2002 IEEE International SO1 Conference, 1WO2
300mm Ultra Thin SO1 Material Using Smart-Cut@Technology
A.J. Auberton-Hervt and C. Maleville
SOITEC SA: Parc Techno. Des Fontaines ; 38926 Crolles Cedex ;France
SO1 technology is evolving since almost 25 count per wafer for 160nm detection level,
years, SO1 material being used initially for niche Unibond@product is close to the best silicon Epi
application such hardened devices. In the last 5 wafer quality.
years, following IBM example, main IC suppliers
agreed that they have to design their device on SO1 300mm SOI wafer manufacturing
to achieve better performance in terms of speed
and power consumption [l]. Materials in general Several IC suppliers are today in qualification and
are coming back at the center of the performance ramp-up of 300mm fab running SO1 based
race as it appears that scaling is not enough to advanced applications.
continue to follow the Moore's law. In the run for As the Smart-Cut@process is based on standards
faster microprocessors, fully depleted designs are equipments from the semiconductor industry, then
now targeted for sub 90nm devices, requiring ultra transition from 200 to 300mm has been enabled by
thin SO1 material. When operating in FD mode, availability of 300mm generation equipments.
transistor threshold voltage is directly linked to 30Omm Unibond" feasibility was demonstrated in
silicon thickness. Thickness uniformity is then 1997, samples built in 2000, and 300mm pilot line
becoming a critical parameter to guarantee Vt is operating in Bemin I since January 2002. Now
control. Looking to ITRS roadmap guidelines, one in ramp-up, this first 300- experience proved
can see that in 2004 timeframe, 20 nm silicon that there is no major limitation for 30Omm
layers, verifymg f 5% uniformity will be needed in Unibond". As 300mm silicon wafers incorporate
high volume [2]. today the most advance silicon wafer engineering,
SO1 material manufachuability is the key to the SO1 quality and manufacturability has been
establish this new breakthrough in the silicon even improved when going to this new diameter.
based industry. Nanotopology improvements are particularly
In this paper we will discuss new ultra thin 300mm beneficial. Table 1 gives a comparison in terms of
Unibond' which fulfill industry requirements in equipments type and configuration between 200
terms of uniformity, quality and availability. and 300mm lines.
300 mm SO1 high volume wafer manufacturing
200mm high volume manufacturing experience
Smart-Cut' process has been the enabling
technology, allowing large volume production SO1
wafers with consistent quality. Bemin facilities,
opened in 1997, is now running at full capacity,
I'
with 900k wafers starts per year. 200mm
experience is demonstrating production stability
and Unibond' products are today qualified in
production by customers in all diameters up to 8"
-
Figure 1: Sum of defects per wafer distribution grouped
and for applications ranging from thin films to per production week for more than 50000 wafers,
thick films. As an example, Fig.1 shows defectivity defects>0.16 p m 1100/2000AUnibond'
chart for more than 50000 wafers, grouped by
production week. When comparing defect counts From a manufacturing point of view, 300mm line
with typical performance for CZ and high quality has been set-up using all 20Omm experience and is
epi wafers, it can be seen that with less than 20 really close from 200mm line. The major change is
0-7803-7439-8/02/$17.0002002 IEEE 1
in the carrier type since 12" is handled in FOUP
for all equipments and all processing steps from Ultrathin products
incoming material to shipment.
Regarding high temperature treatment, boat
designed for 300mm, reducing wafer stress is used. New Unibonpprocess generations
Oxide uniformity is typically same than for
200mm. For the implantation step, the same When reviewing ITRS roadmap targets,
machine is used meaning that hydrogen beam is several challenging items appear. Silicon film
unchanged. A 12" wheel is installed instead of 8" thickness and uniformity are the most aggressive,
wheel and handling system is also converted. From with values typically of 20nm and *
5%, 60.
a throughput point of view, area to be scanned is These requirements lead to lOA thickness
30% higher in 12" and wheel is 13 positions accuracy on a 300mm wafer. As a general trend, it
resulting in a throughput ratio of 50%. New source appears that such high uniformity needs to be
and beam line configurations are now involved guaranteed whatever the spatial wavelength of the
allowing to reach 75 mA current when implanting measurement down to 8, scale what is currently
at 20 keV, a typical energy for new products the domain of roughness measurement. The
.,
eeneration. Such conditions corresoonds to 17 "nano-uniformitv 'Iwill certainly be the key
challenge rising metrology difficulty.
300mm wafers implanted per hour.
Figure 2 shows how Smart-Cut" technology
Table 1: 2 0 0 m and 3 0 0 m tooling set comparison can be extended to very thin films, both for silicon
Processstep I 2 0 0 m I 3 0 0 m I Comment and oxide layers. 500 8, silicon films are already
Oxidation I Vertical I Vertical I Boat running in production while 200 8, SO1 product is
and HT fumace fumace designs today in advanced prototyping. 100/200 8,
anneal Double boat Double boat adapted tc Unibond@ feasibility has been recently
300m
demonstrated.
Implantation Batch Batch Medium
17 wafers 13 wafers current
Cleaning Cassette less Cassette less Exact copy
Bonding Automatic Automatic New
bonder bonder machine
generation
Polishing Multiple Multiple Integrated
headplatens head /platens cleaning
for 3 0 0 m A
Thickness Full wafer Full wafer >4000 pts
measurement reflectometer reflectometer per wafei
in 300mm Figure 2: Smart-Cut@extendability chart
Defectivity SPl-DLS SP1-DLS Also usec
monitoring for Roadmap from table 2 has been defined to address
mapping ultra thin SO1 layers for 65nm node and beyond.
after HI This roadmap is focusing on both 200 and 300 mm
revelation for ultra thin products with a full commonality for
process and toolset technology.
Concerning other processing steps, a few gaps can
be noted with 8" lines. Because of FOUP
operation, dry-in dry-out polishing machine is
used, but End Point Detection by In-situ
Reflectivity Monitoring is of course in place,
lowering wafer to wafer variations for mean
thickness.
L
300mm UT1 process is in ramping-up phase and is
Ultrathin filmprocessing in production capable of +50A total uniformity, 3mm edge
exclusion. All characterization parameters
Present production is designed for f 508, with including defect density, roughness, HF defect
UT1 process generation. In this roadmap, density, secco defects, metallic contamination,
uniformity is calculated at 6 s (Mean *3o) electrical properties are already exhibiting the
assuming that each wafer is measured using more same capability than for high volume 200mm.
than 1700 points in 200mm and 4000 points in
300mm. Then, plotting min-max values for each Towards UT2 and XUT generations
wafer (M-30and M+3o), overall uniformity is
obtained, all wafers, all sites (Figure 3). In Unibond" process, final uniformity is
Uniformity is then driven by 2 parameters, wafer to defined by oxidation, implantation and polishing
wafer mean thickness variation and on-wafer steps.
sigma. For this typical 200mm example, mean In new processes generations, oxidation and
thickness is controlled at +158, while typical on- implantation conditions optimizations led to very
wafer values are around 4.5A. uniform as-split off structures, approaching 1 A
uniformity (1 sigma) (Fig.5). UTl, UT2 and XUT
process are based on such highly uniform (7A
range) SO1 structure. Differences in these
generations appear in the steps involved to erase
surface roughness and obtain final SO1 structure.
Waf- hllm
Figure 3: 200 mm UT1 overall thickness uniformity
Chart.
Uniformity can not be disconnected from surface
roughness. Unibond@' UTI is offering the best
combination regarding these 2 parameters. Both
for 1x1 pm and 10xlOpm AFM scans, we can see
mIs*~
111 '
on AFM pictures from figure 4 that roughness is ~i~~~ 5 : zoomm (as-split ofi) map for new UT
kept at very good levels, especially for Small Scans generation processes showing 1.3.A uniformity (10) -
with less than 28, RMS. Interface roughness Rangeis7.A.
exhibit also low values, typically less than 2p\
RMS I
3
When comparing UTI performance and lTRS
targets, improvements need to be achieved going
towards thinner and even more uniform films.
Regarding thickness, there is no limitation in the
Smart-Cut@process for low energy implantation
and 5 to 10 keV is a typical range. Then, 2008, to
5008, films are obtained and TEM cross-section
(Fig. 6) allows to verify that crystalline quality and
interface sharpness is not degraded for these ultra 0 20 40 60
thin films. This TEM picture also prove that, Wafer number
talking about nano-uniformity, outstanding
'igure 8: UT2 300 mm overall thickness performance
performance can be achieved. preliminary results for 200/15008, product. Total
thickness variation is i20A.
* ai
...
As discussed earlier, roughness and delectivlty are
key parameters to consider when talking about
ultrathin products. When entering ultrathin films
arena, reflectivity effects modifying laser
scattering inspection of SO1 structure is enhanced
because optical absorption is decreased. Anyway,
Figure 6: TEM cross section imagin from a UT2
generation 500/1500 A 300mmUnibond 8 when tuning SP1 machine recipe, 0.3pm threshold
can be achieved. For that detection level, ultra thin
UT2 Unibondm defect density (see example fig.9)
Regarding uniformity at wafer level, next figure is less than 0.2 /cm2, confirmed by HF defect
(Fig. 7) is giving a typical thickness map for a UT2 densities in the 0.05 /cm2 range.
300mm wafer, 50OllSOO~at 3mm edge exclusion.
Standard deviation lower than 58, are achieved and
combined with a *58, control of mean thickness
value, wafer to wafer, UT2 is compatible with
i208, overall uniformity, as shown on figure 9 for
Figure 9 SP1 defect map on UT2 30Omm 200/1500 I%
Unibond", oblique illumination@0.3pm
Following recent publication 131, further
improvements have been made in splitting and
finishing steps allowing surface roughness to be
Figure 7: 300mm UT2 product thickness map. respectively 1 and 3.58, RMS at 1x1 and 10xlOpm
500/lSOOI%, 3mm edge exclusion. Sigma is 3.98, and scans (Fig.10).
range is -251% for 4149 points measured.
a
References :
[11 www.soisolutions.com/news.hhnl
[2] http://public.itrs.net
[3] C.Maleville et al., 2001 IEEE SO1 conference,
p.155.
Figure IO: lOxl0 pm AFM scan on UT2 300mm
200/1500 A Unibond". R= 3.5A RMS
Last figure is imaging what will be XUT
generation with first results obtained in 200mm,
demonstrating that less than 2A standard deviation
is achievable.
Figure 11: 200mm XUT product thickness map.
S80/1500A,3mm edge exclusion. Sigma is 1.9A and
range is <20A for 1765 points measured.
Conclusion
SOITEC has grown a large high volume
production expertise in 200mm, allowing to drive
product defectivity close to epi reference. No
major change was introduced in equipment set and
configuration when switching to 300mm, then
same control and consistent high quality is
achieved. New process strategy are allowing to
improve layer uniformity compatible with IC
supplier roadmaps for 90nm node and below.
