KR19980041860A - Low Pressure Remote Sputtering Device - Google Patents

Abstract

It solves the problems caused by overhang, improving not only bottom coverage but also side coverage.

In a low-pressure remote sputtering configuration having a pressure of 1 mTorr or less and a distance obtained by dividing the distance between the target 2 and the substrate 50 by the size of the substrate 50, the surface of the substrate 50 faces the surface in a space near the surface of the substrate 50. The electric field is set by the electric field setting mechanism 7. The electric field setting mechanism 7 applies a high frequency voltage to the substrate holder 5 holding the substrate 50 to impart a self bias voltage to the substrate 50 by interaction with the plasma. A hole 500 having a certain aspect ratio is formed on the surface of the substrate 50, and sputtered particles deposited at the opening edge 501 of the hole 500 are resputtered by the ions 40 accelerated by an electric field. 500) Film deposition is promoted on the side 503.

Description

Low Pressure Remote Sputtering Device

FIELD OF THE INVENTION

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sputtering apparatus for depositing a desired thin film on the surface of a substrate by sputtering, and more particularly, to a low pressure remote sputtering apparatus which maintains a discharge pressure lower than usual and makes a distance from a target substrate longer than usual.

Conventional technology

Sputtering apparatuses are widely used in the production of LSIs (large scale integrated circuits), LCDs (liquid crystal displays), and information recording discs. FIG. 4 shows a sputtering apparatus used in the related art, and FIG. 5 is a cross-sectional view of the hole showing the profile of the step coverage of the film deposited in the hole by the conventional sputtering apparatus of FIG. 4.

The sputtering apparatus shown in FIG. 4 has a vacuum vessel 1 with an exhaust system 11. In this vacuum container 1, the target 2 and the electrode 3 which produce sputter discharge are arrange | positioned. The vacuum container 1 is provided with the gas introduction system 4 which introduces the discharge gas for sputter discharge. Further, a substrate holder 5 for arranging the substrate 50 coated with the sputtered target 2 material in the vacuum container 1 is disposed.

In such a sputtering apparatus, step coverage improvement has become an important problem in various semiconductor device fields where the degree of integration increases year by year.

Step coverage means coverage of holes, grooves or steps formed in the substrate surface. The step coverage characteristic also includes bottom coverage, which is the ratio of the deposition amount of the thin film to the bottom of the groove or hole (hereinafter collectively referred to as the hole) relative to the deposition amount of the thin film on the upper surface.

When the barrier film is deposited by sputtering into a hole such as a contact hole or a through hole, the diffusion prevention between layers is not sufficient unless a barrier film having a sufficient thickness is deposited at the bottom of the hole, that is, the bottom coverage is not sufficient. In some cases, there is a fatal flaw in device performance called junction leakage.

The higher the degree of integration and the finer the wiring, the narrower the wiring width. On the other hand, the hole depth tends to be deeper due to the complexity of the wiring structure on the background of the high performance of the device. As a result, the aspect ratio (hole depth / hole opening width) of the hole tends to be further increased.

However, in the conventional general sputtering device, film formation in holes having an aspect ratio of about 1 to 2 is a limit, and it is a technical obstacle when manufacturing an integrated circuit of 16 megabits or more. The reason for this is that the conventional sputtering apparatus of FIG. 4 has a large amount of sputtered particles entering the substrate 50 at an inclined angle, and the amount of sputtered particles that can reach the bottom of the hole is small. As a result, as shown in FIG. 5, film deposition on the bottom of the hole or hole 500 of the substrate 50 decreases, and the bottom coverage ((b / a) × 100% of FIG. 5) is considerably lowered.

In order to improve the step coverage, it is important to increase the number of sputter particles which are incident perpendicularly to the substrate 50. A collimated sputtering method is known in which sputter particles are incident vertically. 6 is a schematic display of a conventional collimated sputtering device.

In the sputtering apparatus of FIG. 6, a collimating plate 8 is provided in the space between the target 2 and the substrate 50. The collimating plate 8 forms a flight path through which lattice or honey-comb sputter particles pass.

However, in this collimated sputtering method, sputter particles adhere to and deposit on the collimated plate 8. If the sputtering process is performed for a considerable time, the cross section of the flight path is reduced. As a result, the sputter particle which can pass through the collimate board 8 reduces. The collimated sputtering method has a problem that the film formation speed is lowered, which is a fatal defect in mass production equipment. Since maintenance for the replacement of the collimated plate 8 is required again, there is a problem that sufficient productivity as a mass production device is not secured.

In order to solve such a problem of the collimated sputtering method, the low-pressure remote sputtering apparatus which kept the discharge pressure lower than usual and made the distance of a target and a board | substrate longer than usual has attracted attention recently. 7 is a schematic view of a conventionally known low pressure remote sputtering device.

As can be seen from FIG. 7, this sputtering device has a larger distance (hereinafter, referred to as TS distance) between the target 2 and the substrate 50 than the conventional device. Of the sputter particles emitted from the target 2, only the sputter particles flying in a direction close to the surface of the substrate 50 reach the substrate 50. Sputter particles flying in an oblique direction with respect to the surface of the substrate 50 face the base wall of the vacuum container 1. Therefore, the amount of sputtered particles reaching the surface of the vertically incident substrate 50 becomes relatively large. As a result, step coverage is improved.

In addition, the low-pressure remote sputtering device is designed to lower the discharge force to, for example, about 1 mTorr or less in order to increase the number of sputter particles of vertical incidence. By lowering the pressure, the average free path of the sputter particles is increased, and scattering of the sputter particles is reduced by collision with the gas for discharge. As a result, the number of sputter particles of vertical incidence is increased.

The conventional low pressure remote sputtering device enables a significant improvement in step coverage by efficiently reaching a substrate without scattering sputter particles having an angle of incidence close to vertical due to an increase in TS distance and a decrease in discharge pressure. There is no problem of deterioration in film formation over time as seen in the apparatus for performing the collimated sputtering.

For example, when sputtering a target made of titanium under a condition of a TS distance of 340 mm and a discharge pressure of 0.3 mTorr, a bottom coverage of about 40% for holes having aspect ratio 2 and about 20% for holes having aspect ratio 3.5 is obtained. It is obtained and is promising for the manufacture of integrated circuits over 16 megabits.

However, if the device integration degree is further improved and the aspect ratio is high, there is a possibility that the above-mentioned conventional low pressure remote sputtering device cannot cope with. For example, in the case of 256 megabit or 1 gigabit DRAM, the aspect ratio is 4-5. It is required to form a film with a bottom coverage of about 15% or more for such a high aspect ratio hole. However, in such a high aspect ratio hole, the bottom coverage of about 10% is limited even with a conventional low-pressure remote sputtering device, and there is concern that it will hinder the practical use of the next-generation device.

One of the causes of not improving the coverage for the fine holes is the overhang phenomenon. 8 is a cross-sectional schematic diagram showing an overhang which is a problem of the conventional apparatus.

As illustrated in FIG. 8, when the thin film is sputtered on the surface of the substrate 50 on which the holes 500 are formed, the sputter particles are deposited on the opening edge 501 of the hole 500. There is a tendency for thin films to rise and rise at this edge portion 501. The sediment which rose to this edge is called an overhang. When this overhang 502 occurs, the opening area of the hole 500 becomes small, so that the amount of sputtered particles that reach the hole 500 decreases and the coverage deteriorates. In particular, overhang 502 completely blocks sputter particles flying towards hole 500 side 503. The overhang 502 formation breaks down with the decrease in side coverage {(c / b) × 100 (%)}.

In terms of side coverage, the conventional low pressure remote sputtering device has the following problems. This problem is described in detail with reference to FIG.

9 is a schematic cross-sectional view showing a situation in which a thin film is deposited in a hole formed in the substrate surface. (C) in FIG. 9 shows the deposition state of the thin film on the inner surface of the hole formed in the center portion of the substrate, and (P) shows the deposition state of the thin film on the inner surface of the hole formed in the peripheral portion of the substrate.

As shown in FIG. 9, in the conventional low pressure remote sputtering device, the film deposition on the side surface 503 of the hole 500 tends to be smaller than the film deposition on the bottom surface 504 of the hole 500. The deposition rate on the side surface 503 of the hole 500 is lower than that of the bottom 504. This tendency is more prominent in the central portion than in the peripheral portion of the substrate 50.

This decrease in film deposition on the side of the hole is caused by increasing the amount of sputter particles perpendicularly incident on the substrate 50. Among the sputter particles incident on the substrate 50, Qv is the amount of sputter particles perpendicularly incident to the substrate 50, the amount of the sputter particles is obliquely incident is Qo, and the film formation speed at the bottom surface 504 of the hole 500 is Db, When the film formation speed on the side surface 503 of the hole 500 is set to Ds, it is (Qo / Qs) · (Ds / Db).

In the central portion of the substrate 50, since the amount of sputtered particles which are vertically incident to the peripheral portion is larger than that of the peripheral portion, it is less inclined to the side surface 503 again. That is, when (Qo / Qv) in the center portion is set to Rc and (Qo / Qv) in the peripheral portion is set to Rp, it becomes Rc Rp. Therefore, when (Ds / Db) in the center portion is rc and (Ds / Db) in the peripheral portion is rp, rc rp is obtained. Therefore, the side coverage decreases more noticeably in the central portion than in the peripheral portion.

Such lowering of side coverage reduces, for example, the diffusion preventing effect in the side portion in the case of the barrier film. There is a fear that it will lead to a fatal flaw called the exection.

The present invention has been made to solve such a problem, and an object thereof is to provide a low pressure remote sputtering device capable of improving not only bottom coverage but also side coverage.

BRIEF DESCRIPTION OF THE DRAWINGS It is front sectional drawing which shows the outline of the low pressure remote sputter apparatus which concerns on embodiment of this invention.

2 is a cross-sectional schematic diagram illustrating ion incidence.

3 is a coverage display diagram of aspect ratios in the sputtering apparatus of the present invention and the conventional sputtering apparatus under the conditions of the embodiment.

4 is a configuration display diagram of a sputtering apparatus used in the related art.

FIG. 5 is a profile display diagram of step coverage by the conventional sputtering apparatus of FIG. 4. FIG.

6 is a schematic display diagram of a conventional sputtering apparatus for performing a collimator sputtering method.

7 is a schematic view of a conventional low pressure remote sputtering device.

8 is a cross-sectional schematic diagram showing an overhang in a hole.

9 is a profile display diagram of step coverage in a conventional low pressure remote sputtering apparatus.

(Explanation of symbols for the main parts of the drawing)

1: vacuum container 2: target 3: electrode 34: power supply for discharge

4: gas introduction boundary 5: substrate holder 50: substrate 500: hole

6: shield 7: electric field setting means 71: high frequency power supply

In order to achieve the above object, the present invention is characterized in that, in the low-pressure remote sputter, an electric field for collecting and injecting ions onto the substrate surface by an electric field setting means is set. The low pressure remote sputter is achieved by maintaining the pressure in the vacuum vessel at 1 mTorr or less and at the same time the normalized TS distance, which is a value obtained by dividing the distance between the target and the substrate by the substrate size, to be 1 or more.

In a hole having a constant aspect ratio formed on the substrate surface, ions vertically incident on the substrate surface by the electric field setting means resputter sputtered particles deposited on the opening edge of the hole. As a result, film deposition on the hole side is promoted.

Preferably, the electric field setting means applies a high frequency voltage to the substrate holder to impart a self bias voltage to the substrate by interaction with the plasma.

Embodiment of the invention

EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described.

BRIEF DESCRIPTION OF THE DRAWINGS It is front sectional drawing which shows the outline of the low pressure remote sputter apparatus of embodiment of this invention. The apparatus shown in FIG. 1 has a gas introduction system 4 for introducing a gas for sputter discharge and a vacuum vessel 1 having an exhaust system 11. In this vacuum container 1, the target 2, the electrode 3 which produces sputter | spatter discharge, and the board | substrate holder 5 holding the board | substrate 50 are arrange | positioned.

The vacuum container 1 is an airtight container including a gate valve (not shown). This vacuum vessel 1 is provided with a load-lock chamber (not shown) adjacent to which the substrate 50 is disposed and evacuated before placing the substrate 50 therein. The exhaust system 11 is provided with a vacuum pump such as a cryopump and exhausts up to an reached pressure of about 10 ^-8 Torr.

The target 2 is a circular plate-shaped member made of a material for coating the substrate 50. This target 2 is fixed to the front side of the electrode 3 by screwing. The target shield 35 is provided to cover the periphery of the target 2. This target shield 35 prevents unnecessary discharge around the target 2. It is grounded, covering the periphery of the target 2 with a fixed narrow space | interval.

As the target 2, a slightly larger one than the substrate 50 may be used. The slightly larger target side evenly forms the film around the periphery of the substrate 50.

The low pressure remote sputtering device of the present embodiment is a flat plate magnetron sputtering device. As the electrode 3, a magnetron cathode is employed. The electrode 3 consists of a pair of magnets 31 and 32 provided behind the target 2 and a yoke 33 connecting them. The pair of magnets 31 and 32 are permanent magnets for forming a magnetic force line closed in front of the target 2. It consists of a central columnar magnet (N pole) 31 and a ring-shaped magnet (S pole) 32 surrounding it. A discharge power supply 34 is connected to the electrode 3, and a constant negative DC voltage or a high frequency voltage is applied to the electrode 3.

As the discharge gas, an inert gas such as argon having a high sputtering rate is used. The gas introduction system 4 which introduces a gas for discharge consists of a gas introduction pipe 43 which connects a cylinder (not shown) and the vacuum container 1. The gas introduction pipe 44 is connected to the gas introduction pipe 43. The valve 45 and a flow regulator not shown are provided in the gas introduction pipe 43.

The discharge gas flow rate is adjusted so that the pressure in the vacuum vessel 1 becomes a value at which a low pressure remote sputter effect is obtained. This pressure is generally below 1 mTorr. The flow rate regulator of the gas introduction system 4 is controlled while operating the exhaust system 11 to have a pressure of 1 mTorr or less.

The substrate holder 5 is at a position separated from the target 2 by a TS distance such that a low pressure distance sputtering effect is obtained. The low pressure remote sputter effect is an effect of improving the step coverage as described above. Generally, this effect is sufficiently obtained by making TS distance into 150 mm or more.

It is more suitable to use the standardized TS distance (TS distance / substrate size) divided by the TS distance divided by the board size. In this case, the standardized TS distance is preferably 1 or more. "Substrate size" means diameter when the shape of the board | substrate 50 is circular, and diagonal length in the case of square. In the case of shapes other than this, it shall be "the length which connected the longest of two points on the outline periphery."

The substrate holder 5 is provided with an electrostatic chuck for electrostatically adsorbing the substrate 50 by inducing static electricity on its surface, and a heater for heating the substrate 50 to a constant temperature. The vacuum vessel 1 is grounded, and the substrate holder 5 is insulated from the vacuum vessel 1.

A cylindrical shield 6 is provided inside the vacuum container 1. The shield 6 prevents sputtered particles from adhering to the base wall of the vacuum container 1. It is provided so as to surround the space between the target 2 and the substrate holder 5. The shield 6 is detachably attached to an attachment hole (not shown) provided in the vacuum container 1. The shield 6 is subjected to a surface treatment such as a ballast treatment in which the thin film adhesion strength is increased so that the deposited thin film does not peel off and fall on the substrate 50.

The shield 6 is provided with an exhaust hole 42 for discharging gas. The gas introduction system 4 introduces gas toward the discharge space from near the end portion near the target 2 of the attachment shield 6. The introduced discharge gas is discharged through the exhaust hole 42 of the shield 6 in a substantial amount.

A large feature of the apparatus of this embodiment is that an electric field setting mechanism 7 for setting an electric field perpendicular to the substrate surface is provided in a space near the surface of the substrate 50. The high frequency power supply 71 is used for the electric field setting mechanism 7 in this embodiment. The high frequency power source 71 generates a self bias voltage on the substrate 50 by interacting with the plasma by applying a constant high frequency voltage to the substrate holder 5.

The high frequency power supply 71 has a 400 kHz output of about 150 W. The high frequency electric field is induced near the surface of the substrate 50 by the high frequency voltage applied to the substrate holder 5 by the high frequency power source 71. Electrons or ions floating in the plasma or floating by the high frequency electric field periodically adhere to the substrate 50. In particular, the electrons are much lighter than ions, and thus adhere to the substrate 50 much. As a result, abundant electrons exist on the surface of the substrate 50, and the substrate 50 is biased at a negative potential.

Due to the interaction between the high frequency and the plasma, the surface of the substrate 50 is self-biased at a potential of, for example, about -600V (average value). This self bias potential forms an electric field between the plasmas in the discharge space that is approximately equal to the ground potential. The inclination of the electric field is perpendicular to the surface of the substrate 50, and the cations are extracted in the plasma and made to enter the substrate 50 perpendicularly. The distance to which the "space near the board | substrate" is from the surface of a board | substrate is a distance of about 40-50 mm, for example, depending on a pressure, plasma intensity | strength, and the plasma diffusion state.

In order for the substrate 50 to be biased, it is necessary that a capacitance exists between the high frequency power supply 71 and the substrate 50. Therefore, a part of the substrate holder 5 is formed of a dielectric or a capacitor is provided between the high frequency power supply 71 and the substrate holder 5. If the substrate 50 itself is a dielectric such as an organic substrate, it is biased even if such a mechanism does not exist. A high frequency line between the high frequency power supply 71 and the substrate holder 5 is provided with a matching device (not shown).

The cation drawn out by the electric field set as described above solves the problem caused by the overhang. This point is explained using FIG. FIG. 2 is a cross-sectional schematic diagram illustrating the operation of the electric field setting mechanism 7 in the apparatus of FIG. 1.

As shown in FIG. 2, in the apparatus of the present embodiment, ions 40 are incident toward the substrate 50 by an electric field set by the electric field setting mechanism 7. These ions 40 resputter the overhang 502 accumulated at the edge 501 as shown in FIG. 2. The resputtered sputter particles fall into the hole 500. As a result, the amount of sputtered particles reached in the hole 500 increases, and bottom coverage is improved. In addition, the sputter particles sputtered from the overhang 502 have a random orientation, and thus reach the side surface 503 of the hole 500. As a result, the sputter of the overhang 502 also contributes to the improvement of side coverage.

When ions reach the surface of the substrate 50 that is being deposited, the ions impact the surface to impart energy, thereby promoting the film formation. The film formation promotion method using such an ion bombardment is called an ion assist method. The ion assist method is effective for promoting film formation when the impact energy is relatively low. However, when the ions are accelerated and impacted by high electric field strength, the thin film is resputtered as described above. To what extent a high electric field strength is set, it cannot be determined uniquely that the sputter becomes dominant, but in general, it is thought that the electric field is changed from an ion assist to a sputter by setting an electric field of about 200V or more.

Next, the overall operation of the apparatus of the present embodiment will be briefly described.

First, after the board | substrate 50 is arrange | positioned in the load lock chamber which is not shown in figure, the load lock chamber and the vacuum container 1 are exhausted, and it is set as the pressure of about ^10-8 Torr. A gate valve (not shown) is opened to carry the substrate 50 into the vacuum container 1. The substrate 50 is placed on the substrate holder 5 and held therein. After closing the gate valve, the gas introduction system 4 is operated to introduce a certain amount of gas for discharge into the vacuum vessel 1 while adjusting the pressure by the exhaust system 11. The inside of the vacuum vessel 1 is set to a pressure (for example, 1 mTorr or less) at which a low pressure remote sputtering effect is obtained.

The discharge power supply 34 is operated at this pressure to apply a negative DC voltage or a high frequency voltage to the electrode 3. In parallel, the electric field setting mechanism 7 composed of the high frequency power supply 71 operates to apply a constant high frequency voltage to the substrate holder 5. The discharge gas is ionized by the voltage supplied to the electrode 3 by the discharge power supply 34, and the target 2 is sputtered to generate sputter discharge. The sputtered target 2 material (sputter particles) fly in opposing spaces to reach the substrate 50 and a thin film is deposited.

According to the effect of the low pressure remote sputter, a film is efficiently deposited on the bottom surface 504 of the hole 50 formed on the surface of the substrate 50. As described above, the overhang 502 is sputtered by the electric field set by the electric field setting mechanism 7, and the film is efficiently deposited on the side surface 503 of the hole 500. As a result, not only bottom coverage but also side coverage is improved.

When such sputter film formation is performed and the thin film reaches the desired film thickness, the operation of the discharge power supply 34, the electric field setting mechanism 7 and the gas introduction system 4 is stopped in order to terminate the sputtering process. After completion of the sputtering process, the substrate 50 is carried out after evacuating the inside of the vacuum container 1 again.

Example

Next, the Example at the time of forming into a film using the apparatus of the said embodiment is demonstrated. The case where a titanium film is deposited as a barrier film while using the apparatus of the said embodiment is demonstrated as an example. The film formation of a titanium film is performed under the following conditions.

Target Material: Titanium

Supply power to the electrode 3: 9 kW

Electric field setting mechanism (7): High frequency power supply with frequency 400KHz output 150W

Discharge Pressure: 0.25mTorr

Type of discharge gas: Argon

FIG. 3 is a diagram showing experimental results of investigating coverage of holes in various aspect ratios while operating the apparatus under the conditions of the embodiment. The step coverage is also shown by the conventional low pressure remote sputtering apparatus shown in FIG. 3 shows the aspect ratio and the vertical axis shows the bottom coverage. In Fig. 7, o is the bottom coverage of the center portion of the substrate in the conventional apparatus, o is the bottom coverage of the portion around the substrate in the conventional apparatus, o is the bottom coverage of the center portion of the substrate in the embodiment apparatus, Shows bottom coverage of the portion around the substrate in the example apparatus, respectively.

As shown in Fig. 3, in the bottom coverage of the holes exceeding the aspect ratio 2, a remarkable improvement is seen in the apparatus of this embodiment. There is almost no difference in bottom coverage at the center of the substrate and at the periphery of the substrate. The device of this embodiment also shows good results in terms of the in-plane distribution of the bottom coverage.

Although not shown, in terms of side coverage, about 30% of side coverage is obtained for holes having an aspect ratio of about three.

In the embodiments and examples of the present invention described above, the electric field setting mechanism 7 is made of a high frequency power source 71 and generates a self bias potential on the substrate by the interaction of the high frequency and the plasma. However, the electric field setting mechanism 7 may be a DC power supply.

The electrode 3 may be a magnetron cathode, but may be of a type such as a bipolar (DC) sputter or a high frequency sputter that does not use a magnet. Moreover, as a kind of discharge gas, nitrogen gas other than argon and hydrogen gas may be sufficient.

When using a target of a material with a high sputtering rate such as copper, a method of maintaining a discharge by using only an ionization process of the sputtered material may be employed. This type of discharge is called a self-maintaining sputter. Since a discharge gas such as argon is not used separately, mixing of the discharge gas into the thin film becomes in principle zero, and there is an advantage of becoming a high quality thin film. Even in such a self-maintaining sputter, when the ions are incident on the substrate using the electric field setting mechanism 7, the effect of improving the in-hole step coverage by sputtering the overhang is obtained.

As the type of thin film to be deposited, the apparatus of the present invention can also be used to prepare various conductive or insulating thin films other than barrier films, such as wiring metal thin films and interlayer insulating films. In particular, in the barrier film, a titanium thin film and a titanium nitride thin film may be laminated. In this case, after titanium is sputtered with argon to form a titanium thin film, the titanium nitride thin film is deposited by sputtering titanium with nitrogen in the same manner and assisting the reaction between nitrogen and titanium.

The low pressure remote sputtering device of the present invention can improve not only bottom coverage but also side coverage. In particular, it has great power in the manufacture of semiconductor integrated circuits, which have a high aspect ratio every year, especially next-generation devices after 256 megabits.

Claims (3)

In a low pressure remote sputtering apparatus which maintains a pressure in a vacuum container at 1 mTorr or less and sputters film at a standardized TS distance of 1 or more divided by the size of a target and a substrate, the ion is extracted from the plasma to the surface of the substrate. A low pressure remote sputtering device, characterized in that an electric field setting means is provided for setting an electric field so as to be incident perpendicularly to the plane. The low pressure remote sputtering device according to claim 1, wherein the electric field setting means applies a high frequency voltage to the substrate holder to impart a self bias voltage to the substrate by interaction with the plasma. The pressure in the vacuum vessel is maintained at 1 mTorr or less, the standardized TS distance, which is a value obtained by dividing the distance between the target and the substrate by the substrate size, is set to 1 or more, and the electric field is set to inject ions perpendicularly to the substrate surface in the plasma. Sputtering method