The study investigates a new platform of PFAS-free PAGs and evaluates their lithographic efficiency in comparison to PFAS-containing counterparts in multiple model photoresists, including both negative and positive tones, across a broad range of optical exposure wavelengths. PFAS-free photoresists materials demonstrate comparable / superior lithographic performance in resolution, depth-of-focus (DOF), and exposure latitude (EL) compared with their non-degradable counterparts.
In this study, we present the development of PFAS-free AZ® FZero 3DT positive photoresist and AZ® FZero NX-3015 negative photoresist. These novel photoresists were enabled by the utilization of a newly developed PFAS-free M PAG (photoacid generator). Both AZ® FZero 3DT and AZ® FZero NX-3015 photoresists have exhibited comparable lithography performance to their PFAS-containing comparative examples on both Silicon (Si) and Copper (Cu) substrates. Furthermore, the newly developed PFAS-free M PAG has displayed good stability on Cu substrates, outperforming the commercial oxime sulfonate PAG. This stability is particularly crucial for the successful application of photoresists in the fabrication of re-distribution layers (RDL) in advanced semiconductor packaging.
Metal deposition on a substrate using the lift-off process plays a vital role in the semiconductor industry to generate metal interconnects. The metal deposition on the substrate can be carried out using the process of evaporation or sputtering. In the metal lift-off process, the substrate is first patterned with resist followed by metal deposition using either the evaporation or sputtering process and eventually the photoresist is removed using a remover solvent. In both the deposition techniques, a unique undercut profile of the photoresist is desired. For metal deposition using the evaporation process, the photoresist is required to have a ‘re-entrant’ profile. On the other hand, for deposition using the sputtering process, the photoresist is desired to have a ‘T-shaped’ profile typically achieved using a bi-layer process. The AZ® LNR-003 formulation is a chemically amplified negative tone photoresist developed by EMD Performance Materials Corp. designed to generate a T-shaped profile, suitable for the metal deposition using the sputtering process. The undercut profile can be tailored by modifying the process conditions such as post applied bake temperature, post exposure bake temperature and development conditions. The formulation comprises of a specific combination of photoacid generator, quencher and additive which generates the ‘T-Shaped profile’. The AZ® LNR-003 photoresist can replace the bi-layer process used at present in the semiconductor industry to generate the ‘T-shaped’ profile with a single layer step.
With the progress of advanced packaging, the RDL metal line and μBump stability and super electrical performance were highly concerned. The photoresist with undercut profile is required to obtain the RDL metal line and μBump with footing. The AZ® 3DT-400 series formulation is a chemically amplified positive-tone i-line photoresist developed by EMD Electronics which a special additive was introduced to generate the undercut profile. The undercut size and shape can be adjusted with the loading of the additive. After optimizing the formulation, the desired undercut length larger than 10% of the target CD and the undercut height less than 10% of target CD were achieved.
Despite their long history in the electronics industry, copper metal layers remain important components as interconnection layers in IC fabrication due to their higher thermal and electrical conductivity as well as their higher electromigration resistance. Structuring the copper metal layer via wet chemical etching places demands on the photoresist mask, requiring resistance to harsh etch chemistry and good adhesion to the substrate to prevent delamination and defects. The photoresist formulation AZ® TD-2010 is a positive-tone, DNQ-based i-line photoresist that incorporates an additional surface-grafting component to deliver improved etch performance via enhanced photoresist adhesion on metal substrates. The in-situ priming of the photoresist formulation during the patterning process leads to a greater interfacial adhesion, resulting in steep sidewalls, with a greater than 20° increase in etch angle over formulations without adhesion promoter, while maintaining undercut depth and Cu CD. The AZ®TD-2010 photoresist can also be used at high thickness to cover topography steps formed from underlying layers, while also exhibiting high enough photospeed to maintain production throughput standards for IC manufacturing.
Exceptional post exposure delay (PED), CD stability, up to 72 hours was reported. This study was conducted using two
negative resist formulations identical in their composition except for their PAG type. A mechanism by which the
photoacid is protected from relatively moderate levels of airborne amines is proposed. Evidence of room temperature
interaction between the resist components and the acid during post exposure delay was also suggested. Therefore, the
PED outcome could be the result of two opposing mechanisms.
We report about the development of a thick negative photoresist series, AZ(R) EXP 125nXT, and their use in
electroplating levels up to 160 μm thickness. The new photoresist series enables coatings of 5-120 μm with acceptable
uniformity and edge bead in a single coat step. 200 μm photoresist coating was achieved by a double coating processes.
The lithographic performance of the photoresists was evaluated using broad band aligners and steppers. Optimized
lithographic parameters to achieve straight and nearly vertical side wall profiles are reported. The photoresists show not
only excellent adhesion to copper with no surface treatment and electroplating tolerance in a variety of metal plating
solutions, but is also compatible with silicon and gold substrates. The photoresists have been found to be easily stripped
with no residues in solvent based stripper solutions.
Two types of chemically amplified (CA) negative resists were compared lithographically. An acid catalyzed resist and a photopolymerizable type resist. The optimum lithographic performance of the acid
catalyzed resist on Cu is in the thickness range below 15μm, with vertical profiles. This resist exhibits inverted profiles on Cu above 15μm of thickness. The Photopolymer type resist performs best above 25μm thickness, and can be used for 120μm thick applications with single coat. Top line rounding is more
observed with this resist as its applied thickness is reduced below 20μm. This effect is believed to be
related to oxygen uptake in the resist surface. Thus it has a more pronounced effect at relatively thinner
films. Both resists are compatible with the electroplating process.
The introduction of chemically amplified (CA) resist technology to thick films, 10 to 100 um in thickness introduced a
number of behavior differences not experienced in thinner films to the same magnitudes. Resist image profile
deformation, insensitivity to standing waves and the reduction in polymer deblocking temperatures are significantly
affected in thick films to a larger extend than in thinner films. The major contributing factors to these differences are
discussed in this paper: 1) the influence of photo-acid generator (PAG) structure on its distribution in resist depth on
Cu substrates and 2) thermal acid diffusion, influenced by greater amounts of retained solvents in thick films than in
thinner films.
We report about the development of novel nanocomposite resists that incorporate colloidal silica nanoparticles into
conventional resist materials to yield thick coatings with both excellent lithographic properties and significantly
increased plasma etch resistance. 10-50 wt% silica nanoparticles of 10-15 nm in size were dispersed homogeneously in a
variety of standard resist resins by a simple process. The nanocomposite resists have similar lithographic performances
to conventional resists without silica nanoparticles. The nanocomposite resists also show excellent process window
capability and stability. Oxygen plasma etch and deep reactive ion etching (DRIE) processes were used to evaluate the
etch resistance of the nanocomposite resists. Compared with standard photoresists, the oxygen plasma etch rate is
reduced by 38-80% when the silica content increases from 20 to 50 wt%. The etch selectivity of nanocomposite resists
with 40 wt% silica is increased by 70% in DRIE test.
Adapting chemically amplified (CA) resist technology to thick film applications is demonstrated in this paper over a wide range of thicknesses and types of substrates. Substantial performance differences were observed over copper (Cu) substrates compared to silicon (Si). These differences are attributed to different photo acid generator (PAG) distribution in the resist depth influenced by its structure and the nature of the substrate. Optimized resist formulations were developed to provide acceptable performance on Cu wafers. A family of new chemically amplified thick film resist products is being introduced to the market. This technology offers significant advantages in throughput and performance over conventional novolak / diazonaphthoquinone (DNQ) products at a competitive cost.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.