BOROFLOAT® 33 & Glass Wafers: A Union of Inspiration & Quality

The performance requirements for glass wafers used for anodic bonding or as carrier wafers in wafer thinning processes are mainly determined by their ability to perfectly match those of the silicon wafer to which they shall be permanently or temporarily bonded. Well-adapted thermal expansion behaviour is as important as excellent flatness and process robustness. BOROFLOAT® glass wafers provide such outstanding material properties along with exceptionally high UV transmission – a special requirement for high speed laser de-bonding processes.

BOROFLOAT® - The sum of its properties is what makes it unique for glass wafers!

  • Outstanding thermal resistance
  • Exceptionally high transparency
  • High chemical durability
  • Excellent mechanical strength

Glass wafers made of BOROFLOAT® glass offer outstanding thermal resistance

The glass composition of BOROFLOAT® is tailored to perfectly match the thermal expansion coefficient of silicon which is essential for good bonding behavior.

Wafers are often exposed to thermally changing environments during processing. The low coefficient of linear thermal expansion (C.T.E.) allows BOROFLOAT® glass wafers to easily handle elevated temperatures and – often even more importantly - sudden thermal changes without breaking or warping.
Thermal properties
Coefficient of
Linear Thermal Expansion (C.T.E.) α (20 - 300 °C)
3.25 x 10-6 K-1 *
Specific heat capacity
cp (20 - 100 °C)
0.83 kJ/(kg·K)
Thermal conductivity λ (90 °C) 1.2 W/(m·K)

* According to ISO 7991.
Maximum operating temperatures
For short-term usage (< 10 h)
500 °C
For long-term usage (≥ 10 h) 450 °C
The maximum operation temperatures for BOROFLOAT® should be seen in conjunction with RTG (Resistance to Temperature Gradients) and RTS (Resistance to Thermal Shock) values. Such values and test methods are available on request.

Carrier wafers with unmatched light transmission allow for exceptional UV bonding

Laser de-bonding through glass carrier wafers offers the fastest de-bonding time as well as a good price / performance ratio. Deep UV light transmission at the relevant laser wavelength range is crucial for the principal feasibility and efficiency of this type of wafer de-bonding. The laseractivated release will be achieved through irradiation using a 248 nm or 308 nm excimer laser. Extra-low iron BOROFLOAT® glass of desirable 0.5 mm carrier thickness shows over 90 % transmission at 308 nm and still over 35 % for 248 nm, thus significantly outperforming other thin flat glasses.

Acids, alkalis and organic substances have virtually no negative impact on BOROFLOAT® glass wafers

Outstanding chemical resistance is another critical feature given that wafers are exposed to many chemicals throughout the highly sophisticated etching and chemical mechanical planarization (CMP) processes. In certain technologies, maskbased chemical etching technologies using an aggressive cocktail of corrosive chemicals are also applied in order to create high definition surface channels where the high chemical durability of BOROFLOAT® 33 is key to deliver perfectly shaped design structures of unmatched accuracy with controlled channel depth.
Chemical durability
Hydrolytic resistance
(according to ISO 719 /
DIN 12 111)
(according to ISO 720)
 
HGB 1
 HGA 1
Acid resistance (according to ISO 1776 / DIN 12 116)  1
Alkali resistance (according to ISO 695 /
DIN 52 322)
A 2

Glass wafers made of BOROFLOAT® stand out for their reliable process robustness

Many wafers require microstructures which are often created via ultrasonic drilling, powder blasting or a combination of photolithography and dry etching. Mechanical strength and stability during a process where thousands of accurate features have to be machined are essential in order to produce high precision textured wafers with a consistently perfect surface pattern and accurate size. As shown in the graph below, BOROFLOAT® glass has an exceptional abrasion resistance compared to other alternative substrates.
Trade Fairs & Events
31.
January
Trade fair Photonics West, San Francisco, USA, 31.01 - 02.02.2017