SiGeHBTs中的ELDRS研究： Tsinghua与IBM工艺对比

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"这篇研究论文深入探讨了在不同SiGeCraft.io工艺中增强低剂量率敏感性(ELDRS)的现象。通过对清华大学(THU)和IBM 8HPSiGe工艺制造的SiGe异质结双极晶体管(SiGe HBTs)进行低剂量率和高剂量率的辐射实验，分析了ELDRS的影响。研究表明，THU的SiGe HBTs在低剂量率下的敏感度显著低于IBM 8HPSiGe HBTs，并表现出真正的剂量率效应。利用TCAD（Technology Computer-Aided Design）模型解释了THU和IBM 8HPSiGe HBTs的微观结构差异，揭示了不同SiGe工艺可能涉及不同的HBT结构和器件设计，这些是ELDRS的关键影响因素。" 本文重点在于分析不同SiGe工艺中ELDRS的差异，这是一种在辐射环境中晶体管性能变化的现象。首先，作者通过实验对比了THU和IBM 8HPSiGe工艺的晶体管在低剂量率和高剂量率辐射下的响应。THU的SiGe HBTs在低剂量率下展现出较低的敏感性，这与IBM 8HPSiGe HBTs的表现形成鲜明对比，后者对低剂量率的辐射更为敏感。 TCAD模型的运用是理解这种差异的关键工具。通过模拟，研究人员可以洞察THU和IBM 8HPSiGe HBTs的内部结构，特别是发射器-基区结的几何形状以及隔离结构。这些结构设计上的差异被指出是导致ELDRS效果不同的主要原因。论文中提到的“发射器-基区(spacer)”几何形状是指发射器与基区之间的空间分布，这对电流控制和器件性能至关重要。而隔离结构则涉及到如何防止相邻器件间的互相影响，其设计也直接影响到ELDRS的表现。此外，论文还强调了器件结构和设计在本质上对ELDRS的影响，特别是发射器-基区结的几何特性和隔离技术的选择。这意味着在开发辐射硬化的SiGe HBTs时，优化这些结构参数对于提高器件的辐射耐受性至关重要。该研究揭示了不同SiGe工艺中ELDRS的差异性，并指出了器件结构和设计作为关键因素，为未来SiGe HBTs的优化和辐射环境下的应用提供了重要的理论依据。

IEEE TRANSACTIONS ON NUCLEAR SCIENCE, VOL. 64, NO. 5, MAY 2017 1137

An Investigation of ELDRS in

Different SiGe Processes

Pei Li, Chaohui He, Hongxia Guo, Qi Guo, Jinxin Zhang, and Mohan Liu

Abstract—Enhanced low dose rate sensitivity (ELDRS) in dif-

ferent process Silicon–Germanium heterojunction bipolar tran-

sistors (SiGe HBTs) is investigated. Low and high dose rate

irradiations are performed to evaluate the ELDRS of SiGe HBTs

manufactured by Tsinghua University (THU). THU SiGe HBTs

experience signiﬁcantly low dose rate sensitivity than that of

IBM 8HP SiGe HBTs and behave a “true” dose rate effect.

TCAD models were used to explicate the microcosmic structure

in THU and IBM 8HP SiGe HBTs. Comparison and discussion

show that different SiGe processes may involve different HBT

structures and device designs which are the critical inﬂuence

of ELDRS effect. The different responses of ELDRS should be

ﬁrst attributed to the device structure and design in nature,

particularly the geometry of emitter–base junction and the

isolation structure.

Index Terms— Different silicon–germanium (SiGe) process,

emitter–base (EB)-spacer geometry, enhanced low dose rate

sensitivity (ELDRS), isolation structure.

I. INTRODUCTION

ILICON–Germanium heterojunction bipolar transis-

tors (SiGe HBTs) have been widely used in the global

semiconductor electronics market with its excellent analog

and RF performance, advantages of low-cost, large-scale

integration, and high yield [1], [2]. More importantly, excellent

low-temperature performance, favorable built-in total ionizing

dose (TID) tolerance and recent improvements in single-

event effects performance via radiation hardened by design

techniques, all combine to make SiGe HBT a strong contender

for space applications in extreme environments [3]–[7].

According to the MIL-STD 883 Method 1019.7,

most TID studies involve irradiation at dose rates of

50–300 rad(SiO

)/s which is much higher than that expected

in space or many extreme environments (typically about

0.0001–0.1 rad(SiO

)/s) [8]. As a new type of bipolar

device, the scenario is a major concern for devices intended

for space environment, because the radiation tolerance of

Manuscript received February 17, 2017; revised March 14, 2017; accepted

March 17, 2017. Date of publication March 22, 2017; date of current version

May 16, 2017. This work was supported by the National Natural Science

Foundation of China under Grant 61274106, Grant 61574171, and

Grant 11575138.

P. Li, C. He, and J. Zhang are with Xi’an Jiaotong University, Xi’an 710049,

China (e-mail: lipei89.xjtu@gmail.com; hechaohui@mail.xjtu.edu.cn).

H. Guo is with the Xinjiang Technical Institute of Physics & Chemistry,

CAS, Urumqi 830011, China, and also with the Northwest Institute of Nuclear

Technology, Xi’an 710024, China (e-mail: guohxnint@126.com).

Q. Guo and M. Liu are with the Xinjiang Technical Institute of Physics &

Chemistry, CAS, Urumqi 830011, China (e-mail: guoqi@ms.xjb.ac.cn).

Color versions of one or more of the ﬁgures in this paper are available

online at http://ieeexplore.ieee.org.

Digital Object Identiﬁer 10.1109/TNS.2017.2686429

susceptible devices can be drastically overestimated [9]–[13].

So, it is necessary to investigate the enhanced low dose rate

sensitivity (ELDRS) in SiGe HBTs. Previous studies have

shown that several generations of SiGe HBTs related to

ELDRS experiment are all manufactured by IBM, and the

results show that ELDRS of this SiGe process was found

to be nearly nonexistent [14], [15]. Nevertheless, different

SiGe processes may involve different HBT structures and

device designs which are the critical inﬂuences of ELDRS

effect. To date, no studies on ELDRS for different fabricated

SiGe HBTs have been published.

Thus, in this paper, a

Co-γ irradiation experiment is per-

formed to investigate the ELDRS effect for SiGe HBTs man-

ufactured by Tsinghua University (THU). Compared with the

ELDRS studies of IBM SiGe HBTs reported in [15] and [16],

THU SiGe HBTs experience signiﬁcantly low dose rate sen-

sitivity than that of IBM SiGe HBTs and exhibit a “true”

dose rate effect. The different responses of ELDRS should

be ﬁrst attributed to the device structure and design in nature,

particularly the geometry of emitter and base, the thickness

of emitter–base (EB) spacer, and the structure of oxide layer.

A discussion is provided to explore the impact of EB-spacer

geometry and isolation structure on ELDRS in different SiGe

process.

II. ELDRS

IN DIFFERENT PROCESS SiGe HBTs

A. Device Descriptions

The devices investigated in this paper are designed and fab-

ricated by THU and IBM 8HP process, respectively. Fig. 1(a)

shows the cross section of SiGe HBTs manufactured by THU,

and its basic structure is similar to the bulk silicon vertical

NPN bipolar transistor. The collector contact is routed through

a heavily doped n+ buried layer, and the p+ epitaxial base

is grown above the local oxidation of silicon (LOCOS). The

doping concentration of intrinsic base is about 1× 10

−3

and the content of Ge gradually changes from 0% to 20%

at the emitter–base and base–collector junctions. The doping

concentration of emitter is 1.5×10

−3

, and the dimension

of each emitter ﬁnger is 0.4 μm × 20 μm. A ring wall of

the heavily doped boron leads out substrate contact near the

edge of the device, and the emitter and substrate are connected

together via metal interconnection [17]. Fig. 1(b) shows the

2-D cross section of IBM SiGe HBTs fabricated by IBM 8HP

technology, and the process starts with the formation of a

heavily arsenic-doped subcollector buried layer formed by ion

implantation, on top of which a lightly doped epitaxial layer

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