JP4128770B2 - Sputtering equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a sputtering apparatus, and more particularly to a sputtering apparatus suitable for forming electrodes and wirings on the back surface of a substrate on which a high-density integrated circuit is formed.
[0002]
[Prior art]
In recent years, MMIC (monolithic microwave integrated circuit), FET (field effect transistor), etc. are used as electronic circuits for electronic devices such as microwave communication and mobile communication devices, satellite broadcast receivers, and automobile radars. Compound semiconductor integrated circuits are used. When forming an electrode in a normal semiconductor integrated circuit, a contact hole is formed on the surface of a Si (silicon) substrate, and an aluminum wiring material or a Cu wiring material is buried in the hole through a barrier metal. In this electrode formation method, it is important that the barrier metal is sufficiently deposited on the bottom surface of the hole with a high aspect ratio (bottom coverage 30% or more), and the film thickness of the hole side wall is extremely thin. As long as no increase in resistance or disconnection occurred, the film thickness uniformity at the bottom and side walls was not a significant problem. However, in recent years, as a result of demands for power saving and high efficiency of semiconductor devices, there is a demand for forming an electrode (hereinafter referred to as a “back electrode”) on the back side of a substrate on which a semiconductor integrated circuit is formed on the surface. Has increased. In this back electrode, a via hole having a high aspect ratio is formed from the back surface to the front surface of the substrate, and a back electrode as a current-carrying portion is formed in the via hole. In the configuration of the substrate having the back electrode, the buried electrode is not formed in the via hole as the back electrode, and a conductive film is deposited on the inner wall side surface and the bottom surface of the via hole. It is required to form an electrode having a uniform thickness.
[0003]
FIG. 8 shows a cross-sectional structure of a typical conventional FET. A method of forming the back electrode 102 used in the FET 101 will be described with reference to FIG. The back electrode 102 of the FET 101 shown in FIG. 8 is formed by the following steps (1) to (10).
[0004]
(1) An FET structure 104 is formed on the surface of a gallium arsenide (GaAs) substrate 103 by a semiconductor process. The FET structure 104 includes a drain 104a, a source 104b, and a gate 104c. A buffer layer and other plural layers are formed on the GaAs substrate 103.
(2) A glass substrate (not shown) is bonded to the surface of the GaAs substrate 103 on which the FET structure 104 is formed as described above with an adhesive.
(3) The back surface of the GaAs substrate 103 is polished by a polishing apparatus such as CMP, and the total thickness of the GaAs substrate 103 is reduced to about 100 μm.
(4) A pattern for forming a via hole is formed on the back surface of the GaAs substrate 103 by a photolithography process.
(5) A via hole 105 is formed by dry etching.
(6) The photoresist is removed.
(7) A barrier metal film 106 of Ti, TiN, NiCr or the like is formed in the via hole 105 or the like with a thickness of about several tens of nanometers by vacuum deposition.
(8) A low-resistance metal film such as Au is formed on the barrier metal film 106 to a thickness of several tens of nanometers by vacuum deposition.
(9) A metal film is formed from several μm to several tens of μm by electroplating, and the formation of the back electrode 102 is completed.
(10) The semi-insulating GaAs substrate 103 on which the back electrode 102 is formed as described above is removed from the glass substrate.
[0005]
[Problems to be solved by the invention]
When the back electrode 102 is formed on the back side of the GaAs substrate 103 having the above-described structure, particularly in the formation of a film in the via hole 105 having a high aspect ratio, the straightness of the deposited particles can be achieved according to the vacuum deposition method described above. Therefore, a film cannot be formed over the entire area of the hole. Therefore, a sputtering method in which particles are released based on the cosine law has been adopted. However, according to this sputtering method, on the contrary, the number of particles flying obliquely increases, so that a film is deposited in an eaves shape at the opening of the hole, and the sputtered particle does not reach the inside of the hole. Accordingly, there is a problem that a film hardly adheres to the side wall portion in the hole, and a good back electrode cannot be formed.
[0006]
As described above, the purpose of depositing the barrier metal film 106 such as NiCr is to improve the Schottky characteristics, the characteristics of the diffusion barrier, and the adhesion between the Au film as the back electrode 102 and the GaAs substrate. Therefore, if the NiCr barrier film 106 is partially thin, the leakage current increases, the device characteristics change due to the diffusion of Au into the GaAs substrate 103, and the adhesion between the GaAs substrate 103 and the Au film (back electrode 102). It is thought to cause sex decline.
[0007]
Therefore, as a countermeasure, ionization sputtering, which is a technique that improves the linearity of particles, low-pressure remote sputtering that increases the distance between the target and the substrate, or the film at the hole opening is etched and etched again at the bottom. Adhesion bias method has been adopted. However, according to these methods, the coverage at the bottom of the hole was greatly improved to 20 to 40%, but the coverage at the side wall near the bottom of the hole was only about 4 to 5%.
[0008]
However, since the electrode material is not embedded in the via hole 105 in the back electrode 102 as described above, it is necessary to form a film uniformly over the entire via hole 105 in the barrier film made of barrier metal and the back electrode film formed thereon. Has arisen. For this reason, the method with the non-uniformity in the film thickness in the hole as described above cannot cope with this, and this solution is urgently needed.
[0009]
An object of the present invention is to solve the above-mentioned problems by depositing a film sufficiently on the side wall portion of a fine via hole with a simple structure regardless of the size of the target and extending from the inner surface to the bottom surface of the side wall of the via hole. Another object of the present invention is to provide a sputtering apparatus capable of forming a deposited film with good coverage (uniform film thickness).
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the sputtering apparatus according to the present invention is configured as follows.
[0011]
The first sputtering apparatus (corresponding to claim 1) is a sputtering apparatus for forming a thin film on a substrate by sputtering the target with the substrate to be deposited facing the target attached to the cathode. The substrate center is arranged so as to be eccentric with respect to the center of the target, and covers an outer region having a half area including the center position of the substrate on the surface of the substrate as viewed from the center of the target. It has a shield and a substrate holder on which the substrate is placed , and either the substrate holder or the target is configured to rotate around the center thereof while maintaining the parallel state of the substrate holder and the target .
[0012]
The second sputtering apparatus (Claim 2) is preferably characterized in that, in the above configuration, the eccentric distance between the target and the substrate is equal to the radius of the substrate.
[0013]
The third sputtering apparatus (Claim 3) is preferably characterized by having a high-frequency AC power source for applying a voltage to the substrate holder in the above configuration.
[0014]
In the above-described configuration, the fourth sputtering apparatus (Claim 4) is preferably characterized in that the shielding object is disposed close to the substrate.
[0016]
[Action]
In the sputtering apparatus having the above-described configuration, the traveling direction of the sputtered particles arriving on the surface of the substrate on which the film is formed can be well controlled, so that the film thickness uniformity of the flat portion of the substrate is good and the entire surface of the substrate is It becomes possible to uniformly form the film shape and film thickness of the inner wall side surface and the bottom surface in the via hole. The coverage for the flat portion can be secured to about 10% or more over the inner surface and the bottom surface of the side wall in one via hole formed in the substrate.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Preferred embodiments of the present invention will be described below with reference to the accompanying drawings.
[0018]
The configurations, shapes, sizes, and arrangement relationships described in the embodiments are merely schematically shown to the extent that the present invention can be understood and implemented, and the numerical values and the composition (materials) of each component are illustrated. Only. Therefore, the present invention is not limited to the embodiments described below, and can be modified in various forms without departing from the scope of the technical idea shown in the claims.
[0019]
The configuration of the sputtering apparatus according to this embodiment will be described with reference to FIGS. 1 and 2. FIG. 1 is a longitudinal sectional view showing the configuration of the main part of the sputtering apparatus, FIG. 2 is an enlarged view for explaining the characteristic components of the sputtering apparatus, FIG. 2A is a plan view, and FIG. ) Is a side view.
[0020]
In FIG. 1, a vacuum chamber 12 formed by a vacuum vessel 11 has an airtight structure, and is exhausted by an external exhaust device (not shown) through an exhaust port 13 (arrow). 14). Based on this exhausting action, the inside of the vacuum chamber 12 is brought to a required reduced pressure state. A substrate holder 15 is provided inside the vacuum chamber 12 so as to be rotatable by a rotation driving mechanism (not shown). A substrate 16 is placed on the upper surface of the substrate holder 15. Since sputtering film formation for forming the back electrode is performed on the substrate 16, the substrate 16 placed on the substrate holder 15 is such that the surface on which the integrated circuit is formed is on the lower side and the back surface is on the upper side. Is arranged. A bias voltage is applied to the substrate holder 15 from an alternating current (high frequency) power supply 17 provided outside. On the upper side of the substrate 16, a shielding plate 24 is disposed so as to satisfy the conditions related to a predetermined positional relationship and dimensional relationship in a state of approaching the substrate 16. A cathode 19 incorporating a magnet mechanism 18 is provided on the ceiling 11 a of the vacuum vessel 11. A DC power source 20 for sputtering is connected to the cathode 19 by a cable 21 from the outside. The internal magnet mechanism 18 is rotatably provided by a rotation mechanism, and the lower surface disposed at the inner eccentric position is composed of an N-pole magnet 18a, and the lower surface disposed at the outer peripheral edge is composed of an S-pole magnet 18b. . A target 22 is attached to the lower surface of the cathode 19. The lower surface of the target 22 faces into the vacuum chamber 12 and faces the upper surface of the substrate 16 on the substrate holder 15. A gas introduction mechanism 23 is attached to the vacuum chamber 12, and a process gas for generating plasma for sputtering is introduced into the vacuum chamber 12 by the gas introduction mechanism 23.
[0021]
In FIG. 2, the cathode 19, the target 22, the shielding plate 24, and the substrate 16 are shown. In FIG. 2, the drawings are drawn in such a manner that the two drawings are positioned correspondingly so that the positional relationship between the constituent elements satisfies a predetermined relationship between (A) and (B).
[0022]
In the sputtering apparatus according to the present embodiment, as is apparent from FIGS. 1 and 2, the arrangement position of the substrate 16 is different from that of the conventional sputtering apparatus in that the central axis 16 a of the substrate 16 is the central axis of the target 22. It is set so as to be shifted from 22a by a distance (d1 in FIG. 2) that is half the diameter of the substrate 16. Therefore, the position of the substrate holder 15 is set so as to satisfy the above dimensional relationship. Specifically, in terms of specific dimensions, in the case of the substrate 16 having a diameter of, for example, 100 mm, the substrate 16 is attached so that the substrate center axis 16 a is eccentric by 50 mm with respect to the center axis 22 a of the target 22. Note that the size of the target 22 is, for example, a diameter d2 of 164 mm. Further, the distance d3 (T / S distance) between the target 22 and the substrate 16 is 240 to 250 mm, and this distance is usually longer than the T / S distance of about 100 mm in the sputtering method or the collimating method. The distance is shorter than 300 to 400 mm. The shielding plate 24 is disposed between the target 22 and the substrate 16 and at a position from the substrate 16 and at a position outside the center axis 16a of the substrate 16 eccentric from the target center axis 22a. The shielding plate 24 is preferably brought close to the substrate 16 to such an extent that the substrate 16 can be bias-sputtered, and further has an area that includes the center of the substrate 16 and covers approximately half of the area. The distance d4 between the shielding plate 24 and the substrate 16 is set to about 30 mm, for example.
[0023]
Behind the target 22, the above-described cathode 19 is attached, and the magnet mechanism 18 that can rotate is provided inside. Based on this configuration, magnetron sputtering can be performed. As described above, for example, a DC power source 20 that is a power supply source is connected to the cathode 19, while a high-frequency AC power source 17 is connected to the substrate holder 15 so that the substrate can be biased. The reason for performing the substrate bias is to increase the coverage of a metal film such as Au by applying a power of several hundred W, or to reduce the film stress or improve the adhesion in the case of a NiCr barrier film or the like. Is what we do. In this case, it is only necessary to supply a power of about 70 W, which is much smaller than the normal bias power of several hundred W. In the configuration of the above-described embodiment, the substrate 16 is rotated. However, the substrate 16 may be fixed and the target 22, that is, the cathode 19 side may be rotated.
[0024]
Next, the operation of the sputtering apparatus according to the present embodiment having the above configuration will be described. The substrate 16 is transferred into the vacuum chamber 12 through a gate valve (not shown) and placed on the substrate holder 15. The inside of the vacuum chamber 12 is evacuated to about 10 ⁻⁶ Pa or less in advance, and a process gas such as Ar is introduced by the gas introduction mechanism 23 and is adjusted by the flow rate regulator 23a and the valve 23b so as to have a predetermined pressure. .
[0025]
Next, the DC power source 20 for sputtering and the AC power source 17 for substrate bias are operated. At this time, the substrate holder 15 rotates and the shielding plate 24 always covers the outside of the substrate 16 at a fixed position. Since the central axis of the substrate holder 15 (substantially coincides with the substrate central axis 16a) rotates with respect to the target 22, the film thickness distribution on the entire surface of the substrate 16 becomes substantially uniform. Furthermore, since sputtered particles flying in the downward diagonal direction from the target 22 side are deposited on the surface inside the via hole, a film is deposited not only on the bottom of the hole but also on the side wall of the hole. Further, since the sputtered particles flying outside from the center of the substrate 16 are prevented from being deposited on the substrate surface by the shielding plate 24, the coverage of the substrate center side and the outer peripheral surface on the side wall surface in the hole is almost uniform. become.
[0026]
Although the shielding plate 24 covers almost half of the outer region on the upper surface of the substrate 16, strictly speaking, the shape of the shielding plate 24 is taken into consideration to make the entire surface of the substrate and the film thickness in the hole uniform. Can do. Most of the sputtered particles follow the cosine law, but some elements do not follow this. At this time, the film thickness distribution can be improved by making the shape of the shielding plate 24 appropriate.
[0027]
Next, specific examples belonging to the above embodiment will be described. According to this embodiment, the NiCr thin film for the barrier film can be formed by sputtering film formation under the following conditions. The equipment used is a single process module.
[0028]
【Example】
Sputter film formation is performed under the following conditions (1) to (10).
(1) Sputtering power from DC power supply 20: DC 2.2 kW
(2) Target 22: NiCr having a diameter of 164 mm
(3) Process gas: Ar (argon gas)
(4) Pressure during film formation: 0.1 Pa
(5) Substrate bias power by the high-frequency AC power supply 17: 70 W
(6) Target / substrate distance d3 (T / S distance): 246 mm
(7) Eccentric distance d1: 50 mm from the center of the substrate to the center of the substrate
(8) Size of substrate 16: diameter 100 mm
(9) Hole shape: diameter is 35 μm, aspect ratio is 2.1-2.2
(10) Distance d4 between substrate 16 and shielding plate 24: 33 mm
[0029]
3A to 3E show the results of sputtering film formation on the substrate 16 under the above conditions. The coverage ratio in a via hole having a diameter of 35 μm and an aspect ratio of about 2 measured by SEM observation after dividing the substrate 16 after film formation is shown.
[0030]
A via hole having an aspect ratio of about 2 is denoted by reference numeral 41 in FIG. 4, the substrate 16 shown in the FIG. 2 (A), the shield plate 24, the target 22 is a plan view schematically showing the positional relationship of one of the via holes 41 on the substrate 16. It is assumed that the center of the via hole 41 is at a distance R from the center of the substrate 16 . The center of the via hole 41 is a position passing through the center of the bottom. In FIG. 4, the via holes 41 are exaggeratedly shown as 41a and 41b, and in the figure, the inner wall side surfaces (opening side, bottom (bottom) side, outer peripheral side, center side) and bottom surfaces (center, outer peripheral side, The film thickness measurement points on the center side are pointed out, and display marks (Δ, ▲, ○, ●, ×) of the measurement graph corresponding to each measurement point are shown.
[0031]
In each graph of FIG. 3 (a) ~ (e), the horizontal axis is the distance from the center of the substrate (mm), the vertical axis means the coverage (%). (A) is the bottom coverage in the θ direction, (b) is the side (side) coverage in the θ direction, (c) is the bottom coverage in the R direction, (d) is the side coverage in the R direction (near the bottom), (e) It has been shown to measurement graph of side cover LESSON di R direction (the vicinity of the opening). In the above, the θ direction is the direction indicated by the K1-K1 line cross section in FIG. 4, and the R direction is the direction indicated by the K2-K2 line cross section in FIG.
[0032]
5A and 5B are diagrams schematically showing an enlarged measurement location of the via hole 41 on the substrate 16. FIG. As shown in FIG. 5, the thickness of each film 51 on the center A and the side wall of the bottom of the via hole 41 still has a difference in film thickness, but at least at any measurement location, the film thickness of the flat surface of the substrate 16 is imagewise. As a result, a coverage of about 10% or more can be obtained.
[0033]
For comparison, the shape of a typical film formed by the conventional low-pressure remote method, collimating method, and method according to the present embodiment (the present invention) is shown in a table form (Table 1) in FIG. The data in the case where the film is formed with the same T / S distance based on the above method is shown in a table form (Table 2) in FIG. The measurement locations of each film thickness are the locations shown in FIG. 5 (Bi point, A point, Bo point, Ci point, Co point, Di point, Do point).
[0034]
As shown in Table 1, since the target center and the substrate center are coaxial in the low-pressure remote method, the side wall portion in the substrate outer peripheral portion is in the substrate central portion direction (Ci point, Di point) and the outer peripheral portion direction (Co point, Do point). Then, non-uniformity and film adhesion near the hole bottom (Ci point) on the side wall portion are remarkably deteriorated. In the low-pressure remote method, the coverage of the side wall is worse than the bottom of the hole over the entire substrate, and the difference between the two is significant. On the other hand, in the collimator method, the coverage at the hole bottom (A point, Bi point, Bo point) and the side wall (Ci point, Co point) is almost the same, and especially the coverage of the wall near the bottom inside the substrate is improved. is doing.
[0035]
Next, as shown in Table 2, in the low-pressure remote method, the film thickness uniformity of the entire substrate is very good at ± 2%, but the coverage in the vicinity of the bottom surface of the hole side wall on the outer periphery of the substrate is very poor at about 5%. It has become. In the relationship between the collimator method and the present invention, almost the same film thickness shape is shown. That is, the difference in film shape between the center and the outer periphery of the substrate is small, and the difference in coverage between the bottom and side walls in the hole is also improved. However, in the collimator method, the film is formed through a collimator having a large number of holes of φ10 × (10 to 20) t, so that a film is significantly attached to the collimator, causing a problem of particles due to clogging or film peeling, and There is a problem that the film formation rate is deteriorated with time due to clogging of a large number of holes by the film adhering to the collimator at the initial stage of film formation and during the film formation.
[0036]
On the other hand, according to the sputter film formation of the present invention, it was found that there was no various problems due to the collimator method, and the coverage in the hole could be obtained approximately 10% or more. In the embodiment, since a simple semi-circular plate material is used for the shielding plate 24, the film thickness distribution of the entire flat portion on the upper surface of the substrate is ± 13%. It is possible to further improve the distribution.
[0037]
【The invention's effect】
As is apparent from the above description, according to the present invention, there is provided a sputtering apparatus for sputtering deposition of a substrate having a substrate center that is eccentric from the center of the target. By placing the target between the rotating target and the substrate, the film thickness uniformity of the flat part of the substrate is improved and the film shape and film thickness of the inner wall side surface and the bottom surface in the via hole are uniform over the entire surface of the substrate. It is possible to obtain a coverage ≧ 10% in a fine via hole with a good flat portion thickness distribution and an aspect ratio of 2 or more, and a via hole in each of the central region and the outer peripheral region of the substrate. It is possible to reduce the bias in the coverage of the inner wall. In addition, a film having an excellent film thickness distribution can be formed with a relatively small target. Therefore, the apparatus can be reduced in size and cost, and an apparatus capable of realizing a low running cost can be provided.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional view showing a schematic configuration of a sputtering apparatus according to a typical embodiment of the present invention.
2A and 2B are diagrams showing an arrangement relationship of main components of the sputtering apparatus shown in FIG. 1, wherein FIG. 2A is a plan view and FIG. 2B is a side view.
FIG. 3 is a diagram showing various distribution characteristics on the surface of a substrate with respect to coverage.
FIG. 4 is a diagram showing a position of a via hole on a substrate and a film thickness measurement location in the via hole.
FIG. 5 is a view showing a position (A) of a via hole in a substrate and a film thickness measurement location (B) in the via hole.
FIG. 6 is a list showing a schematic diagram of each configuration of the present invention and the prior art and coverage in a via hole.
FIG. 7 is a table comparing coverages in via holes of the present invention and the prior art.
8 is a typical schematic longitudinal sectional view of a conventional F ET structure.

Claims (4)

In a sputtering apparatus in which a substrate to be deposited is opposed to a target attached to a cathode, and the target is sputtered to form a thin film on the substrate.
The substrate is disposed such that the center of the substrate is eccentric with respect to the center of the target,
A shield provided between the target and the substrate and covering an outer region of a half area including the center position of the substrate on the surface of the substrate when viewed from the center of the target;
A substrate holder for mounting the substrate,
One of the substrate holder and the target is configured to rotate around the center thereof while maintaining the parallel state of the substrate holder and the target .   The sputtering apparatus according to claim 1, wherein an eccentric distance between the target and the substrate is equal to a radius of the substrate.   The sputtering apparatus according to claim 1, further comprising a high-frequency AC power source that applies a voltage to the substrate holder.   The sputtering apparatus according to claim 1, wherein the shielding object is disposed close to the substrate.

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