JPH01194325A - Dry-etching - Google Patents

Abstract

PURPOSE:To round the upper shoulder parts of an etched region and, further, avoid the surface roughness of side walls by a method wherein the deposition rate of a deposited film is large in the initial stage of etching and the deposition rate of the deposited film is reduced in a main etching process. CONSTITUTION:In the initial stage of etching, etching parameters including the mixing ratio between a component which produces active species etching etching material and a component which forms a deposited film on the surface of the etched material, a total pressure, a total gas flow rate, the temperature of the etching material and a radio frequency power are properly predetermined to form deposited films 15 which provide slight tapers on the side walls 11a of a trench 11. Then the etching parameters are varied so as to reduce the deposition rate of the film 15 compared to the deposition rate in the initial etching process. With this constitution, the upper shoulder parts of the etched region is rounded and the degration of a dielectric strength can be avoided and, moreover, the number of ions attacking the side walls is reduced so that the surface roughness of the side walls can be avoided.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a dry etching method used, for example, in the manufacturing process of semiconductor integrated circuits.

(Prior Art) In recent years, semiconductor integrated circuits have undergone rapid development, and LSIs have been developed in which submicron-sized elements are mounted at high density. In such LSIs, the area of each element such as the huge number of transistors and capacitors installed is reduced, so for example, it is difficult to obtain sufficient capacitance by adopting a conventional planar structure for capacitors. I can't. Recently, techniques for trench capacitors and stacked capacitors that use 3i substrates three-dimensionally have been proposed and are beginning to be put into practical use in devices.

Trench capacitor technology, which is one such technology, uses dry etching to create a trench (groove or hole) several micrometers deep in a Si substrate, and forms a capacitor on the sidewall of the trench to achieve the required large capacitance. It is a technique to obtain

FIG. 5 schematically shows the steps of trench capacitor technology employing such a dry etching method.

This process is explained in the order of (n) to (e) in the same figure.
a) S: A mask 21 with a desired pattern is formed on the substrate 20. (b) A trench 22 of a required depth is formed using a reactive ion etching technique, which is a dry etching method. (C) Side wall 2 of trench 22 as required
An impurity diffusion 23 is performed on 2c, and then, after removing the mask 21, a thin 3i oxide 1!124 is formed which becomes the dielectric. (2) Polycrystalline 5i25 is deposited and impurity diffusion is performed to make it conductive. (e) Polycrystalline 5i2 on the surface
5 is patterned by etching to form an electrode 25a, and a trench capacitor having the required capacitance is constructed.

However, trench capacitors formed using such a dry etching method generally have lower dielectric strength and have a higher leakage current than capacitors having a planar structure.

The causes of this are thought to be failures as described in (a) to (d) below. That is, (a) trench trenching using a dry etching method ignores the crystallinity of 3i to form trenches 22 in a shape convenient for the device, and also forms trenches 22 that are diagonal to the substrate surface of the 3i substrate 20. There are many ions that enter the trench 22 and WJM the sidewall 22c of the trench 22. Therefore, fine roughness is likely to occur on the side wall 22c, and the 3i oxide film 2 formed on the side wall
4's dielectric strength deteriorates. (b) Shoulder 22 of trench 22
d and corner portions 22b of the bottom portion 22a, the thickness of the S1 oxide film 24 formed is thinner than in other portions, causing leakage.
2d and the bottom portion 22a, when a voltage is applied after the formation of the trench capacitor, electric field concentration occurs, causing leakage. (d) After the trench 22 is formed, when high-temperature heat treatment associated with the manufacturing process is performed, crystal defects are generated due to stress at the angular corner portions 22b of the bottom portion 22a.

Among the problems caused by the angularity of the shoulder 22d of the trench 22 and the corner portion 22b of the bottom 22a,
It has been confirmed through experiments that the corner portion 22b of the bottom portion 22a can be rounded relatively easily by once forming an S1 oxide film before the step (C) and then peeling it off. , it is possible to solve this problem. However, it was difficult to round the shoulder 22d. - (Problem to be solved by the invention) When a relatively deep groove or hole is drilled in a material to be etched using a dry etching method, the upper shoulder part becomes angular and fine roughness occurs on the side wall. However, if a device such as a capacitor is constructed in the groove or hole, there are problems in that the dielectric strength deteriorates and leakage current increases.

The present invention has been made based on the above-mentioned circumstances, and an object of the present invention is to provide a dry etching method capable of rounding the upper shoulder portion of the etched area such as a groove or hole, and preventing roughening of the side wall. purpose.

[Structure of the Invention] (Means for Solving Problem 1) In order to solve the above problem, the present invention provides a method in which a material to be etched is activated by plasma in a vacuum container equipped with a pair of parallel plate electrodes. A reactive gas containing a component that generates active species to be etched and a component that forms a deposited film on the surface of the material to be etched is introduced, and high-frequency power is applied between the parallel plate electrodes to induce plasma. A dry etching method in which a material to be etched, on which a mask pattern is formed and placed on one of the parallel plate electrodes, is etched by the generated active species, wherein both components in the reactive gas are removed at the initial stage of etching. At the initial stage of etching the material to be etched, the etching parameters including the mixing ratio, total gas pressure, total gas flow rate, temperature of the material to be etched, and frequency power to the etched material are set to required values, and the deposition fall is set to the required amount of deposition. The main etching step comprises: an etching step; and a main etching step of etching the material to be etched by reducing the amount of the deposited film compared to the initial etching step by changing at least one of the etching parameters. do.

(Function) In the above structure, during the initial etching step, more deposited film a is deposited than during the main etching step, and the shoulder portion at the top of the region to be etched, such as the groove, is etched into a rounded shape.

In addition, in the main etching process that follows the initial etching process, by setting the gas pressure, which is one of the etching parameters, as low as on the same order as in the initial etching process, the gas is obliquely incident on the area to be etched and impacts the side wall. Ions are reduced and fine roughness on the sidewalls is prevented.

(Example) Hereinafter, an example of the present invention will be described with reference to FIGS. 1 to 4.

First, the dry etching apparatus applied to this embodiment will be explained using FIG. In the figure, 1 is a vacuum vessel, and a first electrode (cathode) 2 is attached to the lower part of the vacuum vessel 1 insulated from the vacuum vessel 1, and a first Ti electrode has a cooling mechanism. , for example, water cooling pipes 3a, 3b
is provided. A second electrode (anode) 4 is attached to the upper part of the vacuum vessel 1, and the first and second electrodes 2.4 constitute a pair of parallel plate electrodes. The second electrode 4 is grounded together with the vacuum container 1, and the first
A high frequency power source 6 is connected to the electrode 2 via a matching circuit 5. 7 is a gas inlet port for a reactive gas, 8 is an exhaust port, and the exhaust port 8 is connected to a vacuum pump (not shown). Reference numeral 9 denotes a magnet assembly for generating magnetron plasma, which is formed into a disk shape.

Then, a material to be etched 10 is placed on the first electrode 2, and high frequency power generated by a high frequency power source 6 is applied between the first and second IFi electrodes 4 via a matching circuit 5. Ru. On the other hand, a constant amount of reactive gas It is introduced into the vacuum container 1 from the gas introduction lower, and is evacuated by a vacuum pump connected to the exhaust port 8 to maintain a predetermined gas pressure. Furthermore, a magnetic field B which is perpendicular to the electric field E induced by the high frequency power is generated by the magnet assembly 9 disposed outside the second electrode 4.
is given. As a result, magnetron discharge occurs near the first electrode 2 and magnetron plasma, which is high-density plasma, is generated.

In this example, the maximum magnetic field strength near the material to be etched 10 by the magnet assembly 9 is set at approximately 100 Gauss, but in order to generate a high density plasma, the maximum magnetic field strength is set at approximately 100 Gauss.
0 Gauss or more is required, and in order to improve the uniformity of etching, it is preferably about 300 Gauss or less. In order to further improve the uniformity of etching, the disc-shaped magnet assembly 9 is eccentrically rotated by an eccentric shaft 9a.

A large amount of ions are extracted from the high-density plasma thus generated by the cathode drop voltage (Vdc) induced on the surface of the first electrode 2, and are irradiated onto the material 10 to be etched to perform etching. Here, the gas pressure of the reactive gas is lower than 10' to 10-2 Torr used in a normal reactive ion etching apparatus, and is set to 8
By keeping the etching temperature above X10-4 Torr and 1xlO-2 Torr without vortex, the chances of the ions colliding with neutral molecules and atoms while reaching the material 10 to be etched are reduced, and the ions are transferred to the wafer which is the material 10 to be etched. can be drawn perpendicular to the surface of the

As a result, the number of ions bombarding the side surfaces of the grooves, etc., which are the regions to be etched, is reduced, and grooves, etc. without side surface roughness are formed.

Next, specific steps of the dry etching method according to this embodiment will be explained.

First, using (a) to (e) in Fig. 2, we will explain how the etching progresses when etching and deposited film occur simultaneously on the wafer, which is the material to be etched 10. A) to (e) will be explained in order.

0> Due to the impact of the ions 13, the etching of the trench 11 progresses in the vertical direction according to the pattern of the mask 12. (b) Unlike the etching species ions 13, the It deposition species are neutral active species 14 and have no directionality, so that as long as the trench 11 is shallow, a deposited film is formed uniformly over the entire surface. (c) However, the deposited film on the surface of the mask 12 and the bottom of the trench 11 that is bombarded with ions is removed by sputtering, and the 111 film 15 remains only on the side wall of the trench 11. (d) The deposit 11115 remaining on this side wall is
It acts as a mask for the next incident ions 13,
The opening of trench 11 is substantially narrowed. (e) Then, while repeating the steps (2) to (■) above, the trench 11 is
As the etching progresses, a taper is formed on the side wall of the trench 11. In FIG. 2(e), the shape of the side wall is shown as a step, but in reality, the above-described deposition and etching reactions occur simultaneously, so that the side wall has a smooth tapered shape. In this embodiment, such deposition is caused to occur more often at the initial stage of etching, that is, when etching the upper part of the first trench 11, so that the shoulder portion of the trench 11 is etched to have a relatively large taper. Thereafter, by appropriately changing the etching parameters, the deposition is reduced and the etching progresses.

Next, using the dry etching apparatus shown in FIG. 1,
Chlorine C1 as a gas component that produces etching active species
2. Silicon tetrachloride 5iC as a gas component forming the deposited film
An example of performing trench etching on a single crystal Si substrate, which is the material to be etched 10, using a mixed gas consisting of I4 will be described with reference to FIGS. 3(a) and 3(b).

FIG. 3(a) shows the etched shape of the trench 11 when etching (main etching) is progressed with the etching parameters set as follows.

In other words, the setting conditions are a mixed gas of 85% CI2 and 15% 5iC14 at 7.5 x 10'T.
The temperature of the cooling water for the first electrode 2 (temperature of the material to be etched) was 10° C., and the high frequency power applied between the parallel plate electrodes 2.4 was 800 W. At this time, the etching rate for the material 10 to be etched is approximately 1 μm/
min.

The selectivity with respect to the SiM film that is the material of the mask 12 is approximately 15.
Met.

When etching is performed under such etching conditions, a deposited film 15 is formed on the side wall 11a of the trench 11, a slight taper is formed, and ions bombarding the side wall 11a are reduced, resulting in a trench 11 without side wall roughness. It is formed.

As described above, in this embodiment, at least one of the etching parameters described above is changed at the initial stage of the main etching, and the amount of deposited l1115 is increased to round the shoulder portion of the trench 11. The purpose is to give it a certain tinge.

FIG. 3(b) shows the etched shape of the trench 11 when initial etching is performed for 30 seconds at the initial stage of etching with the etching parameters set as follows.

That is, the setting conditions for the initial etching are (a) addition amount of 5tC14 = 15% to the mixed gas during the main etching, and (b) gas pressure crab 5X 10' Torr.
r, (A> illi1m electric crab 600W1 (
d) Cooling water temperature was set at 5°C. These setting conditions are all changed in a direction that causes more deposition compared to the setting line ft during the main etching. Of the above etching parameters, changing the cooling water temperature requires a little more time, but changing the other etching parameters requires less time.
This is an effective method for setting initial etching conditions for a relatively short period of time.

The effects of each of the above condition settings (a) to (d) will be explained. In (a), a large amount of deposited film is produced by increasing the amount of the gas component that forms the deposited film. (B) is a fact revealed from experiments, and it is thought that this is because the lower the gas pressure, the fewer ions are incident diagonally into the trench 11, and the phenomenon of removing the deposited film by impacting the sidewalls is reduced. .

(c) By lowering the energy of incident ions, sputtering, which is the removal effect of the deposited v4FA, is reduced. A similar effect can also be obtained by lowering the energy of the ions by increasing the magnetic field. (
D) is that the removal effect of the deposited film is reduced, and this can be practically set as the initial etching conditions by adopting the following aspect.

That is, to explain this using FIGS. 4(a) and 4(b), as shown in FIG. A plate-shaped material 16, such as AI, having a heat capacity of .

Normally, the temperature of the material 10 to be etched reaches a steady state immediately after the start of etching, as shown by the characteristic line 17a in FIG. 4<b>. However, if the structure shown in FIG. 4(a) is adopted, the heat conduction between the material to be etched 10 and the first electrode #42 is obstructed by the plate-like material 16, and it takes a long time to reach a steady state. It takes time, and during this time the temperature changes slowly (17b). Therefore, by setting the amount of cooling water in advance so that 1rSlx when the steady state is reached becomes the condition for the main etching, the temperature of the monthly etching target 10 during the initial etching can be set as shown in the characteristic line 17c. It becomes possible to easily set it to a low value.

Therefore, during the initial etching, by changing the etching parameters as described above to increase the amount of deposited film 15, (1) the etching taper is increased, as shown in FIG. 3(b).
The shoulder 11b of the trench 11 can be rounded as shown in FIG.

Note that the present invention is not limited to the above-mentioned embodiments; for example, the reactive gas is basically a mixed gas of a component that causes etching and a component that causes deposition;
Etching products (gases) can also be used as deposition gases. As a result of this fact, in the above-mentioned embodiment, almost the same effects as in the above-mentioned embodiment can be obtained by setting the conditions for using only chlorine gas C12.

Gas components for etching include those containing halogen elements such as chlorine and fluorine, and gas components for deposition include carbon, hydrogen, and 70 carbon CFx (X=1~
4) can be used. Furthermore, it is of course possible to use a gas that simultaneously produces etching and ifiM with one gas. However, depending on the type of gas used,
The conditions for increased deposition are different. For this reason, the manner in which the etching parameters are changed during the initial etching is not constant, and it is necessary to find conditions in which the amount of deposition increases and the etching shape becomes tapered for each gas.

Furthermore, as the material to be etched, Ge other than 3i,
Semiconductor materials including compound semiconductors such as lnP and GaAs,
S! 02, S! Insulators or high dielectric materials such as 3N4, AI
, MoSi2, or other metals or metal compounds.

Furthermore, when this invention is applied to etching wiring materials such as AI films, the shoulders become rounded, so the F
When depositing the insulating film on the layer, it is possible to form a film with good coverage, prevent cracks and cavities from forming in the insulating film, and improve the reliability of the wiring. moreover,
The present invention can also be applied to rounding the bottom corner of a region to be etched, such as a trench, by changing the conditions of only the etching shape.

[Effects of the Invention] As explained above, according to the present invention, the amount of deposited film is larger during the initial etching shape than during the main etching process, so that the upper shoulder portion of the etched region such as the groove is In addition, during the main etching process following the initial etching process, even if the gas pressure, which is one of the etching parameters, is set to the same order of magnitude as the initial etching process, the other etching parameters will be lower. Due to this change, the amount of deposited V4 film can be reduced compared to the initial etching process, and by setting the gas pressure low in this way, ions that enter the etched area obliquely and bombard the sidewalls are reduced. This has the advantage of preventing side walls from becoming rough. Therefore, when a device such as a capacitor is formed in a groove formed by etching, the dielectric strength can be improved and leakage current characteristics can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram showing an example of a dry etching apparatus applied to an embodiment of the dry etching method according to the present invention;
FIG. 2 is a process diagram for explaining the progress of etching when etching and deposited film occur simultaneously on the material to be etched, and FIG. 3 is a longitudinal cross-sectional view showing an example of a trench formed in an embodiment of the present invention. , FIG. 4 is a diagram for explaining an example of changing the temperature of the material to be etched, which is one of the etching parameters, and FIG. 5 is a diagram showing the manufacturing process of a trench capacitor using a conventional dry etching method. It is a diagram. DESCRIPTION OF SYMBOLS 1: Vacuum vessel, 2: First electrode, 4: Second electrode constituting a parallel plate electrode together with the first electrode, 6: High frequency power supply, 7: Gas inlet, 10: Material to be etched, 11: To be etched. A trench, 11b, is an example of an etching region.
= rounded trench shoulder, 12: mask, 15: deposited film.

Claims (1)

[Claims] A component that is activated by plasma to generate active species that etch the material to be etched and a component that forms a deposited film on the surface of the material to be etched are placed in a vacuum container equipped with a pair of parallel plate electrodes. introducing a reactive gas containing and applying high frequency power between the parallel plate electrodes to induce plasma;
A dry etching method for etching a material to be etched on which a mask pattern is formed and placed on one of the parallel plate electrodes using the active species generated by the plasma, the dry etching method comprising: The etching parameters including the mixing ratio of both components in the reactive gas, the total gas pressure, the total gas flow rate, the temperature of the material to be etched, and the high frequency power are set to required values, and the material to be etched is set to the required amount of deposited film. an initial etching step in which the material to be etched is etched; and a main etching step in which the material to be etched is etched by changing at least one of the etching parameters to reduce the amount of the deposited film than in the initial etching step. A dry etching method characterized by: