JPH06291096A - Manufacture of semiconductor device - Google Patents

Abstract

PURPOSE:To form a hole like a through hole in an insulating film like an layer insulating layer, the diameter of which hole becomes larger as it approaches the layer surface. CONSTITUTION:When a hole 7 is formd in an interlayer insulating layer 3 by reactive ion etching the diameter of which becomes larger as it approaches the layer surface, etching is performed while etching condition is changed as follows; the condition that the etching mainly progresses in an isotropic manner is changed intermittently or continuously to the condition that the etching progresses in an anisotropic manner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device in which an insulating film such as an interlayer insulating layer is formed with a hole such as a through hole having a larger hole diameter toward the front side.

[0002]

2. Description of the Related Art Conventionally, a hole such as a through hole, a contact hole or a via hole formed in an insulating film such as an interlayer insulating layer of a semiconductor device (simply called a hole).
In order to improve the adhesion of the conductor to its inner wall,
It is known that it is necessary to increase the pore diameter toward the surface side. That is, conventionally, a hole formed in an insulating film of a semiconductor device is formed in a taper shape in which the hole diameter gradually increases toward the front surface side, or in a shape in which the hole diameter increases stepwise toward the front surface side. Next, a method of manufacturing the hole of such a conventional semiconductor device will be described.

FIG. 3 shows a manufacturing process according to the first method.
As shown in FIG. 3, first, a wiring metal layer 2, an interlayer insulating layer 3 and a photoresist film 4 are sequentially provided on the semiconductor substrate 1, and then a hole 4a is formed at a position corresponding to the hole of the photoresist film 4. (Step (a)). Then, the photoresist film 4 is heat-treated to form the hole 4a into a tapered hole 4b having a large hole diameter on the surface side, and in this state, the interlayer insulating layer 3 is anisotropically etched (step (b)). By this anisotropic etching, the interlayer insulating layer 3 is etched while the hole diameter of the hole 4b of the photoresist film 4 is increased,
A hole 5 having a tapered inner wall is formed in the interlayer insulating layer 3 (step (c)).

FIG. 4 shows a manufacturing process according to the second method.
As shown in FIG. 4, the interlayer insulating layer 3 provided on the wiring metal layer 2 on the semiconductor substrate 1 is formed by the lower layer film 3A which is difficult to be etched and the upper layer film 3B which is easily etched (step (a)). Next, a photoresist film 4 is provided on the interlayer insulating layer 3, holes 4a are formed at positions corresponding to the holes in the photoresist film 4, and then the interlayer insulating layer 3 is subjected to isotropic etching (step (b )). At this time, since the upper layer film 3B is more easily etched in the radial direction than the lower layer film 3A, a hole 5 having a larger hole diameter is formed in the interlayer insulating layer 3 toward the surface side (step (c)).

As a third method, there is a method of performing isotropic etching by a wet etching method using buffered hydrofluoric acid, and then performing anisotropic etching by a plasma etching method.

[0006]

As described above, in the conventional case, when the hole diameter of the hole formed in the insulating film is increased toward the surface side, the pattern forming step in the photoresist film is performed as in the first method. In addition, one more step must be added, or the insulating film must be formed of two layers of different types as in the second method, and there is a problem that the number of steps is increased and becomes complicated. Further, the third method has problems that the side etch amount is too large due to the etching film thickness and the etching controllability is poor.

In view of such circumstances, an object of the present invention is to
It is an object of the present invention to provide a method of manufacturing a semiconductor device in which a hole such as a through hole having a larger hole diameter on the surface side is formed in an insulating film such as an interlayer insulating layer.

[0008]

In order to achieve such an object, the method of manufacturing a semiconductor device of the present invention is characterized in that etching conditions are set when forming a hole having a larger hole diameter on the surface side in an insulating film by reactive ion etching. It is to perform etching while changing intermittently or continuously from a condition in which the etching mainly proceeds isotropically to a condition in which the etching mainly proceeds anisotropically.

Here, as a method of changing the etching conditions, a main reaction gas and an additive gas added thereto are used for etching, and the etching conditions are changed by changing the addition conditions of the additive gas, or A method of changing the etching condition by changing the pressure in the etching chamber can be used. In addition,
Examples of the method of changing the pressure in the etching chamber include a method of adjusting the flow rate of gas introduced into the etching chamber and a method of adjusting the ability to exhaust the inside of the etching chamber.

[0010]

In the method of manufacturing a semiconductor device of the present invention, since the etching mainly proceeds isotropically in the initial stage of etching,
The insulating film is etched not only in the depth direction but also in the radial direction.
On the other hand, if the etching mainly progresses anisotropically thereafter, the insulating film becomes difficult to be etched in the radial direction.
Therefore, in the insulating film, a hole having a larger hole diameter is formed on the surface side.

This action will be specifically described by taking dry etching using CF ₄ gas as an example. In the dry etching with CF ₄ gas, as shown below, a reaction of F radicals (F ^* ) with Si by CF ₄ discharge occurs CF ₄ → F ^* , CF ₃ ^* , CF ₂ ^* , CF ^* , C ^* Si + F ^* → SiF _{4 In} such dry etching, there is a phenomenon that addition of a small amount of additional gas affects the etching rate. This is because the activation energy of the reaction can be greatly changed by adding a small amount of additional gas. For example, CF ₄
In the case of + O ₂ , F is generated due to the generation of CO, CO ₂ and COF _2.
The amount of radicals (F ^* ) generated increases, and Si, SiO ₂ , S
It is considered that the etching rate of iON and the like increases. Then, due to the increase in the etching rate, an undercut easily occurs, and the insulating film is etched not only in the depth direction but also in the radial direction. Note that when the addition of the additional gas is stopped, the etching rate decreases and the insulating film is less likely to be etched in the radial direction.

By the way, in dry etching,
Phenomena other than plasma chemistry coexist and plasma sputter composite etching occurs. Sputter etching is etching by a physical effect that particles having kinetic energy are incident on a solid surface, and this sputter effect is generated by particles having a certain amount of kinetic energy. In addition to the high-frequency electric field used for plasma excitation, the sputtering effect includes a direct-current electric field applied from the outside and a direct-current electric field due to self-bias of electrodes generated in the apparatus during high-frequency discharge.

In the parallel plate type dry etching apparatus,
It is known that the shape of the etching cross section is changed by changing the gas pressure (= pressure in the etching chamber). When the gas pressure is increased, the undercut becomes large, and when the gas pressure is decreased, the electric field direction, that is, the The etching has sharp directivity along the charged particle collision direction, resulting in a sharp cross-sectional shape. At high gas pressure, it is considered that particles with kinetic energy lose their kinetic energy due to collision between particles in the discharge space, and etching is mainly due to plasma chemistry and ion chemical reaction. It is considered that at low gas pressure, particles enter the surface without losing kinetic energy, so that the sputtering effect is effective and the etching becomes directional (anisotropic etching).

Therefore, the insulating film is etched not only in the depth direction but also in the radial direction by adjusting the gas flow rate and the ability to exhaust the inside of the etching chamber, and when the gas pressure is high, the insulating film is etched in the radial direction as well as the depth direction. The film is less likely to be etched in the radial direction.

[0015]

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

FIG. 1 is a sectional view showing a manufacturing process of an embodiment of a method of manufacturing a semiconductor device of the present invention. As shown in FIG. 1, first, a wiring metal layer 2, an interlayer insulating layer 3 and a photoresist film 4 are sequentially provided on a semiconductor substrate 1, and then a hole 4a is formed at a position corresponding to the hole of the photoresist film 4. (Step (a)). Next, the interlayer insulating layer 3 is subjected to reactive ion etching under the condition that the etching proceeds isotropically. Under this condition, etching is likely to occur not only in the depth direction but also in the radial direction.
A recess 6 is formed which is wider in the radial direction than the hole diameter of a (step (b)). Subsequently, during the etching, the etching conditions are set so that the etching proceeds anisotropically. Under this condition, it becomes difficult for the etching to proceed in the radial direction, and the etching mainly proceeds in the depth direction. Therefore, in the interlayer insulating layer 3, a hole 7 having a larger hole diameter on the front surface side and a smaller hole diameter on the back surface side as a whole is formed (step (c)). Finally, the photoresist film 4 is removed by O ₂ plasma ashing or the like (step
(d)). After that, carry out the desired steps based on the usual method,
A semiconductor device is manufactured. Next, a more specific example will be described.

As a first specific example, the interlayer insulating layer 3 is a SiON film having a film thickness of 8000Å formed by plasma CVD (Chemical Vapor Deposition), and an inner wall is formed on the SiON film by using a parallel plate type reactive ion etching apparatus. An example in which a tapered hole is formed will be described.

An example of the parallel plate type reactive ion etching apparatus is shown in FIG. As shown in FIG. 2, a flat plate-shaped anode 12 and a cathode 13 are arranged in parallel in the etching chamber 11 so as to face each other. The cathode 13 has a high-frequency power source via a matching circuit 14 having a blocking capacitor. 15 is connected. Etching room 1
1 has a reaction gas introduction port 11a and an exhaust port 11b,
These reaction gas inlet 11a and exhaust port 11b are
A reaction gas introduction system and an exhaust system (not shown) are connected to each other.

Further, on both sides of the etching chamber 11, a load side preliminary exhaust chamber 16 for introducing a wafer and an unload side preliminary exhaust chamber 17 for discharging the wafer are provided, each of which is not shown in FIG. The air is exhausted by the system, and a load port 18 and an unload port 19 are provided on each boundary wall. The wafer 20 to be etched is placed on the cathode 13.

A wafer to be etched (in the state of step (a) in FIG. 1) is placed on the cathode 13 of such an apparatus. Then, CF ₄ gas as a main reaction gas is supplied from a reaction gas introduction system (not shown) through the reaction gas introduction port 11a.
0 sccm and 5 sccm of O ₂ gas as an additive gas are introduced into the etching chamber 11, and the etching chamber 11 is exhausted through an exhaust port 11b by an exhaust system (not shown) so that the pressure in the etching chamber 11 becomes 15 Pa. Adjust to. Next, the cathode 13 is set to 1
A high frequency power of 3.56 MHz is applied at 0.16 W / cm ² , and etching is started. Under these etching conditions,
The etching proceeds isotropically, and as shown in step (b) of FIG. 1, the etching proceeds to form a recess 6 in the interlayer insulating layer 3 that is wider than the hole diameter of the hole 4a in the radial direction. Under this condition, the SiON film is etched to a thickness of about 4000Å, and then the introduction of O _{2 as} an additive gas is stopped. Under this condition, the isotropy of etching is weakened as compared with the introduction of O ₂ , and the etching progresses anisotropically. As a result, etching progresses as shown in step (c) of FIG.
A tapered hole 7 having a larger hole diameter on the surface side is formed in the interlayer insulating layer 3. In this example, the holes 4a formed in the photoresist film 4 have a hole diameter of 1.0 μm, and the interlayer insulating layer 3 has a hole diameter of 1.5 μm on the front surface side and a hole diameter of 1.0 μm on the back surface side. 7 was formed.

As a second specific example, an example in which the etching conditions are changed by changing the pressure in the etching chamber will be described. This specific example also uses the parallel plate type reactive ion etching apparatus shown in FIG. 2, and the same S as in the first specific example is used.
A hole is formed in the iON film.

First, as in the first specific example, a wafer to be etched (in the state of step (a) in FIG. 1) is placed on the cathode 13, and then the reaction gas introduction port 11a is used. CF ₄ gas of 95 sccm as a reaction gas is introduced into the etching chamber 11, and the etching chamber 11 is evacuated through the exhaust port 11b to adjust the pressure in the etching chamber 11 to 25 Pa. Next, the high frequency power supply 15
As a result, a high frequency power of 13.56 MHz is applied to the cathode 13 at a level of 0.
16 W / cm ^{2 is} applied to start etching. Under this etching condition, the etching proceeds isotropically as shown in step (b) of FIG. 1, and a recess 6 is formed in the interlayer insulating layer 3 so as to be wider than the diameter of the hole 4a in the radial direction. After etching the SiON film to a thickness of about 4000Å under these conditions, the pressure in the etching chamber 11 is set to 7 Pa by reducing the amount of CF ₄ introduced or increasing the amount of exhaust. Under this condition, the isotropy of etching is weakened and the etching progresses anisotropically as compared with the case where the pressure is 25 Pa. As a result, etching as shown in step (c) of FIG. 1 progresses, and a tapered hole 7 having a larger hole diameter on the surface side is formed in the interlayer insulating layer 3. In this specific example, the hole diameter of the holes 4a formed in the photoresist film 4 is 10
When the thickness was set to μm, a hole 7 having a hole diameter of 1.6 μm on the front surface side and a hole diameter of 1.0 μm on the back surface side was formed.

As described above, according to the method of the present invention, by changing the etching conditions in the middle of the etching process without drastically changing the manufacturing process for forming holes perpendicular to the insulating film, the hole diameter in the insulating film can be changed. It is possible to form a larger hole on the surface side.

In the above-mentioned embodiment, the etching condition is intermittently changed to two steps, but it may be intermittently changed to three steps or more or gradually and continuously, and the etching condition is changed. The method is also not limited to the above. Furthermore, it is not always necessary to change the etching conditions during the etching, and the shape of the holes is not limited to the above.

[0025]

As described above, according to the method for manufacturing a semiconductor device of the present invention, the etching condition of the reactive etching is changed so that the etching is mainly anisotropic. It is possible to form a hole having a larger hole diameter on the front surface side in the insulating film by changing the state to a state in which the hole advances.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing main steps of an embodiment of a method for manufacturing a semiconductor device of the present invention.

FIG. 2 is a schematic view of a parallel plate type reactive ion etching apparatus used in an embodiment of the present invention.

FIG. 3 is a cross-sectional view showing a process example of a method for manufacturing a semiconductor device according to a conventional technique.

FIG. 4 is a cross-sectional view showing a process example of a method for manufacturing a semiconductor device according to a conventional technique.

[Explanation of symbols]

 1 semiconductor substrate 2 wiring metal layer 3 interlayer insulating layer 4 photoresist film 7 holes

Claims (5)

[Claims] 1. When forming a hole having a larger pore size on the surface side in an insulating film by reactive ion etching,
A method of manufacturing a semiconductor device, wherein etching is performed while intermittently or continuously changing the etching condition from a condition in which the etching mainly proceeds isotropically to a condition in which the etching mainly proceeds anisotropically. 2. The method of manufacturing a semiconductor device according to claim 1, wherein a main reaction gas and an additive gas added thereto are used for etching, and the etching condition is changed by changing the addition condition of the additive gas. A method for manufacturing a characteristic semiconductor device. 3. The method of manufacturing a semiconductor device according to claim 1, wherein the etching condition is changed by changing the pressure in the etching chamber. 4. The method of manufacturing a semiconductor device according to claim 3, wherein the pressure in the etching chamber is adjusted by adjusting the flow rate of gas introduced into the etching chamber. 5. The method of manufacturing a semiconductor device according to claim 1, wherein the pressure inside the etching chamber is adjusted by adjusting the ability to exhaust the inside of the etching chamber.