Modeling Incomplete Conformality during Atomic Layer Deposition in High Aspect Ratio Structures

2025-05-06 0 0 4.03MB 25 页 10玖币

侵权投诉

Modeling Incomplete Conformality during Atomic Layer

Deposition in High Aspect Ratio Structures

Luiz Felipe Aguinskya,∗

, Frˆancio Rodriguesa, Tobias Reiterb, Xaver

Klemenschitsb, Lado Filipovicb, Andreas H¨ossingerc, Josef Weinbuba

aChristian Doppler Laboratory for High Performance TCAD, Institute for

Microelectronics, TU Wien, Gußhausstraße 27-29, 1040, Wien, Austria

bInstitute for Microelectronics, TU Wien, Gußhausstraße 27-29, 1040, Wien, Austria

cSilvaco Europe Ltd., Compass Point, St Ives, Cambridge, PE27 5JL, United Kingdom

Abstract

Atomic layer deposition allows for precise control over ﬁlm thickness and

conformality. It is a critical enabler of high aspect ratio structures, such

as 3D NAND memory, since its self-limiting behavior enables higher confor-

mality than conventional processes. However, as the aspect ratio increases,

deviations from complete conformality frequently occur, requiring compre-

hensive modeling to aid the development of novel technologies. To that

end, we present a model for surface coverage during atomic layer deposi-

tion where incomplete conformality is present. This model combines ex-

isting approaches based on Knudsen diﬀusion and Langmuir kinetics. Our

model expands the state-of-the art by (i) incorporating gas-phase diﬀusiv-

ity through the Bosanquet formula as well as reaction reversibility in the

modeling framework ﬁrst proposed by Yanguas-Gil and Elam, and (ii) being

eﬃciently integrated within level-set topography simulators. The model is

∗Corresponding author

Email address: aguinsky@iue.tuwien.ac.at (Luiz Felipe Aguinsky)

Preprint submitted to Solid-State Electronics December 19, 2022

arXiv:2210.00749v2 [physics.comp-ph] 16 Dec 2022

manually calibrated to published results of the prototypical atomic layer de-

position of Al2O3from TMA and H2O in lateral high aspect ratio structures.

We investigate the temperature dependence of the H2O step, thus extracting

an activation energy of 0.178 eV which is consistent with recent experiments.

In the TMA step, we observe increased accuracy from the Bosanquet formula

and we reproduce multiple independent experiments with the same parame-

ter set, highlighting that the model parameters eﬀectively capture the reactor

conditions.

Keywords: Atomic layer deposition, thin ﬁlms, high aspect ratio, Langmuir

kinetics, topography simulation

1. Introduction

Atomic layer deposition (ALD) is a thin ﬁlm deposition technique which

enables greater control over ﬁlm thickness and conformality than conven-

tional chemical vapor deposition (CVD) [1]. ALD has become a key tech-

nology in semiconductor processing, having found application in, e.g., the

deposition of technologically relevant oxides and nitrides [2]. Due to its in-

creased control over conformality, ALD is a key enabler of high aspect ratio

(HAR) structures such as dynamic random-access memory (DRAM) capac-

itors [3] and three-dimensional (3D) NAND ﬂash memory [4].

In contrast to conventional CVD, ALD divides the growth process into

at least two sequential, self-limiting processing steps, which repeat in cy-

cles [2]. From the many precursor chemistries enabling ALD, the deposition

of aluminum oxide (Al2O3) from trimethylaluminum (TMA, or Al(CH3)3)

and water (H2O) has emerged as a paradigmatic system [5]. Even though this

process has found application in, e.g., high-κcapacitor ﬁlms for DRAM [3],

its main importance stems from the near-ideal aspects of the involved sur-

face chemistry. Thus, a signiﬁcant body of research has emerged for this

process, and it became the de facto standard against which novel approaches

are tested.

In an irreversible self-limiting reaction with ﬁxed reactor conditions, com-

plete conformality is theoretically achievable by adapting the step pulse time

tpto the involved HAR structure. Thus, the conformal ﬁlm thickness could

be straightforwardly controlled via the growth per cycle (GPC) parameter,

determined by the involved reactants and reactor conditions, and the to-

tal number of cycles (Ncycles). However, in real-world conditions, deviations

from complete conformality in HAR structures are observed [1] since (i) the

true surface chemistry is not perfectly self-limiting, and (ii) reactant trans-

port becomes severely constricted. Accordingly, as semiconductor technology

advances towards ever higher aspect ratios, the challenge of understanding

incomplete conformality in ALD must be addressed with a joint experimental

and modeling approach.

To that end, ﬁrst-order Langmuir models have been developed and ap-

plied to predict saturation times [6–8], to model growth kinetics [9], to derive

scaling laws [10], and to estimate the clean surface sticking coeﬃcient (β0)

using either Monte Carlo methods [11, 12] or simpliﬁed analytical expres-

sions [13]. These approaches are very powerful, however, they do not evaluate

the resulting thickness proﬁles in a manner which is compatible with level-

set topography simulators. This is a requirement for the integration of ALD

models with additional processing steps and for process-aware device simu-

lation within a design-technology co-optimization (DTCO) framework [14].

In the past, we addressed this issue in the context of the ALD of tita-

nium compounds by developing a topography simulation integrating detailed

Langmuir surface models with Monte Carlo ray tracing calculations of local

reactant ﬂuxes [15]. Nevertheless, the use of Monte Carlo ray tracing as

well as the calculation of the growth on a cycle-by-cycle basis leads to high

computational costs. Therefore, only a few deposition cycles were simulated.

For a topography simulation of realistic ALD processes involving hundreds

of cycles, not only the surface coverages but also the level-set velocity ﬁeld

must be accurately and eﬃciently calculated.

Here, we present a model for ALD surface coverage in HAR structures

based on one-dimensional (1D) diﬀusive particle transport, building upon the

model proposed by Yanguas-Gil and Elam [8] by combining it with physical-

chemical phenomena highlighted in previous works [6, 9, 16]. Namely, the

model now includes reversible reactions and gas-phase diﬀusion through the

Bosanquet formula [17]. For the calculation of thickness proﬁles, the model

is eﬃciently integrated with level-set based topography simulators [18–21]

through the bundling of multiple cycles via the introduction of an artiﬁcial

time unit. Our model is then manually calibrated to reported ALD thick-

nesses of Al2O3in both the H2O- and TMA-limited regimes, allowing for a

deeper analysis of the role of temperature and geometrical parameters for

this prototypical process.

2. Methods

2.1. Surface kinetics and ﬂux modeling

As with most ALD modeling approaches [1], our model assumes that the

processes are limited by the reactive transport of a single reactant species.

For clarity, our discussion focuses on the H2O-limited regime during ALD of

Al2O3. However, the same insights are valid for the TMA-limited case and to

similar reactants. We employ a ﬁrst-order Langmuir surface model, combined

with diﬀusive reactant transport for the calculation of the surface coverage

θ, building upon the model ﬁrst proposed by Yanguas-Gil and Elam [8] by

considering reversible kinetics and the impact of gas-phase diﬀusivity [6, 9,

16].

The following reaction pathways for an impinging water ﬂux ΓH2O(m−2s−1)

are considered, represented in Fig. 1: Adsorption-reﬂection, mediated by a

θ-dependent sticking coeﬃcient β(θ) = β0(1 −θ), and desorption, given by

an evaporation ﬂux Γev (m−2s−1). In the original model [8] as well as in

subsequent developments [10, 22, 23], irreversible kinetics are assumed, i.e.,

Γev = 0. However, other works have highlighted the necessity of consider-

ing the reaction reversibility, leading to the following equation for the time

evolution of θat each surface point ~r [6, 9, 16]:

dθ(~r)

dt = ΓH2O(~r)

β(θ)

z }| {

β0(1 −θ(~r)) −Γevθ(~r) (1)

Equation (1) describes an empirical model with two phenomenological

parameters: β0and Γev. The surface site area s0(m2) can be estimated with

a “billiard ball” approximation from the deposited ﬁlm density ρ(kg m−3)

and GPC (˚

A) [9]. In contrast to the steady-state assumption applied in, e.g.,

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

ModelingIncompleteConformalityduringAtomicLayerDepositioninHighAspectRatioStructuresLuizFelipeAguinskya,,Fr^ancioRodriguesa,TobiasReiterb,XaverKlemenschitsb,LadoFilipovicb,AndreasHossingerc,JosefWeinbubaaChristianDopplerLaboratoryforHighPerformanceTCAD,InstituteforMicroelectronics,TUWien,Guhausst...

展开>> 收起<<

Modeling Incomplete Conformality during Atomic Layer Deposition in High Aspect Ratio Structures.pdf

共25页,预览5页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

Modeling Incomplete Conformality during Atomic Layer Deposition in High Aspect Ratio Structures

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: