Patent Application
20130189843
The present invention relates generally to chemical mechanical polishing of photoresist.
In the process of fabricating modern semiconductor integrated circuits (IC), it is often necessary to planarize the outer surface of the substrate.
Chemical mechanical polishing (CMP) is one accepted method of planarization. This planarization method typically requires that a substrate be mounted on a carrier head. The exposed surface of the substrate is typically placed against a rotating polishing pad. The polishing pad can have a durable roughened surface. An abrasive polishing slurry is typically supplied to the surface of the polishing pad. The carrier head provides a controllable load on the substrate to push it against the polishing pad while the substrate and polishing pad undergo relative motion.
One step in the manufacture semiconductor integrated circuits (IC) and microelectromechanical (MEM) devices, is to deposit a layer of photoresist on a substrate. For some applications, e.g., FinFETs, it would be useful to planarize the photoresist. Unfortunately, planarization of photoresist appears to have been unsuccessful so far. For example, slurry compositions that are proposed for photoresist tend to either not remove the photoresist (e.g., the removal rate is zero or so low as to be commercially impractical), or result in delamination of the photoresist layer. Without being limited to any particular theory, one problem may be the softness of the photoresist and the low adhesion to the underlying substrate makes planarization more challenging. However, new slurry formulations, e.g., with proper selection of an oxidizer and/or surface activation chemical, may be able to provide satisfactory performance.
In one aspect, a slurry for planarization of a photoresist includes abrasive particles, an oxidizer, a surface activation chemical, and a solvent.
Implementations can include one or more of the following features. The abrasive particles may include alumina oxide or silicon dioxide. The abrasive particles may be 0.1-10 wt % of the slurry. The oxidizer may include ammonium peroxide or hydrogen peroxide. The oxidizer may be 0.5-10 wt % of the slurry. The oxidizer may be ammonium peroxide, and the oxidizer may be 2-4 wt % of the slurry. The oxidizer may be hydrogen peroxide, and the oxidizer may be 0.5-2 wt % of the slurry. The solvent may be water. The surface activation chemical may include glycine, carboxy acid or citric acid. The surface activation chemical may be 0.5-2 wt % of the slurry.
In another aspect, a method of polishing includes bringing a substrate having a photoresist layer disposed over a cobalt barrier layer into contact with a polishing pad, supplying a slurry described above to the polishing pad, and generating relative motion between the substrate and the polishing pad to planarize the photoresist layer.
Advantages may include optionally one or more of the following. A photoresist can be planarized at a commercially practical removal rate without delamination. Planarization can be performed without scratching of the substrate, thus avoiding defects. In conjunction with cleaning, the resulting substrate can have a low defect count. For example, the post barrier polishing defect count can be comparable to a silicon polishing process. The polishing rate can be tunable between about 100-8000 Å/min. Planarization efficiency can be in a range of 50%-90%.
Referring to
Referring to
As noted above, commercial slurries for polishing of photoresist do not give satisfactory performance.
A proposed slurry chemistry that might potentially address these problems can include (1) abrasive particles, (2) an oxidizer, (3) a surface activation chemical, and (4) a solvent such as water.
Typically, the range for the chemical components in the slurry is given below in Table 1.
The abrasive particles can be an oxide, such as fumed or colloidal aluminum oxide (Al2O3) or silica oxide (SiO2). The size of the abrasive particles can be in a range of 20 nm-100 nm. For example, the abrasive particles can be, or can be similar to, those from B8755C or TSV-D1001 from Cabot.
The oxidizer can be ammonium persulfate (APS) and/or hydrogen peroxide. The oxidizer can be present in a concentration of 0.5-10 wt % of the slurry, e.g., 1-3 wt % of the slurry for hydrogen peroxide, or e.g., 1-5 wt % of the slurry for ammonium persulfate.
The surface activation chemical can be glycine, carboxy acid or citric acid.
Without being limited to any particular theory, the surface activation chemical can modify the hydrophobic surface of the photoresist. This can permit the oxidizer to interact with the chemistry of the photoresist. As a result, the surface can be weakened sufficiently to increase the polishing rate to commercially viable rates.
If necessary, the slurry can also include a pH adjustor to set the pH of the slurry, although this is optional. The pH adjustor can be KOH.
Polishing can be conducted at an applied pressure of 1-1.5 psi and at a platen rotation rate of 73-113 rpm.
Planarization of a layer of an Applied Material photoresist composition can be conducted, e.g., at a platen of a Mirra™ or Reflexion™ polishing system. Polishing can be performed using a soft microporous polyurethane pad, e.g., a Dura-soft or D200 polishing pad from Praxair. Polishing can be conducted at a pressure of 1.0 psi, and at a platen rotation rate of 73-113 rpm.
Slurry for the polishing can be provided by modifying a B8755C Cabot slurry by adding the following components:
The resulting slurry can have a pH of 3-4; no pH adjustor is required.
Polishing with the Dura-soft pad at a platen rotation rate of 93 rpm resulted in a removal rate of 2000 Å/min without delamination and with acceptable post-cleaning defect count. Polishing with the D200 pad at a platen rotation rate of 93 rpm resulted in a removal rate of 1000 Å/min without delamination and with acceptable post-cleaning defect count. The polishing rate can be increased or decreased by increasing or decreasing, respectively, the platen rotation speed.
Planarization of a layer of an Applied Material photoresist composition can be conducted, e.g., at a platen of a Mirra™ or Reflexion™ polishing system. Polishing can be performed using a soft microporous polyurethane pad, e.g., a Fujibo polishing pad. Polishing can be conducted at a pressure of 1.0 psi, and at a platen rotation rate of 73-113 rpm.
Slurry for the polishing can be provided by modifying a TSV-D1001 Cabot slurry by adding the following components:
No pH adjustor is required.
Polishing with the Fujibo pad resulted in a removal rate of 1200 Å/min without delamination and with acceptable post-cleaning defect count.
This application claims priority to U.S. Provisional Application Ser. No. 61/590,271, filed Jan. 24, 2012, the entire disclosure of which is incorporated by reference.
| Number | Date | Country | |
|---|---|---|---|
| 61590271 | Jan 2012 | US |
