Method for improving alignment signals accuracy of step-projection photoetching machine

Abstract

The invention relates to a method for improving alignment signals of a step projection photoetching machine. Under the condition of not occupying more layout space, permutations and combinations of target crosses and alignment crosses are made to be as more as possible to improve alignment accuracy and yield of silicon wafers, the common problem of difference of alignment signals caused by product process diversity in the conventional step protection photoetching machine, including the influence of production line process fluctuation or product process change on the alignment signals, can be solved, the traditional one mode for selecting the alignment signals by singly modifying plate parameters is changed into two modes of modifying plate and workbench parameters, and the two modes are combined for selecting the alignment signals. Through the change, the alignment modes are greatly enriched.

Description

technical field [0001] The invention relates to a signal alignment method, in particular to a method for improving the alignment signal accuracy of a projection stepping photolithography machine. Background technique [0002] At present, the mainstream lithography machine used in the large-scale integrated circuit production line is basically a stepper projection lithography machine. In the step-by-step exposure method, the lithography plate does not include all chip graphics on the silicon wafer, but only includes Part of the repeated chip pattern, only a part of the silicon wafer is exposed at a time, and the entire silicon wafer is exposed by repeated stepping exposure. [0003] The main working principle of the projection stepper is to use the mirror system to project the pattern on the entire mask plate of the 1:1 image onto the surface of the silicon wafer. The machine board positioning, silicon wafer global alignment, silicon wafer field-to-field alignment all adopt ...

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Problems solved by technology

[0004] Since the alignment of the UT machine is mainly carried out by the target cross and the alignment cross, the corresponding results of the target cross and the alignment cross are related to the signal strength of the silicon chip, which is reflected on the silicon chip, which is the difference in the alignment result. According to the general layout, under the same machine type and light intensity, the time to expose a batch of silicon wafers with good signals is short, the probability of die abnormality is low, and the yield rate is high. When exposing a batch of silicon wafers with poor signals, it takes Multiplied, which greatly affects the production capacity in the fab, and the probability of abnormalities such as registration due to poor signal is high, the rework rate is high, and the yield rate is low

The traditional way of using a special version to confirm the target cross and align the cross through a short process can solve the alignment problem of quite a few varieties with the same process. Assuming that the process parameters are stable, the normal mass production of such products can be guaranteed; However, there is a problem with this experimental method: that is, every time a new process is added, or a new process is added, the verification experiment of the target cross and the alignment cross must be carried out. Or there are fluctuations in the process of the aluminum layer, even if it is within the qualified range, it will have a direct impact on the alignment of the photolithography

[0005] According to the traditional layout, the area occupied by the target cross and the alignment cross on the layout should not be too large, otherwise the relative effective die will be reduced. According to different processes, the current popular layout method is to arrange 9 to 16 columns in the X direction, and arrange 9 to 16 columns in the Y direction. Arrange the target cross-alignment cross in the way of 2 rows up and down in the direction; according to this layout method, the user can generally choose only 2 rows up and down when aligning. If there is a fear of process fluctuations, there will be signal differences In other cases, it is necessary to increase the combination of the alignment cross and the target cross, which will occupy the effective die space; if the combination of the alignment cross and the target cross is not increased, it is easy to have abnormal registration or no exposure; Lithography consumes more time and energy for such exposure problems and alignment cross-target cross experiments

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