JP4683163B2 - Photomask pattern drawing method - Google Patents

Description

  The present invention corrects the dimensional variation due to the position in the photomask surface without substantially affecting both the proximity effect correction (PEC) and the fogging effect correction that are originally performed, and further performs drawing. The present invention relates to a photomask pattern drawing method capable of correcting variations in pattern dimensions due to PED (Post Exposure Delay) in vacuum from the start to the end.

  With the recent high integration of semiconductor integrated circuits, photomasks used in the manufacture of semiconductor integrated circuits are required to have finer patterns and higher precision. Therefore, in the photomask manufacturing process, it is required to refine the pattern after drawing and increase the accuracy in the drawing process by the electron beam drawing apparatus.

  The following problems occur in the drawing process by the electron beam drawing apparatus. One of them is dimensional variation in the photomask surface. Even within the surface of one photomask, variation in dimensions may occur depending on the position in the surface. Even if the dimensional variation generated with a tendency is about 1 to 2 nm, it becomes a problem level.

  The other is a variation in dimensions due to PED (Post Exposure Delay) in a vacuum. PED is a delay in time from drawing to PEB (Post Exposure Bake). In particular, in the case of using a chemically amplified resist, the dimensions fluctuate between drawing in vacuum and PEB. The reason for this is that chemically amplified resist accelerates the reaction using the acid generated by drawing as a catalyst, and the resist is insolubilized or solubilized, but the generated acid diffuses from the exposed area to the unexposed area in the resist. Or when the basic component is present in the atmosphere, the basic component is adsorbed on the resist, thereby impairing the activity of the acid. The dimensional variation due to PED in vacuum has been ignored in the past. However, when the drawing time takes several tens of hours, there is a possibility that the drawing may fluctuate by several nanometers at the beginning and end of drawing.

  To deal with variations in the pattern dimensions in the photomask surface, there is a method of drawing while correcting the exposure amount (Dose amount) of the electron beam in the surface. For example, the beam shot time is changed depending on the location in the surface. The method of changing the dimensions and offsetting the fluctuations in dimensions, and the method of offsetting the fluctuations in dimensions by changing the blank sensitivity by changing the temperature depending on the location in the surface by baking after exposure have been put into practical use. .

  Further, there was no particularly effective method for dimensional variation due to PED in vacuum. For example, there is a method of drawing while correcting the exposure amount as the drawing time elapses.

  However, if drawing is performed while changing the exposure amount in order to correct the dimensional variation in the photomask surface, the exposure amount including the proximity effect correction (PEC) and the fogging effect correction is changed. And misalignment of the fogging effect correction occurs.

As a specific example of the proximity effect, in electron beam exposure, in which a resist film applied on a substrate is irradiated with an electron beam to draw a pattern, electron scattering in the resist film or back scattering from the substrate is repeated, whereby electrons are Charges are also accumulated in the peripheral part of the position irradiated with the beam. For this reason, the pattern formed by the subsequent development processing is formed in accordance with the amount of accumulated charge, and thus the pattern may be formed at an unexpected position. These phenomena are referred to as proximity effects, and are an impediment to high-precision pattern formation.

There are the following methods for correcting the proximity effect. That is, as an exposure condition at the time of electron beam exposure, for example, there is a method of controlling an electron beam irradiation amount and an acceleration voltage so that a prescribed pattern image is obtained. In this case, the distortion of the pattern due to the proximity effect when the electron beam exposure is performed based on the drawing data is calculated.
Further, a calculation for correcting the distortion is performed, and the calculation result is added to the control data of the electronic drawing exposure apparatus in the drawing data to update the drawing data. Thereafter, exposure is performed by an electron beam exposure apparatus to which the updated drawing data is input.

  As another method for correcting the proximity effect, exposure amount correction data at the time of electron beam writing determined by the correction amount of the optical proximity effect generated in the photolithography process is added to the mask pattern data, and at the time of electron beam writing. A method of manufacturing an optical proximity correction mask that performs electron beam exposure by changing the exposure amount in accordance with exposure amount correction data has been proposed (see, for example, Patent Document 1).

  As a specific example of the fogging effect, when the exposure area density varies from region to region, there is a problem that a difference occurs in the opening size of the resist pattern formed between regions having different exposure areas. This is because the electron beam is reflected by the light-shielding body, and the reflected electrons are further reflected by the objective lens of the electron beam exposure apparatus and irradiated to the resist. This is because the region having a larger exposure area density is exposed by the exposure amount by electron reflection according to the exposure time. This is said to be a fogging effect.

  There are the following methods for correcting the fogging effect. Currently, in order to correct the fogging effect, the area affected by the fogging effect and the amount affected by the fogging effect are calculated in advance from the drawing density, and the exposure amount of the pattern affected by the fogging effect during drawing is reduced. Thus, a method of correcting the dimensional variation due to the fogging effect is used.

  The above correction, which is corrected depending on the location in the mask plane, cannot correct time-dependent fluctuations such as dimensional changes that change over time. Some drawing machines do not have a function of changing the exposure amount depending on the location in the plane.

JP 2000-047365 A

  The present invention has been devised in view of the above problems, and does not substantially affect both the proximity effect correction (PEC) and the fogging effect correction that have been originally applied, and the position within the surface of the photomask. The present invention provides a photomask pattern drawing method that corrects variations in pattern dimensions due to PED, and further enables correction of changes in pattern dimensions due to PED in vacuum from the start to the end of drawing. With the goal.

In order to solve the above-mentioned problems in the present invention, in claim 1 , in the photomask pattern drawing by the electron beam, the offset value added to the shot size of the electron beam drawing apparatus is gradually increased according to the elapsed time from the drawing start. The photomask pattern drawing method is characterized in that offset correction is performed to increase or decrease, and pattern drawing is performed by changing the shot size.

  According to the photomask pattern drawing method of the first aspect of the present invention, it is possible to correct the dimensional variation depending on the position in the surface of the photomask without changing the exposure amount. In addition, no complicated calculation or control is required, and the vacuum from drawing to completion without adversely affecting both the proximity effect correction (PEC) and the fogging effect correction originally applied. It is possible to correct dimensional variations due to PED inside.

(A)-(c) shows the change of the shot size at the time of offset correction of 1 nm and -1 nm with respect to the shot size of 1 micrometer. (A) shows a shot size of 1 μm without offset correction. (B) shows a shot size of 0.999 μm with an offset correction of −1 nm for a shot size of 1 μm. (C) shows a shot size of 1.001 μm with an offset correction of 1 nm for a shot size of 1 μm. (A) And (b) shows an example of the variation variation of the pattern dimension in the photomask surface, and (a) schematically shows the variation variation of the pattern size when the photomask surface is divided into 36 parts. Show. (B) shows variation data of the pattern dimension when the in-plane of the photomask is divided into 36 parts. An example of offset correction according to each position in the photomask surface of this invention is shown. (A) and (b) apply an offset correction corresponding to each position in the plane shown in FIG. 3 to the photomask showing the variation in pattern dimensions in the plane of FIGS. 2 (a) and 2 (b). FIG. 6 shows variation in the pattern dimension in the surface of the photomask 200 obtained by changing the shot size and drawing the pattern. FIG. 5A shows the variation in pattern dimension when the photomask surface is divided into 36 parts. Is shown schematically. (B) shows variation data of the pattern dimension when the in-plane of the photomask is divided into 36 parts. The pattern size variation example according to PED (Post Exposure Delay) in a vacuum from the start to the end of the drawing, in accordance with the elapsed time from the writing start according to claim 1 of the present invention, the electron beam drawing apparatus An example of offset correction while gradually decreasing the offset value added to the shot size is shown.

An embodiment of the invention will be described.
FIGS. 1A to 1C show changes in shot size when offset correction of 1 nm and −1 nm is performed on a shot size of 1 μm.
FIG. 1A shows a shot size of 1 μm without offset correction. FIG. 1B shows a shot size of 0.999 μm when an offset correction of −1 nm is performed for a shot size of 1 μm, and a gap of 0.2 nm is left between shots. FIG. 1C shows a shot size of 1.001 μm when an offset correction of 1 nm is performed with respect to a shot size of 1 μm, and an overlap of 0.1 nm can be made between shots. As described above, when the offset correction of 1 nm and −1 nm is performed for the shot size of 1 μm, there is a gap between shots or double exposure, but if the deviation is about 1 to 2 nm, the pattern shape is changed. There is no effect.

2 (a) and 2 (b) show an example of variation in the pattern dimension in the photomask surface. FIG. 2 (a) shows the variation in pattern dimension when the photomask surface is divided into 36 parts. FIG. 2B schematically shows variation in the pattern dimension when the in-plane of the photomask is divided into 36 by data, and the variation range of the pattern dimension in the photomask plane is 2 nm.

  FIG. 3 shows an example of offset correction according to each position in the photomask surface. Here, the inside of the photomask surface is divided into 9 of 3 × 3, and the shot size is 1 μm at each position. Specific examples of shot sizes at respective positions obtained by performing offset correction of −1 nm and 1 nm will be shown.

  4 (a) and 4 (b) apply offset correction corresponding to each position in the plane shown in FIG. 3 to the photomask showing the variation in the pattern dimensions in the plane in FIGS. 2 (a) and 2 (b). The variation in the pattern dimension in the surface of the photomask 200 obtained by changing the shot size and drawing the pattern is shown. In this way, by performing offset drawing according to each position in the photomask surface and changing the shot size to draw the pattern, there is 2 nm variation variation in the pattern size in the surface when no offset correction is applied. Is improved to 0.8 nm. If the offset correction area is divided finely, it is possible to further improve the variation in the pattern dimension in the plane.

FIG. 5 shows an electron beam drawing apparatus according to an elapsed time from the start of drawing according to claim 1 for an example of pattern dimension variation due to PED (Post Exposure Delay) in vacuum from the start to the end of drawing. 3 shows an example of offset correction while gradually decreasing the offset value added to the shot size. The y-axis shows the variation in pattern dimension at each drawing time, and the x-axis shows the elapsed time from the start of drawing.
In the uncorrected graph of FIG. 5, the variation amount of the pattern dimension 20 hours after the start of drawing occurs 2.0 nm. For this reason, in the graph with correction, an offset correction that reduces the shot size by 0.1 nm every hour can be used to control the pattern dimension fluctuation amount after drawing to within 0.1 nm. As described above, variation in the pattern dimension in the surface of the photomask obtained by pattern drawing can be suppressed.

100, 200: Variation in pattern size of photomask 110: Example of offset correction according to each position in the photomask surface

Claims (1)

  In photomask pattern drawing with an electron beam, offset correction is performed to gradually increase or decrease the offset value added to the shot size of the electron beam lithography system according to the elapsed time from the start of drawing, and the pattern is changed by changing the shot size. A photomask pattern drawing method characterized by drawing.