Key Photolithographic Outputs

Transcription

1 Exposure latitude Depth of Focus Exposure latitude Vs DOF plot Linearity and MEEF Isolated-Dense Bias NILS Contrast Swing Curve Reflectivity Curve 1

2 Exposure latitude:the range of exposure energies (usually expressed as a percent variation from the nominal) which keeps the linewidth within specified limits. Example:A minimum exposure latitude of 10% is needed for this process in order to get adequate CD control. % = [Exposure for low CD spec - Exposure for high CD spec]/ Exposure dose for Target CD DUV Photoresist FEM Photoresist linewidth CD (um) Upper Spec CD Target CD Lower Spec CD y = x R 2 = Exposure Dose (mj/cm2) 2

3 Depth of Focus 200 nm spacewidth: Focus range for target CD +/- 10% DUV: UV6 ( 6275A) on SiON on Polysilicon 600 Spacewidth CD nm ( 1:1 200nm) Focus microns 8 mj/cm2 9 mj/cm2 10 mj/cm2 11 mj/cm2 12 mj/cm2 13 mj/cm2 14 mj/cm2 15 mj/cm2 16 mj/cm2 17 mj/cm2 18 mj/cm2 19 mj/cm2 20 mj/cm2 2 1 mj/cm2 22 mj/cm2 23 mj/cm2 24 mj/cm2 2 5 mj/cm2 3

4 Depth of Focus 250nm linewidth: Prolith setup with TARC ( JSR NFC- 540) and BARC ( SiON) 4

5 Depth of Focus 250nm linewidth: Focus range for target CD +/- 10% 248nm DUV UV6 with TARC/BARC 250nm L/S Photoresist CD nm ( 1:1=250nm) best focus = -0.35u mj/cm2 6 mj/cm2 6.5 mj/cm3 7 mj/cm2 7.5 mj/cm4 8 mj/cm2 8.5 mj/cm5 9 mj/cm2 9.5 mj/cm6 10 mj/cm mj/cm7 11 mj/cm mj/cm8 12 mj/cm mj/cm9 13 mj/cm mj/cm10 14 mj/cm2 DOF = 1.0u Focus Microns 5

6 Depth of Focus 250nm linewidth: Sidewall angle ( >80 degrees) and CD spec range( CD target +/-10%) specs are met! 6

7 Best Focus 250nm linewidth: Optimal focus = centered in focal range for best dose to achieve maximum sidewall angle and target CD 7

8 Exposure latitude Vs DOF plot from Prolith example: Depth of Focus 250nm linewidth: Taken from CD Vs Focus plot ( FEM) Maximum process rectangle that contains CDs and sidewall angles meeting the specified criteria. The Exposure latitude is taken as the height of the rectangle and the DOF as the base of the rectangle. Maximum DOF = single dose( 0% exposure latitude), while Maximum exposure latitude = 0 DOF (1 focus setting) % Expsoure Latitude Exposure latitude Vs DOF 300nm dense Linewidth from Prolith DOF microns 8

9 Linearity and MEEF(Mask Error Enhancement Factor): Slope of Wafer CD Vs Reticle CD (scaled to 1X): Ideal MEEF =1.00. See plot at right. For small CDs the change in the wafer CD is greater than the reticle CD. MEEF = δcd image /δcd mask 9

10 Isolated-Dense Bias: Caused by diffraction differences CDS are same size on reticle scaled to 1X ISO-DENSE BIAS = Isolated wafer CD - Dense wafer CD 10

11 Isolated-Dense Bias: Caused by diffraction differences CDS are same size on reticle scaled to 1X ISO-DENSE BIAS = Isolated wafer CD - Dense wafer CD 11

12 NILS The slope of the image intensity as a function of position (di/dx) measures the steepness of the image at the transition from bright to dark 12

13 NILS NILS : Normalized image log slope: slope of aerial image intensity (NILS) pattern multiplied by the feature width. This is a metric for the quality of the aerial image. Values between 6 8 are good! Can use in Prolith for quick Simulations to investigate OPTICAL effects. NILS says nothing about Photoresist patterns. 13

14 NILS NILS : Normalized image log slope: 14

15 NILS NILS : Normalized image log slope: 15

16 NILS NILS : Normalized image log slope: 16

17 NILS NILS : Normalized image log slope: 17

18 NILS NILS : Normalized image log slope: As image goes out of focus the image slope (NILS) decreases 18

19 NILS PROLITH Simulation NILS : Normalized image log slope: Typical NILS Vs Defocus curve 19

20 NILS PROLITH Simulation NILS : Normalized image log slope: Typical NILS Vs Defocus curve with multiple wavelengths ( Run simulation using wavelenth min, max step, then Use Prolith s Multi-line function. Focus = X axis; NILS = Y axis; wavelength = Z axis) 20

21 : Contrast Photoresist Contrast definition 21

22 : Contrast Photoresist Contrast definition Image edge Partially exposed defines sidewall angle 22

23 : Contrast Photoresist Contrast definition 23

24 Swing Curve: Thin films interference Effect: Key photoresist CD variation Effects: Swing Curve: Interference of r 1 and r 12 Standing Waves: Interference of i 1 and r 1 Swing CurveSpace width CD nm 850 Medium n o i 1 r 1 r 12 Spacewidth CD nm Space width CD nm Reflective substrate n s Photoresist Thickness nm 24

25 Reflectivity Curve: Prolith set up 25

26 Reflectivity Curve: Prolith SiON Reflectivity: 248nm Wavelength on Polysilicon : SiON k effect 0.46 Photoesist Reflectivity % n= 2.15; k = 0.72 n= 2.15; k = 0.22 n= 2.15; k = 0.92 n= 2.15; k = SiON thickness nm 26