RU2472248C2 - High-voltage high-temperature quick-acting thyristor with field control - Google Patents

Abstract

FIELD: electricity.

SUBSTANCE: in a high-voltage high-temperature quick-acting thyristor with field control, comprising an anode area from a highly alloyed substrate of p⁺-type conductivity, a basic area from serial epitaxial layers of n^--type and high-resistance n⁺-type of conductivity, a gate area arranged from local interrelated areas of p⁺-type conductivity in a near-surface volume, also in grooves of the basis area, a cathode area made of local interrelated shallow areas of n⁺-type conductivity arranged between gate p⁺-areas, the thyristor structure is made based on gallium arsenide, at the same time between the anode and basic areas of the structure there are epitaxial layers of p⁺-p-p^--type with a sharp, smooth, sharp transition of differential concentration of acceptor and donor admixtures from at least 10¹⁹ cm^-3 to 10¹¹ cm^-3 and below, and the epitaxial i - area with differential concentration of acceptor and donor admixtures by not more than 10¹¹cm^-3.

EFFECT: invention makes it possible to increase efficiency of a thyristor with field control several times, to increase working temperature of a crystal 1,5-2 times, radiation resistance.

3 cl, 3 dwg

Description

The invention relates to the field of semiconductor devices, in particular, to the design of high-voltage high-temperature high-current high-speed field-controlled thyristors operating at high reverse voltages, high current densities, high operating temperature and high speed.

Field-controlled thyristors are used in converter technology with an increased switching frequency and high values of the reverse voltage rise rates.

Known designs of silicon thyristors with field shutdown, which are described in a number of information sources, they have high speed - several tens of kilohertz - switching frequency, high voltage rise rate dU / dt, low voltage drop in the open state.

Such constructive solutions are shown in works such as Field-Controlled Thyristor (ECT) - A New Electronic Component by D.T. Houston, S. Krishna, D. Piccone, R.J. Finke, Y.Sun - International Electronic Devices Meeting, Washington, D.C. 1975 (1); “Physics of thyristors” A. Blikher, Leningrad, Energoizdat, 1981, p.118 (2), but the closest prototype in terms of efficiency and design is the thyristor design in the scientific and technical report on scientific research (R&D) “Comparative analysis of static characteristics of insulated-gate bipolar transistors and field-controlled thyristors in the open state ”, performed by the Solid State Electronics Department of the Physicotechnical Institute named after A.F. Ioffe RAS, St. Petersburg under the contract No. 9/05 of 03/01/2005, p. 4 (3).

The given prototype (3) of a field-controlled thyristor has large limiting current densities of hundreds of amperes per square centimeter at a reverse breakdown voltage of 1200 V and a direct current-voltage characteristic that is almost similar to the current-voltage characteristic of forward biased silicon diodes with a typical cut-off of 0.75 ÷ 0.85 V ( 3).

The design of the known prototype consists of a p ⁺⁺ type single crystal silicon anode substrate, a highly doped acceptor impurity, for example, boron, an epitaxial thin buffer layer of the opposite type of n ^- type conductivity, doped with a donor impurity, such as phosphorus or antimony, a thin high resistance n ^- type epitaxial layer , lightly doped donor impurity, such as phosphorus, are locally formed in the surface layer of the n ^- region -epitaksialnoy or grooves in the surface of the epitaxy noy n ^- type region diffusion of high acceptor impurity (boron) p ⁺ -regions (gate) located on the structural and calculated distance from each other, but at least two or three Debye lengths silicon p ⁺ -n ^- junction, locally made thin heavily , for example, phosphorus, the n ⁺ layer of the cathode part of the structure located between the gate p ⁺ regions. A single external p ⁺ zone with dividing p or p ⁺ ring regions representing the construction of a planar pn junction or an etched mesa region with the corresponding protection of a planar or mesplanar pn junction is formed along the external perimeter of local p ⁺ bands. Metal non-rectifying contacts are made to the anode, cathode and gate parts. The disadvantage of this structure is the insufficiently high speed, low, ≤175 ° С, the operating temperature of the thyristor crystal structure, the strong dependence of the thyristor switching rate on the operating temperature in the active regions of the structure, a sharp increase in dynamic switching losses when adjusting the lifetime of minority carriers in the peripheral regions and central the basic field of radiation technologies, for example, doping (irradiation) with high-energy electron and proton fluxes, especially the latter, with given mean free path in the crystal lattice and the irradiation doses. At the same time, the direct voltage drop in the open state increases sharply, several times, which reduces the dynamic properties of the thyristor switch.

The purpose of the invention is a sharp, several-fold increase in the speed of field-controlled thyristor, a sharp increase in the working temperature of the crystal by 1.5 ÷ 2 times, a several-fold increase in radiation resistance, an increase in the resistance to dU / dt and dI / dt current growth rates and voltages in hard resonant switching mode.

The fundamentally set goal is achieved in that instead of a silicon crystal of the thyristor structure with field control, gallium arsenide (GaAs) structure or a combined heterostructure gallium arsenide-aluminum-gallium arsenide (GaAs-AlGaAs) are used.

A constructive solution to this problem is that, in contrast to the known solution [3] of a field-controlled thyristor structure containing a single crystal substrate of p ⁺ type conductivity 1 doped with an acceptor impurity with an atomic concentration of at least 10 ¹⁹ cm ^-3 , the buffer n-type epitaxial layer 2 with a significantly higher concentration of donor impurity than in the subsequent base high-resistance n ^- type epitaxial layer 3, lightly doped donor-type impurity, for example 10 ¹⁴ cm ^-3 , shallow areas of n ⁺ -type n conductivity 5, performed between local p ⁺ -regions 4, with a concentration of doping donor impurities of not less than 10 ¹⁸ cm ^-3 , the following is true:

1. On the p ⁺ -type substrate, a preliminary epitaxial layer is grown with a dominant acceptor-type impurity and consisting of three interconnected p ⁺ -p-p ^- type conductivity regions with sharp (three orders of magnitude), smooth (several times, but no more than one and a half orders of magnitude) and again a sharp (three to four orders of magnitude) stepwise decrease in the differential concentration of acceptor and donor impurities from the concentration level of acceptors and donors in the substrate (not less than 10 ¹⁹ cm ^-3 ) to the level of the differential concentration of acceptor and donor impurities more than 10 ¹¹ cm ^-3 and a thickness of at least 20 microns.

2. On the surface of the p ⁺ -p-p ^- type epitaxial layer, an additional preliminary i-layer is grown — region 7 with a difference concentration of acceptor and donor impurities of not more than 10 ¹¹ cm ^-3 with a thickness of 5 to 50 microns.

рассчитывается эффективность канала.The essence of the invention is illustrated in figure 1, which shows the p ⁺ -substrate 1, p ⁺ -p-p ^- epitaxial layer 6, epitaxial i-region 7, epitaxial buffer n-type layer 2, epitaxial n ^- type layer 3, local regions of the p ⁺ type of conductivity 4, local n ⁺ types of the region 5. The doping profiles in the structure of FIG. 1 along the axes of sections A and B are shown in FIGS. 2, 3. In the structure shown in FIG. 1, the maximum operating reverse voltages provided Embodiment of p ⁺ -n transition in the cathodic part of a thyristor structure field councils HAND formed by regions 3, 4, electrophysical parameters layers 7, 2, 3, the distance between the p ⁺ region 4, depth of n ⁺ -type region 5 and a number of other factors. With the correct selection of the depth of the pn junction of the p ⁺ gate, the distances between the p ⁺ gates, taking into account the Debye length

channel efficiency is calculated.

Region i or pin region allows you to adjust the concentration and the thickness of the buffer layer, and with an optimal ratio of dopant concentrations, lifetimes, diffusion length of minority carriers it can be equal in electrophysical properties to the n ^- high-resistance layer and be its component without a significant reduction in the maximum voltage blocking on a thyristor with field control (figure 2, 3 dashed line shows such a distribution of the concentration of impurities in zone 2).

As can be seen from Fig. 1, in the direct-on state at zero bias on the p ⁺ gate, such a structure is equivalent to the direct-on p ⁺ -p ⁺ -p-p ^- -nn ^- -n ⁺ GaAs diode in which the density of electron-hole pairs is equivalent to the distribution of such pairs in silicon p ⁺ -nn ^- -n ⁺ diodes.

The cutoff of the direct characteristic of GaAs diodes begins with 1.1 ÷ 1.12 V with a sharp increase in current with increasing forward bias at the pn junction. The slope (or current growth angle) of such a current-voltage characteristic is determined by the injection coefficient of holes of the forward biased pn junction, the thickness, ohmicity, τ _p and L _{p of the} barrier n-layer and the high-resistance layer of the base of the n ^- type conductivity and the sharp influence of the resistance of the cathode n ^- -n ⁺ a channel formed between the gate regions.

канала будет зависеть от расстояния между p⁺-затворами, которое диктуется электрическими параметрами цепей управления, т.е. напряжение отсечки прикатодного канала n⁺-n не должно превышать разумных значений, к примеру при каскодном управлении тиристора полевым транзистором с изолированным затвором данная величина не должна превышать 30 В. Исходя из этого, ширина n⁺-n канала будет равна нескольким длинам Дебая (ширина ОПЗ при собственном потенциале φ_T на p⁺-n^- переходе), но ни в коем случае не меньше

Cathode resistance

the channel will depend on the distance between the p ⁺ gates, which is dictated by the electrical parameters of the control circuits, i.e. the cutoff voltage of the near-cathode channel n ⁺ -n should not exceed reasonable values, for example, with cascode control of the thyristor by a field-effect transistor with an insulated gate, this value should not exceed 30 V. Based on this, the width of the n ⁺ -n channel will be several Debye lengths (width IPF at its own potential φ _T on p ⁺ -n ^- junction), but in any case not less than

To reduce the channel resistance, a second buffer n ^' zone 8 can be introduced, which is doped by 2–3 orders of magnitude and weaker than the n ⁺ region of the cathode 5, while the depth of the n ^' zone 8 is much less than the depth of the p ⁺ - n transition gate SIT thyristor.

The structure shown in Fig. 1 with a cascade-switched field effect transistor with a MOSFET gate and the correct selection of electric circuits in the gate part can make it possible to create a key equivalent to an IGBT silicon transistor key, but with almost the same chip area (current density through the SIT structure of the thyristor due to the efficiency of the modulation depth and n ^- base layer 3 ÷ 2 times higher than that of the IGBT transistor) to create fast keys with the frequency conversion is 5 ÷ 10 times higher than that of IGBT, without losing on pad NIJ voltage in the open state. Those. it is possible to create an effective competitor to a silicon MOSFET transistor (lower control capacity, 25 or more times less resistance in the open state, the same speed), while this structure is fundamentally different from the latter. This difference is that at a working temperature of about 100 ÷ 150 ° C, the switching frequency of the field-controlled GaAs thyristor remains almost unchanged, while the switching frequency of the MOSFET drops by 30 ÷ 50%, and at 175 ° C it is no longer key.

Frequency and dynamic properties when switching this structure are improved by irradiation:

- high-energy electrons with an energy of 1 ÷ 7 MeV and a flux density of 10 ¹⁵ ÷ 10 ¹² cm ^-2 ;

- high-energy protons with energies from 0.8 MeV to 3 MeV and a flux density of 10 ¹⁵ ÷ 10 ¹² cm ^-2 ,

- high-energy alpha particles with energies from 0.5 MeV to 2 MeV, with a flux density of 10 ¹⁰ to 10 ¹² cm ^-2 .

At the same time, it was found that upon irradiation with electrons up to 1 MeV and a density of up to 10 ¹⁵ ÷ 10 ¹² cm ^-2 in the high-resistance region small-lying trap centers were formed.

At higher energy fluxes, recombination centers were formed at a large depth (closer to the middle of the forbidden zone).

When irradiated with protons with energies of 5 MeV and alpha particles of 3 MeV with a flux density of 10 ¹² cm ^{-2, the} high-resistance GaAs n-region changed its properties, while the bulk resistance increased, and a semi-insulating layer formed on the surface of the GaAs n-region (region )

The creation of this near-surface semi-insulating layer made it possible to reduce the electric field strength on the surface of the pn junction. During high-energy irradiation with heavy particles - protons and alpha particles, nuclear reactions occur in the crystal lattice of gallium arsenide, resulting in the need for exposure of the samples for a long time to eliminate the induced radioactivity. The structures were annealed after irradiation at T = 250–350 ° C.

Studies of the processing of GaAs structures by high-energy electron, proton, and α-particle beams (doping with hydrogen and helium fluxes) showed a significant difference in the values of the direct voltage drop at the anode p-junction; if it increases several times in silicon, then in GaAs it increases by 1.15–1.5 times, i.e. with the correct selection of the technological parameters of radiation treatment using combined electron-proton fluxes or electrons - α-particles, it is possible to achieve exceptional dynamic properties of SIT. With the correct selection of the distribution profiles of the radiation-implanted hydrogen and helium atoms in the GaAs crystal thyristor lattice in the most critical distribution zones of minority carriers, such as the near-cathode (gate) region, the regions of n ^- -i and i-p ^- -p SIT thyristor GaAs structure.

Preliminary studies have shown that there are additional technological design solutions that strongly affect the dynamics of the thyristor key with field control, in particular, this is associated with the use of an n ⁺ n ⁺ type conductivity heterostructure based on AlGaAs instead of the n ⁺ -GaAs cathode region 5. Such a structure, due to the large band gap by 0.2–0.4 V than that of n ^- GaAs, will have an increased ability to inject electrons from the surface n or n ⁺ cathode zone into the n ^- channel connecting the cathode region with n ^- -base, with the injection of hotter and faster electrons from the heterojunction. The effective mass of electrons injected from heterojunctions ^is 1.2–1.3 times higher than that of electrons in the n ^- base of GaAs and, therefore, they are weaker scattered at the trap centers of the crystal lattice in the n ^- base, thereby contributing to more efficient and rapid creation of an electron-hole plasma in the n ^- base and deeper modulation of the conductivity of the base rectifier n ^- layer of the SIT thyristor.

When stitching the band diagrams of n (n ⁺ ) AlGaAs and n ^- GaAs, it is obvious that a potential barrier of 0.2–0.4 V appears in the conduction band at the boundary of the heterojunction, and the gap in the valence band is negligible - a few kT. This shows that in the adjacent zone of the heterojunction (i.e., in the channel) an increased concentration of electrons is formed, which are transferred from the n (n ⁺ ) AlGaAs zone with high energy to the GaAs n ^- zone with a lower energy zone; these electrons act as a modulator of a high-resistance channel of the cathode region. Another very necessary quality is introduced by the n (n ⁺ ) -type AlGaAs heterostructure; it consists in the fact that the direct voltage drop across the open thyristor decreases by the value of the potential barrier in the heterojunction region, i.e. by about 0.3 V, and this is very significant, i.e. leads to an improvement in the dynamic properties of SIT structures during switching.

The crystal structure is created as follows (specific example).

Using the LPE technology, zinc-doped GaAs p ⁺ type substrate (acceptor impurity concentration is about 3 · 10 ⁹ cm ^-3 ) with a diameter of 2 ÷ 3 inches are grown by epitaxial GaAs layers - p ⁺ -layer with a decrease in concentration by three orders of magnitude or more from the substrate with a thickness of the order of 7 ÷ 10 μm, then the p-layer with an average concentration of acceptor impurities up to 10 ¹¹ or less. Then a thick epitaxial zone is grown, the so-called i-region with a difference concentration of donor and acceptor impurities of not more than 10 ¹¹ cm ^-3 . A thin buffer epitaxial n-layer is grown on it, on the surface of which a thin n ⁺ layer with a concentration of not less than 10 ¹⁸ cm ^{-3 is formed} .

These epitaxial layers are doped with tellurium, tin, or others. By the method of implantation of zinc atoms and thermal diffusion into local areas on the surface of the epitaxial layer of the cathode, p ⁺ zones are created, as well as ring regions of a planar transition (or planar transition). In the case of an AlGaAs heterostructure growing on the surface of the n ^- layer, the donor concentration increases insignificantly or remains equal in volume. If necessary, the periphery is not planar p ⁺ -n ^- transition mesa region is created with a depth alignment to p ⁺ -zone anode is passivated and fotoimidom or other protective coatings to stabilize the high areas of the upper and lower p-n transition (gate-base and anode-base ) This is another advantage of this structure over silicon IGBTs, i.e. it is able to withstand reverse surges on the SIT thyristor, i.e. when turned on, for example, an inductive load in the anode circuit when the stored energy E = LI ^2/2 creates conditions for the reversed polarity at the anode.

Contacts to the anodic, cathodic, and gate regions of the structure are created on the basis of systems of the following atomic compounds: Si, Au, Ge, Ti, Ni, Ag, etc. with a thickness of hundreds of nanometers to several thousand.

The technical and economic advantage of these field-controlled thyristor structures is that they can completely displace functional analogs - electronic keys based on silicon IGBTs and MOSFETs and create conditions for the development of significantly more efficient converters in the current range up to 1.0 kA, voltages up to 1200 V and switching frequencies 0.3 ÷ 1.0 MHz.

Claims (3)

1. High-voltage field-controlled high-temperature high-speed thyristor, containing an anode region of a highly doped p ⁺ type conductivity substrate, a base region of consecutive n-type epitaxial layers and a high-resistance n ^- type conductivity, a gate region made of local interconnected p ⁺ - regions type of conductivity in the near-surface volume, including in the recesses (grooves) of the base region, the cathode region made of local interconnected n ⁺ -type conductivity of shallow areas located between the gate p ⁺ regions, characterized in that the thyristor structure is based on gallium arsenide, while between the anode and base regions structures are epitaxial layers p ⁺ -p-p ^- -type sharp, smooth, sharp concentration drop difference acceptor and donor impurities from not less than October ¹⁹ to 10 ¹¹ cm ^-3 or less and the epitaxial region with i-difference concen walkie acceptor and donor impurities are not more than 10 ¹¹ cm ^-3. 2. The high-voltage high-temperature fast-acting thyristor with field control according to claim 1, characterized in that the local cathode n ⁺ -regions are made in the form of local heterostructures of n- or n ⁺ -type conductivity based on aluminum, gallium and arsenic compounds. 3. High-voltage high-temperature field-effect thyristor according to claim 1, characterized in that the active regions of the structure are radiation-doped with high-energy electrons, protons, and alpha particles.

Images