Plating analysis method

Details Plating analysis method Plating analysis method

2000-11-17

2003-04-01

Picard, Leo (Department: 2125)

Data processing: generic control systems or specific application

Specific application, apparatus or process

Product assembly or manufacturing

C205S081000, C205S082000, C205S083000, C205S084000, C205S096000, C205S097000, C205S724000

Reexamination Certificate

active

06542784

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a computer-assisted analysis method for predicting the growth rate distribution of a plated film in electroplating to obtain a uniform plating thickness distribution. More particularly, the invention relates to a method preferred for analysis of the plating rate distribution of a metal intended for wiring on a semiconductor wafer.
2. Description of the Related Art
In a system in which an anode and a cathode constitute a cell via an electrolyte and form a potential field in the electrolyte, a potential distribution and a current density distribution are important for such a problem as a plating or corrosion problem. To predict these distributions in the system, computer-assisted numerical analysis by the boundary element method, the finite element method, or the finite difference method has been attempted. This analysis is conducted based on the facts that the potential in the electrolyte is dominated by Laplace's equation; that the potential and current density on the anode surface and the cathode surface are ruled by an electrochemical characteristic, called a polarization curve (nonlinear functions found experimentally for showing the relationship between potential and current density), determined by a reaction caused when the anode and the cathode are disposed in the electrolyte; and that the current density is expressed as the product of a potential gradient and the electrical conductivity of the electrolyte.
In electroplating, the plating rate of a metal deposited on the cathode can be calculated from the analyzed current density of the cathode by Farady's law. Thus, the above-mentioned numerical analysis enables the plating rate distribution to be predicted beforehand according to the conditions, such as the structure of a plating bath, the type of a plating solution, and the types of materials for the anode and the cathode. This makes it possible to design the plating bath rationally.
In recent years, it has been attempted to utilize electroplated copper for wiring in a semiconductor integrated circuit. In this case, as shown in
FIG. 1A
, fine grooves
2
are formed by etching in a surface of an interlayer insulator film
1
of SiO
2
or the like on a semiconductor wafer W. Copper, a material for wiring, is buried in the grooves
2
by electroplating. To prevent mutual diffusion between the copper and the SiO2 film, a barrier layer
3
of TaN or the like is formed beforehand on the surface of the SiO
2
film by a method such as sputtering. Since SiO
2
and TaN are insulators or high resistance materials, a thin film (called a seed layer)
4
of copper, which acts as a conductor and an electrode for electroplating, is formed on the TaN by a method such as sputtering.
The seed layer
4
of copper formed beforehand is as thin as about several tens of nanometers in thickness. While a current is flowing through this thin copper seed layer, a potential gradient occurs in this seed layer because of its resistance. If plating is carried out with a layout as shown in
FIG. 1A
, a nonuniform thickness of plating, i.e., thick on the outer periphery and thin on the inner periphery, arises as shown by a solid line
5
in the drawing, since a current flows more easily nearer to the outer peripheral region. As shown in
FIG. 1B
, moreover, when a metal such as copper is buried in fine holes or fine grooves by plating, a potential gradient appears in the copper seed layer because of the resistance of the seed layer. As a result, the plating rate increases near the entrance of the hole or groove, and defects, such as portions void of copper, occur in the hole or groove. An additive for suppressing the reaction is used to bring down the preferential growth rate of a plating in the vicinity of the groove, thereby preventing the occurrence of internal defects.
Many conventional methods of plating analysis are based on the concept that a potential gradient occurs only in an electrolyte, and the resistances of an anode and a cathode are so low as to be negligible. In analyzing the current density distribution and the voltage distribution of electroplating on a semiconductor wafer, however, the resistance on the electrode side cannot be neglected, and needs to be considered.
An example of a plating analysis method taking the electrode-side resistance into consideration has been attempted by the finite element method. According to this method, the interior of a plating solution region is divided into elements. Resistance conditions for the plating solution are put into these elements, and the electrode with resistance is divided into elements as deposition elements. Resistance conditions for the electrode are put into these elements. Furthermore, an element called an overvoltage element is newly created at a position, on the surface of the electrode (mainly cathode), in contact with the plating solution. In this element, the conditions for polarization resistance of the electrode are placed. The entire element is regarded as a single region, and analyzed by the finite element method. The deposition elements correspond to a plated film. The thickness of the plated film at the start of plating is zero. Then, the film thickness determined by the current density calculated at elapsed time points is accumulated, and the values found are handled as the thickness.
A suitable structure of the plating bath and a suitable arrangement of electrodes are devised by numerical calculation or based on a rule of thumb. To make the plating rate uniform, placement of a shield plate in the plating solution for avoiding concentration of a current in the outer peripheral portion, for example, has been proposed and attempted. However, a sufficient effect has not been obtained. Nor has any rational method concerning a design of the shield plate been established up to now.
It is generally pointed out that the boundary element method requiring no element division of the interior is advantageous in analyzing problems (such as plating, corrosion and corrosion prevention problems) for which a potential distribution and a current density distribution on the surface of a material are important. The boundary element method is applied to the analysis of a plating problem requiring no consideration for the resistance of an electrode, and its effectiveness has already been confirmed. However, it has not been known that the boundary element method can be applied for a plating problem requiring consideration for the resistance of an electrode.
As described above, the finite element method has been applied to a plating problem requiring consideration for the resistance of an electrode. However, the finite element method requires the division of the interior into elements, thus involving a vast number of elements. Consequently, this method takes a long time for element division and analysis.
SUMMARY OF THE INVENTION
The present invention has been accomplished under these circumstances. An object of the invention is to provide a plating analysis method which can obtain a current density distribution and a potential distribution efficiently for a plating problem requiring consideration for the resistance of an electrode. Another object of the invention is to provide a plating analysis method for optimizing the structure of a plating bath designed to uniformize a current, which tends to be concentrated near an outer peripheral portion of a cathode, thereby making the plating rate uniform.
A first aspect of the present invention is a plating analysis method for electroplating in a system. The method comprises: giving a three-dimensional Laplace's equation, as a dominant equation, to a region containing a plating solution between an anode and a cathode; discretizing the Laplace's equation by a boundary element method; giving a two-dimensional or three-dimensional Poisson's equation dealing with a flat surface or a curved surface, as a dominant equation, to a region within the anode and/or the cathode; discretizing the Poisso

Affiliated with

Also associated with

Rating

Plating analysis method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Plating analysis method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Plating analysis method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3108357