JPH02220436A - Dry etching - Google Patents

Abstract

PURPOSE:To realize an etching operation as a unit of an atomic layer of a semiconductor crystal by a method wherein it is controlled by a difference in an equilibrium vapor-pressure temperature whether a reaction product is evaporated or remains. CONSTITUTION:In a first process in which a reactive gas 16 is reacted with a constituent element of a compound semiconductor 11, a gas with which a gas 17 whose composition is identical to that of a reaction product 18 produced when the reactive gas 16 has been reacted with the constituent element of the compound semiconductor 11 has been mixed only in a saturated vapor-pressure amount is used as an etchant gas. As a result, an etching operation is stopped in a state that the surface of the compound semiconductor is covered with the reaction product 18. Then, in a second process, a temperature of the compound semiconductor is raised to a sufficiently high temperature; thereby, the reaction product 18 on the surface of the compound semiconductor formed in the first process is disconnected. Only one layer of an atomic layer or a molecular layer of the compound semiconductor is etched by using the first process and the second process as one cycle. Thereby, when a changeover operation of a substrate temperature is repeated, the atomic layer as a unit can be etched.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for dry etching compound semiconductor crystals in atomic layer units.

[Conventional technology]

Conventional dry etching has been performed mainly by collision, adsorption, reaction, and desorption of ions and neutral diradicals generated by discharge plasma of a reactive gas with the substrate surface. Ions are normally accelerated to several tens of eV to several hundreds of eV and enter the substrate, which requires too much energy to strip off the surface layer of the substrate in units of atomic layers, and defects on the substrate surface cannot be ignored. A known etching method that minimizes defects is photo-excited etching, which irradiates a neutral reactive gas with light (electromagnetic waves) of an appropriate wavelength and utilizes a photochemical reaction between the generated neutral radicals and the substrate surface. It is being Photo-stimulated etching avoids defects on the substrate surface due to excessive energy, and can also lower the manufacturing process temperature. It is also superior to discharge excitation in terms of precise control of the etching process.

An example of photoexcited elaking in GaAs is presented in the GalliumArsenide and Related Combined International Physics Conference Series, No. 60.
Re1ated Compounds, Int, Ph
ys, Conf, ser, NO, 60)
Yokoyama, T Inouuni, Wai Yamakage, And, M Hiros (S, Yokoyaw+a, T, Yam
akage, and M, Hirose)
Laser-Induced Photochemical Etching of Gallium Arsenide and Its Characterization Pi
mical etching of GaAs and
Its Characterization by X-R
ay Photoelectron Spectrosc
opyand Luminescence). This example uses GaAs crystals with HCI (5%) and H
ArF with a wavelength of 193 nm in a mixed gas of e (95%)
Etching is performed by irradiation with excimer laser light. An etching rate of about 200 people/min was obtained for an insulating GaAs substrate under conditions of a mixed gas pressure of 6.65×10' Pa and a substrate temperature of 20° C. As an elementary process of the reaction, HC
I dissociates upon irradiation with excimer laser light, generating C1 radicals. This CI radical reacts with GaAs, and the reaction of GaAs+6HC1 -*GaC13+AsC13+3H2 progresses, and etching progresses.

[Problem to be solved by the invention]

In conventional photo-excited etching, the conditions for etching one element of a compound semiconductor are the same as the conditions for etching another element. In other words, there is no reaction preference in the etching process. For this reason, in the case of GaAs, it is not possible to strip off one Ga atomic layer, then strip off the underlying As atomic layer, and perform etching one atomic layer at a time.

The present invention has been made to solve these conventional problems, and its purpose is to provide an etching technology in atomic layer units by providing highly controllable reaction selectivity to the etching process of chemical semiconductors. shall be.

[Means to solve the problem]

In the present invention, a compound semiconductor composed of two elements is treated with an etchant gas ( a first step of reacting with the reactive gas in a mixed gas) and a temperature of the compound semiconductor that has undergone the first step to a temperature that gives a saturated vapor pressure equal to the partial pressure added to the added reaction product gas. This is an etching method in units of atomic layers, in which a second step of removing reaction products generated in the first step on the surface of the compound semiconductor is alternately repeated in a state where the etching rate is high.

[Operation] In the present invention, in the first step in which the reactive gas and the constituent elements of the compound semiconductor react, when the reactive gas and the constituent elements of the chemical semiconductor react with the reactive gas as an etchant gas. A gas with the same composition as the reaction product produced in the saturated vapor pressure is used. Therefore, the reaction product of the same type as the reaction gas contained in the etchant gas does not desorb from the surface of the compound semiconductor, and etching stops with the reaction product covering the surface.

Next, in the second step, the temperature of the compound semiconductor is raised to a sufficiently high temperature, so that the reaction products on the surface of the compound semiconductor formed in the first step are desorbed. The first step and the second step constitute one cycle, and only one atomic layer or molecular layer of the compound semiconductor is etched.

Therefore, by repeatedly changing the substrate temperature, etching can be performed in units of atomic layers.

[Example] Hereinafter, an example of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a sectional view of a processing apparatus showing an embodiment of the invention, and shows etching of GaAs molecular layers. Ga
Reaction products of As and C12 gas GaCl3 and AsCl
It is 3. Therefore, etching chamber 1 on the low temperature side
The etchant gases introduced into the chamber 13 on the high temperature side include GaC1 and gas 17 in addition to the CI□ gas 16.
The amount of saturated vapor corresponding to the temperature of the GaAs substrate is mixed. At a substrate temperature of 25° C., the total pressure of C1, gas 16 and GaC1, gas 17 is set to ITorr, and the partial pressure of GaC13 gas 17 is set to lXl0-'Torr. Figure 2 shows GaC
The above settings, which indicate the equilibrium vapor pressure of 13 and AsCI, are:
The gas pressure (ITorr) is indicated by the mark ◎ in FIG. 2, and when the substrate temperature is 25° C., the etchant gas pressure is lower than the vapor pressure of AsCl3 and higher than the Gac11 vapor pressure.

Furthermore, by irradiating the GaAs substrate 11 with XeC1 excimer laser light 15 having a wavelength of 308 nm in the etchant gas in the etching chamber 12, C1, gas 16 and Ga or As of GaAs react with each other.
, AsC13 are generated. Since the equilibrium vapor pressure of AsC13 is l QTo r r at 25° C., which is higher than the etchant gas pressure ITor, AsC13 is desorbed from the surface of the GaAs substrate. However, the equilibrium vapor pressure of GaCl3 is 25
℃, as low as 1
Since only 10-" Tor r is contained, it remains on the substrate surface. Therefore, the As layer is removed in the form of AsC1319, and the Ga layer reacts with C12 gas and remains on the surface in the form of GaCl318, stopping etching. do.

Next, the GaAs substrate with GaCl3 remaining on the surface was
When transferred to the chamber 13 on the high temperature side where the temperature is 100° C. or higher, the GaCl 318 boils and evaporates. In this way, GaC
When 13 is desorbed from the surface of the GaAs substrate, the next As
The etching of the zero-order As layer, which results in the appearance of a single monolayer etching cycle, involves sequentially repeating the above etching process by returning the GaAs substrate 11 to the etching chamber 12 and repeating the process described above. Therefore, etching can always be stopped at the As layer in the chamber 13, and since two layers, the As layer and the Ga layer, can be removed in one cycle, the etching layer thickness can also be controlled by the number of etching cycles. GaAs (
The etching rate per cycle for the 100) surface is 2.8
Three people/one cycle, which corresponds to one molecular layer, realizes etching at the molecular layer level.

In this embodiment, a case is shown in which two layers, an As layer and a Ga layer, are etched in one cycle, but it is also possible to etch one Ga layer and one As layer in one cycle, as shown below. Firstly, CI.

Photo-excited etching of GaAs was performed using an etchant gas mixed with AsC13 saturated vapor pressure.
s Cl3 is generated and remains on the GaAs surface.The next GaAs substrate is moved to a high temperature chamber and AsC13 is generated.
Atomic layer etching of only one As layer can be realized by removing only As. Second, the GaAs with the Ga layer exposed on the surface is transferred to the low-temperature side chamber 12, and photo-excited etching is performed using an etchant gas in which C12 gas and GaC13 gas are mixed at the saturated vapor pressure in the same manner as in the previous embodiment. , GaCl3 is generated and left on the GaAs surface.The zero-order GaAs substrate is moved to a high-temperature chamber, and only 1g of GaCl is removed, thereby realizing atomic layer etching of only one Ga layer. By repeating the above steps, it is possible to perform atomic layer etching in which only one Ga layer or As layer is etched in one cycle.

Further, in this embodiment, GaAs is used as the compound semiconductor, but the present invention can also be applied to a compound semiconductor composed of other two elements such as InP.

In this example, the reaction product remaining on the substrate surface was removed by moving the substrate to a chamber with a different temperature, but other methods, such as keeping the substrate in one chamber and using a gas Alternatively, a method may be used in which the supply of the substrate is stopped and the temperature of the substrate is changed.

〔Effect of the invention〕

As explained above, according to the atomic layer etching of the present invention, it is possible to control whether a reaction product evaporates or remains depending on the difference in equilibrium vapor pressure temperature in dry etching of a compound semiconductor. It is possible to provide distinct reaction selectivity between the reaction etching one type of element and the reaction etching another type of element.

For the above reasons, it is possible to etch the semiconductor crystal in units of atomic layers, and only 11 or 2 atomic layers are removed in one cycle of substrate movement or gas switching. Therefore, the amount of etching can be determined only by the number of cycles, making it possible to precisely control the amount of etching.

Chamber, 13...low temperature side chamber 16...
CI2 gas, 17- Ga Cl3 gas, 18-.
-Residual GaC13,19...AsC13.

Claims (1)

[Claims] A compound semiconductor composed of two elements is heated in a mixed gas atmosphere in which a reactive gas that reacts with the compound semiconductor is added with a gas of a reactive organism composed of the constituent elements of the reactive gas and the compound semiconductor. A first step of reacting with the mixed gas at a temperature lower than a temperature that gives a saturated vapor pressure of , and a temperature of the semiconductor that has undergone the first step of blocking the reactive gas in the mixed gas, A dry etching method comprising alternately repeating a second step of increasing the temperature to a temperature higher than the saturated vapor pressure temperature to remove reaction products generated in the first step on the semiconductor surface.