RU1114242C - Method of manufacturing powerful silicon &&& -p- &&& transistors - Google Patents

Abstract

METHOD FOR PRODUCING POWERFUL HIGH-FREQUENCY TRANSISTOR STRUCTURES, including local doping of the substrate to obtain a surface impurity concentration of the opposite conductivity type substrate of at least IlO CM, followed by the formation of an external base for the impurity from doped regions to the substrate, creating an active base and emitter, as well as contacts in the structure region characterized in that, in order to improve the electrical parameters of transistor structures and simplify the method, locally doped regions of the shape mite with a gap of 0.2-1.0 of the maximum thickness of the outer base, and the active base is created by distillation of impurities from the doped regions to their closure

Description

The invention relates to the production of semiconductor devices, in particular to the technology of manufacturing transistors, and can be used in the manufacture of high-power high-frequency transistors and bipolar

integrated circuits

I

A known method of manufacturing high-power high-frequency transistor structures, including local doping of the substrate to obtain a surface concentration of an impurity of the type opposite to the substrate (at least 1-1 °), followed by the formation of an external base by distillation of the impurity from the doped regions into the substrate.

The active base, as well as externally, is created by the combined acceleration of the impurity deep into the substrate from the doped regions.

cl

with

This is followed by the creation of an emitter and metallized contacts to the emitter and base regions of the transistor structure.

The disadvantage of this method is the uneven current distribution over the width of the emitter region and a rather high gain level. With increasing emitter current density of 100-300 A / cm2 due to increasing

of the transverse component of the base current in the active base region, the emitter current is pushed to the periphery of the emitter pn junction. As a result, the peripheral part of the emitter junction region is loaded at an insignificant distance from the metallurgical border of the pn junction

The remaining part of the emitter region remains passive and experiences little current load. This is explained by the fact that this method of manufacturing powerful RF transistor structures provides an active base region with an impurity gradient (maximum concentration at the bottom of the emitter region and minimum E} close to the collector pn junction) 5 directed deep into the substrate, in the transverse direction - perpendicular to the fractional distribution of the impurity uniformly and constantly (as well as resistivity) о However, with increasing density of the emitter and, accordingly, recombination base current in the direction from In the middle of the periphery of the emitter, the voltage drop increases in the transverse direction of the active base region with its maximum value near the lateral boundary of the emitter region c. This circumstance causes an uneven displacement of the emitter pn junction, the maximum at its periphery and the minimum at the center, which leads to uneven current distribution and deterioration of amplifying current properties h 21 e, power - Chick. In addition, to increase the gain in the transistor structure, the method does not provide and a different ratio of the dopant in the active and external (near the emitter pn junction) parts of the base region The closest technical solution is a method for manufacturing high-power high-frequency transistor structures, including local doping of the substrate to obtain a surface concentration of the impurity opposite to the substrate, such as conductivity at least 1-10 cm3 followed by the formation of an external base by distillation of the impurity from the doped regions into the substrate, the creation of an active base and emitters, as well as cycles to the fields of the structure to contact the emitter region is carried out through a window by doping the emitter diffusion and contact to the outer base is carried out through a separate window. Moreover, first, a base contact window is created in the masking layer, and then a region of the same conductivity type as the base region that connects to the active base region The base contact window is left open during the base and emitter diffusion, while the surface concentration of the impurity in the base the contact window after diffusion. is so high that upon subsequent doping with an emitter impurity it does not fall below the value necessary to connect the active and external bases. Separate formation of the active and external base regions makes it possible, in contrast to the analogue, to independently select the degree of doping of each of the regions to obtain a more uniform current distribution over the width of the emitter region and to improve the amplification properties. However, it is impossible to achieve acceptable equalization of the current distribution because the emitter current density is squeezed out the emitter current to the periphery of the emitter-base junction due to the flow of the transverse component of the base In this case, the ohmic voltage drop in the central portion of the active base region uniformly doped in the transverse direction uniformly transversely distributed along the emitter width leads to a deterioration in the amplification properties of the transistor: in current (h 21 e) and in power (), it reduces the collector current () and That is, In the method, although it is provided that the active base region is formed separately from the outer one, however, it is impossible to obtain an active region with a much lower degree of doping, since these two regions and they adjoin at the lateral diffusion fronts and are interdependent on one another in their degree of doping. In addition, the separate operation of forming an active base region by the impurity sheath is of some difficulty. Creating small diffusion layers to obtain a high level of gain also does not appear possible, since the gap span of diffusion fronts, obtained by photo-engraving the windows of the active and external base regions, cannot be brought to a controlled micron level The aim of the invention is to improve the electrical parameters of trans

zistor structures and simplification of the method

The goal is achieved in that in a method for manufacturing high-power high-frequency transistor structures, including local doping of the substrate to obtain a surface concentration of an impurity opposite to the substrate, such as conductivity of at least c, subsequent to the formation of an external base by distilling the impurity from the doped regions into the substrate, creating an active base and emitter, as well as contacts to structural regions, locally doped regions are formed with a gap of 0.2-1.0 of the maximum thickness of the external base, and the active base is created by distillation of impurities from doped regions to their closure

The sequence of technological operations is shown in Figs. 1-5, where: Figs. 1 show an n-type silicon semiconductor substrate with a high resistance epitaxial p-layer and a surface masking coating - a thin layer of silicon dioxide and a non-oxidizing masking layer of silicon nitride; FiGc2 shows a semiconductor substrate, a high-fat p-layer, a surface masking coating, which forms a protrusion between highly doped regions of the opposite type of conductivity, comprising 0.2-1.0 of the maximum thickness of the dispersed external base; Oig No. 3 shows a substrate, a high-resistance layer masking a hardening, dispersed external base regions with a masking dielectric coating, and an active base created by distilling impurities from the doped regions to their closure; phiGo1 - shows the substrate, high-resistance layer, external base, active base and emitter region; Fig. 5 shows a completed high-frequency transistor structure, including a high-doped p-conductivity semiconductor substrate, a high-resistance epitaxial p-layer, an external base p-region with a masking dielectric coating, an active base p-region, a highly balanced emitter n-region and metallized contacts to external base and emitter area m.

26

Accepted designations: creg, n ev. semiconductor substrate 1, epitaxial layer 2, silicon dioxide layer 3, silicon nitride layer, highly alloyed regions 5, masking dielectric coating 6, active base 7, emitter region 8, metallized contacts to base 9, metallized contacts to emitter 1.a. ,

An example oc illustrates a method

On a highly doped silicon pad of n-tmp conductivity doped with antimony to a specific resistance of 0.01 Ohms, with a high-resistance epitaxially expanded p-layer 2 doped with phosphorus to a specific resistance of t, 5 Ohm-cm, form

thermal oxidation of silicon, a layer of silicon dioxide SiO 3 with a thickness of 0.1 μm and a layer of silicon nitride 0.75 μm thick is deposited on it due to the reaction of dichlorosilane with ammonia

at T 710 ° C. Then, through a photoresist mask by plasma-chemical etching at the PlazmabOOT installation by local etching, a protrusion of the masking dielectric coating between the heavily doped regions of the local layer is left by local etching, after obtaining an impurity concentration surface opposite to the p-type substrate of at least

1-cm is ionized by boron ion doping at the Vesuvius P ion-beam accelerator unit with energy Qf, km-Kul

she - LE keV and a dose of 100 5

CM

as a result of ion implantation, an impurity surface concentration of 2 is obtained. Degree of surface doping with a lower limit of 1

X is due to the necessity of following the thermal distillation of the impurity to form an external and active base1, since a lower degree of doping does not provide

the necessary depth of thermal distillation of the impurity,

The distillation of impurities from the p-type aseco-chyrololamic regions is carried out thermally in an oxygen medium at 1200 ° C to a depth of 11 μm in the outer base region. During the distillation, a masking dielectric coating of silicon dioxide grows 6. When the gap width between heavily doped p-type regions is 2.2 microns, i.e. 0.2 of the maximum base thickness (11 microns), which ensures the closure of the lateral diffusion fronts of the outer base region. The method described in this example is suitable for transistors with a significant depth and thickness of the active base region. With a gap width of 11 microns equal to the maximum thickness of the outer base, the region of mutual overlap of the lateral diffusion fronts is set to the minimum acceptable level of 3 microns, which is advisable for higher frequency transistors, since reducing the overlap region accordingly reduces the depth of the active base region in the middle part. In this case, the degree of surface doping in the overlapping part should not be less than 5 X to exclude puncture by the volume charges of the emitter and collector junction of the base region. Otherwise, additional dimming through the emitter window of the active base region is performed. The masking dielectric coating of silicon nitride and a thin layer of silicon dioxide 3 is removed first by selective etching, and then on the basis of hydrofluoric acid HF, ammonium fluoride and water. It should be noted that the width of the emitter region may exceed the total width of the mutual overlapping of the diffusion layers, so as well as being less than it, depending on a certain level of output power, the private range of the transistor, and the resistance of the high-resistance collector layer with So, for higher voltage For transistors, it is advisable to have a wide emitter region wider than the width of the overlap region, and for low-voltage high-power B.Ch. transistors, the emitter width is the same level as the overlap region. Then, an emitter region 8 is formed through an open window by diffusion of phosphorus from phosphorus oxychloride POC. Phosphorus lifting in the first example is carried out at T to a depth of 6.5 microns, and in the second at T 960 ° C to 0.2 microns. This is followed by opening by engraving the contact windows to the outer base region 5 and emitter 8, respectively, applying a metallized coating of aluminum and again engraving the localization by etching the metallized base 9 and emitter 10 contacts. The main distinguishing feature of the active base region is that it gradually increases its width and depth from the middle to its peripheral part and further to the external base area. Accordingly, the degree of impurity doping with a maximum gradient dN directed not normal to the surface deep into the substrate, as in the analogue method and the prototype, but in the direction of acceleration of the lateral diffusion front of the outer base region, from which the active base region is formed, also increases. The gap between the locally doped regions is 0.2-1.0 of the maximum thickness of the outer base, as explained below. With a gap of less than 0.2 ml, the gradient dN „,: is the impurity in the active base, and the diffusion depths of the impurity in the active and external base are almost equal to each other. With a gap of more than 1.0, the concentration of the dopant in the active base will be less than 5-10, which will lead to a puncture of the base region with bulk charges of the emitter and collector junctions. Thus, when a transistor with high current densities (300 A / cm2) is operating, the displacement of the emitter current is reduced due to the redistributed ohmic base resistance for the transverse resistance of the base current in a monotonically expanding active base region. The main factor in aligning the current distribution across the width of the emitter region is the gradual decrease in the resistance of the active base region from the middle to the periphery. With a variable base thickness increasing towards the periphery, its cross section increases and the resistance of the base layer decreases, not only due to geometrical expansion, but also as a result of the gradient distribution of the impurity in the transverse direction. This contributes to a shift in the lines of the emitter current to the central part of the base. In addition, this method is simpler than the prototype method, since it excludes the operation of a doped corrugated impurity of the active base region, which is lower than for the external base, and is replaced by the combined operation of forming the external base region.

A lower degree of doping of the middle suit of the active base region increases the efficiency of the emitter and increases the amplifying properties of the transistor hj | g.

The use of this method for the manufacture of a transistor, similar

KT-805, as a result of alignment of the current distribution along the width of the emitter region, allows increasing the output power level by 20, increasing the safe operation area of the transistor, and improving the current-amplifying properties

-.

iX

7

FIG. g

figure 5