dose.
  • the doses radiated in the middle of the pattern before adjustment are all substantially equal to a percentage of a normal dose.
  • the percentage of a normal dose is set at a value substantially equal to 70% of said normal dose.
  • said adjustment comprises at least one spacing without radiation and at least one radiated dose.
  • a dose is radiated outside the pattern to be etched.
  • said at least one dose radiated outside the pattern to be etched is spaced from the pattern to be etched by a distance of between 0.2 times and 3 times the bandwidth.
  • the invention also provides a computer program comprising program code instructions for performing the radiation lithography method of at least one pattern to be engraved on a resinated support when the program is performed on a computer, said program comprising a module for calculating modulation of at least one radiated dose and a module for calculating at least one adjustment to be made to said pattern to be etched in at least one direction of the medium, said program of computer characterized in that said adjustment calculation to be made to the pattern is a function of the energy latitude of the process at the point where the radiated dose is received and in that the modulation of the radiated dose is changed according to the at least one adjustment of the at least one pattern.
  • the invention also has the advantage of correcting the adverse effects of prior art proximity correction methods, such as the loss of linearity, the increase in the IDB (Isolated Dense Bias ie difference between critical dimensions for isolated and dense structures), increased shortening of line endings ("Line End Shortening” or “LES”), loss of precision due to corner rounding effects, reduction energy latitude (“Energy Latitude” or “EL”) that occur when these methods are applied.
  • These defects of proximity effect correction methods such as those described in US Pat. No. 6,107,207 have been exposed in particular in the S. Manakli publication, “New Electron Beam Proximity Effect Correction Approach for 45 and 32 nm Nodes", Japanese Journal of Applied Physics, Vol. 45, No. 8A, pp. 6462-6467.
  • FIGS. 1 a and 1 b respectively show schematically a network of dense lines to be etched and a distribution of the radiated doses after application of a correction method of the prior art to the radiated doses;
  • FIG. 2 is a graphical representation of the proximity effect correction function applied by a method of the prior art
  • FIG. 3 represents the distribution of the dose radiated in one direction with respect to the critical dimension
  • FIG. 4 represents the radiated dose distribution with and without correction of proximity effects in the case of a network of dense lines;
  • FIG. 5 represents a transversal view and an aerial view of the radiated dose distribution showing the energy latitude
  • FIG. 6 illustrates the principle of optimizing the energy latitude on the edges of a network of dense lines according to one embodiment of the invention
  • FIG. 7 shows the new process window resulting from the application of the method of the invention in one of its embodiments
  • FIG. 7bis illustrates the principle of optimizing the energy latitude on the edges of a network of dense lines according to one embodiment of the invention in which at least one pattern is etched outside said network;
  • FIGS. 8a and 8b illustrate the results of the application of the method of the invention to a dense network
  • FIG. 9 represents a flowchart of the central part of the method for implementing the invention according to one of its embodiments.
  • FIG. 10 graphically illustrates the central portion of the proximity effect correction method in one embodiment of the invention.
  • FIGS. 1a and 1b respectively show schematically a network of dense lines to be etched and a distribution of the radiated doses after application of a correction method of the prior art to the radiated doses.
  • Figure 1a shows a dense network of lines to be engraved on a portion of wafer or mask.
  • the spacing between lines of the network will typically be from one to several tens of nanometers.
  • the beam (s) of electrons used for etching this grating diffuse notably in short distance (forward scattering or blur) in the resin and the substrate on the edges of the center of the beam, which increases the size of the beam and reduces the contrast.
  • the electrons are completely backscattered over a long distance (backward scattering).
  • the radiated dose distribution around the desired critical dimension of etching in a sectional plane of a line of the grating is illustrated in FIG. 3.
  • the alpha, 31, and beta regions 32 of the different lines are superimposed on each other. which causes a gap between the etched network and the drawn network created by these proximity effects resulting from these diffusions which are mixed. At the end of the line and at the edge of the network, there is no overlap.
  • the patterns of the network are therefore modified asymmetrically as illustrated by curve 41 of FIG. 4: the dose received at the edge of the network is smaller than that received in the middle of the network.
  • a conventional method of correcting the proximity effects of a lithography process then consists of modulating the radiated doses and increasing those applied to the lines situated at the edge of the network to compensate for this relative decrease in exposure.
  • the result of the application of such a method on the radiated dose distribution is illustrated by the curve 42 of FIG.
  • the unit is first fractured and then the radiated dose modulations are calculated for each unit element.
  • computation using a convolution is one of the most efficient, one can imagine other types of calculations:
  • a convolution function of the electron distribution in the material is applied for calculating the modulation to be applied to the radiation at each etching step.
  • Said convolution function is given in FIG. 2 in which:
  • - D (x, y) represents the distribution in the plane of the substrate (x, y) of the dose received on the pattern to be etched;
  • f (x, y) represents the surface distribution of the dose emitted with modeling of proximity effects; the hypothesis of a Gaussian distribution of proximity effects is generally made, as shown in Figure 3; the distribution function is modeled by dual integration of the Point Spread Function ("PSF") which is itself a combination of Gaussian error functions (ERF function); f (x, y) is modeled by the formula:
  • PSF Point Spread Function
  • ERP Gaussian error functions
  • o a is the width of the direct radiation
  • o ⁇ is the ratio of direct and backscattered radiation intensities.
  • ⁇ , ⁇ and ⁇ are determined experimentally for a given process. These parameters depend on the acceleration voltage of the machine. Typically for an acceleration voltage of the order of 50KV, a is of the order of 50nm, ⁇ of the order of 10 ⁇ and ⁇ of the order of 0.5.
  • error modeling is used with two ERF functions. One can also use error modeling with one, three, four or even more ERF functions. It is also possible to use other types of modeling, for example polynomials.
  • the application of the inverse transformation (deconvolution) makes it possible to calculate the modulation to be applied to the radiated dose at each step of the process.
  • the inversion can also be done other than by deconvolution, for example by applying an optimization function, a resolution of a system of equations or an iterative procedure.
  • Other exemplary embodiments are given in the present description.
  • Figure 1b illustrates the distribution of radiated doses after applying the above correction method to the line network of Figure 1a.
  • the significant increase in radiated doses to be applied at the edge of the network significantly increases the duration of the necessary exposure, which is a limitation of this prior art that the present invention overcomes.
  • the exposure time must be multiplied by a factor of 2 to 4 on the network edges with respect to the center.
  • FIG. 5 is a simplified representation, in the case of application of a method of the prior art presented above, of the distribution of the radiated doses over the entire width of the network in the modulation method described above (bars 51 of Figure 5) and an aerial view of this distribution (curve 52 of Figure 5) which represents the process window.
  • the line 53 represents the sensitivity threshold of the resin at 0.5 times the normal dose.
  • a threshold of 0.5 is advantageous, but other values may also be chosen.
  • the chosen threshold value then constitutes a parameter that can chosen in the computer program designed to implement the method of the invention.
  • the line 54 represents the energy latitude slope of the process at the point of shot applied by the radiation device.
  • the size of a shot 55 located in the middle of the pattern is in the exemplary embodiment described here of 1.6 m ⁇ 1.6 ⁇ m.
  • the dose applied at these points away from the edges of the pattern will be equal to the standard dose (standardized to 1).
  • the devices of the prior art apply much higher doses (typically from 2 to 4 or even 6) with smaller shots, typically 1 ⁇ x 1 ⁇ .
  • the increase in the exposure time results both from the increase in the number of shots related to the specific physical fracturing performed at the edges (almost doubled) and the increase of the doses radiated on these shots of the edges.
  • FIGS. 6 and 7 The method of the invention, and its distinguishing characteristics with respect to the methods of the prior art presented above are illustrated in FIGS. 6 and 7 which must be read in comparison with FIG. 5.
  • radiation dose 61 1a, 612a, 613a, 614a, 615a, (and their symmetries on the other edge of the network to be etched) which are applied by a method of the prior art and which can be removed by a method according to a first embodiment of the invention, the radiated doses 61 1, 612, 613, 614, 615 (as well as doses radiated on the other edge of the network of lines to be etched).
  • the gain in exposure time is of the order of 62% (the cumulative dose increases from 90 to 34 normal doses).
  • the gain is squared and is therefore in the above example of the order of 86%.
  • FIG. 7 illustrates the impact of the method of the invention on the curve of the received dose which is shifted from 710 to 720.
  • the received dose resulting from the application of the method of the invention 720 thus has, as illustrated, a straight front which translates a greater energy latitude, and slightly shifted towards the outside of the network, which translates an elimination of the effects of proximity.
  • the methods for the joint calculation of the doses radiated at each shot, the widening of the edges of the network and the energy latitude are explained later in the description in comments in FIGS. 9 and 10.
  • FIG. 7bis illustrates the principle of optimization the energy latitude on the edges of a network of dense lines according to one embodiment of the invention wherein at least one pattern is etched outside said network.
  • Another advantageous embodiment consists in leaving a space, 620bis, between the pattern to be etched and the band added, 61 Obis, and, optionally, adding at least a second outer band, 630bis, also separated from the first by a space.
  • this spacing improves the energy latitude of the process.
  • the dose applied to the medium of the motif can be reduced, for example by 30%, to 0.7 times the normal dose without degradation of the quality of engraving.
  • Other values are however possible. These values constituting a parameter that can be chosen in the computer program configured to implement the method of the invention.
  • Figures 8a and 8b illustrate the results of the application of the method of the invention to a dense network.
  • FIG. 8a illustrates, on the one hand, the pattern to be engraved, 810, on the other hand the pattern corrected by the method of the invention, 820.
  • Figure 8b illustrates the actually etched pattern.
  • FIG. 9 represents a flowchart of the central part of the method for implementing the invention according to one of its embodiments.
  • the illustrated example is that of a combination of a resizing of the patterns to be etched and a dose modulation as shown in FIG.
  • the method of the invention begins with a reading of the design.
  • the lay-out of the patterns to be engraved is conventionally encoded in files in GDS II format (Graphie Data System version2) or OASIS (Open Artwork System Interchange Standard).
  • the data is normally grouped by cell.
  • the pattern to be etched is then pre-fractured into compatible subassemblies of the transfer device (direct or electronic etching, manufacture of masks for electronic or optical etching, etc.).
  • the ideal dose of the shot is calculated so that, on average, all midpoints of the edges of the shot shot are adjusted to the threshold of sensitivity of the resin, for example to 0.5 times the normal dose, other values being possible, said threshold can be set as a parameter in the computer program configured to implement the method of the invention.
  • the slope EL of the dose curve is calculated at this point which is equal to the process window or energy latitude.
  • next step 930 a linear interpolation is calculated at this point of the dose curve.
  • next step 940 the point of intersection between the linear interpolation and the 0.5 threshold is calculated.
  • the Edge Placement Error (EPE) is calculated which is equal to the distance between the intersection point at the exit of step 940 and the edge of the shot.
  • the edge of the pattern to be engraved is corrected by applying to the initial pattern the distance oriented at the output of the preceding step.
  • This basic process is adjusted to take into account the space available on both sides of the pattern. If there is enough space to add extra bands to the outside of the design, this is the preferred solution.
  • a uniform normal dose (or reduced to 0.7, as indicated above) is applied inside the pattern in substitution for modulations calculated everywhere except on the border (s) on the outside of the pattern.
  • the dose applied outside the initial design pattern can be calculated by applying the convolution formulas discussed above or by using an experience parameter table.
  • the resizing is limited and the results of the dose modulation calculation are used.
  • the dose modulation is then readjusted from the design correction.
  • the correction process is repeated until the dose variation from one iteration on the loop to the next is less than a threshold.
  • the process is repeated 2 or 3 times to take into account the profiles introduced on the neighboring patterns. For example, initialize with a resizing of 500 nm and stop at 1 or 1, 5 ⁇ . In this case the slope EL does not move from one iteration to another.
  • Figure 10 graphically illustrates the method of correcting proximity effects in one embodiment of the invention.
  • Segments 1010 represent the initial shot.
  • Curve 1020 represents the dose received.
  • the line 1030 represents the threshold at 0.5.
  • the line 1040 represents the interpolated line at the output of step 930.
  • the oriented segment 1050 represents ⁇ which gives the correction applied to the initial pattern to be engraved.
  • ⁇ which gives the correction applied to the initial pattern to be engraved.
  • TEL defined as the slope of Dose (x).
  • the method of the invention has been described in an exemplary application to a direct write electronic lithography method. It can also be applied to another direct writing method using other particles such as ions, photons or electronic or optical lithography methods using masks.

Abstract

The invention relates to a method for the lithography of a pattern to be etched onto a support, especially a method using electron radiation writing directly onto the support. Until now, the methods for correcting proximity effects for dense network geometries (line spacings of between 10 and 30 nm) have resulted in a significant increase in the radiated doses and therefore the exposition time. According to the invention, the patterns to be etched are modified according to the energy latitude of the method, enabling the radiated doses to be reduced.

Description

PROCEDE DE LITHOGRAPHIE A OPTIMISATION COMBINEE DE L'ENERGIE RAYONNEE ET DE LA GEOMETRIE DE DESSIN La présente invention s'applique au domaine de la lithographie électronique. Pour permettre la gravure de motifs dont la dimension critique est inférieure à 50nm, il faut intégrer dans les procédés de photolithographie optique des méthodes de correction des distorsions optiques de plus en plus complexes à la fois au stade de la conception et de la production des masques et au stade de l'exposition. Les coûts des équipements et des développements pour une nouvelle génération de technologie augmentent en conséquence dans des proportions très élevées. Aujourd'hui, les dimensions critiques accessibles en photolithographie sont supérieures ou égales à 65 nm. La génération 32-45 nm est en cours de développement et il n'existe pas de solution viable envisagée pour les nœuds technologiques inférieurs à 22 nm. De son côté, la lithographie électronique permet dores et déjà la gravure de motifs de 22 nm ; elle ne nécessite pas de masque et offre un temps de développement assez court, ce qui permet une meilleure réactivité et flexibilité dans la réalisation d'améliorations aux technologies et aux designs. En revanche, les temps de production sont structurellement sensiblement plus élevés qu'en photolithographie puisqu'il faut réaliser une exposition par pas (avec un « stepper »), alors que la photolithographie ne nécessite qu'une exposition par couche. De plus, en lithographie électronique comme en photolithographie, se produisent des effets de proximité, notamment entre lignes voisines d'un motif qui ne sont séparées que de 10 à 30 nm. Pour garantir la fidélité du dessin, il est donc nécessaire de corriger ces effets de proximité. Les méthodes de l'art antérieur, notamment celle décrite dans le brevet US 6,107,207, réalisent ces corrections en augmentant les doses de rayonnement en bord de ligne. Cette augmentation de dose se traduit par une nouvelle augmentation des temps d'exposition, ce qui constitue un handicap très important pour la diffusion industrielle de cette technologie. La présente invention résout ce problème en procurant une méthode d'optimisation combinée de l'énergie du rayonnement électronique appliqué et de la zone d'application qui permet de réduire dans des proportions importantes l'augmentation nécessaire de la dose de rayonnement et donc des temps d'exposition. A cet effet, l'invention prévoit un procédé de lithographie par rayonnement d'au moins un motif à graver sur un support résiné comprenant une étape de calcul de modulation d'au moins une dose rayonnée et une étape de calcul d'au moins un ajustement à apporter audit motif à graver selon au moins une direction du support, ledit procédé étant caractérisé en ce que ledit ajustement est fonction de la latitude en énergie du procédé au point où est reçue la dose rayonnée et en ce que la modulation de la dose rayonnée est modifiée en fonction dudit au moins un ajustement dudit au moins un motif. Avantageusement, l'étape de calcul de modulation d'au moins une dose rayonnée est opérée par convolution dudit motif avec une fonction de répartition de ladite dose rayonnée sur ledit support. The present invention applies to the field of electronic lithography. To allow the etching of patterns whose critical dimension is less than 50nm, methods of correcting optical distortions that are more and more complex both at the mask design and production stage must be integrated into optical photolithography processes. and at the exhibition stage. The costs of equipment and developments for a new generation of technology are consequently increasing in very high proportions. Today, the critical dimensions accessible in photolithography are greater than or equal to 65 nm. The 32-45 nm generation is under development and there is no viable solution for technology nodes below 22 nm. On the other hand, electronic lithography already allows etching patterns of 22 nm; it does not require a mask and offers a short development time, which allows a better reactivity and flexibility in the realization of improvements to technologies and designs. On the other hand, the production times are structurally significantly higher than in photolithography since it is necessary to realize a stepwise exposure (with a "stepper"), whereas the photolithography requires only one exposure per layer. Moreover, in electronic lithography as in photolithography, proximity effects occur, especially between lines close to a pattern which are only separated by 10 to 30 nm. To guarantee the fidelity of the drawing, it is therefore necessary to correct these proximity effects. The methods of the prior art, in particular that described in US Pat. No. 6,107,207, make these corrections by increasing the radiation doses at the edge of the line. This dose increase results in a further increase in exposure times, which is a very important handicap for the industrial spread of this technology. The present invention solves this problem by providing a method of combined optimization of the energy of the applied electronic radiation and the area of application which makes it possible to reduce in significant proportions the necessary increase in the radiation dose and therefore the times. exposure. For this purpose, the invention provides a method of radiation lithography of at least one pattern to be etched on a resinated support comprising a step of calculating modulation of at least one radiated dose and a step of calculating at least one adjustment to be made to said pattern to be etched in at least one direction of the medium, said method being characterized in that said adjustment is a function of the energy latitude of the process at the point where the radiated dose is received and in that the modulation of the dose radiated is modified according to said at least one adjustment of said at least one pattern. Advantageously, the modulation calculation step of at least one radiated dose is performed by convolution of said pattern with a function of distributing said radiated dose on said support.
Avantageusement, ladite dose rayonnée est calculée avant modulation sous contrainte que la dose moyenne rayonnée se situe sensiblement à un niveau du seuil de sensibilité de la résine choisi comme paramètre. Advantageously, said radiated dose is calculated before modulation under stress that the average radiated dose is substantially at a level of the sensitivity threshold of the resin chosen as a parameter.
Avantageusement, le paramètre de niveau de seuil de sensibilité de la résine est choisi sensiblement égal à 0,5. Advantageously, the sensitivity threshold level parameter of the resin is chosen substantially equal to 0.5.
Avantageusement, la latitude en énergie (EL) du procédé au point où est reçue la dose rayonnée est calculée comme appartenant au groupe constitué par la pente de la tangente en ce point à la courbe des doses reçues, le contraste des doses rayonnées et la pente de dose. Advantageously, the energy latitude (EL) of the process at the point where the radiated dose is received is calculated as belonging to the group consisting of the slope of the tangent at this point to the curve of the doses received, the contrast of the radiated doses and the slope of dose.
Avantageusement, l'ajustement à apporter au motif centré sur un des points de réception d'une dose rayonnée selon la au moins une direction est calculé comme étant égal à la distance orientée sur la droite de seuil de sensibilité de la résine à 0,5 du procédé entre l'intersection de ladite droite de seuil avec d'une part la tangente de pente EL à la courbe des doses reçues audit point de réception et d'autre part la courbe de dose rayonnée. Advantageously, the adjustment to be made to the pattern centered on one of the reception points of a dose radiated in the at least one direction is calculated as being equal to the distance oriented on the sensitivity threshold line of the resin at 0.5. the process between the intersection of said threshold line with the tangent of slope EL to the curve of the doses received at said reception point and secondly the radiation dose curve.
Avantageusement, les étapes de calcul de modulation de dose rayonnée et d'ajustement du motif à graver sont répétées tant que la variation de dose rayonnée sur un point de réception d'un calcul de modulation au précédent reste supérieure à une valeur de seuil prédéterminée. Advantageously, the calculation steps for modulation of the radiated dose and adjustment of the pattern to be etched are repeated for as long as the dose variation radiated on a reception point of a modulation calculation to the previous one remains greater than a predetermined threshold value.
Avantageusement, l'étape de calcul de modulation d'au moins une dose rayonnée est opérée en utilisant une table de paramètres. Advantageously, the modulation calculation step of at least one radiated dose is performed using a parameter table.
Avantageusement, les doses rayonnées au milieu du motif avant ajustement sont toutes sensiblement égales à une dose normale. Avantageusement, les doses rayonnées au milieu du motif avant ajustement sont toutes sensiblement égales à un pourcentage d'une dose normale. Advantageously, the doses radiated in the middle of the pattern before adjustment are all substantially equal to a normal dose. Advantageously, the doses radiated in the middle of the pattern before adjustment are all substantially equal to a percentage of a normal dose.
Avantageusement, le pourcentage d'une dose normale est fixé à une valeur sensiblement égale à 70% de ladite dose normale. Advantageously, the percentage of a normal dose is set at a value substantially equal to 70% of said normal dose.
Avantageusement, ledit ajustement comprend au moins un espacement sans rayonnement et au moins une dose rayonnée. Advantageously, said adjustment comprises at least one spacing without radiation and at least one radiated dose.
Avantageusement, une dose est rayonnée à l'extérieur du motif à graver. Advantageously, a dose is radiated outside the pattern to be etched.
Avantageusement, ladite au moins une dose rayonnée à l'extérieur du motif à graver est espacée du motif à graver d'une distance comprise entre 0,2 fois et 3 fois la largeur de bande. Advantageously, said at least one dose radiated outside the pattern to be etched is spaced from the pattern to be etched by a distance of between 0.2 times and 3 times the bandwidth.
Pour mettre en œuvre le procédé, l'invention prévoit également un programme d'ordinateur comprenant des instructions de code de programme permettant l'exécution du procédé de lithographie par rayonnement d'au moins un motif à graver sur un support résiné lorsque le programme est exécuté sur un ordinateur, ledit programme comprenant un module de calcul de modulation d'au moins une dose rayonnée et un module de calcul d'au moins un ajustement à apporter audit motif à graver selon au moins une direction du support, ledit programme d'ordinateur étant caractérisé en ce que ledit calcul d'ajustement à apporter au motif est fonction de la latitude en énergie du procédé au point où est reçue la dose rayonnée et en ce que la modulation de la dose rayonnée est modifiée en fonction dudit au moins un ajustement dudit au moins un motif. To implement the method, the invention also provides a computer program comprising program code instructions for performing the radiation lithography method of at least one pattern to be engraved on a resinated support when the program is performed on a computer, said program comprising a module for calculating modulation of at least one radiated dose and a module for calculating at least one adjustment to be made to said pattern to be etched in at least one direction of the medium, said program of computer characterized in that said adjustment calculation to be made to the pattern is a function of the energy latitude of the process at the point where the radiated dose is received and in that the modulation of the radiated dose is changed according to the at least one adjustment of the at least one pattern.
L'invention présente en outre l'avantage de corriger les effets défavorables des méthodes de correction des effets de proximité de l'art antérieur, tels que la perte de linéarité, l'augmentation de l'IDB (Isolated Dense Bias ie différence entre les dimensions critiques pour des structures isolées et denses), l'augmentation du raccourcissement des fins de ligne (Line End Shortening ou « LES »), la perte de précision due aux effets d'arrondissement des coins (« corner rounding »), la réduction de la latitude en énergie («Energy Latitude ou « EL ») qui se produisent lorsque ces méthodes sont appliquées. Ces défauts des méthodes de correction des effets de proximité telles que celles décrites dans le brevet US 6,107,207 ont été exposés notamment dans la publication de S. Manakli, « New Electron Beam Proximity Effect Correction Approach for 45 and 32 nm Nodes », Japanese Journal of Applied Physics, Vol. 45, N °8A, pp. 6462-6467. The invention also has the advantage of correcting the adverse effects of prior art proximity correction methods, such as the loss of linearity, the increase in the IDB (Isolated Dense Bias ie difference between critical dimensions for isolated and dense structures), increased shortening of line endings ("Line End Shortening" or "LES"), loss of precision due to corner rounding effects, reduction energy latitude ("Energy Latitude" or "EL") that occur when these methods are applied. These defects of proximity effect correction methods such as those described in US Pat. No. 6,107,207 have been exposed in particular in the S. Manakli publication, "New Electron Beam Proximity Effect Correction Approach for 45 and 32 nm Nodes", Japanese Journal of Applied Physics, Vol. 45, No. 8A, pp. 6462-6467.
En outre, compte tenu des modalités de calcul des corrections, une automatisation des calculs de correction de manière intégrée aux outils de conception assistée par ordinateur est réalisable, ce qui procure l'avantage inestimable d'offrir aux utilisateurs du système et du procédé selon l'invention une conversion de leurs bibliothèques de composants standard à coût réduit. In addition, taking into account the correction calculation modalities, automation of correction calculations in an integrated manner to computer-aided design tools is feasible, which provides the invaluable benefit of providing system and process invention a conversion of their libraries of standard components at reduced cost.
L'invention sera mieux comprise, ses différentes caractéristiques et avantages ressortiront de la description qui suit de plusieurs exemples de réalisation et de ses figures annexées dont : The invention will be better understood, its various features and advantages will emerge from the following description of several embodiments and its accompanying figures, including:
- Les figures 1 a et 1 b représentent respectivement de manière schématique un réseau de lignes denses à graver et une répartition des doses rayonnées après application d'une méthode de correction de l'art antérieur aux doses rayonnées;  FIGS. 1 a and 1 b respectively show schematically a network of dense lines to be etched and a distribution of the radiated doses after application of a correction method of the prior art to the radiated doses;
- La figure 2 représente de manière graphique la fonction de correction des effets de proximité appliquée par une méthode de l'art antérieur ; FIG. 2 is a graphical representation of the proximity effect correction function applied by a method of the prior art;
- La figure 3 représente la distribution de la dose rayonnée selon une direction par rapport à la dimension critique ; - La figure 4 représente la distribution de dose rayonnée avec et sans correction d'effets de proximité dans le cas d'un réseau de lignes denses ; FIG. 3 represents the distribution of the dose radiated in one direction with respect to the critical dimension; FIG. 4 represents the radiated dose distribution with and without correction of proximity effects in the case of a network of dense lines;
- La figure 5 représente une vue transversale et une vue aérienne de la répartition de dose rayonnée mettant en évidence la latitude en énergie ;  FIG. 5 represents a transversal view and an aerial view of the radiated dose distribution showing the energy latitude;
- La figure 6 illustre le principe d'optimisation de la latitude en énergie sur les bords d'un réseau de lignes denses selon un mode de réalisation de l'invention;  FIG. 6 illustrates the principle of optimizing the energy latitude on the edges of a network of dense lines according to one embodiment of the invention;
- La figure 7 montre la nouvelle fenêtre de procédé résultant de l'application du procédé de l'invention dans un de ses modes de réalisation ;  FIG. 7 shows the new process window resulting from the application of the method of the invention in one of its embodiments;
- La figure 7bis illustre le principe d'optimisation de la latitude en énergie sur les bords d'un réseau de lignes denses selon un mode de réalisation de l'invention dans lequel au moins un motif est gravé à l'extérieur dudit réseau ;  FIG. 7bis illustrates the principle of optimizing the energy latitude on the edges of a network of dense lines according to one embodiment of the invention in which at least one pattern is etched outside said network;
- Les figures 8a et 8b illustrent les résultats de l'application du procédé de l'invention à un réseau dense ;  FIGS. 8a and 8b illustrate the results of the application of the method of the invention to a dense network;
- La figure 9 représente un organigramme de la partie centrale du procédé pour mettre en œuvre l'invention selon un de ses modes de réalisation ;  FIG. 9 represents a flowchart of the central part of the method for implementing the invention according to one of its embodiments;
- La figure 10 illustre de manière graphique la partie centrale du procédé de correction des effets de proximité dans un mode de réalisation de l'invention.  FIG. 10 graphically illustrates the central portion of the proximity effect correction method in one embodiment of the invention.
Les figures 1 a et 1 b représentent respectivement de manière schématique un réseau de lignes denses à graver et une répartition des doses rayonnées après application d'une méthode de correction de l'art antérieur aux doses rayonnées. FIGS. 1a and 1b respectively show schematically a network of dense lines to be etched and a distribution of the radiated doses after application of a correction method of the prior art to the radiated doses.
La figure 1 a représente un réseau dense de lignes à graver sur une portion de wafer ou de masque. Dans les applications visées par le procédé de l'invention, l'espacement entre lignes du réseau sera typiquement de une à quelques dizaines de nanomètres. Le ou les faisceaux d'électrons utilisés pour effectuer la gravure de ce réseau diffusent notamment sur courte distance (forward scattering ou blur) dans la résine et le substrat sur les bords du centre du faisceau, ce qui accroît la taille du faisceau et en réduit le contraste. De plus, les électrons sont complètement rétrodiffusés sur une longue distance (backward scattering). La distribution de dose rayonnée autour de la dimension critique recherchée de la gravure dans un plan de coupe d'une ligne du réseau est illustrée sur la figure 3. Les régions alpha, 31 , et bêta, 32, des différentes lignes se superposent, ce qui entraîne un écart entre le réseau gravé et le réseau dessiné créé par ces effets de proximité résultant de ces diffusions qui se mélangent. En bout de ligne et en bord de réseau, il n'y a pas de superposition. Les motifs du réseau sont donc modifiés de manière dissymétrique comme illustré sur par la courbe 41 de la figure 4 : la dose reçue en bord de réseau est inférieure à celle qui est reçue au milieu du réseau. Figure 1a shows a dense network of lines to be engraved on a portion of wafer or mask. In the applications targeted by the method of the invention, the spacing between lines of the network will typically be from one to several tens of nanometers. The beam (s) of electrons used for etching this grating diffuse notably in short distance (forward scattering or blur) in the resin and the substrate on the edges of the center of the beam, which increases the size of the beam and reduces the contrast. In addition, the electrons are completely backscattered over a long distance (backward scattering). The radiated dose distribution around the desired critical dimension of etching in a sectional plane of a line of the grating is illustrated in FIG. 3. The alpha, 31, and beta regions 32 of the different lines are superimposed on each other. which causes a gap between the etched network and the drawn network created by these proximity effects resulting from these diffusions which are mixed. At the end of the line and at the edge of the network, there is no overlap. The patterns of the network are therefore modified asymmetrically as illustrated by curve 41 of FIG. 4: the dose received at the edge of the network is smaller than that received in the middle of the network.
Une méthode classique de correction des effets de proximité d'un procédé de lithographie consiste alors à moduler les doses rayonnées an augmentant celles appliquées aux lignes situées en bord de réseau pour compenser cette baisse relative d'exposition. Le résultat de l'application d'une telle méthode sur la distribution de dose rayonnée est illustré par la courbe 42 de la figure 4.  A conventional method of correcting the proximity effects of a lithography process then consists of modulating the radiated doses and increasing those applied to the lines situated at the edge of the network to compensate for this relative decrease in exposure. The result of the application of such a method on the radiated dose distribution is illustrated by the curve 42 of FIG.
Des méthodes de correction de ce type sont décrites notamment dans le brevet US 6,107,207 (« Procédure for generating information for producing a pattern defined by design information », inventeurs Wass, Hartmann) et dans plusieurs publications, notamment H. Eisenmann, T. Waas, H. Hartmann, « Proximity effect correction by convolution », J. Vac. Sci. Technol. B1 1 (6), 2741 -2745 (1993). Dans le procédé décrit par ces publications, le dispositif de lithographie électronique applique pas à pas sur le substrat enduit de résine une dose de rayonnement électronique d'énergie réglée en fonction des caractéristiques du substrat, de la résine et des motifs à dessiner. Dans les procédés décrits par ces publications, de même que dans le procédé de l'invention, on peut utiliser n'importe quel dispositif de lithographie électronique, par exemple une machine de marque SB 3054 de VISTEC™ configuré avec un logiciel de modulation de dose de marque PROXECCO™ .  Correction methods of this type are described in particular in the US Patent 6,107,207 ("Procedure for generating information for a pattern defined by design information", inventors Wass, Hartmann) and in several publications, including H. Eisenmann, T. Waas, H. Hartmann, Proximity effect correction by convolution, J. Vac. Sci. Technol. B1 1 (6), 2741-2745 (1993). In the process described by these publications, the electronic lithography device applies stepwise on the resin-coated substrate a dose of electronic energy radiation adjusted according to the characteristics of the substrate, the resin and the patterns to be drawn. In the processes described by these publications, as well as in the process of the invention, any electronic lithography device, for example a VISTEC ™ brand machine SB 3054 configured with a dose modulation software, can be used. PROXECCO ™ brand.
On commence par fracturer le motif à reporter en éléments unitaires puis, pour chaque élément unitaire on calcule les modulations de doses rayonnées. Bien que le calcul à l'aide d'une convolution soit un des plus efficaces, on peut imaginer d'autres types de calculs : The unit is first fractured and then the radiated dose modulations are calculated for each unit element. Although computation using a convolution is one of the most efficient, one can imagine other types of calculations:
- un calcul à base de tirage de monte-carlo  - a calculation based on the drawing of monte-carlo
- éventuellement, un calcul basée sur une recherche totale ou partielle dans des tables précalculées  - possibly, a calculation based on a total or partial search in pre-calculated tables
- on peut aussi avoir une étape par convolution qui modélise l'effet purement électronique suivi d'un calcul qui prend en compte d'autres phénomènes qui se produisent au cours de l'étape de lithographie, telles que la contribution de la résine, de la gravure, ou d'autres éléments.  - we can also have a convolution step that models the purely electronic effect followed by a calculation that takes into account other phenomena that occur during the lithography step, such as the contribution of the resin, engraving, or other elements.
Dans le cas de l'exemple décrit, on applique pour cela une fonction de convolution de la distribution des électrons dans la matière pour calculer la modulation à appliquer au rayonnement à chaque pas de gravure. Ladite fonction de convolution est donnée par la figure 2 dans laquelle : In the case of the example described, a convolution function of the electron distribution in the material is applied for calculating the modulation to be applied to the radiation at each etching step. Said convolution function is given in FIG. 2 in which:
- D(x, y) représente la répartition dans le plan du substrat (x, y) de la dose reçue sur le motif à graver ;  - D (x, y) represents the distribution in the plane of the substrate (x, y) of the dose received on the pattern to be etched;
- f(x, y) représente la répartition surfacique de la dose émise avec modélisation des effets de proximité ; l'hypothèse d'une répartition gaussienne des effets de proximité est généralement faite, comme illustré sur la figure 3 ; la fonction de répartition est modélisée par double intégration de la fonction de proximité (Point Spread Function ou « PSF ») qui est elle-même une combinaison de fonctions d'erreurs de Gauss (fonction ERF) ; f(x, y) est modélisée par la formule : - f (x, y) represents the surface distribution of the dose emitted with modeling of proximity effects; the hypothesis of a Gaussian distribution of proximity effects is generally made, as shown in Figure 3; the distribution function is modeled by dual integration of the Point Spread Function ("PSF") which is itself a combination of Gaussian error functions (ERF function); f (x, y) is modeled by the formula:
Avec les notations suivantes :  With the following notations:
o a est la largeur du rayonnement direct;  o a is the width of the direct radiation;
o β est la largeur de rétrodiffusion ;  o β is the backscattering width;
o η est le ratio des intensités des rayonnements direct et rétrodiffusé.  o η is the ratio of direct and backscattered radiation intensities.
Les valeurs des paramètres α, β et η sont déterminées expérimentalement pour un procédé donné. Ces paramètres sont fonction de la tension d'accélération de la machine. Typiquement pour une tension d'accélération de l'ordre de 50KV, a est de l'ordre de 50nm, β de l'ordre de 10 μιτι et η de l'ordre de 0.5. Dans cet exemple de réalisation, on utilise une modélisation des erreurs avec deux fonctions ERF. On peut également utiliser des modélisations d'erreurs avec une, trois, quatre voire plus fonctions ERF. On peut également utiliser d'autres types de modélisation, par exemple polynomiales. The values of the parameters α, β and η are determined experimentally for a given process. These parameters depend on the acceleration voltage of the machine. Typically for an acceleration voltage of the order of 50KV, a is of the order of 50nm, β of the order of 10 μιτι and η of the order of 0.5. In this exemplary embodiment, error modeling is used with two ERF functions. One can also use error modeling with one, three, four or even more ERF functions. It is also possible to use other types of modeling, for example polynomials.
- R(x, y) est la géométrie du motif à dessiner.  - R (x, y) is the geometry of the pattern to draw.
L'impact de la dose rayonnée (shot) par le dispositif électronique est donc calculé par la formule :  The impact of the shot dose by the electronic device is therefore calculated by the formula:
D(x, y) = f(x, y) ® R(x, y) D (x, y) = f (x, y) ® R (x, y)
L'application de la transformation inverse (déconvolution) permet de calculer la modulation à appliquer à la dose rayonnée à chaque pas du process.  The application of the inverse transformation (deconvolution) makes it possible to calculate the modulation to be applied to the radiated dose at each step of the process.
On peut également faire l'inversion autrement que par une déconvolution, par exemple en appliquant une fonction d'optimisation, une résolution d'un système d'équations ou une procédure itérative. D'autres exemples de réalisation sont donnés dans la présente description.  The inversion can also be done other than by deconvolution, for example by applying an optimization function, a resolution of a system of equations or an iterative procedure. Other exemplary embodiments are given in the present description.
La figure 1 b illustre la répartition des doses rayonnées après application de la méthode de correction ci-dessus au réseau de lignes de la figure 1 a. L'augmentation significative des doses rayonnées à appliquer en bord de réseau accroît de manière significative la durée de l'exposition nécessaire, ce qui est une limitation de cet art antérieur que la présente invention permet de surmonter. Typiquement, la durée d'exposition doit être multipliée par un facteur 2 à 4 sur les bords de réseau par rapport au centre. Figure 1b illustrates the distribution of radiated doses after applying the above correction method to the line network of Figure 1a. The significant increase in radiated doses to be applied at the edge of the network significantly increases the duration of the necessary exposure, which is a limitation of this prior art that the present invention overcomes. Typically, the exposure time must be multiplied by a factor of 2 to 4 on the network edges with respect to the center.
La figure 5 représente de manière simplifiée, dans le cas d'application d'un procédé de l'art antérieur présenté ci-dessus, la distribution des doses rayonnées sur toute la largeur du réseau dans le procédé de modulation décrit ci-dessus (barres 51 de la figure 5) ainsi qu'une vue aérienne de cette distribution (courbe 52 de la figure 5) qui représente la fenêtre de procédé. La droite 53 représente le seuil de sensibilité de la résine à 0,5 fois la dose normale. On peut définir la dose normale comme étant la dose nécessaire pour imprimer à leur taille nominale des motifs denses (par exemple rapport ligne/espace=1 ) de grande taille (typiquement de l'ordre du micron). Elle est aussi couramment appelée "base dose". FIG. 5 is a simplified representation, in the case of application of a method of the prior art presented above, of the distribution of the radiated doses over the entire width of the network in the modulation method described above (bars 51 of Figure 5) and an aerial view of this distribution (curve 52 of Figure 5) which represents the process window. The line 53 represents the sensitivity threshold of the resin at 0.5 times the normal dose. The normal dose can be defined as the dose necessary to print at their nominal size dense patterns (for example ratio line / space = 1) of large size (typically of the order of one micron). It is also commonly called "base dose".
Un seuil de 0,5 est avantageux, mais d'autres valeurs peuvent également être choisies. La valeur de seuil choisie constitue alors un paramètre qui peut être choisi dans le programme d'ordinateur réalisé pour mettre en œuvre le procédé de l'invention. A threshold of 0.5 is advantageous, but other values may also be chosen. The chosen threshold value then constitutes a parameter that can chosen in the computer program designed to implement the method of the invention.
La droite 54 représente la pente de latitude en énergie du process au point du shot appliqué par le dispositif de rayonnement.  The line 54 represents the energy latitude slope of the process at the point of shot applied by the radiation device.
La dimension d'un shot 55 situé au milieu du motif est dans l'exemple de réalisation décrit ici de 1 ,6 m x 1 ,6 μιτι. Typiquement la dose appliquée en ces points éloignés des bords du motif sera égale à la dose standard (normalisée à 1 ). Pour corriger les effets des proximité particulièrement sensibles aux bords du motif, les dispositifs de l'art antérieur appliquent des doses beaucoup plus élevées (typiquement de 2 à 4 voire 6) avec des dimensions de shots plus réduites, typiquement 1 μιτι x 1 μιη. L'augmentation du temps d'exposition résulte donc à la fois de l'augmentation du nombre de shots liée à la fracturation physique spécifique effectuée aux bords (quasi doublement) et de l'augmentation des doses rayonnées sur ces shots des bords. Dans l'exemple de réalisation illustré sur la figure 5, on rajoute une dizaine de shots, chacun des shots ajoutés ayant une dose supérieure à l'unité (jusqu'à atteindre 6). Le temps d'exposition (proportionnel à l'intégrale des doses sur le nombre de shots) est multiplié par environ 3,6 par rapport à une exposition uniforme (la dose cumulée - ou intégrée - passe de 25 à 90 doses normales). The size of a shot 55 located in the middle of the pattern is in the exemplary embodiment described here of 1.6 m × 1.6 μm. Typically the dose applied at these points away from the edges of the pattern will be equal to the standard dose (standardized to 1). To correct the effects of particularly sensitive proximity to the edges of the pattern, the devices of the prior art apply much higher doses (typically from 2 to 4 or even 6) with smaller shots, typically 1 μιτι x 1 μιη. The increase in the exposure time results both from the increase in the number of shots related to the specific physical fracturing performed at the edges (almost doubled) and the increase of the doses radiated on these shots of the edges. In the embodiment illustrated in Figure 5, we add a dozen shots, each shot added with a dose greater than one unit (up to 6). The exposure time (proportional to the integral of the doses over the number of shots) is multiplied by about 3.6 compared to a uniform exposure (the cumulated dose - or integrated - goes from 25 to 90 normal doses).
Le procédé de l'invention, et ses caractéristiques distinctives par rapport aux procédés de l'art antérieur présentés précédemment sont illustrés par les figures 6 et 7 qui doivent être lues par comparaison avec la figure 5. Sur la figure 6, sont représentées les augmentations de dose de rayonnement 61 1 a, 612a, 613a, 614a, 615a, (ainsi que leurs symétriques sur l'autre bord du réseau à graver) qui sont appliquées par un procédé de l'art antérieur et qui peuvent être éliminées par un procédé selon un premier mode de réalisation de l'invention des doses rayonnées 61 1 , 612, 613, 614, 615 (ainsi que des doses rayonnées sur l'autre bord du réseau de lignes à graver).  The method of the invention, and its distinguishing characteristics with respect to the methods of the prior art presented above are illustrated in FIGS. 6 and 7 which must be read in comparison with FIG. 5. In FIG. radiation dose 61 1a, 612a, 613a, 614a, 615a, (and their symmetries on the other edge of the network to be etched) which are applied by a method of the prior art and which can be removed by a method according to a first embodiment of the invention, the radiated doses 61 1, 612, 613, 614, 615 (as well as doses radiated on the other edge of the network of lines to be etched).
Ces diminutions de doses à appliquer sont obtenues en élargissant la géométrie du dessin à graver dans des proportions illustrées par la droite 620 et en appliquant une dose 616 sur la partie extérieure du nouveau motif. Mais, selon l'invention, les shots sur les bords conservent les mêmes dimensions qu'au milieu du motif (1 ,6 pm x 1 ,6 μιτι dans l'exemple de la figure), ce qui réduit le nombre de shots et donc le temps d'exposition, par exemple dans le cas de la figure, de l'ordre de 29% par rapport à une solution de l'art antérieur (la dose cumulée passe de 90 à 64 doses normales), quand on réduit les surdosages de chacun des shots à modulation de dose d'environ 0,25. These dose decreases to be applied are obtained by widening the geometry of the drawing to be engraved in proportions illustrated by the line 620 and by applying a dose 616 on the outer part of the new pattern. But, according to the invention, the shots on the edges retain the same dimensions in the middle of the pattern (1, 6 pm x 1, 6 μιτι in the example of the figure), which reduces the number of shots and therefore the exposure time, for example in the case of the figure, of the order of 29% relative to a solution of the prior art (the cumulative dose increases from 90 to 64 normal doses), when reducing the overdoses of each dose-modulated shots by about 0.25.
On constate en réalité expérimentalement que l'on peut supprimer les surdosages réalisés sur les bords internes du motif à graver, 61 1 à 615, sans affecter la qualité du motif gravé. Dans ce cas, le gain en temps d'exposition est de l'ordre de 62% (la dose cumulée passe de 90 à 34 doses normales). Aux coins des motifs, le gain est porté au carré et est donc dans l'exemple ci- dessus de l'ordre de 86%. Ainsi, avantageusement, selon un deuxième mode de réalisation de l'invention, on applique la même dose sur tout le motif et on « surdose » sur la bande rajoutée. Ce phénomène avantageux est dû au fait que la bande ajoutée permet à la fois d'écarter et de redresser les flancs de la courbe de dose comme illustré sur la figure 7, ceci de manière plus efficace que les augmentations de doses sur plusieurs shots à l'intérieur du motif qui ont un rendement plus faible en raison des pertes d'énergie créées par les effets de proximité qui se recoupent entre shots.  It is actually found experimentally that it is possible to eliminate the overdoses made on the internal edges of the pattern to be engraved, 61 1 to 615, without affecting the quality of the engraved pattern. In this case, the gain in exposure time is of the order of 62% (the cumulative dose increases from 90 to 34 normal doses). At the corners of the patterns, the gain is squared and is therefore in the above example of the order of 86%. Thus, advantageously, according to a second embodiment of the invention, the same dose is applied over the entire pattern and "overdose" on the added band. This advantageous phenomenon is due to the fact that the added band allows both to spread and straighten the sides of the dose curve as illustrated in FIG. 7, this more effectively than the dose increases on several shots at the same time. pattern that have a lower yield due to energy losses created by proximity effects that intersect between shots.
La figure 7 illustre l'impact du procédé de l'invention sur la courbe de la dose reçue qui est déplacée de 710 en 720. La dose reçue résultant de l'application du procédé de l'invention 720 présente ainsi, comme illustré, un front plus droit qui traduit une plus grande latitude en énergie, et légèrement décalé vers l'extérieur du réseau, ce qui traduit une élimination des effets de proximité. Les modalités du calcul conjoint des doses rayonnées à chaque shot, de l'élargissement des bords du réseau et de la latitude en énergie sont expliquées plus loin dans la description en commentaires aux figures 9 et 10. La figure 7bis illustre le principe d'optimisation de la latitude en énergie sur les bords d'un réseau de lignes denses selon un mode de réalisation de l'invention dans lequel au moins un motif est gravé à l'extérieur dudit réseau. Un autre mode de réalisation avantageux consiste à laisser un espace, 620bis, entre le motif à graver et la bande rajoutée, 61 Obis, et, éventuellement, à ajouter au moins une deuxième bande extérieure, 630bis, séparée également de la première par un espace. Dans toutes les configurations, cet espacement améliore la latitude en énergie du procédé. Expérimentalement, on constate qu'un espacement compris entre 0,2 fois la largeur de bande et 3 fois la largeur de bande est efficace. FIG. 7 illustrates the impact of the method of the invention on the curve of the received dose which is shifted from 710 to 720. The received dose resulting from the application of the method of the invention 720 thus has, as illustrated, a straight front which translates a greater energy latitude, and slightly shifted towards the outside of the network, which translates an elimination of the effects of proximity. The methods for the joint calculation of the doses radiated at each shot, the widening of the edges of the network and the energy latitude are explained later in the description in comments in FIGS. 9 and 10. FIG. 7bis illustrates the principle of optimization the energy latitude on the edges of a network of dense lines according to one embodiment of the invention wherein at least one pattern is etched outside said network. Another advantageous embodiment consists in leaving a space, 620bis, between the pattern to be etched and the band added, 61 Obis, and, optionally, adding at least a second outer band, 630bis, also separated from the first by a space. In all configurations, this spacing improves the energy latitude of the process. Experimentally, it is found that a spacing between 0.2 times the bandwidth and 3 times the bandwidth is effective.
On constate également que dans le cas où l'on applique une surdose sur une bande à l'extérieur du motif, on peut diminuer la dose appliquée au milieu du motif, par exemple de 30%, à 0,7 fois la dose normale sans dégradation de la qualité de la gravure. D'autres valeurs sont cependant possibles. Ces valeurs constituant un paramètre qu'il est possible de choisir dans le programme d'ordinateur configuré pour mettre en œuvre le procédé de l'invention. It is also found that in the case where an overdose is applied to a band outside the pattern, the dose applied to the medium of the motif can be reduced, for example by 30%, to 0.7 times the normal dose without degradation of the quality of engraving. Other values are however possible. These values constituting a parameter that can be chosen in the computer program configured to implement the method of the invention.
Les figures 8a et 8b illustrent les résultats de l'application du procédé de l'invention à un réseau dense. Figures 8a and 8b illustrate the results of the application of the method of the invention to a dense network.
La figure 8a illustre d'une part le motif à graver, 810, d'autre part le motif corrigé par le procédé de l'invention, 820. FIG. 8a illustrates, on the one hand, the pattern to be engraved, 810, on the other hand the pattern corrected by the method of the invention, 820.
La figure 8b illustre le motif réellement gravé. Figure 8b illustrates the actually etched pattern.
Il existe des cas où le resizing est réalisé vers l'extérieur et d'autres où il est réalisé vers l'intérieur.  There are cases where the resizing is done to the outside and others where it is done inwards.
La figure 9 représente un organigramme de la partie centrale du procédé pour mettre en œuvre l'invention selon un de ses modes de réalisation. FIG. 9 represents a flowchart of the central part of the method for implementing the invention according to one of its embodiments.
L'exemple illustré est celui d'une combinaison d'un resizing des motifs à graver et d'une modulation de dose tel que représenté sur la figure 6. The illustrated example is that of a combination of a resizing of the patterns to be etched and a dose modulation as shown in FIG.
De manière classique pour un homme de l'art, le procédé de l'invention commence par une lecture du design. Le lay-out des motifs à graver est classiquement encodé dans des fichiers au format GDS II (Graphie Data System version2) ou OASIS (Open Artwork System Interchange Standard). Les données sont normalement regroupées par cellule. Le motif à graver est ensuite pré-fracturé en sous-ensembles compatibles du dispositif de transfert (gravure électronique ou ionique directe, fabrication de masques pour gravure électronique ou optique...) In a conventional manner for a person skilled in the art, the method of the invention begins with a reading of the design. The lay-out of the patterns to be engraved is conventionally encoded in files in GDS II format (Graphie Data System version2) or OASIS (Open Artwork System Interchange Standard). The data is normally grouped by cell. The pattern to be etched is then pre-fractured into compatible subassemblies of the transfer device (direct or electronic etching, manufacture of masks for electronic or optical etching, etc.).
Ensuite, à l'étape 910 du procédé de l'invention, on calcule la dose idéale du shot de manière que, en moyenne, tous les points milieux des bords du shot émis soient ajustés au seuil de sensibilité de la résine, par exemple à 0,5 fois la dose normale, d'autres valeurs étant possibles, ledit seuil pouvant être réglé comme paramètre dans le programme d'ordinateur configuré pour mettre en oeuvre le procédé de l'invention. Then, in step 910 of the method of the invention, the ideal dose of the shot is calculated so that, on average, all midpoints of the edges of the shot shot are adjusted to the threshold of sensitivity of the resin, for example to 0.5 times the normal dose, other values being possible, said threshold can be set as a parameter in the computer program configured to implement the method of the invention.
A l'étape suivante, 920, on calcule la pente EL de la courbe de dose en ce point qui est égale à la fenêtre de procédé ou latitude en énergie.  In the next step, 920, the slope EL of the dose curve is calculated at this point which is equal to the process window or energy latitude.
A l'étape suivante, 930, on calcule une interpolation linéaire en ce point de la courbe de dose. A l'étape suivante, 940, on calcule le point d'intersection entre l'interpolation linéaire et le seuil à 0,5.  In the next step, 930, a linear interpolation is calculated at this point of the dose curve. In the next step, 940, the point of intersection between the linear interpolation and the 0.5 threshold is calculated.
A l'étape suivante, 950, on calcule l'erreur de placement (Edge Placement Error ou « EPE ») qui est égale à la distance orientée entre le point d'intersection en sortie d'étape 940 et le bord du shot.  In the next step, 950, the Edge Placement Error ("EPE") is calculated which is equal to the distance between the intersection point at the exit of step 940 and the edge of the shot.
A l'étape suivante, 960, on corrige le bord du motif à graver en appliquant au motif initial la distance orientée en sortie de l'étape précédente.  In the next step, 960, the edge of the pattern to be engraved is corrected by applying to the initial pattern the distance oriented at the output of the preceding step.
Ce procédé de base est ajusté pour tenir compte de la place disponible de part et d'autre du motif. S'il y a suffisamment de place pour pouvoir ajouter des bandes supplémentaires à l'extérieur du motif, c'est la solution qui est privilégiée. Dans ce cas, une dose normale uniforme (ou réduite à 0,7, comme indiqué plus haut) est appliquée à l'intérieur du motif en substitution aux modulations calculées partout sauf sur la ou les bordures à l'extérieur du motif. La dose appliquée à l'extérieur du motif du design initial peut être calculée par application des formules de convolution exposées ci-dessus ou par utilisation d'une table de paramètres d'expérience.  This basic process is adjusted to take into account the space available on both sides of the pattern. If there is enough space to add extra bands to the outside of the design, this is the preferred solution. In this case, a uniform normal dose (or reduced to 0.7, as indicated above) is applied inside the pattern in substitution for modulations calculated everywhere except on the border (s) on the outside of the pattern. The dose applied outside the initial design pattern can be calculated by applying the convolution formulas discussed above or by using an experience parameter table.
Dans le cas où la place est contrainte on limite le resizing et on utilise les résultats du calcul de modulation de dose.  In the case where the place is constrained, the resizing is limited and the results of the dose modulation calculation are used.
On réajuste ensuite la modulation de dose à partir de la correction de design. On renouvelle le procédé de correction jusqu'à ce que la variation de dose d'une itération sur la boucle à la suivante soit inférieure à un seuil. Typiquement, on réitère le processus 2 ou 3 fois pour tenir compte des profils introduits sur les motifs voisins. On initialise par exemple avec un resizing de 500 nm et on s'arrête à 1 ou 1 ,5 μιτι. Dans ce cas-là la pente EL ne bouge pas d'une itération à l'autre. The dose modulation is then readjusted from the design correction. The correction process is repeated until the dose variation from one iteration on the loop to the next is less than a threshold. Typically, the process is repeated 2 or 3 times to take into account the profiles introduced on the neighboring patterns. For example, initialize with a resizing of 500 nm and stop at 1 or 1, 5 μιτι. In this case the slope EL does not move from one iteration to another.
Enfin, les données sont converties au format machine et l'exposition réalisée. La figure 10 illustre de manière graphique le procédé de correction des effets de proximité dans un mode de réalisation de l'invention. Finally, the data is converted to the machine format and the exposure made. Figure 10 graphically illustrates the method of correcting proximity effects in one embodiment of the invention.
Les segments 1010 représentent le shot initial. Segments 1010 represent the initial shot.
La courbe 1020 représente la dose reçue. Curve 1020 represents the dose received.
La droite 1030 représente le seuil à 0,5. The line 1030 represents the threshold at 0.5.
La droite 1040 représente la droite interpolée en sortie de l'étape 930.  The line 1040 represents the interpolated line at the output of step 930.
Le segment orienté 1050 représente ΙΈΡΕ qui donne la correction appliquée au motif initial à graver. Pour mettre en œuvre le procédé de l'invention, on peut également utiliser des concepts voisins du concept d'EL, par exemple:  The oriented segment 1050 represents ΙΈΡΕ which gives the correction applied to the initial pattern to be engraved. To implement the method of the invention, it is also possible to use concepts that are close to the EL concept, for example:
- le contraste : (lmax-lmin)(lmax + Imin), où I représente ici la dose reçue ; le contraste est souvent utilisé, notamment pour les motifs périodiques ;  the contrast: (lmax-lmin) (lmax + Imin), where I represents here the dose received; contrast is often used, especially for periodic patterns;
- on utilise aussi couramment le "logslope" ILS: d(ln(dose))/dx ou le "normalized Image Log slope NILS = ILS .CD  ILS is also commonly used: d (ln (dose)) / dx or the normalized Image Log slope NILS = ILS .CD
Ces critères peuvent être utilisés en substitution de TEL, définie comme la pente de Dose(x).  These criteria can be used in substitution of TEL, defined as the slope of Dose (x).
La méthode de l'invention a été décrite dans un exemple d'application à un procédé de lithographie électronique par écriture directe. Elle peut également être appliquée à un autre procédé d'écriture directe utilisant d'autres particules telles que des ions, des photons ou à des procédés de lithographie électronique ou optique utilisant des masques. The method of the invention has been described in an exemplary application to a direct write electronic lithography method. It can also be applied to another direct writing method using other particles such as ions, photons or electronic or optical lithography methods using masks.
Les exemples décrits ci-dessus sont donc donnés à titre d'illustration certains de modes de réalisation de l'invention. Ils ne limitent en aucune manière le champ de l'invention qui est défini par les revendications qui suivent.  The examples described above are therefore given by way of illustration of some embodiments of the invention. They in no way limit the scope of the invention which is defined by the following claims.

Claims

REVENDICATIONS
1 . Procédé de lithographie par rayonnement d'au moins un motif à graver sur un support résiné comprenant une étape de calcul (910) de modulation d'au moins une dose rayonnée et une étape de calcul (920, 930, 940, 950, 960) d'au moins un ajustement à apporter audit motif à graver selon au moins une direction du support, ledit procédé étant caractérisé en ce que ledit ajustement est fonction de la latitude en énergie du procédé au point où est reçue la dose rayonnée et en ce que la modulation de la dose rayonnée est modifiée en fonction dudit au moins un ajustement dudit au moins un motif. 1. Method for radiation lithography of at least one pattern to be etched on a resinous support comprising a calculation step (910) for modulating at least one radiated dose and a calculation step (920, 930, 940, 950, 960) at least one adjustment to be made to said pattern to be etched in at least one direction of the support, said method being characterized in that said adjustment is a function of the energy latitude of the process at the point where the radiated dose is received and in that the modulation of the radiated dose is changed according to the at least one adjustment of the at least one pattern.
2. Procédé de lithographie selon la revendication 1 , caractérisé en ce que l'étape de calcul (910) de modulation d'au moins une dose rayonnée est opérée par convolution dudit motif avec une fonction de répartition de ladite dose rayonnée sur ledit support. 2. lithography process according to claim 1, characterized in that the calculation step (910) of modulation of at least one radiated dose is performed by convolution of said pattern with a function of distribution of said dose radiated on said support.
3. Procédé de lithographie selon la revendication 2, caractérisé en ce que ladite dose rayonnée est calculée avant modulation sous contrainte que la dose moyenne rayonnée se situe sensiblement à un niveau du seuil de sensibilité de la résine choisi. comme paramètre. 3. lithography process according to claim 2, characterized in that said radiated dose is calculated before modulation under stress that the average radiated dose is substantially at a level of the sensitivity threshold of the chosen resin. as a parameter.
4. Procédé de lithographie selon la revendication 3, caractérisé en ce que le paramètre de niveau de seuil de sensibilité de la résine est choisi sensiblement égal à 0,5. 4. Lithography process according to claim 3, characterized in that the sensitivity threshold level parameter of the resin is chosen substantially equal to 0.5.
5. Procédé de lithographie selon l'une des revendications 3 ou 4, caractérisé en ce que la latitude en énergie (EL) du procédé au point où est reçue la dose rayonnée est calculée comme appartenant au groupe constitué par la pente de la tangente en ce point à la courbe des doses reçues, le contraste des doses rayonnées et la pente de dose. 5. lithography method according to one of claims 3 or 4, characterized in that the energy latitude (EL) of the process at the point where the radiated dose is received is calculated as belonging to the group consisting of the slope of the tangent in this point to the curve of the doses received, the contrast of the radiated doses and the dose slope.
6. Procédé de lithographie selon la revendication 5, caractérisé en que l'ajustement à apporter au motif centré sur un des points de réception d'une dose rayonnée selon la au moins une direction est calculé comme étant égal à la distance orientée sur la droite de seuil de sensibilité de la résine à 0,5 du procédé entre l'intersection de ladite droite de seuil avec d'une part la tangente de pente EL à la courbe des doses reçues audit point de réception et d'autre part la courbe de dose rayonnée. 6. Lithography process according to claim 5, characterized in that the adjustment to be made to the pattern centered on one of the reception points a radiated dose according to the at least one direction is calculated as being equal to the distance oriented on the sensitivity threshold line of the resin at 0.5 of the process between the intersection of said threshold line with, on the one hand, the tangent of slope EL to the curve of the doses received at said reception point and secondly the radiated dose curve.
7. Procédé de lithographie selon l'une quelconque des revendications 2 à 6, caractérisé en ce que les étapes de calcul de modulation de dose rayonnée et d'ajustement du motif à graver sont répétées tant que la variation de dose rayonnée sur un point de réception d'un calcul de modulation au précédent reste supérieure à une valeur de seuil prédéterminée. 7. A method of lithography according to any one of claims 2 to 6, characterized in that the calculation steps of radiated dose modulation and adjustment of the pattern to be etched are repeated as the dose variation radiated on a point of reception of a modulation calculation to the previous one remains greater than a predetermined threshold value.
8. Procédé de lithographie selon la revendication 1 , caractérisé en ce que l'étape de calcul (910) de modulation d'au moins une dose rayonnée est opérée en utilisant une table de paramètres. 8. Lithography process according to claim 1, characterized in that the step of calculating (910) modulation of at least one radiated dose is performed using a parameter table.
9. Procédé de lithographie selon l'une quelconque des revendications 1 à 8, caractérisé en ce que les doses rayonnées au milieu du motif avant ajustement sont toutes sensiblement égales à une dose normale. 9. lithography process according to any one of claims 1 to 8, characterized in that the doses radiated in the middle of the pattern before adjustment are all substantially equal to a normal dose.
10. Procédé de lithographie selon l'une quelconque des revendications 1 à 8, caractérisé en ce que les doses rayonnées au milieu du motif avant ajustement sont toutes sensiblement égales à un pourcentage d'une dose normale. 10. A lithography method according to any one of claims 1 to 8, characterized in that the doses radiated in the middle of the pattern before adjustment are all substantially equal to a percentage of a normal dose.
1 1 . Procédé de lithographie selon la revendication 10, caractérisé en ce que le pourcentage d'une dose normale est fixé à une valeur sensiblement égale à 70% de ladite dose normale. 1 1. Lithography method according to claim 10, characterized in that the percentage of a normal dose is set at a value substantially equal to 70% of said normal dose.
12. Procédé de lithographie selon l'une quelconque des revendications 1 à 1 1 , caractérisé en ce que ledit ajustement comprend au moins un espacement sans rayonnement et au moins une dose rayonnée. 12. A lithography method according to any one of claims 1 to 1 1, characterized in that said adjustment comprises at least one spacing without radiation and at least one radiated dose.
13. Procédé de lithographie selon l'une quelconque des revendications 1 à 12, caractérisé en ce que au moins une dose est rayonnée à l'extérieur du motif à graver. 13. Lithography process according to any one of claims 1 to 12, characterized in that at least one dose is radiated outside the pattern to be etched.
14. Procédé de lithographie selon la revendication 13, caractérisé en ce que ladite au moins une dose rayonnée à l'extérieur du motif à graver est espacée du motif à graver d'une distance comprise entre 0,2 fois et 3 fois la largeur de bande. 14. lithography method according to claim 13, characterized in that said at least one dose radiated outside the pattern to be etched is spaced from the pattern to be etched by a distance between 0.2 times and 3 times the width of bandaged.
15. Programme d'ordinateur comprenant des instructions de code de programme permettant l'exécution du procédé de lithographie par rayonnement d'au moins un motif à graver sur un support résiné selon l'une des revendications 1 à 14 lorsque le programme est exécuté sur un ordinateur, ledit programme comprenant un module de calcul de modulation d'au moins une dose rayonnée et un module de calcul d'au moins un ajustement à apporter audit motif à graver selon au moins une direction du support, ledit programme d'ordinateur étant caractérisé en ce que ledit calcul d'ajustement à apporter au motif est fonction de la latitude en énergie du procédé au point où est reçue la dose rayonnée et en ce que la modulation de la dose rayonnée est modifiée en fonction dudit au moins un ajustement dudit au moins un motif. A computer program comprising program code instructions for performing the radiation lithography method of at least one pattern to be engraved on a resinous support according to one of claims 1 to 14 when the program is executed on a computer, said program comprising a module for calculating modulation of at least one radiated dose and a module for calculating at least one adjustment to be made to said pattern to be etched in at least one direction of the medium, said computer program being characterized in that said adjustment calculation to be made to the pattern is a function of the energy latitude of the process at the point where the radiated dose is received and that the modulation of the radiated dose is changed according to said at least one adjustment of said at least one reason.
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US9250540B2 (en) 2016-02-02
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