Wednesday, October 31, 2007

Latest Developments in Lithography !!

This article is written by flashG

Visit flashG Blogs
Visit flashG Videos
Visit flashG - Build Own PC Computer Guide

----------------------------------------------


Introduction

Moore’s law has governed the growth of the semiconductor industry. The main factor of producing complex devices at lower cost is lithography. Optical lithography has been reaching the physical limit and therefore leads to the development of alternate techniques. Immersion lithography has recently attracted interest in the research industry. Of other alternatives, many consider extreme ultraviolet lithography and nano-imprint lithography as potential successors to optical lithography. Lastly we also analyze the potential of x-ray lithography and electron beam lithography as possible candidates.

Immersion Lithography

The uniqueness about Immersion Lithography is seen in the replacement of air with ultrapure water as the medium between the lens and the wafer. This pushes the physical limits of NA for the exposure systems beyond NA=1 for air, given the following relation: NA=n sin alpha = d/2f. Ultra pure water is highly suitable as it has a refraction index of 1.47, absorption of <5%>

Extreme Ultraviolet Lithography

EUVL uses light sources with wavelength (13.4nm) 10 times shorter than current wavelengths (139nm). This will make possible fabrication of circuit lines smaller than 0.1 microns in width, extendable to below 30nm. EUVL masks are reflective masks, with a patterned absorber of EUV radiation placed on top of an ML (multilayer thin film with alternating layers of Mo and Si) reflector deposited on a robust and solid substrate, such as a silicon wafer. The key requirement is to make a mask with essentially no defects. The strong absorption of EUV radiation by all materials poses the main problem in developing a satisfactory photoresist for EUV lithography. . The thin layer imaging is already a mature technology, thus resist is no longer a critical issue. Printed lines as small as 50nm in photoresist has already been achieved.

The Virtual National Laboratory (VNL) formed by the three Laboratories - Lawrence Livermore, Lawrence Berkeley, and Sandia/California, has developed and built a prototype extreme ultraviolet lithography (EUVL) system called the engineering test stand (ETS). This ETS has produced test patterns with a line-to-spacing ratio of 1:1 with high fidelity down to line widths of 70 nm using its Set-2-optic. By adjusting the illumination pattern and the exposure dose, the team printed less densely spaced lines with widths down to 39 nm. It is thus able to meet the production requirements set for chips with 1 billion transistors and up in the years 2007 to 2010.

X-ray Lithography

The basic set up of a typical XRL system is by using a synchrotron as an x ray source. Synchrotron-based XRL provides a wide exposure-dose window, which is very important in ULSI fabrication. Insensitivity to dust is another advantage, which will affect the amount of pattern defects. The source is an electromagnetic wave, which is generated when high-energy electrons are accelerated. To minimize x ray absorption, the mask substrate is made of a thin membrane consisting of materials with a low atomic number. The issue pertaining to this method is that here is a need for an overlay accuracy which will meet the requirements of sub -0.1-um ULSI fabrication, while another issue is throughput. By properly choosing of median wavelength, proximity x-ray lithography (PXRL) can be extended to 50nm using relatively large mask/wafer gaps. This can be achieved by increasing the energy of the storage ring, decreasing the incident angle on the beamline mirror, and utilizing a diamond mask substrate. Increasing the median energy to 2.6 to 2.7keV allows printing of smaller features down to 35nm by using a harder spectrum, choosing the appropriate materials for the mask and the resist match the transmission and absorption at this high energies.

Electron beam lithography

Electron beam lithography applies direct writing method to scan electron beam across various material surface covered with resist film to create desired extensive patterns on the substrates. Because of the high energy electron beam (tens to hundred eV), it totally eliminates the diffraction effect; however, it can make damages to the substrate material. The resolution is now limited by aberration of electron optics and scattering effects which is more severe. Through scattering effect correction, it can reach a resolution about 10-20nm. As the pattern generation is carried out through scanning the surface pixel by pixel controlled by computer aided design (CAD), this leads to very slow speed, thus very low throughput. Although this E-beam direct writing does not require a mask which usually costs a lot for specific material, delicate equipment cost and frequent maintains are usually very expensive up to millions of dollars, thus mass production is economically unfavorable. These speed and cost considerations limit its application in mass commercial production for 50 nm feature size although it has a high level resolution. Instead this technique is used to produce high quality mask with good resolution and also widely used in research purpose.

Nano-imprint Lithography (NIL)

NIL creates a resist relief pattern by deforming the resist physical shape with embossing, instead of modifying the resist chemical structure with radiation or creating the pattern by self-assembly. The pattern is then transferred into the material to be etched (a Si wafer for example) using the resist as a mask. The key advantage of this lithographic technique is the ability to pattern sub-25 nm structures over a large area with a high-throughput and low-cost. Unlike conventional lithography methods, imprint lithography itself does not use any energetic beams. Therefore, nano-imprint lithography’s resolution is not limited by the effects of wave diffraction, scattering and interference in a resist, and backscattering from a substrate.

There are two advancements in this technology recently. A new UV based nanoimprint lithography (UV-NIL) has been developed and demonstrated at AMO as attractive alternative to the hot embossing technique. The low pressure (<1bar) style="">Researchers at Princeton University, US, have shown that photocurable nanoimprint lithography (P-NIL) can produce lines of polymer resist just 7 nm wide with a pitch (or pattern repeat) of only 14 nm. The technique also produced reliable results over the whole area of a 4 inch wafer.

Comparison

In choosing the most promising technology that could allow for 50nm feature size and below, we considered the following factors in our decision. They are the cost of the technology, the throughput of the method, the amount of constraints that it is facing at the moment and the possibility of the technology to produce 50nm feature size.

37 comments:

消化 said...

道歉是人類一定必要的禮節 ..................................................

無尾熊可愛 said...

wonderful...................................................

明秋明秋 said...

very popular to u! ........................................

明偉誠秋 said...

great msg for me, thanks a lot dude˙﹏˙

DesiraeF_Creech0709 said...

Make hay while the sun shines.........................................

雲亨 said...

成人無碼片線上看18限成人影片論壇成人鴛鴦成人影片一葉晴視訊力小遊戲力的小遊戲力的色小遊戲力的色遊戲力的遊戲十八成人網站十八歲成人十八歲成人論壇十八禁小遊戲十八禁小說三級片線上觀看下載日本電影下載免費看日本av女優電影八五街八大成人圖庫人做愛姿勢一葉貼圖區一葉貼影片一葉貼影片區一葉影色站一葉擎一碼丁子褲丁字褲免費a片gogogirl視訊美女 網路小說 成人文學嘟嘟貼圖區

玄雨 said...

may the blessing be with you.........................................

feli5289xv_ferrari said...

感謝分享哦~會再來看看的~............................................................

姜姜 said...

你的部落格很棒,我期待更新喔.............................................

Jero思翰eded said...

好的部落格,希望您能繼續堅持!!!..................................................

burtong said...

失意人前,勿談得意事;得意人前,勿談失意事。 ..................................................

佳皓 said...

It is easier to get than to keep it...................................................................

政倫政倫 said...

It is no use crying over spilt milk...................................................................

育財 said...

你的BLOG真有心~看都不膩.................................................................

王邦鈺 said...

在莫非定律中有項笨蛋定律:「一個組織中的笨蛋,恆大於等於三分之二。」......................................................................

家谷家谷 said...

may the blessing be always with you!!.................................................................                           

明霖明霖 said...

當一個人內心能容納兩樣相互衝突的東西,這個人便開始變得有價值了。............................................................

佳皓佳皓 said...

希望能常常看到你的更新.......................................................

宜FH定博林P'韓T彥 said...

到處逛逛~~來繞繞留個言囉~~~~.......................................................

吳婷婷 said...

有夢最美啦~~加油!元氣滿點!............................................................

宥妃宥妃 said...

Words are not living in dictionary. Words are living in mind.............................................................

RodrigoR_倪 said...

I have nothing to offer but blood, toil, tears and sweat..................................................................

紹函紹函 said...

先為別人的快樂著想,是超人;先為自己的快樂著想,是凡人;使別人不快樂,自己也不快樂的,是笨人。..................................................

吳婷婷 said...

雖天地之大,萬物之多,而惟吾蜩翼之知。..................................................

ju吳phe宇te佳ns said...

Some people cannot see the wood for the trees.............................................................

劉佳仲 said...

It is never too late to learn.......................................................................

淑吳玲 said...

嘩做左推介BLOG 果然人氣勁旺............................................................

許泓v辛 said...

Pen and ink is wits plough...................................................................

韋陳富 said...

Learn wisdom by the follies of others.............................................................

蔡曼鄭美玉屏 said...

愛情是盲目的,但婚姻恢復了它的視力。..................................................................

偉曹琬 said...

No pains, no gains.......................................................................

黃智樺黃智樺 said...

拒絕冒險和成長的人,終將被生命的潮流陶汰。..................................................

童建李宜昌智 said...

做些小善事,說些愛的字句,世界更快樂。..................................................

翊翊翊翊張瑜翊翊翊 said...

謝謝大大無私分享 感恩唷(>o<)............................................................

翊翊翊翊張瑜翊翊翊 said...

不論做什麼事,相信自己,別讓別人的一句話,把你擊倒。..................................................

翊翊翊翊張瑜翊翊翊 said...

人生像一杯茶,若一飲而盡,會提早見到杯底..................................................

佳陳容 said...

看得見您的用心~~希望這裡愈來愈熱鬧哦~~..................................................................

Google
-----------------------------

For more great stuffs and exciting blogs, visit

http:\\www.diypc.wordpress.com
My Other Interesting Blogs!!

Feel Free to email me at
jimmyleespore@yahoo.com.sg

Simple Step by Step PC Assembly Videos at MetaCafe
Click to learn Now !!

Add to Google Reader or Homepage