JPH0219968B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (a) Field of the Invention The present invention relates to a plasma etching method and apparatus, and more particularly to a plasma etching method and apparatus used for submicron processing.

(b) Background of the technology When plasma etching is used to manufacture semiconductor devices with submicron patterns such as VLSIs, damage caused by side etching and ion bombardment can be avoided in order to improve the manufacturing yield of the semiconductor devices. It is extremely important to reduce this as much as possible.

(c) Prior Art and Problems A typical conventional etching method that causes less side etching is the reactive ion etching method. In the reactive ion etching method, as shown in the cross-sectional schematic diagram of the apparatus shown in FIG. The substrate 5 to be processed is placed on top, the etching gas pressure in the etching chamber 3 is maintained at about 10 ^-1 to 10 ^-3 [Torr], and the pressure between the target electrode 4 and the counter electrode 6 is 0.3 to 2 [KW]. Plasma 7 is generated by applying high frequency RF of a certain level, and the surface of the substrate 5 to be processed is etched by the ions and radicals of the etching gas excited and formed by the plasma. In the reactive ion etching method, an electric field perpendicular to the substrate surface formed above the substrate 5 to be processed imparts directionality to the etching gas ions, thereby reducing the amount of side etching.

However, in the above-mentioned reactive ion etching, since etching is performed in a high-temperature plasma, side etching of about 0.2 to 0.3 [μm] caused by thermal movement of ions and radicals of the etching gas, and the above-mentioned side etching occur. There is a problem in that damage to a depth of about 0.5 [μm] that occurs on the surface of the substrate to be processed due to the impact of etching gas ions accelerated by high voltage is unavoidable. These problems were not so much of a problem in ordinary semiconductor integrated circuit devices (ICs), but they were
This is a major cause of deterioration in the performance and manufacturing yield of devices and the like.

In addition, as a method to extremely reduce side etching, only charged ions are separated and extracted from the plasma using a magnetic field, etc., and the ions are given directionality using a magnetic field etc. to collide with the substrate to be processed for etching. There is also an ion shower method that performs etching, but this method has the problem that the etching rate is slow because etching is performed only by ions in the etching gas excited by the plasma. Since the gas pressure in the etching chamber is lowered by about one order of magnitude compared to the etching method, the distance over which ions can move increases, resulting in greater damage to the surface to be etched.

(d) Object of the Invention In view of the above-mentioned problems, the object of the present invention is to provide a plasma etching method in which the amount of side etching and the amount of damage to the etched surface are extremely small, and the etching speed is comparable to reactive ion etching. and to provide its equipment.

(e) Structure of the Invention That is, the present invention generates plasma by applying microwaves to an etching gas in a plasma generation chamber, generates ions and radicals in the etching gas, and removes the ions and radicals. The generated etching gas is cooled by the Joel-Thompson effect and supplied to the etching chamber, and the ions and radicals contained in the cooled etching gas are placed near the surface to be etched in the etching chamber. A plasma etching method characterized by etching a surface to be etched by projecting an electric field or a magnetic field perpendicularly to the surface to be etched, and a plasma etching method by applying microwaves to an etching gas. a means for cooling the etching gas excited by the microwave to generate ions and radicals by the Juul-Thompson effect; A plasma characterized by having an electric field or magnetic field forming means that applies a force perpendicular to the plasma.
This invention relates to an etching device.

(f) Embodiments of the Invention The present invention will be described in detail below with reference to embodiments of the present invention using a schematic cross-sectional view of an embodiment of the apparatus shown in FIG.

For example, as shown in FIG. 2, the plasma etching apparatus of the present invention has an etching gas inlet 11.
It consists of a vacuum vessel 14 having a vacuum exhaust port 12 and a microwave transmission window 13 made of quartz glass or the like hermetically fixed to the upper part. The inside of the vacuum chamber 14 is divided into a plasma generation chamber 15 and an etching chamber 16, and a gas ejection hole 19 having a shutter 18 and a desired diameter is provided in a barrier 17 separating these chambers. Further, an opening of the waveguide 20 is installed above the μ-wave transmission window 13 of the plasma generation chamber 15. Further, a target electrode 22 whose pillar portion is led out to the outside through an insulating bushing 21 is disposed within the etching chamber 16, and a grid 23 is further disposed near the upper part of the target electrode 22. . (In the figure, 24 indicates a heat insulating material.) When performing selective etching of, for example, a silicon (Si) substrate using the plasma etching apparatus of the present invention, the Si substrate 25 to be processed is coated with a mask film made of photoresist or the like. Target electrode 2
After evacuating the inside of the plasma generation chamber 15 and etching chamber 16 to about 10 ^-6 [Torr],
The shutter 18 between the plasma generation chamber 15 and the etching chamber 16 is closed, and carbon tetrafluoride (CF ₄ ) gas is flowed into the plasma generation chamber 15 as an etching gas at a flow rate of, for example, about 20 [cc/min]. The shutter 18 is opened intermittently to eject a desired amount of CF ₄ gas into the etching chamber 16 in pulses, and the pressure inside the plasma generation chamber 15 is maintained at 1 to _several Torr. The gas is irradiated with μ-waves of about several [GHz]·1 [KW] through the waveguide 20 to generate high-density plasma (P) in the plasma generation chamber 15 to excite the CF ₄ gas. At this time, the pressure inside the etching chamber 16 is increased by the excited gas ejected from the plasma generation chamber 15 through the gas ejection hole 19.
10 ^-2 ~ depending on the balance between _CF4 gas and vacuum evacuation
The pressure is adjusted to about 10 ^-3 [Torr]. Etching is then performed while the grid 23 is grounded (G) and a DC negative bias (E) of several volts is applied to the target electrode 22.

In the above etching process state, the CF ₄ gas in the plasma generation chamber 15 contains ions (CF ₃ ⁺ , etc.) that are excited by the high-density plasma and contribute to etching.
and radicals (CF ^*, etc.) are formed in high density.
and contains these ions and radicals at high density.
_CF4 gas is transmitted through the gas nozzle 19 to several hundredths
It is intermittently ejected into the etching chamber 16, which has a pressure as low as 1/1000, expands adiabatically, and is cooled to an extremely low temperature due to the Joel-Thompson effect.
Note that the above-mentioned cooling is desirably carried out to a temperature close to the liquefaction temperature of the etching gas, and in the case of the above-mentioned CF ₄ gas, approximately -120 [° C.] is appropriate. The etching chamber 16 is filled with the CF ₄ gas cooled to an extremely low temperature at a pressure of about 10 ^-2 to 10 ^-3 . In such extremely low temperature CF ₄ gas, ions (CF ⁺ etc.) and radicals (CF ₄ ^* etc.) that contribute to etching
The thermal motion of has almost stopped. Therefore, the above-mentioned ions (CF ⁺ etc.) are caused by the weak electrostatic field perpendicular to the surface of the substrate 14 formed above the Si substrate 25 to be processed via the grid 23, and the above-mentioned radicals (CF ^* etc.) whose direction of motion is controlled by gravity
The etching is aligned in a direction perpendicular to the Si substrate surface and collides with the Si substrate surface to be processed at a slow speed given by a weak electric field, gravity, etc., and etching is predominantly performed in the direction perpendicular to the substrate surface. Ru.

Note that when etching a phosphorous-doped polycrystalline silicon layer in the above embodiment, the etching gas pressure in the etching chamber was set to 1×10 ^-3 Torr.
Approximately 1000Å/min, 1×10 ^-2 Torr when adjusted to
When the etching rate was adjusted to a certain level, an etching rate of about 2000 Å/min was obtained. This etching rate is approximately the same as the etching rate in reactive ion etching, and is a value sufficient for practical use.

Furthermore, directionality may be imparted to the movement of ions by a magnetic field instead of the electric field. For example, a coil is wound around the outer circumference of the vacuum container 14, and the magnetic field is
If a current is passed toward the Si substrate surface, the ions will have directionality along the magnetic field.

(g) Effects of the Invention As shown in the above embodiments, in the present invention, the surface of the substrate to be processed is etched by the ions and radicals of the etching gas that collide perpendicularly without being disturbed by thermal motion. Ru. Therefore, the amount of side etching is significantly reduced compared to the conventional method, and can be suppressed to 0.1 [μm] or less. In addition, the speed at which ions and radicals collide with the surface of the substrate to be processed is extremely slow, so the depth of damage caused to the surface of the substrate to be processed can be reduced to several hundred angstroms or less, and at the same time, damage to the mask film can be reduced. Since the mask film is reduced, it becomes possible to form a thin mask film, and pattern accuracy can also be improved in this respect.

As explained above, according to the present invention, it is possible to improve etching accuracy and reduce etching damage, so that submicron patterns can be processed.

In the present invention, since radicals also contribute to etching as described above, the etching rate is not inferior to reactive ion etching.

[Brief explanation of drawings]

Figure 1 is a schematic cross-sectional view of a reactive ion etching device, and Figure 2 is a schematic cross-sectional view of a reactive ion etching device.
1 is a schematic cross-sectional view of an embodiment of an etching apparatus. In the figure, 11 is the etching gas inlet;
2 is a vacuum exhaust port, 13 is a microwave transmission window, 14
15 is a vacuum vessel, 15 is a plasma generation chamber, 16 is an etching chamber, 17 is a barrier, 18 is a shutter, 19 is a gas outlet, 20 is a waveguide, 21 is an insulating bushing, 22 is a target electrode, 23 is a grid, 2
4 is a heat insulating material, 25 is a silicon substrate to be processed, P is a plasma, G is a ground, and E is a negative bias.

Claims (1)

[Scope of Claims] 1. Plasma is generated by applying microwaves to an etching gas in a plasma generation chamber to generate ions and radicals in the etching gas, and the etching process generates the ions and radicals. The gas is cooled by the Joel-Thompson effect and supplied to the etching chamber, and the ions and radicals contained in the cooled etching gas are exposed to an electric or magnetic field provided near the surface to be etched in the etching chamber. A plasma etching method characterized in that the surface to be etched is etched by projecting it perpendicularly to the surface to be etched. 2. means for generating plasma by applying microwaves to the etching gas; means for cooling the etching gas excited by the microwave to generate ions and radicals by the Juul-Thompson effect; and the cooled etching. - A plasma etching apparatus characterized by comprising an electric field or magnetic field forming means that applies a force perpendicular to the surface to be etched to the ions and radicals contained in the gas.