ES2929674A1 - DIAMOND METAL-INSULATION-SEMICONDUCTOR FIELD-EFFECT TRANSISTOR (MISFET) FOR HIGH POWER WITH OPTO-ACTIVATED CHANNEL AND MANUFACTURING PROCEDURE THEREOF (Machine-translation by Google Translate, not legally binding) - Google Patents

Abstract

High power diamond metal-insulating-semiconductor field effect transistor (MISFET) with opto-activated channel and manufacturing method thereof. The invention comprises the design of the fabrication of a diamond MISFET with opto-activated gate for high power using an IR-LED light emitter and lateral/selective growth. The use of an opto-activated gate gives it a novel operation that, together with the use of standard vertical growth on the substrate and selective lateral growth for the source and drain contacts, gives the MISFET device a three-dimensional structure. This device prevents gate leakage due to oxide, avoids edge effects of metal contacts and high internal electric fields, improves the crystalline quality of the diamond and reduces the time, cost and size of the device, in turn providing it with greater versatility for its implementation on more complex architectures. (Machine-translation by Google Translate, not legally binding)

Description

DESCRIPTION

DIAMOND METAL-INSULATION-SEMICONDUCTOR FIELD-EFFECT TRANSISTOR (MISFET) FOR HIGH POWER WITH OPTO-ACTIVATED CHANNEL AND MANUFACTURING PROCEDURE THEREOF

TECHNIQUE SECTOR

Industrial sector: Power electronics and Microelectronics.

BACKGROUND OF THE INVENTION

The development of power electronics has been guided by semiconductor silicon power devices, favoring their continuous improvement with a large number of implications in the industry, especially in large-scale electric power transmission and distribution (T&D). At present, great advances have been made in the development of SiC devices, giving it its niche of application. However, the physical limits of both SiC and silicon are exceeded by the requirements of new power electronics. Therefore, the new generation of power devices must be developed in a new semiconductor material. In this sense, synthetic diamond clearly expands the limits of Silicon and SiC technology thanks to its spectacular electrical and thermal properties. Its resistance to dielectric breakdown is three times higher than that of SiC and more than thirty times better than that of Si. Furthermore, the mobility of carriers in diamond is very high for both electrons and holes and its thermal conductivity is unmatched, being 5 times higher than that of copper.

In the current context, Si semiconductor power switches used in 90% of the power application market are MOS gate drive devices (VDMOS, IGTB). Furthermore, thyristor-based structures are still widely used for high-frequency and high-voltage applications mainly due to the lack of equivalent MOS-controlled devices. This is something that SiC, with breakdown voltages below 10kV, and diamond or Ga ² O ³ , with breakdown voltages above 10kV, could solve.

The major advantage of MOS-controlled switches is the low impulse energy required to switch the circuit and the associated circuit simplification. In addition, devices controlled by MOS gates have no current flow when the gate is not biased (normally-off), thus avoiding short circuits in the electrical load in the event of a power failure.

Diamond is theoretically the ideal semiconductor for the fabrication of unipolar power semiconductors. However, the starting material is expensive and the size of the wafers is really small (2.25 cm2 maximum). In addition, the density of defects in the substrates is still high and highly variable from one sample to another, even coming from the same batch from a single supplier. The surface quality also varies greatly from one substrate to another and it is common for them to require extra polishing.

Intrinsic diamond is an insulating material, which requires doping to acquire semiconductor behavior. The two main elements for diamond doping are boron (p-type doping) and phosphorus (n-type doping). The incorporation of both dopants is not easy and, although in the case of boron the technique is more advanced, few laboratories manage to grow highly doped diamond of both types with good crystalline quality. The high incorporation of dopants generates a high density of dislocations [D. Araujo et al. Appl. Phys. Lett. 118, 052108 (2021)], while in the case of phosphorus it is very difficult to even achieve a high concentration. The main need for high dopant concentrations is the high activation energy of both elements (0.39 eV for boron and 0.57 eV for phosphorus), which causes very few ionized atoms at room temperature and, therefore, Therefore, the conductivity is very low. This supposes an important limitation for the achievement of devices with high current. Therefore, nowadays a diamond device can work at high voltages, but it is limited in current, which is essential to obtain a high power.

To these inherent drawbacks of the starting material, we must add the problems due to technological processing, more specifically those related to local doping and interface passivation.

The main challenge for MOS technology is to obtain a reliable performance and interface between the semiconductor and the dielectric. Silicon has a natural oxide (SiO ² ), which is of relatively good quality, giving silicon today's success in all electronic applications, including power electronics. SiC also has a natural oxide (SiO ² like Si) but the interface quality is worse than Si due to, among other problems, the presence of carbon atoms. Other semiconductor materials like germanium, III-V (GaAs) and GaN have very poor native oxides. But for diamond it is even worse, it has no native oxide.

That is why the scientific community works with oxides such as ZrO ² , Al ² O ³ or SiO ² . The former seem to offer the best results in terms of low leakage and allow better control of the required oxide gate thickness as a result of their high dielectric constant. However, all of them with a slightly higher bandwidth than diamond show gate leakage as a result of interface states with diamond and its relatively poor microstructure. In fact, while in Si technology the amorphous oxides that are needed make its bandwidth lower, this does not affect the behavior of the Si gate. For diamond, its bandwidth must not decrease too much since it must be a barrier for the carriers and, in addition, it must not "crystallize" when the MOSFET works at high temperatures. This scenario is very difficult to solve, so the diamond needs a completely different approach to be competitive in this field.In addition, the very deep level of dopants in diamond (0.36 eV and 0.57 eV for boron and phosphorus respectively) makes it difficult to activate carriers.It is just the opposite than with SiC: the device performs better at high temperature than at room temperature.This results in a very low drain current density and field effect mobility at room temperature (in the range of 2 mA/ mm and 8.0 cm2/Vs, respectively).

EXPLANATION OF THE INVENTION

The present invention corresponds to a completely new activation MISFET structure, based on the combination of standard processing with selective epilayer regrowth, and includes the novelty of using an optically activated gating channel. The use of IR (Infrared Light Emitting Diode) LEDs allows the same activation of the dopant at any temperature and allows reaching very high currents. In the case of diamond, and due to the high ionization energy of both p (Boron) and n (Phosphorus) dopants, very few dopants generate charge carriers (electrons or holes depending on the doping) and the material is very resistive at temperature. ambient. Therefore, a device could only work correctly if temperatures above 200°C are reached. This makes the behavior of the device highly dependent on temperature, performing poorly at room temperature (when the Si works fine) and improving at high temperatures (when the Si stops working). In order to allow a "uniform" operation with temperature and that the device works both at room temperature and at temperatures of 250°C-300°C, an optical activation of dopants is proposed as an invention that allows achieving a constant density of carriers with To make this possible, it is proposed to incorporate a gate of the MISFET of nodoped diamond and transparent to the IR radiation necessary for the activation of dopant in the boron-doped channel.This device of undoped layer and IR "illumination" (LED with a wavelength in the range of 1.3-1.5pm), which modulates its intensity, form the setting of the MISFET. By means of this new device, currents greater than 10 A can be achieved by MISFET with boron doping of only 1017 cm-3. The IR LED passes through the insulating undoped diamond without any absorption to activate the channel dopants and achieve high currents. The high thickness of undoped diamond allows for high voltage applications.

As a gate activator - LED emitter - a higher light energy is needed than that of boron activation (0.36 eV) but not too much so that the undoped diamond layer is transparent even if it has crystalline defects (<1 eV ). This makes any LED in the infrared (IR) range suitable and IR emitting LEDs between 1111nm and 2000nm in wavelength are proposed.

The structure, designed entirely in diamond, solves the problem of diamond doping through an alternative method that maximizes low doping ranges. The absence of acute angles avoids the generation of areas with intense electric fields inside the device and the lateral growth reduces the lithography steps. As high doping active zones are not necessary and thanks to manufacturing the ohmic contacts by lateral growth, the main sources of defect generation are avoided. Said structure also allows a long arbitrary field and, as anticipated, substantially reduces the number of photolithography processes. This new structure improves the efficiency of the device and reduces manufacturing times.

On the other hand, the use of CVD techniques for growth allows high crystalline quality with relatively low deposition times. The device has been designed to minimize clean room steps by achieving the three-dimensional structure with only one etching step. The quality of this engraving is also not critical to the operation of the device.

On a suitably polished (100)-oriented diamond substrate of electronic quality, a first layer of low boron-doped diamond, p-, ([B] <1017cm-3) is grown by CVD. On this, a second layer of undoped diamond is deposited.

After this first step, the last layer deposited, the non-doped one, is etched. Using ion etching techniques, table-like parallelepiped structures of the same depth as the width of the undoped layer are fabricated. That is, the bilayer is etched until the low-doped diamond layer is reached.

On these structures, a layer of diamond highly doped with boron, p+, (1017 cm-3 < [B] < 1023 cm-3) is selectively grown laterally.

An infrared light emitter is placed on the undoped diamond layer.

Finally, on the structure, the Ohmic contacts are manufactured, which are annealed to guarantee the formation of a carbide layer at the diamond/contact border.

The possibilities offered by the new design geometry presented in this invention make this design and manufacturing method of great interest in all industrial sectors that make use of power electronics, especially in the energy sector due to the interest that the diamond awakens for power converters and other devices that require working at high voltages and high currents without the need to cool the device more than what is expected in a classic packaging and in a very small chip.

The use of devices designed and manufactured as shown here will mean great energy savings and a great miniaturization of the dimensions.

By means of this design, the conductivity limitation of diamond is mainly solved and will thus allow reaching high powers (10kV, 10A) and also avoids the following underlying problems in current diamond-based power devices:

- Gate losses: Associated with the gate insulator and very common in diamond because it does not have a native oxide. It is solved by using undoped diamond as the gate of the transistor.

- Quality of the highly doped layer, activation of the dopants. It is solved by using layers with low doping and ensuring the activation of all of them by means of an IR emitter (opto-activation).

- Edge effects of metallic contacts: They are avoided by using smooth geometries without sharp angles.

- High internal electric fields: The geometry of the design reduces the curvature of the field lines favoring a homogeneous distribution of the electric field.

- Problems associated with etching near active areas of the device: The etching for source and drain does not influence the operation of the device as they are located on low-doped diamond. The possible generation of defects does not lead to short circuits in the device.

- Dislocations and “killer defects”: The reticular defects generated during the growth of the different layers are counteracted thanks to the lateral growth. In addition, as mentioned in the previous point, the possible generation of defects does not lead to short circuits in the device.

- Defects due to the growth of highly doped diamond: As there are only other diamond layers on top of the highly doped one, the possible generation of defects in these does not have electrical consequences.

Additionally, this design provides:

- Activation of charge carriers: By opto-activating the gate channel, all dopants are activated, improving the conductivity of the diamond and allowing high currents. - Improvements in crystalline quality: Lateral/selective growth and, above all, the absence of high-doping active regions, decreases the density of crystalline defects.

- Reduction of manufacturing times and costs. Lateral and selective growth makes it possible to reduce the etching steps and the time and financial costs associated with them.

- Reduction of the size of the device: the three-dimensional design allows a greater miniaturization of the system.

- Greater design versatility: The use of selective growth opens the design to its implementation on more complex architectures.

- Greater versatility in operation: being opto-activated, the possible applications of the final device increase.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1: Schematics the growth on a (100)-oriented diamond (1) substrate of electronic quality and suitably polished, of a layer (2) of low-doped diamond, p-, and a thicker layer (3) of undoped diamond.

Figure 2: Schematics the etching of the last layer (3) by ICP using aluminum for the mask. Table structures are thus manufactured.

Figure 3: Represents selective growth around layer (4) of highly p+-doped diamond.

Figure 4: Represents the deposition of the IR LED emitting material (5) on the channel (manufacturing of the optoactivated gate).

Figure 5: It incorporates the manufacture of the ohmic contacts (drain and source) and the LED-IR.

Figure 6: Operation diagram of the MISFET object of the invention.

PREFERRED EMBODIMENT OF THE INVENTION

A preferred embodiment of the object of the developed invention is described below.

On a (100)-oriented diamond substrate of electronic quality and suitably polished, a first layer of low boron-doped diamond p-, ([B]<1017cm-3) thicker than 50 nm is grown by MPCVD. Growth conditions will depend on the reactor you are working with, but should be standard for growth in this orientation. This growth is followed by the deposition of 5 ^m of undoped diamond. The criteria in the selection of the growth parameters of this layer is the same.

A lift-off photoliography process is carried out on the sample by which aluminum masks with rectangular geometry are drawn. By ICP engraving, the mesa structures are manufactured with a depth of 5 ^m.

On these structures, a layer of highly doped p+ diamond, (1017 cm-3 < [B] < 1023 cm-3) approximately 500 nm thick, is selectively grown. As previously referenced, lateral selective growth is achieved by using low methane concentrations in the MPCVD reactor.

Two alternative options are presented on the undoped diamond layer: (i) The integration of a commercial LED by means of gluing and physical support by "packaging"; (ii) depositing an IR LED light-emitting material, such as InGaAsN. The only real restriction is that its radiation energy is greater than 0.36 eV but the undoped diamond layer remains transparent to it.

On this structure the Ohmic contacts of the source and the drain are manufactured. The ohmic contacts consist of a first deposit of titanium 30nm thick due to the good adhesion of the titanium carbide layer that forms at the interface with the diamond. On this, 50 nm of platinum are deposited to avoid the diffusion through the contact of the 40 nm of gold that are deposited as the last layer. This gold guarantees good thermal stability (>600°C) and low contact resistivity. The sample is annealed for 30 minutes at 500°C to create the titanium carbide layer.

Claims (8)

1. High power diamond metal-insulating-semiconductor field effect transistor (MISFET), characterized by the fact that it incorporates an optically activated gate channel. 2. Metal-insulating-semiconductor field-effect transistor (MISFET) of diamond for high power, according to claim 1, characterized in that it incorporates a low-doped diamond gate, covered with a non-doped one and transparent to infrared radiation, which is optically active. 3. High power diamond metal-insulator-semiconductor field effect transistor (MISFET), according to claim 2, characterized in that the activation of the dopant is carried out by means of an infrared light emitter. 4. High power diamond metal-insulator-semiconductor field effect transistor (MISFET), according to claim 3, characterized in that the infrared light emitter has a radiation energy greater than 0.36 eV. 5. High power diamond metal-insulator-semiconductor field effect transistor (MISFET), according to previous claims, characterized in that it comprises: a) a substrate (100)-oriented diamond of electronic quality and suitably polished. b) a first layer of low boron-doped diamond, p-, ([B]<1017cm"3). c) a second layer of undoped diamond. d) a third layer of highly boron-doped diamond, p+, (1017 cm-3 < [B] < 1023 cm-3) grown laterally. e) An infrared light emitter on the undoped diamond layer. 6. Metal-insulating-semiconductor field-effect transistor (MISFET) of diamond for high power, according to claim 5, where the light emitter consists of a commercial led integrated on the undoped diamond layer by means of gluing and physical support by "packaging". ”. 7. High power diamond metal-insulator-semiconductor field-effect transistor (MISFET), according to claim 5, wherein the light emitter consists of a layer of infrared light-emitting material. 8. Process for manufacturing the metal-insulator-semiconductor field effect transistor (MISFET) of diamond for high power, according to previous claims, characterized in that it comprises the following stages carried out on (100)-oriented electronic quality diamond and conveniently polished: a) growth by CVD of a low boron-doped diamond layer, p-, ([B]<1017cm"3) thicker than 50 nm. b) growth of a larger undoped diamond layer or equal to 5 pm. c) carry out the etching of the last deposited layer, to generate table-like parallelepiped structures of the same depth as the width of the undoped layer. d) performing on these structures the lateral selective growth of a layer of diamond highly doped with boron, p+, (1017 cm-3 < [B] < 1023 cm-3) between 300 nm thick and one micron. e) depositing the infrared light emitter on the undoped diamond layer. f) manufacturing the ohmic contacts on the structure, which are annealed to guarantee the formation of a carbide layer at the diamond/contact border.