JP2002075925A - Surface planarization treatment method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a surface planarization treatment method for preventing shape fail by solving the problem that the shape fail such as thinning and dishing occurs on a treated surface depending on the size of the local contact stress between a workpiece and a polishing pad caused by the unevenness of foundation in the surface planarization treatment method by chemical machine polishing, and the shape fail makes difficult the focusing of the optical system of a projection exposure system in an element manufacture process where the fining of a large-scale integrated circuit semiconductor device is advanced. SOLUTION: The formation of CuO onto a copper or cupper thin-film surfaces to be machined is accelerated by electric or chemical operation, thus increasing the polishing speed of the workpiece. Also, by the same operation, the formation of oxide onto the surface of the workpiece is inhibited, and Cu2O is formed on the surface of the workpiece, thus nearly preventing the cupper surface from being polished. The two effects are combined, thus obtaining a high polishing speed and an excellent machining shape.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and an apparatus for flattening a solid surface by chemical mechanical polishing at a level applicable to a manufacturing process of a semiconductor device. In particular, by controlling the formation of the oxide of the workpiece material on the surface of the workpiece or the composition of the oxide of the workpiece material to be formed by using electrical or chemical means, the surface of the workpiece is controlled. Is characterized by controlling the polishing characteristics of the substrate. Further, the surface state of the workpiece by the electrical or chemical means is controlled according to a change in the polishing amount of the workpiece.

[0002]

2. Description of the Related Art At present, in the manufacture of large-scale integrated circuit semiconductor devices based on silicon, in addition to the conventional methods of miniaturizing one-dimensional patterns and increasing the diameter of two-dimensional silicon wafers. In recent years, higher integration, higher speed, and higher added value have been attempted by using three-dimensional multilayer wiring between elements. Conventionally, after a transistor and a capacitor, which are basic components of a semiconductor element, are arranged near the surface of a silicon wafer, an insulating layer such as a silicon oxide film is formed thereon, and an opening is formed at a desired position to open the insulating layer. A metal such as tungsten is buried, and a layer of a metal such as aluminum is formed thereon to wire between the elements. However, as the degree of integration increases, the number of insulating and wiring layers is steadily increasing, and the number of logic elements currently ranges from seven to eight. In such a case, if the film is formed after the opening, the opening portion is depressed, and if the film is formed on a columnar structure, the portion becomes convex. The unevenness generated in this way becomes a serious problem in a lithography process performed on the assumption that the surface is flat. For example, after forming a metal wiring film, the difference between the high and low surface areas is 1 μm.
m (this value is typical in practice), the currently used resolution of 0.25 μm
The depth of focus of a projection exposure type optical system using a krypton fluoride or argon fluoride laser as a light source before and after is 0.3 μm.
m or less, it is obvious that the level of surface irregularities described above makes focusing of the lithography process very difficult. Therefore, in order to solve such a problem, it is necessary to remove the unevenness on the surface after the film forming step as described above by some method and to make the surface flat.

Conventionally used methods for flattening a surface include an etch-back method, a film forming method, and a fluidizing method. The etch-back method is a method of flattening by combining film deposition of a metal or an interlayer insulating film with etching such as sputtering or reactive ion etching. The fluidization method is
A silicon oxide film to which phosphorus, boron, or the like is added is deposited, or an inorganic or organic SOG (Spin on Glass) is applied, and then heat treatment is performed to flatten the surface. However, it has been pointed out that these flattening techniques are problematic in that processing is appropriate depending on a film type such as a metal film or an interlayer insulating film, and that a flattable region is extremely narrow from several nm to 100 nm. It is considered that these methods cannot be applied when the multilayer wiring is further advanced.

[0004] In view of the above background, as a method of performing a flattening process almost uniformly over the entire surface regardless of the material of the surface to be flattened, recently, chemical mechanical polishing (Chemical Mechanical Polishing) has been proposed.
A method called polishing (CMP) for flattening the surface by polishing is proposed, and is actually being applied to products.

The method of flattening by surface polishing by CMP is basically the same as the polishing method for obtaining a mirror-finished silicon wafer which is said to have the highest flatness on the earth. That is, pads of various hardness (polishing cloth)
The surface of the workpiece is pressed against the surface of the workpiece, and the pad and the workpiece are polished by rotating the pad and the workpiece while supplying a turbid liquid (slurry) in which abrasive grains having various particle diameters are dispersed. This is realized by positively utilizing the chemical action of, the mechanical action of the pad or abrasive grain with the surface of the workpiece, and the combined action of these.

[0006]

However, unlike the polishing of a silicon wafer surface, which has been applied so far, the semiconductor element manufacturing process which requires a processing accuracy of the order of submicrons while maintaining the ultimate cleanliness. As one,
There are various problems in applying this CMP. Most of these problems are due to physical contact (mechanical interaction) between the pad and the surface to be polished, which enables planarization by CMP.

When a copper (Cu) thin film used as a wiring material of a large-scale integrated circuit semiconductor device is polished by CMP, the surface of Cu, which is a workpiece, is immersed in a slurry and its outermost surface is polished. Is formed with an oxide film, the oxide film is polished by the action of abrasive grains, slurry or a pad, and the Cu surface appearing thereafter is sequentially oxidized and further polished. It is supposed to progress. During the polishing of the Cu surface, the oxides of Cu posted on the Cu surface include CuO and Cu.
There are two types of ₂ O, C which is a workpiece such as a slurry.
The composition ratio of the two types of Cu oxides is determined according to the environmental conditions to which the u surface is exposed.
It is determined by the composition ratio of the oxide. Therefore, in the conventional polishing, the concentration and the composition of the slurry solution in which the Cu oxide composition ratio is selected so as to increase the polishing amount are selected from the demand of the production efficiency, and the polishing state of the Cu surface is microscopically determined. In observation, since the load (pressure) from the contacting pad is shared by the projections of the pattern on the surface to be processed, the degree of progress of the processing differs depending on the density and size of the wiring pattern. That is, the processing proceeds preferentially in the portion of the high-density wiring pattern, and as a result, there occurs a place called overwork of the wiring metal called thinning. Similarly, in the over-processing of the wiring portion, the so-called dishing (Dish), in which the center portion of the wiring portion is rapidly processed and dents occur mainly due to the elasticity of the polishing pad and the chemical action of the slurry.
ing). Such a problem is a problem that must be avoided in CMP that originally aims at flattening the surface of the workpiece.

[0008]

As described above, copper has two kinds of oxides, CuO and Cu ₂ O. However, when the copper surface is exposed to the air, the copper surface is near the outermost surface. There is a lot of CuO. This is because, when comparing two copper oxides, the ratio of oxygen atoms per copper atom is higher in CuO than in Cu _2.
O, it is Cu on the surface side where oxygen is easily supplied.
This is because O is easily formed. CuO has properties of being higher in hardness and brittle than Cu. Therefore,
When a load is applied via abrasive grains to a place where CuO is formed on Cu as a base, the Cu
Is soft, the hard and brittle CuO loaded by the abrasive grains is locally broken. Then, the broken and small pieces of CuO are removed from the surface. After that, the underlying Cu appears at the place where CuO is removed,
This Cu surface is soon oxidized and a CuO film is formed again. And again, the load is applied to the abrasive grains to cause destruction and removal. By repeating this, Cu
Is polished by CMP. On the other hand, Cu ₂ O has a lower hardness than CuO, and the Cu ₂ O film formed on Cu has elasticity or elasticity together with the underlying Cu even when a load is locally applied through abrasive grains. It is considered that only plastic deformation occurs and no brittle fracture leading to surface polishing does not occur.
The surface on which u ₂ O is formed is not polished or has a significantly lower polishing rate than the surface on which CuO is formed. Similarly, the surface of Cu itself does not cause brittle fracture even when a load is locally applied through the abrasive grains, so that the polishing rate by CMP is not polished compared to the surface on which CuO is formed. Or the polishing rate is remarkably low.

Therefore, in the present invention, when the Cu surface is polished by CMP, the potential of the surface of the workpiece is controlled by controlling the potential, or the chemical action such as ozone is applied to the surface of the workpiece. The presence or absence of oxide formation on the Cu surface,
Alternatively, the composition of the oxide to be formed was controlled, and the polishing state was further controlled. For example, if a high polishing rate is to be obtained, it is advantageous that the surface of the workpiece be dominated by CuO, and when the polishing end point is approached, the surface of the workpiece is Cu or Cu _2. By setting to O, it is possible to prevent unnecessary progress of polishing.

[0010]

FIG. 1 shows the structure of a surface flattening apparatus according to the present invention. Reference numeral 1 denotes a workpiece, which has a silicon wafer (2) as a substrate and a copper thin film (3) formed on the surface thereof. The processing head (4) holds and rotates the workpiece (1) by the wafer holder (5). The rotation of the processing head (4) is performed by transmitting the output of the motor (6) via the speed reducer (7).
Reference numeral 8 denotes a polishing cloth, and 9 denotes a polishing pad for holding and rotating the polishing cloth 8. The polishing pad (9) is connected to the rotating support (1).
0). In the present apparatus, the rotation of the polishing pad (9) is passively performed by the rotation of the processing head (4). However, by providing a rotation driving mechanism on the rotation support (10), the polishing pad (9) is activated. You may rotate it. Further, the rotation support part (10) comprises a workpiece (1) held by a processing head (4) and a polishing pad (9).
And also serves as a pressure mechanism for bringing the pressure into contact. Abrasive grains (1
The turbid liquid (12) in which 1) is dispersed is supplied to the turbid liquid supply mechanism (1).
According to 3), it is supplied to the surface of the workpiece (1) and the surface of the polishing pad (9). Reference numeral 14 denotes a monitor device for observing a change in the polishing state of the workpiece (1) during the polishing process based on a change in infrared light absorption on the surface. Reference numeral 15 denotes an electrode for continuously applying a voltage to the surface of the workpiece (1) even during rotation, and reference numeral 16 denotes an electrode for applying a voltage to the turbid liquid. The two electrodes and the power supply (17) together form a power supply (18). 19 is a gas supply device for irradiating the surface of the workpiece with gas.

Hereinafter, the principle of the present invention will be described with reference to results obtained by using the present apparatus. FIG. 2 shows changes in infrared light absorption on the surface of the copper thin film observed by a monitor device (14) when the surface of the copper thin film is formed on a silicon wafer and subjected to a surface flattening process. . The processing conditions were as follows: 1 to 10 ⁻³ M KOH solution as abrasive grains (11).
wt% fumed silica was added to the turbid liquid (1
2) As the pressing stress of the polishing pad (9), 55.5 k
Polishing was performed with Pa at a rotation speed of the processing head (4) of 50 rpm. Fig. 2 shows the time change of infrared light absorption at that time.
(A). The polishing rate at this time is 1 nm / min.
Met. In addition, during the treatment, absorption indicated by “Cu ₂ O” is seen in the figure, and it can be seen that Cu ₂ O is always formed on the copper surface. On the other hand, FIG. 2B shows a case where 1% by weight of hydrogen peroxide was added to the turbid liquid (12) during the same surface treatment. At this time, the polishing rate is 2
It increased remarkably to 0 nm / min. Also, no absorption by Cu ₂ O was seen at any point in the treatment. In addition, since absorption of CuO formed on the copper surface in the air was not observed in any case, observation was performed by X-ray photoelectron spectroscopy (XPS) which is another surface analysis method. FIG. 3 shows the observation results. From XPS observation,
CuO was not found on the surface of the copper thin film after polishing.

Here, the effect of the addition of the hydrogen peroxide solution on the copper surface in the above-mentioned flattening treatment is described as follows.
(urbaix) diagram is shown in FIG. From the figure, it can be seen that when no aqueous hydrogen peroxide is added, both CuO and Cu ₂ O should be formed, and when the aqueous hydrogen peroxide is added, only CuO is formed. Then, it was next examined why CuO which should be originally formed is not found on the surface during or after the planarization treatment. First, when a workpiece (1) having a copper thin film surface formed on a silicon surface was immersed in a heated hydrogen peroxide solution, a CuO thin film having a thickness of 200 nm was formed on the copper surface. Next, the workpiece (1) was subjected to surface flattening by a flattening apparatus. FIG. 5 shows the change in infrared light absorption on the copper surface at this time. A large absorption corresponding to 200 nm of CuO is observed on the surface before the treatment. However, this absorption disappeared 30 seconds after the start of the treatment, indicating that CuO was completely removed from the surface during this period. From this, in the above-described planarization treatment of the copper surface to which the aqueous hydrogen peroxide was added, CuO was once formed on the copper surface by the action of the aqueous hydrogen peroxide, but CuO was very brittle. It is thought that it was easily removed by contact with the polishing pad (8). That is, in the planarization process, the brittle Cu
A high surface polishing rate can be obtained under the processing conditions in which O is formed, while the polishing rate is low under conditions in which Cu ₂ O is formed.

Next, by expanding the study based on the Pourbaix diagram and applying a voltage to the copper surface, it is possible to control the formation state of the copper oxide on the surface in a wider range. Therefore, the relationship between the current density and the polishing rate during the planarization process was determined next. Processing conditions are 10 ⁻³ M
A KOH solution to which 1% by weight of hydrogen peroxide was added was used as the turbid liquid (12). However, no abrasive grains were used here. The pressing stress and the rotation speed of the processing head (4) are the same as the above. FIG. 6 shows the measurement results. In the figure, the place where the bulb density is 0 mA / cm ² is the same condition as in the previous experiment when hydrogen peroxide solution was added without applying a voltage. First, as the current density is increased in the positive direction, the polishing rate is correspondingly increased. This is considered to be because the formation rate of brittle CuO is increased and the polishing amount is increased by increasing the current density from the Pourbaix diagram. Conversely, in the negative direction, here -0.20 mA /
When a voltage of cm ² was applied, the copper surface was not polished. At this current density, no Cu ₂ O is formed on the copper surface, and the copper surface remains unoxidized. On the copper surface that has not been oxidized, even if the abrasive grains are pressed, the surface only undergoes elastic deformation or compositional deformation, and is considered not to be detached from the surface. Conceivable.

[0014]

Embodiment 1 First Embodiment Copper is physically vapor-deposited on a surface having a fine groove structure as shown in the sectional view of FIG. 7A, and is buried as shown in FIG. 7B. At this time, an extra copper layer having irregularities was removed and flattened using the apparatus shown in FIG. A suspension obtained by suspending silica fine particles in a 10 ⁻³ MKOH solution as a turbid solution and further adding 1 wt% of hydrogen peroxide as an oxidizing agent was used. When the removal rate of the copper layer at this time was previously checked, it was about 200 nm per minute. From now on, FIG.
As shown in FIG. 7 (c), the time required for the polishing of the surface of the workpiece to be exposed as shown in FIG. It was found that the shape was obtained. Further, when ozone is dissolved as an oxidizing agent in the turbid liquid, when ozone is sprayed on the surface of the workpiece during polishing, a current of +0.1 mA / cm ² is applied to the copper surface in the turbid liquid to perform anodic oxidation. The shape as shown in FIG. 7C was obtained even when the polishing was performed. Further, a method of detecting when the polishing reaches the silicon oxide layer in FIG. 7 (c) from a change in the reflectance when infrared light is projected onto the surface of the workpiece and a method from the change in the motor torque are tried. As a result, it was found that both could accurately detect the end point.

Second Embodiment The grooves formed of silicon oxide shown in FIG. 7A do not have the same depth, but have a slight variation in the height of the silicon oxide layer. When embedding in the deposition and shaving off an extra copper layer, after polishing reaches the silicon oxide layer, polishing must be performed by an extra amount due to the variation in height of the silicon oxide layer, and a layer in which silicon oxide and copper are mixed Must be polished. This is necessary for improving the process margin. Therefore, first, polishing and flattening are performed by a flattening method as shown in the first embodiment to a place where the silicon oxide layer and the copper layer are mixed. Generally, since the polishing rate of copper is higher than that of other materials, if polishing is performed as it is, a so-called dishing in which the copper layer portion is cut off occurs. Therefore, the polishing from there was used as a turbid liquid and 10 ^−3.
Hydrogen was dissolved in the MKOH solution to reduce the oxidation-reduction potential of copper, and polishing was performed while suppressing oxidation of the copper surface in the turbid solution. At this time, the polishing rate of copper can be controlled by the concentration of dissolved hydrogen, and the concentration is set so that the polishing rates of copper and silicon oxide become substantially equal. As a result, a layer in which copper and silicon oxide were mixed was able to be polished without causing dishing. Furthermore, even when polishing was performed while suppressing the formation of an oxide layer on the surface by flowing a negative current to copper in the turbid liquid, a layer in which copper and silicon oxide were mixed was able to be polished without dishing. .

[0016]

As described above, in the planarizing method according to the present invention, the formation of CuO on the copper surface or copper thin film surface to be processed is promoted by an electric or chemical action, whereby It has become possible to increase the polishing rate of the workpiece. In addition, by the same action, the formation of oxides on the surface of the workpiece is suppressed, or Cu ₂ O is formed on the surface of the workpiece so that the copper surface is hardly polished. did it. By combining the respective effects of this planarization treatment method and controlling the composition of the copper oxide formed on the surface in accordance with the increase in the polishing amount, immediately after the start of polishing, by polishing at a high polishing rate, In addition, it is possible to increase the production efficiency and suppress the polishing rate in the vicinity of the polishing end point, thereby suppressing shape defects in flattening such as thinning and dishing.

[Brief description of the drawings]

FIG. 1 shows the configuration of an apparatus according to the present invention.

FIG. 2 shows a change in infrared light absorption of a copper thin film surface during a surface flattening process.

FIG. 3 shows the results of XPS observation of the surface of the copper thin film after the surface flattening treatment.

FIG. 4 is a Pourbaix diagram showing a hydrogen peroxide solution effect in the surface flattening process.

FIG. 5 shows a change in infrared light absorption during surface flattening treatment of copper having a CuO thin film formed on the surface with a heated hydrogen peroxide solution.

FIG. 6 shows a relationship between a current density and a polishing rate during a planarization process.

FIG. 7 is a diagram showing a state of a workpiece surface subjected to a flattening process.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Workpiece 2 Silicon wafer 3 Copper thin film 4 Processing head 5 Wafer holder 6 Motor 7 Reduction gear 8 Polishing cloth 9 Polishing pad 10 Rotation support part 11 Abrasive grains 12 Cloudy liquid 13 Cloudy liquid supply mechanism 14 Monitor device 15 Electrode 16 Electrode 17 Power supply 18 Power supply device 19 Gas supply device 21 Silicon oxide 22 Silicon nitride 23 Silicon substrate 24 Copper

Continued on the front page (72) Inventor Hiroki Ogawa 2-18-1, Shin-Yokohama, Kohoku-ku, Yokohama-shi, Kanagawa Prefecture Century Shin-Yokohama Room 701 (72) Inventor Jun Kikuchi 2--14-6, Shirokanedai, Minato-ku, Tokyo F-term (reference) 3C058 AA12 AC01 AC02 AC04 BA01 BA06 BA09 CB01 CB02 CB03 DA02 DA12 DA17

Claims (10)

[Claims] 1. A processing head which holds copper or a workpiece having a copper thin film on its surface and holds a rotating processing head and a polishing cloth,
A polishing pad to be rotated, a pressing mechanism for pressing the workpiece held by the processing head into contact with the polishing pad, and a surface of the workpiece and a polishing pad containing a turbid liquid in which abrasive grains are dispersed. It has a turbid liquid supply mechanism for supplying to the surface, and a monitor device for observing the polishing state of the workpiece, and further, a voltage is continuously applied to the surface of the workpiece even during rotation of the workpiece. A power supply device comprising an electrode for applying a voltage and an electrode for applying a voltage to the turbid liquid and a power supply for supplying a voltage to the two electrodes, or a gas supply device for irradiating a gas to the surface of the workpiece In a surface flattening treatment device for a workpiece having both or any of the devices, while applying a voltage so that the potential of the surface of the workpiece becomes positive with respect to the turbid liquid,
Alternatively, while applying a voltage so that the potential of the surface of the workpiece becomes negative with respect to the turbid liquid, or while supplying a turbid liquid obtained by mixing a chemical such that the turbid liquid has an oxidizing property, Alternatively, while supplying a turbid liquid in which the turbid liquid is mixed with a chemical liquid having a reducing property, or while irradiating an oxidizing gas to the surface of the workpiece, or using two or more of the above-described methods. A surface flattening method characterized by processing a workpiece surface while combining. 2. A processing head which holds copper or a workpiece having a copper thin film on its surface and holds a rotating processing head and a polishing cloth,
A polishing pad to be rotated, a pressing mechanism for pressing the workpiece held by the processing head into contact with the polishing pad, and a surface of the workpiece and a polishing pad containing a turbid liquid in which abrasive grains are dispersed. It has a turbid liquid supply mechanism for supplying to the surface, and a monitor device for observing the polishing state of the workpiece, and further, a voltage is continuously applied to the surface of the workpiece even during rotation of the workpiece. A power supply device comprising an electrode for applying a voltage and an electrode for applying a voltage to the turbid liquid and a power supply for supplying a voltage to the two electrodes, or a gas supply device for irradiating a gas to the surface of the workpiece A surface flattening treatment apparatus for a workpiece having both or any of the above. 3. The potential of copper forming the surface of the workpiece in the turbid liquid according to claim 1 is a potential at which CuO, which is a divalent oxide, can be stably present on the copper surface. A surface flattening treatment method characterized by the above-mentioned. 4. The potential of copper constituting the surface of the workpiece in the turbid liquid according to claim 1, wherein the surface of the copper is charged with a monovalent oxide of Cu ₂ O or non-oxidized metallic copper. Surface flattening method, characterized in that the potential is set to a potential that can stably exist. 5. A surface flattening method according to claim 1, wherein the turbid liquid has an oxidizing property, and the chemical is hydrogen peroxide. 6. A method for flattening a surface according to claim 1, wherein the turbid liquid according to claim 1 is a liquid in which hydrogen is dissolved. 7. A surface flattening method according to claim 1, wherein the oxidizing gas is ozone (O ₃ ). 8. The surface flattening method according to claim 1, wherein the monitoring device for observing the polishing state of the workpiece is a method for measuring a lapse of processing time from the start of polishing. Processing method. 9. A method according to claim 1, wherein the monitor for observing the polishing state of the workpiece is a method for measuring a rotational torque required to rotate the processing head or the polishing pad during polishing. A surface flattening method. 10. A monitor device for observing a polished state of the workpiece according to claim 1, which is a method for measuring a change in light absorption or reflection state of a surface of the workpiece during polishing processing. A surface flattening treatment method characterized by the above-mentioned.