US20070089995A1

US20070089995A1 - Damascene copper plating for coils in thin film heads

Info

Publication number: US20070089995A1
Application number: US11/258,570
Authority: US
Inventors: Jennifer Loo; Murali Ramasubramian; Rebecca Simmons
Original assignee: Hitachi Global Storage Technologies Netherlands BV
Current assignee: HGST Netherlands BV
Priority date: 2005-10-24
Filing date: 2005-10-24
Publication date: 2007-04-26

Abstract

An optimized plating bath composition suitable for plating coil structures in thin film magnetic heads is disclosed. The disclosed bath composition is based on Shipley High Acid Damascene copper electroplating baths containing A-2001 accelerator and S-2001 suppressor components.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to the plating of coil structures for thin film magnetic heads. More specifically, the invention discloses plating solution compositions for damascene copper plating of coil structures for thin film heads.
2. Description of the Related Art
Historically, coil structures in thin film heads of the prior art have utilized traditional through mask plating technology. As head pitch (the distance between adjacent heads) continues to shrink, coil structures shrink with the head pitch, requiring the use of damascene copper plating processes. Damascene plating processes are commonplace in the semiconductor manufacturing arena, but have been optimized for sub-micron geometries. Thin film heads require plating of critical dimensions on the order of a few microns, which is generally an order of magnitude greater than those seen in semiconductor manufacturing. When semiconductor damascene plating chemistries are used for the larger micron sized dimensions, defects occur in the filled, plated structures. This is generally due to the fact that bath additives, copper concentrations, current densities, and other factors have been optimized for sub-micron geometries.
In the article “Automated Control of Plating Bath Additives Increases Wafer Yield”, by Bratin et al., a new generation of online Damascene plating bath analyzers based on cyclic voltammetric stripping (CVS) is described. The tight process window typically required for void free filling of sub-micron high aspect ratio structures makes it important that additives be kept within a tight range, typically within a few percent.
In the article “Cu Plating Today and Tomorrow: Managing the Terminal Effect” by John Klocke of Semitool, the impact of various Damascene plating solution variables on the filling efficiency and thickness uniformity are described.
The Rohm and Haas product brochure entitled “Ultrafill™ 2001 Additive System for Bottom-up Feature Plating”, discloses the features and benefits of the Ultrafill plating chemistries and the manufacturer's recommended operating conditions and parameters for sub-micron semiconductor applications. These recommended operating conditions are targeted for via fill applications of 0.18 microns at aspect ratios greater than 5:1, and trench fill applications of 0.13 microns at aspect ratios of greater than 10:1. For these conditions, the S-2001 suppressor solution recommended concentration is 25 ml/l, and the A-2001 accelerator solution recommended concentration is 1 ml/l.
U.S. Pat. No. 5,407,530 discloses a method of forming a fine conductive pattern. The method allows the fine conductive pattern whose thickness is relatively large to be formed. An insulating layer is formed on a substrate. A pattern resist is formed on the insulating layer. Then, the insulating layer is etched downward based on a profile of the pattern resist in a first etching step, and sidewalls of each of groove portions formed by the etching step of the insulating layer are etched sideways in a second etching step, so that overhang portions are defined at the lower edges of the pattern resist portions. Then, conductive film portions are formed by depositing a conductor on the pattern resist, and conductive films that are on the pattern resist are lifted off, so that a fine conductor pattern can be prepared.
U.S. Pat. No. 6,195,872 discloses a method of manufacturing a thin film magnetic head including a first magnetic layer, a second magnetic layer, a gap layer, and a thin film coil consisting of one or more thin film coil layers. According to the method, the step of forming a first thin film coil layer of the thin film coil comprises, in succession, the steps of: forming a first inorganic insulating layer on a part of the first magnetic layer; forming coil-shaped recesses in the first insulating layer by a reactive ion etching such that the recesses have a width and a spacing which are equal to a width and a spacing of coil windings of the thin film coil layer to be formed and have a depth which is deeper than a height of the coil windings; depositing an electrically conductive material within the recesses by a chemical vapor deposition such that the recesses are completely filled with a deposited electrically conductive material and the surface of the first insulating layer is completely covered with the deposited electrically conductive material; polishing the deposited electrically conductive material such that coil windings are formed in the recesses and the surface of the first insulating layer is exposed to form a flat surface consisting of the exposed surface of the first insulating layer and upper surfaces of the coil windings; and forming a second insulating layer on the flat surface consisting of the exposed surface of the first insulating layer and the upper surfaces of the coil windings.
U.S. Pat. No. 6,377,423 discloses a write head having a second pole tip layer, a coil layer and a write coil insulation layer that are planarized at their top surfaces. A thin top insulation layer insulates the top of the coil layer from a yoke portion of the second pole piece which is connected to the second pole tip layer in the pole tip region and connected to a first pole piece layer in a back gap region. In one embodiment the write gap layer extends throughout the yoke region and provides the only insulation between the first pole piece layer and the coil layer. Further, it is preferred that the write coil insulation layer be an inorganic material such as silicon dioxide (SiO.sub.2). Several embodiments of the write head are provided along with methods of making.
U.S. Pat. No. 6,570,739 discloses a hard disk drive including a magnetic head having a high aspect ratio induction coil. The magnetic head includes a first pole tip piece that is formed upon a first magnetic pole and a second pole tip piece that is part of the second magnetic pole, where the write gap is formed between the first pole tip piece and the second pole tip piece. The use of the two pole tip pieces increases the spacing between the first magnetic pole layer and the second magnetic pole layer such that an induction coil having high aspect ratio coil turns can be formed within the insulation layers. A reactive ion etch (RIE) process is used to form the coil trenches within which the high aspect ratio coil turns are created. An RIE etch stop layer is formed upon the first magnetic pole layer to prevent the RIE etch process from creating coil turn trenches that make contact with the first magnetic pole layer. Where high aspect ratio coil pattern is formed, a finer pitch coil is fabricated, such that the yoke length of the magnetic head is reduced and the flux rise time of the magnetic head is decreased, whereby the magnetic head has an increased data writing rate.
Patent Application Publication No. US2001/0009488 discloses an inorganic insulation underlying layer and an organic insulation underlying layer are formed on a lower core layer behind a recording region. Also, a coil layer is formed on the organic insulation underlying layer. As a result, the withstand voltage between the lower core layer and the coil layer can be improved.
Patent Application Publication No. US2002/0181162 discloses a disk drive write head having a bottom pole, a first insulation layer formed on the bottom pole, a coil formed on the first insulation layer, a second insulation layer formed on the coil, a write gap layer formed on the second insulation layer, and a top pole formed on the write gap layer, where the top pole is substantially flat. A second embodiment is described which is produced by a damascene process.
Patent Application Publication No. US2003/0090834 discloses a writer coil that includes an insulator layer having a top surface and a bottom surface, a dielectric layer positioned on the top surface of the insulator layer, and at least a first and a second coil structure having a pitch of less than about 2 microns. The publication also discloses a method of fabricating a writer coil by depositing an insulator layer, depositing a dielectric layer on the insulator layer, and forming at least one coil space and at least one coil structure within the dielectric layer by a Damascene process.
FIG. 1(a)-(c) (Prior Art) illustrates the simplified process steps of the traditional through mask plating of thin film coil structures of the prior art. A metal seed layer 102 is deposited on the top surface of a substrate. A photo-resist layer 104 is then deposited and patterned on the top surface of seed layer 102, leaving openings where the coil is to be deposited. The seed layer 102 acts as an electrode for the electrochemical deposition of copper 106, which is deposited from the seed layer surface to the top of the mask layer. The mask is then removed (by for example oxidation or “ashing”), followed by the removal of the seed layer, leaving the finished coil structure. Due to the “bottom up” nature of the plating process, this process has limitations as the dimensions approach the micron level, and/or the aspect ratio of the coil elements (depth to width) gets larger.
FIG. 2(a)-(c) (Prior Art) illustrates a simplified damascene process. In this process the seed layer 202 is deposited after the deposition and patterning of mask layer 204. As shown in FIG. 1(a), the seed layer is deposited on all surfaces of the mask layer. The copper 206 is deposited on all surfaces covered by the seed layer, and is grown not only from the bottom of the coil cavities, as is shown in FIG. 1, but from the sides as well. Following the copper deposition, chemical-mechanical-planaraization (CMP) may be utilized to planarize the structure and remove excess copper, as shown in FIG. 2(c).
This process can be utilized to fill very small geometries with large aspect ratios. However, to prevent voids from being formed in the center of the deposit, special additives are required. For example, these additives may include an accelerator, a suppressor, a leveler, and chloride. The plating performance depends on the balance of these components, and a recipe optimized for sub-micron geometries used in the semiconductor manufacturing processes will not give optimum performance for plating coils in thin film magnetic heads. What is needed is a damascene plating solution chemistry optimized for plating coils in thin film magnetic heads.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a copper plating bath for depositing coil structures in thin film magnetic heads containing a Shipley Ultrafill ST2001 High Acid Bath and an additive package including Ultrafill A-2001 accelerator having a concentration less than 1.0 ml/liter and greater than or equal to 0.1 ml/liter.
It is another object of the present invention to provide a copper plating bath for depositing coil structures in thin film magnetic heads comprising a Shipley Ultrafill ST2001 High Acid Bath having a copper concentration between 17.5 and 21 grams/liter and a sulfuric acid concentration between 175 and 210 grams/liter, Ultrafill A-2001 accelerator having a concentration less than 1.0 ml/liter and greater than or equal to 0.1 ml/liter, and Ultrafill S-2001 suppressor having a concentration less than 25 mL/liter and greater than or equal to 5 mL/liter.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be better understood when consideration is given to the following detailed description thereof. Such description makes reference to the annexed drawings, wherein:
FIG. 1(a)-(c) (prior art) is a sequence of partial cross sectional views illustrating a through mask plating process;
FIG. 2(a)-(c) (prior art) is a sequence of partial cross sectional views illustrating a Damascene plating process;
FIG. 3(a), (b) are electron micro-graph cross sections of a pair of coil structures filled with copper electroplated from a plating bath at two aspect ratios (AR) according to embodiments of the present invention;
FIG. 4 is an electron micro-graph cross section of a series of 2 micron coil structures filled with copper electroplated from a Shipley High Acid Ultrafill Bath according to an embodiment of the present invention;
FIG. 5(a)-(c) are electron micro-graph cross sections of a series of coil structures filled with copper electroplated from a plating bath containing various concentrations of accelerator A-2001 according to embodiments of the present invention;
FIG. 6(a), (b) are electron micro-graph cross sections of a pair of coil structures filled with copper electroplated from a plating bath at two current densities according to embodiments of the present invention; and,
FIG. 7(a), (b) are electron micro-graph cross sections of a pair of coil structures filled with copper electroplated from a plating bath at two bath ages according to embodiments of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Today's modern Damascene plating baths contain complex mixtures of interactive and complimentary components that must be balanced to obtain void free fills of high aspect ratio trenches and vias. Due to the sheer volume of sub-micron copper filling applications required to manufacture ULSI semiconductor devices, manufacturers have generally optimized the copper Damascene plating baths for sub-micron geometries. Often, the concentration of each component in the additive package must be held within a few percent of the manufacturer's suggested operating conditions to obtain the desired result. Filling of vias and trenches significantly larger or smaller that the manufacturer's targeted application range can produce unsatisfactory results.
For the manufacture of thin film magnetic heads, the coil structure is commonly electroplated as demonstrated in FIGS. 1 and 2, discussed above. The coil structure is effectively a spiral trench. As previously mentioned, the shrinking head pitch has required a complimentary shrinkage in coil dimensions, such that conventional plating techniques are no longer usable. The Damascene process is potentially suitable to fill the micron sized coil “trenches”, if the proper chemistries can be determined. While it might seem obvious to one of ordinary skill in the art to use the sub-micron plating bath formulations commonplace in the semiconductor manufacturing arena, the coil “trenches” are still about an order of magnitude greater than vias and trenches found in modern semiconductor integrated circuit devices. This size difference is significant, and plating bath formulations suitable for sub-micron via and trench fill will not fill larger micron sized trenches effectively without the production of voids or defects.
It is an object of the present invention to provide a copper plating bath composition suitable for depositing the coil structures of thin film magnetic heads. The plating bath of the present invention comprises a number of components:
(1) Copper salt (such as copper sulfate)
(2) An electrolyte (such as sulfuric acid)
(3) An additive package
The additive package further comprises:
(3a) An accelerator (containing sulfur compounds such as thiols, sulfides, disulfides, sulfonates)
(3b) A suppressor (containing long chain organic compounds such as poly-ethylene glycol, molecular weight>5000)
(3c) A leveler (containing medium chain polymers and sulfur containing compounds such as thiourea)
(3d) Chloride
A suitable plating bath in accordance with the present invention can be made from components supplied by Rohm and Haas:
(1) Shipley High Acid Ultrafill bath ST-2001
(2) Ultrafill S-2001 suppressor
(3) Ultrafill A-2001 accelerator
The specific chemistry and plating bath composition can be derived from reviewing the experimental results shown in the following figures.
FIG. 3(a), (b) are electron micro-graph cross sections of a pair of coil structures filled with copper electroplated from a plating bath at two aspect ratios (AR) according to embodiments of the present invention. In FIG. 3(a), an aspect ratio (defined as the depth 804 to the width 802) of 4:1 is shown with no defects. In FIG. 3(b), depth 808 is increased and width 806 is slightly decreased, yielding an AR of 5:1, with no defects in the deposition.
FIG. 4 is an electron micro-graph cross section of a series of 2 micron coil structures filled with copper electroplated from a Shipley High Acid Ultrafill Bath according to an embodiment of the present invention. Notice the absence of voids and defects in the plated copper layer 402. The Shipley High Acid Ultrafill Bath (ST-2001) is deemed suitable. The Shipley High Acid Ultrafill Bath contains approximately 17.5 g/l copper and 175 g/l sulfuric acid.
FIG. 5(a)-(c) are electron micro-graph cross sections of a series of coil structures filled with copper electroplated from a plating bath containing various concentrations of accelerator A-2001 according to embodiments of the present invention. In FIG. 5(a), plated copper layer 502 is deposited with small defect voids 504. These defects 504 appear as the accelerator A-2001 concentration drops below 0.1 ml/l. In FIG. 5(b), no defects are observed at an accelerator A-2001 concentration of 0.5 ml/l. In FIG. 5(c), defects 506 appear for accelerator A-2001 concentrations greater than about 1.0 ml/l. Note that 1.0 ml/l is the manufacturer's recommended accelerator concentration, which would be unsuitable for void free filling of coil structures. A plating bath of the present invention should contain an accelerator A-2001 concentration greater than 0.1 ml/l and less than 1.0 ml/l, preferably between 0.5 ml/l and 0.1 ml/l.
FIG. 6(a), (b) are electron micro-graph cross sections of a pair of coil structures filled with copper electroplated from a plating bath at two current densities according to embodiments of the present invention. In FIG. 6(a), a deposition current density of 15 mA/cm²results in defects 604 being formed in plated layer 602. In FIG. 6(b), no defects are observed at a current density of 7 mA/cm². A plating bath of the present invention should be used with a current between 15 mA/cm²and 7 mA/cm².
FIG. 7(a), (b) are electron micro-graph cross sections of a pair of coil structures filled with copper electroplated from a plating bath at two bath ages according to embodiments of the present invention. Deposition from an older bath is shown in FIG. 7(a), where the accelerator A-2001 concentration has dropped to 0.4 ml/l, producing defects 704 in plated layer 702. The defect free deposition of a new bath is shown in FIG. 7(b). These results indicate that it is desirable to replenish the depleted components in the plating bath as the bath ages. Not that the performance of the old bath shown in FIG. 7(a) cannot be compared with the results shown in FIG. 5, as the old bath contains depleted components in addition to the accelerator, whereas the bath compositions of FIGS. 5(a)-(c) are all new baths.
With the forgoing in mind, a plating bath of the present invention can be described:
Bath Composition (new bath):
(1) Shipley Ultrafill St-2001 High Acid Bath containing between 17.5 g/l and 21 g/l Cu; between 175 g/l and 210 g/l sulfuric acid; and, between 60 ppm and 72 ppm chloride.
(2) Ultrafill A-2001 accelerator, having a concentration greater than or equal to 0.1 ml/l and less than 1.0 ml/l.
(3) Ultrafill S-2001 suppressor, having a concentration greater than or equal to 5 ml/l and less than 25 ml/l.
The present invention is not limited by the previous embodiments heretofore described. Rather, the scope of the present invention is to be defined by these descriptions taken together with the attached claims and their equivalents.

Claims

1. A copper plating bath for depositing coil structures in thin film magnetic heads comprising:

a Shipley Ultrafill ST2001 High Acid Bath; and,

an additive package containing Ultrafill A-2001 accelerator having a concentration less than 1.0 ml/liter and greater than or equal to 0.1 ml/liter.

2. The copper plating bath as recited in claim 1 wherein said Ultrafill A-2001 accelerator concentration is between 0.1 mL/liter and 0.5 mL/liter.

3. The copper plating bath as recited in claim 1 wherein said additive package further contains Ultrafill S-2001 suppressor having a concentration less than 25 mL/liter and greater than or equal to 5 mL/liter.

4. The copper plating bath as recited in claim 1 wherein said Shipley Ultrafill ST2001 High Acid Bath has a copper concentration between 17.5 and 21 grams/liter and a sulfuric acid concentration between 175 and 210 grams/liter.

5. A copper plating bath for depositing coil structures in thin film magnetic heads comprising:

a Shipley Ultrafill ST2001 High Acid Bath having a copper concentration between 17.5 and 21 grams/liter and a sulfuric acid concentration between 175 and 210 grams/liter;

Ultrafill A-2001 accelerator having a concentration less than 1.0 ml/liter and greater than or equal to 0.1 ml/liter; and,

Ultrafill S-2001 suppressor having a concentration less than 25 mL/liter and greater than or equal to 5 mL/liter.

6. The copper plating bath as recited in claim 5 wherein said Ultrafill A-2001 accelerator concentration is between 0.5 ml/liter and 0.1 ml/liter.