Intrinsic SiGe Research Articles

Selective Epitaxial Growth of SiGe(:B) for Advanced p-Type Fd-SOI

We focus here on various Selective Epitaxial Growth (SEG) processes used during the manufacturing of advanced p-MOSFET devices: (i) 20 nm thick in-situ boron doped Si0.7Ge0.3 layers grown at 650 °C, 20 Torr then capped with 5 nm of Si:B (at 730 °C, 20 Torr) for Raised Sources and Drains (RSDs) and (ii) 8 nm intrinsic SiGe layers grown at 650–700 °C, 20 Torr for channels. Those layers were grown with a heavily chlorinated chemistry to maintain full selectivity versus SiN hard-mask or SiCO sidewall spacers. The impact of diborane, germane and hydrochloric acid mass-flows on growth kinetics and doping were first of all quantified on blanket wafers. Epitaxial processes were optimized in terms of (i) doping and growth rates, which should be as high as possible while still having superior structural and electrical properties and (ii) selectivity against dielectrics. In a second part, we highlight some of difficulties encountered when switching to patterned substrates. The morphology, faceting and loading effects in such layers are discussed.

Enhancing subthreshold slope and ON-current in a simple iTFET with overlapping gate on source-contact, drain Schottky contact, and intrinsic SiGe-pocket

In this paper, we present a new novel simple iTFET with overlapping gate on source-contact (SGO), Drain Schottky Contact, and intrinsic SiGe pocket (Pocket-SGO iTFET). The aim is to achieve steep subthreshold swing (S.S) and high ION current. By optimizing the gate and source-contact overlap, the tunneling efficiency is significantly enhanced, while the ambipolar effect is suppressed. Additionally, using a Schottky contact at the drain/source, instead of ion implantation drain/source, reduces leakage current and thermal budget. Moreover, the tunneling region is replaced by an intrinsic SiGe pocket posing a narrower bandgap, which increases the probability of band-to-band tunneling and enhances the ION current. Our simulations are based on the feasibility of the actual process, thorough Sentaurus TCAD simulations demonstrate that the Pocket-SGO iTFET exhibits an average and minimum subthreshold swing of S.Savg = 16.2 mV/Dec and S.Smin = 4.62 mV/Dec, respectively. At VD = 0.2 V, the ION current is 1.81 times 10–6 A/μm, and the ION/IOFF ratio is 1.34 times 109. The Pocket-SGO iTFET design shows great potential for ultra-low-power devices that are required for the Internet of Things (IoT) and AI applications.

Investigation on RF/Analog Performance in SiGe Pocket n-Tunnel FET

In this paper, a SiGe pocket n-TFET is designed and its electrical performance is extracted using a TCAD simulator. Initially, a comparative study of input characteristics among conventional TFET (Device 1), intrinsic SiGe pocket TFET (Device 2), and doped SiGe pocket TFET (Device 3) is presented. It is seen that Device 2 shows an improved switching ratio (ION/IOFF) compared to other Devices. Furthermore, the RF/analog performance such as transconductance (gm), output conductance (gd), intrinsic gain (gm/gd), gate capacitance (Cgg), cut-off frequency (fc), transconductance frequency product (TFP), gain frequency product (GFP), and gain transconductance frequency product (GTFP) is reported for the variation in x of SiGe pocket from 0 to 1. The eBTBT rate and electron density are plotted for the variation in x of SiGe pocket Vertical TFET. The results reveal that the increase in x leads to an improvement in RF/analog performance and the tunneling rate in SiGe pocket Vertical TFET.

(Best Student Presentation Award) Reduced Pressure – Chemical Vapor Deposition of Monocrystalline and Polycrystalline Si(:B) and SiGe(:B) Layers on Blanket Wafers

Monocrystalline SiGe alloys can be used instead of monocrystalline Si in order to increase the performances of devices such as heterojunction bipolar transistors (HBTs) [1]. The epitaxial growth of blanket, monocrystalline SiGe layers on Si with a dichlorosilane + germane + hydrochloric acid chemistry was extensively investigated in the literature [2,3]. Similarly, a switch from polycrystalline Si to polycrystalline SiGe can be favorable, for instance, in Complementary-MOS (C-MOS) devices [4,5]. However, the blanket growth by Reduced-Pressure Vapor Deposition (RP-CVD) of polycrystalline Si and SiGe has not been systematically investigated. We have thus performed a one-to-one comparison in terms of growth kinetics and electrically active dopant incorporation between blanket monocrystalline and polycrystalline Si(:B) and SiGe(:B) layers.Epitaxies or depositions were performed, in 300 mm RP-CVD chambers, on two types of templates (Fig.1): i) N-type Si substrates (Fig.1(a)) and ii) poly-Si/oxide/ P-type Si substrates (Fig.1(b)). The poly-Si layer in stack 1.(b) was obtained thanks to amorphous Si deposition followed by annealing at 750 °C, resulting in a poly-Si film. SiH4+HCl+H2 (named Process 1) and SiH2Cl2 (DCS)+HCl+GeH4+H2 (named Process 2) chemistries were used to deposit Si and SiGe layers between 675-750 °C and 10-20 Torr.Monocrystalline and polycrystalline SiGe growth kinetics for two process conditions: i) 750 °C, 10 Torr with a HCl partial pressure of 0.05 Torr and ii) 725 °C, 10 Torr, with a HCl partial pressure of 0.06 Torr, were similar to that in the literature [1-3, 6-8]. As already shown for monocrystalline layers, there was an increase of the intrinsic SiGe growth with the germane partial pressure and the temperature. Meanwhile, it was reduced when adding HCl (Fig.2). Very similar growth rates and evolutions were however obtained whatever the crystalline state of the layers.When diborane was added the gaseous mixture, different behaviors were evidenced depending on i) the crystallinity and ii) the stoichiometry. The Si:B and SiGe:B growth rates increased with the B2H6 flow whatever the chemistry (Fig.3). This was due to a hydrogen desorption increase on boron surface sites [5,10-11]. Growth rates were otherwise higher for monocrystalline than for polycrystalline layers. The electrical resistivities of c-Si:B and c-SiGe:B layers were one decade lower than those of poly-Si:B and poly-SiGe:B layers, however (Fig.4). Resistivity values were otherwise higher for c-Si:B than for c-SiGe:B. This was likely due to i) a better incorporation of B atoms into SiGe than in Si [3,8,9] and ii) a better hole mobility in SiGe [10]. An opposite behavior was observed for polycrystalline layers, with higher resistivities for poly-SiGe:B than for poly-Si:B. We otherwise had similar resistivity evolutions as the partial pressure of diborane Pp(B2H6) increased for all types of layers. A decrease was observed first, followed by a resistivity plateau then some resistivity re-increase for really high diborane flows. Such a phenomenon was already observed for monocrystalline layers and was explained by a crystalline quality degradation [3,8,9] that reduced the hole mobility. A similar behavior was assumed for poly-layers, with a morphological transition to the amorphous phase [11,12]. Top-view Scanning Electron Microscopy (SEM) images (Fig. 5) confirmed the morphological evolution of c-Si:B, poly-Si:B, c-SiGe:B and poly-SiGe:B as the diborane partial pressure increased.New data points for c-SiGe and c-SiGe:B will also be provided for other process conditions. For intrinsic layers, we will show that Refs. [1,2] x2/(1-x) = n×(F(GeH4)/F(SiH2Cl2)) relationship between the Ge concentration x and the germane over dichlorosilane mass-flow ratio is also valid at 10 Torr, with n = 3 at 700 °C with a F(SiH2Cl2)/F(H2) Mass-Flow Ratio (MFR) of 0.005 and a F(HCl)/F(H2) MFR of 0.006. Various characterization techniques were also used to determine the concentration of substitutional Boron atoms in SiGe:B layers and the lattice contraction coefficient (β = 9.11×10-24 cm3). The value of the latter, which is most useful to assess the compressive strain compensation by small boron atoms in SiGe layers, will be compared to literature values.[1] J. Appl. Phys. 88 (2000) 4044[2] J. Crystal Growth 305 (2007) 113[3] J. Crystal Growth 310 (2008) 62[4] J. Microelec. Sys. 16 (2007) 68[5] International Electron Devices Meeting (1991) 567[6] Appl. Phys. Lett. 56 (1990) 1275.[7] S. Chang et al., ECS Proceedings 87–8 (1987) 122[8] J Mater Sci: Mater Electron (2007) 18:747[9] ECS Trans. 75, 8 (2016) 265[10] Mater. Sci. Eng. B 114–115 (2004) 318[11] Appl. Phys. Lett. 66 (1995) 195[12] ECS Trans. 35, 30 (2011) 45 Figure 1

Reduced Pressure – Chemical Vapor Deposition of Monocrystalline and Polycrystalline Si(:B) and SiGe(:B) Layers on Blanket Wafers

In this paper, epitaxial growths or depositions were performed, in 300 mm RP-CVD chambers, on two types of templates: N-type Si substrates or poly-Si/oxide/ P-type Si substrates. SiH4+HCl+H2 and SiH2Cl2+HCl+GeH4+H2 chemistries were used to deposit Si and SiGe layers between 675-750°C and 10-20 Torr on such wafers. Monocrystalline and polycrystalline growth kinetics were similar for intrinsic SiGe. Meanwhile, growth kinetics and boron incorporation were different for mono-Si:B, mono-SiGe:B, poly-Si:B and poly-SiGe:B layers. While the impact of B atoms is well documented in monocrystalline layers, it is still poorly understood for polycrystalline layers. An attempt has therefore been made to quantify it by measuring the poly-structure, with a focus on the poly-grains size and the number of grain boundaries. A lattice contraction coefficient β = - 9.82 * 10-24 cm3 has otherwise been extracted from an in-depth study of the incorporation of B atoms into substitutional sites of the SiGe epitaxial lattice.

A fabrication process for self-connected horizontal SiGe nanowires

We present in this paper a low thermal budget process for self-connecting horizontal silicon‑germanium nanowires. The guided nanowires on amorphous oxide layer have been elaborated by a chemical vapor deposition (CVD), using vapor-liquid-solid (VLS) mechanism, via a gold catalyst. We have optimized the growth parameters on reference samples with pre-patterned electrodes on SiO2/Si substrate. To control and eliminate the random growth of horizontal NWs, we have developed a technological process to guide these nanowires in nanotrenches created in the oxide to locate gold catalysts and confine planar growth. The silicon germanium nanowire (SiGe NW) connected the predefined electrodes showed an electrical behavior of an intrinsic SiGe NW.

Computational Investigation to Improve the Efficiency of Multi-junction SiGe/Si Solar cell

The Intrinsic SiGe layer is implemented in the designing of thin-film SiGe solar cell in order to optimize and improve the electrical and optical behavior of the commercially available SiGe solar cells. The proposed device is simulated with Silvaco ATLAS TCAD by placing the intrinsic SiGe layer on a silicon base. Various parameters like molefraction of germanium in Si1-XGeX, thickness of newly introduced intrinsic region etc. were optimized to enhance the efficiency of thin-film SiGe solar cell. At a molefraction of x=0.48 of germanium and at a approximate thickness of 1μm of the intrinsic region, the efficiency of the designed cell is significantly improved and is found to be around 23.2% and the maximum value of cathode current density is 162mA/cm2, achieved at an open circuit voltage of 1.32V. In this regard the variation of photo-luminescence Intensity with wavelength for different mole fraction of germanium has been observed.

A Benchmark of Germane and Digermane for the Low Temperature Growth of Intrinsic and Heavily in-situ Boron-Doped SiGe

We have recently demonstrated the interest of using Si2H6 + GeH4 for the 450°C-500°C epitaxy of (i) intrinsic SiGe layers and (ii) SiGe:B raised sources and drains [1-4]. One way of further increasing performances (in terms of growth rates at really low temperatures and Ge contents reachable) could be to use a higher order Ge precursor, such as digermane (Ge2H6). We have thus benchmarked GeH4 and Ge2H6 for the Reduced Pressure–Chemical Vapor Deposition (RPCVD) of SiGe and SiGe:B in an Applied Materials 200 mm Epi Centura 5200 tool. We have first of all compared the impact of the GeH4 and Ge2H6 mass-flows on the SiGe growth kinetics (at 500°C, 20 Torr and with a fixed Si2H6 flow). Whatever the source of Ge atoms, we had a linear increase of the SiGe growth rate with the Ge flow (cf. Figure 1, top). This was due to the catalysis of H desorption by Ge surface atoms, freeing sites for incorporation. Because of its higher reactivity, the SiGe growth rate was 8 to 10 times higher with Ge2H6 than with GeH4, however. We were also faced with a sub-linear increase of the Ge content x with F(Ge)/F(Si) (bottom of Figure 1). Using Ge2H6 instead of GeH4 otherwise yielded much higher Ge contents for a given disilane flow: in the 35-48% range instead of 20-33% only. The evolution of x with the F(Ge) flow was well accounted for by x2/(1-x)=nF(Ge)/F(Si) relationships (F(Ge) = F(GeH4) or 2F(Ge2H6)), with n = 0.47 for germane and n = 1.74 for digermane. We have then studied the evolution of the SiGe growth rate with temperature (Figure 2), for both types of Ge precursors. The use of GeH4 led to an exponential increase of the 20 Torr SiGe growth rate with temperature (with a 42 kcal.mol.-1 activation energy), together with a slight linear decrease of the Ge concentration. The situation was very different with Ge2H6. As the growth temperature increases, we were faced with a slow exponential increase of the SiGe growth rate (Ea = 15 kcal.mol.-1), together with a huge linear decrease of the Ge content. We have also quantified the impact HCl, an etchant gas, had on the growth kinetics of intrinsic SiGe with fixed amounts of disilane and digermane. Adding HCl led at 500°C, 20 Torr to a significant decrease of the growth rate (from 7.8 down to 4.2 nm min.-1), together with a significant Ge concentration increase (from 35% up to 55%). We have otherwise studied the impact of the B2H6 flow on the SiGe:B growth kinetics at 500°C, 20 Torr. The SiGe:B growth rate and the real or “apparent” Ge contents associated with such SiGe:B layers are plotted in Figure 3 as a function of the B2H6 mass-flow. Adding small amounts of diborane to Si2H6 + Ge2H6 + HCl led to a dramatic increase of the SiGe:B growth rate, from 5.8 up to 13.2 nm.min.-1. H desorption was indeed catalysed by the presence of B surface atoms. The “apparent” Ge concentration is coming from X-Ray Diffraction when supposing that an in-situ boron-doped SiGe layer behaves as an intrinsic one. This is however not true for high doping levels. Boron atoms, which are much smaller than Si or Ge atoms, then compensate the compressive strain in SiGe layers, yielding Ge concentrations artificially lower than the real ones. The concentration difference thus reflects the compressive strain compensation by substitutional B atoms. There is in Fig. 3 a definite decrease of the real and “apparent” Ge concentration with the B2H6 flow, from 47% down to 15% and 20%, respectively. We have also performed SIMS depth profiling of the B atoms in those SiGe:B layers. Their concentration increased linearly with the B2H6 mass-flow, reaching at most 3.6x1020 cm-3 in single crystalline layers (Figure 4, left) The associated resistivity (Figure 4, right) was as low as 0.43 mΩ.cm. For higher B2H6 flows, we had a resistivity increase, which was likely due to the crystalline quality degradation then the transformation into poly-SiGe:B evidenced in X-Ray Diffraction. Small islands were otherwise present in limited numbers on the surface of those SiGe:B layers, with no clear dependence on the B2H6 flow. [1]J.M. Hartmann et al. ECS J. Sol. State Sci. and Technol. 3 (11) P382 (2014). [2] J.M. Hartmann et al. Thin Sol. Films 557, 19 (2014). [3] J. Aubin et al. Thin Sol. Films 602, 36 (2016). [4] J. Aubin et al. Semicond. Sci. Technol. 30, 115006 (2015). Figure 1

Very low temperature (450 °C) selective epitaxial growth of heavily in situ boron-doped SiGe layers

We have investigated the feasibility of selectively growing SiGe:B layers at 450 °C, 20 Torr in a 300 mm industrial reduced pressure chemical vapor deposition tool. A reduced H2 carrier gas mass-flow has been used in order to have acceptable growth rates at such a temperature, which is very low indeed. We have first of all studied on blanket Si wafers the in situ boron doping of SiGe with Si2H6, GeH4 and B2H6. A growth rate increase by a factor close to 7 together with a Ge concentration decrease from 53% down to 32% occurred as the diborane mass-flow increased. Very high B+ ion concentrations were obtained in layers that were single crystalline and smooth. Their concentration increased almost linearly with the B2H6 mass-flow, from 1.8 up to 8.3 × 1020 cm−3. The associated resistivity dropped from 0.43 down to 0.26 mΩ cm. We have then tested whether or not selectivity versus SiO2 could be achieved by adding various amounts of HCl to Si2H6 + GeH4 +B2H6. Single crystalline growth rates of intrinsic SiGe(:B) on Si were very similar to poly-crystalline growth rates on SiO2-covered substrates irrespective of the HCl flow. Straightforward selectivity was thus not feasible with a co-flow approach. As a consequence, a 450 °C deposition/etch (DE) process was evaluated. Growth occurred at 20 Torr with the above-mentioned chemistry, while the selective etch of poly-SiGe:B versus c-SiGe:B was conducted at 740 Torr with a medium HCl mass-flow (F(HCl)/F(H2) = 0.2) and a high H2 flow. A 2.2 etch selectivity was achieved while retaining single crystalline if slightly rough SiGe:B layers.

Epitaxial growth of Si and SiGe at temperatures lower than 500 °C with disilane and germane

We have investigated the feasibility of growing in a 300mm industrial reduced pressure chemical vapor deposition tool Si and SiGe layers at 500°C and lower thanks to disilane (Si2H6) and germane (GeH4). We have first of all evidenced the beneficial impact of the disilane partial pressure P(Si2H6) on the silicon growth rate (GR). Increasing P(Si2H6) by 5 (through a growth pressure increase or a H2 mass-flow reduction) enabled us to increase by more than 2 the Si GR. We were thus able to lower the Si growth temperature threshold (for which GR≥1nm·min−1) from 475°C down to 460°C only. Islands were present on the surface of the resulting Si layers, however. We have then studied the SiGe growth kinetics at 2666Pa (20Torr) with a H2 mass-flow divided by 5. Intrinsic SiGe growth rates were 3 times higher than Si GR in the 450°C–500°C temperature range. This is due to the catalysis of H desorption from the surface by Ge surface atoms, freeing sites for growth. A slight Ge concentration increase (from 37.5% up to 40.5%) together with a significant surface roughening was otherwise evidenced when increasing the growth temperature from 450°C up to 500°C. We have then evaluated the impact of the GeH4 mass-flow on the 450°C growth kinetics of SiGe. An almost linear increase of the SiGe growth rate (from 1 up to 3nm·min−1) together with a sub-linear increase of the Ge content x (from 22% up to 38%) occurred when increasing the GeH4 flow.

Selective epitaxy growth of Si1−xGex layers for MOSFETs and FinFETs

This article reviews the selective epitaxy growth of intrinsic, B- and C-doped SiGe layers on recessed (or flat) exposed Si areas for MOSFETs as well as on Si-fins for FinFETs. A detailed empirical model for the growth, integration issues including epitaxy quality, selectivity, dopant incorporation, and pattern dependency (or loading effect) is presented.

Electron holography of devices with epitaxial layers

Applicability of electron holography to deep submicron Si devices with epitaxial layers is limited due to lack of the mean inner potential data and effects of the sample tilt. The mean inner potential V0 = 12.75 V of the intrinsic epitaxial SiGe was measured by electron holography in devices with Ge content CGe = 18%. Nanobeam electron diffraction analysis performed on the same device structure showed that SiGe is strain-free in [220] direction. Our results showed good correlation with simulations of the mean inner potential of the strain-free SiGe using density function theory. A new method is proposed in this paper to correct electron holography data for the overlap of potentials of Si and the epitaxial layer, which is caused by the sample tilt. The method was applied to the analysis of the dopant diffusion in p-Field-effect Transistor devices with the identical gate length L = 30 nm, which had alternative SiGe geometry in the source and drain regions and was subjected to different thermal processing. Results have helped to understand electrical data acquired from the same devices in terms of dopant diffusion.

Lumped Models for Assessment and Optimization of Bipolar Device RF Noise Performance

We present a method for simulation of RF noise characteristics of both intrinsic and complete Si(Ge) heterojunction bipolar transistors (HBT's), aiming at support for device design and optimization. RF noise at the intrinsic device level is addressed through an equivalent circuit based on a discretization of partial differential equations describing the transport of minority carriers in quasi-neutral regions. Effects of nonuniform impurity/bandgap distribution and finite velocity recombination at the polysilicon emitter contact are accounted for. Accuracy is verified against analytical results at intrinsic device level. Assessment of noise characteristics of a complete industrial SiGe HBT demonstrates the practical relevance of nonquasi-static effects on noise characteristics. Exploration of the impact of intrinsic base doping profiles on noise performance demonstrates the potential for device optimization.

Potentialities of disilane for the low temperature epitaxy of intrinsic and boron-doped SiGe

The disilane (Si2H6)+germane (GeH4) chemistry has been evaluated for the reduced pressure (2660Pa, i.e. 20Torr), low temperature growth of intrinsic and heavily boron-doped SiGe. A SiGe growth rate “plateau” has been evidenced between 650°C and 750°C. Meanwhile, the Ge concentration x was rather steady in the 500°C–700°C range. A linear increase of the SiGe growth rate with the GeH4 flow occurred at 500°C, 550°C and 675°C. The increase of x with the GeH4 mass-flow otherwise changed from linear to sub-linear as the growth temperature was reduced from 675°C down to 500°C–550°C. Be it with Si2H6 or SiH4, the SiGe growth rate fell by a factor of ~7–8 when switching from 550°C to 500°C. For the same x, growth rate was nevertheless 3–9 times higher with Si2H6 than with SiH4. We have also studied the impact of B2H6 on the 500°C growth kinetics of SiGe with Si2H6. Large substitutional boron concentrations were obtained in single-crystalline SiGe:B layers: [B]subst.~3.7×1020 cm−3. Surface B atoms otherwise catalysed H desorption, resulting in growth rates ~5 times higher for SiGe:B than for intrinsic SiGe. Finally, a monotonic decrease of the SiGe(:B) growth rate together with a significant increase of the Ge concentration were evidenced at 500°C and 675°C when adding HCl to the gaseous mixture. At 500°C, SiGe:B growth rates still stayed 3 times higher than the intrinsic SiGe ones. Adding HCl had otherwise no clear impact on [B]subst.

Low temperature RPCVD epitaxial growth of Si1−xGex using Si2H6 and Ge2H6

The growth of intrinsic SiGe and, n- and p-type doping of Si and SiGe layers was studied using a Reduced Pressure Chemical Vapor Deposition AIXTRON TRICENT® cluster tool. Most emphasis was placed on the growth kinetics in the low temperature regime of 450–600°C which is characterized by surface limited reactions. A low growth activation energy of 0.667eV was achieved by using Si2H6 and Ge2H6 precursors. Fully strained SiGe layers with Ge contents up to 53% at a record thickness of 29nm were grown at a very low growth temperature of 450°C. The dopant incorporation in Si strongly increases with the B2H6 flux but saturates rapidly with increasing PH3 flow. High dopant concentrations of 1.1×1020cm−3 and 1×1021cm−3 were obtained for Si:P and Si:B doping, respectively, at a growth temperature of 600°C. For Si0.56Ge0.44 layers the maximum dopant concentrations achieved were 5×1020cm−3 for P at 500°C and 4×1020cm−3 for B doping at 600°C.

N-p-n Array Yield Improvement in a 0.18-μm Deep Trench SiGe BiCMOS Process

The deep trench (DT) process module shows a strong impact on SiGe BiCMOS n-p-n array yield. DT liner oxidation introduces large tensile stress at the top of DT corners and in the vicinity of intrinsic SiGe base/collector regions. The increased tensile stress can result in dislocations in silicon. By replacing the 100-nm wet oxidation DT liner with a TEOS deposition liner, n-p-n array collector-emitter leakage yield can be improved from 64% to 94% in the investigated 0.18-μm DT SiGe BiCMOS process, comparable to the yield of a non-DT low-cost SiGe BiCMOS process.

Low temperature boron and phosphorous doped SiGe for recessed and raised sources and drains

We have first of all studied the growth kinetics of boron and phosphorous doped, 20–30 nm thick Si 0.65Ge 0.35 layers, the aim being their integration in recessed and raised sources and drains. Those layers have been grown at low pressure (20 Torr) and low temperature (650 °C) with a heavily chlorinated chemistry (in order to be selective versus SiO 2 (isolation) and Si 3N 4 (sidewall spacers)). We have quantified the impact of the diborane and phosphine flow on (i) the SiGe crystalline quality and strain state, (ii) the amount of boron or phosphorous atoms incorporated in it and (iii) the SiGe:B or SiGe:P growth kinetics. As the diborane flow increases, the SiGe:B growth rate definitely increases, while the real Ge concentration (from Time-Of-Flight Secondary Ions Mass Spectrometry) is more or less steady. B atoms, being much smaller than Si or Ge, partially compensate the compressive strain in the SiGe:B layers, leading to a decrease in the apparent Ge concentration (from X-ray diffraction). Opposite trends are observed for SiGe:P. There is indeed a definite decrease in the SiGe:P growth rate together with a definite increase in both the apparent and real Ge concentration as the phosphine flow increases. The Boron atomic concentration increases linearly with the diborane flow, with however a practical limit around 3.5×10 20 cm −3 in order to stay monocrystalline. Meanwhile, the phosphorous atomic concentration saturates quite rapidly at values close to 8–9×10 19 cm −3 as the phosphine flow increases (most likely due to surface segregation). In the second part we have highlighted some of the difficulties encountered when trying to selectively grow intrinsic SiGe raised S/Ds at 650 °C on patterned, extra-thin Silicon-On-Insulator wafers and some of the solutions identified in order to obtain 2D thick films. Amongst those, we can mention the 750 °C deposition of a thin Si buffer or the in-situ high HCl partial pressure etch at 650 °C of a few nm of Si prior to SiGe Selective Epitaxial Growth (SEG), the drastic reduction of the incoming HCl flow during SiGe SEG, etc.

Collector junction depletion-layer width model of SiGeheterojunction bipolar transistor with intrinsic SiGe layer

By solving Poisson equation, models of voltage and electric field distribution are build respectively in collector junction depletion layer of SiGe HBT (heterojunction bipolar transistor) with intrinsic SiGe layer. On this basis, models of the collector junction depletion layer width and delay time are obtained. Applying MATLAB, the impact of physical and electrical parameters on SiGe HBT collector junction depletion layer width and depletion delay time are quantitatively analyzed. When base doping concentration and collector junction reverse bias are large, the depletion delay time is quite long. But, when base doping external diffusion depth and collector region doping are large, the depletion delay time is quite short.

Investigation of Process Parameters on the Properties of Selective Epitaxial Growth SiGe Structure

This work presents the effect of process parameters such as substrate condition, flow rate of precursors and dopant on selective epitaxial growth (SEG) of Si1-XGeX layer in recessed source and drain (S/D) regions of pMOSFET structure. It was observed that the growth rate of SEG Si1-XGeX on patterned wafer was slightly less than that of Si1-XGeX on bare wafer as GeH4 flow rate increased. And an in-situ boron-doped SiGe layer exhibits lower growth rate and Ge content than intrinsic SiGe layer due to a decrease of GeH4 partial pressure. Nano beam electron diffraction (NBD), which is an efficient method to measure induced compressive strain in Si channel, is applied on both intrinsic and in-situ boron doped Si1-XGeX layers with a different Ge content. NBD patterns confirmed that higher Ge concentration introduces more strain in the channel region and in-situ boron doping of Si1-XGeX does not affect the channel strain.

Bandgap changes in excited intrinsic (heavily doped) Si and Ge semiconductors

Our results for the bandgap changes in highly excited intrinsic (heavily doped-HD) Si (Ge) for any majority-carrier density N and temperature T have been investigated and expressed in terms of (i) the bandgap narrowing (BGN>0) due to many-body carrier–carrier interactions and screening effect on carrier-impurity (or electron–hole) potential energies, (ii) the bandgap widening (BGW<0) due to the effects of Fermi Dirac statistics, and (iii) the apparent BGN defined by ABGN≡BGN+BGW<BGN. Since those ABGN and BGN can be extracted from respective electical-and-optical measurements, this relation thus suggests a conjunction between electrical-and-optical bandgaps (EBG-and-OBG). Then, our results for BGN, ABGN, OBG, and EBG have been computed and also compared with other theoretical and experimental ones, giving rise to a satisfactory description of both electrical-and-optical data in those materials. Furthermore, in the p-type HD base of Si 1− x Ge x hetero bipolar transistors for x≤0.3, using a same assumption taken by Eberhardt and Kasper (EK) [Mater. Sci. Eng. B 89 (2002) 93–96], we have obtained the results for ABGN and EBG, which are found to be in good accordance with the respective EK-ones.