Method and system of reducing charged particle beam write time

#The present disclosure is related to lithography, and more particularly to the design and manufacture of a surface which may be a reticle, a wafer, or any other surface, using charged particle beam lithography.

#Three common types of charged particle beam lithography are unshaped (Gaussian) beam lithography, shaped charged particle beam lithography, and multi-beam lithography. In all types of charged particle beam lithography, charged particle beams shoot energy to a resist-coated surface to expose the resist.

#Shaped charged particle beam lithography may be variable shaped beam (VSB) or character projection (CP), in which a shot of a precise electron beam is shaped and steered so as to expose a resist-coated surface, such as the surface of a wafer or the surface of a reticle. In VSB, these shapes are simple shapes, usually limited to rectangles of certain minimum and maximum sizes and with sides which are parallel to the axes of a Cartesian coordinate plane (i.e. of “manhattan” orientation), and 45 degree right triangles (i.e. triangles with their three internal angles being 45 degrees, 45 degrees, and 90 degrees) of certain minimum and maximum sizes. At predetermined locations, doses of electrons are shot into the resist with these simple shapes. The total writing time for this type of system increases with the number of shots. In CP, there is a stencil in the system that has in it a variety of apertures or characters which may be complex shapes such as rectilinear, arbitrary-angled linear, circular, nearly circular, annular, nearly annular, oval, nearly oval, partially circular, partially nearly circular, partially annular, partially nearly annular, partially nearly oval, or arbitrary curvilinear shapes, and which may be a connected set of complex shapes or a group of disjointed sets of a connected set of complex shapes. An electron beam can be shot through a character on the stencil to efficiently produce more complex patterns on the reticle. In theory, such a system can be faster than a VSB system because it can shoot more complex shapes with each time-consuming shot. Thus, an E-shaped pattern shot with a VSB system takes four shots, but the same E-shaped pattern can be shot with one shot with a CP system.

#FIG. 1 illustrates an example of a variable shaped beam (VSB) charged particle beam system, as known in the art.

#FIG. 2 illustrates an example of an electro-optical schematic diagram of a multi-beam exposure system, as known in the art.

#FIGS. 3A-3D illustrate various types of shots, as known in the art.

#The present disclosure describes methods for reducing charged particle beam write time by reducing the dose required to expose a shot or a shape in a relatively low-density exposure area by casting an artificial background dose in the area.

#The cost of charged particle beam lithography is directly related to the time required to expose a pattern on a surface, such as a reticle or wafer. Conventionally, the exposure time is related to the amount of exposure required to write the pattern. For the most complex integrated circuit designs, forming the set of layer patterns, either on a set of reticles or on a substrate, is a costly and time-consuming process. It would therefore be advantageous to be able to reduce the exposure required to form these patterns, on a reticle and other surfaces, such as by reducing the time required to write them.

#Referring now to the drawings, wherein like numbers refer to like items, FIG. 1 illustrates an embodiment of a lithography system, such as a charged particle beam writer system, in this case an electron beam writer system 100, that employs a variable shaped beam (VSB) to manufacture a surface 112. The electron beam writer system 100 has an electron beam source 114 that projects an electron beam 116 toward an aperture plate 118. The plate 118 has an aperture 120 formed therein which allows the electron beam 116 to pass. Once the electron beam 116 passes through the aperture 120 it is directed or deflected by a system of lenses (not shown) as electron beam 122 toward another rectangular aperture plate or stencil mask 124. The stencil 124 has formed therein a number of openings or apertures 126 that define various simple shapes such as rectangles and triangles. Each aperture 126 formed in the stencil 124 may be used to form a pattern in the surface 112 of a substrate 134, such as a silicon wafer, a reticle or other substrate. An electron beam 130 emerges from one of the apertures 126 and passes through an electromagnetic or electrostatic reduction lens 138, which reduces the size of the pattern emerging from the aperture 126. In commonly available charged particle beam writer systems, the reduction factor is between 10 and 60. The reduced electron beam 140 emerges from the reduction lens 138 and is directed by a series of deflectors 142 onto the surface 112 as a pattern 128. The surface 112 is coated with resist (not shown) which reacts with the electron beam 140. The electron beam 122 may be directed to overlap a variable portion of an aperture 126, affecting the size and shape of the pattern 128. Blanking plates (not shown) may be used to deflect the beam 116 or the shaped beam 122 so as to prevent the electron beam from reaching the surface 112 during a period after each shot when the lenses directing the beam 122 and the deflectors 142 are being re-adjusted for the succeeding shot. Stencil 124 may in itself act as a deflector by having the beam 116 be deflected to hit unopened portions of the stencil 124. Typically the blanking plates are positioned so as to deflect the electron beam 116 to prevent it from illuminating aperture 120. Conventionally, the blanking period may be a fixed length of time, or it may vary depending, for example, on how much the deflector 142 must be re-adjusted for the position of the succeeding shot. Note that VSB systems can be thought of as a special (simple) case of character projection, where the characters are just simple characters, usually rectangles or 45 degree right triangles. It is also possible to partially expose a character. This can be done by, for instance, blocking part of the particle beam. In this disclosure, partial projection is used to mean both character projection and VSB projection.