JPH0691048B2 - Substrate dry processing method and apparatus - Google Patents

Description

FIELD OF THE INVENTION The present invention relates to a method and apparatus for dry processing assembly of devices from a substrate. In particular, the substrate is exposed to the effluent of a gaseous plasma that has at least one reactive specie but is virtually free of charged particles, while at the same time UV light is used to increase the reaction rate in a controlled manner. Is illuminated by.

[Conventional technology and its problems]

The use of gas plasmas in the fabrication of solid state devices is known in the prior art. The plasma is used for etching the semiconductor substrate (hereinafter simply referred to as corrosion), and strips the photoresist layer from the substrate.
Used to remove and remove.

Plasma treatment, also known as dry treatment or RIE (Reactive Ion Etching-Reactive Ion Corrosion), has the distinct advantage over many conventional treatments known as chemical or wet treatments. Moisture treatments are commonly used to remove photoresist from substrates or corrode layers of material,
Use toxic composition. Certain chemical compositions can be dangerous to both the operator and the environment if not used carefully. Waste disposal associated with wet corrosion treatment can also be a problem.

Wet corrosion is isotropic in that the corrosion progresses at virtually equal rates in all directions, which causes the corrosion not only to extend downward in the desired direction, but also laterally. Isotropicity creates an unwanted undercutting effect, often making the distance between adjacent corrosions unacceptably small. Wet corrosion may not be used if the line width, ie the lateral distance between adjacent corrosions, must be kept within the very close tolerances required for the small features of many LSI or VLSI devices. is there. In many of these devices, line tolerances can often be compared to the thickness of the film being corroded, thus anisotropy is essential.

Isotropic corrosion resulting from wet processing becomes more unacceptable as the density of circuit elements placed on a single semiconductor substrate increases. Linewidths decrease as device density increases and isotropic corrosion becomes more unacceptable. Therefore, the need for anisotropic or straight wall corrosion was increased.

Compared to wet corrosion, dry corrosion provides the ability for anisotropic corrosion to keep linewidths within specified tolerances. In a standard dry etch system, the semiconductor wafer or substrate being processed is placed directly into a plasma etch chamber in the plasma or glow discharge region where charged particles and relatively strong electric fields are present. The presence of charged particles in the high electric field region achieves the anisotropy of the corrosion process because the electric field imparts directionality to the charged corrosion species.

However, if the LSI, for example a dielectric layer of silicon dioxide,
Or the semiconductor layer on a VLSI device is relatively thin, perhaps on the order of a micron, and the ion bombardment from charged particles accelerating into the layer by an electric field is commonly known as radiation damage to the layer. This may result in physical anomaly or unacceptable damage. As the thickness of the oxide layer increases, the number of defective chips per wafer and the reduction in chip yield due to radiation damage increases to unacceptable rates.

Radiation damage is a problem in dry photoresist strips as well and is not limited to plasma corrosion. In addition, electrostatic charges are accumulated on the surface of the exposed dielectric layer.
For example, EPROM devices always incorporate a dielectric oxide layer that is only 100 Å thick. The electrostatic charge charging action of the dielectric layer during dry stripping of the photoresist can result in dielectric breakdown of the device and consequent inoperability.

Dry etchers, or "downstream" etchers, in which the corroding substrate is separated from the plasma itself are known in the art.
However, while the problem of radiation damage is reduced, standard downstream equipment suffers from the same inadequacies of wet corrosion equipment in that corrosion is unacceptable isotropic because the downstream equipment has corrosion species. There is no electric field that gives any direction to. Nishizawa's US Patent No.
4,233,100 discloses a plasma corrosion method using a plasma generator which ionizes a reaction gas into a plasma state. The generator is connected by a nozzle to the process chamber and directs the plasma into the chamber containing the workpiece to be processed.

The use of photons to affect the operation of plasma reactors is also known. US Pat. No. 4,183,780 to Mckenna et al.
The photon-enhanced-reac
method and apparatus for plasma etching, wherein a plasma reactor emits selected wavelengths of vacuum ultraviolet radiation and directs this radiation into a plasma, preferably adjacent a substrate to control plasma processing, particularly at the substrate. A plasma directing device is included. US Pat. No. 4,404,072 to Kohl and US Pat. No. 4,478,677 to Chen et al. Disclose the use of light in a corrosion process.

However, these statements, either alone or in combination,
No downstream plasma reactor method or apparatus is shown that combines the desired directional capability of active species for the fabrication of LSI or VLSI devices with the reduction or avoidance of radiation damage.

[Means for solving problems]

The present invention provides a method and apparatus for treating the surface of a substrate. The method includes exposing the substrate to a gas having at least one reactive species but substantially free of charged particles while simultaneously irradiating the substrate with ultraviolet light.
The substrate may also be heated by irradiation with infrared light.

[Objectives and Effects of Invention]

In a preferred embodiment of the invention, the substrate is exposed to the effluent from a gaseous plasma, where the charged particles generate a plasma remotely from the substrate and recombine the charged particles prior to their introduction into the reaction chamber. By removing or removing the plasma, the plasma is effectively removed.

A preferred embodiment for carrying out the method of the invention is at least one
A means for generating a gas plasma having two reactive species and a chamber operatively connected to the plasma generator for receiving the gas plasma effluent, containing the substrate to be processed and exposing the substrate to the plasma effluent The means for containing is sufficiently separated from the plasma generator,
Thereby any charged particles in the plasma include means such as the chamber where the plasma effluent is extinguished before reaching the substrate and means for irradiating the substrate with ultraviolet light. Also,
An apparatus is also included that irradiates the substrate with infrared light to heat the substrate.

The present invention allows the type of reactive species at plasma effluent, UV stimuli, and temperature to be uniquely controlled to optimize photoresist stripping or corrosion treatment. In conventional prior art plasma systems, these three parameters are intricately combined and cannot be independently controlled or optimized.

Since the process of the present invention is essentially a chemical process performed in the substantial absence of ions and relatively low particle energies, substrates that are to be extremely dilute and corroded to minimize substrate damage. The chemical selectivity of the above materials to achieve high corrosion rates can be controlled much better than with typical prior art plasma systems. Also, the unique chemoselectivity, which may be temperature dependent, provides a means to control additional processing.

One object of the present invention is to provide a dry corrosion method and apparatus in which the detrimental effects of radiation damage are minimized.

Another object of this invention is to provide a dry corrosion method and apparatus in which anisotropic corrosion can be achieved using downstream equipment.

Another object of the present invention is to provide a method and apparatus for effectively dry stripping photoresist from a semiconductor wafer with minimal destructive corrosion and radiation damage.

Other advantages of the apparatus and method of the present invention will be apparent from the following brief description of the drawings and detailed description of the preferred embodiment.

〔Example〕

FIG. 1 shows an apparatus 10 for processing a substrate. This treatment is the erosion of semiconductors or other substrates such as silicon or polysilicon, the stripping or removal of organic photoresist layers from the substrate, or other similar treatment of the substrate surface.

The apparatus 10 includes a reaction chamber 12 having at least one substrate 36 to be processed therein. Chamber 12 can be any suitable device with a substrate, typically a sealed chamber capable of holding a vacuum down to about 0.01 mm Hg. A pump P, shown as 15 in FIG. 1, together with a valve V, shown as 16, controls the evacuation of chamber 12 to maintain a vacuum. The exhaust of the device is controlled independently of the gas input, which is described in detail below, which allows the flow rate to be controlled regardless of the pressure in the chamber and the time the gas is present. Pressure monitor 18 provides an indication of the pressure or vacuum maintained inside chamber 12.

Chamber 12 has a thick, vacuum rated, transparent fused quartz window 20 located on the first side of chamber 12, shown as the upper side of FIG. Ultraviolet light (UV) from an ultraviolet source 22 may be directed through a window 20 to a substrate 36 being processed inside the chamber 12, as described in detail below. The window 20 can comprise any suitable material that is transparent to ultraviolet light other than quartz, such as fused silica. Chamber 12 further consists of crystal,
An optical sensor 26 has a window 24 for monitoring the chemiluminescent radiation. Chamber 12 further comprises infrared permeable calcium fluoride, zinc selenide, and other materials,
The infrared detector 30 has a window 28 for monitoring the substrate temperature.

The reaction chamber 12 includes an inlet 32 that receives a gaseous plasma effluent 33 from a plasma generator, generally indicated at 34. The chamber 12 further comprises means for directing a plasma stream through a plurality of openings 37 and onto the substrate 36, such as, for example, a "Pirvox" gaseous prenium 35. This Plenium
35 Other means are transparent to UV light but can control the gaseous plasma flow and the distribution of reactive species on the substrate surface.
The plasma generator 34 will be described in more detail below.

Chamber 12 contains a substrate to be processed, shown as 36 in FIG. Substrate 36 can be, for example, any semiconductor such as silicon, germanium, or gallium arsenide, or a semiconductor on which a layer of oxide such as silicon dioxide has been grown. The device shown in FIG.
With slight variations that will be apparent to those skilled in the art, they are also suitable for other substrate processing such as chromium or methane masks.

As can be seen in more detail in FIG. 2, the wafer 36 is shown as having a patterned layer of photoresist 38 deposited thereon, the pattern of which is an exposed portion 40 of the wafer 36 and other covered portions. A part 42 is left. FIG. 2 also shows a wafer 36 having corrosion 40 formed therein. Corrosion 40 has a floor 64 and sidewalls 62, though it should be understood that these floors or sidewalls need not be planar as shown in FIG.

In the preferred embodiment of FIG. 1, the substrate or silicon wafer 36 includes a first surface 39 and a second surface 41. The wafer 36 is supported by a set of three elongated pointed quartz pin members 44 so as to have a minimum contact area with the wafer 36, so that the first surface 39 is illuminated by the UV source 22. It has been placed. This set of pins 44 is desirable in that such a support device ensures that the substrate heats the substrate uniformly from below, but any suitable device for holding the substrate 36 can be used as well.

An infrared source 46 is placed inside the chamber 12 below the substrate. The infrared source 46 provides infrared radiation having a wavelength of about 1-10 microns to heat the wafer by illuminating the second surface 41. In the case of a silicon substrate, the silicon is essentially transparent to infrared radiation and a film, such as a layer of photoresist 38, is heated from below by an infrared source 46, virtually without heating the silicon substrate. Thus, the photoresist 38 film is heated virtually independently of the UV irradiation.

A gas plasma 48 providing at least one reactive species to erode the substrate and strip the photoresist from the substrate is created by the plasma generator 34. A gas or mixture of gases suitable for the particular substrate 36 or photoresist to be removed is introduced through the inlet 48 and flows through the conduit 50 into the plasma chamber 52. An example of such a gas is Freon
14 or oxygen etc. Gas input and mass flow control devices are well known in the art and are not shown.

The microwave exciter 54 activates the gas in the plasma chamber 52 into plasma 43. Microwave exciter 54 is driven by a microwave generator including a magnetron having a frequency of about 2450 MHz and an output of less than about 500 Watts.
The microwaves are directed into chamber 52 where a plasma or glow discharge region is created. Of course, the scope of the invention is not limited to the microwave plasma generators described herein, but applies equally to any means for generating a gaseous plasma, such as a radio frequency generator.

Gas plasma 43 created by microwave energy
Typically includes ions, free electrons, atoms, molecules, free radicals, and other excited species such as electronic excited species. Free radicals have no net charge. However, the constituent gas entering the inlet 48 can be selected so that the resulting free radicals contain at least one reactive species that is reactive with the substrate material to be removed. This allows the substrate material and photoresist to be corroded to be removed from the substrate. For example, if the constituent gas is oxygen (O ₂ ), the synthetic plasma will contain at least free radicals or reactive species O (atomic oxygen) that will react with materials such as organic photoresists. The component gas mixture is controlled by well known precision mass flow control devices. It may also be desirable to inject other gases downstream of the plasma generator.

This plasma 43 in the glow discharge region of the plasma chamber 34 will also contain ions and free electrons, or they will bombard, possibly damaging the substrate 36 if the substrate 36 is adjacent to or in the glow discharge region. Let's do it. However, the plasma generator 34 is located in a region relatively far from the reaction chamber 12 located downstream thereof. The reaction chamber 12 is connected to the plasma chamber 34 by a conduit 58, which conducts ions and free electrons in the plasma in the chamber 34 before the plasma 43 flows through the conduit 58 to the downstream chamber 12. It has a certain length that allows most of it to recombine or disappear.

Therefore, the plasma effluent 33 entering the reaction chamber is virtually free of ions and electrons. The surface of the substrate is thereby capable of reacting with at least one surface without the presence of charged particles.
It is subjected to dry treatment by being exposed to a gas containing two reactive species. Particularly suitable reactive species include at least one free radical such as an oxygen atom.

Based on a lifetime of about a few microseconds for ions and free electrons and about a few milliseconds to a few seconds for free radicals and reactive species, in the device 10 described herein, the conduit 58
The preferred length is about 4-12 inches at a plasma flow rate of 1000 SCC / M. The mass change rate in chamber 12 is preferably greater than about 100 change / min, about 800 change / min.
Minutes is most desirable. Reactive species, which have a significantly longer lifetime than ions and free electrons, reach the reaction chamber 12 in order to react with the substrate 36, whereby the substrate 36 thereby receives a substantially free plasma stream 33 of charged particles.

The UV source 22 illuminates the substrate 36 with UV light, which causes the chamber 36 to
It is provided to enhance the reaction rate of at least one reactive species in the plasma effluent introduced into 12. Suitable UV sources for use in the present invention emit electromagnetic radiation in the range of about 1000 to 3000 Angstroms, although other types of UV radiation, such as vacuum UV radiation, can be used.

The UV source 22 also collimates the UV light through a standard array of mirrors and lenses so that the UV light strikes the floor 64 of the substrate surface and the corrosion 40 exposed at an angle substantially perpendicular to the floor 64 of the corrosion. . As can be seen more clearly in FIG. 2, the ultraviolet light, generally indicated by arrow 60, is adapted to strike substrate 36 at an angle of approximately 90 ° by the precise aiming of the collimated ultraviolet light. Ultraviolet light practically does not enter the side wall 62 of the corrosion 40. Therefore, the corrosion rate is 40 floors
Augmented at 64 and effectively slower at sidewall 62. Thus, anisotropic corrosion is achieved using such constantly collimated UV light.

The above-described apparatus of FIG. 1 not only by creating a substantially straight walled corrosion 40 in the substrate 36,
It will be appreciated that it may also be used in the process of making a solid state device if it is necessary to remove certain portions of the layer of material from the surface of the substrate 36. For example, removing the developed organic photoresist 38 from the surface of a substrate 36, such as a silicon wafer, is accomplished in exactly the same manner that silicon may be removed by an erosion process.

The first step in the method is to expose a portion of the material layer to be removed to the plasma outflow 33. Plasma 43 is the substrate
Since it is created in a region relatively remote from 36, the substrate is not subject to the relatively strong electric field combined with the glow discharge region of the plasma, nor the ion bombardment. The part to be removed can be predetermined by standard photolithographic methods.

The gas plasma effluent 33 is selected to contain at least one reactive species, ie the charged particles are in fact virtually removed from the plasma effluent, so that the effluent is virtually free of ions and free electrons, and As a result, damage to the substrate due to ion bombardment is minimized. This de facto removal of charged particles is accomplished by transferring the plasma to the reaction chamber 12 for a long distance such that any charged particles, such as ions or free electrons, are extinguished by recombination.

At the same time as being exposed to the plasma outflow 33, the portion of the substrate layer where the reaction rate, such as the corrosion rate or photoresist strip rate, is to be enhanced is irradiated by electromagnetic waves including ultraviolet light 60. The substrate may also be irradiated with electromagnetic waves, including infrared radiation, preferably in the wavelength range of about 1-10 microns, to heat the substrate.

If anisotropic corrosion is to be achieved, the UV light is always collimated to give the reactive species proper directionality.

To describe the stripping operation in more detail, the throughput rate, that is, the rate at which the wafer is stripped is an important parameter. However, the strip reaction rate may be too fast or the underlying film may be corroded with the photoresist strip if a highly reactive corrosive gas is used on the heated substrate. However, when UV extension is used, the reaction rate due to the use of pure oxygen or other non-corrosive gas mixture is enhanced to the point where the actual strip rate is obtained. It is not necessary to use Freon 14 which creates a unique corrosive effect when combined with oxygen. Therefore, the method of the present invention reduces the need for both dielectric breakdown and catastrophic corrosion.

Although the method and apparatus of the present invention are described for dry processing using effluent from a gas plasma, it should be understood that the present invention may be used with ultraviolet light to selectively enhance the reaction rate of certain portions of the substrate, such as free radicals. Any dry treatment with chemically reactive species is contemplated. The use of effluent from a gas plasma that is virtually free of charged particles is desirable as a particularly effective way of practicing the present invention.

It will be appreciated that various changes and modifications of the above described preferred method and implementation will be apparent to those skilled in the art. Such changes and modifications are made without departing from the spirit and scope of the present invention, and accordingly, such changes and modifications shall be covered by the appended claims.

[Brief description of drawings]

FIG. 1 is a side sectional view of an apparatus for carrying out the method of the present invention. FIG. 2 shows a cross section of a substrate as made by the method and apparatus of the present invention.

Claims (11)

[Claims] 1. A method of removing photoresist from the surface of a substrate, comprising: (a) generating a gas plasma containing at least one reactive species that reacts with the photoresist and has atomic oxygen as free radicals. A first step, (b) a second step of producing a plasma effluent from which substantially all charged particles have been removed from the gas plasma, and (c) irradiation of the plasma effluent onto the surface of the substrate. And a third step of illuminating the surface with electromagnetic radiation including ultraviolet radiation of a continuous wavelength. 2. A second device including infrared light in the third step
A method according to claim 1, characterized in that the substrate is irradiated with the electromagnetic radiation of 3. The removal of charged particles is accomplished by passing the gaseous plasma from a relatively remote area a distance sufficient to dissipate any charged particles. The method according to item 1. 4. The method of claim 1 wherein the wavelength of said ultraviolet light is in the range of about 1000 angstroms to about 3000 angstroms. 5. An apparatus for removing a photoresist from the surface of a substrate, the plasma generator generating a gas plasma containing at least one reactive species that reacts with the photoresist, and connected so as to communicate with the plasma generating means. A conduit having a length sufficient to obtain a plasma effluent from which substantially all of the charged particles have been removed from the gas plasma, and a plurality of conduits connected in communication with the conduit and along the substrate. An apparatus comprising: a box-shaped member having an opening; an ultraviolet ray source for irradiating the substrate with electromagnetic radiation containing ultraviolet rays having continuous wavelengths; and a sealed container for accommodating the substrate and the box-shaped member. . 6. The apparatus of claim 5, further comprising an infrared source for illuminating the substrate with a second electromagnetic radiation including infrared. 7. The substrate provided in the hermetically sealed container,
6. The device according to claim 5, further comprising a holding member that holds the front surface of the ultraviolet source and the back surface of the infrared source. 8. The sealed container according to claim 5, further comprising a window portion which is kept in a vacuum and transmits the ultraviolet ray from the ultraviolet ray source to irradiate the substrate. apparatus. 9. The apparatus of claim 5 wherein said retaining member comprises at least one pair of elongated quartz members and said window portion comprises quartz. 10. The apparatus of claim 5 wherein the wavelength of said ultraviolet light is in the range of about 1000 angstroms to about 3000 angstroms. 11. The wavelength of the infrared light is from about 1 micron to about
Device according to claim 5, characterized in that it is in the range up to 10 microns.