Device to generate excited/ionized particles in a plasma

Details Device to generate excited/ionized particles in a plasma Device to generate excited/ionized particles in a plasma

2000-07-21

2004-03-16

Hassanzadeh, Parviz (Department: 1763)

Adhesive bonding and miscellaneous chemical manufacture

Differential fluid etching apparatus

With microwave gas energizing means

C156S345420, C118S7230ME, C118S7230MR, C118S7230ER, C315S111210

Reexamination Certificate

active

06706141

ABSTRACT:

The present invention pertains to a device to generate excited or ionized particles in a plasma.
Integrated circuits, in particular memory components or microprocessors, are produced in a number of process steps. The manufacturing costs for these circuits are governed by the process complexity and the physical processing time. Highly complex components frequently require several hundred individual process steps and a number of days for the product to pass through the process.
A portion of the process steps is dedicated to the specific application and the specific removal of material to or from the semiconductor surface. The etching or deposition techniques used for this, in addition to the lithography and the doping methods, are fundamental processes that are used repeatedly in the set of process steps to manufacture the highly integrated circuits (in general, see “Technologie hochintegrierter Schaltungen,” [Technology of highly integrated circuits], D. Widmann, H. Mader, H. Friedrich, Springer Pub., 1988, in particular, sections 3.1.1 and 5.2.2-4).
An important method for deposition of material onto the surface of a semiconductor is the chemical gas-phase deposition method, also called the CVD-method (chemical vapor deposition). In this method, selected process gases are fed over the heated semiconductor substrates onto which the desired layer is to be deposited. The result is a reaction of the process gas on the hot substrate surface, so that as reaction product, first the desired layer is produced, and second, other reaction gases are generated which are vented from the reactor. Now for a number of reasons it may be undesirable to heat the semiconductor substrate up to the high temperature required for the completion of the chemical reaction. Therefore, today it is often standard practice to implement an excitation of the initial reaction gases to create dissociated, highly reactive components and to initiate the deposition reaction not primarily by an increase in the temperature of the semiconductor substrate, but rather by a plasma or by high-energy radiation.
To produce an integrated circuit, however, it is not sufficient to apply material coatings only on one semiconductor substrate. To generate the desired structures, parts of these layers must be specifically removed again. In this case, a number of methods can be employed, and dry chemical etching and dry chemical-physical etching are the most frequently used methods. Now in dry chemical etching a chemical reaction takes place between the particles of a gas and the atoms of the surface to be etched. In chemical-physical dry etching, the chemical reaction occurs between the particles of a gas and the atoms of the surface to be etched, by means of an additional exposure of the etch surface to ions, electrons or photons. And again, for a number of reasons it may be undesirable to heat the semiconductor substrate to the high temperature needed for the completion of the chemical reaction. Therefore, in dry chemical or dry chemical-physical etching it is standard practice to cause an excitation of the reaction gases into dissociated, highly reactive components and to initiate the etching reaction by a plasma.
For successful implementation of this kind of etching and deposition process it is important to generate high-energy and therefore highly reactive, neutral particles, in particular, radicals, with a sufficiently high efficiency. The technical solution to this problem is being increasingly linked with the simultaneous need to satisfy the additional requirements for prevention of the influence of electric fields and charged particles on the process substrate, and for the broadest possible operating pressure range for the etching and deposition processes.
Usually high-frequency discharges are used to generate highly reactive, neutral particles. A system of this kind is shown, for example, in
FIG. 4
, which is described in the sales brochure “Model CDE-VIII Microwave Downstream Etching System,” Specification #840008, Apr. 1, 1986 Revision 2, by TYLAN/TOKUDA, USA. This document presents schematically a known, commercial downstream etching system with microwave excitation.
FIG. 4
presents a microwave generator
1
which produces microwaves which are injected into a hollow waveguide system
2
. By means of a tuning unit
4
and due to the dimensioning of the hollow waveguide system
2
, a standing wave will form through which the microwave energy is concentrated at defined sites of the hollow waveguide system
2
. The non-tuned, reflected and non-converted energy must be absorbed somewhere in the hollow waveguide system
2
, for example, in the T-piece
3
or at the end of the hollow waveguide
2
, which usually takes place by means of a water load. To generate radicals by means of microwave energy, a plasma discharge tube
5
—which is aligned in the direction of the electric field of the standing wave—is passed through the hollow waveguide system
2
. If suitable process gases are sent to the input
6
of the plasma discharge tube
5
and the plasma is ignited, then stimulated, neutral particles are produced, plus other particles. These neutral particles are then transported by means of a supply line
7
, which is about 1 m long, to the etching reaction/reaction chamber
8
.
Thus, excited, neutral particles move to the surface of substrate wafers
10
attached to a rotary table, where they trigger the desired etching reactions. The reaction chamber
8
is evacuated by a pump
9
and the volatile reaction products are vacuumed off.
For a smooth operation of the device, the plasma discharge tube must be manufactured from a material that hardly absorbs microwaves and which is resistant to the chemically aggressive radicals generated in the plasma. In this regard, as a rule, metal oxides or quartz is used. However, these materials are severely attacked by reducing gases, such as hydrogen, in the plasma zone, so that conducting islands can be created in the surfaces of these materials, which, in turn, leads to an increased absorption of the microwave energy.
The problem with this kind of downstream etching system is the tuning of the standing wave. The standing wave must be tuned so that exactly one voltage maximum will be available to the plasma discharge. Even minor faults in tuning will result in significant changes in the process parameters, which in turn can result in an overload of the microwave generator. This overloading of the microwave generator can be prevented, of course, with complicated and high-cost means. However, these activities reduce the efficiency and in addition, result in a definite increase in the size of the entire device. Due to the size of the device, these systems are very difficult to integrate into semiconductor production facilities. If it is necessary to replace worn parts, such as the microwave generator or plasma discharge tube, then the entire device has to be retuned.
In spite of an accurate tuning, however, a significant portion of the energy is not converted into stimulating energy, but rather is reflected and has to be absorbed in the hollow waveguide, usually in a water load, in order not to damage the microwave generator, for example, a magnetron. This partial conversion of the available microwave energy proves to be troublesome, in particular in light of the requirement already mentioned above for a broad operating pressure range, since precisely the low pressure range below about 13, especially below 1.3 Pa, is of interest to and is an advantage for semiconductor engineering. Low pressures, for example, are important to surface-controlled CVD processes to avoid depositions with undesirable layering properties. Also, in etching processes, a high etching rate and the prevention of microload effects—that is a local etching rate dependent on the environment—can often only be obtained at very low pressures. However, ignition difficulties occur in the plasma discharge even in the pressure range below 13 Pa, since the excitation density and thus also the efficiency of generati

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