Experimental demonstration of in situ surface and thickness profile measurements of thin film during deposition using a grating array based wavefront sensor

Abstract

Here we introduce an in situ and non-intrusive surface and thickness profile monitoring scheme of thin-film growth during deposition. The scheme is implemented using a programmable grating array based zonal wavefront sensor integrated with a thin-film deposition unit. It provides both 2D surface and thickness profiles of any reflecting thin film during deposition without requiring the properties of the thin-film material. The proposed scheme comprises a mechanism to nullify the effect of vibrations which is normally built in with the vacuum pumps of thin-film deposition systems and is largely immune to the fluctuations in the probe beam intensity. The final thickness profile obtained is compared with independent off-line measurement and the two results are observed to be in agreement.

Orthogonality of Zernike modes in phase profiles estimated using Zonal wavefront sensor and transport of intensity phase retrieval method

“…is given by: ∂I(x, y; z) ∂z = I 1 (x, y; z 0 + ∆z) − I 2 (x, y; z 0 − ∆z) 2∆z (11) where I 1 and I 2 are intensity distributions at mentioned coordinates.…”

“…We then measure this shift to find the slope and estimate the phase using the equations (8,9). For a Z 5 Zernike aberration mode, the reconstructed phase using SHWS is shown in fig.…”

“…4,5 Therefore, these modes find applications in testing optical systems, adaptive optics, wavefront sensing and free space optical (FSO) communication systems. [6][7][8][9] Zernike modes have been used in ophthalmology for corneal study, 10 wavefront corrections for surface and thickness profile mesurement of thin film 8,11,12 and wavefront estimation, 13,14 aberration correction in microscopy [15][16][17] and micromanipulation of optical trapping. 18,19 In all these applications, the orthogonal property is the primary reason for their use.…”

Improvement in wavefront measurement accuracy in grating array-based zonal wavefront sensors by modulating the intensity profile of the incident beam

“…For the past few decades, wavefront sensors have played a significant r ole i n d iverse a reas s uch a s: i n a stronomy to build adaptive optics for astronomical telescopes, 1 in ophthalmology for perfect correction of human vision, [2][3][4] in the semiconductor industry for analysis of flatness o f t he surface, 5,6 a nd i n s urface a nd t hickness profile measurement. [7][8][9] It has also been used in free-space optical communication to transmit and receive the data accurately. [10][11][12][13][14] Shack-Hartmann wavefront sensor (SHWS) is a well-known and widely used wavefront sensor that employs an array of microlenses to measure the shape of the wavefront.…”

Direct defocus measurement using single astigmatic lens: a theoretical study

“…If the measurement demands to be carried out at the focal plane of the optical system, any deviation from it highly affect the output of the measurement. Thus, in applications such as optical microscopy, 1-3 optical communication, [4][5][6] ophthalmology, 7,8 astronomy, 9 surface and thickness profile measurements of thin film, [10][11][12] etc. the measurement if carried out at an unknown out of focus plane, will lead to wrong outcome.…”