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SEMI P43-0304 © SEMI 2004 15 allowing compensation of area gain and area los s. In case of, e.g., corner area devation uniformity , line-edge roughness will influence th e measurement result. NOTICE: SEMI makes no warran…

SEMI P43-0304 © SEMI 2004 14

8.4.2.1 In the center-of-gravity (COG) method the

COG of actual and nominal features are superimposed.

8.4.2.2 In the area based method the absolute feature

area deviation between the actual and nominal features

is minimized.

8.4.2.3 In the line-edge based method, alignment is

performed by minimizing the distance between multiple

actual and nominal edges.

(a)

(b)

Figure 22

Alignment of nominal and actual feature

(a) by center of gravity (COG) only, left is the

intended overlay, right is actual overlay from the

COG method, leading to an incorrect result.

(b) by the use of alignment markers.

8.4.3 Alignment is preferably done on dedicated

alignment features (markers), which are symmetric and

not clipped, and their position does not suffer from the

resolution of the imaging process. Crosses are typically

used, as they have X and Y components, which can be

used to correct for rotational error if only one marker

were present.

8.4.4 Additional markers allow for more accurate

rotational compensation and decouple magnification

errors of the feature to be measured from sizing errors.

8.4.5 If no markers are present, one of the methods

above can be attempted on the feature to be measured

or on other features in the ROI, but in such situation

alignment may be less accurate, especially if these

features are clipped (see Figure 22).

8.5

Measured Values

8.5.1 By analogy to Section 7 (1D Mask Qualification

Terminology) a measured qualification parameter can

be defined for every 2D (true) qualification parameter

defined in Section 8.2. In Section 7 this was done

immediately after the definition of the true parameter,

whereas here the measured parameter is treated in a

generic way. Thereby, one 2D qualification parameter

is used for the explanation, i.e., measured corner area

difference and its uniformity, as examples for all other

2D qualification parameters and their uniformity.

NOTE 43: The most critical feature in terms of impact of the

measurement details to the measured values is the size of a

contact near the resolution limit of the metrology tool and of

the mask patterning process.

8.5.2 measured corner area difference — measured

value of corner area difference, stating as mandatory

information, in addition to that of corner rounding

(Section 8.2.3.1):

• calibration method used

• measurement method used (SEM, optical

reflection, optical transmission, AFM, etc.) and its

resolution limit,

• edge detection algorithm and parameters,

• precision (SEMI P24),

and as optional information :

• measurement tool (vendor, model or any tool

specific options).

8.5.3

measured corner area difference uniformity —

measured value of corner area difference uniformity,

thereby stating as mandatory information in addition to

that of corner area difference uniformity and of

measured corner area difference:

• the number of measurement points used,

and as optional information:

• the spatial distribution of measurement locations,

e.g., by coordinates of measurement locations.

DEFAULT is spread evenly over the measurement

area.

NOTE 44: Edge roughness, either originating from the

process (Note 19 in Section 8.2.2) or from the measurement

technique used, may influence the measurement result. This

is not the case for the two examples treated above, as the

difference parameter filters out the effect of roughness by

4 See reference document in Section 4.2.

allowing compensation of area gain and area loss. In case of,

e.g., corner area devation uniformity, line-edge roughness

will influence the measurement result.

NOTICE: SEMI makes no warranties or

representations as to the suitability of the standards set

forth herein for any particular application. The

determination of the suitability of the standard is solely

the responsibility of the user. Users are cautioned to

refer to manufacturer’s instructions, product labels,

product data sheets, and other relevant literature,

respecting any materials or equipment mentioned

herein. These standards are subject to change without

notice.

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