KR20040094794A - Use of light emitting chemical reactions for control of semiconductor production processes - Google Patents

Abstract

The low pressure processing vessel 3 used to manufacture the semiconductor is equipped with a light-sensing detector 1, for example in the exhaust line 2, at a distance from the reaction point. The detector 1 is used to detect light emitted by an intermediate product that mitigates or recombines the emitted light at a particular wavelength, and the intermediate is long enough to allow the detector 1 to be located at a relatively distant location. Have a lifetime.

Description

USE OF LIGHT EMITTING CHEMICAL REACTIONS FOR CONTROL OF SEMICONDUCTOR PRODUCTION PROCESSES

There are various ways of detecting the endpoint according to the optical technology. These methods suffer from complex optical phenomena that occur in the process chamber as the manufacturing or cleaning process proceeds.

TECHNICAL FIELD The present invention relates to control of processes used in semiconductor manufacturing, and in particular, but not limited to, endpoint determination of semiconductor etching processes, or endpoint determination of deposition equipment cleaning processes.

1 is a schematic cross-sectional view of a chemical process system used in one embodiment of the present invention;

2 is a detailed view of a portion of the device of FIG. 1;

3 is a graph showing an example of an output signal; And

4 shows a second embodiment similar to FIG. 1;

It is an object of the present invention to provide a method and apparatus that can be used for improved form of process control.

The present invention takes advantage of the fact that many chemical reactions, especially those involving free radicals and ions formed in the plasma, are processed in a number of steps in a stable state or through a series of intermediates before the compound is prepared. . This intermediate step may have a lifetime of several nanoseconds to several milliseconds. The transition from one stage to another involves light emission. If the chemical reactions are studied, studied and understood to recognize that long-lived intermediate steps relax or recombine light emission at specific wavelengths, detectors operating at these wavelengths may be located near the outside of the direct reaction point. Placed in position, its output can be used to monitor the concentration of species as a surrogate for the material etch rate and, consequently, the cleaning process of the vacuum processing system or the manufacturing process, optionally using dry etching.

Accordingly, the present invention provides a method of controlling a chemical process occurring in a low pressure enclosure, the process forming species that emit photons of known wavelengths or wavelength distributions by specific chemical recombination or debonding processes. Wherein the species has a lifetime characteristic that can be detected at a "significant distance" from the primary reaction site at the pressure of the enclosure, and the method detects photons at that distance while rejecting another photon. And using the rate at which the photons are detected to control the process.

The term " significant distance " as used herein refers to a significant distance relative to the size of the region where the first order reaction occurs within, and is typically at least 5 cm, preferably 0.5 m. It has more than size.

The method can be used in particular to control silicon processing using fluorine radicals, wherein the chemical mitigation process includes the combination of silicon difluoride radicals and fluorine radicals, which are subsequently grounded with emission light between 380 and 650 nm. Calculate the electrically excited silicon trifluoride radicals that are returned.

Silicon processes typically include dry etching of silicon / silicon dioxide, or cleaning of silicon deposited on the enclosure walls during other processing. “Silicone” should be understood to include silicon dioxide or other silicon based deposits. The cleaning process involves plasma enhanced chemical vapor etching, typically a plasma is formed in the enclosure. The radicals are preferably formed upstream of the enclosure.

Preferably photon detection can be performed in an exhaust line from the enclosure or in a vacuum pump connected to the exhaust line.

In another aspect, the present invention relates to a low pressure enclosure that acts as a reaction chamber to generate a chemical process that forms species that emit photons at known wavelengths or wavelength distributions by specific chemical recombination or debonding processes. Device having a lifespan characteristic that can be detected at a distance from the first reaction point at the pressure of the enclosure, the device having a photon detector arranged at a distance from the first reaction point, and Means for monitoring the photon detection rate.

According to the present invention there is also provided a chemical processing apparatus comprising a low pressure chamber and an exhaust line extending from the chamber to a vacuum pump; The chamber forms a location that is used to generate a chemical process that forms a species that emits photons of a known wavelength or wavelength distribution by a specific chemical recombination or debonding process, wherein the species reacts first at the pressure of the enclosure. Has a lifespan characteristic that can be detected at a distance from the point of; The apparatus further includes a photon detector disposed at a distance from the position, and means for monitoring the photon detection speed.

The photon detector is preferably mounted on the exhaust line of the enclosure, or on a vacuum pump connected to the exhaust line.

Preferably, the photon detector has a light baffle for canceling off-axis light and / or a light trap that prevents entry into the detector.

Embodiments of the present invention are disclosed with reference to the drawings, which are only examples.

Before looking at the drawings, the physical principles underlying the embodiments are explained in detail.

Many chemical reactions are processed via a number of intermediates. For example, the reaction of the following substance (M) with free radicals (R) is considered.

In reaction a) the material is removed from the solid surface into the gas phase by bonding with one or more individual radical species. In reaction b), stepwise coupling yields an electrically activated intermediate that decays to ground with the emitting photons. Stepwise addition provides the final stability product pumped from the system.

In general, in the absence of a quenching agent, the light generated in step c) is proportional to the concentration of the electrically excited intermediates and used as an indicator to treat the material (M) removal (etching) reaction. Can be.

In this particular situation, reaction b) is the rate limiting the entire cascade reaction, and the intermediate is light that is generated in step c) which requires a very fast process if b) is sufficiently stable as the dominant reaction. It is a quantitative surrogate for the rate of removal. Reaction b) is a rate that does not limit the presence of light generation that can be used as an endpoint indicator for material (M) removal.

If process pressure and radical (R) concentration are desired, the light emitted in connection with the etching process is located far from the surface of the material (M) and can extend several meters into the surrounding space.

If the normal operating pressure in the vacuum processing system is in the low mtorr range during device fabrication by cleaning, protective maintenance phase, or optionally dry etching, the average free path of the intermediate product is the geometry of a typical process equipment. High compared to the structure. In addition, the concentration of the reactants at this pressure is low, so that the half-life of the intermediate (MR _n ) is enhanced so that the emitted light from step c) is selectively etched from the surface of the vacuum processing system for the cleaning process itself, or optionally Occurs one meter away from the material produced during the process. The distance is simply inferred from the half-life of the species MR _n and its diffusion rate.

Since the monitoring of the emitted light is done away from the reaction zone, the monitoring can be performed without interference or destruction of the reaction itself. For example, the measuring means can be suitably positioned on the exhaust line from the processing vessel without bias in the technical overview.

Without bias in the technical overview, useful exemplary reactions of the type described above typically include, but are not limited to, silicon etching by fluorine radicals generated by plasma decomposition of compounds including fluorinated hydrocarbons, sulfur hexafluorides and nitrogen trifluorides. It is not limited.

In a typical silicon etching process, the base pressure ranges from 1 to 100 m torr, and the silicon difluoride radicals formed by reaction 4) have a lifetime of a few milliseconds, and the immediate relaxation of the excited state and the commutation of photons It can be diffused a considerable distance before conversion to the trifluoride radical, which is a com- mate production.

The emitted light is in the quasi-continuum range of 380-650 nm. Given the typical process chamber geometry, a significant amount of the light is emitted from the exhaust line.

A first embodiment of the present invention will be described with reference to FIGS.

1 shows a typical vacuum process vessel 3 having a diameter on the order of 1 meter. The process vessel 3 is maintained at low pressure by the vacuum pump 11 via the exhaust line 2.

In a typical vacuum process technique, the basic function of the vessel is not limited, but by depositing polysilicon by injecting a compound, such as an organo-silicon compound, into the vessel, the compound decomposes on the heated substrate surface 5. A side effect of this process is that silicon is deposited on the walls of the process vessel 3. It should be appreciated that "silicone" includes silicon dioxide or other silicon based deposits. This silicone is a disadvantage in the basic function of the container as it contributes to particulates and consequent device defects. A typical cleaning technique is to inject nitrogen trifluoride into the upstream plasma region 4 which decomposes to yield free fluorine radicals. The fluorine radicals react with the silicon deposited on the walls of the vessel to carry out the reaction sequence outlined above for the silicon. The pressure in the reaction vessel during the cleaning process is 1 to 100 mtorr.

In order to maximize the efficiency of the cleaning process, it is desirable to monitor the etch rate of the silicon contaminants to stop the cleaning process once the etch rate drops below a predetermined level.

In FIG. 1, the detector 1 is connected to the exhaust line 2 of the process vessel 3. FIG. 2 shows in detail a suitable form of a detector consisting of a light-baffle 7 in front of the wavelength identification filter 8 and the photomultiplier tube 9. Facing the detector 1 the light-trap 6 is arranged. In this embodiment, the light-baffle 7 consists of a plurality of opaque parallel plates which are arranged in front of the filter 8 and each of which has a plurality of openings, which are reflected from the reaction zone along the exhaust line 2. Has a pattern and spatial arrangement with the ability to reject. The light-trap 6 comprises an open-ended cylinder whose wall has a projection baffle, and all the inner surfaces are matt black for maximum light absorption.

In a particular embodiment, the photo-baffle 7 consists of a series of opaque plates with openings in the plates arranged in sequence, so that only on-axis light can reach the photon detector.

The openings in the plate are arranged in such a way that the pattern distribution in the planar direction of each plate is arranged in an irregular manner so as to prevent the situation where off-axis light passes through one opening in the first plate at a certain angle, so that the light of the next plate Multiple rules permitting passage through one off-axis rather than the associated line-of-sight openings are allowed, with the same multiple rules allowing light to pass through another aiming line opening in a sequential plate. The size of the openings is arranged to increase from one plate to another, such that the smallest opening is in the plate adjacent to the photon detector and the largest opening is in the plate adjacent to it by the observer located at the photon detector. It is within the furthest plate due to the increase in size arranged so that only the opening edges can be seen and no edges of the openings in the plate not adjacent to it.

The combination of the light-baffle 7 and the opposing light-trap 6 has the effect of detecting only the light emitted within the tightly defined detection area.

3 shows a typical output from a photomultiplier in graphical form that can be used to detect the rate of removal of silicon contaminants. With reference to historical wash cycle data, digital signal processing techniques such as, but not limited to, curve shape identification and perturbation analysis can be used to yield endpoint detection that can be used to automate the wash cycle.

4, a second embodiment is used to control silicon etching.

4 shows a typical vacuum process vessel 3 having a diameter on the order of 1 meter. Typical process techniques etch silicon by injecting a fluorine source, such as sulfur hexafluoride, into the vessel as a gas. The pressure range in the reaction vessel is 1 to 100 mtorr, and an electric field is applied to the two electrodes 13 so that a plasma is formed between the two electrodes 13. The etched silicon substrate 14 is located at an electrode connected to ground and the fluorine radicals formed by decomposition of the sulfur hexafluoride reagent react with the silicon according to the reaction sequence described above.

In this embodiment, it should be noted that the silicon dioxide layer is present in the silicon wafer 14, which is preferably etched down to the buried layer and the etching is stopped in an appropriate manner. When the silicon etch reaches the silicon dioxide layer, the etch rate is reduced and in this case a decrease in the concentration of the silicon reaction intermediate is detected.

In FIG. 4, the detector 1 is connected to the exhaust line 2 of the process chamber 3 as in FIG. 1. The detector 1 is preferably the same as that shown in FIG. 2, and the output from the detector is of the same form as that shown in FIG. 3.

Modifications of the above embodiments may be made within the scope of the invention in accordance with the appended claims. The detector may be located within the process vessel itself at an appropriate distance from the reaction point or may be integrated with a vacuum pump; However, the positioning of the detector in communication with the exhaust line is considered to be the best arrangement. The present invention can be used in processes other than silicon / fluorine where suitable light-emitting intermediate steps are present.

Claims (18)

A method of controlling a chemical process occurring in a low pressure enclosure, The process forms species that emit photons of known wavelengths or wavelength distributions by specific chemical recombination or relaxation processes, which species can be detected at a distance from the first reaction point, at the pressure of the enclosure. Having a lifetime characteristic, wherein the method includes detecting the photon at the distance while rejecting another photon, and using the detected photon velocity to control the process. The method of claim 1, wherein the distance is at least 5 cm. 3. The method of claim 2, wherein said far distance is at least 0.5 m. The method according to any one of claims 1 to 3, The chemical process includes treating silicon with fluorine radicals, the chemical relaxation process using an emission photon between 380 and 650 nm to yield an electrically excited silicon trifluoride radical that is subsequently returned to ground. Chemical process control method comprising combining a fluorine radical and a silicon difluoride radical. 5. The method of claim 4, wherein said silicon process is a dry etch of silicon / silicon dioxide. 5. The method of claim 4, wherein the silicon process is a cleaning of silicon / silicon dioxide or other silicon based material deposited on the walls of the enclosure during other processing. 7. The method of claim 6, wherein said cleaning process utilizes plasma enhanced chemical vapor etching, and wherein said plasma is formed in said enclosure. 8. The method of claim 7, wherein the plasma is formed from radicals formed upstream of the enclosure. The method according to any one of claims 1 to 8, And said photon detection is performed in an exhaust line from said enclosure or in a vacuum pump connected to said exhaust line. A device used in combination with a low pressure enclosure, The low pressure enclosure serves as a reaction chamber in which a chemical process is carried out to form species that emit photons of known wavelengths or wavelength distributions by a particular chemical recombination or relaxation process, the species being at pressure of the enclosure. Apparatus using a low pressure enclosure having a lifetime characteristic that can be detected at a distance from the first reaction point, the device including a photon detector disposed at a distance from the first reaction point, and means for monitoring the photon detection rate. . As a chemical processing device, The apparatus includes a low pressure chamber and an exhaust line extending from the chamber to a vacuum pump, the chamber being used to form species that emit photons of known wavelengths or wavelength distributions by specific chemical recombination or relaxation processes. And the species have a lifespan characteristic that can be detected at a distance from the first reaction point at the pressure of the enclosure, and the device comprises a photon detector disposed at a distance from the position, and a photon detector. And a means for monitoring the speed. 12. Chemical processing apparatus according to claim 10 or 11, wherein the photon detector is mounted on an exhaust line or a vacuum pump connected to the exhaust line. 13. The chemical processing apparatus of claim 10, wherein the photon detector has an optical baffle that cancels off-axis light and / or an optical trap that impedes entry into the detector. 14. The chemical processing apparatus of claim 13, wherein the optical baffle comprises a plurality of plates having irregularly arranged openings. 15. The chemistry of claim 14, wherein the aperture size is arranged to increase in sequence such that the smallest aperture is located in a plate adjacent to the photon detector and the largest aperture is located in the plate furthest from the photon detector. Processing unit. 16. The chemistry of claim 15, wherein the size and arrangement of the openings is such that an observer positioned at the photon detector can only see the opening edges in the plate adjacent to it and not the opening edges in the plate not adjacent thereto. Processing unit. 17. The chemical processing apparatus of claim 10, wherein the photon detector is at least 5 cm away from the location. 18. The chemical processing apparatus of claim 17, wherein the photon detector is spaced at least 0.5m from the position.