What is the name of adhesion promoter used in case of positive photo resist ?
Hexa Methyl Di Silane
The compound is HMDS — hexamethyldisilazane — and among the four spellings offered only option 1, "Hexa Methyl Di Silane", carries the correct methyl root. The other three substitute "methane" or corrupt the silicon part of the name, so the answer is option 1.
Why an adhesion promoter is needed at all. A silicon wafer's surface is hydrophilic: the native oxide terminates in silanol (Si-OH) groups that readily hold a molecular film of adsorbed water. Photoresist, by contrast, is an organic, hydrophobic polymer. Spinning resist onto a damp hydrophilic surface gives poor wetting and weak bonding, so the pattern lifts or undercuts during development and wet etching — the defect known as resist lifting.
How HMDS fixes it. Applied as a vapour before the resist, it reacts with the surface hydroxyls:
Si-OH + HMDS → Si-O-Si(CH3)3 + NH3
The silanol groups are replaced by trimethylsilyl groups, whose methyl tails point outward. The surface is converted from hydrophilic to hydrophobic and now bonds strongly to the organic resist. The ammonia by-product is carried away, and the treatment is applied in a heated vapour-prime oven rather than by spinning, so the layer is only a molecule or two thick.
| Before HMDS | After HMDS |
|---|---|
| Si-OH terminated | Si-O-Si(CH3)3 terminated |
| Hydrophilic, holds water | Hydrophobic, repels water |
| Poor resist adhesion | Strong resist adhesion |
Where it sits in the process flow : wafer clean → dehydration bake → HMDS prime → resist spin → soft bake → align and expose → develop → hard bake → etch → strip. The dehydration bake immediately before priming matters, since HMDS cannot displace bulk water — only the chemisorbed hydroxyl layer.
Positive resist in particular is more vulnerable because its developer is an aqueous alkaline solution (typically TMAH), which attacks a poorly bonded interface aggressively. The priming step is therefore all but mandatory for positive-resist processes.
Hence, the adhesion promoter is HMDS, option 1.
Similar Questions
Match the following :
List - I List - II (a) Lift - off (i) Fick's Equation (b) Dry Etching (ii) PMMA (Poly Methyl Methacrylate) (c) Lithography (iii) Bombardment of Plasma (d) Diffusion (iv) Structures of Target Material on the Surface of Substrate Codes :
Match the following :
List - I List - II (a) Lift OFF (i) Etching (b) Rant's Rule (ii) Crystal Growtd (c) Hydrofluoric acid (iii) Packaging (d) Float zone (iv) Metallisation Codes :
What is the correct sequence of the following step in the fabrication of a monolithic, bipolar junction transistor ?
1. Emitter diffusion
2. Base diffusion
3. Buried layer formation
4. Epi-layer formationSelect the correct sequence using the codes given below :
When silicon dioxide of thickness d is grown, the Silicon consumed is :
Match List - I with List - II.
List - I List - II (A) Annealing (I) Isolation (B) Sealing (II) Doping (C) Ion implantation (III) Packing density (D) Oxidation (IV) Crystal restoration Choose the correct answer from the options given below :
Arrange the following in ascending order based on their diffusivity :
(A) Boron
(B) Arsenic
(C) Antimony
(D) PhosphorusChoose the most appropriate answer from the options given below :
The idea of using diffusion techniques was disclosed in patent by Pfann in the year :
A thin layer of dopant is deposited onto silicon surface with a fixed total amount of dopants QT per unit area. If D is the diffusivity of dopants, then the surface concentration is :
Fick's second law of diffusion in one dimensional form can be expressed as :
For a diffused layer that forms a p-n junction an average sheet resistance RS is defined and related to junction depth xj, the carrier mobility μ, and impurity distribution C(x) as :
Important Questions from Semiconductor Process Flow
Which one of the following processes is preferred to form the gate dielectric (SiO2) of MOSFETs?
Arrange the following in the correct sequence of steps for MOS fabrication
A. Wafer formation
B. Photolithography
C. Oxidation
D. Gate and source/drain formation
E. Metallization
Choose the correct answer from the options given below:Which of the following statements are true for optical photoresists
A. Solubility of a photo-resist changes on exposure to light in developer solution.
B. Solubility of a photo-resist does not change on exposure to light in developer solution.
C. A negative photo-resist on exposure to light becomes less soluble in developer solution.
D. A positive photo-resist on exposure to light becomes more soluble in developer solution.
Choose the correct answer from the options given below:- In particle beam lithography, the resolution depends upon :
A. For impurity diffusion in semiconductor, concentration gradient is the only essential requirement.
B. Annealing is a mandatory step after ion-implantation.
C. Wet etching is normally anisotropic
D. High temperature is required for the growth of $SiO_2$ because oxidation reaction takes place at high temperature
E. Bird's beak formation is a characteristic of LOCOS isolation
Choose the correct answer from the options given below:
