JPH0642467B2 - Plasma etching method - Google Patents

Description

Description: TECHNICAL FIELD OF THE INVENTION The present invention uses a plasma etching apparatus having parallel plate electrodes to etch an etching target material deposited on a silicon oxide film or a nitride film. The present invention relates to a highly reliable plasma etching method that suppresses the breakdown voltage deterioration of a silicon oxide film or a nitride film due to charge accumulation by placing an insulator between a material placement side electrode and a semiconductor substrate that constitutes a material to be etched.

[Prior art and its problems]

2. Description of the Related Art In recent years, in integrated circuit (IC) manufacturing processes, there is a strong demand for fine processing of devices as the integration density and speed of ICs increase. Therefore, reactive ion etching (Reactive Ion Etching) that can achieve vertical etching shape without undercut
Ion Etching: RIE) method is in the spotlight. For example, by applying high-frequency power to the electrode on which the material to form the pattern is placed, the reactive gas in the reduced pressure state introduced into the chamber is glow-discharged. At this time, a negative self-bias is generated in the high frequency electrode due to the difference in mobility of electrons and ions and the difference in the area ratio between the high frequency electrode and the counter electrode (including the inner wall of the chamber at the ground potential in this case). This negative self-bias is called the cathode drop voltage, and is shown as Vdc, measured from ground potential. The positive ions in the plasma accelerated by Vdc vertically collide with the surface of the material to be etched adsorbing the etching species to accelerate the reaction between the etching species and the material to be etched, thereby gasifying the material to be etched. Proceed with etching.

For example, when making contact holes in silicon oxide,
CF ₄ + H ₂ or CHF ₃ may be used. Also, when etching polycrystalline silicon and aluminum (Al) which are widely used as silicon wafers or electrode wiring materials, Cl _{4 is used.}
A chlorine-based gas such as Cl ₂ or Cl ₂ is used.

When stainless steel forming a vacuum container is used as the electrode material, iron (Fe) and Ni (nickel) are released during etching, which causes heavy metal contamination of the element and significantly deteriorates it. Therefore, quartz (SiO ₂ ) and alumina (Al ₂ O ₃ )
By covering the electrode with, it is possible to prevent heavy metal contamination,
Oxygen is released from SiO ₂ and Al ₂ O ₃ . When the trace amount of oxygen is mixed in the system, a large amount of chlorine radicals are generated, and polycrystalline silicon and aluminum, especially phosphorus (P) and arsenic (A
Undercutting is likely to occur remarkably in polycrystalline silicon containing s). On the other hand, a polymer thin film such as polyester can remove the above-mentioned drawbacks, but during etching, the polymer from the polymer thin film redeposits on the material surface to be etched, and as a result, after etching, on the material surface. Since the polymer thin film is also etched at the same time as the residue is likely to be produced, it is necessary to periodically replace the polymer thin film in the mass production apparatus, which is not preferable because the productivity is lowered.

Therefore, it can be said that a conductive carbon (carbon: C) plate that is not easily sputtered is the most suitable material as an electrode material that does not cause heavy metal contamination.

When the material to be etched is etched by the reactive ion etching method, anisotropic etching without undercutting is achieved as described above. Etching at a higher speed than that of SiO ₂ which is a base material for other materials such as resist and polycrystalline silicon, that is, so-called selective etching, is required, and it is necessary that the element is not contaminated. Recently, memory devices (eg, dynamic random access memory (DRAM) have been highly integrated,
Currently, 1M bit DRAM is being researched and developed from 256K DRAM, but in such an element, the minimum dimension width becomes 2 μm or less, and at the same time, the oxide film thickness of the gate oxide film and the memory part becomes 200 Å or less, which is extremely thin. When the polycrystalline silicon or refractory metal having such a structure and the silicide compound are etched by the reactive ion etching method, the withstand voltage of the underlying oxide film is significantly deteriorated, which may cause a large problem that the insulating film may not function as an insulating film. It has newly occurred.

[Object of the Invention]

The present invention has been made in view of the above circumstances, and provides a reactive ion etching method for preventing dielectric breakdown of an insulating film such as a silicon oxide film on a semiconductor substrate due to charge accumulation.

[Outline of Invention]

According to the present invention, the above object is achieved by placing an insulator between the electrode on the material arrangement side and the semiconductor substrate constituting the material to be etched.

Example of Invention

 Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a schematic structure of the etching device used. Reference numeral 1 denotes a stainless steel vacuum container body, in which an upper electrode 2 and a lower electrode 3 forming a parallel plate electrode are arranged so as to face each other so as to form a part of the container. These electrodes 2,
Reference numeral 3 is electrically insulated from the vacuum container body 1 by Teflon rings 4 and 5, respectively. Sample 6 is lower electrode 3
Placed on top of. Reference numerals 7 and 8 are water cooling tubes for cooling the electrodes 2 and 3, respectively. The exhaust pipes 9 and 10 are connected to an exhaust system (not shown) having, for example, an oil diffusion pump and a rotary pump. Reference numeral 11 denotes a dispersion pipe, and the reactive gas introduced from the gas introduction port 12 is supplied from the dispersion pipe 11 into the container with good uniformity. Reference numeral 13 is an RF power source, the output of which is switched by a coaxial switch 14 and selectively to the electrode 2 via the coaxial cable 15 and the matching device 16 or to the lower electrode 19 via the coaxial cable 17 and the matching device 18. Is being applied to. Further, the electrodes 2 and 3 are respectively connected by switches 19 and 20 so that when RF power is applied to one of them, the other is grounded. The vacuum container body 1 is always grounded. A quartz monitoring window 21 is provided on the side of the vacuum container main body 1, and an etching monitor including a spectroscope, a photoelectric tube, a recorder, etc. for monitoring the progress of etching by spectrally analyzing the gas plasma outside the quartz monitoring window 21. 22 are provided. 23 is a pressure gauge.

In such an apparatus, a carbon plate is used for the upper electrode 2 and the lower electrode 3, and as shown in FIG. 2, a 4-inch single crystal silicon wafer 30 which is a semiconductor substrate is oxidized as a sample 6 to a thickness of 400 Å by a thermal oxidation method. A film is formed, and silane (SiH
₄ ) Low pressure vapor phase epitaxy (LPCV) using thermal decomposition (750 ℃)
1) after depositing polycrystalline silicon (4000Å) 32 by D)
Positive type resist 33 after phosphorus (P) diffusion at 000 ℃
An experiment was conducted using a mask formed of (OFPR-800: manufactured by Tokyo Ohka). The etching conditions are as follows: Cl ₂ is 20cc / mim H ₂ is 6cc / mim mixed gas 0.07T
RF power to be applied is set to 13.5
The frequency was 6 MHz and 0.25 w / cm ² . RF power was applied to the lower electrode 3.

FIG. 3 shows the measured withstand voltage of the thermal oxide film of a sample obtained by etching the polycrystalline silicon 32 with a fluorine-nitric acid solution and then removing the resist 33 with a sulfuric acid solution. The electrode area of the polycrystalline silicon 32 was 10 mm, and the breakdown voltage was defined when a current of 1 μA flowed. As is clear from FIG. 3, the breakdown voltage is distributed at 10 Mv / cm and 6 Mv / cm. 10 Mv
/ Cm is a breakdown voltage peculiar to the thermal oxide film, and 6 Mv / cm is due to a process problem in forming the thermal oxide film, such as dust.

The sample 6 having such a breakdown voltage distribution was formed by using the reactive ion etching method under the etching conditions described above.
FIG. 4 shows the result of measuring the withstand voltage of the thermal oxide film 31, although the etching was performed and the resist 33 was removed with a sulfuric acid-based solution.

It can be seen that the breakdown voltage of the thermal oxide film 31 on the single crystal silicon wafer 30 is significantly deteriorated, and the thermal oxide film 31 does not function as an insulating film.

As described above, when the sample 6 is arranged on the conventionally known carbon plate electrode 3 and etched, the withstand voltage of the oxide film 31 is remarkably deteriorated. However, as shown in FIG. When the film 40-2 was pasted on the carbon plate 3, the withstand voltage characteristics of the oxide film 31 showed good characteristics without any change from the withstand voltage distribution of the oxide film by the solution etching shown in FIG. It is not clear at present why the oxide film of the sample is not destroyed by etching if the sample placement side electrode is composed of a conductive material such as carbon plate and an insulating material such as polyester film, but it is inferred as follows. .

The cathode drop voltage is mostly generated in the sheath formed between the plasma and the sample and the electrode, and even when the oxide film is extremely thin, less than 500Å, the insulating material in the blocking capacitor, etc. that is bonded to the electrode is 10 μm or more. Then, even if the cathode drop voltage Vdc is 500 V, the DC voltage applied to the oxide film due to charge accumulation is at most several V, and does not reach the voltage until dielectric breakdown of the oxide film. That is, the withstand voltage of the oxide film does not deteriorate in the charge accumulation accompanying the cathode drop voltage generation in the steady state, and the electrode material may be only the conductive material. However, since the withstand voltage of the oxide film of the sample actually deteriorates at the electrode of the conductor material, the conductor material is contacted with the conductor material within a very short time (within a few mm seconds) until the steady state is reached immediately after the etching. Although the semiconductor substrate has the same potential as before etching, the potential of the absolute value of polycrystalline silicon is lower than that of the semiconductor substrate.
It is considered that the potential difference causes dielectric breakdown of the oxide film.
On the other hand, if the electrode is composed of a conductive material and an insulating material, the electric potentials of the semiconductor substrate and the polycrystalline silicon will reach a constant electric potential at the same rate even immediately after etching, so that dielectric breakdown does not occur. Conceivable.

In the above-mentioned one embodiment, high frequency power is applied to the electrode 3 on the side where the sample 6 is placed. However, in the case of low high frequency power of 400 KHz, even if high frequency power is applied to the upper electrode 2, anisotropic etching without undercutting occurs. Can be achieved. In this case, unlike high-frequency power such as 13.56 MHz, negative self-bias does not occur, but the positive ion energy in the plasma increases, and when the sample 6 is placed on the lower electrode 3 at the ground potential for etching, the lower electrode is Dielectric breakdown of the oxide film occurs when it is a conductor material, and when the sample 6 placement electrode 3 is composed of a conductor material and an insulation material, no breakdown voltage occurs at all, similar to high frequency power such as 13.56 MHz.

Similar results were obtained with a film obtained by directly thermally nitriding silicon instead of the thermal oxide film of the sample. Furthermore, instead of polycrystalline silicon, high melting point metals such as Al, tungsten (W), molybdenum (Mo), and The effect was exactly the same when etching those silicide compounds.

〔The invention's effect〕

As described above, according to the present invention, the electrode on which the sample is arranged is composed of the conductive material and the insulating material, and the capacitance per unit of the insulating material, or the single crystal silicon of the sample and the conductive material to be etched. If the capacity of the insulating film is 20 times or more, the dielectric breakdown of the insulating film in the sample will not occur due to etching. An extremely high reliability LSI manufacturing process is established.

[Brief description of drawings]

FIG. 1 is a schematic view of a device used for explaining the present invention,
FIG. 2 is a configuration diagram of an object to be etched, FIG. 3 is a withstand voltage distribution diagram of a silicon insulating film when a conductor layer of the object to be etched is etched by a solution, and FIG. FIG. 5 is a diagram showing a withstand voltage distribution of the silicon insulating film of the object to be etched when the conductor material of FIG. 1 ... Stainless steel vacuum container, 2 ... Upper electrode, 3 ... Lower electrode, 4,5 ... Teflon, 6 ... Etching object, 7,8 ... Water cooling pipe, 9, 10 ... Exhaust pipe, 13 ... High frequency power supply, 16 , 18 ... Matching circuit, 30 ... Single crystal silicon wafer, 31 ... Silicon insulating film, 32 ... Conductor material layer, 33 ... Photoresist, 40-2 ... Insulating polymer thin film, 41-2 ... Conductor material layer.

Claims (7)

[Claims] 1. A plasma etching apparatus having parallel plate electrodes arranged opposite to each other, wherein a first layer made of a silicon single crystal and a second layer made of a silicon insulating film formed on the first layer are laminated. When an object to be etched having a conductive material layer formed on a material and an etching mask patterned on the conductive material layer is placed on one of the parallel plate electrodes and etched, the material is exposed to plasma. The insulating material layer is provided between the object to be etched and the electrode on the side of the electrode on which the object to be etched is installed, and the upper surface of the electrode exposed to plasma around the installation location of the object to be etched is the electrode. A plasma etching method characterized by being a conductive substance. 2. The plasma according to claim 1, wherein a conductive material layer is provided on the electrode, and the insulating material layer is formed on the electrode via the conductive material layer. Etching method. 3. The plasma etching method according to claim 2, wherein the conductive material layer is carbon. 4. The insulating material layer is fluorine-based, fluorine carbide-based,
The plasma etching method according to any one of claims 1 to 3, wherein the plasma etching method is a chlorine hydrocarbon-based or silicon-based insulating polymer. 5. The plasma etching method according to claim 1, wherein the second-layer silicon insulating film of the object to be etched is a thermal oxide film or a thermal nitride film. 6. A conductive material layer of the object to be etched is a refractory metal such as polycrystalline silicon, amorphous silicon, tungsten or molybdenum, a silicide compound of the refractory metal, and further polycrystalline silicon and the above. The plasma etching method according to claim 1, wherein the plasma etching method is a laminate with a refractory metal or a silicide compound thereof. 7. The unit area capacitor capacitance of the second-layer silicon insulating film of the object to be etched is 20 times or more the unit area capacitor capacitance of the insulating material layer of the electrode. The plasma etching method according to item 1.