Ultraclean Low-pressure Chemical Vapor Deposition Research Articles

(Invited) Strain Control of Si and Si1-x-yGexCy Layers in Si/Si1-x-yGexCy/Si Heterostructures by Low-Pressure Chemical Vapor Deposition

The epitaxial growth of strained Si1-x-yGexCy layer with high Ge fraction and high C fraction on unstrained and tensile-strained Si(100) is performed at 500 or 550oC by ultraclean low-pressure chemical vapor deposition. Evaluating the Si1-x-yGexCy layer by high resolution X-ray photoelectron spectroscopy (XPS), X-ray diffraction and Raman scattering spectroscopy, it is proposed that XPS C1s peak at around 283.3 eV is attributed to substititional C in Si1-x-yGexCy layer. The relationship between Raman shift and vertical lattice constant for the strained layer is explained qualitatively and it is confirmed that growth characteristics as well as electrical activity of impurity in the strained layer are influenced by the substrate surface strain before the layer growth. By stripe-shape patterning unstrained Si cap layer/strained Si1-x-yGexCy layer/Si(100) heterostructure, the compressive- and tensile-strained Si layer formation is performed.

Heavy atomic-layer doping of nitrogen in Si 1 − xGe x film epitaxially grown on Si(100) by ultraclean low-pressure CVD

N atomic-layer doping in a nanometer-order Si/Si 1 − x Ge x /Si(100) heterostructure using ultraclean low-pressure chemical vapor deposition and its thermal stability at 650 °C were investigated. In the Si 0.5Ge 0.5 epitaxial layer, it is found that a N doping dose of 6 × 10 14 cm − 2 can be confined within an about 1.5 nm-thick region even after 650 °C heat treatment in contrast to the result for Si cap layer growth on the thermally nitrided Si(100) with a N doping dose of 6 × 10 14 cm − 2 which was found to be amorphous. Moreover, it is suggested that the confined N atoms in Si 1 − x Ge x preferentially form Si–N bonds and that formation of Si 3N 4 is enhanced by the heat treatment at 650 °C.

Heavy carbon atomic-layer doping at Si 1 − xGe x/Si heterointerface

Heavy C atomic-layer doping of about 10 14 cm − 2 at the heterointerface between Si 1 − x Ge x and Si using an ultraclean low-pressure chemical vapor deposition has been investigated. By heavy C atomic-layer doping at heterointerface between a Si cap layer and a Si 0.55Ge 0.45 layer in Si/Si 0.55Ge 0.45/Si(100) heterostructure, the intermixing between Si and Ge at heterointerface is effectively suppressed. For 4 nm thick Si 0.55Ge 0.45 cap layer/Si(100) heterostructure with C atomic-layer doping, Ge fraction of 0.45 and strain scarcely change with the heat treatment at 750 °C, while those without C atomic-layer doping are reduced. For 40 nm thick Si 0.55Ge 0.45 cap layer/Si(100) heterostructure, whose Si 0.55Ge 0.45 thickness is close to the critical thickness, it is found that the strained Si 0.55Ge 0.45 cap layer is relaxed by C atomic-layer doping at heterointerface. These results suggest that the heavy C atomic-layer doping suppresses strain relaxation as well as intermixing between Si and Ge at the Si 1 − x Ge x /Si heterointerface especially for the heterostructure composed of nm-order thick films.

Impact of Si cap layer growth on surface segregation of P incorporated by atomic layer doping

In atomic layer doping of P using an ultraclean low-pressure chemical vapor deposition (CVD), the relationship between surface segregation of P during Si cap layer growth at 450 °C with Si 2H 6 partial pressure of 3–20 Pa on P atomic layer formed on Si 0.3Ge 0.7/Si(100) and the incorporated P amount at initial position has been investigated. For higher Si 2H 6 partial pressure and for the initial P atom amount of P atomic layer below about 4 × 10 14 cm − 2 , the incorporated P atoms are almost confined within the 1 nm region around the heterostructure interface. The P amount is nearly the same as the initial one. For initial P atom amount higher than 4 × 10 14 cm − 2 , P segregation on surface is enhanced, and the incorporated P atom amount around the heterointerface tends to saturate to maximum value of about 4 × 10 14 cm − 2 . This maximum value decreases with decreasing Si 2H 6 partial pressure. These results suggest that the number of site at the heterointerface between Si cap layer and Si 0.3Ge 0.7 layer, in which P atoms are incorporated, is about 4 × 10 14 cm − 2 and in the case of low Si 2H 6 surface coverage, the incorporated P atom amount at the heterointerface decreases due to surface segregation.

Si epitaxial growth on self-limitedly B adsorbed Si 1 − xGe x(100) by ultraclean low-pressure CVD system

B atomic-layer doping in Si/Si 1 − x Ge x (100) ( x = 0.3, 1) heterostructure utilizing BCl 3 reaction on Si 1 − x Ge x (100) and subsequent Si epitaxial growth by SiH 4 reaction was investigated by ultraclean low-pressure chemical vapor deposition. On 1/3–1/2 atomic layer (2.3–3.5 × 10 14 cm − 2 ) B formed Si 1 − x Ge x (100) achieved self-limitedly with high Cl coverage, the adsorbed Cl atoms are effectively removed by SiH 4 exposure at 300 °C after BCl 3 exposure. Furthermore, it was found that the SiH 4 reaction at 300 °C on Ge(100) is enhanced by B adsorption.

Heavy atomic-layer doping of B in low-temperature Si epitaxial growth on Si(1 0 0) by ultraclean low-pressure chemical vapor deposition

Electrical characteristics of B atomic-layer doped Si epitaxial films on Si(1 0 0) formed by B atomic-layer formation on Si(1 0 0) at 180 °C and subsequent capping Si deposition at 500 °C using ultraclean low-pressure chemical vapor deposition were investigated. From evaluation results of carrier concentration in the films, by low-temperature SiH 4 exposure at 180–300 °C before the capping Si deposition at 500 °C, 70% improvement of B electrical activity was confirmed, and it is suggested that lowering the temperatures for B atomic-layer formation on Si(1 0 0) as well as SiH 4 exposure before the capping Si deposition is effective to suppress B clustering and to achieve B atomic-layer doped Si films with extremely high carrier concentration.

Atomic-Order Thermal Nitridation of Si1-xGex(100) at Low Temperatures by NH3

Atomic order thermal nitridation of Si1-xGex(100) (x=0, 0.4, 1) by NH3 gas environment at low temperature of 400ºC has been investigated using an ultraclean low-pressure chemical vapor deposition system. After NH3 exposure (NH3 partial pressure of 550 Pa for 30 min), it is found that Si(100), Si0.6Ge0.4(100) and Ge(100) are nitrided in atomic-order. In the case of Ar purging at cooling period after the nitridation, N atom amounts on Si(100) and Ge(100) are 8.0x1014 and 5.5x1014 cm-2, and the amount on Si0.6Ge0.4(100) is 12.5x1014cm-2. In the case of H2 purging at the cooling period, it is found that slight reduction of the N atom amount on Si(100) down to 5.6x1014 cm-2(70 %) is observed, although the N atom amount on Ge(100) is significantly reduced to 1.2x1014 cm-2 (22 %).

A Study on B Atomic Layer Formation for B-Doped Si1-xGex(100) Epitaxial Growth Using Ultraclean LPCVD System

B atomic layer formation on Si1-xGex(100) (x=0, 0.3, 1) using BCl3 gas has been investigated by ultraclean low-pressure chemical vapor deposition. At 450ºC, in the case using BCl3-He-H2 gas mixture, B amount tends to increase beyond one atomic layer (6.8x1014 cm-2) with increasing BCl3 exposure time on Si0.7Ge0.3(100) and Ge(100). On the other hand, in the case using BCl3-He-Ar mixture gas, 1/3-1/2 atomic layer (2.3x1014 cm-2) formation is achieved self-limitedly with high Cl coverage on the surface. The Cl atoms on the B adsorbed Si1-xGex(100) are effectively removed by H2 introduction at 450ºC after BCl3exposure. In this way, atomically-controlled B atomic layer formation on Si1-xGex/Si(100) was demonstrated by using the self-limited surface reaction of BCl3 at 450ºC.

Electrical properties of N atomic layer doped Si epitaxial films grown by ultraclean low-pressure chemical vapor deposition

Sheet carrier concentration and Hall mobility of the N atomic layer doped Si epitaxial films on Si(1 0 0) were obtained by Hall effect measurement. It is found that the N atoms act as a donor. Donor activation ratio tends to decrease with increasing N amount, and the typical ratio is about 0.4% at the N amount of 5×10 13 cm −2/layer. Sheet carrier concentration in the temperature region higher than 160 K drastically increases with increase of the measurement temperature. The ionization energy of the donor level is estimated about 150–180 meV and almost independent of the N amount. Measured Hall mobility is as high as that of the uniformly P-doped Si with the P concentration of 10 16–10 17 cm −3 in the measurement temperature range of 160–300 K.

Electrical properties of W delta doped Si epitaxial films grown on Si(1 0 0) by ultraclean low-pressure chemical vapor deposition

Electrical properties of W delta doped Si epitaxial films grown on Si(1 0 0) by ultraclean low-pressure chemical vapor deposition were investigated. In the temperature range of 290–130 K, it is found that the W atoms in Si act as donor, and the sheet carrier concentration is proportional to the W amount. Moreover, the ionization energy is estimated to be about 340 meV on the assumption without the acceptor compensation and is scarcely affected by change of the W amount. Therefore, it is suggested that formation of the donor level is independent of degradation of crystallinity. Slope of the temperature dependence of Hall mobility was much larger than that of the uniformly donor doped Si.

Formation of heavily P-doped Si epitaxial film on Si(1 0 0) by multiple atomic-layer doping technique

Phosphorus (P) incorporation process during Si epitaxial growth by SiH 4 reaction in ultraclean low-pressure chemical vapor deposition (CVD) and the electrical characteristics of the heavily P-doped epitaxial Si film on Si(1 0 0) have been investigated. Si layer growth on the P layer formed on Si(1 0 0) at 500 °C at SiH 4 partial pressure of 6 Pa is observed when the surface P amount becomes below 7×10 14 cm −2. It is also found that about 1.1×10 14 cm −2 P atoms segregate onto the Si surface and the other desorbs. On the other hand, by lowering the Si growth temperature to 450 °C and increase in the SiH 4 partial pressure to 220 Pa, P incorporation occurs and about 1.5×10 14 cm −2 P atoms are buried at the initial position without segregation. By using the multiple atomic-layer doping technique, very low-resistive heavily P-doped epitaxial Si film on Si(1 0 0) can be formed with effective suppression of the electrically inactive P formation.

Epitaxial growth of N delta doped Si films on Si(1 0 0) by alternately supplied NH 3 and SiH 4

Atomic-layer doping of N in Si epitaxial growth by alternately supplied NH 3 and SiH 4 was investigated using an ultra-clean low-pressure chemical vapor deposition (LPCVD). Atomic layer order nitrided Si(1 0 0) with N amount of 3×10 14 cm −2 are formed by NH 3 exposure at 500 Pa and 400 °C. By subsequent SiH 4 exposure at 25 Pa and 500 °C, Si is epitaxially grown on the nitrided Si(1 0 0) with N amount of 3×10 14 cm −2. High quality epitaxial growth of the multi-layer N-doped Si film composed of the N layers of 3×10 14 cm −2 and the 3.0 nm Si spacer is achieved. On the other hand, in case of 0.5 nm Si spacer, the crystallinity of N-doped Si film is degraded by the increase of N atoms with Si 3N 4 structure after the second nitridation.

Atomic-layer doping in Si by alternately supplied NH3 and SiH4

Low-temperature Si growth on the atomic-layer order nitrided Si(100) surface with N amount of 1–6×1014 cm−2 formed by NH3 reaction at 400 °C were investigated using an ultraclean low-pressure chemical vapor deposition system. The epitaxial growth of Si film on the nitrided Si(100) with the initial N amount as high as about 3×1014 cm−2 is realized at 500 °C, although the film becomes amorphous in the case at the initial surface N amount of 6×1014 cm−2. By the analysis of the x-ray photoelectron spectroscopy, it is observed that the surface structure of the atomic-layer order nitrided Si(100) is changed into Si3N4 structure by the increase of the surface N amount. It is suggested that the crystallinity of Si film deposited on the atomic-layer order nitrided Si(100) is degraded by the existence of Si3N4 structure. Depth profile of N atomic-layer doped Si film clearly shows that most of the N atoms are confined within about 1-nm-thick region.

W delta doping in Si(1 0 0) using ultraclean low-pressure CVD

W delta doping in Si epitaxial growth by WF6 and SiH4 reaction has been investigated using an ultraclean cold-wall low-pressure chemical vapor deposition (CVD) system. Atomic-layer order W deposition is performed on wet-cleaned Si(100) substrate at 100°C using WF6 and SiH4. Si epitaxial growth is achieved by SiH4 reaction at 480°C on 4×1013cm−2 W deposited Si(100), however, it is found that almost all the deposited W atoms segregate on the deposited Si film. It is also found that such segregation is suppressed by the atomic-order W diffusion into Si(100) substrate by the heat treatment at 520°C before the Si deposition. In the case of the Si film deposited on the 1.3×1014cm−2 W diffused Si, the reflection high-energy electron diffraction (RHEED) pattern indicates the crystallinity and the roughness degrade. In the case of the Si film deposited on the 5×1013cm−2 W diffused Si, the RHEED pattern shows streaks with Kikuchi lines. As a result, the W delta doping in the Si epitaxial growth is achieved, in which the W concentration is as high as 6×1020cm−3 and the incorporated W atoms is confined within 2nm-thick region.

Epitaxial growth of heavily P-doped Si films at 450 °C by alternately supplied PH3 and SiH4

Epitaxial growth of heavily P-doped Si films at 450°C by alternately supplied PH 3 and SiH 4 has been investigated using an ultraclean low-pressure chemical vapor deposition (CVD) system. By exposing the Si(100) surface to PH 3 at a partial pressure of 0.26Pa at 450-750°C, two or three atomic-layers of P are adsorbed. Thermal desorption of P occurs at 650°C and only slightly at 450°C. By alternately supplied PH 3 at 300-450°C and SiH 4 at 450°C, epitaxial growth of heavily P-doped Si films of average P concentrations of ∼10 21 cm -3 are achieved. In the case of 4 cycles of alternately supplied PH 3 and SiH 4 at 450°C, 26nm-thick P-doped epitaxial Si film, with the average P concentration of 6x10 20 cm -3 , is formed. It is found that about 60% of P is electrically active even in the heavily P-doped epitaxial Si film and the resistivity is as low as ∼3x10 -4 Ωcm. By annealing the film at 550°C and above, it is found that the carrier concentration decreases and the resistivity increases. It is suggested that very low-resistive epitaxial Si film is formed by alternately supplied PH 3 and SiH 4 only at a very low-temperature such as 450°C.

Atomic-order thermal nitridation of Si(100) and subsequent growth of Si

Atomic-order nitridation by NH3 on Si(100) and subsequent Si growth by SiH4 were investigated using an ultraclean low-pressure chemical vapor deposition system with a Xe flash lamp. In thermal nitridation on Si(100), it is found that nitridation occurs even at 260 °C with flash heating, and the N atom concentration tends to saturate to about 2.4×1015 cm−2. In Si deposition on the ultrathin Si nitride, it is found that N desorption from the Si nitride films hardly occurs, and Si grew on Si nitride at 385 °C in an SiH4 environment with and without the flash lamp light irradiation. An incubation period of Si growth is observed and increases with increasing N atom concentration of the Si nitride film. On Si with N atom concentration of about 2×1014 cm−2, the incubation period is hardly observed and the reflection high energy electron diffraction patterns indicates that Si epitaxially grew. Layer-by-layer growth control of Si nitride is proposed by combining atomic-order nitridation on Si and atomic-layer growth of Si on the Si nitride.

Doping and electrical characteristics of in-situ heavily B-doped Si 1− x− yGe xC y films epitaxially grown using ultraclean LPCVD

Doping and electrical characteristics of in-situ heavily B-doped Si 1− x− y Ge x C y (0.22< x<0.6, 0< y<0.02) films epitaxially grown on Si(100) were investigated. The epitaxial growth was carried out at 550°C in a SiH 4–GeH 4–CH 3SiH 3–B 2H 6–H 2 gas mixture using an ultraclean hot-wall low-pressure chemical vapor deposition (LPCVD) system. It was found that the deposition rate increased with increasing GeH 4 partial pressure, and only at high GeH 4 partial pressure did it decrease with increasing B 2H 6 as well as CH 3SiH 3 partial pressures. With the B 2H 6 addition, the Ge and C fractions scarcely changed and the B concentration ( C B) increased proportionally. The C fraction increased proportionally with increasing CH 3SiH 3 partial pressures. These results can be explained by the modified Langmuir-type adsorption and reaction scheme. In B-doped Si 1− x− y Ge x C y with y=0.0054 or below, the carrier concentration was nearly equal to C B up to approximately 2×10 20 cm −3 and was saturated at approximately 5×10 20 cm −3, regardless of the Ge fraction. The B-doped Si 1− x− y Ge x C y with high Ge and C fractions contained some electrically inactive B even at the lower C B region. Resistivity measurements show that the existence of C in the film enhances alloy scattering. The discrepancy between the observed lattice constant and the calculated value at the higher Ge and C fraction suggests that the B and C atoms exist at the interstitial site more preferentially.

Atomic-layer doping in Si by alternately supplied PH 3 and SiH 4

Atomic-layer doping of P in Si epitaxial growth by alternately supplied PH 3 and SiH 4 was investigated using ultraclean low-pressure chemical vapor deposition. Three atomic layers of P adsorbed on Si(100) are formed by PH 3 exposure at a partial pressure of 0.26 Pa at 450°C. By subsequent SiH 4 exposure at 220 Pa at 450°C, Si is epitaxially grown on the P-adsorbed surface. Furthermore, by 12-cycles of exposure to PH 3 at 300–450°C and SiH 4 at 450°C followed by 20-nm thick capping Si deposition, the multi-layer P-doped epitaxial Si films of average P concentrations of ∼10 21 cm −3 are formed. The resistivity of the film is as low as 2.4×10 −4 Ω cm. By annealing the sample at 550°C and above, it is found that the resistivity increases and the surface may become rough, which may be due to formation of SiP precipitates at 550°C and above. These results suggest that the epitaxial growth of very low-resistive Si is achieved only at a very low-temperature such as 450°C.

Atomic-layer adsorption of P on Si(100) and Ge(100) by PH 3 using an ultraclean low-pressure chemical vapor deposition

Atomic-layer adsorption of P on Si(100) and Ge(100) at 200–750°C by PH 3 was investigated using an ultraclean low-pressure chemical vapor deposition (CVD) system. At 300°C, the PH 3 adsorption was suppressed on the H-terminated Si surface, but PH 3 was adsorbed dissociatively on the H-free Si surface with saturation tendency to subatomic layer. At 450–750°C, the P atom concentration on the Si surface tended to saturate to about two or three atomic layers by exposing PH 3 with little influence of the carrier gas (H 2 or He). When the P-adsorbed Si was kept in Ar and in H 2 at 650°C after PH 3 exposure, the P atom concentration decreased to about one atomic layer by thermal desorption and also by reduction due to hydrogen. On the Ge surface, PH 3 adsorption was suppressed by H-termination at 200°C, P atom concentration saturated to the single atomic layer at 300–450°C. Furthermore, P desorption from the Ge surface at 450°C occurred much faster than that from the Si surface at 650°C, while P bonded to Ge was stable at 300°C.

Doping and electrical characteristics of in situ heavily B-doped Si 1− xGe x films epitaxially grown using ultraclean LPCVD

Doping and electrical characteristics of in situ heavily B-doped Si 1− x Ge x ( 0.15 < x < 0.80) films epitaxially grown on Si(110) were investigated. The epitaxial growth was carried out at 550 °C in a SiH 4-GeH 4-B 2H 6-H 2 gas mixture by using an ultraclean hot-wall low pressure chemical vapor deposition (LPCVD) system. With increasing B 2H 6 partial pressure, the deposition rate decreased only at the higher GeH 4 partial pressure, and the B concentration ( C B ) in the film increased proportionally up to 10 22 cm −3. The Ge fraction scarcely changed with the B 2H 6 addition. The carrier concentration was nearly equal to cb up to about 2 × 10 20 cm −3, and it tended to be saturated at around 5 × 10 20 cm −3 at C B < ~ 10 22 cm −3 . In other words, electrically inactive B increased with increasing C B above 2 × 10 20 cm −3. The resistivity decreased with increasing carrier concentration at c b <~ 10 22 cm −3 and was influenced by alloy scattering. Discrepancy of the lattice constants from Vegard's law was observed at higher cb in the order of 10 20 cm −3 and above, which corresponded with the saturation of the carrier concentration.