Cleaning and etching compositions

Details Cleaning and etching compositions Cleaning and etching compositions

1999-07-21

2001-09-04

Gupta, Yogendra N. (Department: 1751)

Cleaning compositions for solid surfaces, auxiliary compositions

Cleaning compositions or processes of preparing

For cleaning a specific substrate or removing a specific...

C252S079100, C438S689000, C134S002000, C134S003000

Reexamination Certificate

active

06284721

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a composition for cleaning and etching electronic display devices and substrates, and more particularly to a composition for etching Si, SiO
2
, SiN
X
, and metallic thin layers while also removing contaminants formed on the surfaces of the etching layers during the manufacturing process of electronic display devices, quartz devices, and semiconductor substrates.
2. Description of the Prior Art
In general, the manufacture of electronic display devices and substrates commonly involves cleaning and etching steps. For example, in the manufacture of Cathode Ray Tube (CRT), a multi-step cleaning is implemented. Prior to coating process, CRT bulb is subjected to a cleaning process which involves 10~18% hydrofluoric Acid (HF) solution. Then, the steps of inner panel black coating, screen coating, lacquer coating, aluminizing, funnel inner graphite coating, panel/funnel frit sealing, neck washing, mounting and exhausting, funnel outer graphite coating, and panel face coating are performed. For the panel face coating, the coating materials may include In
2
O
3
, Sb
2
O
3
, and SiO
2
, and prior to face coating, the surface contaminants are removed by cleaning with 1~2% HF or hydrogen ammonium fluoride (or ammonium bifluoride) solution. For defective coating layers, a 10~30% ammonium bifluoride solution is used (before sintering process) and polishing with CeO
2
is required (after backing).
In the manufacture of another electronic display device LCD, the manufacturing process may include cleaning and etching during lithography. Here, in the surfaces of a large substrates, it is important to etch uniformly to obtain a high degree of accuracy.
The table below shows compositions for cleaning and etching solutions commonly used and the types of materials to be cleaned and etched for LCD and semiconductor wafer.
For cleaning SiO
2
1. H
2
SO
4
:H
2
O
2
(6:1), 120° C.
2. 50% HF:H
2
O (1:100~1000)
3. NH
4
OH:H
2
O
2
:H
2
O (1:1:7) SC-1
4. Hcl:H
2
O
2
:H
2
O (1:1:6) SC-2
5. D.I.W. (deionized water) rinse
For etching SiO
2
layer
1. 40% NH4F:50% HF (7:1) BOE
2. 40% NH4F:50% HF (7:1) +H
2
O
2
For etching SiN
x
layer
H
3
PO
4
:H
2
O (85:1) or
40% NH
4
F:50% HF (20:1)
For etching Al and its alloy layer
H
3
PO
4
:CH
3
COOH:HNO
3
:H
2
O
(65:5:5:25)
The required conditions of above cleaning and etching solutions may include control of cleaning and etching rate, etching selectivity for upper and lower layers, control of etching profile, control of etching within the multi-layers, stability and homogeneity of the solutions, and reproducibility of etching process.
For quartz devices which are used for manufacturing of wafer, the manufacturing process is outlined as follows:
Raw material-cleaning (11~16.5% HF solution, 2~3 minutes)—waxing—cutting and polishing—dewaxing—ultrasonic washing—cleaning (15% HF solution, 5 minutes)—benching—cleaning (11~16.5% HF solution, 5 minutes)—drying—heating (1200° C.)—cleaning (11~16.5% HF solution, 5 minutes)—drying.
Here, a high concentration of HF solution are used for removing the surface contaminants and thermally oxidized layer formed during the above process, but HF solution may cause problems relating to smoothness, etching damage, crack, etc. The quartz devices thus obtained are then used for depositing layers and further heat-treating a wafer, and the contaminants formed during the latter processes are also cleaned by the utilization of HF solution at 2~25% concentration.
The following outline describes the fabrication process of semiconductor wafers:
I. Wafer Manufacturing Process
1. Growing single crystal silicon.
2. Slicing.
3. Lapping (approximately 60 micro-meters by mechanical polishing).
4. Chemical etching (approximately 30 micro-meters by etching).
5. Polishing (etching approximately 10 micro-meters by polishing three times to acquire desired roughness).
6. Cleaning.
II. Semiconductor Device Fabrication Process
7. Initial cleaning.
8. Oxidization (prior to oxidization, the substrate surface is occupied by Si layer).
9. Diffusing (prior to diffusing, the substrate surface is occupied by Si/SiO
2
/Si
3
N
4
layers).
10. Ion dopping (prior to ion dopping, the substrate surface is occupied by SiO
2
/Si
3
N
4
layer).
11. Epithexial growth (prior to epithexial growth, the substrate surface is occupied by Si layer).
12. Forming of insulating and conductive layer—CVD (prior to forming insulating and conductive layer, the substrate surface is occupied by poly-Si/SiO
2
layers).
13. Forming of electrodes—PVD (prior to forming electrodes, the substrate surface is occupied by Si/SiO
2
layers).
The above processes 8~12 are accompanied by photolithography process. As silicon substrate is subjected to the processes, chemical etching involving silicon and silicon oxide are performed, and during etching, ionic, non-ionic and other contaminants which should be removed are formed on Si and SiO
2
layers.
The cleaning and etching processes which are essential in the manufacture of semiconductors are described in more details by the following.
The oxidizing process 8 includes a pre-washing step prior to forming SiO
2
layer on the substrate, however, the pre-washing solution such as solvent, sulfuric acid, and/or hydrogen peroxide may produce a thin silicon oxide layer in a thickness of 100-200 angstroms on the surface while washing. Such thin silicon oxide silica layer should be removed by HF solution (HF:H2O=10:1).
Diffusing process 9 also includes a pre-washing step prior to diffusing. The washing solution such as a mixed solution of sulfuric acid and hydrogen peroxide or a mixed solution of ammonium hydroxide and hydrogen peroxide can usually remove organic contaminants and ionic contaminants by dipping for 10~20 minutes at an elevated temperature. However, such washing causes a formation of undesirable oxidized layer on the air-exposed part of silicon surface, which should by removed by dipping a wafer in a diluted HF solution.
In a photolithography process, etchant is used to define the portion to be ion-implemented or diffused and the portion be left intact on the surface of substrates.
Here, etching is a process which selectively removing the thin layers under a photoresist film after the development of the exposed photoresist film in accordance with the necessity. The portion covered by the photoresist film is protected in etching and thus remains after etching. The exposed portion under the photoresist film is etched and then removed.
Conventionally, there are two kinds of etching, one is wet etching or chemical etching and the other is dry etching or plasma etching. Etching includes the removing of the photoresist film.
Wet etching utilizes a chemical solution which causes a chemical reaction between the etching solution and the layer to be etched or removed to solubilize the reaction products. The chemical to be used and its composition ratio in an etching solution varies according to the types of layer to be etched.
The principle of conventional wet etching of silicon oxide layer is described by the following.
First, SiO
2
layer is formed by two conventionally utilized methods. In one method, SiO
2
layer is grown on silicon substrate at a high temperature, and the other is a CVD method which deposits SiO
2
on various films. The SiO
2
layer formed by these two methods and other existing conventional methods is susceptible to the dissolving nature of HF, as shown by the following formula for the thermal-grown SiO
2
layer.
HF→H
+
+F
−
The dissociated F
−
ion reacts with SiO
2
layer to perform etching as follows.
SiO
2
+4HF→SiF
4
+2H
2
O
2HF+SiF
4
→↑H
2
SiF
6
As shown by the above formula, F
−
ion decreases as etching proceeds, and hydrogen ion concentration decreases as the solution becomes diluted by increased H
2
O. As a result, in the subsequent etching processes the etching rate changes due to the unstable composition of the solution, which is significant drawback in obtaining uniformit

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