RU2408950C1 - Reactor for plasma treatment of semiconductor structures - Google Patents

Abstract

FIELD: physics. ^ SUBSTANCE: reactor for plasma treatment of semiconductor structures includes a magnetic system which creates a constant magnetic field whose field lines are directed on the axis of the reactor. Axial magnetic field created by the magnetic system prevents electrons coming out of the plasma to the wall of the reactor, thereby increasing ionisation efficiency and increasing plasma density with the same power consumed by the charge. In the simplest case, the magnetic system has a coil placed outside the reactor and powered by direct current. To increase efficiency of the magnetic field, the magnetic system can consist of two coils connected in the same direction. In that case, a magnetic trap forms in space over the electrode-substrate holder, which more efficiently holds electrons, thereby increasing degree of ionisation of the plasma. Homogeneity of etching a plate with diametre of 100 mm is not less than 97%. ^ EFFECT: reactor with transformer-bonded plasma with inductive discharge exciting system, which enables to increase plasma density and, as a result, increase rate of plasmachemical treatment. ^ 3 dwg

Description

The invention relates to microelectronics, in particular to reactors for high-density and high-frequency plasma processing of semiconductor structures.

When creating modern VLSI, one of the main problems that prevented a further reduction in the size of elements to 0.5-0.25 microns was identified, primarily due to the limitations of the existing plasma-chemical technology and equipment for reproducing such elements with acceptable characteristics. In relation to the element sizes indicated above, the required technological parameters can be obtained only with a simultaneous combination of such incompatible characteristics for traditional plasma-chemical reactors as high ion current density (1-10 mA / cm ² ) and low ion energy (20-50 eV). The overwhelming majority of existing plasma chemical reactors provide one or two orders of magnitude lower ion current density with a correspondingly higher, up to 1000 eV, ion energy.

Attempts to reduce ion energy by reducing the discharge power lead to a sharp decrease in the etching rate, as well as attempts to increase anisotropy by lowering the operating pressure.

It is generally recognized that the difficulty in working with RF sources at low pressure lies in the rapid drop in the ion current density with a decrease in pressure. This, in turn, causes a decrease in the etching rate and productivity. An increase in the power or bias voltage on the wafer leads to an increase in the etching rate, but this causes problems with high-energy ions due to increased defect formation in semiconductor structures. The advantage of working at low pressure is the high anisotropy, which allows reproducing submicron sizes, as well as the "purity" of the process, since at low pressure the etching reaction products are more volatile and easy to remove, minimizing the formation of polluting particles and precipitation. Thus, the plasma-chemical reactor for modern VLSI technology should provide a very high plasma density at very low pressure.

These reactors include reactors based on electron cyclotron resonance (ECR) [1]. There are great opportunities for improving plasma ECR processes. However, in industrial use, ECR reactors lose because of their high cost, since they can be three times more expensive than conventional plasma reactors. Therefore, the so-called ICP and TCP reactors with an induction discharge excitation system are now widely used [2].

Closest to the claimed is a reactor for plasma processing of semiconductor structures [3], containing a chamber with a gas supply and exhaust system, a substrate holder installed in the base of the chamber with the ability to supply bias potential to it, and a plasma generation system consisting of a spiral inductor and matching system for connecting a spiral inductor with an RF generator. A through hole is made in the upper part of the chamber, closed by a dielectric screen, above which a spiral inductor is placed, the matching system contains a transformer with a ferrite core, an inductance and a capacitance, the capacitance being connected in parallel with the spiral inductor, and a chain of additional inductances was used to supply the bias potential to the substrate holder and capacitance connected to the matching system.

In the known reactor, a rather high rate (0.4-0.5 μm / min) of etching of SiO _{2 is} achieved. But in some cases, for example, with deep etching of SiO ₂ and silicon to create sensitive elements of micromechanical systems, an even higher processing speed is required (of the order of 1 μm / min for SiO ₂ and several microns / min for silicon) while the etching process is highly uniform and ensuring the smoothness of the walls of the formed structures.

The technical result of the invention is to increase the plasma density and, as a consequence, increase the speed of plasma-chemical treatment.

The specified technical result is achieved in that in a reactor for plasma processing of semiconductor structures, comprising a chamber with a gas supply and exhaust system; an electrode-substrate holder installed in the base of the chamber with the possibility of supplying a bias potential to it; a plasma generation system consisting of a spiral inductor and a matching system for connecting the spiral inductor to the RF generator, a magnetic system is introduced that creates a constant magnetic field, the lines of force of which are directed along the axis of the reactor. The axial magnetic field created by the magnetic system limits the escape of electrons from the plasma to the walls of the reactor, thereby increasing the ionization efficiency and increasing the plasma density at a constant power consumed by the discharge.

The principle of implementation of the claimed reactor is schematically depicted in figure 1, where 1 is the reactor lid with a through hole; 2 - dielectric quartz screen; 3 - gas distribution ring; 4 - spiral inductor; 5 - electrode-substrate holder; 6 - magnetic system.

Figure 2 shows a typical dependence of the ion current density on the current of the coils of the magnetic system. As can be seen from the drawing, the dependence of the current density on the magnetic field created by the magnetic system has a maximum. The magnitude of the optimal magnetic field increases with increasing RF discharge power.

It is obvious that the claimed reactor is characterized in that for each value of the RF discharge power, the optimal value of the magnetic field created by the magnetic system is set, which provides the maximum plasma density, in accordance with the curve shown in Fig.3. This provides the required etching rate (of the order of 1 μm / min for SiO ₂ and 2-4 μm / min for silicon) with high (97%) etching uniformity.

The reactor has a cover with a through hole 1 in the upper part of the camera body. The dielectric quartz screen 2 is located in the window and cuts off the internal volume of the working chamber, but at the same time allows the magnetic field that is created by the spiral inductor 4 to penetrate through it into the plasma excitation zone. A spiral inductor is placed within and near the dielectric shield. To improve the heat removal from the processed substrate, water cooling of the electrode-substrate holder and the supply of gaseous helium into the gap between the electrode-substrate holder and the substrate are provided. The working gas mixture is fed into the internal volume of the reactor through an opening in the side wall. To increase the uniformity of gas distribution in the internal volume of the reactor, a dividing ring 3 is used, which is located near the electrode-substrate holder. This allows the reaction gas entering the working volume to be evenly distributed in the region of the electrode-holder. Vacuum pumping out of the internal volume of the working chamber is carried out from the side opening of the reactor using mechanical and turbomolecular pumps, providing an operating pressure of P = 1-5 Pa. A plasma discharge excited by the inductor 4 fills the volume between the dielectric quartz screen 2 and the electrode-substrate holder 5.

The magnetic system in the simplest case contains a coil located outside the reactor, which is powered by direct current (see figa). To increase the efficiency of the magnetic field, the magnetic system can consist of two coils located outside the reactor and included in one direction (see figb). In this case, a magnetic trap is formed in the space above the electrode-substrate holder, which more effectively holds the electrons, which leads to an increase in the degree of plasma ionization. The variant of the magnetic system shown in Fig. 1c allows one to obtain the optimal value of the magnetic field with a lower value of the current of the coils, due to the fact that the lower coil is as close as possible to the plasma zone.

The use of a magnetic system made it possible to increase the ion current density from 12 mA / cm ² to 25 mA / cm ² with an RF discharge power of W = 750 W, a bias voltage of U _cm = -50 V, and an argon plasma pressure of P = 3 Pa with increasing magnetic current coils from 0 to 3.8 A (which corresponds to a magnetic field of about 2300 A / m). In the inventive reactor, when etching SiO ₂ in a fluorine-containing plasma, etching rates V _tr are obtained _. = 1.0 μm / min with an RF power of W = 1000 W, an operating pressure of P = 3 Pa and a bias voltage of U _cm = -50 V. A uniform etching was achieved on a plate with a diameter of 100 mm no worse than 97%.

Information sources

1. H. Kimura et al. Highly selective contact hole etching using ECR plasma. Jpn.J.Appl.Phys. Vol. 34 (1995), p. 214-2118.

2. US 4,948,458 A, H01L 21/306, 1990.

3. RF patent №2133998 - prototype.

Claims (1)

A reactor for plasma processing of semiconductor structures, comprising a chamber with a gas supply and exhaust system, a substrate holder installed at the base of the chamber with the possibility of supplying a bias potential to it, and a plasma generation system consisting of a spiral inductor and a matching system for connecting the spiral inductor to the RF generator , in the upper part of the chamber there is a window closed by a dielectric screen, over which a spiral inductor is placed, the matching system contains a transformer with a ferrite heart com, inductance and capacitance, characterized in that the reactor contains a magnetic system that creates a constant magnetic field, the lines of force of which are directed along the axis of the reactor, and made in the form of one or two coils located outside the reactor, or two coils, one of which is located outside reactor, and the second inside the substrate-holder electrode.

Images