the novel stress simulation method for contemporary...
TRANSCRIPT
The Novel Stress Simulation Method for Contemporary DRAM Capacitor Arrays
Kyu-Baik Chang*a,b, Yun Young Kima, Jiwoong Suea, Hojoon Leea, Won-Young Chunga,
Keun-Ho Leea, Young-Kwan Parka, EunSeung Junga and Ilsub Chungb
aCAE Team, Semiconductor R&D Center, Samsung Electronics Co., LTD. San #16 Banwol-dong, Hwasung, Gyeonggi, 445-701, Korea (E-mail:[email protected])
bSchool of Information and Communications Engineering, Sungkyunkwan University, Suwon, Gyeonggi, 440-746, Korea
Abstract— The increasing of aspect ratio in DRAM
capacitors causes structural instabilities and device failures as the generation evolves. Conventionally, two-dimensional and three-dimensional models are used to solve these problems by optimizing thin film thickness, material properties and structure parameters; however, it is not enough to analyze the latest failures associated with large-scale DRAM capacitor arrays. Therefore, beam-shell model based on classical beam and shell theories is developed in this study to simulate diverse failures. It enables us to solve multiple failure modes concurrently such as supporter crack, capacitor bending, and storage-poly fracture.
Keywords—capacitor stress; large-scale simulation; beam-shell model
I. INTRODUCTION
The demands for high-performance DRAM (Dynamic Random Access Memory) with low power consumption lead the continuous development of HAR (High Aspect Ratio) structure capacitor. This HAR structure, however, is the primary source of structural instability and process failure, e.g. top-bridge and capacitor leaning. To prevent these problems, a MESH-type (Mechanically Enhanced Storage node for virtually unlimited Height) capacitor having supporter structure is required and developed [1-4] (Fig. 1).
Figure 1: SEM image of MESH type capacitor with supporter.
Recently, multilayered thin film supporter to prevent capacitor leaning becomes the reason of process failures such as storage-poly fractures, supporter crack and capacitor bending. Capacitors can be modeled with simple two-dimensional structure or partial three-dimensional structure until now. However, these methods cannot deal with various failures associated with each other. Moreover, new model should be developed on each occasion. This paper reviews the models and results of simple two-dimensional and localized three-dimensional analysis with conventional method and introduces the novel method of integrated stress simulation that enables to simulate approximately 60 thousand capacitors in maximum based on beam and shell theory.
II. SIMPLE 2D MODEL
Two-dimensional stress analysis using simple composite model focuses on the determination and improvement of process failure. This analysis predicts single capacitor behavior depending on vertical movement of supporter or lateral movement of capacitor i.e. bending and adherent due to capillary force during cleaning process. Fig. 2 shows fragmentary failure analysis of unit block shrinkage after SiGe passivation process and it has enough predictability with very high correlation between simulation data and experiment data.
Figure 2: SEM images and simulation results of unit block shrinkage after SiGe passivation process. The Simulation result is magnified by original scale.
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Somewhat, such analyses have a understanding and improvement of the procunit block shrinkage, in case of same genersimulated and verified that the unit bloproportional with the number of capacitor, iblock (Fig. 3). It can be easily observed on cblock.
Figure 3: Shrinkage along with various numis verified by fabrication data.
Contrastively, the shrinkage of two 2capacitor blocks in DRAM devices are preand it makes useful guide for chip size desigshows us fabrication difficulty is going high4).
Figure 4: Shrinkage along with two kinds shows fabrication condition is getting wgeneration development.
III. LOCALIZED 3D MODE
Reasonably, simulation with full
structure about whole area is ideal; howe
major role in cess failures. As to ration device, it is ock shrinkage is .e. the size of unit cell and peripheral
mbers of capacitors
2x nm generation edicted differently
gn. Also, this result her than ever (Fig.
of design rule. It
worse along with
EL
three-dimensional ver, localized i.e.
partially discretized three-dimeby 3 to 8 by 8 unit size is simcomputational resources like simulation time. The major faidimensional model are storageand capacitor bending. Since tbe simulated with large-scastructure should be simplified unit. Storage-poly fracture andwith intrinsic stress value andsupporter materials. These kinoptimization of stress value and
Furthermore, the idea of sdeveloped to optimize capacitoand crack. The size of discretogether to avoid capacitor leanon this simulation, the fabrstructure is obtained successfull
Figure 5: Discrete supportecapacitor leaning and bendingits fabrication.
As mentioned earlier, abovlocalized three-dimensional understand mechanical failure engineering and optimization othey have a limitation that thphenomenon of capacitor with Also, these methods cannot anaSo we propose the novel melarge-scale capacitor as below.
IV. LARGE-SCALE IN
In DRAM capacitor, the stability is getting complicatedimensional model has abovemand prediction of stress fsimulation should be introducestress simulation is develop
nsional model composed from 3 mulated due to the limitation of the limitation of memory and lure analyses of localized three-e-poly fracture, supporter crack three-dimensional model cannot le capacitor unit, the failure or partially modeled with small
d capacitor bending are analyzed d Young’s modulus of various nds of failure are improved by d thickness of supporter.
small size discrete supporter is or modulus and prevent bending ete supporter is well optimized ning and bending (Fig. 5). Based rication of discrete supporter ly without any failures.
er size optimization between
g. And top-view SEM image of
ve simple two-dimensional and model are very useful to in a point of view local stress-
of thin film intrinsic stress. But, hey cannot simulate complicate full three-dimensional structure. alyze various correlated failures. ethod of stress simulation with
NTEGRATED MODEL stress analysis for structural
ed. Since the localized three-mentioned limitations in analysis failure, integrated large-scale d. Therefore, a novel method of
ped for contemporary DRAM
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capacitor arrays based on the beam theory oand Timoshenko and shell theory of KiMindlin-Ressner [5-8]. The essential methodcapacitors are described as beam elementstheory point of view and supporters are selements (Fig. 6).
Figure 6: Beam and shell elements are mscale capacitor simulation.
Three-dimensional capacitor shapes canbeam element as below. After modeling of shapes surrounded dielectric film on top andmeasure the displacement and deformation apaxial and lateral direction. And calculate eqmodulus from capacitor with single matedisplacement and deformation. In other woYoung’s modulus for the beam elemenhomogenizing the material property of full model, and validated by comparing its deflect7). In our study, error between three-dimenbeam element is less than single figure percen
Figure 7: An equivalent Young’s modulhomogenizing the material property of full 3D
In the same way, the shell element mobehavior of multiple composite layers [9].
Through this one-step integrated method,array capacitors can be simulated and vario
of Euler-Bernoulli irchhoff-Love and d of this model is s from the elastic simplified as shell
modeled for large
n be substituted to f detailed capacitor d bottom electrode, pplying force with quivalent Young’s erial to get same rds, an equivalent
nt is derived by three-dimensional
tion behavior (Fig. nsional shape and ntage.
lus is derived by D model.
odel considers the
, up to 120 by 120 ous stress induced
failure modes can be detectecapacitors with symmetry cond
Figure 8: Large-scale simulativarious stress failure like crack
This means the relationshipand quantitative simulation basalso simulated. In additionconvergence of simulation iincrease of simulation domain. enough to represent full size of
Figure 9: Solution convergenumber of capacitors.
Lately, we predict the cramaterials using the beam-shellimprove capacitance of DRAMmore vulnerable supporter thickness, material property andoptimized.
ed at a time, i.e. 60 thousand dition (Fig. 8).
ion is able to analyze integrated
k, fracture and bending at a time.
p between these various failures sed on material properties can be n, the reliability error and is enhanced according to the And it shows our domain size is
f capacitor (Fig. 9).
nce result in accordance with
ack stress with new supporter l model. Thinner supporter can M, but this makes the structure
crack. Therefore, supporter d pattern of open area should be
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Fig. 10 shows crack stress change with sand two kinds of supporter material. It showslead to less crack stress and material 2 is moFig. 11 shows crack stress change with supporter material. Normally intrinsic stress controlled by process temperature and deposstress is measured at the point of crack occurWith this result, we can choose supporter matthickness and intrinsic stress.
Figure 10: Crack stress change along with suand material.
Figure 11: Crack stress change along with stress.
With this method, we can solve vassociated with HAR structure capacitor anstress-induced failures with structurally stablWe can also enhance capacitance with mthickness to maximize area of surface.
V. CONCLUSIONS
A various failure in capacitor with HAincrease upon DRAM scaling causes delayperiod and rising of development cost. Toinduced failures we have optimized procesvarious failures through two-dimensiodimensional simulation model. Due to
upporter thickness s thicker supporter ore stable to crack. intrinsic stress of of material can be
sition rate. Critical rred in fabrication. terial and optimize
upporter thickness
supporter intrinsic
various problems nd prevent various le capacitor block. minimal supporter
AR structure that y of development
o minimize stress-sses and analyzed
onal and three-the increase of
complexity in capacitor structscale simulation is needed. integrated analysis model withbased on the beam and shell thand capacitance are enhanced afabrication.
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ture and stress analysis, large-Therefore, we developed an
h up to 60 thousand capacitors heory. As a result, process yield and verified successfully through
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