JP4607623B2 - Electron beam writing method and apparatus - Google Patents

Description

The present invention relates to electron beam portrayal method and apparatus.

  The electron beam drawing apparatus is an apparatus that draws and forms a pattern on a material surface such as a dry plate with a resist using an electron beam. When this electron beam drawing apparatus draws a pattern on a dry plate, various causes that prevent accurate drawing are known. The cause will be described below.

(A) Proximity Effect Correction (abbreviated as PEC)
When a fine pattern is formed in an electron beam drawing apparatus, there is a problem of proximity effect that a pattern as designed is not formed due to scattering of the electron beam in the resist and the substrate. In an isolated thin pattern, electrons that have entered the resist spread while being scattered at a fine angle with respect to the traveling direction (forward scattering), and the pattern becomes finer than the design value due to a phenomenon in which the stored energy intensity decreases. On the other hand, in the portion sandwiched between large patterns, electrons incident on the adjacent exposed portion are greatly scattered by the substrate (backscattering), and the unexposed resist is exposed.

  The proximity effect based on the forward scattering and the back scattering is referred to as an intra-pattern proximity effect and an inter-pattern proximity effect, respectively. A technique for obtaining a pattern according to the design value by predicting the scattering state of the electron beam and changing the drawing pattern shape and the exposure amount according to the pattern density and pattern size is called proximity effect correction.

(B) In-plane exposure correction (Plate Dose Error Correction: PDEC for short)
This is a process for correcting the variation in the dimension of the drawing pattern depending on the position on the material. The following error components are taken into account as factors for the occurrence of such variations, and corrections are made respectively.

1) Fogging error The electron beam irradiated on the material to draw the pattern is reflected from the material surface (or secondary electrons are generated), which is reflected on the electron optical system components of the electron beam drawing apparatus. This is due to the phenomenon of irradiation over a wide range on the material surface.

  This phenomenon causes variations in the dimensions of the drawn pattern according to the drawing area density of the drawn pattern and the distance of the pattern drawn adjacent thereto (drawing area / distance-dependent error). In order to correct this error, a pattern is drawn by adjusting the electron beam irradiation amount for each drawing field in accordance with the distribution of the fog error on the material.

2) Process error This is an error due to non-uniformity of the process when developing or etching the material on which the pattern is drawn on the material surface. This development causes variations in the dimensions of the drawn pattern in accordance with the position of the pattern drawn on the material (drawing position-dependent error). In order to correct this error, a pattern is drawn by adjusting the electron beam irradiation amount for each drawing field in accordance with the distribution of process errors on the material.

3) Transfer error An error generated when a pattern is formed on a wafer by an exposure apparatus (stepper) using a reticle and mask drawn by an electron beam drawing apparatus. This error is due to distortion of the optical system of the exposure apparatus (stepper). Due to this phenomenon, the dimension of the pattern drawn on the wafer by the exposure apparatus varies according to the position of the pattern drawn on the reticle and mask (drawing position-dependent error). In order to correct this error, the pattern is drawn by adjusting the electron beam irradiation amount for each drawing field according to the distribution of the transfer error.

4) Global (or micro) loading effect In an etching process which is a post-processing of pattern drawing by an electron beam drawing apparatus, it means a phenomenon in which the etching rate of a fine pattern portion is lower than that of a large pattern portion. This phenomenon causes variations in the dimensions of the drawn pattern according to the drawing area density of the drawn pattern and the distance of the pattern drawn adjacent thereto (drawing area / distance-dependent error). In order to correct this error, a pattern is drawn by adjusting the electron beam irradiation amount for each drawing field in accordance with the influence distribution of the global (or micro) loading effect on the material.

  This type of conventional apparatus uses a provisional exposure amount that varies depending on each position of the sample, and includes the fog exposure energy component including the influence from the periphery of each target position. In addition, a technique is known in which a backscattering exposure energy component is calculated, and a corrected exposure amount at each position is calculated based on the fog exposure energy component and the backscattering exposure energy component (see, for example, Patent Document 1).

  Further, the exposure data size is collated with the existing mask data, the corrected exposure data size is determined based on the collation result, and the design dimensional intensity calculation and the backscattering intensity calculation are performed using the corrected exposure data size. A technique for calculating a corrected exposure dose is known (see, for example, Patent Document 2).

Further, a step of exposing a plurality of patterns on the exposure surface at a predetermined interval, measuring a line width of the specific pattern, a step of changing the pattern interval to measure the exposure and the line width, and forward scattering of the exposure surface A step of calculating gazette scattering by simulation, a step of fitting a simulation result with a measurement result using an aberration of the optical system as a variable, a step of obtaining an aberration of the optical system, a step of obtaining a flare from a deviation between the measurement result and the simulation result, There is known a beam profile measuring method including a step of determining the acid diffusion by changing the process temperature (see, for example, Patent Document 3).
Japanese Unexamined Patent Publication No. 2004-140311 (paragraphs 0018 to 0048, FIG. 1) JP 2003-332225 A (paragraph 0029 to paragraph 0042, FIG. 1) JP 2002-353130 A (paragraphs 0031 to 0050, FIGS. 1 and 2)

  Even when proximity effect correction (PEC) and dry plate in-plane dose correction (PDEC) are performed at the same time, each calculates the shot time modulation amount (Smod and Smodpdec) without considering the influence of each other's electron beam dose correction. However, the shot time calculation unit of the normal drawing hardware data transfer system only adds up the shot time modulation amount Smodtotal. The calculation formula of Smodtotal is shown below.

  That is, despite the fact that the incident electron energy is changed by the in-plane irradiation dose correction, the proximity effect correction ignores it and calculates the magnitude of the proximity effect and calculates the shot time modulation amount. . For this reason, when the change of the shot time modulation amount due to the in-plane irradiation amount correction is large, the estimation of the proximity effect size by the proximity effect correction is far from the actual proximity effect size.

  As a result, the proximity effect cannot be sufficiently corrected, and as a result, a pattern as designed is not formed in electron beam writing. In order to solve this problem, it is necessary to adjust the coefficient for estimating the magnitude of the proximity effect, that is, the backscattering coefficient η representing the magnitude of the proximity effect according to the change in the incident electron energy by the in-plane exposure correction. is there.

The present invention was made in view of such problems, provide an electron beam drawing Ekata method and apparatus capable of accurately drawing optimally performing proximity correction and dry plate plane dose correction The purpose is to do.

(1) The invention described in claim 1 is a dry plate surface that irradiates a material surface with an electron beam to draw a predetermined pattern on the material surface and corrects variations in pattern dimensions depending on the position on the material surface. In the electron beam drawing method for performing proximity effect correction considering internal dose correction, the backscattering coefficient η representing the magnitude of the proximity effect is adjusted based on the correction value of dry plate in-plane irradiation correction for each drawing field , and the adjustment The amount of modulation of proximity effect correction is determined from the backscattering coefficient η and the ratio Ebp of accumulated energy obtained by integrating the amount of scattered electron energy, and the shot time of the electron beam is adjusted in consideration of the amount of modulation. A predetermined pattern is drawn.
(2) The invention described in claim 2 divides the drawing area on the material into a plurality of minute areas, and the correction value of the proximity effect and the variation in the drawing pattern dimensions depending on the position on the material for each minute area. Determine the correction value of the in-plane irradiation correction to be corrected, and the drawing hardware that adjusts the shot time to draw the drawing pattern on the material based on the correction value, and the proximity effect that calculates the correction value of the proximity effect Correction hardware, and in the proximity effect correction hardware,
A stored energy conversion table including a relationship between a backscattering coefficient η representing the magnitude of the proximity effect, a ratio Ebp of the magnitude of the stored energy for each drawing field, and a modulation amount for proximity effect correction ; Proximity effect correction is performed by a backscattering coefficient η based on a change in modulation amount of dry plate in-plane irradiation correction that corrects position-dependent pattern dimension variation, and a ratio Ebp of stored energy magnitude for each drawing field. The modulation amount is obtained.

(1) According to the first aspect of the present invention, the proximity effect correction and the dry plate in-plane irradiation correction amount occur optimally and accurate drawing can be performed.
(2) According to the second aspect of the invention, the optimum energy drawing is performed by providing the stored energy conversion table, obtaining the optimum beam shot time from this table, and adjusting the shot time to perform the beam drawing. be able to.

Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a block diagram showing an embodiment of the present invention. In the figure, reference numeral 1 denotes a beam drawing data and, in addition to an apparatus control computer system (hereinafter simply referred to as a computer) that performs various controls, 10 receives drawing data from the computer 1 and draws a pattern such as an LSI on a mask or the like. A normal drawing hardware data transfer system 20 is a proximity effect correction hardware data transfer system that provides drawing correction data to the normal drawing hardware data transfer system 10.

  The drawing data of the normal drawing hardware data transfer system 10 is given to the lithography system 3 after being corrected by the proximity effect correction hardware data transfer system (PEC). The lithography system 3 performs drawing using the drawing data supplied from the normal drawing hardware data transfer system as a mask.

  In the normal drawing hardware data transfer system 10, reference numeral 11 denotes a library expansion unit for registering the same repeated drawing data portion based on drawing data given from the computer 1, and 12 denotes a data memory (DM) provided with two libraries. It is connected to the developing unit 11. When one of the data memories 12 is being read, the other is in a read mode. 13 is a shot dividing unit that divides drawing graphic data given from the library development unit 11 into predetermined blocks, 14 is a dry plate surface dose correction register that stores dry plate surface dose correction data supplied from the computer 1, A shot time calculation unit 15 receives the drawing data given from the shot division unit 13 and calculates a shot time. The shot time calculator 15 is supplied with correction data from the dry plate surface dose correction register 14.

  A memory 16 stores a shot rank conversion table, a memory 17 stores a shot size conversion table, and a memory 18 stores a proximity effect correction amount map. These memories 16 to 18 give respective data to the shot time calculation unit 15. The shot time calculation unit 15 receives these data and performs a shot time calculation. Two memories 18 for storing the proximity effect correction amount map are provided.

  In the proximity effect correction hardware data transfer system 20, reference numeral 21 denotes a memory that receives data from the computer 1 and stores energy distribution reference data, and reference numeral 22 denotes a drawing area calculation unit that receives data from the computer 1 and calculates a drawing area. , 30 is an initial calculation unit to which data from the energy distribution reference table memory 21 and data from the drawing area calculation unit 22 are given. Reference numeral 40 denotes a recalculation unit to which the output of the drawing area calculation unit 22 is given.

  In the initial calculation unit 30, 23 receives an output from the energy distribution reference table memory 21 and the drawing area calculation unit 22, an electronic energy integration unit that integrates electronic energy, and 24 receives an output from the electronic energy integration unit 23. A memory for storing a stored energy distribution map, 25 is a stored energy conversion unit that converts the stored energy by receiving the output of the stored energy distribution map 24, and 26 stores a proximity effect correction amount by receiving the output of the stored energy conversion unit 25 Memory.

  In the recalculation unit 40, 23 ′ is an electronic energy integration unit that integrates the electron energy by receiving outputs of the drawing area calculation unit 22, the energy distribution reference table memory 21 and the proximity correction amount map memory 26, and 24 ′ is an electronic energy integration unit A memory for storing the stored energy distribution map by receiving the output of 23 ', 25' a stored energy conversion unit for converting the stored energy by receiving the output of the stored energy distribution map 24 ', and 26' for the stored energy conversion unit 25. It is a memory that receives the output of ′ and stores the proximity effect correction amount. The output of the memory 26 'is given to the proximity correction amount map memory 18 of the normal drawing hardware data transfer system 10, and is transferred only for the drawing field.

  Reference numeral 27 denotes a memory that stores an initial stored energy conversion table that receives control data from the computer 1, and reference numeral 27 ′ denotes a memory that stores a recalculated stored energy conversion table that also receives control data from the computer 1. These memories 27 and 27 'are provided as many as the number of drawing fields. The operation of the system configured as described above will be described as follows.

  First, an overall rough operation will be described. The energy distribution reference table and the stored energy conversion table are transferred in advance to the memory 21 in which the energy distribution reference table of the hardware transfer system 20 for proximity effect correction is stored and the memories 27 and 27 ′ in which the stored energy conversion table is stored. deep. In the proximity effect correction hardware data transfer system 20, all the pattern data to be subjected to the proximity effect correction drawing are sequentially one by one for the proximity effect correction for the proximity effect correction at the same time as the start of drawing (loading of drawing material). Data is transferred to the hardware data transfer system 20. At this time, the ratio of the incident electron energy at the time of drawing the pattern for each minute region (section) having the designated size is calculated.

  Prior to drawing one field, the proximity effect correction hardware data transfer system 20 has a distribution shown in the memory 21 that stores an energy distribution reference table in accordance with the ratio of the incident electron energy amount for each minute region (section). Is accumulated in a memory 24 that stores an accumulated energy distribution map for each minute region (section). In order to create a stored energy distribution map for one field to be drawn, the same amount of scattered electron energy is accumulated for neighboring field data (the creation of the memory 24 for storing the accumulated energy distribution map). Consider the effect of scattered electron energy from

  When the stored energy distribution map 24 for one field to be drawn is completed, the map is converted into the memory 26 for storing the proximity correction amount map using the memory 27 for storing the stored energy conversion table. When recalculation is performed, the proximity correction amount map obtained here is multiplied by the ratio of the incident electron energy amount for each minute region (section) to recreate the stored energy distribution map, and the stored energy conversion table 27 ' The operation of converting to the proximity correction amount map using is repeatedly performed according to the designated recalculation count. The obtained proximity correction amount map is transferred to the memory 18 that stores the proximity correction amount map of the normal drawing hardware data transfer system 10.

  On the other hand, the normal drawing hardware data transfer system 10 starts drawing of a field when reception of the proximity correction amount map of the drawing field is completed. At this time, the memory 18 on the side that receives the proximity correction amount map has a double buffer configuration so that the proximity correction amount map of the next drawing field can be received while one field is being drawn.

  With the start of drawing, in the normal drawing hardware data transfer system 10, the shot time is calculated by the shot time calculation unit 15 from the memory 18 that stores the proximity correction amount map according to the shot position of the electron beam to be drawn. When the size of the electron beam shot is larger than the size of the minute area (section) of the stored energy distribution map (when the electron beam shot spans a plurality of minute areas), the minute area (section) including the center of the electron beam shot ) Is considered to be effective for the electron beam shot. The pattern is drawn by applying the shot time obtained in this way to each electron beam shot.

  Here, a specific configuration of the present invention will be described. Stored energy conversion tables prepared using several types of backscattering coefficients η are stored in the memories 27 and 27 ′ for storing the stored energy energy conversion tables. On the other hand, depending on the shot time correction value of dry plate surface dose correction (PDEC) set in the dry plate surface dose correction register 14 from the computer 1, the stored energy conversion table initial calculation memory 27 and the stored energy conversion table. A mechanism for controlling from the computer 1 which shot time correction value of proximity effect correction (PEC) corresponding to which backscattering coefficient η stored in the recalculation memory 27 ′ is applied is added.

  In the proximity effect correction (PEC), the backscattering coefficient η representing the magnitude of the proximity effect is used to change the amount of incident electron energy by dry plate surface dose correction (PDEC), that is, the shot time by dry plate surface dose correction (PDEC). Correct according to the amount of modulation.

  In the computer 1, stored energy conversion table data and stored energy conversion recalculation data calculated using a plurality of types of backscattering coefficients η are stored in the memories 27 and 27 ′ in advance. Also stored is a variable C3 representing the rate of increase / decrease in the value of the backscattering coefficient η with respect to the shot time modulation amount (the rate of increase / decrease in shot time) by dry plate surface dose correction (PDEC). Here, C3 is obtained by experience.

When drawing is started, the stored energy conversion table initial calculation memory 27 and the stored energy conversion table recalculation memory 27 ′ respectively store the stored energy conversion table for initial calculation (the table of FIG. 2 described later). ) And stored energy conversion table recalculation (table of FIG. 3 described later) are transferred and stored.

Thereafter, in the initial calculation of the proximity effect correction system shown in the figure, the proximity effect is estimated using the same formula as the conventional technique (the formula (2) shown below), and the stored energy distribution map Ebp _{(n , m)} . The stored energy distribution map shows the ratio (E (k) _{n, m} ) of the amount of electron energy incident on each section (n, m) and the incident electrons when drawing an arbitrary figure (k). From the distribution (Eid _{i, j} ) of the backscattered electron energy intensity given to the peripheral section (i, j) by the hardware, the hardware calculates an equation for Ebp _{(n, m)} .

Here, the ratio (E (k) _{n, m} ) of the amount of incident electron energy is expressed as a ratio in which the energy when the electron beam is incident on the entire minute region (section) at a constant speed is 100%. To do. The backscattered electron energy intensity is expressed as a ratio where the backscattered electron energy intensity in the section irradiated with the electron beam is 4095, for example. The distribution of the backscattered electron energy intensity is specified by a separate parameter. r is the number of sections to the surrounding section in consideration of the influence of backscattered electrons, and f is the number of figures included in the pattern data.

  In the computer 1, the shot time modulation amount Smodpdec (k) of the dry plate surface dose correction (PDEC) of the pattern data k drawn in the drawing field including the minute area (section m, n) is the same as the conventional method. At the same time, the backscattering coefficient η (k) at that time is calculated according to the following equation.

η (k) = (C3 × Smodpde c (k) +1) × ηstd (3)

At the same time, η (k) is used as the component of η (k) for the initial calculation of the stored energy conversion table (table of FIG. 2 to be described later) to be applied in the converted energy conversion, for the first time of the stored energy conversion table. Used to control the calculation.

Thereafter, the stored energy is converted according to the component of η (k), and a proximity correction amount map (Smod map) for each drawing field is created. In the case of performing recalculation, similarly, in the recalculation of the PEC system, the proximity effect is estimated using the same formula (formula (4) shown below) as in the prior art, and the stored energy distribution map Ebp for each drawing field 'Calculate _{(m, n)} , calculate η (k) as a component of η (k) for recalculation of stored energy conversion table (table shown in Fig. 3 to be described later). A proximity correction amount map (Smod ′ map) for each field is created. Ebp ′ _{(m, n)} is expressed by the following equation.

Here, Smod is a shot time modulation amount. In the first recalculation, Smod given in the equation (4) is a shot time modulation amount for each minute region (section) obtained in the first calculation (0th recalculation).

  FIG. 2 is a diagram showing an example for the initial calculation of the stored energy conversion table. As described above, the computer 1 stores the stored energy conversion table for initial calculation. The X axis shows the stored energy distribution map Ebp (%) for each drawing field, the Y axis shows the backscattering coefficient η (k), and the Z axis shows the shot time modulation amount Smod (%). The shot time modulation amount Smod (%) is such that a is 0 to 10%, b is -10 to 0%, c is -20 to -10%, d is -30 to -20%, and e is -40 to -30. %, F is −50 to −40%, and g is −60 to −50%. The point where the value of the stored energy distribution map Ebp and the backscattering coefficient η (k) intersect is extended in the Z-axis direction, and the point intersecting the curved surface is the target shot time modulation amount Smod (%). The stored energy conversion unit 25 performs energy conversion with the shot time modulation amount Smod, and the proximity correction amount map memory 26 obtains a proximity correction amount map, which is reflected in the shot time calculation unit 15 and input to the lithography system 3. As a result, an optimum beam shot is performed.

FIG. 3 is a diagram showing an example for recalculation of the stored energy conversion table . In the Z axis, a is 0 to 20%, b is -20 to 0%, c is -40 to -20%, d is -60 to -40%, e is -80 to -60%, and f is -100. ~ 80%. This recalculation of the stored energy conversion table is given from the computer 1 for each drawing field. 'If the proximity correction amount map in the same storage from the energy conversion table first calculation 27 (Smod' stored energy conversion table recalculated for 27 obtains the map), the Smod 'proximity correction amount map memory 26 a map of the' To the proximity correction amount map 18 of the normal drawing hardware data transfer system 10, and the data calculated by the shot time calculation unit 15 is supplied to the lithography system 3. As a result, the shot time for each drawing field is calculated and given to the lithography system 3. Thereafter, pattern data is drawn by controlling the shot time of the electron beam in the same manner.

  As described above, according to the present invention, it is possible to optimally perform the proximity effect correction and the dry plate in-plane irradiation amount correction to perform accurate drawing. Further, in the electron beam drawing apparatus, each point on the surface of the dry plate is subjected to proximity effect correction (PEC) in consideration of dose correction (PDEC) in the dry plate surface such as fogging error correction (FEC). The backscattering coefficient η representing the magnitude of the proximity effect can be adjusted with respect to the correction value of the PDEC applied to the drawing at. Even when the change in the shot time modulation amount due to PDEC is large, the magnitude of the proximity effect due to PEC can be accurately estimated without departing from the magnitude of the actual proximity effect. Furthermore, the proximity effect can be sufficiently corrected.

It is a block diagram which shows one embodiment of this invention. It is a figure which shows the example for stored energy conversion table initial calculation. It is a figure which shows the example for stored energy conversion table recalculation.

Explanation of symbols

1 Computer system for computer control (computer)
2 3 Lithography system 10 Normal drawing hardware data transfer system 11 Library development unit 12 Data memory 13 Shot division unit 14 Dry plate surface dose correction register 15 Shot time calculation unit 16 Shot rank conversion table memory 17 Shot size conversion table memory 18 Proximity Correction Amount Map Memory 20 Proximity Effect Correction Hardware Data Transfer System 21 Energy Distribution Reference Table 22 Drawing Area Calculation Unit 23 Electronic Energy Integration Unit 23 ′ Electronic Energy Integration Unit 24 Accumulated Energy Distribution Map Memory 24 ′ Accumulated Energy Distribution Map Memory 25 stored energy conversion unit 25 'stored energy conversion unit 26 proximity correction amount map memory 26' proximity correction amount map memory 27 storage energy conversion table initial calculation memory 7 'stored energy conversion table recalculated memory 30 first calculation unit 40 recalculator

Claims (2)

Proximity effect correction in consideration of in-plane irradiation dose correction that irradiates an electron beam onto a material surface to draw a predetermined pattern on the material surface and corrects variations in pattern dimensions depending on the position on the material surface. In the electron beam drawing method to be performed,
Adjust the backscattering coefficient η representing the magnitude of the proximity effect based on the correction value of the dry plate in-plane irradiation correction for each drawing field ,
The modulation amount of the proximity effect correction is determined from the adjusted backscattering coefficient η and the ratio Ebp of the accumulated energy obtained by integrating the scattered electron energy amount,
Drawing the predetermined pattern by adjusting the shot time of the electron beam in consideration of the modulation amount ,
An electron beam drawing method characterized by the above. The drawing area on the material is divided into a plurality of minute areas, and the correction value of the proximity effect and the correction value of the in-plane irradiation correction that corrects the variation of the drawing pattern dimension depending on the position on the material are divided for each minute area. Drawing hardware that adjusts the shot time to draw a drawing pattern on the material based on the correction value ;
The proximity effect correction hardware for calculating the proximity effect correction value ,
In the proximity effect correction hardware,
A backscattering coefficient η representing the magnitude of the proximity effect,
A ratio Ebp of the magnitude of stored energy for each drawing field;
Establish a stored energy conversion table consisting of the relationship with the modulation amount of proximity effect correction ,
Backscattering coefficient η based on a change in modulation amount of dry plate in-plane irradiation correction for correcting variations in pattern dimensions depending on the position on the material surface,
An electron beam drawing apparatus, wherein a modulation amount for proximity effect correction is obtained from a ratio Ebp of the magnitude of stored energy for each drawing field .

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