1. Field of the Invention
The present invention relates to patterning processes for fabricating IC devices. More particularly, the present invention relates to a method for forming a composite pattern that includes different types of patterns, especially narrower and wider patterns, with more than one masks and etching steps.
2. Description of the Related Art
In IC manufacturing, a composite pattern including different types of patterns, e.g., narrower and wider patterns, can be formed using more than one masks of different types. For example, U.S. Pat. No. 6,573,010 to Kling et al. teaches a double-exposure method for forming gate line patterns with wider portions on the field oxide, wherein an alternating phase-shift mask (Alt-PSM) is used to define the narrower gate regions and a binary mask is used to define the wider portions.
However, because the trimming effect is isotropic, the line end of each narrower portion 200e having a line end is also shortened, so that the predetermined line length cannot be achieved and the required electrical characteristics cannot be obtained.
In view of the foregoing, the present invention provides a method for forming a composite pattern, which includes different types of patterns, with more than one masks and etched steps.
Another object of this invention is to provide a method for forming a pattern having a narrower portion and a wider portion with two masks and two etched steps.
Still another object of this invention is to provide a method for forming a gate line pattern or a split-gate pattern that includes a narrower gate region having a line end, which does not suffer from the line-end shortening problem.
The method for forming a composite pattern including different types of patterns of this invention is described as follows. A substrate having a material layer thereon and multiple masks each having at least one type of pattern thereon are provided. Then, the following steps (1)-(3) are conducted for multiple cycles, with a different mask being used in each cycle, until all of the masks have been used. In step (1), one mask is used to form one photoresist pattern over the substrate. In step (2), the material layer is etched/patterned with the photoresist pattern as a mask. In step (3), the photoresist pattern is removed. In the method, the imaginary pattern defined by the overlap between the patterns of all of the masks includes the at least one type of pattern of each mask.
The method for forming a target pattern having a narrower portion and a wider portion is based on the above method for forming a composite pattern of this invention, wherein two masks including a first mask and a second mask are used, and an etching step is conducted after each mask is used to formed a photoresist pattern. The pattern of the first mask includes the pattern of the narrower portion and also covers the area of the wider portion, and the pattern of the second mask includes the pattern of the wider portion and also covers the area of the narrower portion. In the method, the first mask can be used before or after the second mask, and an additional trimming step may be conducted after the first mask is used to further reduce the width of the narrower portion.
In an embodiment of this invention, the narrower portion of the target pattern has a line end, and the first mask has an opaque layer and two transparent regions in the opaque layer thereon. The portion of the opaque layer between the two transparent regions defines the narrower portion, and the second pattern of the second mask has a boundary passing the corresponding position of the line end on the second mask. Thus, a line end of the narrower portion can be defined by the boundary of the photoresist pattern formed with the second mask. Such a first mask may be an Alt-PSM, for example, where the two transparent regions in the opaque layer are a pair of zero-shift region and π-shift region.
In addition, the target pattern in the above embodiment may be a gate line pattern with narrower gate regions and wider portions on field oxide, while the gate line pattern may be a split-gate pattern.
According to the above embodiment of this invention, since the first mask causes two openings separated by a narrower pattern to form in the first photoresist layer, there is no line end of the first photoresist pattern, while the line end of the target pattern is defined by the non-trimmed second photoresist pattern formed with the second mask. Therefore, the trimming after formation of the first photoresist pattern merely reduces the width of the narrower pattern of the first photoresist pattern, so that the narrower portion of the patterned material layer has a reduced width without line-end shortening.
It is to be understood that both the foregoing general description and the following detailed description are exemplary, and are intended to provide further explanation of the invention as claimed.
This invention will be further explained with formation of a pattern including wider and narrower portions as an example, which is not intended to restrict the scope of this invention. This invention can also be applied to the cases where more than two masks are used to define a more complex composite pattern.
In step (b), a lithography process using a mask having the same opaque pattern of the Alt-PSM 10 of
In step (c), a trimming step is conducted to reduce the width of the narrower pattern 320a to a predetermined width, as indicated by the small arrows. Since there is no line end of the narrower pattern 320a present, no line-end shortening occurs in the trimming step.
In step (d), the material layer 310 is etched using the patterned photoresist layer 320 as a mask, so that openings 312 are formed in the material layer 310 exposing portions of the substrate 300 and defining the narrower patterns 310a in the trimming-reduced width with no line end. The patterned photoresist layer 320 is then removed.
In step (e), a new photoresist layer 330 is formed over the substrate 300 and then patterned using a mask having the same pattern of the mask 20 of
In step (f), the material layer 310 is etched again using the patterned photoresist layer 330 as a mask, so that wider patterns 310b are formed. Meanwhile, since the line end position of each narrower portion 310a requiring a line end in design is passed by a boundary of the patterned photoresist layer 330, each of such narrower portions 310a is cut by the etching at the predetermined line-end position to form a line end thereof. The narrower portions 310a, which include those having a line end and those without a line end, and the wider portions 310b together constitute the target pattern 310c. After that, the patterned photoresist layer 330 is removed.
Moreover, the pair of transparent regions (e.g., the pair of zero-shift region 16 and π-shift region 14) for defining a narrower portion 310a with a line end may be designed substantially extending beyond the corresponding line-end position on the first mask (e.g., Alt-PSM 10), so as to make the narrower pattern 320a and 310a respectively in steps (c) and (d) substantially extend beyond the predetermined line-end position. Thus, even if the photoresist layer 330 formed later is mis-aligned in the direction of the line end making the boundary thereof exceeding the predetermined line-end position, a narrow line end can still be defined successfully.
Alternatively, the patterning process using the second mask 20 can be conducted before that using the first mask (e.g., Alt-PSM 10), while a trimming step can also be performed to the patterned photoresist layer formed with the first mask in such cases. Briefly speaking, in the alternative method, a patterned photoresist layer 330 as shown in
Since there is no line end of the narrower photoresist patterns present in the trimming step and the line ends of the target pattern are defined by another photoresist pattern formed with another mask without being trimmed, no line-end shortening occurs to the narrower portions of the target pattern.
It will be apparent to those skilled in the art that various modifications and variations can be made to the structure of the present invention without departing from the scope or spirit of the invention. In view of the foregoing, it is intended that the present invention covers modifications and variations of this invention provided they fall within the scope of the following claims and their equivalents.