碩 士 論 文 中 華 大 學

中 華 大 學

碩 士 論 文

題目:高介電係數材料氧化鈦鉿之 n 型場效電晶 體之研製

The Fabrication and Characterization with High-ૂ Dielectric HfTiO n-MOSFETs

系所別:電機工程學系碩士班 學號姓名:M09601033 羅方鴻

指導教授:謝焸家博士、荊鳳德博士

中華民國九十八年七月

i

高介電係數材料氧化鈦鉿之 n 型場效電晶體之研製

研究生:羅方鴻

指導教授:謝焸家教授、荊鳳德教授

中華大學 電機系研究所 電子電路組

摘 要

隨著傳統元件尺寸微縮面臨了越來越多困難的挑戰，一些新的解決方法能

夠持續元件的微縮。其中之一，就是使用金屬閘極來替代傳統的多晶矽閘極。可

消除多晶矽的空乏、硼穿透及高阻抗的問題。而另一個方法則是使用高介電係數

材料去取代傳統的絕緣層-二氧化矽，來解決過大的漏電流問題。因此，我們將

探討高介電係數材料絕緣層及閘極材料的研究與應用。對高介電係數材料來說，

必須要有夠高的介電係數，能隙寬度也要夠寬。氧化鈦有著相當高的介電係數，

但能隙寬度不夠寬，而氧化鉿有夠寬的能隙，也有足夠的介電係數，因此，吾人

提出將兩種材料混合的高介電係數材料取代二氧化矽做絕緣層。

ii

The Fabrication and Characterization with High-ૂ Dielectric HfTiO n-MOSFETs

Student：

： ：Fang-Hung Lo ：

Advisor：

： ： ：Dr. Ing-Jar Hsieh and Dr. Albert Chin

Chung Hua University

Abstract

As traditional device scaling is facing increasingly difficult challenges, some novel solutions are enabling continued performance scaling. One way to the continued performance improvements has been to use metal gate electrodes to replace the polycrystalline silicon (poly-Si) gate electrodes. The metal gate will eliminate the poly-Si depletion, boron penetration and high resistivity problems. The other way, which has used high-κ dielectric to replace traditional insulator layer-SiO² , to solve the large leakage current problem. As the result, we will investigate the application of high-κ dielectric and metal gate process technologies. For high permittivity materials, we must have high enough permittivity and wide bandgap. TiO2 has very high permittivity but narrow bandgap. HfO2 has high enough permittivity and wide bandgap .As the result, we combine these two high permittivity materials to replace SiO₂ for gate insulator.

iii

Acknowledgement

First of all, I would like to thank my advisor Prof. I. J. Hsieh and Prof. Albert Chin for their fruitful discussions and illuminative suggestions during the period of my working toward master degree. Their inspiration benefits me a lot on the creative ideas, effective schedule control and the integrity to the processing tasks. I am also grateful to ED633 group members – Dr. N. C. Su, Dr. C. H. Wu, Dr. W. B. Chen, Dr.

K. Y. Cho, Dr. M. F. Zhang, Dr. S. H. Lin, and my classmate C. C. Tang for their enthusiastic assistance and cooperation.

Moreover, I am appreciative of the financial and equipment supports form National Science Council, National Nano Device Lab (NDL), and Semiconductor Center of NCTU. I am also grateful to those who ever assisted this work.

Finally, I greatly appreciate my parents and family. Without them, I can’t finish this dissertation.

iv

Contents

Abstract (in Chinese)………i

Abstract (in English)...ii

Acknowledgement...iii

Contents... ...iv

Figure Captions………...………vi

CHAPTER 1 Introduction 1.1 High-ૂ Gate Dielectrics Materials………

1

1.2 Motivation Metal Gate Electrodes……….4

CHAPTER 2 The Basic MOSFET Operation 2.1 MOSFET Structure………...……9

2.2 Current-Voltage relationship……….10

2.3 Transconductance………...14

2.4 The CMOS Technology……….………..16

CHAPTER 3 Experimental steps 3.1 Device Fabrication Process………..27

3.2 The n-MOSFET Device of Fabrication……….28

CHAPTER 4 Result and Discussion 4.1 C-V and J-V Characteristics measured and analysis………...45

4.2 I-V Characteristics measured and analysis………..46

4.3 Mobility Characteristics measured and analysis………...47

v

CHAPTER 5 Conclusion and Suggestion for Future Work

5.1 Conclusion……….………....59

5.2 Suggestion for Future Work……….…60

Reference………61

Vita………...67

vi

Figure Captions

CHAPTER 1

Fig. 1-1 The High Performance Logic of CMOS technology requirements (ITRS2008).

Fig. 1-2 The band offset of popular high-κ materials.

CHAPTER 2

Fig. 2-1 Cross section for an n-channel enhancement-mode MOSFET

Fig. 2-2 Cross section for an n-channel depletion-mode MOSFET

Fig. 2-3 The n-channel enhancement mode MOSFET with an applied gate voltage V_GS− V_T

Fig. 2-4 ID versus VDS characteristics for small values of VDS at three VGS

voltages

Fig. 2-5 Cross section and ID versus VDS curve when VGS > VT for a small VDS value

Fig. 2-6 Cross section and ID versus VDS curve when VGS > VT for a large VDS value

Fig. 2-7 Cross section and ID versus VDS curve when VGS > VT for a value of VDS = VDS(sat)

Fig. 2-8 Cross section and ID versus VDS curve when VGS > VT for a value of VDS > VDS(sat)

Fig. 2-9 Family of ID versus VDS curves for a n-channel enhancement mode MOSFET

Fig. 2-10 Family of ID versus VDS curves for a n-channel depletion mode MOSFET

Fig. 2-11 CMOS structures p-well

vii Fig. 2-12 CMOS structures n-well

Fig. 2-13 CMOS inverter ciriuit

Fig. 2-14 Simplified integrated circuit cross section of CMOS inverter

Fig. 2-15 The splitting of the basic pnpn structure and two-transistor equivalent circuit of the four-layered pnpn device

CHAPTER 3

Fig. 3-1 RCA clean

Fig. 3-2 Filed-oxide growth Fig. 3-3 PR deposition 1st

Fig. 3-4 Source and Drain region define Fig. 3-5 Devlope 1st

Fig. 3-6 Hard Bake 1st Fig. 3-7 Etch SiO2

Fig. 3-8 Remove PR 1st

Fig. 3-9 Implantation with phosphorus Fig. 3-10 Activation

Fig. 3-11 PR deposition 2nd Fig. 3-12 Source and Drain define Fig. 3-13 Devlope 2th

Fig. 3-14 Hard Bake 2nd Fig. 3-15 Etch SiO2 on gate Fig. 3-16 Remove PR 2nd

Fig. 3-17 HfO₂ and TiO₂ deposition Fig. 3-18 PDA

Fig. 3-19 PR deposition 3rd Fig. 3-20 Mask 3#

Fig. 3-21 Devlope 3rd Fig. 3-22 Hard bake 3rd

Fig. 3-23 Etch HfTiO on Source and Drain Fig. 3-24 Remove PR 3rd

Fig. 3-25 Al deposition Fig. 3-26 PR deposition 4th Fig. 3-27 Mask 4#

viii Fig. 3-28 Devlope 4th

Fig. 3-29 Hard bake 4th Fig. 3-30 Etch Al

Fig. 3-31 Remove PR 4th Fig. 3-32 n-MOSFET device

CHAPTER 4

Fig. 4-1 C-V characteristics of Al/HfTiO in N2 at different temperatures

Fig. 4-2 C-V characteristics of Al/HfTiO in O2 at different temperatures

Fig. 4-3 J-V characteristics of Al/HfTiO in N2 at different temperatures

Fig. 4-4 J-V characteristics of Al/HfTiO in O2 at different temperatures

Fig. 4-5 C-V characteristics of Al/HfTiO and TaN/HfTiO capacitors

Fig. 4-6 J-V characteristics of Al/HfTiO and TaN/HfTiO capacitors

Fig. 4-7 The I_d-V_d characteristics of Al/HfTiO n-MOSFET, the gate length is 4µm

Fig. 4-8 The I_d-V_d characteristics of TaN/HfTiO n-MOSFET, the gate length is 4µm

Fig. 4-9 The I_d-V_g characteristics of Al/HfTiO n-MOSFET, the gate length is 4µm

Fig. 4-10 The I_d-V_g characteristics of TaN/HfTiO n-MOSFET, the gate length is 4µm

Fig. 4-11 The extracted electron mobility from I_d-V_g characteristics of Al/HfTiO n-MOSFET.

1

Chapter1

Introduction

1.1 High-
Dielectrics Materials

Since the very beginning of the microelectronics era, the SiO₂ gate oxide in the first transistors was a few hundred nanometers, the functionality and performance of state-of-the-art devices currently rely on gate oxide that are just a few atomic layers (~1-2 nm) thick. Until recently, the evolutionary scaling of the gate dielectric and ULSI devices in general has been accomplished by shrinking physical dimensions. As the physical thickness of SiO₂-based gate oxides approaches ~2 nm, a number of fundamental problems arise. In this ultrathin regime, some key dielectric parameters degrade: gate leakage current, oxide breakdown, boron penetration from the polysilicon gate electrode, and channel mobility. To prevent form short channel effect in high speed transistor, direct tunneling and mobility degradation. To solve the problem above, scientists use high dielectric constant material that get thicker physical thickness with the same EOT as silicon oxide for gate dielectric film.

2

The purpose of CMOS scaling is to enhance the performance of circuit and increase the packing density in a chip. Driving current of a MOSFET Ids can be well modeled by the following equation [1],

I

= 1 2  C

µ

(W L ⁄ )(V

− V

)(V

)

[Eq-1]

Where µ_n is the effective mobility, C_OX is the gate capacitance, W is the channel width, L is channel length. Obviously, drive current is inversely proportional to the channel length L. Therefore, the shrinkage of channel length is the most effective way to promote the driving current of a transistor. Another way to improve the Ids is increasing the C_OX , i.e. scaling down oxide thickness. [1]

C

=

_

A

[Eq-2]

However, thinning gate dielectrics inevitably accompany with larger direct tunneling current. The more recent high-κ approach is to increase the physical thickness to reduce the direct tunneling current, at the same time obtain higher values of gate capacitance using a dielectric material with a higher dielectric constant (high-κ) Relative to SiO₂, [1]

_

=

_κ

[Eq-3]

Therefore, we still have enough capacitance value to obtain excellent gate control ability, lower leakage current and sufficiently large drive current. The gate leakage current through the gate oxide increases significantly because direct tunneling

3

is the primary conduction mechanism in down-scaling CMOS technologies. To reduce the leakage current related higher power consumption in highly integrated circuit and overcome the physical thickness limitation of silicon dioxide, the conventional SiO₂ will be replaced with high dielectric constant (high-κ) materials as the gate dielectrics beyond the 65 nm technology mode [1]-[6]. Therefore, the engineering of high-κ gate dielectrics have attracted great attention and played an important role in VLSI technology. Although high-κ materials often exhibit smaller bandgap and higher defect density than conventional silicon dioxide, using the high-κ gate dielectric can increase efficiently the physical thickness in the same effective oxide thickness (EOT) that shows lower leakage characteristics than silicon dioxide by several orders without the reduction of capacitance density [2]-[5]. According to the ITRS (International Technology Roadmap for Semiconductor) [7], the suitable gate dielectrics must have κ value more than 8 for 50-70 nm technology nodes and that must be more than 15 when the technology dimension less than 50 nm. Fig.1-1 shows the evolution of CMOS technology requirements.

Research on finding an appropriate substitute to the superior SiO₂ has been going on for almost a decade. Oxy-nitrides (SiO_xN_y) have been introduced to extend the use of SiO₂ in production but eventually it has to be replaced by a high-κ material, such as Ta₂O₅, TiO₂, HfO₂, ZrO₂, Al₂O₃, La₂O₃ or mixtures of them or metal-oxide-silicates of the mentioned compounds. Fig. 1-2 shows the summaries of the κ value and band offset for popular high-κ dielectric candidates.

4

1.2 Motivation of metal-gate electrodes

The poly depletion for reduces the gate capacitance in the inversion regime and hence the inversion charge density, leading to a lower gate over drive and thus degrading the device performance. As the result, metal-gate electrodes will be required for complementary metal-oxide-semiconductor (CMOS) transistors to eliminate the gate depletion and dopant penetration problems that are associated with the conventional polycrystalline silicon (poly-Si) gate electrode [7]. In selecting metal-gate materials for device integration, the metal work function is an important consideration since it directly affects the threshold voltage and the performance of a transistor [8]-[10].

However, thermal instability of the effective metal electrode work function (Φ) on underlying gate dielectric as well as the equivalent oxide thickness (EOT) of the gate stack remains a major concern for CMOS integration. In addition, an understanding of how the gate dielectric affects Φ of the metal gate stack is scientifically and technologically important. Although the interfacial dipole theory was proposed to describe the dependence of Φ on underlying gate dielectrics [11], it is not clear whether it can be applied to explain the work functions instability during high-temperature source/drain annealing.

The work functions (Φ_m) of metal shown in Fig. 1-3 [] play an important role for metal-gate/high-κ CMOSFETs. The preferred work function of the metals are ~5.2 eV for p-MOSFETs and ~4.1 eV for n-MOSFETs. Recently, lots of metal or metal-nitride

5

materials have been widely researched and successfully intergraded in advanced CMOSFETs, such as TiN, TaN, Pt, Mo and Ir. And Al is one of the most commonly used metals in the industry, more cheap, low resistance, and low work function.

Fig.1-1 The 1 The High Performance LogicHigh Performance Logic (ITRS 2008)

6

High Performance Logic of CMOS technology requirements (ITRS 2008)

of CMOS technology requirements of CMOS technology requirements of CMOS technology requirements

7

Fig. 1-2 The band offset of popular high

-

Fig. 1

Fig. 1-3 The values of work functioThe values of work functio

8

The values of work function for different metal materialsn for different metal materialsn for different metal materialsn for different metal materials

9

Chapter 2

The Basic MOSFET Operation

2.1 MOSFET Structures

There are four basic MOSFET device types. Fig. 2-1 show an n-channel enhancement mode MOSFET. Implicit in the enhancement mode notation is the idea that the semiconductor substrate is not inverted directly under the oxide with zero gate voltage. A positive gate voltage induces the electron inversion layer, which then

“connects” the n-type source and the n-type drain regions. The source terminal is the source of carriers that flow through the channel to the drain terminal. For this n-channel device, electrons flow from the source to the drain conventional current will enter the drain and leave the source. The conventional circuit symbol for this n-channel enhancement mode device is also shown in this figure.

Fig. 2-2 shows an n-channel depletion mode MOSFET. An n-channel region exists under the oxide with zero volts applied to the gate. However, we have shown that the threshold voltage of an MOS device with a p-type substrate may be negative;

this means that an electron inversion layer already with zero gate voltage applied.

Such a device is also considered to be a depletion mode device. The n-channel shown in this figure can be an electron inversion layer or an intentionally doped n-region.

The conventional circuit symbol for the n-channel depletion mode MOSFET is also shown in the figure.

10

2.2 Current-Voltage Relationship

Fig. 2-3 shows the MOSFET with an applied gate voltage such that V_GS > V_T. An electron inversion layer has been created so that, when a small drain voltage is applied, the electrons in the inversion layer will flow from the source to the positive drain terminal. The conventional current through the oxide to the gate terminal and leaves the source terminal. In this ideal case, there is no current through the oxide to the gate terminal.

For small V_DS values, the channel region has the characteristics of a resistor, so we can write

I

= g

V

[Eq-4]

Where g_ is defined as the channel conductance in the limit as VDS → 0. The channel conductance is given by

g

=

∙ µ

#Q

# [Eq-5]

Where µ_n is the mobility of the electrons in the inversion layer and #Q_"^′ # is the magnitude of the inversion layer charge per unit area. The inversion layer charge is a function of the gate voltage; thus, the basic MOS transistor action is the modulation of the channel conductance by the gate voltage. The channel conductance, in turn determines the drain current.

11

The I_D versus V_DS characteristics, or small values of V_DS, are shown in Fig. 2-4.

When V_GS < V_T, the drain current is zero. As V_GS becomes larger than V_T, channel inversion charge density increases, which increases the channel conductance. A larger value of g_d produces a larger initial slope of the I_D versus V_DS characteristic as shown in the figure.

Fig. 2-5 shows the basics MOS structure for the case when V_GS> V_T and the applied V_DS voltage is small. The thickness of the inversion channel layer in the figure qualitatively indicates the relative charge density, which is essentially constant along the entire channel length for this case. The corresponding I_DS versus V_DS curve is shown in the figure.

Fig. 2-6 shows the situation when the V_DS value increases. As the drain voltage increases, the voltage drop across the oxide near the drain terminal decreases, which means that the induced inversion charge density near the drain also decreases. The incremental conductance of the channel at the drain decreases, which the means that the slope of the I_D versus V_DS curve will decrease. This effect is shown in the I_D versus V_DS curve in the figure.When V_DS increases to the point where the potential drop across the oxide at the drain terminal is equal to V_T, the induced inversion charge density is zero at the drain terminal. This effect is schematically shown in Fig. 2-7. At this point, the incremental conductance at the drain is zero, which means that the slope of the I_D versus V_DS curve is zero. We can write

V

− V

&sat* = V

[Eq-6]

12

Or

V

&sat* = V

− V

[Eq-7]

Where V_DS&sat* is the drain-to-source voltage producing zero inversion charge density at the drain terminal.

When V_DS becomes larger than the V_DS&sat* value, the point in the channel at which the inversion charge is just zero moves toward the source terminal. In this case, electrons enter the channel at the source, travel through the channel toward the drain, and then, at the point where the charge goes to zero, the electrons are injected into the space charge region where they are swept by the E-filed to the drain contact. If we assume that the change in channel length ∆L is small compared to the original length L, then the drain current will be constant for V_DS> VDS&sat*. The region of the I_D versus V_DS characteristic is referred to as the saturation region. Fig. 2-8 shows this region of operation.

As V_GS changes, the I_D versus V_DS curve will change. We saw that, if V_GS increase, the initial slope of I_D versus V_DS increases. We can also note from eq-7 that the value of V_DS&sat* is a function of VGS. We can generate the family of curves for this n-channel enhancement mode MOSFET as shown in Fig. 2-9. The general I_D versus V_DS family of curves for an n-channel depletion mode MOSFET is show in Fig. 2-10.

13

In the non-saturation region, we will obtain

I

=

22&V

− V

*V

− V

3

[Eq-8]

And, in the saturation region, we will have

I

=

&V

− V

*

[Eq-9]

14

2.3 Transconductance

The MOSFET transconductance is defined as the charge in drain current with respect to the corresponding change in gate voltage, or

g

=

GS

[Eq-10]

The transconductance is sometimes referred to as the transistor gain. If we consider an n-channel MOSFET operating in the non-saturation region, then, using [Eq-6], we have

g

=

GS

=

∙ V

[Eq-11]

The transconductance increases linearly with V_DS but is independent of V_GS in the non-saturation region. The I-V characteristics of an n-channel MOSFET in the saturation region were given by [Eq-6]. The transconductance in this region of operation is given by

g

=

GS

=

&V

− V

*

[Eq-12]

In the saturation region, the transconductance is a linear function of V_GS and is independent of V_DS.

The transconductance is a function of the geometry of the device as well as of carrier mobility and threshold voltage. The transconductance increases as the width of

15

the device increase, and it also increases as the channel length and oxide thickness decrease. In the design of MOSFET circuits, the size of the transistor, in particular the channel width W, is an important engineering design parameter.

16

2.4 The CMOS technology

The primary objective of this text is to present the basic physics of semiconductor materials and devices without considering in detail the various fabrication processes; this important subject is left to other texts. However, there is one MOS technology that is used extensively, for which the basic fabrication techniques must be considered in order to understand essential characteristics of these devices and circuits. The one MOS technology we will consider briefly is the complementary MOS, or CMOS, process.

We have considered the physics of both n-channel and p-channel enhancement mode MOSFETs. Both devices are used in a CMOS inverter, which is the basis of CMOS digital logic circuits. The dc power dissipation in a digital circuit can be reduced to very low levels by using a complementary p-channel and n-channel pair.

It is necessary to form electrically isolated p- and n-substrate regions in an integrated circuit to accommodate the n- and p-channel MOSFET will be fabricated.

A diffused p-region, called a p well, is formed in which the p-channel MOSFET will be fabricated. A diffused p-region, called a p well, is formed in which the n-channel MOSFET will be fabricated. In most cases, the p-type substrate doping level must be larger than the n-type substrate doping level to obtain the desired threshold voltages.

The larger p doping can easily compensate the initial n doping to form the p well.

A simplified cross section of the p-well CMOS structure is shown in Fig.2-11.The notation FOX stands for field oxide, which is a relatively thick oxide separating the

17

devices. The field oxide prevents either the n or p substrate from becoming inverted and helps maintain isolation between the two devices. In practice, additional processing steps must be included; for example, providing connections so that the p well and n substrate can be electrically connected to the appropriate voltages. The n substrate must always be at a higher potential than the p well; therefore, this pn junction will always be reverse biased.

With ion implantation now being extensively used for threshold voltage control, both the n-well CMOS process and twin-well CMOS process can be used. The n-well CMOS process, shown in Fig. 2-12, starts with an optimized p-type substrate that is used to form the n-channel MOSFETs.(The n-channel MOSFETs, in general, have superior characteristics, so this starting point should yield excellent n-channel devices.) The n well is then added, in which the p-channel devices are fabricated. The n-well doping can be controlled by ion implantation.

The twin-well CMOS process, shown in Figure xxx, allows both the p-well and n-well regions to be optimally doped to control the threshold voltage and transconductance of each transistor. The twin-well process allows a higher packing density because of self-aligned channel stops.

One major problem in CMOS circuits has been latch-up. Latch-up refers to a high-current, low-voltage condition that may occur in a four-layer pnpn structure. Fig.

2-13 shows the circuit of a CMOS inverter and Fig. 2-14 shows a simplified integrated circuit layout of the inverter circuit. In the CMOS layout, the p⁺-source to n-substrate to p-well to n⁺-source forms such a four-layer structure.

18

The equivalent circuit of this four-layer structure is shown in Fig. 2-15. The silicon controlled rectifier action involves the interaction of the parasitic pnp and npn transistors. The npn transistor corresponds to the vertical n⁺ source to p well to n substrate to p⁺-source structure. Under normal CMOS operation, both parasitic bipolar transistors are cut off. However, under certain conditions, avalanche breakdown may occur in the p-well to n-substrate junction, driving both bipolar transistors into saturation. This high-current, low-voltage condition latch-up can sustain itself by positive feedback. The condition can prevent the CMOS circuit from operating and can also cause permanent damage and burn-out of the circuit.

Latch-up can be prevented if the product β"β< is less than unity at all times, where β_" and β_< are the common-emitter current gains of the npn and pnp parasitic bipolar transistors, respectively. One method of preventing latch-up is to “kill” the minority carrier lifetime. Minority carrier lifetime degradation can be accomplished by gold doping or neutron irradiation, either of which introduces deep traps within the semiconductor. The deep traps increase the excess minority carrier recombination rate and reduce current gain. A second method of preventing latch-up is by using proper circuit layout techniques. If the two bipolar transistors can be effectively decoupled, then latch-up can be minimized or prevented. The two parasitic bipolar transistors can also be decoupled by using a different fabrication technology. The silicon-on-insulator technology, for example, allows the p-channel MOSFETs to be isolated from each other by an insulator. This isolation decouples the parasitic bipolar transistors.

19

Fig. 2-1 Cross section for an n-channel enhancement-mode MOSFET

Fig. 2-2 Cross section for an n-channel depletion-mode MOSFET

20

Fig. 2-3 The n-channel enhancement mode MOSFET with an applied gate voltage VGS− VT

Fig. 2-4 ID versus VDS characteristics for small values of VDS at three VGS

voltages

21

Fig. 2-5 Cross section and ID versus VDS curve when VGS > VT for a small VDS

value

Fig.2-6 Cross section and ID versus VDS curve when VGS > VT for a large VDS

value

22

Fig. 2-7 Cross section and ID versus VDS curve when VGS > VT for a value of VDS = VDS(sat)

Fig. 2-8 Cross section and ID versus VDS curve when VGS > VT for a value of VDS > VDS(sat)

23

Fig. 2-9 Family of ID versus VDS curves for a n-channel enhancement mode MOSFET

Fig. 2-10 Family of ID versus VDS curves for a n-channel depletion mode MOSFET

24

Fig.2-11 CMOS structures p-well

Fig. 2-12 CMOS structures n-well

25

Fig. 2-13 CMOS inverter ciriuit

Fig. 2-14 Simplified integrated circuit cross section of CMOS inverter

26

Fig. 2-15 The splitting of the basic pnpn structure and two-transistor equivalent circuit of the four-layered pnpn device

27

Chapter 3

The Experimental Steps

3.1 Device Fabrication Process

In this study we use a p-type silicon and clean it by a full process from RCA clean. For device isolation, 500nm oxide was deposited by furnace and device active region was defined by photolithography and wet etching in BOE for about 5 minutes.

The source and drain regions in the active device region were formed by ion-implantation with phosphorus (35 Kev at 5×10¹⁵cm^-2) and activated at 900℃ for 30 minutes annealing in N₂ ambient. The second mask was used to remove silicon oxide in the gate region, and again RCA clean was done to assure the high-κ/Silicon interface. The third mask was used to remove high-κ dielectrics which on the source and drain regions by BOE for about 2 minutes. 90 nm thick HfTiO was deposited by PVD as the gate dielectric, following by a 600℃ post deposition annealing (PDA).

Then gate was formed by depositing 300 nm Al using PVD. Finally, the n-MOSFET was completed by gate definition with the fourth mask process.

3.2 2 The n

1. RCA clean P

n-MOSFETs Device

1. RCA clean P-type silicon wafer

MOSFETs Device

type silicon wafer

Fig. 3

28

MOSFETs Device of F

type silicon wafer

Fig. 3-1 RCA clean

Fabrication

RCA clean

abrication

2. Filed

3. Photoresist deposition 2. Filed-oxide grow in H

3. Photoresist deposition oxide grow in H₂

3. Photoresist deposition

4800 sccm and O

Fig. 3-

Fig. 3

29

4800 sccm and O₂ 3000 sccm at 1050

-2 Filed-oxide grow

Fig. 3-3 PR deposition 1st 3000 sccm at 1050

oxide growth

PR deposition 1st

3000 sccm at 1050℃ by furnaceby furnace

4. Source and Drain region define (Mask 1#) 4. Source and Drain region define (Mask 1#) 4. Source and Drain region define (Mask 1#)

Fig. 3

4. Source and Drain region define (Mask 1#)

Fig. 3-4 Source and Drain region define

30

4. Source and Drain region define (Mask 1#)

Source and Drain region define Source and Drain region define Source and Drain region define

5. Devlope 45 sec

6. Hard bake at 120 5. Devlope 45 sec

6. Hard bake at 120

5. Devlope 45 seconds by FHD

6. Hard bake at 120 ℃ 3 minutes ds by FHD-5

Fig. 3 3 minutes

Fig. 3

31

Fig. 3-5 Devlope 1st

Fig. 3-6 Hard Bake 1st Devlope 1st

Hard Bake 1st

7. Etching SiO

8. Remove PR by ACE 7. Etching SiO2

8. Remove PR by ACE

2 on Source and Drain region by BOE

8. Remove PR by ACE

on Source and Drain region by BOE

Fig. 3

Fig.3

32

on Source and Drain region by BOE

Fig. 3-7 Etch SiO

Fig.3-8 Remove PR on Source and Drain region by BOE

Etch SiO2

Remove PR 1st

9. Source and Drain imp

10. Activation in N 9. Source and Drain imp

10. Activation in N

9. Source and Drain implantation with phosphorus (35

Fig. 3 10. Activation in N2 at 900

lantation with phosphorus (35

Fig. 3-9 Implantation with phosphorus 00 ℃ for 30 min

Fig. 3

33

lantation with phosphorus (35

Implantation with phosphorus 30 minutes

Fig. 3-10 Activation

lantation with phosphorus (35 Kev at 5

Implantation with phosphorus

Activation

ev at 5x10¹⁵ cm

Implantation with phosphorus

cm^-2)

11. Photoresist deposition

12. Source and Drain region define (Mask 2#) 11. Photoresist deposition

12. Source and Drain region define (Mask 2#) 11. Photoresist deposition

12. Source and Drain region define (Mask 2#) 11. Photoresist deposition

Fig. 3-

12. Source and Drain region define (Mask 2#)

Fig. 3-12

34

-11 PR deposition 2nd 12. Source and Drain region define (Mask 2#)

Source and Drain define PR deposition 2nd

Source and Drain define Source and Drain define

13. Devlope

14. Hard bake 3. Devlope

14. Hard bake 14. Hard bake

Fig. 3

Fig. 3

35

Fig. 3-13 Devlope 2th

Fig. 3-14 Hard Bake 2nd Devlope 2th

Hard Bake 2nd

15. Etch SiO

16. Remove PR

15. Etch SiO2 on gate by BOE

16. Remove PR

on gate by BOE

16. Remove PR

on gate by BOE

Fig. 3-

Fig. 3

36

-15 Etch SiO

Fig. 3-16 Remove PR 2nd Etch SiO2 on gate

Remove PR 2nd

17. Hf

18. PDA 600 17. HfO2 and TiO

18. PDA 600℃

and TiO2 deposition by PVD

℃ 5 minutes

deposition by PVD

Fig. 3-17 HfO s

37

deposition by PVD

HfO2 and TiO

Fig. 3-18 PDA

and TiO2 deposition

PDA

deposition

19. Photoresist deposition

20. Mask 3#

19. Photoresist deposition

20. Mask 3#

19. Photoresist deposition 19. Photoresist deposition

Fig. 3-

Fig. 3

38

-19 PR deposition 3rd

Fig. 3-20 Mask 3#

PR deposition 3rd

Mask 3#

21. Develope

22. Hard bake 21. Develope

22. Hard bake 22. Hard bake

Fig. 3

Fig. 3-

39

Fig. 3-21 Devlope 3rd

-22 Hard bake 3rd Devlope 3rd

Hard bake 3rd

23. Etch Hf

24. Remove PR by ACE

23. Etch HfTiO on Source and Drain region

24. Remove PR by ACE

TiO on Source and Drain region

Fig. 3 24. Remove PR by ACE

TiO on Source and Drain region

Fig. 3-23 Etch HfTiO on Source and Drain

Fig. 3

40

TiO on Source and Drain region by BOE

Etch HfTiO on Source and Drain

Fig. 3-24 Remove PR 3rd y BOE

Etch HfTiO on Source and Drain

Remove PR 3rd

Etch HfTiO on Source and Drain

25. Al 500 nm deposition by PVD

26. Photoresist deposition

25. Al 500 nm deposition by PVD

26. Photoresist deposition

25. Al 500 nm deposition by PVD

26. Photoresist deposition

25. Al 500 nm deposition by PVD

Fig. 3 26. Photoresist deposition

Fig. 3-

41

Fig. 3-25 Al deposition

-26 PR deposition 4th Al deposition

PR deposition 4th

27. Metal region definition (Mask 4#)

28. Develope

27. Metal region definition (Mask 4#)

28. Develope

27. Metal region definition (Mask 4#) 27. Metal region definition (Mask 4#)

Fig. 3

Fig. 3

42

27. Metal region definition (Mask 4#)

Fig. 3-27 Mask 4#

Fig. 3-28 Devlope 4th Mask 4#

Devlope 4th

29. Hard bake

30. Etch Al 29. Hard bake

30. Etch Al 29. Hard bake

Fig. 3

Fig. 3

43

Fig. 3-29 Hard bake 4th

Fig. 3-30 Etch Al Hard bake 4th

Etch Al

31. Remove

32. Source 31. Remove PR

32. Source, Gate and Drain definition PR by ACE

, Gate and Drain definition Fig. 3 , Gate and Drain definition

Fig. 3-

44

3-31 Remove PR 4th , Gate and Drain definition

-32 n-MOSFET device Remove PR 4th

MOSFET device

45

Chapter 4

Result and Discussion

4.1 C-V and J-V Characteristics measured and analysis

Figs. 4-1, Fig. 4-2, Fig. 4-3 and Fig. 4-4 shows the C-V and J-V characteristics of different PDA temperature and different gas for Al/HfTiO capacitors. We could found a large capacitance density about 1.8 (µF/cm²) and low leakage current about 7

×10^-3 (A/cm²) where is PDA in N2 at 600℃. An equivalent oxide thickness (EOT) of

~1.9 nm is measured. Combining the EOT with a physical thickness of 9 nm, the dielectric constant of this PVD HfTiO is about 18.3, which is a high value to overcome the more severe gate leakage current problem for MOSFETs. Fig. 4-5 and Fig. 4-6 shows the C-V and J-V characteristics of different metal gate n-MOS capacitors. We could found the value of V_FB from Al/HfTiO capacitor is lower than the value of V_FB from TaN/HfTiO.

46

4.2 I-V Characteristics measured and analysis

Fig. 4-7 and Fig. 4-8 shows the transistor I_d-V_d characteristics as a function of Vg-Vt for Al/HfTiO and TaN/HfTiO n-MOSFETs. Al/HfTiO has a large I_dsat about 8mA when V_G and V_D =2 V. It is good enough for a high performance n-MOSFET.

Fig. 4-9 and Fig. 4-10 shows the Id-Vg characteristics of Al and TaN n-MOSFETs with HfTiO film as the gate dielectric. The V_th is as low as 0.35 V and 0.38 V are obtained from the linear I_d-V_g plot, which is consistent with the φ_m,eff of 4.1 eV and 4.3 eV from C-V curves.

47

4.3 Mobility Characteristics measured and analysis

Figs. 4-11 show the extracted electron motility versus gate electric field from measured Id-Vg curves of n-MOSFETs. High electron mobility of 121 cm²/V-s is obtained at peak value and 1 MV/cm effective field for Al/HfTiON n-MOSFETs.

48

Fig. 4-1 C-V characteristics of Al/HfTiO in N2 at different temperatures

49

50

Fig. 4-3 J-V characteristics of Al/HfTiO in N2 at different temperatures

51

Fig. 4-4 J-V characteristics of Al/HfTiO in O2 at different temperatures

52

Fig. 4-5 C-V characteristics of Al/HfTiO and TaN/HfTiO capacitors

53

Fig. 4-6 J-V characteristics of Al/HfTiO and TaN/HfTiO capacitors

54

Fig. 4-7 The I_d-V_d characteristics of Al/HfTiO n-MOSFET, the gate length is 4µm

55

Fig. 4-8 The I_d-V_d characteristics of TaN/HfTiO n-MOSFET, the gate length is 4µm

56

Fig. 4-9 The I_d-V_g characteristics of Al/HfTiO n-MOSFET, the gate length is 4µm

57

Fig. 4-10 The I_d-V_g characteristics of TaN/HfTiO n-MOSFET, the gate length is 4µm

58

Fig. 4-11 The extracted electron mobility from I_d-V_g characteristics of Al/HfTiO n-MOSFET.

59

Chapter 5

Conclusion and Suggestion for Future Work

5.1 Conclusion

We have fabricated and characterized high-performance n-MOSFET which incorporates high-κ HfTiO dielectric with low work-function Al metal gate that provides good dielectric properties such as low threshold voltage and low leakage current. These devices exhibit excellent electrical characteristics and high drive current.

Investigation on the temperature variation of HfTiO n-MOSFETs shows improved electrical characteristics for 600℃ in N2. It is improved not only capacitance density but also low leakage current.

60

5.2 Suggestion for Future Work

Although we have fabricated Al gated n-MOSFETs on HfTiO gate dielectric with 1.9 nm EOT. The fully Al/HfTiO device has high effective work function of 4.2 eV, high peak electron mobility of 121 cm²/V-s, several works are worthy to do in the future and are recommended here：

1. We need to find the way how to fabricate the device of CMOSFET.

2. Because the threshold voltage is not small enough, we need to search new electrode of high-κ metal gate to improve the thermal voltage.

3. In future, we will apply this work in my investigation to the present circuit design in order to check the influences of short channel effects in the advanced CMOSFET technology.

4. We should also measure the reliability of the Al/HfTiO CMOSFET.

61

References

[1] E. P. Gusev, D. A. Buchanan, E. Cartier, A. Kumar, D. DiMaria, S. Guha, A.

Callegari, S. Zafar, P. C. Jamison, D. A. Neumayer, M. Copel, M. A. Gribelyuk, H. Okorn-Schmidt, C. D Emic, P. Kozlowski, K. Chan, N. Bojarczuk, L. -A.

Ragnarsson and Rons, “Ultrathin high-κ gate stacks for advanced CMOS devices,” in IEDM Tech. Dig., pp. 20.1.1-20.1.4, 2001.

[2] M. Koyama, K. Suguro, M. Yoshiki, Y. Kamimuta, M. Koike, M. Ohse, C.

Hongo and A. Nishiyama, “Thermally stable ultra-thin nitrogen incorporated ZrO₂ gate dielectric prepared by low temperature oxidation of ZrN,” in IEDM Tech. Dig., pp. 20.3.1-20.3.4, 2001.

[3] W. Zhu, T. P. Ma, T. Tamagawa, Y. Di, J. Kim, R. Carruthers, M. Gibson and T.

Furukawa, “HfO₂ and HfAlO for CMOS: thermal stability and current transport,”

in IEDM Tech. Dig., pp. 20.4.1-20.4.4, 2001.

[4] L. Kang, K. Onishi, Y. Jeon, Byoung Hun Lee, C. Kang, Wen-Jie Qi, R. Nieh, S.

Gopalan, R. Choi and J. C. Lee, “ MOSFET devices with polysilicon on single-layer HfO₂ high-κ dielectrics,” in IEDM Tech. Dig., pp. 35-38, 2000.

[5] R. Choi, Chang Seok Kang, Byoung Hun Lee, K. Onishi, R. Nieh, S. Gopalan, E.

Dharmarajan and J. C. Lee, “High-quality ultra-thin HfO₂ gate dielectric MOSFETs with TaN electrode and nitridation surface preparation,” in IEDM Tech. Dig., pp. 15-16, 2001.

[6] Z. J. Luo, T. P. Ma, E. Cartier, M. Copel, T. Tamagawa and B. Halpern,

“Ultra-thin ZrO₂ (or silicate) with high thermal stability for CMOS gate applications,” in Symp. on VLSI Technology, pp. 135-136, 2001.

62

[7] International Technology Roadmap for Semiconductor, 2008.

[8] D.-G. Park, T.-H. Cha, K.-Y. Lim, H.-J. Cho, T.-K. Kim, S.-A. Jang, Y.-S. Suh, V.Misra, I.-S. Yeo, J.-S. Roh, J. W. Park, and H.-K. Yoon, “Robust ternary metal gate electrodes for dual gate CMOS devices,” in IEDM Tech. Dig., 2001, pp.

671-674

[9] Y.H. Kim, C. H. Lee, T, S. Jeon, W. P. Bai, C. H. Choi, S. J. Lee, L. Xinjian, R.

Clarks, D. Roberts, and D. L. Kwong, “High quality CVD TaN gate electrode for sub-100 nm MOS devices,” in IEDM Tech. Dig., 2001, pp. 667-670

[10] J. H. Lee, H. Zhong, Y.-S. Suh, G. Heuss, J. Gurganus, B. Chen, and V. Misra,

“Tunable work function dual metal gate technology for bulk and nonbulk CMOS,” in IEDM Tech. Dig., 2002, pp. 359-362.

[11] C. Hobbs, L. Fonseca, V. Dhandapani, S. Samavedam, B. Taylor, J. Grant, L. Dip, D. Triyoso, R. Hegde, D. Gilmer, R. Garica, D. Roan, L. Lovejoy, R. Rai, L.

Hebert, H. Tseng, B. White, and P. Tobin, “Fermilevel pinning at the polySi/metal oxide interface,” in Symp. on VLSI Tech.Dig.,2003,pp. 9-10.

[12] H.-H. Tseng, C. C. Capasso, J. K. Schaeffer, E. A. Hebert, P. J. Tobin, D. C. Gilmer, D. Triyoso, M. E. Ramón, S. Kalpat, E. Luckowski, W. J. Taylor, Y. Jeon, O. Adetutu, R. I. Hegde, R. Noble, M. Jahanbani, C. El Chemali, and B. E. White, “Improved short channel device characteristics with stress relieved pre-oxide (SRPO) and a novel tantalum carbon alloy metal gate/HfO₂ stack,” in IEDM Tech. Dig., pp. 821-824, 2004.

[13] H. -J. Cho, C. S. Kang, K. Onishi, S. Gopalan, R. Nieh, R. Choi, E. Dharmarajan and J.C. Lee, “ Novel nitrogen profile engineering for improved TaN/HfO₂ Si MOSFET performance,” in IEDM Tech. Dig., pp. 30.2.1-30.2.4, 2001.

63

[14] D. S. Yu, Albert Chin, C. H. Wu, M.-F. Li, C. Zhu, S. J. Wang, W. J. Yoo, B. F.

Hung and S. P. McAlister, “Lanthanide and Ir-based Dual Metal-Gate/HfAlON CMOS with Large Work-Function Difference,” in IEDM Tech. Dig., pp.

634-637, 2005.

[15] Y. T. Hou, M. F. Li, T. Low, and D. L. Kwong, “ Impact of metal gate work function on gate leakage of MOSFETs,” in DRC Symp., pp. 154-155, 2003.

[16] Dae-Gyu Park, Kwan-Yong Lim, Heung-Jae Cho, Tae-Ho Cha, Joong-Jung Kim, Jung-Kyu Ko, Ins-Seok Yeo and Jin Won Park, “ Novel damage-free direct metal gate process using atomic layer deposition,” in Symp. on VLSI Technology, pp.

65-66, 2001.

[17] C. Cabral Jr. , J. Kedzierski, B. Linder, S. Zafar, V. Narayanan, S. Fang, A.

Steegen, P. Kozlowski, R. Carruthers, and R. Jammy,” Dual work function fully silicided metal gates,” in Symp. on VLSI Technology, pp. 184-185, 2004.

[18] S. J. Rhee, H. S. Kim, C. Y. Kang, C. H. Choi, M. Zhang, F. Zhu, T. Lee, I. Ok, M. S. Akbar, S. A. Krishnan, and Jack C. Lee, “Optimization and Reliability Characteristics of TiO₂/HfO₂ Multi-metal Dielectric MOSFETs,” in Symp. on VLSI Technology, pp. 168-169, 2005.

[19] S. B. Samavedam, L. B. La, J. Smith, S. Dakshina-Murthy, E. Luckowski, J.

Schaeffer, M. Zavala, R. Martin, V. Dhandapani, D. Triyoso, H. H. Tseng, P. J.

Tobin, D. C. Gilmer, C. Hobbs, W. J. Taylor, J. M. Grant, R. I. Hegde, J. Mogab, C. Thomas, P. Abramowitz, M. Moosa, J. Conner, J. Jiang, V. Arunachalarn, M.

Sadd, B.-Y. Nguyen, and B. White,” Dual-metal gate CMOS with HfO₂ gate dielectric,” in IEDM Tech. Dig., pp. 433-436, 2002.

64

[20] D. S. Yu, A. Chin, C. C. Laio, C. F. Lee, C. F. Cheng, W. J. Chen, C. Zhu, M.-F.

Li, S. P. McAlister, and D. L. Kwong, “3D GOI CMOSFETs with novel IrO₂ (Hf) dual gates and high-κ dielectric on 1P6M-0.18µm-CMOS,” in IEDM Tech. Dig., pp. 181-184, 2004.

[21] D. S. Yu, A. Chin, C. C. Liao, C. F. Lee, C. F. Cheng, M. F. Li, Won Jong Yoo, and S. P. McAlister, “3D Metal-Gate/High-κ/GOI CMOSFETs on 1-Poly-6-Metal 0.18-µm Si Devices,” IEEE Electron Device Letters, Vol. 26, pp.

118-120, Feb. 2005.

[22] C. Hobbs, R. Hegde, B. Maiti, H. Tseng, D. Gilmer, P. Tobin, O. Adetutu, F.

Huang, D. Weddington, R. Nagabushnam, D. O’Meara, K. Reid, L. La, L. Grove and M, Rossow, “Sub-Quarter Micron CMOS Process for TiN-Gate MOSFETs with TiO₂ Gate Dielectric formed by Titanium Oxidation,” in Symp. on VLSI Technology, pp. 133-134, 1999.

[23] X. P. Wang, C. Shen, Ming-Fu Li, H.Y. Yu, Yiyang Sun, Y. P. Feng, Andy Lim, Hwang Wan Sik, Albert Chin, Y. C. Yeo, Patrick Lo, and D.L. Kwong,” Dual Metal Gates with Band-Edge Work Functions on Novel HfLaO High-κ Gate Dielectric,” in Symp. on VLSI Technology, pp. 12-13, 2006.

[24] J. H. Lee, H. Zhong, Y.-S. Suh, G. Heuss, J. Gurganus, B. Chen, and V. Misra,”

Tunable work function dual metal gate technology for bulk and nonbulk CMOS,”

in IEDM Tech. Dig., pp. 359-362, 2002.

[25] H. Y. Yu, M. F. Li, and D.L. Kwong, “Thermally Robust HfN Metal as a Promising Gate Electrode for Advanced MOS Device Application,” IEEE Transactions on Electron Devices, vol. 51, Apr., 2004.

65

[26] A. Veloso, K. G. Anil, L. Witters, S. Brus, S. Kubicek, J.-F. de Marneffe, B. Sijmus, K. Devriendt, A. Lauwers, T. Kauerauf, M. Jurczak, and S. Biesemans, “Work function engineering by FUSI and its impact on the performance and reliability of oxynitride and Hf-silicate based MOSFETs,” in IEDM Tech. Dig., pp. 855-858, 2004.

[27] S. J. Rhee, C. S. Kang, C. H. Choi, C. Y. Kang, S. Krishnan, M. Zhang, M. S. Akbar, and J. C. Lee, “Improved electrical and material characteristics of hafnium titanate multi-metal oxide n-MOSFETs with ultra-thin EOT (~8Å) gate dielectric application,” in IEDM Tech. Dig., pp.837-840, 2004.

[28] E. P. Gusev, D. A. Buchanan, E. Cartier, A. Kumar, D. DiMaria, S. Guha, A.

Callegari, S. Zafar, P. C. Jamison, D. A. Neumayer, M. Copel, M. A. Gribelyuk, H. Okorn-Schmidt, C. D Emic, P. Kozlowski, K. Chan, N. Bojarczuk, L. -A.

Ragnarsson and Rons, “Ultrathin high-κ gate stacks for advanced CMOS devices,” in IEDM Tech. Dig., pp. 20.1.1-20.1.4, 2001.

[29] V. Mikhelashvili and G. Eisenstein, “High-κ Al2O₃-HfTiO Nanolaminates With Less Than 0.8-nm Equivalent Oxide Thickness,” IEEE Electron Device Letters, VOL. 28, NO. 1, pp. 24-26, Jan. 2007.

[30] C. H. Wu, B. F. Hung, Albert Chin, S. J. Wang, F. Y. Yen, Y. T. Hou, Y. Jin, H.

J.Tao, S. C. Chen, and M. S. Liang, “HfSiON n-MOSFETs Using Low Work Function HfSix Gate,” IEEE Electron Device Letters, Vol. 27, Issue 9, pp.762-764, 2006.

[31] C. H. Wu, B. F. Hung, Albert Chin, S. J. Wang, F. Y. Yen, Y. T. Hou, Y. Jin, H.

J. Tao, S. C. Chen, and M. S. Liang, “HfAlON n-MOSFETs Incorporating Low Work Function Gate Using Ytterbium-Silicide,” IEEE Electron Device Letters, Vol. 27, Issue 6, pp. 454-456, June 2006.

66

[32] A. Chin, C. C. Liao, C. H. Lu, W. J. Chen, and C. Tsai, “Device and reliability of high-κ Al₂O₃ gate dielectric with good mobility and low D_it,” in Symp. on VLSI Tech. Dig., 1999, pp. 133-134.

[33] K. C. Chiang, Albert Chin, C. H. Lai, W. J. Chen, C. F. Cheng, B. F. Hung, C. C.

Liao, “Very high-κ and high density TiTaO MIM capacitors for analog and RF applications,” in Symp. on VLSI Tech. Dig., 2005, pp. 62-63.

[34] D. S. Yu, A. Chin, C. H. Wu, M.-F. Li, C. Zhu, S. J. Wang, W. J. Yoo, B. F. Hung and S. P. McAlister, “Lanthanide and Ir-based dual metal-gate/HfAlON CMOS with large work-function difference,” in IEDM Tech. Dig., 2005, pp. 649-652.

67

Vita

姓名:羅方鴻

性別:男

出生年月日:民國 74 年 9 月 28 日

籍貫:台北市

住址:台中市西區模範街 40 巷 4-1 號 1 樓

學歷:私立中華大學電機工程學系

(92 年 9 月~96 年 6 月)

私立中華大學電機工程研究所電子電路組

(96 年 9 月~98 年 6 月)

論文題目:

高介電係數材料氧化鈦鉿之 n 型場效電晶體之研製

The Fabrication and Characterization with High-κ Dielectric HfTiO nMOSFETs