Wet etching is a kind of etching method, which is a technology of immersing etching materials in etching solution for corrosion. It is a pure chemical etching with excellent selectivity. After etching the current film, it will stop without damaging the film of other materials below. Because all wet etching is isotropic, the width of transverse etching is close to the depth of vertical etching, no matter the etching of oxide layer or metal layer.
Bulk etching
In batch etching, multiple wafers can be simultaneously etched, filtered, and recirculated to prevent particles from reaching the wafer. Since the concentration of the chemical decreases with each processing of the wafer, it must be updated frequently. The corrosion rate, in other words, per wear, must be well known to ensure a renewable process. Precise tempering is necessary because the corrosion rate increases with temperature.
Spray etching
Jet etching is comparable to jet development in lithography. The uniformity of the etching chemistry is very good because the rotation of the wafer is simultaneously stably updated. Because the wafer rotates so fast, there are no bubbles inside the wafer that must be processed separately. As an alternative to the single wafer process, jet etching can be performed on multiple wafers one wafer at a time. In a rotary etcher, the wafer is placed around the nozzle and then rotates concentrically. The wafers are then dried in a hot nitrogen environment.
Process purpose: The PN junction on the back and around the silicon chip is corroded by chemical reaction, so as to achieve the purpose of insulation on the front and back, and remove the phosphorous silicon glass layer on the front
Process materials: qualified polycrystalline silicon sheet (after diffusion), H2SO4 (98%, electronic grade), HF (40%, electronic grade), KOH (50%, electronic grade), HNO3 (65%, electronic grade), DI water (greater than 15MQ-cm), compressed air (6bar, oil removal, water removal, dust removal), cooling water (4bar), etc.
Process principle: The Rena Inoxide etching process consists of three main parts: sulfuric acid, nitric acid, and potassium hydrochlorate
In this process, nitric acid oxidizes the back and edge of the silicon wafer to form silicon dioxide, hydrogen acid reacts with silicon dioxide to form complex hexaoxilic acid, so as to achieve the purpose of etching.
After etching, the porous silicon on the wafer surface is removed by KOH solution, and the unwashed acid carried from the etching tank is removed.
Finally, the phosphosilicate glass on the front of the silicon wafer was removed with HF acid. The wafer was rinsed with DI water and finally the surface of the wafer was blown dry with compressed air.
The reaction equation is as follows:
Process: feeding → mixed acid corrosion → wind knife 1→DI water flushing →KOH corrosion → wind knife 2→DI water flushing → corrosion → wind knife 3→DI water flushing → compressed air drying → blanking, process conditions: deionized water pressure is 4, the pressure of compressed air is 6
Ambient temperature: 25±3℃
Relative humidity: 40%-60%, without condensation
Corrosion tank temperature: 6-9°
Tank temperature: about 18℃
Main control points:
1. The corrosion depth is controlled between 1.2±0.2
2, etch width D≤1, each piece measured four points, measuring points in the middle of each side, 20 points (5 lanes) or 32 points (8 lanes) average.
3, insulation resistance ≥1.
The above three parameters should be measured at least every hour during normal production. When the liquid medicine is changed, the production is stopped for a period of time and the parameters are abnormal, the measurement times should be increased.
4, corrosion tank circulation flow requirements are set between 30-35. Too small circulation flow will lead to insufficient corrosion, and even the silicon wafer edge can not be completely removed: over circulation, the general assembly will lead to over corrosion phenomenon and the etching width of the silicon wafer edge shadow seriously cause surface disqualification.
5. The temperature of the corrosion tank is guaranteed to be 7±1℃. With the increase of temperature, the corrosion rate will be accelerated, but the density of the liquid will be reduced, so that the corrosion phenomenon occurs. Therefore, production is prohibited when the temperature is not down to the process control range.
6, alkali washing tank temperature requirements ≤23℃. When the temperature of alkali bath exceeds the control range, inform the relevant person in charge to check and adjust in time.
7, alkali bath spray quantity requirements, and first ensure that the spray quantity is sufficient, so that the porous silicon on the back of the silicon wafer corrosion is sufficient.
8. The control of the frequency and flow of the air cutter at the air drying place of compressed air is too small, which is easy to cause that the silicon chip cannot be completely air dried; Too large is liable to produce debris. The premise is that the upper and lower surfaces of the silicon wafer can be completely air dried. Recommended frequency of blade: 80%~85%; Compressed air flow: (8 channels) ≥20 cubic meters per hour.
Process Preparation:
1. Tooling tools: Prepare PVC gloves, face mask, protective eye mask, protective mask, protective sleeve, protective suit, acid and alkali resistant gloves, acid and alkali resistant rubber shoes for process production.
2. Equipment preparation: Ensure that the equipment can operate normally, and the pressure and flow of DI water and compressed air are normal. Confirm the set etching process, alkali washing process and HF corrosion process name and parameters.
3. Process clean management: wear purification clothes, wear masks, and wear clean PVC gloves when operating.
4. Raw material preparation: Observe whether the appearance is normal. Common nonconforming chips include silicon chips with missing corners, cracks, handprints, holes, etc.
Metal etching needs attention
(1) During the operation of production, gloves and masks must be worn, and gloves must be changed frequently to ensure the cleanliness of production.
(2) Pay attention to the transmission status of silicon wafers in the equipment at any time to avoid the occurrence of a large number of cards. If the card occurs in the corrosion tank, the acid - resistant tool can be used to channel it.
If the situation is serious, drain the water immediately, drain the acid into the storage tank, wear a full set of protective equipment, and remove the card manually.
(3) In addition to equipment maintenance and liquid medicine replacement, it is strictly prohibited to flow water into the liquid medicine tank when using the DI-water spray gun.
(4) During the process: check the equipment operation, transmission speed, gas flow and other parameters and the liquid level of each tank regularly.
(5) After completion, fill in the completion delivery form in detail with neat handwriting and accurate information, and transfer it to PECVD process together with the silicon wafer.
Only the silicon wafer with qualified surface can be transferred to the next process.
Asset Metal technology company is a focusing on CNC machining, metal stamping, metal(chemical) etching and surface treatment of OEM/ODM metal parts Processing.
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