High Reliability of 0.1 pm InGaAsnnAiAdInP HEMT MMICs on 3-inch InP Production Process

Y.C. Chou, D. Leung, R. Lai, J. Scarpulla, M. Barsky, R. Grundbacher, D. Eng, P.H. Liu, A. Oki and D.C. Streit

TRW, Inc., Redondo Beach, CA 90278 Tel: (310) 812-8254, Fax: (310) 813-0418, Email: yeong-chang.chou@trw.com

Abstract- The high-reliability performance of K- band MMIC amplifiers fabricated using 0.1 pm T-gate InGaAs/InAlAs/inP HEMTs on 3-inch wafers using a high volume production process is reported. Operating at an accelerated life test condition of Vds=1.2 V and lds=150 d m m , two-stage balanced amplifiers were lifetested at three- temperatures (T1=215"C, T2=230"C and T3=250"C) in a N2 ambient. The activation energy (Ea) is as high as 2 eV, achieving a projected median-time-to-failure (MTF) > lxlOx hours at a 125°C junction temperature. MTF was determined by 3- temperature constant current stress using I AS21 I > 1.0 dB as the failure criteria. This is the first demonstration of 3-temperature high reliability 0.1 pm InGaAsDnAlAsfinP HEMT based on small-signal microwave characteristics of HEMT MMIC. This result demonstrates a robust InGaAs/InAlAsAnP HEMT production technology.

I. INTRODUCTION

TRW has demonstrated state-of-the-art of millimeter wave performance over the frequency range of 100 GHz [l], 118 GHz [2,3], 155 GHz [4], 183 GHz [5], and 190 GHz [6,7,8] using InGaAsAnAIAshnP HEMT MMIC technology to meet the strong demand of present and future commercial and military electronic systems. With InGaAsAnAlAsAnP HEMTs becoming a preferred technology for either system performance improvement or the next generation system design, the demonstration of a robust technology for providing reliable, high performance MMICs at low cost and high yield to both the space/defense and commercia1 markets is essential. The published data of InGaAsfinAlAsAnP HEMT reliability has been mostly focused on discrete devices only [9-131, few have investigated the reliability of InGaAsAnAlAsnnP HEMT MMICs [14-171. MMIC lifetest allows the reliability assessment on InGaAsAnAlAsnnP HEMT devices and passive elements, such as via-hole integrity, thin film resistors, MIMCAPs, and metal interconnects. Accordingly, it is important to have InGaAsAnAlAdInP HEMT MMIC amplifier reliability information in order to assure the success of InP HEMT MMICs insertion for both comercia1 and military applications in the millimeter wave frequency band.

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While 2-temperature high reliability of 0.1 pm InGaAsAnAlAsAnP HEMT MMIC amplifiers on 3-inch InP substrates was reported by Y.C. Chou et.al. [16], the

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industry-standard 3-temperature lifetest for the acceptance of a new technology has not been demonsatrated. In this paper, high reliability of 0.1 pm InGaAsAnAlAsAnP HEMT MMIC amplifiers on 3-inch InP substrates based upon 3-temperature lifetest is demonstrated. The results benefit both millimeter and wireless communities by demonstrating a reliable and robust InGaAsAnAlAsAnP HEMT production technology, a critical factor in widespread acceptance of InGaAsAnAlAsAnP HEMT MMIC amplifiers for millimeter wave and wireless applications.

II. EXPERIMENTAL

The InP HEMT epitaxial layer structures were grown by molecular beam epitaxy on 3-inch semi- insulating InP substrates. The single-side doped pseudomorphic IQ.~G%.~AS channel HEMT structures were grown with channel electron density, n,, of 3 . 5 ~ 1 0 ' ~ cm-' and electron mobility > 9,000 cm2N-s at room temperature. Ti/Pt/Au is used for the gate contact. A 0.1 pm T-gate shown in Fig. 1 was patterned by two layers (PMMA, P(MMA-MAA)) electron beam lithography. The gate recess profile was controlled by wet-etch process. The devices and circuits are fully passivated with a thickness of 750 %, silicon nitride. The MIM capacitors were fabricated by a double-layer nitride process with a capacitor value targeted at approximately 300 pF/mm2. In addition, the burnout voltage of MIMCAPs is greater than 100 volts, indicating a robust MIMCAP process. The thin film resistor was fabricated with NiCr metal films with a precision resistor value of 100 ohmshquare, demonstrating a reliable operation at 0.6 mA/pm. Upon completion of front-side processing, wafers are thinned to a thickness of 75 pm. A dry-etch (electron-cyclotron resonance) backside via process is used to connect the front-side elements to the backside wafer ground plane [ 181. The dry- etch process gases were Ar, Hl, BC13, and HBr.

During the process, in-line on-wafer testing at both post-gate and completion of front-side process was implemented to monitor device characteristics, including transconductance (Gm), gate-source breakdown voltage (BVgsr), gate-drain breakdown voltage (BVgdr), off/on state burnout voltage, Schottky diode and pinch off characteristics. Device parameters are monitored

2001 IEEE GaAs Digest

statistically to assure that the process is reproducible. As shown in Fig. 2, the typical Gm-Vgs characteristics of 0.1 pm InP HEMT on 3-inch substrates is very tight and uniform. The cumulative distribution of Gmp (peak transconductance) for the historical wafers has an average Gmp of 970 mS/mm and standard deviation of 46 mS/mm. The average F, is approximately 177 GHz with a sigma of 6.8 GHz on our 0.1 pm InP HEMT technology.

-12 m =lo 2 . 8 ' LL

SiN Passivation Source Drain

lnAlAs I I I I - A(- I I I - I

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Fig. 1: Cross section of an InGaAsfinfUAsAnP HEMT for low noise amplifier applications (Insert: 0.1 prn T-gate).

-12 m =lo 2 8 . LL

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4

vgs (Volts)

Fig. 2: Typical Grn-Vgs characteristics of 0.1 prn InP HEMTs on 3-inch InP substrates (22 sites per wafer), showing a uniform and tight distribution.

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111. STANDARD EVALUATION CIRCUIT (SEC)

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To evaluate the reliability of 0.1 pm InP HEMT technology, a K-band balanced MMIC amplifier of ALH211C was designed for the standard evaluation

I

circuitry (SEC). ALH21 IC is a two-staged balanced amplifier with a total gate periphery of 160 pm on the lst stage and 400 pm on the 2nd stage. A micrograph of an ALH21 IC is shown in Fig. 3.

Fi.g. 3: Micrograph of a K-band 2-staged balanced MMIC low noise amplifier operating over 27-40 GHz fabricated by a 0.1 pm InP HEMT technology on 3-inch InP substrates.

As shown in Fig. 4, the ALH211C operates in the frequency range of 27-40 GHz with average gain of 17.5 dB and average noise figure of 2.5 dB at 35 GHz. Prior to lifetest, amplifiers were subjected to a temperature step stress under bias to determine the suitable temperature for lifetest. The temperature step stress conditions were Tmbient

from 150°C to 250°C with Vds=1.2 V, Ids=150 mA/mm. S21 starts to degrade drastically as Tambienl > 250°C. Accordingly, Tmbienl =2 15"C, 230"C, and 250°C were chosen for the 3-temperature lifetest. After each lifetest cycle, both full DC characterization and S-parameter measurement were performed at room temperature. I AS21 I > 1.0 dB at 35 GHz was chosen for the failure ~

I criteria in our 3-temperature lifetest.

0 ' 27 28 29 30 31 32 33 34 35 36 37 38 39 40

Frequency (GHz)

Fig. 4: S2land noise-figure characteristics of an ALH211C low- noise amplifier (LNA) using 0.1 krn 1nP HEMTs.

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As shown in Fig. 5, S21 reduction at 230°C after 240 hours is accompanied by changes of transistors in DC characteristic. Changes of DC characteristics were characterized with the gradual decrease of both Gm and Ids without affecting either Vgp (Vg at peak Gm) or Vpo. This differs from the degradation mechanisms dictated by the gate metal sinking effect of GaAs HEMT subjected to the high temperature stress [19]. In GaAs HEMTs, both Gm and Vpo were shifted towards more positive gate voltage followed by the Gm reduction [20].

10

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! 240 hrs 16

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. -0.5-0.4-0.3-0.2-0.1 0 0.1 0.2 0.3 8 4 , Vgs(V0lts)

400

- 300 E 250 $

; 200 5 150

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1E7

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e 1E5 E: lE4

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~ _ _ _ _ IE9r--- Ea = 2eV; MTF> lE8 hrs at Tj=125"C 4

4 1

j

Fig. 5: S21 reduction after 240 hours lifetest at 230°C accompanied by the changes of DC characteristics of transistors (Insert).

IV. 3-TEMPERATURE LIF'ETEST RESULTS -~

The lifetest failure based upon I AS21 I > 1.0 dB it 35 GHz for each temperature exhibits a log-normal listribution characteristics. The lifetest failure distribution it 215"C, 230°C and 250°C is plotted on a log-normal scale

in Fig. 6. The measured sigma at 230°C and 250°C was approximately 0.55 while the measured sigma at 215°C is approximately 0.9.

Figure 7 is an Arrhenius life-temperature model based on the median-time-to-failure at each lifetest temperature: 215"C, 230°C and 250°C. The estimated junction rise at Vd=l.2V, Ids=150 mA/mm has been factored into Fig. 7. The Arrhenius model projects a MTF > 1x108 hours at a 125°C junction temperature with an Ea of approximately 2 eV. At Tj,,~,,=125"C, the average failure rate of e lo-' FITS (failure per billion device hours) has been calculated for a 15 year mission life. The reliability achieved here is sufficient to meet the requirement of typical flight applications (>1x106 hours at

Tj=125"C) with 0.1 pm InP HEMT technology. This is the state-of-the-art of 3-temperature reliability results on 0.1 Fm 3-inch InP HEMT MMIC amplifiers stressed at high T, in a Nz ambient.

l- 1 0 2 - 2500c '

Fig. 7: Arrhenius plot of 0.1 pm InP HEMT MMIC amplifiers subjected to 3T lifetest at 215°C. 230"C, and 250°C.

V. CONCLUSIONS

TRW has demonstrated the superior performance of InP HEMT MMICs, both manufacturability and tight control on 3-inch 0.1 pm InGaAsfinAlAsAnP HEMT technology. The further demonstration of high reliability from 3-temperaure lifetest (with Ea=2 eV, MTF > 1x108 hours at T,=125"C) assures the reliability of next

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generation system inserted with InP HEMT MMICs. The results achieved by TRW demonstrate a robust InP HEMT technology, a critical factor for the successful acceptance of InP HEMT technology for next generation applications.

ACKNOWLEDGEMENTS

The authors acknowledge D. Okazaki, A. Kono, and B. Yamada for support in this work. The authors also acknowledge the TRW labs and personnel: 3D, D1, MBE, EBL, backside, layout, and RF test.

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