JP3408311B2 - Digital etching method and apparatus - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an ultra LSI and an ultra LS.
The present invention relates to a digital etching method and device in a manufacturing process.

[0002]

2. Description of the Related Art The etching method used in a conventional wafer process is mainly parallel plate reactive ion etching (RIE), in which high frequency power is supplied to a floating substrate through a blocking capacitor to utilize self-bias generated. Then, the ions in the plasma are extracted and etched. Other than RIE, ECR and helicon plasma are also used, but in principle RI
The same etching mechanism as in E is used. That is,
The gas containing halogen atoms introduced into the vacuum vessel is decomposed in the plasma, and the radicals generated thereby are adsorbed and react on the surface of the wafer or substrate, and at the same time, the ions generated in the plasma collide with the reaction surface. , Breaks the bonds between atoms and gives energy to the atoms present on the surface, and acts to accelerate the reaction. Through these processes, the surface atoms become volatile halides and are desorbed from the surface. These series of processes are collectively called an etching process. Therefore, ion bombardment greatly contributes to the etching process, and RIE has been used as a method of positively utilizing these processes.

By the way, with the progress of VLSI, the device process is further miniaturized, and a high aspect ratio (depth / width) structure such as a trench or a multilayer wiring is formed, and an insulating material or a metal is embedded in that portion. Low damage processes and the like have been required. However, the conventionally used parallel plate type RIE apparatus cannot satisfy the above requirements because high energy ions are used. That is, when an ion energy is lowered in an etching process by a parallel plate type RIE apparatus that achieves fine processing by transferring momentum of ions, chemical reaction becomes dominant and fineness deteriorates. An etching process using a parallel plate type RIE device cannot be practically used for the fine processing as described above. 256M, 1GDR with finer device structure
In AM and ultra-ultra-miniaturized LSIs that are finer than AM, in the above-described RIE technology that has been conventionally used, the processing line width and the contact hole are reduced to 0.5 μm or less, and the line width is reduced or expanded by ion irradiation or Since damage to deep portions occurs and damage due to ion irradiation extends to several hundred angstroms, there is a possibility that such RIE technique cannot be used. By the way, what is required as an etching method with low damage and suitable for fine processing is to thoroughly control the surface reaction rate and control the etching on an atomic scale. That is, it is necessary to artificially perform a digital process for each atom / molecule layer so as not to damage the underlying substrate at all.
Therefore, in Japanese Patent Application No. 2-61255 (Japanese Patent Application Laid-Open No. 3-263827) and Japanese Patent Application No. 2-75556 (Japanese Patent Application Laid-Open No. 3-276791), etching is performed for each atomic layer that does not cause damage to the substrate. A possible digital etching method was proposed. In this method, only one layer of the etchant generated by the first plasma source is adsorbed on the substrate, and the substrate is irradiated with ions whose energy is controlled so that only the adsorption layer on the substrate is separated by the second plasma source. Then, in synchronization with the second plasma source, a bias voltage for attracting the ions generated by the second plasma source to the substrate side is applied to the substrate to achieve digital etching. In the present specification, the term “condensation” means a phenomenon generally used in vacuum technology in which molecules are trapped on a low temperature surface and physically adsorbed.

[0004]

In order to reliably achieve the etching for each atomic layer, the amount of the etchant adsorbed should be a sufficient amount or sufficient for etching only one atomic layer. Two methods are conceivable: one in which the etchant is adsorbed and the amount of ions to be irradiated is controlled to the amount required for one atomic layer etching. First, Japanese Patent Application No. 2-61
The digital etching proposed in 255 (JP-A-3-263827) is an example of the latter. Although it is possible to perform digital etching by this method, it is very difficult to control the irradiation ion amount in order to truly achieve etching of one atomic layer. In view of this, in the present invention, the method and apparatus for digital etching are arranged so that the etching amount of the etchant is controlled to one atomic layer and the etching of each atomic layer can be surely performed by a method that does not require accurate control of the ion irradiation amount. Is intended to provide.

[0005]

In order to achieve the above object, according to the first aspect of the present invention, a substrate holding portion and a discharge portion are provided in a vacuum container so as to face each other, and a gas is discharged. In a digital etching method in which decomposition is performed by etching, a reactive gas is decomposed by pulsed discharge, and a condensed layer is formed by introducing the decomposed product onto a substrate cooled below the condensation temperature of the decomposition product, After that, the temperature of the substrate is raised to a temperature higher than the condensation temperature of the decomposition product by heating with an infrared lamp to accelerate the reaction to form a monoatomic reaction layer and evaporate extra condensed molecules, and further to lower the monoatomic reaction layer with low energy. It is characterized in that etching is carried out for each atomic layer by irradiating neutral or charged particles having a certain amount. That is, in the method of the present invention,
For example, a gas containing F on a substrate cooled to 170K or less (NF
3, SF6, F2, etc.) are supplied after being decomposed by pulse plasma, and the substrate temperature is raised to 200 K by irradiation with an infrared lamp. By this operation, an F reaction layer of one atomic layer is formed on the substrate.
After this, non-reactive ions or neutral particles having an energy of 20 to 100 ev are irradiated to separate the monoatomic reaction layer. For example, when the substrate is Si (100), a monoatomic reaction layer of SiF ₂ is formed, and the monoatomic reaction layer is peeled off by ion irradiation. The liberated SiF ₂ can exist as stable radicals, and is thus exfoliated.

According to a second aspect of the present invention, a discharge part for decomposing gas by pulsed discharge in a vacuum container and a condensation temperature of a decomposition product positioned opposite to the discharge part and lower than the condensing temperature There is provided a digital etching apparatus having a substrate holder capable of cooling, a substrate heating mechanism by an infrared lamp, and a discharge unit having a particle irradiation mechanism for etching an adsorption layer on the substrate. . In the device of the present invention, the discharge part may be a cathode-coupled discharge part, and the monoatomic reaction layer is etched by ion irradiation. Further, the discharge part may be composed of a plasma generating mechanism provided at a position facing the substrate, and the monoatomic reaction layer is etched by plasma irradiation. Alternatively, the discharge part may be composed of a neutral particle generating mechanism provided at a position facing the substrate, in which case the monoatomic reaction layer is etched by irradiation of neutral particles.

[0007]

In the digital etching method thus constructed, it is not necessary to control the discharge gas supply time,
It suffices to form a pseudolayer of an etchant sufficient to form the one-atom reaction layer on the substrate. When the radical temperature of plasma-decomposed F-containing radical species is condensed on the substrate by raising the substrate temperature to the condensation temperature of the decomposition product or lower and the temperature is raised to the condensation temperature of the decomposition products or higher, the molecule having high reactivity among the condensed molecular species. The seed reacts with the outermost one atomic layer of the substrate and the excess etchant evaporates. Such a mechanism is called self-limiting reaction (Self-Limiting
Reaction). That is, it is important that this self-regulating reaction occurs, and the radical temperature is condensed by setting the substrate temperature to the condensation temperature of the decomposition product or less, and then raised to the condensation temperature of the decomposition product or more to generate the monoatomic reaction layer. Can only form.

[0008]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 shows an example of an apparatus for carrying out the digital etching method of the present invention. In FIG. 1, the vacuum container 1 is designed so that it can be evacuated by a vacuum pump (not shown) of an appropriate type through an exhaust port 1a. Inside the vacuum container 1, an insulating seal member is provided as shown in the drawing. A substrate holder 3 is inserted through the substrate holder 2. The substrate holder 3 is configured so that a suitable coolant such as liquid nitrogen can be circulated therein, and a substrate to be processed is placed on the substrate holder 3. 4 is placed. Further, a power source 5 capable of applying a negative bias voltage Vb is connected to the substrate holder 3. A Kauffman-type plasma source 6 that generates ions for separating the one-atom adsorption layer is arranged at a position facing the substrate holding table 3. The plasma source 6 includes an acceleration power source 7 for accelerating ions and an extraction power source 8 for extracting ions.
And a coil 6a on the outer circumference of the vacuum container. Ions for peeling the one-atom reaction layer enter the surface of the substrate 4 with energy determined by the potential difference between the acceleration voltage Va of the plasma source 6 and the bias voltage Vb of the substrate holding table 3. Further, in FIG. 1, reference numeral 9 is an F-based plasma source, and this F-based plasma source 9 is configured to plasma-decompose and supply a gas containing radicals for forming a condensed layer of an etchant on the substrate 4. An infrared lamp 10 is provided in the vacuum chamber 1 between the substrate 4 and the plasma source 6.
Is provided, and functions to heat the condensed layer formed on the substrate 4 to evaporate and remove excess condensed molecules and to form a monoatomic reaction layer. A shutter 11 is arranged between the infrared lamp 10 and the plasma source 6.

In the operation of the illustrated apparatus thus configured, the operation of each part is controlled as shown in the time-sequential chart of FIG. 2, that is, first, the substrate 4 is cooled to 140 K or less by liquid nitrogen and the F-based plasma is used. An NF ₃ gas is introduced into the source / source portion, and a pseudolayer of an etchant sufficient to form a monoatomic reaction layer is formed on the substrate 4. After that, the infrared lamp 10 is energized, and only the surface of the substrate 4 is heated by the light irradiation to fluorinate the outermost surface and desorb the adsorption layer. Next, the shutter 11 is opened, and the remaining monoatomic reaction layer is peeled off by irradiation of non-reactive ions generated by the plasma source 6 provided at a position facing the substrate 4. These processes are schematically shown in FIG. As a result of performing the experiment according to the time sequence shown in FIG. 2, it was confirmed that the etching was performed almost every atomic layer.

In FIG. 4, the substrate 4 is cooled to below 140 K by liquid nitrogen, and NF ₃ gas is introduced into the F-based plasma source 9,
Infrared reflection absorption spectrum (R
AS). When exposed to plasma-decomposed F-based gas for 300 seconds, a broad peak indicating that a thick condensed layer is formed is seen around 800 to 900 cm ^-1 . FIG. 5 shows the result of measuring the RAS spectrum while irradiating the sample on which the condensed layer is formed, that is, the substrate, with the infrared lamp 10 and raising the temperature of the substrate 4. At 200 K, a peak showing the bond of SiF ₂ suddenly appears, and the broad peak showing the condensed layer appearing at 800 to 900 cm ^-1 disappears.
This is because by raising the temperature, active molecules containing free F atoms in the condensed layer react with Si, which is a constituent atom of the substrate, to form a SiF ₂ bond, and other extra molecules that cannot react with the outermost surface layer of the substrate. It shows that the adsorbed molecules have evaporated. Then, another non-reactive discharge gas is introduced into the discharge chamber, that is, the plasma source 6 installed at a position facing the substrate, and the potential difference between the substrate and the discharge chamber is set to 20 so that the potential of the discharge chamber becomes high.
When the discharge is carried out while keeping at about 100 ev, the ions generated in the discharge chamber are irradiated to the substrate, and the monoatomic reaction layer formed on the substrate is sputter-etched by the ion irradiation. As a result, only the one-atom reaction layer on the substrate is peeled off. In this case, the energy of the rare gas ions is controlled by the potential difference between the substrate 4 and the discharge chamber 6 so that only the one-atom reaction layer on the substrate is separated. When the substrate 4 is floated with a blocking capacitor, a high frequency is applied to the substrate 4, a rare gas is introduced, and when the one-atom reaction layer is peeled off in the same manner as in normal RIE, the high frequency power applied is controlled. Power so that only one atomic reaction layer can be peeled off.

In the illustrated example, a Kauffman type plasma source is used as the plasma source, but other discharge methods such as ECR may be used. A high frequency bias may be used instead of the bias power source applied to the substrate holding table.

[0012]

As described above, according to the present invention, the self-limiting reaction is generated, so that it is necessary to control the adsorption amount of the etchant to one atomic layer and accurately control the ion irradiation amount. Without doing so, it becomes possible to reliably carry out etching for each atomic layer.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of an apparatus for carrying out a digital etching method of the present invention.

FIG. 2 is a time-sequential chart showing a process of operation of the apparatus of FIG.

FIG. 3 is a principle diagram showing the method of the present invention.

FIG. 4 is a diagram showing an infrared reflection absorption spectrum on a substrate.

FIG. 5 is a diagram showing infrared reflection absorption spectra on a substrate at various temperatures.

[Explanation of symbols]

1: Vacuum container 2: Insulation sealing member 3: substrate holder 4: Substrate to be processed 5: Bias power supply 6: Plasma source (discharge chamber) 7: Accelerating power supply 8: Power supply for drawer 9: F-based plasma source 10: Infrared lamp 11: Shutter

Continuation of front page (56) Reference JP-A 63-141316 (JP, A) JP-A 3-263827 (JP, A) JP-A 4-302426 (JP, A) JP-A 5-47716 (JP , A) JP-A-3-110844 (JP, A) JP-A-5-55186 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00 JISST File (JOIS)

Claims (5)

(57) [Claims] 1. A digital etching method in which a substrate holding portion and a discharge portion are provided in a vacuum container so as to face each other, and gas is decomposed by discharge to perform etching.
The reactive gas is decomposed by pulsed discharge and introduced onto the substrate cooled below the condensation temperature of the decomposition products to form a condensation layer, and then the substrate is heated above the condensation temperature of the decomposition products by infrared lamp heating. By raising the temperature and promoting the reaction, a one-atom reaction layer is formed and excess condensed molecules are evaporated, and further, this one-atom reaction layer is irradiated with neutral or charged particles having a low energy to generate one atom. A digital etching method characterized by performing layer-by-layer etching. 2. A vacuum vessel, a discharge section for decomposing gas by pulsed discharge, a substrate holding section positioned facing the discharge section and capable of cooling to a temperature not higher than the condensation temperature of decomposition products, and a red section. A digital etching apparatus having a substrate heating mechanism by an outer lamp, and a discharge unit having a particle irradiation mechanism for etching an adsorption layer on the substrate. 3. The discharge unit comprises a cathode-coupled discharge unit, 1
The digital etching apparatus according to claim 2, wherein the atomic reaction layer is etched by ion irradiation. 4. The digital etching apparatus according to claim 2, wherein the discharge part comprises a plasma generation mechanism provided at a position facing the substrate, and the monoatomic reaction layer is etched by plasma irradiation. 5. The digital etching apparatus according to claim 2, wherein the discharge part comprises a neutral particle generating mechanism provided at a position facing the substrate, and the monoatomic reaction layer is etched by irradiation of the neutral particles.