JPH08115904A - Plasma processing method and plasma processing apparatus - Google Patents

Abstract

(57) [Abstract] [Purpose] In a plasma process for a semiconductor substrate or the like, damage generated on the substrate is limited to an ultra-thin layer on the surface, and the amount of the damaged layer removed by subsequent wet etching is minimized to achieve a semiconductor device. A plasma process method and its apparatus that do not impair the fineness of [Composition] A gas used for an etching reaction is introduced into a plasma chamber 2 through a gas inlet 1, and a microwave 4 generated by a high frequency power source 13 is introduced into the plasma chamber 2 through a waveguide.
The plasma 5 is generated by electron cyclotron resonance with the magnetic field generated by the magnetic field coil 3. By intermittently generating the plasma 5, the plasma light 11 and the plasma particles 12 reaching the sample substrate 9 are temporally separated. Let
Prevent simultaneous irradiation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technique of plasma process used for manufacturing semiconductor devices, etc.
The present invention relates to a plasma process method and a device therefor in which damage to a sample is minimized.

[0002]

2. Description of the Related Art Generally, in the fabrication of fine and highly integrated semiconductor devices, etc.
In addition, it is necessary to perform processing such as etching, cleaning, film attachment, and crystal growth that do not damage the material. Among these processing techniques, recently, a processing technique using excited particles is widely used. For example, reactive ion etching, plasma sputtering, plasma vapor deposition method, and the like. Hereinafter, these plasma process techniques will be described by taking a typical plasma etching as an example.

First, in plasma etching, a reactive gas is brought into a plasma state by high-frequency or high-voltage discharge to generate excited atoms (neutral radicals), ions, etc., and these active particles are irradiated to a sample. By doing so, processing is performed. Generally, the plasma chamber and the etching chamber are separated, and the particles are guided straight to the plasma chamber by the electric field, the magnetic field, or the like, or proceed while gradually diverging, and are guided to the sample.

FIG. 6 shows an example of the device configuration. The etching gas guided from the gas inlet 1 to the plasma chamber 2 produces high-density ionized plasma 5 by electron cyclotron resonance generated by the magnetic field generated by the air-core coil 3 and the microwave 4. The generated plasma particles 12 in the plasma 5 travel to the etching chamber 7 together with the plasma light 11 and are applied to the substrate 9 on the sample holder 8. As a result, the substrate 9 is etched. At this time, if a bias potential is applied to the sample holder 8, the ions in the plasma particles 12 can be accelerated. Also, the plasma chamber 2
The same applies when a bias potential is applied to. Since this processing technique is etching that uses the straightness of particles, it is excellent in forming fine patterns and vertical processing. The inside of the apparatus is evacuated to a vacuum by the exhaust port 10.

[0005]

By utilizing the reactivity of active particles, this plasma process enables a highly efficient reaction even when incident with low kinetic energy, as compared with processing by merely physical impact of particles. Therefore, the feature is that it can be processed with low damage. However, the occurrence of damage is still unavoidable, which is a serious problem. The occurrence of this damage is
Even though the incident energy is as small as several hundred eV or less, the ion implantation range is far exceeded, and it is less than 0.1% from the surface.
It reaches as deep as 1 μm. Therefore, the problem of damage is particularly serious in the etching of compound semiconductors, which are often used for fine processing of element active layers.

Therefore, in the actual device manufacturing process, after forming a structure by plasma etching, a method of removing a damaged layer on the surface by wet etching with less damage is used so long as it does not affect device operation. There is. In this case, what is important is to suppress the intrusion of damage into the inside, to minimize the removal layer, and not to impair the fineness of the formed structure and the processing accuracy. However, conventionally, due to lack of understanding of damage behavior, in particular, deep penetration mechanism into the interior, no effective countermeasure can be found, and deep wet etching for removing damaged layer sacrifices fineness and processing accuracy. It is the current situation.

As described above by taking plasma etching as an example, plasma process technology is indispensable for miniaturization and high integration of elements, but damage due to impact of plasma particles is unavoidable, and , Fineness,
As a method for obtaining a surface that is not damaged and the processing accuracy is not impaired as much as possible, there has been a strong demand for a method in which a region where damage due to plasma irradiation is generated is stopped in an extremely thin layer on the surface.

The present invention has been made to solve the above-mentioned problems, and limits the occurrence of damage in a plasma process to an ultrathin layer on the surface of a substrate, and removes the damaged layer by a method such as wet etching thereafter. An object of the present invention is to provide a plasma processing method and a plasma processing apparatus which are minimized and do not impair the fineness of a semiconductor element.

[0009]

To achieve this object, in the present invention, plasma excitation in a plasma generation region for generating plasma particles or plasma light is intermittently performed, and this excitation duration is set to The arrival time of the particles to reach the surface of the substrate to be processed is set to be equal to or less than the arrival time, and the excitation interruption time is set to be equal to or more than the arrival time to prevent the plasma particles and the plasma light from reaching the processed substrate at the same time. At this time, since the plasma lifetime still remains after the plasma excitation is interrupted, the remaining plasma lifetime is added to the above-described plasma excitation duration to keep the plasma particle arrival time below the arrival time.

A blocking mechanism is provided between the plasma generation region and the processed substrate to open and close in synchronism with the intermittent plasma excitation. The blocking mechanism is closed during plasma excitation and opened when plasma particles pass through. The plasma particles are allowed to pass, but the plasma light is blocked from entering the substrate.

On the other hand, in the plasma processing apparatus, a speed selector for selectively passing only particles having a certain speed is provided between the plasma generation region and the processed substrate. As this speed selector, the positions of the openings are displaced from each other, and the speed selector is composed of two blocking plates with openings provided at intervals, and these blocking plates are perpendicular to the path of the plasma particles. The particles are rotated synchronously in the plane, and only particles having a velocity capable of sequentially passing through both openings are selectively passed, while the passage of other, for example, plasma light is always blocked.

[0012]

In the method and apparatus for plasma processing of semiconductors according to the present invention, the method for intermittently exciting plasma or the provision of a blocking mechanism for passing only plasma particles and blocking plasma light provides And the plasma particles are temporally separated to irradiate the processed substrate, or the plasma light is always shut off to irradiate the processed substrate only with the plasma particles. This was devised based on the discovery of the inventors that the diffusion of damage (defects) induced in the semiconductor substrate by the plasma process is significantly accelerated and promoted by the photoexcited carriers. Hereinafter, this matter will be described in detail.

It has been conventionally known that in a plasma process such as dry etching, a defect that acts as a carrier killer occurs even in a deep portion of a bulk layer that is far deeper than an ion implantation range. However, the mechanism of its occurrence was unknown. The present inventors investigated the damage of GaAs in the case of irradiating with additional light in the plasma etching process, and the irradiation of the laser light having the energy higher than the band gap causes the damaged region to spread to a significantly deep position. Was revealed (199
4th 6th International Conference on Shallow Level Centers for Semiconductors). For example, although defects without laser irradiation plasma irradiation alone subsurface 50nm to 10 ¹⁷ / cm ³ is penetrated by diffusion, in a region where laser light is irradiated, 10 ¹⁷ /
It was found that the defects of cm ³ penetrated to 100 nm below the surface and the diffusion distance was doubled. That is, it was found that the defect penetrated into the deep portion of the bulk due to the phenomenon of diffusion promotion by laser light excitation. Similar effects are observed not only for Ar ions but also for irradiation of light element hydrogen (H) and helium (He) ions, which is a universal phenomenon observed in point defects generated in GaAs by plasma process. Is. That is, it is considered that laser light excitation caused a phenomenon of promoting diffusion of defects that occurs under the injection of a large amount of electrons and holes, which has been attracting attention in the field of point defect physics in recent years. Therefore, it has been found that it is important to reduce or eliminate the irradiation light intensity during processing in order to reduce damage. By the way, as shown in FIG. 6, in the semiconductor plasma process including plasma etching, the surface of the substrate 9 is exposed to the plasma light 11 as well as the plasma particles 12. Since the plasma light 11 generally has strong light emission in an energy range higher than the band gap of the semiconductor, a large number of electron-hole pairs are generated on the surface of the substrate 9 as in the case of the above laser light irradiation. . Therefore, the present inventors have found that the main cause of point defects occurring in the bulk layer far deeper than the injection range of the plasma particles 12 due to the plasma process such as plasma etching is the electron excitation diffusion promotion effect by the plasma light 11. I focused on things. Therefore, the present inventors have already proposed a method of separating the plasma light and the ions in the plasma particles by bending the range of the charged particles (ions) by using an electric field or a magnetic field. Japanese Patent Application No. 6-126308). However, this method has an effect on charged ions but cannot separate electrically neutral particles such as neutral radicals from plasma light.

The present inventors have proceeded with research on the electron-excited diffusion promoting effect, and found that this effect occurs when the excited plasma light and plasma particles reach the processed substrate at the same time. That is, in GaAs, etc., the lifetime of excited electron-hole pairs is several nanoseconds or less. Therefore, when plasma light and plasma particles are incident on the substrate after several nanoseconds or more, electron excitation diffusion occurs. There is no accelerating effect. The present invention is characterized by preventing the simultaneous incidence of plasma light and plasma particles on the substrate by utilizing the speed difference between light and particles, and has an advantage that it can be applied regardless of the presence or absence of electric charge of particles.

On the other hand, recently, a "time modulation plasma etching method" has been proposed as a process for intermittently exciting plasma (eg, Nikkei Microdevice, July 1994, p99). This method positively utilizes the transient state of the plasma by intermittently exciting the plasma to improve high selectivity and high speed of etching. However, the feature of this method is that the plasma density is maintained even during the interruption of the plasma excitation by intermittently exciting the plasma for about 10 microseconds, which is shorter than the lifetime of the plasma (several tens of microseconds), and the plasma itself continuously irradiates the substrate. It is a thing. On the other hand, the present invention is characterized by interrupting the plasma particles that are incident on the processed substrate to prevent simultaneous incidence with plasma light, and is a completely different invention from the “time modulation plasma etching method”.

As described above, the present invention relates to an apparatus and method for a semiconductor plasma process based on the discovery and consideration of a new phenomenon of point defect behavior. In the plasma irradiation process, plasma particles are generated on the substrate surface. By positively preventing the plasma light from being exposed at the time of collision, diffusion of point defects is significantly suppressed.

[0017]

【Example】

(Embodiment 1) Regarding the plasma processing method and apparatus according to the present invention, in Embodiment 1, the C of GaAs semiconductor is used.
A description will be given by taking etching by l ₂ gas plasma as an example.
In the first embodiment, the plasma excitation in the plasma generation chamber is intermittently performed to prevent simultaneous incidence of plasma light and plasma particles on the surface of the processed substrate and suppress the diffusion promotion phenomenon due to the optical excitation. .

First, FIG. 1 (a) shows a device configuration of a first embodiment according to the present invention. This is a diagram showing etching of a semiconductor substrate in a semiconductor material processing apparatus. Here, plasma excitation is performed intermittently by intermittently operating the high frequency power supply 13. FIG. 1B is a time chart showing an excited state of plasma, and temporal changes in arrival of photons and particles on a substrate.

Next, the operation of the apparatus to prevent plasma light and plasma particles from reaching the processed substrate at the same time will be described.

First, a gas (chlorine gas) used for the etching reaction is introduced into the plasma chamber 2 through the gas inlet 1. The microwave generated by the high frequency power source 13 (2,450
The MHz) 4 is introduced into the plasma chamber 2 by the waveguide. A magnetic field of 875 Gauss under electron cyclotron resonance (ECR) conditions is applied to the plasma chamber 2 by the magnetic field coil 3 to generate plasma 5. Active plasma particles (chlorine) 12 generated by this and plasma photon 11
Proceeds to the etching chamber 7 and the substrate 9 on the sample holder 8
(GaAs) is irradiated. After that, the gas that has completed the reaction is discharged from the exhaust port 10.

In the present invention, the arrival time of the plasma particles 12 and the plasma photons 11 at the substrate 9 is separated by oscillating the high frequency power source 13 in a pulsed manner. This is shown in the time chart of FIG. After the excitation, the plasma light 11 exponentially decreases with a time constant corresponding to the plasma life. In Example 1, the plasma excitation time was selected so that the light emission during the plasma life after the excitation was also separated from the particles. That is, the total time of the excitation time and the plasma life was set to be a time equal to or shorter than the particle arrival time. As a result, the time for the plasma particles 12 to reach the substrate 9 is after the end of the plasma emission (excitation time + lifetime). Therefore, the plasma light 11 and the plasma particles 12
It is possible to prevent both of them from reaching the substrate 9 at the same time.

The depth dependency of the carrier concentration was investigated for GaAs thus etched to a depth of 100 nm. The results are shown in Fig. 2 (a). For the measurement of the carrier, the surface was etched by 10 nm by wet etching and examined by the photoreflectance method. For reference, the result of continuous excitation is also shown. Immediately below the surface, reduction of carriers can be seen due to damage due to etching. However, it can be seen that, due to the intermittent excitation according to the present invention, the carrier reduction region is 1/5 or less as compared with the case of continuous excitation. Further, FIG. 2B shows the change in carrier concentration depending on the length of the excitation interruption time. The excitation time is 20 microseconds, and the carrier concentration is shown when etching is performed by changing the excitation interruption time. When the excitation interruption time becomes long, the decrease in carrier concentration decreases, and the particle arrival time (80 microseconds) becomes almost constant. This is because the interruption time of the excitation is longer than the arrival time of the particles and longer than the plasma excitation and the life of the plasma. Therefore, the substrate 9 of the plasma light 11 and the plasma particles 12 is
This is the result of being able to completely separate the arrival at time.

(Embodiment 2) In Embodiment 2, a method of performing plasma excitation intermittently and causing only the plasma particles to enter the processed substrate by a blocking plate which opens and closes in synchronization with this will be described. FIG. 3A shows a configuration diagram of the present invention.
The introduction of gas, the intermittent excitation method of plasma, and the like are the same as in the case of FIG. The blocking plate 6 having an opening is rotated in synchronization with the intermittent plasma. The time chart,
It is shown in FIG. The plasma emission time is the time of plasma excitation time + time of plasma life, during which the plasma light 11 is blocked by the blocking plate 6. After that, when the plasma particles 12 reach the blocking plate 6, the rotation speed is selected so that the opening comes. As a result, the plasma particles 12 pass through the opening and reach the processed substrate 9. As a result, the plasma light 11 does not reach the processed substrate 9 and the plasma particles 1
Only 2 can be reached.

When etching is performed by the above method,
An example of reducing damage is shown in FIG. FIG. 4A shows a sample structure to be processed, which is AlGaAs / GaAs / AlGaAs.
Quantum well structure consisting of layers from the sample surface 15, 20, 2
It was prepared at each depth of 5 nm. The surface of each sample was etched by 10 nm by the method of continuous excitation of Cl ₂ plasma, intermittent excitation, and intermittent excitation + synchronization blocking plate. The emission intensity from each quantum well of this sample is measured by the photoreflectance method, and is shown in FIG. It can be seen that the intermittent excitation method causes less damage than the etching by continuous excitation, and further, the use of the synchronous blocking plate makes it possible to almost completely eliminate the damage to the deep quantum well.

(Third Embodiment) In the third embodiment, plasma excitation is continuously performed to block light between the plasma chamber and the substrate.
An apparatus for injecting only plasma particles into a processed substrate by a speed selector that allows only particles having a certain speed to pass will be described. First, FIG. 5A shows a block diagram of the present invention. Gas introduction, plasma excitation method, etc. are shown in FIG.
Is the same as in.

Next, FIG. 5 (b) is a schematic view of the blocking plate 6 which allows only the plasma particles 12 to pass in the third embodiment. The rotatable first blocking plate 6-1 and the second blocking plate 6-2 are held at positions where their centers are parallel to the direction of the plasma flow and their openings are offset. Then, place them at a certain distance. When this blocking plate 6 is rotated, the plasma light 11 that has passed through the first blocking plate 6-1 has a high speed, so that the second blocking plate 6 is rotated.
-2 is blocked. On the other hand, in the case of the plasma particles 12 having a finite velocity, it takes a certain time from passing through the first blocking plate 6-1 to reaching the second blocking plate 6-2.
At this time, the rotation speed of the blocking plate 6 is adjusted so that the opening of the second blocking plate 6-2 comes. As a result, the processed substrate 9 can be irradiated with only the plasma particles 12 having a certain speed.

In the same manner as in Example 1, the depth dependency of the carrier concentration was examined for the GaAs thus etched to a depth of 100 nm. The result was almost the same as that of FIG. 2A of Example 1, and etching was possible with low damage.

[0028]

As described above, in the plasma processing method and apparatus according to the present invention, the plasma particles are irradiated onto the processing surface of the semiconductor substrate regardless of the presence or absence of charging while preventing the incidence of plasma light. Therefore, it is possible to suppress the damage generated by the plasma particle irradiation from diffusing from the substrate surface to the inside, and it is possible to confine the damage to the shallow region of the substrate surface. Therefore, the removal amount of the surface layer by the wet etching performed after the plasma etching can be minimized, the fineness and accuracy of the substrate surface processing can be maintained, and the integration degree of the semiconductor device can be improved. It will be possible.

[Brief description of drawings]

FIG. 1 is a diagram showing an apparatus configuration (a) of a plasma process apparatus according to a first embodiment of the present invention and a plasma excitation timing (b).

FIG. 2 is a diagram showing a carrier concentration reduction preventing effect obtained by plasma etching according to the present invention (a), (b).

FIG. 3 is a diagram showing an apparatus configuration (a) of a plasma process apparatus according to a second embodiment of the present invention and a timing (b) between plasma excitation and opening / closing of a blocking plate.

FIG. 4 is a diagram showing a photoluminescence emission intensity reduction prevention effect obtained by plasma etching according to the present invention.

FIG. 5 is an apparatus configuration (a) of a third embodiment of the plasma process apparatus according to the present invention, and a schematic diagram (b) of its shutoff plate.
It is the figure which showed.

FIG. 6 is a diagram showing a configuration of a conventional plasma process apparatus.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Gas inlet 2 ... Plasma chamber 3 ... Magnetic field coil 4 ... Microwave 5 ... Plasma 6 ... Blocking plate 7 ... Etching chamber 8 ... Sample holder 9 ... Substrate 10 ... Exhaust port 11 ... Plasma light 12 ... Plasma particles 13 ... Micro Wave power

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI Technical display location H05H 1/46 C 9216-2G H01L 21/306 SN

Claims (5)

[Claims] 1. A plasma process method for generating a plasma and thereby processing a substrate, wherein plasma excitation is intermittently performed in a plasma generation region for generating plasma particles and plasma light, and the duration of the plasma excitation is set. ,
The plasma particles have a flying time of less than or equal to the surface of the substrate to be processed, and the plasma excitation interruption time is not less than the flying time, and the plasma particles and plasma light reach the substrate at the same time. A method of plasma processing, characterized in that the substrate is processed by the plasma particles while suppressing the above. 2. The plasma process according to claim 1, wherein the sum of the excitation duration of the plasma and the lifetime of the plasma after completion of the excitation is set to be equal to or less than the flight time of the plasma particles. Method. 3. A blocking mechanism is provided between the plasma generation region and the substrate, the blocking mechanism opening and closing in synchronization with the interruption of the plasma excitation, and the blocking mechanism is closed during the plasma excitation to allow passage of the plasma particles. The plasma process method according to claim 1 or 2, wherein the plasma process is opened at times. 4. A plasma process apparatus comprising a velocity selector for selectively passing only particles having a certain velocity in a path from a plasma generation region to a processed substrate. 5. The positions of the openings are displaced from each other, and
The speed selector which rotates the 1st and 2nd blocking plate with an opening provided at intervals in synchronism within the surface perpendicular | vertical to the path | route of a plasma particle, The said 4 characterized by the above-mentioned. Plasma process equipment.