JPH09209138A - Sputtering method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form aluminum films free from breaks between the flanks and base of recessed parts by executing the impression of a low voltage after the impression of a high voltage at the time of sputtering aluminum electrode films on an integrated circuit wafer having a perpendicular difference in level on the surface. SOLUTION: The sputtering quantity to the surface and recessed parts of the wafer is increased by the sputtering to impress the high voltage using a film forming device having a power source of the variable impressed voltages at the time of executing the sputtering. The sputtering to impress the low voltage having the decreased perpendicular components is then executed to increase the aluminum changed in the flying direction by the bombardment of the sputtered aluminum and gaseous argon, by which the aluminum is adhered to the flanks of the recessed parts. At this time, a period for increasing the impressed voltage before the impression of the high voltage continued for the specified period is disposed and the period for decreasing the low voltage to be shifted to the impression of the low voltage continued for the specified period after the impression of the high voltage is disposed. The ratio of the high voltage to the low voltage is specified to >=1.3.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering method used for manufacturing a semiconductor device having a step on its surface.

[0002]

2. Description of the Related Art With the miniaturization of semiconductor devices and the improvement in the degree of integration, it is necessary to make the surface three-dimensional and to increase the surface area. For this reason, a step is made large in the vertical direction, and this step is also made vertical so that the vertical surface is also used as a surface layer.

An example of the sputtering apparatus used for forming the electric wiring on the surface layer having the step will be described with reference to FIG.

In the figure, 61 is a vacuum vessel, 62 is an anode having a flat upper surface 62a disposed below the vacuum vessel 61,
Reference numeral 63 denotes an integrated circuit wafer having a step (not shown) on the surface placed with the surface on which the film is formed on the upper surface of the anode 62 facing upward, and 63a denotes near the center of the integrated circuit wafer 63, and 63a.
b is near the left end of the integrated circuit wafer 63. Reference numeral 64 is an aluminum target larger than the integrated circuit wafer 63, which is arranged parallel to the upper surface 62a of the anode and is separated by a predetermined distance.
64a is near the center of the aluminum target, 64b is near the left end of the aluminum target, and 64c is near the right end of the aluminum target. 65 is the target 6
4, a target holder (not shown, which has a separate drainage pipe for cooling water) that holds 4 in close contact with the cooling water flowing from the water supply pipe 65a to cool the aluminum target 64.
And is the cathode.

66 is a vacuum container 61 and a target holder 6
An insulating ring for insulating between 5 and 67 is a target holder 6
5, a shield plate for preventing discharge between the vacuum container 61 and the vacuum container 61, 68
Is an electromagnet for confining the plasma between the anode 62 and the cathode 65. Reference numeral 69 is an exhaust pipe provided under the vacuum container 61 and connected to an exhaust pump (not shown), and reference numeral 70 is a gas pipe for supplying argon gas to the vacuum container 61.

A method of operating this device will be described below. First, the surface of the aluminum target 64 and the anode 62 are disposed in parallel with each other with a distance of approximately 65 mm. Next, the exhaust pipe 69
After being evacuated with a vacuum pump, argon gas is supplied from the gas pipe 70 and kept at 10 −2 Torr. Then,
Cooling water is caused to flow through the target holder 65. Subsequently, the electromagnet is energized to apply a constant voltage between the target holder 65 and the anode 62 for a certain time.

Using the sputtering apparatus of FIG. 2, the state of formation of a vapor deposition film by sputtering in the vicinity of the central portion (63a in FIG. 2) of an integrated circuit wafer having a vertical step on the surface of a semiconductor wafer is shown in FIGS. It will be described from b).
At this time, description will be made with reference to FIG. 2 as well.

In FIG. 3A, reference numeral 1 is an integrated circuit wafer, 2 is a central portion of the integrated circuit wafer 1 (63 in FIG. 2).
In the concave portion vertically formed by dry etching in a), the depth from the integrated circuit wafer surface 1a to the bottom surface 2a of the concave portion is 1 μm, and the width between the left side surface 2b and the right side surface 2c of the concave portion is 1 μm.
μm and 3 are aluminum electrodes having a thickness of 0.8 μm formed by sputtering, and the side faces 2b and 2c of the recess become thinner as they approach the bottom face 2a of the recess. The bottom surface 2a of the recess is thickest in the middle portion and becomes thinner as it approaches the side surfaces 2b, 2c of the recess. In addition, the left side protruding portion 3 in which the aluminum electrode 3 protrudes most inside the recess 2 above the recess 2
a and the right protrusion 3b are formed. In the vicinity of the boundary 2d between the bottom surface 2a of the recess and the side surfaces 2b, 2c of the recess, the aluminum electrode 3 is very thin and sometimes is not connected.

By sputtering, the aluminum electrode in the recess 2 near the center 63a of the integrated circuit wafer 63 is shown in FIG.
The reason for forming as shown in (a) will be described. Aluminum vertically sputtered from the vicinity 64a of the center of the aluminum target forms an aluminum electrode in the vicinity 63a of the center of the integrated circuit wafer. Vertically sputtered aluminum forms aluminum electrodes 3 on the surface 1a of the integrated circuit wafer and on the bottom surface 2a of the recess. Part of the aluminum that has flown into the recess 2 collides with argon ions, changing the flight direction and changing the side surface 2 of the recess.
A thin aluminum electrode 3 is formed on b and 2c.

Since most of the aluminum sputtered in the oblique direction travels linearly, as it goes from the left end vicinity 64b to the center vicinity 64a of the aluminum target depending on the position where the aluminum jumps out, the vicinity of the surface 1a of the right side surface 2c of the recess is close. The aluminum electrode 3 is formed from only to the deep position in the direction of the bottom surface 2a. The aluminum electrode 3 is not formed on the right side surface 2c of the recess in the component that goes straight from the right end vicinity 64c to the center vicinity 64a of the aluminum target. However, part of the aluminum collides with argon ions, changes the flight direction, and adheres to the shadow of the recess 2. A similar aluminum electrode 3 is formed on the left side surface 2b of the recess for the same reason.

Next, the formation state of the aluminum electrode in the recess having a wide opening will be described with reference to FIG. 3 (b). FIG.
In (b), 11 is an integrated circuit wafer, 12 is a recess formed vertically in the vicinity of the central portion of the integrated circuit wafer 11 (63a in FIG. 2) by dry etching, from the integrated circuit wafer surface 11a to the bottom surface 12a of the recess. The depth is 1μ
m, the width between the left side surface 12b and the right side surface 12c of the recess is 2
μm, 13 is 0.8 μm thick formed by sputtering
With the aluminum electrode of, the side surfaces 12b and 12c of the recess become thinner as they approach the bottom surface 12a of the recess. Also,
The bottom surface 12a of the recess has the thickest middle portion and the side surface 12 of the recess.
It becomes thinner as it gets closer to b and 12c. Also, the recess 1
A left side protruding portion 13a and a right side protruding portion 13b where the aluminum electrode 13 protrudes most inside the concave portion 12 are formed above 2. The bottom surface 12a of the recess and the side surface 12 of the recess
The aluminum electrode 13 is very thin near the boundary 12d between b and 12c, and sometimes it is not connected. However, it is less likely to occur than in the case of FIG.

By sputtering, the aluminum electrode in the recess 12 near the center 63a of the integrated circuit wafer 63 is shown in FIG.
The reason for forming as shown in (b) will be described. Aluminum vertically sputtered from the vicinity 64a of the center of the aluminum target forms an aluminum electrode in the vicinity 63a of the center of the integrated circuit wafer. Vertically sputtered aluminum forms aluminum electrodes 13 on the surface 11a of the integrated circuit wafer and on the bottom surface 12a of the recess. Part of the aluminum that has flown into the recess 12 collides with argon gas to change the flight direction and form thin aluminum electrodes 13 on the side surfaces 12b and 12c of the recess.

Since most of the aluminum sputtered in the oblique direction advances linearly, the position where the aluminum jumps out is near the left end 6 of the aluminum target.
As the aluminum protrudes from 4b toward the center 64a, the aluminum electrode 13 is formed from only the vicinity of the surface 11a of the right side surface 12c of the recess to a position deeper in the direction of the bottom surface 12a. The aluminum electrode 13 is not attached to the right side surface 12c of the recess from the right end vicinity 64c to the center vicinity 64a of the aluminum target. However, part of the aluminum collides with the argon gas, changes the flight direction, and adheres to the shadow of the recess 12. A similar aluminum electrode 13 is formed on the left side surface 12b of the recess for the same reason.

However, since the side surfaces 12b and 12c of the recess are wider than those in FIG. 3A, even if the distance from the vicinity 64a of the center of the aluminum target is the same as that of FIG. Aluminum adheres to the side surface 12c closer to the bottom surface 12a of the concave portion to form the aluminum electrode 13. Therefore, the probability that the aluminum electrode 13 is disconnected at the boundary 12d between the bottom surface 12a of the recess and the side surfaces 12b and 12c of the recess is reduced.

This is because the space between the side surfaces 12b and 12c of the recess is large, and thus the aluminum sputtered from the portion closer to the right end 64c of the aluminum target 64 adheres to the left side surface 12b of the recess.
The same applies to the right side surface 12c of the recess.

Here, the depth / width is called an aspect ratio,
This ratio has recently become larger with the miniaturization of integrated circuits and the improvement of the degree of integration, and has become 1 or more. Here, the aspect ratio is 1 in FIG. 3A and 0.5 in FIG. 3B.
It is.

The state of formation of the deposited film by sputtering near the left side of the peripheral portion of the semiconductor integrated circuit wafer having such a vertical step will be described with reference to FIG. At this time, description will be made with reference to FIG. In FIG.
21 is an integrated circuit wafer, 22 is an integrated circuit wafer 21
Is a recess formed vertically by dry etching near the left end of the recess (63b in FIG. 2), the depth from the integrated circuit wafer surface 21a to the bottom surface 22a of the recess is 1 μm, and the left side surface 2 of the recess is
The width between 2b and the right side surface 22c is 1 μm, 23 is an aluminum electrode having a thickness of 0.8 μm formed by sputtering, and the side surfaces 22b and 22c of the recess are thinner as they approach the bottom surface 2a of the recess. Moreover, the thickness of the aluminum electrode 23 on the right side surface 22c is smaller than that of the left side surface 22b at the same depth of the recess 22. The bottom surface 22a of the recess is thickest in the middle portion and becomes thinner as it approaches the side surfaces 22b and 22c of the recess. Further, the aluminum electrode 23 above the recess 22 has the left side protruding portion 23 protruding most inside the recess 22.
a and the right side protruding portion 23b are formed. The aluminum electrode 3 may not be connected in the vicinity of the boundary 22d between the bottom surface 22a of the recess and the side surfaces 22b and 22c of the recess.
At this time, the aluminum electrode 2 on the right side surface 22c of the recess is
3 is thin, and there is a high probability that no connection is made in this part.

The reason why the aluminum electrode 23 in the recess 22 near the left end 63b of the integrated circuit wafer 63 is formed by sputtering as shown in FIG. 4 will be described. Aluminum vertically sputtered from the left end vicinity 64b of the aluminum target is the left end vicinity 6 of the integrated circuit wafer.
An aluminum electrode is formed on 3b. Aluminum electrodes are formed on the surface 21a of the integrated circuit wafer and on the bottom surface 22a of the recess for vertical sputtering. Part of the aluminum that has flown into the recess 22 collides with argon ions and changes the flight direction, so that the side surfaces 2b, 2b of the recess 2
A thin aluminum electrode 3 is formed by c.

Most of the obliquely sputtered aluminum advances linearly. Therefore, the surface 21a of the left side surface 22b of the recess is moved from the right end vicinity 64C to the left end vicinity 64b of the aluminum target due to the position where the aluminum protrudes. Only near the bottom 22a
The aluminum electrode 23 is formed to a position deep in the direction. The aluminum electrode 23 does not adhere to the right side surface 22c of the recess as a straight-ahead component of aluminum from the right end vicinity 64c to the left end vicinity 64b of the aluminum target. However, a part of the aluminum sputtered from the aluminum target 64 to the left end vicinity 64b of the aluminum target collides with the argon gas, changes the sputtering direction, and adheres to the right side surface 22c of the recess in a very small amount to form the aluminum electrode 3. .

However, when the voltage becomes low, the vertical component becomes thin, and the amount of obliquely sputtering increases. In addition, the energy of sputtered aluminum is small, and the sputtering direction is likely to change due to collision with argon atoms. Therefore, the aluminum sputtered from the vicinity of the right end 64c of the aluminum target to the vicinity of the left end 64b is the right side surface 2 of the recess.
The aluminum electrode 23 is formed by adhering also to 2c.

Therefore, at low voltage, both sides 2 of the recess are
Almost equal amounts of aluminum adhere to 2b and 22c to form a film.

Depending on the sputtering material, the voltage with a large amount of vertical component and the voltage with a small amount of vertical component are different, and the ratio of the vertical component is also different.

In this description, the apparatus for sputtering one sheet at a time has been described, but the same applies to the case of sputtering a large number of sheets at one time. The only difference is that the vicinity of the left end of the wafer is the wafer near the left end of the anode.

[0023]

When a film is formed by a sputtering method on an integrated circuit wafer having a concave portion, as shown in FIG.
As shown in (a), when the aspect ratio is increased, the electrode metal in the vicinity of the bottom surface 2a of the side surface 2b becomes thin, and finally there is a problem that the wire is broken.

At a high voltage, more components are vertically sputtered and relatively easily adhere to the bottom surface 2a, but the straightness of the sputtered particles is strong, and the outer side surface of the recess 22 in the outer peripheral portion of the wafer is large. The difference in adhesion between the inner side surface 22c and the inner side surface 22c becomes remarkable.
It becomes extremely thin with c.

Further, at a low voltage, many components are inclined and sputtered, and the energy is small, so that they collide with argon and are scattered, and a large amount of the sputtered substance adheres to the side surface of the concave portion, blocking the opening of the concave portion. There is little adhesion of sputtered material to the bottom of the recess.

Thus, it is quite difficult for sputtering to uniformly cover the entire surface of an integrated circuit having a complicated surface morphology. This is because shadowing occurs where atoms cannot enter the shadow of the protrusion. Particularly, where the shape changes in a stepwise manner, it is an important subject to attach a thin film to the side surface of the staircase, that is, step coverage.

[0027]

DISCLOSURE OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems and has a power supply for variably applying a voltage, and sputtering for forming a film on the surface of a substrate arranged in a vacuum container. Provided is a method for forming a film on a surface of a substrate having a step using an apparatus, in which a low voltage is applied after applying a high voltage.

Further, there is provided a sputtering method having an applied voltage rising period in which the voltage is increased to a high voltage before the high voltage is applied.

Also provided is a sputtering method having an applied voltage decreasing period in which the sputtering voltage is decreased from high voltage application to low voltage application.

Also provided is a sputtering method having an applied voltage lowering period in which a high voltage is applied for a certain period of time and then a low voltage is applied after a fixed period of applied voltage.

Also provided is a sputtering method in which the sputtering voltage is lowered with the passage of time during the applied voltage lowering period.

Also provided is a sputtering method in which the sputtering voltage has a plurality of applied voltage constant periods, and the low voltage applied voltage constant period is followed by the high voltage applied voltage constant period.

Also provided is a sputtering method in which immediately after a high voltage applied voltage constant period, a low voltage applied voltage constant period is entered.

Also provided is a sputtering method in which the ratio of the high voltage to the low voltage is 1.3 or more.

The above terms "high voltage" and "low voltage" are not given by absolute criteria. Depending on the material of the target, the ratio of the components in which the sputtering direction is vertical is different even with the same sputtering voltage, and it is necessary to select the sputtering voltage for each material in order to obtain the appropriate effect.

In any of the materials, the higher the sputtering voltage is, the higher the ratio of vertically sputtered is. Therefore, sputtering is performed at a relatively high voltage in the early stage of film formation and at a lower voltage in a later stage. It means that.

[0037]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows the relationship between sputtering voltage and time according to the present invention when aluminum sputtering is performed with a DC sputtering apparatus. FIG. 1 (a) shows that the aluminum electrode initially has a high voltage A with many vertical components.
Is applied, and sputtering is performed while gradually lowering the voltage, and the voltage is lowered to the low voltage B in the applied voltage lowering period t1 hour.

First, a high voltage A having a large vertical flight component for depositing a sputtering substance on the surface of the integrated circuit wafer and the bottom surface of the recess is applied, and then a low voltage B having a small vertical flight component is gradually applied. By lowering to, the flight component in the vertical direction is gradually reduced. Increased aluminum flying in an inclined direction and sputtered aluminum or aluminum whose flight direction was changed by collision with argon gas was made to adhere to the side surface of the recess, and an aluminum electrode with no break was formed between the side surface and the bottom surface of the recess. Form.

In FIG. 1 (b), initially, a high voltage A with many vertical flight components is applied for a period of t2 for a fixed period of high voltage application, and then the applied voltage gradually decreases to a low voltage B with few vertical components. By gradually lowering over the period (t3 -t2), the flight component in the vertical direction is gradually reduced.
Increased aluminum flying in an inclined direction and sputtered aluminum or aluminum whose flight direction was changed by collision with argon gas was made to adhere to the side surface of the recess, and an aluminum electrode with no break was formed between the side surface and the bottom surface of the recess. Form.

In FIG. 1 (c), a high voltage A with a large amount of vertical flight components is continuously applied for t4 hours for a constant application voltage period, and then a low voltage B with a small amount of vertical flight components is applied. The voltage is applied for a fixed period of time (t5-t4). Increased aluminum flying in an inclined direction and sputtered aluminum or aluminum whose flight direction was changed by collision with argon gas was made to adhere to the side surface of the recess, and an aluminum electrode with no break was formed between the side surface and the bottom surface of the recess. Form.

It is not necessary to apply the above-mentioned high voltage first, and in consideration of the characteristics of the equipment, the applied voltage may be increased in a short time from the low-voltage application to the high-voltage application.

If the ratio of the high voltage to the low voltage is 1.3 or more, the step coverage defect can be effectively reduced.

First, aluminum is deposited on the surface of the integrated circuit wafer and the bottoms of the recesses for a certain period of time with a high voltage having a large vertical flight component, and then a low voltage with a small amount of vertical component is applied for a certain period of time. The tilted and sputtered aluminum is changed in the flight direction by collision with argon ions and attached to the side surface of the recess to form a continuous aluminum electrode between the side surface and the bottom surface of the recess. That is, the step coverage is improved.

The present invention is not limited to aluminum sputtering, but can be applied to other metals and other than metals.

Further, the present invention is not limited to the integrated circuit wafer, but can be applied to those having irregularities on the surface.

The sputtering apparatus is not limited to the DC sputtering apparatus.

[0047]

EXAMPLE An example in which the method of the present invention is applied to aluminum sputtering will be described with reference to FIG. Conventionally, it was applied at 12 kW for 50 seconds. At this time, there was about 2% of characteristic defects due to the problem of step coverage.

On the other hand, when the positional relationship between the aluminum electrode and the integrated circuit wafer is kept substantially parallel with the distance between the aluminum electrode and the integrated circuit wafer at a distance of about 65 mm as in the conventional case, the applied voltage and time of the present invention are changed. Relationship is first 2
A voltage of 0 KV is applied for 5 seconds, and then the voltage is gradually reduced to 10 KV in 30 seconds.

The conventional method for applying a constant voltage had a characteristic defect of 2% due to step coverage, but the voltage applying method of the present example resulted in 0%.

[0050]

According to the present invention, the sputtering voltage is set to a high voltage having a large vertical component to increase the amount of sputtering on the surface of the integrated circuit wafer and the bottom of the recess, and then the sputtering voltage is reduced to a low vertical component. Reduce to voltage. This increases the tilted sputtered aluminum or aluminum whose flight direction has been changed by collision with argon gas, and attaches it to the side surface of the recess to form a continuous aluminum electrode between the side surface and the bottom surface of the recess. Form.

[Brief description of drawings]

FIG. 1 Relationship between sputtering voltage and time according to the present invention

FIG. 2 is a sectional view of a sputtering device.

FIG. 3 is a cross-sectional view of a recess near the center of a conventional integrated circuit wafer.

FIG. 4 is a sectional view of a recess near the left end of a conventional integrated circuit wafer.

[Explanation of symbols]

 A high voltage B low voltage

Claims (8)

[Claims] 1. A method of forming a film on a surface of a substrate having a step using a sputtering apparatus for forming a film on the surface of a substrate arranged in a vacuum container, the method comprising a power source for variably applying a voltage, comprising a sputtering voltage. Is applied after a high voltage is applied, and a low voltage is applied. 2. The sputtering method according to claim 1, further comprising an applied voltage rising period during which the high voltage is applied before the high voltage is applied. 3. The sputtering method according to claim 1 or 2, wherein the sputtering voltage has an applied voltage decreasing period during which the high voltage is applied to the low voltage. 4. The sputtering method according to claim 3, further comprising an applied voltage decreasing period in which the high voltage is applied for a fixed period of time, and thereafter, the applied voltage is reduced to the low voltage. 5. The sputtering method according to claim 3, wherein the sputtering voltage is lowered with the passage of time during the applied voltage lowering period. 6. The method according to claim 1, wherein the sputtering voltage has a plurality of applied voltage constant periods, and the low voltage has a constant applied voltage period after the high voltage applied voltage constant period. 2. The sputtering method according to 2. 7. The sputtering method according to claim 6, wherein the low voltage applied voltage constant period is immediately followed by the low voltage applied voltage constant period. 8. The ratio of the high voltage to the low voltage is 1.3 or more, claim 1, claim 2, claim 3, claim 4, claim 5, claim 6, and claim 6. The sputtering method according to claim 7.