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EP-3938837-B1 - IMPROVED SELF-MOIRÉ GRATING DESIGN FOR USE IN METROLOGY

EP3938837B1EP 3938837 B1EP3938837 B1EP 3938837B1EP-3938837-B1

Inventors

  • LEVINSKI, VLADIMIR
  • YOEL, Feler

Dates

Publication Date
20260506
Application Date
20200320

Claims (13)

  1. A grating (100) for use in metrology comprising: a periodic structure (102) comprising a plurality of units (104) having a pitch P, at least one unit of said plurality of units comprising: at least a first periodic sub-structure (110) having a first sub-pitch P1 between two adjacent elements of the first periodic sub-structure (110), P1 being smaller than said pitch P, and at least a second periodic sub-structure (112) arranged along-side, separated from, and non-interlaced with said first periodic sub-structure within said at least one unit and having a second sub-pitch P2 between two adjacent elements of the second periodic sub-structure (112), P2 being smaller than said pitch P and different from said first sub-pitch P1, P1 and P2 being selected to yield at least one Moiré pitch P m = P1·P2/(P2 - P1), said pitch P being an integer multiple of said first sub-pitch P1 and of said second sub-pitch P2; the elements of the first periodic sub-structure (110) being arranged in a co-linear configuration with the elements of the second periodic sub-structure (112).
  2. The grating according to claim 1, wherein P/ P m is: substantially equal to 1; or substantially equal to 2.
  3. The grating according to claim 1, wherein P ≥ 200 nm.
  4. The grating according to claim 3, wherein P1 and P2 < 200 nm.
  5. The grating according to claim 1, wherein said first and second periodic sub-structures (110, 112) lie along a common axis, P1 and P2 being defined along said common axis.
  6. A metrology target (300) for measurement of misregistration between layers of a semiconductor device, said target comprising at least two gratings (100), at least one of said at least two gratings comprising the grating of claim 1, said at least two gratings being arranged in a mutually layered configuration.
  7. The metrology target according to claim 6, wherein said at least two gratings have: the same Moiré pitch; or mutually different Moiré pitches.
  8. A method for forming a grating (100) for use in metrology comprising: providing a periodic structure (102) comprising a plurality of units (104) having a pitch P, at least one unit of said plurality of units comprising: at least a first periodic sub-structure (110) having a first sub-pitch P1 between two adjacent elements of the first periodic sub-structure (110), P1 being smaller than said pitch P, and at least a second periodic sub-structure (112) arranged along-side, separated from, and non-interlaced with said first periodic sub-structure within said at least one unit and having a second sub-pitch P2 between two adjacent elements of the second periodic sub-structure (112), P2 being smaller than said pitch P and different from said first sub-pitch P1, P1 and P2 being selected to yield at least one Moiré pitch P m = P1·P2/(P2 - P1), said pitch P being an integer multiple of said first sub-pitch P1 and of said second sub-pitch P2; the elements of the first periodic sub-structure (110) being arranged in a co-linear configuration with the elements of the second periodic sub-structure (112).
  9. The method according to claim 8, wherein P/ P m is: substantially equal to 1; or substantially equal to 2.
  10. The method according to claim 8, wherein P ≥ 200 nm; or wherein P ≥ 200 nm; and wherein P1 and P2 < 200 nm.
  11. The method according to claim 8, and also comprising arranging said first and second periodic sub-structures (110, 112) to lie along a common axis, P1 and P2 being defined along said common axis.
  12. The method according to claim 8, and also comprising arranging at least two gratings in a mutually layered configuration so as to form a metrology target for measurement of misregistration between layers of a semiconductor device, at least one of said at least two gratings comprising the grating of claim 1.
  13. The method according to claim 12, wherein said at least two gratings have: the same Moiré pitch; or mutually different Moiré pitches.

Description

FIELD OF THE INVENTION The present invention relates generally to metrology and more particularly to gratings for use in metrology. BACKGROUND OF THE INVENTION Various types of gratings for use in metrology are known in the art. US2018/081193 discloses self-moiré target design principles for measuring unresolved device-like pitches. SUMMARY OF THE INVENTION The present invention seeks to provide novel, readily printable gratings for use in metrology targets for providing highly accurate measurements. There is thus provided in accordance with a preferred embodiment of the present invention a grating for use in metrology as recited in claim 1. There is also provided a metrology target for measurement of misregistration between layers of a semiconductor device as recited in claim 6. There is additionally provided in accordance with another preferred embodiment of the present invention a method for forming a grating for use in metrology as recited in claim 8. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will be understood and appreciated more fully from the following detailed description, taken in conjunction with the drawings in which: Fig. 1 is a simplified schematic top view illustration of a grating useful in metrology measurements, constructed and operative in accordance with a preferred embodiment of the present invention;Fig. 2 is a simplified schematic top view illustration of a unit forming part of a grating of the type shown in Fig. 1;Fig. 3 is a simplified schematic side view illustration of a metrology target including mutually layered gratings constructed and operative in accordance with another preferred embodiment of the present invention;Fig. 4 is a simplified schematic side view illustration of a metrology target including mutually layered gratings, constructed and operative in accordance with yet another preferred embodiment of the present invention; andFig. 5 is a simplified flowchart illustrating a metrology method using a grating of the type shown in any of Figs. 1 - 4. DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Reference is now made to Fig. 1, which is a simplified schematic top view illustration of a grating useful in metrology measurements and to Fig. 2, which is a simplified schematic top view illustration of a unit forming part of a grating of the type shown in Fig. 1, constructed and operative in accordance with a preferred embodiment of the present invention. As seen in Figs. 1 and 2, there is provided a grating 100 comprising a periodic patterned structure 102 formed by a plurality of repeating units 104. Here, by way of example, a portion of grating 100 is shown including two complete units 104 shown to be mutually identical. Grating 100 is preferably adapted for formation on a semiconductor device, in order to facilitate metrology measurements relating to the device based on measurements obtained from the grating formed thereon. Such metrology measurements may include imaging measurements, Moire interference based measurements, scatterometry based measurements or other types of measurements. It is appreciated that such measurements are performed on structures such as grating 100, rather than directly with respect to the device itself, since the design rule pitch of the device is typically of a scale that is unresolved by optical measurement tools. Particularly preferably, grating 100 may be incorporated in a target comprising multiple layers of gratings and used for the measurement of misregistration between layers in the manufacture of semiconductor devices, as is further detailed hereinbelow with reference to Figs. 3 and 4. Units 104 preferably form periodic structure 102 having a pitch P. Pitch P is preferably of a magnitude so as to be resolvable by standard optical measurement tools, such as, by way of example only, Archer family tools commercially available from KLA Corporation of California, USA, for example A700 and ATL100. By way of example, pitch P may be of the order of several hundred or several thousand nanometers. In accordance with one preferred embodiment of the present invention, pitch P may be in the range of 200 - 4500 nm. In accordance with another preferred embodiment of the present invention, pitch P may in the range of 1200 - 2500 nm. It is appreciated that such a pitch is typically much larger than the pitch of the device design rule of the semiconductor device upon which grating 100 is formed. As seen most clearly in Fig. 2, at least one unit of units 104 comprises at least a first periodic sub-structure 110 and at least a second periodic sub-structure 112 aligned therewith. Here, by way of example, each of units 104 of grating 100 is shown to comprise therewithin first periodic sub-structure 110 and second periodic sub-structure 112. First and second periodic sub-structures 110 and 112 are preferably arranged in a side-by-side configuration along a common axis 114 so as to combinedly extend along substantially an entirety of unit 104, thus d