JP2001181895A - Process window for electrochemical deposition of high aspect ratio structures - Google Patents

Abstract

(57) Abstract: Provided is a method for plating metal on a substrate having an opening with a high aspect ratio without defects. Kind Code: A1 A metal having a molar concentration of about 0.2 M to about 1.2 M, a suppression additive having a concentration of about 3.75 mL / L to about 15 mL / L of the total solution, and about 0.175 mL / L of the total solution. L
A plating method performed in a solution containing a promoting additive at a concentration of about 2.1 mL / L. The temperature of the plating solution is less than about 30 ° C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

FIELD OF THE INVENTION The present invention relates to a novel formulation of a metal plating solution designed to fill small features, eg, sub-micron scale features, formed on a substrate. In particular, the invention relates to defect-free filling in the form of copper.

[0002]

BACKGROUND OF THE INVENTION As circuit densities move toward the next generation of very large scale integration, copper has become the metal of choice for filling sub-micron high aspect ratio interconnected features on substrates. . Because copper and its alloys
This is because the low efficiency is lower than aluminum, and the electromigration resistance is extremely higher than aluminum. These features are important to support the high current densities experienced at high levels of integration and increasing device speeds. The aspect ratio for a feature, ie, the ratio of feature height to feature width, increases with each generation of integration. Many conventional deposition processes have aspect ratios of 4:
Structures exceeding 1, among which the aspect ratio is 10:
It was difficult to fill structures that exceeded 1 and were 350 nanometers wide. Further, as the feature width decreases, the associated features will receive increased current densities, requiring the metal to be formed without defects within the associated features. Thus, there is a great deal of research and development towards defect-free, submicron, high aspect ratio features.

[0003] Despite the desirability of using copper in the manufacture of semiconductor devices, the choice of how to make copper in a very high aspect ratio form is limited. This is because general chemical vapor deposition and physical vapor deposition have yielded only unsatisfactory results. Electrodeposition of metal is considered to be a promising technology in the manufacture of integrated circuits and flat panel displays, and it has been predicted that it may be an economical and viable solution to the demands of future copper coordination. Therefore, to design hardware and chemistry with the aim of providing a high quality film on the substrate that fills or conforms to a uniform and very small feature over the entire surface of the substrate More and more efforts are being concentrated in this area. In general, the chemistry used in conventional plating cells, i.e., chemical recipes and conditions, will result in acceptable plating results when used for many different applications on many different cell designs in many different cell designs. Is designed to obtain Extremely uniform current density (and deposition thickness distribution) for specific plated parts
For cells that are not specifically designed to obtain a high electrodepositivity, use a highly conductive solution to achieve good coverage on all surfaces to be plated.
(Also known as high Wagner numbers). Generally, a supporting electrolyte, such as an acid or base, and a conductive salt are included in the plating solution to provide the plating solution with the high ionic conductivity required to achieve high "throwing power". ing. The supporting electrolyte does not participate in the electrode reaction, but reduces the resistivity inside the electrolyte to provide a conformal coating of the material to be plated over the surface of interest. Otherwise, the high low efficiency that occurs can cause non-uniform current density across the plating surface.

A problem encountered with conventional plating solutions is that the deposition process into small features is not due to the strength of the electric field, as is common for large features, but the mass transport (diffusion) of reactants into the feature, And the kinetics of the electrolytic reaction. In other words, the filling rate at which plating ions are provided to the target surface can limit the plating rate regardless of the voltage or current density applied to the plating surface. Thus, conventional conductive electrolyte solutions that impart "throwing power" have little significance in obtaining good coating and filling in very small forms. Furthermore, in the presence of an excess of acid or base supporting electrolyte (even with a relatively slight excess), the transport rate is reduced by almost half (or the concentration depletion for the same current density is almost doubled). This can lead to poor deposition quality, which can lead to filling defects, especially on small features. Most of the copper plating solutions used for electrodeposition are multi-component systems, including copper electrolytes, inhibitors, and accelerators or brighteners. Inhibitors and accelerators compete for adsorption sites on the plating surface. Suppressors (hereinafter additive "Y") inhibit or reduce copper deposition in the adsorption area, whereas brighteners or accelerators (hereinafter additive "X"). Promotes the growth of copper in the adsorption area. One problem encountered as a result of this competition for adsorption sites is that the accumulator accumulates in the via / trench openings and the via / trench is not filled before the via / trench is completely filled.
The problem is that the opening of the trench may be closed, resulting in defects in the via / trench. Another problem is that various parameters, such as temperature, electrode voltage, and acidity of the solution, affect the ability of the inhibitors and accelerators to provide a bottom-up coating in form.

[0005]

As a result of these chemical limitations in electrochemical deposition, a method of plating metal in small features (eg, submicron dimensions and smaller features) on a substrate is disclosed. There is a need for a method of providing defect-free filling to very small features.

[0006]

SUMMARY OF THE INVENTION The present invention relates to a method for manufacturing a liquid crystal display comprising:
About 1.2 M molar concentration of metal ions, about 3.7 of total solution
The substrate and the suppressed plating solution comprising a suppressive additive at a concentration of 5 mL / L to about 25 mL / L and a promoting additive at a concentration of about 0.175 mL / L to about 5 mL / L of the total solution. A method is provided for plating metal on a substrate having a high aspect ratio opening, comprising the step of disposing an anode. The metal is electro-deposited into features on the substrate without forming defects on the substrate. The pH of the plating solution is about 2.
It is less than 75, preferably, the pH is less than about 1.6. The temperature of the plating solution is typically less than about 30 ° C.,
Preferably it is between about 15C and about 20C. Defect-free filling is improved by increasing the flow rate of the plating solution even further, e.g.
Flow rates exceeding gallons (gpm) can be used. In another aspect of the invention, a wafer loading voltage is applied that is applied to the substrate while immersing the substrate in a plating solution. If the pH of the plating solution is about 1.6 or above, the filling of the morphology can be improved with a wafer loading voltage of about -4.0V, and the pH of the plating solution can be about 1
If it is, the filling of the features can be improved with a wafer loading voltage of about -0.8V.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention generally provides a deposition method for defect-free filling of associated features having a high aspect ratio (eg,> 4: 1) on a substrate. The associated features are typically formed in a dielectric layer on the substrate.
A conformal barrier layer is typically deposited over the dielectric layer, including associated features, to prevent copper from diffusing into adjacent layers, typically silicon dioxide, silicon, or other dielectric materials. I do. Barrier layers for copper applications are effective for interlayer dielectric applications and include titanium (Ti), titanium nitride (TiN), tantalum (Ta), tantalum nitride (T
aN _x ), tungsten (W), tungsten nitride (W
N _x ) or a combination of these layers. The most preferred barrier materials are Ta and / or TaN, which are usually provided as PVD layers. The barrier layer is deposited and forms a substantially continuous cap over the dielectric layer and may be treated with nitrogen to improve barrier properties or adhesion to adjacent layers. A conformal metal seed layer is deposited over the barrier layer to facilitate electroplating. In the case of electrochemical deposition of copper, the seed layer may include a copper seed layer deposited by PVD or CVD.

The method of the present invention comprises the steps of placing a substrate (biased as a cathode) and an anode in a suppressed plating solution, and then plating metal ions on the substrate in the plating solution. Including. The plating solution comprises a molar concentration of about 0.2 M to about 1.2 M metal ions,
It includes a suppressive additive at a concentration of about 3.75 mL / L to about 25 mL / L of the total solution and a promoting additive at a concentration of about 0.175 mL / L to about 5 mL / L of the total solution. P of plating solution
H is less than about 2.75 and the temperature of the plating solution is typically less than about 30 ° C. For an 8 inch substrate, it is preferred to introduce the plating solution into the electrochemical deposition cell at a flow rate greater than about 2 gallons per minute (gpm).

The experimental data presented below has some standard conditions and components. Using a manufacturing condition recommended by the device manufacturer, a conformal TaN barrier layer approximately 250 Å thick was patterned using a Vectra IMP source available from Applied Materials, Inc. of Santa Clara, California. An applied Si / SiO ₂ dielectric layer was deposited on an 8 ″ substrate above. Applied Materials, Santa Clara, Calif. Was then fabricated using the manufacturing conditions recommended by the device manufacturer. A 2000 Angstrom thick PVD Cu seed layer was deposited over the TaN barrier layer using an Electra Cu source available from the company, Inc. For the experimental data shown below, the starting composition of the plating solution selected was: Suitable additives (suppressors and accelerators)
Is about 2.75 after the addition of copper sulfate, and the pH value of copper sulfate is 0.10.
85M. The plating process was performed on an Electra ECP system available from Applied Materials. The temperature of the plating solution from 15 ° C to about 25
The temperature was changed from 2.75 to 0.5 while examining the effect on via / trench filling while changing the temperature to <0> C. The additives used, accelerator "X" and inhibitor "Y", were supplied by Lear Lonal (New York, USA) and are known as Electraplate XRev1.0 and Electraplate YRev1.0, SB
It is also known as an additive. Scanning electron microscopy (SEM) and focused ion beam (FIB) techniques were used to examine via trench filling.

Generally, aqueous copper plating solutions containing copper sulfate, preferably those containing about 32 to about 192 grams per liter (g / L) of copper sulfate pentahydrate in water (H ₂ O). , Used as electroplating solution. In addition to copper sulfate, the present invention contemplates utilizing other copper salts such as copper fluoroborate, copper gluconate, copper sulfamate, copper sulfonate, copper pyrophosphate, copper chloride, copper cyanide, and the like. I have. Some of these copper salts exhibit higher solubility than copper sulfate and may be advantageous in this regard. The process of depositing small (ie, submicron) features is controlled not by the strength of the electric field, but by the mass transport (diffusion) of the reactants into the features and the kinetics of the electrolytic reaction. Thus, the filling rate at which plating ions are provided to the surface of the form may limit the plating rate, regardless of voltage. Generally, as the flow rate of the material increases, the plating rate increases. For vias with a 4: 1 aspect ratio,
Experimental data collected on gap filling at various flow rates shows that higher flow rates achieve better gap filling. Therefore, in order to obtain good quality deposition, the mass transport rate needs to be faster than the consumption rate of the reactant concentration near or inside the small form. Plating solutions having high copper concentrations (ie,> 0.4M) are advantageous in overcoming mass transport limitations when plating small features. In particular, for sub-micron scale features with high aspect ratios, the electrolyte usually flows only minimally or not at all, so ion transport is a diffusion for deposition of metal into such small features. Only depends on. Generally about 0.2M
約 1.2 M, preferably about 0.4 M
High copper concentrations in the electrolyte, such as or above, improve the diffusion process and reduce or eliminate mass transport limitations. The metal concentration required for the plating process may depend on other factors such as the acid concentration of the electrolyte and the temperature.

[0011] The copper plating electrolyte increases the conductivity of the electrolyte in the solution by about 4 per liter (L) of H ₂ O.
5g of H ₂ SO ₄ (0.45M) ~ about 110g / L (1.
12 M) of sulfuric acid. Due to the high conductivity, as encountered with conventional electroplating cells,
Non-uniformity of the deposited thickness due to cell configuration and variously shaped components can be reduced. The plating solution may include inhibitors and accelerators to assist in filling small forms. The suppressor adsorbs to the wafer surface and inhibits or reduces copper deposition in the adsorbed area. The inhibitor added to the plating solution may include a binary polyethylene glycol-based inhibitor, such as an inhibitor consisting of a random / block copolymer of ethylene oxide and propylene oxide mixed in a wide range of ratios. . The promoter competes with the inhibitor for adsorption sites and promotes copper growth in the adsorption area. The accelerator used in the plating solution may include a sulfur-containing compound, such as sulfite or disulfate. Accelerators have relatively small molecular dimensions,
Can diffuse faster than accelerators. Because the inhibitor inhibits copper growth, and the inhibitor and promoter are ubiquitous around the via / trench, small overhangs in the seed layer can block the via / trench opening and cause defects in the via. Can be brought. Therefore, the most desirable plating solution is
At the top of features with topographical features, the suppression is primarily active, and within the trench or via, the promoter is more active dominant than the suppressor, achieving bottom-up growth. is there. In one aspect, the plating solution comprises a promoter at a concentration of 0.175 mL / L to 5 mL / L, and an inhibitor at a concentration of 3.75 mL / L to 25 mL / L.

Experimental data for inhibitor ("Y") and accelerator ("X") compositions were used for electrochemical gap fill deposition to fill vias using various compositions of "X" and "Y". Collected. The data showed that as the concentration of X relative to the concentration of Y increased, the performance for defect-free gap filling deteriorated. The activity of the inhibitors and accelerators depends on the temperature, the pH of the plating solution,
And various parameters such as the chloride concentration in the plating solution. The temperature effect of the activity of an additive is related to the polarity dependence of the additive on temperature. Detailed studies of gap filling in vias using various concentrations of "X" and "Y" indicate that medium to high aspect ratios (4: 1 aspect ratio) with plating solution temperatures of 15-20C. Has shown that a relatively good and defect-free via / trench filling can be obtained. However, the temperatures at which this defect-free filling can be achieved will be different for different plating solution compositions and for different additives in the plating solution. In addition to temperature, the pH of the plating solution also affects the quality of the defect-free fill. Experimental data shows that lowering the pH of the plating solution, ie, increasing the concentration of sulfuric acid, improves the results of gap filling. The plating solution of the present invention also converts halide ions such as chloride from about 30 ppm to about 100 pp.
m.

The control of the deposition rate of the electrochemical solution is improved by the addition of inhibitors and accelerators. Since retarders and accelerators tend to fill the via / trench openings as soon as the wafer comes into contact with the plating solution, any delay between immersing the wafer in the plating solution and starting the actual plating will not occur. , Defects in the morphology due to random distribution of additives, and etching of the seed layer. To reduce such defect activity, a wafer loading bias of about -0.2V to about -20V is applied to the substrate plating surface while the substrate is immersed in the plating solution. The experimental data collected show that applying a loading bias of about -0.4 V for plating solutions having a high pH above 1.6 while loading the wafers can provide a defect-free form of filling. ing. For plating solutions having a pH of less than 1.0, immersion loading bias of about 0.8 V or more will provide good defect-free filling. This observation can be linked to reduced seed layer etching due to the acidity of the plating solution and the associated polarity of the additive at these voltages. Rotating the substrate during the plating process while immersing the substrate in the plating solution can improve plating results. The substrate may be loaded into the plating solution at a rotation speed from about 10 rpm to about 50 rpm. About 1r during plating
The substrate may be rotated at a speed from about pm to about 50 rpm.
The plating process is from about ² mA / cm ² to about 80 mA / c
The current density may be in the range of m ² . The plating process may be performed using a multi-step process, in which case about 2
An initial current density between mA / cm ² and about 20 mA / cm ² is applied to the plating surface until the associated features are substantially filled, and then from about 20 mA / cm ² to about 80 mA
/ Cm ² applied to the plating surface
The formation of the metal layer on the substrate is completed. The initial low current density provides conformal plating and defect-free filling of the plating surface. After the form is substantially filled, the current density applied to the plating surface is increased to increase the plating rate and reduce the process time required to complete the deposition of the metal layer on the substrate. Good.

Although the preferred embodiments of the present invention have been described above, without departing from the basic scope of the present invention,
Other or further forms of the invention may be devised, the scope of which is defined by the claims.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Alan DuBois, USA 94086 Sunnyvale Bryant Avenue 668 (72) Inventor Srinivas Gandicota United States of America 95051 Santa Clara Monroe Street 2727 (72) Inventor Shu Neo, United States of California 95051 Santa Clara Halford Avenue 1556-292 (72) Inventor Rian Yu Chen United States of America 94404 Foster City Melbourne Street 1400 (72) Inventor Robin Cheung United States of America 95104 Coupertino Crujic Place 21428 (72) Inventor Daniel car United States, California 94566 Pleasanton Pomezia coat 2161

Claims (18)

[Claims] 1. A method of plating metal on a substrate having a high aspect ratio opening, comprising: disposing a substrate and an anode in a plating solution, wherein the plating solution comprises about 0.2M About 1.2 M molar concentration of metal ions, about 3.75 mL / L of total solution to about 25 mL / L inhibitory additive, and about 0.175 mL / L to about 5 mL / L of total solution. Concentration promoting additive, comprising, said step, and the step of plating metal ions on a substrate in a plating solution,
The above method, comprising: 2. The method of claim 1, wherein the pH of the plating solution is less than about 2.75. 3. The plating solution has a pH of less than about 1.6.
The method of claim 1. 4. The temperature of the plating solution is less than about 30 ° C.
The method of claim 1. 5. The method of claim 1, wherein the temperature of the plating solution is between about 15 ° C. and about 20 ° C. 6. The method of claim 1, wherein the plating solution comprises a molar concentration of about 0.85M metal ions. 7. The method of claim 1, wherein the metal ion is a copper ion. 8. The method of claim 1, further comprising the step of biasing the substrate with a loading bias between about -0.2V and about -20V while immersing the substrate in the plating solution. 9. The method of claim 1, further comprising rotating the substrate at a speed between about 10 revolutions per minute to about 50 revolutions per minute while immersing the substrate in the plating solution. 10. During plating, about 1 revolution per minute to about 50 revolutions per minute.
Further comprising rotating the substrate at a speed during the rotation.
The method according to claim 9. 11. The method according to claim 1, wherein the plating solution comprises a halide ion. 12. The plating solution according to claim 1, wherein the plating solution has a concentration of about 30 ppm to about 100 ppm.
2. The method according to claim 1, comprising a concentration of chlorine between ppm. 13. The method of claim 1, wherein the plating is performed during plating from about ² mA / cm ² to about 80.
The method of claim 1, wherein the substrate is biased at a current density between mA / cm ² . 14. The method according to claim 1, wherein the first step is about ² mA / cm ² to about 20 mA.
/ Cm ² at a first current density, then about 20 mA
/ Cm ² to about 80 mA / cm ² at a second current density,
The method of claim 1, wherein the substrate is biased. 15. The method according to claim 1, wherein the inhibitor comprises a mixture of polyethylene glycol. 16. The method according to claim 1, wherein the inhibitor comprises a copolymer of ethylene oxide and propylene oxide. 17. The method of claim 1, wherein the accelerator is a sulfur-containing compound. 18. The method of claim 1, wherein the flow rate of the plating solution is greater than about 2 gallons per minute.