Patent Application
20150311035
1. Field of the Invention
The present invention relates to a lithography apparatus, and a method of manufacturing an article.
2. Description of the Related Art
As circuit patterns in semiconductor integrated circuits have become finer and more highly integrated, attention has been given to drawing apparatuses that form a pattern (latent pattern) on a substrate using a charged particle beam (electron beam). In drawing apparatuses, the spatial modulation method is used as a method for controlling the dose with respect to pixels on the substrate. The spatial modulation method is a method in which drawing is performed on a substrate by, for example, binarizing the target values of doses for pixels expressed by a large number of tones (gradation or gray scale pixels), and controlling the switching on and off of the charged particle beam at the pixels based on the binarized information.
In this spatial modulation method, error can arise between the binarized dose values and the target values. For this reason, Japanese Patent Laid-Open No. 2012-527764 proposes a method in which, while successively performing binarization on pixels, the binarization-related error arising at the target pixel is diffused into the target value of the subsequent pixel adjacent to the target pixel.
In drawing apparatuses, operating lag (operating delay) generally occurs in the blanker when the charged particle beam is switched on and off. For this reason, the actual dose on the substrate can differ from the planned dose. The method disclosed in Japanese Patent Laid-Open No. 2012-527764 is therefore not sufficient in terms of the fidelity of pattern formation (patterning).
The present invention provides, for example, a technique that is advantageous in terms of fidelity of patterning.
According to one aspect of the present invention, there is provided a lithography apparatus that performs patterning on a substrate with a beam, the apparatus comprising: a blanker configured to perform blanking of the beam; and a controller configured to control the blanker based on a quantized value of dose with respect to each of pixels on the substrate, wherein the controller is configured to determine the quantized value of dose with respect to each of the pixels based on an error between a target value of dose and each of a plurality of predicted values of dose that are based on a plurality of quantized values of dose.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Exemplary embodiments of the present invention will be described below with reference to the accompanying drawings. Note that the same reference numerals denote the same members throughout the drawings, and a repetitive description thereof will not be given. Also, although a drawing apparatus that forms a pattern on a substrate by irradiating the substrate with charged particle beams serving as the beams is described in the following embodiments, the present invention is not limited to this. For example, the present invention can also be applied to a lithography apparatus such as an exposure apparatus that exposes a substrate using light (a light beam) as the beam.
A drawing apparatus 100 of a first embodiment of the present invention will be described below with reference to
The drawing unit 100a will be described first. The drawing unit 100a can include a charged particle source 1, a collimator lens 2, a first aperture array 3, condenser lenses 4, a second aperture array 5, a blanker array 6, a blanking aperture 7, a deflector array 8, and an objective lens array 9, for example. The drawing unit 100a can also include a movable stage 11 that holds the substrate 10.
The charged particle source 1 can be a thermionic emission electron source that includes an electron emission material such as LaB6 or BaO/W, for example. The collimator lens 2 is an electrostatic lens for condensing a charged particle beam using an electrical field, for example, and is used for forming the charged particle beam emitted from the charged particle source 1 into a parallel beam, and causing the parallel beam to be incident on the first aperture array 3. The first aperture array 3 has multiple openings arranged in a matrix, and divides the incident parallel charged particle beam into multiple beams. The divided charged particle beams obtained by the first aperture array 3 pass through the condenser lenses 4 and are then incident on the second aperture array 5. The second aperture array 5 includes multiple sub arrays 5a that each include multiple openings. The sub arrays 5a are arranged so as to correspond to the divided charged particle beams obtained by the first aperture array 3, and further divide the charged particle beams to generate charged particle beams. In the first embodiment, each sub array 5a has 16 (4×4) openings 5b, for example, and can further divide a divided charged particle beam obtained by the first aperture array 3 into 16 (4×4) charged particle beams.
The divided charged particle beams obtained by the sub arrays 5a in the second aperture array 5 are caused to be incident on the blanker array 6, which includes blankers that individually deflect the charged particle beams. The blankers included in the blanker array 6 each include two opposing electrodes, for example, and can deflect a charged particle beam by generating an electrical field by applying a voltage between the two electrodes. The charged particle beams deflected by the blanker array 6 do not arrive at the substrate 10 due to being blocked by the blanking aperture 7 arranged downstream of the blanker array 6. On the other hand, the charged particle beams not deflected by the blanker array 6 pass through openings formed in the blanking aperture 7 and arrive at the substrate 10. In other words, the blanker array 6 switches between irradiation (ON) and non-irradiation (off) of the substrate 10 with the charged particle beams. The charged particle beams that pass through the blanking aperture 7 are incident on the deflector array 8, which is for scanning the substrate with the charged particle beams. The deflector array 8 includes multiple deflectors, and the deflectors deflect the charged particle beams all together in the X direction (scanning direction) for example, in parallel with the deflection of the charged particle beams by the blankers in the blanker array 6. Accordingly, the substrate can be scanned with the charged particle beams that passed through the objective lens array 9. Although the deflector array 8 shown in
Next, the controller 100b will be described. The controller 100b can include a blanking controller 12, a data processor 13, a deflection controller 14, a stage controller 15, a pattern data memory 16, a data convertor 17, an intermediate data memory 18, and a main controller 19, for example. The blanking controller 12 individually controls the blankers included in the blanker array 6. The data processor 13 has a buffer memory for storing intermediate data, and generates control data for control of the blanker array 6 by the blanking controller 12, based on the stored intermediate data. The deflection controller 14 controls the deflector array 8. The stage controller 15 controls the positioning of the stage 11 based on signals from a measuring instrument (not shown) that measures the position of the stage 11. The measuring instrument can include a laser interferometer, for example.
The pattern data memory 16 stores design data (pattern data) defining a pattern that is to be drawn on the substrate. The data convertor 17 divides the design data stored in the pattern data memory into units of stripes, and performs conversion into intermediate data in order to make the drawing processing easier to perform. A stripe is an area drawn by multiple charged particle beams in the drawing unit 100a by scanning the stage 11 one time in a predetermined direction (e.g., the Y direction), for example. The intermediate data memory 18 stores the converted intermediate data obtained by the data convertor 17. The main controller 19 transfers intermediate data to the buffer memory of the data processor 13 according to the pattern that is to be drawn, and performs overall control of the drawing apparatus 100 by controlling the above-described controllers, processors, and the like. Note that these constituent elements included in the controller 100b of the first embodiment are merely one example, and can be changed as appropriate.
The following describes an example of a raster scan drawing method used by the drawing apparatus 100 having the above configuration. Charged particle beams are scanned over a scanning grid on the substrate that is determined by the position of the stage 11 and the deflection performed by the deflector array 8, and the switching on and off of the charged particle beams on the substrate is controlled by the blanker array 6 according to the pattern that is to be drawn on the substrate. This scanning grid is a grid defined by a pitch GX in the X direction and a pitch GY in the Y direction, and the elements constituting the grid defined by the pitch GX and the pitch GY correspond to the smallest dot that can be drawn by one charged particle beam (i.e., correspond to a pixel). The controller 100b deflects charged particle beams using the deflector array 8 so as to scan the substrate in the X direction, while successively moving the substrate 10 in the Y direction using the stage 11. In parallel with deflecting the charged particle beams in the X direction using the deflector array 8, the controller 100b uses the blanker array 6 to control the switching on and off of the charged particle beams for each pixel defined by the pitch GX.
In
Next, deflection of the charged particle beams in the blanker array 6 will be described with reference to
For example, when a gate driver 66 supplies a signal (voltage) to one gate electrode line 69a, all of the FETs 67 in the one row connected to that gate electrode line 69a are switched on. At this time, the voltages applied to the source electrode lines 69b are applied to the blankers 6a, and the capacitors 68 connected to the switched-on FETs 67 accumulate (become charged with) charges corresponding to the voltages applied to the source electrode lines. When the charging of one row of capacitors 68 ends, the gate driver 66 switches the gate electrode line 69a to which the voltage is applied. At this time, the aforementioned one row of blankers 6a lose the voltage from the source electrode line 69b, but can maintain a necessary voltage until the next voltage application due to the charges accumulated in the capacitors 68. In this way, with an active matrix driving method using the FETs 67 as switches, voltages can be applied to a large number of blankers 6a in parallel using the gate electrode lines 69a and the source electrode lines 69b. For this reason, it is possible to handle an increase in the number of blankers 6a with a small number of wires. In the example in
Then, in order to generate command values indicating the switching on or off of the charged particle beams at the pixels, the controller 100b converts the multivalued pattern data into binary pattern data using an error diffusion method for example. For example, conventionally, for each pixel in the multivalued pattern data indicated by 52 in
The controller 100b controls the blanker array 6 in accordance with the binary pattern data. For example, at a pixel for which the command value is set to “10”, a voltage is not applied to the two electrodes at the blanker 6a, and the charged particle beam passes through the blanking aperture 7 and is incident on the substrate 10 without being deflected by the blanker 6a. On the other hand, at a pixel for which the command value is set to “0”, a voltage is applied to the two electrodes at the blanker 6a, and the charged particle beam is deflected by the blanker 6a and blocked by the blanking aperture 7, and thus is incident on the substrate 10. In this way, when the charged particle beams are switched on and off by the blanker 6a, a time period is required for charge to be accumulated in the capacitor 68 that is parallel-connected to the blanker 6a, and response lag (response delay) can occur before the charged particle beams are deflected by the blanker 6a. Specifically, the blanker 6a has an operating characteristic (transfer characteristic (transfer function)) in which an operating lag (operating delay) occurs when switching charged particle beams on and off, and a time period can be required between when a command value is supplied to the blanker and when the charged particle beams are switched on and off. For this reason, the change in the irradiation intensity of the charged particle beam on the substrate 10 is gradual in a pixel immediately after giving the blanker an instruction to switch the charged particle beam on or off. As a result, a difference can occur between the planned irradiation dose (command value) at that pixel and the actual irradiation dose (actual dose) at that pixel.
For example, envision a pixel irradiated with a charged particle beam immediately after giving the blanker an instruction to switch the charged particle beam from off to on, as with the third pixel from the left in
Also, the difference between the planned irradiation dose at a pixel and the actual irradiation dose at that pixel fluctuates according to the past charged particle beam control history. In the case where the switching on and off of the charged particle beam (state transition) occurs consecutively, the transition occurs in a state in which the voltage applied to the blanker 6a has not reached the maximum value, and therefore the difference between the planned irradiation dose and the actual dose at a pixel can increase even further. For example, take the tenth pixel from the left in
In this way, if an operating lag occurs in the blanker 6a when switching the charged particle beams on and off, immediately thereafter, a difference can arise between the planned irradiation dose (command value) at a pixel and the actual irradiation dose (actual dose) at that pixel. For this reason, if the command value is simply determined by binarizing (quantizing) the dose target value using a threshold value as in conventional drawing apparatuses, it is not necessarily the case that the command value can be determined so as to reduce the error between the target value and the actual dose value of the irradiated charged particle beam on the substrate 10. For example, envision the case of determining the command value at a target pixel for which the target value of the charged particle beam dose is “4”. In this case, in a conventional drawing apparatus, if the threshold value were set to “5”, the command value would be set to “0”, and the error between the command value and the target value would be “−4”. However, if the charged particle beam is off at the pixel before the target pixel, and then the charged particle beam is switched on at the target pixel, the actual charged particle beam dose value at the target pixel would be “6” due to the operating lag of the blanker 6a, and the error between this value and the target value would be “2”. Accordingly, in this case, if the threshold value were used, the command value for the target pixel would be determined so as to switch off the charged particle beam, but switching on the charged particle beam would reduce the absolute value of the error with respect to the target value. In other words, in a conventional method that uses a threshold value, it is not necessarily the case that the command value can be determined so as to reduce the error between the target value and the actual dose value of the irradiated charged particle beam on the substrate 10, and it has not been possible to form a pattern on the substrate 10 with sufficient precision.
In view of this, in the drawing apparatus 100 of the first embodiment, for each pixel on the substrate, taking into consideration the operating lag of the blanker 6a, the controller 100b predicts the irradiated charged particle beam dose at the pixel in both the case of instructing the switching on of the charged particle beam and the case of instructing the switching off of the charged particle beam. The controller 100b then determines the command value so as to achieve, out of these two cases, the case in which the absolute value of the difference between the predicted value and the target value for the charged particle beam dose is smaller (minimized).
(1) Preparation Processing
First, in the data convertor 17, conversion processing 102 is performed to convert pattern data 101 into intermediate data 103. The data convertor 17 performs proximity effect correction on the pattern data 101, and changes the tones of the pattern data 101. The data resulting from the proximity effect correction is divided into units of stripes corresponding to the stripe drawing area SA. In the present embodiment, stitching is performed by performing double drawing (double exposure) with adjacent charged particle beams, and therefore a redundant area having a width of 0.1 μm is added to each side to generate intermediate data 103 having a width of 2.2 μm (the redundant portions of adjacent intermediate data can be the same data).
(2) Multivalue Processing
The following describes the flow of processing after the substrate 10 is introduced to the drawing apparatus 100. In the controller 100b, the main controller 19 transfers the intermediate data 103 from the intermediate data memory 18 to the data processor 13. The data processor 13 stores the transferred intermediate data 103 as pieces of multivalued pattern data (data 104) in units of stripes. These pieces of multivalued pattern data are data expressing target values for charged particle beam doses at pixels. Here, the vector intermediate data 103 is converted into multivalued pattern data pieces in the grid coordinate system of the drawing apparatus 100. Specifically, for example, conversion can be performed based on the area density of the intermediate data at the pixels, a correction coefficient that is based on the irradiation intensity of the charged particle beams for drawing the stripes, or the dose correction factor in the double drawing area (basically 0.5).
(3) Correction Processing
The data processor 13 performs correction processing 105 that includes the processes described in (3-1) to (3-3) below on the multivalued pattern data for each stripe, in parallel with drawing.
(3-1) Coordinate Transformation
In order to perform overlaid drawing in a shot area on a substrate, the data processor 13 performs coordinate transformation using Equation 1 based on information for obtaining the layout of the shot area on a substrate that has been measured in advance (e.g., a magnification coefficient βr, a rotation coefficient θr, and translation coefficients (shift coefficients) Ox and Oy). Here, x and y represent coordinates in the multivalued pattern data for each stripe before correction, and x′ and y′ represent coordinates in the multivalued pattern data for each stripe after correction. Also, Ox and Oy can include an offset amount for correcting positional shift from the designed positions of charged particle beams corresponding to a stripe.
(3-2) Binarization Processing
Processing for converting the multivalued pattern data resulting from the above-described coordinate transformation into binary pattern data (command values indicating the switching on and off of charged particle beams) will be described below with reference to
For example, envision the case where the target pixel is the fourth pixel from the left in
The prediction of the irradiated charged particle beam dose at the target pixel can be performed by, for example, referencing a look-up table that has been created in advance. For example, as shown in
In step S94, the data processor 13 determines whether or not command values have been determined for all of the pixels. If command values have been determined for all of the pixels, the data processor 13 ends the processing for determining command values. On the other hand, if command values have not been determined for all of the pixels, the data processor 13 returns to step S91 and determines a command value for the next pixel. Here, using the example shown in
(3-3) Serial Data Conversion
The data processor 13 generates control data 106 for the blankers by sorting the binarized data (command values) for the pixels for each charged particle beam and in the drawing order. The control data 106 generated in this way is successively sent to the blanking controller 12, and supplied to the blanker array 6 by the blanking controller 12.
As described above, for each pixel on the substrate, taking into consideration the operating lag of the blanker 6a, the drawing apparatus 100 of the first embodiment predicts the irradiated charged particle beam dose at the pixel in both the case of instructing the switching on of the charged particle beam and the case of instructing the switching off of the charged particle beam. The controller 100b then determines the command value so as to achieve, out of these two cases, the case in which the absolute value of the difference between the predicted value and the target value for the charged particle beam dose is smaller. Accordingly, error arising at the pixels can be reduced, thus making it possible to reduce position shift and blurring or slurring (e.g., shrinking line widths) in the pattern drawn on the substrate 10, and precisely form the pattern on the substrate 10.
Embodiment of Method of Manufacturing an Article
A method of manufacturing an article according to this embodiment of the present invention is favorable in, for example, manufacturing articles such as microdevices (e.g., semiconductor devices) and elements having a fine structure. The method of manufacturing an article of the present embodiment includes a step of forming a pattern on a substrate using the above-described lithography apparatus (drawing apparatus) (step of perform drawing on a substrate), and a step of processing the substrate on which the pattern was formed in the previous step. Furthermore, this manufacturing method includes other known steps (e.g., oxidation, film formation, vapor deposition, doping, planarization, etching, resist peeling, dicing, bonding, and packaging). The method of manufacturing an article of the present embodiment is advantageous over conventional methods in at least one of article performance, quality, productivity, and production cost.
For example, although the above description is given taking the example where the blanker array 6 includes an array of electrode pairs that can be driven individually, the present invention is not limited to this, and it is sufficient that the array has elements having a blanking function. For example, as disclosed in the specification of U.S. Pat. No. 7,816,655, the blanker array 6 can include a reflective electron patterning device that selectively reflects charged particle beams. This device includes a pattern on the top surface, an electron reflective portion of the pattern, and an electron non-reflective portion of the pattern. This device further includes an array of circuitry for dynamically varying the electron reflective and non-reflective portions of the pattern using independently-controllable pixels. In this way, the blanker array may be an array of elements (blankers) that perform charged particle beam blanking by changing charged particle beam reflective portions into non-reflective portions. Note that the configuration of the charged particle optical system that includes this reflective device can of course be different from the configuration of a charged particle optical system that includes a transmissive device for selectively transmitting charged particle beams as with an electrode pair array.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-093166 filed on Apr. 28, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-093166 | Apr 2014 | JP | national |
