Wafer Probe Test Process and Wafer Test Analysis Methods

1 Wafer test environment

Wafer test belongs to the Fab completed after a process, but also need to be carried out in a clean room environment, also requires strict electrostatic control. Usually wafer test clean room environment level 1000, 10000 level requires the use of organic platform. However, for some sensor chips, Class 100 may be required. Operators must wear anti-static clothing and gloves, and ion fans are installed in production and storage areas to eliminate static electricity.

The clean room environment carries a temperature of 22 degrees ± 2 degrees. Temperature: 55% ± 5%, the quality of the clean environment controls the growth of particles and bacteria.

2 wafer testing process flow

The basic process of wafer testing can be divided into material acceptance, acceptance inspection, testing,wafer test ink inspection, final inspection and shipping inspection steps. As shown in the figure below. Some special chips can be tested for the first time after laser repair (Focused Ion Beam technology FIB) and then tested for the second time. The following figure shows the process flow

Figure 1 Wafer testing process flow

1) Material Receiving

After the wafers come out of the Fab, it is necessary to obtain the wafer WAT test data and record the wafer lot number, product model and quantity in the material system. At the same time, the whole fab box is put into the nitrogen cabinet for preservation.

2) Wafer Appearance Inspection

Before wafer testing, it is necessary to visually inspect the wafer appearance under a metallurgical microscope to check whether the wafer has missing corners, scratches, pollution, discoloration of pads, pinholes,wafer level testing slots, and whether the wafer number is consistent. Generally large factories use automatic scanners to pick up all wafer lines. The scanner uses an image recognition algorithm to compare and judge the defective templates, mark the defective locations of the wafers, and then manually confirm them. Judgment is made according to wafer inspection standards and operating instructions. If any abnormality is found, it is marked according to the operation instructions. Pass the inspection and put the qualified wafers into the system for the next operation.

3) Wafer Probe Test

The automatic probe test bench loads and unloads wafers automatically. The operator only needs to place the wafers on the pre-alignment bench for pre-alignment, and then the wafers are sent to the wafer carrier to be processed by the host. It also sends the host-tested wafers back to the magazine. The test flow is as follows

4) Ink Dotting

After the wafer test work is completed, failure analysis the good and bad impact of each grain or through the classification, the results we usually save for the wafer map map, to the back-channel packaging coring when the students use. There are also their own core in the back-channel does not apply map map, but to the bad chip technology directly on the ink spot, ink spot wafers need to be baked by the enterprise will be ink spot adhesive drying fixed on the surface of the grain. Subsequent placement of the core is also China according to these image information recognition system for automatic sorting core.

(1) playing ink dot

After the final inspection of the dot wafers, check the wafer lot number, lot number, customer lot number and other information to confirm. Visual inspection is then performed to check for defects in the wafers during the previous wafer test. This is consistent with previous wafer appearance inspection standards, but the role of wafer probes for wafer liner is increasingly being emphasized. Pinhole and so on.

3 wafer test defective

The purpose of product testing is to find product design errors as far as possible, while using the test results to monitor the process stability of the pre-product, and timely feedback to the design and process. But the premise of the problem of the product itself is found to test its stability and reliability. So the test machine itself needs to ensure reliability, repeatability and reproducibility. The evaluation of the tester can be realized through repeatability and interchangeability testing (GRR).

Repeatability refers to repeated testing of the same batch of test samples by the same operator with consistent results. Interchangeability is the consistency of test results for a batch of products by different operators. There are two main types of product testing

1) A good product tested results in a failing grade, which is called overkill.

2) Badly affected products are tested PASS is called Missing Information (Undekill).

The probability of loss in mass production is very small and the main misleading problem due to machine or operational reasons. And mismanagement can lead to waste of the product itself, lower test yields, or repeated tests lead to lower test efficiency. At the same time, repeated tests on the chip can cause multiple pin marks, and excessive pin marks can cause subsequent package wiring reliability. However, mis-slaughter is only a phenomenon in product testing, and the causes of mis-slaughter need to be further analyzed.

3.1 Methods to analyze the problem

Industrial products have a variety of quality characteristics, but due to a variety of input factors in the production process, such as materials, personnel, equipment, environment, methods, etc., the quality of the product will appear a variety of different quality characteristics.

In order to solve quality problems, the relationship between quality characteristics (results) and causes is elucidated, and in quality control, the factors that cause quality problems are called critical factors. Therefore, a diagram is utilized to show the elements of quality characteristics is called a characteristic element diagram. It is also called a fishbone diagram because it is shaped like a fish with no meat and only bones.

(1) Human analysis:

Defects arising from processes in which the operator plays a dominant role can generally be controlled by the operator. The main causes of operational errors are.

① Poor quality consciousness;

② Carelessness in operation;

③ Non-compliance with operating procedures;

④ Low skills and unskilled application of technology by the operator;

Boredom due to simple and repetitive work.

How to improve productivity should first be explored from the existing employees, to utilize their characteristics as much as possible, to stimulate their motivation and to increase their enthusiasm for work. Human resource course is a science that specializes in how to improve the efficiency of employees per unit of time and how to motivate them to work. Simply put, personnel management is the most complex and difficult to understand and apply in production management.

-Control measures that can be taken:

(1) Strengthen the quality awareness education of "quality first, customer first, the next step is the user", and establish a sound quality responsibility system.

(2) Prepare clear and detailed operating procedures, strengthen the professional training of the process, and issue operating certificates;

(3) Strengthen the relevant inspection work, and appropriately increase the frequency of inspection;

Eliminate the boredom of operating personnel by adjusting the staffing between jobs and enriching work experience;.

⑤ Extensively carry out QCC quality control circle activities to promote self-improvement and self-improvement capabilities.

(2) Analysis of machines:

Refers to the equipment and tools used to produce auxiliary production equipment. Good equipment can improve production efficiency and product quality. In production, both the normal operation of the equipment, the quality of the tool is another factor that affects the production schedule and product quality. An enterprise in the development, in addition to the improvement of the quality of people, the external image of the enterprise in the promotion; can be analyzed from the following aspects

① Selection of the right type?

② maintenance problems?

① Are there three corresponding machines?

④ Is the person who learns the machine correct? Is the operation and management method of the machine correct? Is it possible to adapt to the environment in which the machine is placed?

The main control measures are:

① Strengthen the maintenance of equipment, regular testing of key precision and performance indicators of machinery and equipment, the establishment of equipment key components daily inspection system, the process of equipment quality control points to focus on control;; ② The use of first-piece inspection, verification of corporate positioning or quantification of the machine.

② Use the first piece of inspection to verify the amount of adjustment of the enterprise positioning or quantitative analysis device;

Where possible, configure automatic display and automatic recording of positioning data to reduce the dependence on the reliability of worker adjustment.

(3) Analysis of methods:

Refers to the rules and regulations to be followed in the production process. It includes: process manuals, standard process guides, production drawings, production schedules, product operation standards, inspection standards, various operating procedures, and so on. Their role here is to standardize the production process, timely and accurate reflection of product quality requirements. Strictly following the regulations is a condition to ensure product quality and production schedule.

① can be done according to the correct method?

② see the understanding?

③Is it written in a clear way?

④ Is the method suitable?

⑤ Is there a clear regulation?

6 Is the method given to the counterpart? Methods in this environment?

Error prevention and control measures for process methods;

(1) Ensure the accuracy of the positioning device, strictly inspect the first piece, and ensure the accuracy of the positioning center to prevent the processing characteristic value data distribution center from deviating from the specification center; and

(2) Strengthen the technical and business training, so that the operator is familiar with the installation and adjustment methods of the positioning device, and configure the device that displays the positioning data as far as possible;

(3) Strengthen the sharpening and management of stereotyped tools or edged tools, and implement the national mandatory to carry out the replacement work system;

Actively implement the control chart management, in order to take timely measures to adjust.

(5) Serious process discipline, check and supervise the implementation of operating procedures.

Strengthen the management of molds and measuring instruments, and do a good job of regular inspection of molds and regular calibration of measuring instruments.

(4) Analysis of the environment

Generally refers to the temperature, humidity, noise interference, vibration, lighting, indoor purification, pollution level of the production site. In addition to ensure that the product on the environmental conditions of the special requirements, should also do a good job on-site organization, reorganization and cleaning work, vigorously civilized production, for the lasting production of high-quality products to create conditions.

① Has the environment changed on the timeline?

Light, temperature, humidity, altitude, pollution considerations

(3) Is the environment safe

(4) Is the environment man-made? Can small and large environments be compatible?

(5) Analysis of materials

It refers to raw materials, semi-finished products, accessories, and raw materials. Product materials in the production management work, must pay attention to the semi-finished products sent before treatment, warehouse accessories, their own production of semi-finished or finished products process progress. A good manager is a person who can see the whole picture, a person who can think for everyone.

①Is it real?

② Is the model right?

③Is there a shelf life?

③Is there a warranty period? ④Is it inspected in the factory?

⑤Is the material used in accordance with the specifications?

(6) Is the material adapted to the social environment, is the material compatible with the machine, and does the material and other materials learn from each other?

(7) Analysis of measurement

It mainly involves measurement tools, measurement methods, and trained and authorized surveyors. The use of prescribed, regular testing of measuring tools, uniform standards of measurement methods, to ensure that the same measurement point, the same measuring tools, different measurement personnel to minimize the error of measurement data. Measurement data shall be recorded in the production process.

①Is the responsible person designated

② the use of prescribed measuring tools

③ At the specified measurement point

④Apply the correct measurement method

⑤Measurement is performed at a certain frequency.

(vi) Records are kept.

The main control measures include:

(i) Determine the measurement task and required accuracy, and select the use, with the required accuracy and precision capability of the test equipment.

② Periodic confirmation, calibration and adjustment of all measurement and test equipment.

③ Provide for the conduct of the necessary calibration protocols. Its content mainly includes the type of enterprise equipment data, number, location, calibration cycle, calibration method, acceptance management method, acceptance criteria, and measures to be taken when developmental problems occur in society.

④ Keep calibration records.

If it is found that the measurement and test equipment is not in a calibrated state, the validity of the previous measurement and test results will be immediately evaluated and recorded in the relevant documents.

3.2 Adverse Phenomena

In the process of wafer testing, it will bring some defects to the wafer itself. So wafer defects can be divided into

1) The chip itself is not good, including chip design and chip process is bad.

2) Test introduced defects, including the wrong test and damage to the wafer.

Chip itself is bad, in the wafer testing process research can be obtained from the test test data information management analysis, to find their own design problems or process reasons, teaching design and process improvement. For the test process itself can be effective use of the above analysis and processing methods need to be man-machine-material method of ring fishbone diagram analysis.

Operator problems:

In the wafer test process, the operator's operating parameters are not set in accordance with the requirements, or the operator is not skillful operation.

Must be in the test work process or through the test process tooling fixture design anti-dumbing measures can be avoided negligent omissions. And regularly carry out training enterprise staff vocational skills, prepare some simple and easy to understand training documents. Qualified by the examination to be on duty. And in a timely manner to understand the company's staff mentality to avoid bad mentality leading to the actual operation is not serious.

Probe machine table problem:

Pressure design, pressure variation, collet straightness and spindle maintenance will affect the pressure accuracy and positional accuracy of the probe. Carry out regular maintenance on the machine, formulate a maintenance plan, and statistically analyze frequent failures for early warning maintenance.

Probe card problems:

Probe card is an important material for wafer testing and plays an important role in the test results. When the probe card is used more often in the test process, the probe of the probe card will wear out, which is manifested as the probe tip is too short and uneven, and the probe tip becomes thicker. Especially after the number of tests is less than the lifetime of the probe, the probability of test errors after repeated use increases greatly. Establish a maintenance program for the probe card, set up a statistical usage table for the probe card management system, and confirm the status of the probe card before and after testing to ensure that the status of the probe card is correct. Mark abnormal probe cards to avoid misuse.

Test Methods:

In the process of wafer testing work, the design and use of the test system program to test the consistency of the downward pressure of the probe. Test analysis software for reading the data of the processing method is appropriate. Test technology standard system is in the chip parameters of the Margin will have a direct impact on the judgment of the test results of the study.

Environmental issues:

The temperature and humidity of the test environment, as well as changes in high and low temperature conditions will affect the test parameters of the test probe and test card. The vibration of the test environment will have a great impact on the whole test. Therefore, it is very important to study the test conditions. Take measures to control and monitor the temperature and humidity of the test shop.