CN101211773A - Method to prevent chip backside metal from peeling off - Google Patents

Abstract

The invention discloses a method for preventing the metal on the back of a chip from being stripped, which comprises the steps that: the thinning process is applied to the back of the chip adopting a predetermined number of microsections and the damaged silicon layer on the back of the chip is removed using the chemical corrosion solution; the chip is washed using the water so as to remove the residual sully. The method disclosed by the invention can prevent the metal on the back of the chip from being stripped, and can be used for accurately deciding whether the phenomenon of metal stripping exists. The use of the corrosion method effectively removes the damaged silicon layer so as to reduce the mechanical stress. The adoption of the method of controlling the process temperature in the process of evaporization reduces the stress mismatch of the Ti, Ni and Ag three different metals so as to realize solving the problem of the metal stripping on the back of the chip without causing the organic sully.

Description

Method to prevent chip backside metal from peeling off

technical field

The invention relates to a method for metallizing the back of a chip in a semiconductor manufacturing process, more specifically, a method for preventing metal peeling off on the back of a chip in a semiconductor manufacturing process.

Background technique

There are many methods for backside metallization of chips. Magnetron sputtering and electron beam evaporation are the most commonly used methods for backside metallization, and their processes have been widely used. Deposition by magnetron sputtering has a high degree of automation, but the throughput is relatively low, and it is an ideal process method below 0.6 μm. In contrast, the method of electron beam evaporation has the following advantages:

1) The deposited film has high purity and less sodium ion pollution;

2) Since the evaporation source is only vaporized near the center of the surface, there is no contamination of the crucible;

3) The integration process is simple and the cost is low. Compared with sputtering targets, the use of electron beam evaporation can greatly reduce the cost;

4) Since the electron beam energy can be adjusted, the evaporation rate can be controlled. At the same time, the use of thermal isolation bushings can greatly increase the evaporation rate and improve the yield of silicon wafers. It is especially suitable for the metal deposition process on the back of silicon wafers with a thickness greater than 1 μm.

Existing electron beam evaporation equipment (such as CHA Mark50) mostly uses manual loading and unloading, and the process chamber of the evaporation process is very large, and after each round of process is completed, the process chamber needs to be opened, which is more susceptible to various contamination and clean room The water vapor adsorption will affect the quality of the evaporation film. In addition, the organic pollution introduced due to equipment failure or maintenance has a fatal impact on the quality of the metal film (especially the adhesion of the metal film).

In addition to contamination, stress is also critical for metal-to-substrate silicon and metal-to-metal adhesion. Generally speaking, in order to increase the contact area between the metal layer and the silicon substrate, it is often used to increase the roughness on the back of the silicon wafer. The greater the roughness, the larger the contact area between the metal layer and the silicon substrate, but at the same time Mechanical damage and stress will also increase substantially, resulting in increased fragmentation rates and wafer deformation. At the same time, due to the presence of a large number of silicon shavings and damaged layers on the surface of the silicon wafer after grinding, the adhesion between the deposited metal film and the substrate decreases and peeling occurs. At the same time, due to the existence of stress, it is possible to Peeling occurs between metal films (usually Ti/Si or Ni/Ag) as time goes by. The peeling off of the back metal layer is the most common and serious failure mode of the back gold film deposited by electron beam evaporation.

Therefore, there is a need for a method for solving metal peeling on the backside of the chip and preventing organic contamination.

Contents of the invention

The object of the present invention is to provide a method for solving the metal peeling off on the back of the chip and preventing organic contamination.

According to the present invention, a method for preventing metal peeling off on the back of a chip is provided, comprising: using a grinding plate with a predetermined grinding number to perform a thinning process on the back of the chip; using a chemical etching solution to remove the silicon damage layer on the back of the chip; washing the chip with water to remove residual contamination.

According to an embodiment of the present invention, the use of a chemical etching solution to remove the damaged silicon layer on the back of the chip includes an etching method using a combination of various etching solutions and various etching times.

According to an embodiment of the present invention, the various chemical etching solutions include: stress relief etching solution KK-8, the contained substances and their components are: HNO ₃ :CH ₃ COOH:HF ratio of 95:4:1; Decontamination and corrosion solution, the contained substances and their components are: NH ₄ F: _{H 2} O ₂ :H ₂ O ratio of 2:1:5; buffered oxide layer corrosion solution KK-2, the contained substances and their components The ratio is: HF:NH ₄ F is 1:10. The various etching times include: 1 second, 2 seconds and 5 seconds. And the collocation of using multiple corrosion solutions and multiple corrosion times includes: 1 second of stress relief corrosion solution KK-8 corrosion; 2 seconds of stress relief corrosion solution KK-8 corrosion; 5 seconds of decontamination corrosion solution corrosion; 1 second of buffered oxide layer etching solution KK-2 etching; 2 seconds of buffered oxide layer etching solution KK-2 etching; where each etching solution is used for one etching.

Preferably, 5 times of water washing are carried out after each etching with a chemical etching solution.

According to an embodiment of the present invention, during the evaporation process, the method of controlling the process temperature in stages is adopted to reduce the stress mismatch of the three different metals of Ti, Ni and Ag.

According to an embodiment of the present invention, the predetermined grinding number of grinding discs is: 2000 (BG1010) fine grinding discs or 360 (BG0401) rough grinding discs.

According to an embodiment of the present invention, the method further includes: the step of measuring the metal adhesion force on the back of the chip, including: sticking a film, sticking a film on the back metal layer; dicing, cutting the chip; picking up the chip, removing it from the sticking film Chip, check whether there is residual metal on the iron fan. If there is metal residue, it means that there is metal peeling on the back. If there is no residual metal, it means that there is no metal peeling on the back.

The method disclosed by the present invention for preventing metal peeling on the back of the chip can accurately judge whether there is metal peeling phenomenon; the silicon damage layer is effectively removed by corrosion to reduce the mechanical stress; The stress mismatch of three different metals, Ti, Ni, and Ag, can effectively solve the problem of metal peeling on the back of the chip and will not create organic contamination.

Description of drawings

The features, properties and advantages of the present invention will become more apparent from the following description in conjunction with the accompanying drawings and embodiments, in which the same reference numerals denote the same features throughout, wherein,

Fig. 1-Fig. 8 is the schematic diagram of the silicon surface condition on the back of the chip after being treated with different parameters according to the method for preventing metal peeling on the back of the chip according to the present invention;

FIG. 9 is a flow chart of a method for preventing metal peeling off the backside of a chip according to an embodiment of the present invention.

Detailed ways

The purpose of the present invention is in order to improve the bonding force between the metal on the back side and the deposition substrate silicon, reduce gold-semi-contact resistance simultaneously, seek suitable silicon wafer surface roughness, reduce as far as possible the mechanical stress and the mechanical stress caused by the grinding wafer damage, find an appropriate silicon etching process, and optimize the back gold evaporation process parameters.

The root of the improvement of the adhesion is to increase the contact area between the metal film and the substrate, so in theory, a backside thinning process with a relatively rough grinding number should be used as much as possible. But in fact, the coarser the grinding number, the more mechanical damage and gravitational force will increase linearly, resulting in an increase in the inline chip loss rate, and at the same time, it will also cause chip cracks and other negative problems during subsequent packaging. Therefore, it is necessary to select an appropriate grinding number

After grinding, the silicon wafer needs to be stress-relieved. Since the by-products produced during the reaction of the traditional silicon wafer etching solution will adhere to the surface of the silicon wafer, it is difficult to use simple cleaning methods such as water rinse. To remove, these deposits will greatly reduce the adhesion of the metal. Therefore, it is also necessary to find an appropriate silicon etching method that can effectively remove defects such as stress, damage, and silicon shavings caused by grinding without causing new contamination.

In actual operation, it is found that metal peeling on the back side usually occurs when the chip is packaged. When the chip after dicing is picked up from the fixed film (tape), the metal film deposited on the back of the chip falls off from the back of the chip and remains on the fixed film. On the film (tape).

In order to effectively improve the entire back-gold process, it is first necessary to effectively measure the back-gold adhesion. Usually, adhesive tape is often used to measure metal adhesion in production, but this method has poor sensitivity and can only detect serious peeling problems, but cannot detect critical states such as more common partial peeling. The method of the present invention provides a film-scribing-chip-picking detection method to detect whether there is metal residue on the film (tape), thereby judging whether there is metal peeling off. The test results show that this is an effective production monitoring Methods.

For the mechanical damage and mechanical stress caused by the grinding disc, the present invention adopts the method of etching away a certain thickness of silicon on the surface of the silicon wafer to reduce the mechanical stress and remove the mechanical damage layer.

In addition, during the evaporation process, the Young's modulus of different metal films Ti, Ni, and Ag differs greatly, and the stress between the films does not match, which may easily cause warping of the silicon wafer and decrease in adhesion. Therefore, the present invention adopts the method of controlling the process temperature in stages to reduce the stress mismatch as much as possible.

The present invention provides a method for preventing metal peeling on the back of the chip, as shown in FIG. 9 , including the following steps:

S100. Thinning the backside of the chip by using a grinding plate with a predetermined grinding number. Among them, the predetermined number of grinding discs are: 2000 (BG1010) fine grinding discs or 360 (BG0401) coarse grinding discs.

S102. Using a chemical etching solution to remove the damaged silicon layer on the back of the chip. Removing the silicon damage layer on the backside of the chip by using chemical etching solution includes an etching method using a combination of various etching solutions and various etching times. A variety of chemical corrosion solutions used include: stress relief corrosion solution KK-8, the contained substances and components are: HNO ₃ : CH ₃ COOH: HF is 95:4:1; decontamination corrosion solution, contained The substance and its components are: NH ₄ F: _{H 2} O ₂ :H ₂ O is 2:1:5; the buffer oxide layer corrosion solution KK-2 contains the substance and its components are: HF:NH4F is 1 : 10. Various etch times used include: 1 second, 2 seconds, and 5 seconds. Generally speaking, the combination of various etching solutions and various etching times includes: 1 second of stress relief corrosion solution KK-8 corrosion; 2 seconds of stress relief corrosion solution KK-8 corrosion; 5 seconds of decontamination corrosion solution Corrosion; 1 second of buffered oxide layer etchant KK-2 corrosion; 2 seconds of buffered oxide layer etchant KK-2 corrosion; where each corrosion solution was used for one corrosion.

S104. Washing the chip with water to remove residual contamination. A better way is to wash with water 5 times after each corrosion with chemical corrosion solution.

After that, in the evaporation process, the method of controlling the process temperature in stages is used to reduce the stress mismatch of the three different metals of Ti, Ni, and Ag.

The method of the present invention also provides the step of determining the backside metal adhesion of the chip, comprising,

Film, film on the back metal layer;

Scribing, cutting the chip;

Pick up the chip, remove the chip from the film, and check whether there is residual metal on the iron fan. If there is metal residue, it means that there is metal peeling on the back. If there is no residual metal, it means that there is no metal peeling on the back.

The determination step can be used as a detection step after the whole process, or can be used alone as a determination method.

A set of examples is described below.

Table 1

Table 1 lists a group of wafers (Wafer), respectively No. 1 to No. 8 wafers (Wafer No.1-8), they will be processed through different parameters, and then observe the situation of the silicon layer on the back of the wafer, because the chip is from The wafer is diced so that the silicon layer on the backside of the wafer is identical to the silicon layer on the backside of the chip.

In the above table:

Stress relief (1m) represents the use of stress relief corrosion solution KK-8 (contained substances and their components: HNO ₃ :CH ₃ COOH:HF ratio of 95:4:1) for 1 second of chemical etching.

Stress relief (2m) represents chemical etching for 2 seconds using stress relief corrosion solution KK-8 (contained substances and their components are: HNO ₃ :CH ₃ COOH:HF in a ratio of 95:4:1).

Stain Removal (5m) represents chemical etching for 5 seconds using a decontamination corrosion solution (contained substances and their components: NH ₄ F:H ₂ O ₂ :H ₂ O in a ratio of 2:1:5).

Buffered oxide etch (1m) represents chemical etching for 1 second using buffered oxide etchant solution KK-2 (the substance and its components are: HF:NH4F is 1:10).

Buffered oxide etch (2m) represents chemical etching for 2 seconds using buffered oxide etchant solution KK-2 (the substance and its components are: HF:NH4F is 1:10).

As mentioned above, according to the present invention, each chemical etching solution will be used, but the etching time experienced by each chemical etching solution is different. As shown in Table 1, each wafer was corroded by three kinds of chemical etching solutions, wherein "○" indicates the selected etching method.

In addition, for wafer No. 1-4, a grinding disc with a grinding number of 2000 (BG1010) is used for backside thinning grinding, while for wafer No. 5-8, a grinding disc with a grinding number of 360 (BG0401) is used for backside thinning grinding.

Wafer #1 underwent processing including:

2000 (BG1010) grinding disc;

Stress relief corrosion solution KK-8 (contained substances and its components are: HNO ₃ :CH ₃ COOH:HF 95:4:1) chemical corrosion for 1 second;

Decontamination and corrosion solution (contained substances and their components are: NH ₄ F: _{H 2} O ₂ :H ₂ O is 2:1:5) chemical corrosion for 5 seconds;

Buffer oxide layer etching solution KK-2 (contained substances and its components are: HF:NH4F is 1:10) chemical etching for 1 second;

Wherein each chemical etching step is followed by 5 times of water washing.

After the above-mentioned treatment, the situation of the silicon layer on the back side of No. 1 wafer is shown in FIG. 1 .

Wafer #2 underwent processing including:

2000 (BG1010) grinding disc;

Stress relief corrosion solution KK-8 (contained substances and components are: HNO ₃ :CH ₃ COOH:HF 95:4:1) chemical corrosion for 2 seconds;

Decontamination and corrosion solution (contained substances and their components are: NH ₄ F: _{H 2} O ₂ :H ₂ O is 2:1:5) chemical corrosion for 5 seconds;

Buffer oxide layer etching solution KK-2 (contained substances and its components are: HF:NH4F is 1:10) for 2 seconds of chemical etching;

Wherein each chemical etching step is followed by 5 times of water washing.

After the above-mentioned treatment, the condition of the silicon layer on the back side of the No. 2 wafer is shown in FIG. 2 .

Wafer #3 underwent processing including:

2000 (BG1010) grinding disc;

Stress relief corrosion solution KK-8 (contained substances and components are: HNO ₃ :CH ₃ COOH:HF 95:4:1) chemical corrosion for 2 seconds;

Decontamination and corrosion solution (contained substances and their components are: NH ₄ F: _{H 2} O ₂ :H ₂ O is 2:1:5) chemical corrosion for 5 seconds;

Buffer oxide layer etching solution KK-2 (contained substances and its components are: HF:NH4F is 1:10) chemical etching for 1 second;

Wherein each chemical etching step is followed by 5 times of water washing.

After the above-mentioned treatment, the condition of the silicon layer on the back side of the No. 3 wafer is shown in FIG. 3 .

Wafer #4 underwent processing including:

2000 (BG1010) grinding disc;

Washing with water was performed 5 times.

After the above-mentioned treatment, the condition of the silicon layer on the back side of the No. 4 wafer is shown in FIG. 4 .

Wafer 5 underwent processing including:

360 (BG0401) abrasive grinding;

Stress relief corrosion solution KK-8 (contained substances and its components are: HNO ₃ :CH ₃ COOH:HF 95:4:1) chemical corrosion for 1 second;

Decontamination and corrosion solution (contained substances and their components are: NH ₄ F: _{H 2} O ₂ :H ₂ O is 2:1:5) chemical corrosion for 5 seconds;

Buffer oxide layer etching solution KK-2 (contained substances and its components are: HF:NH4F is 1:10) chemical etching for 1 second;

Wherein each chemical etching step is followed by 5 times of water washing.

After the above-mentioned treatment, the condition of the silicon layer on the back side of the No. 5 wafer is shown in FIG. 5 .

Wafer 6 underwent processing including:

360 (BG0401) abrasive grinding;

Stress relief corrosion solution KK-8 (contained substances and its components are: HNO ₃ :CH ₃ COOH:HF 95:4:1) chemical corrosion for 1 second;

Decontamination and corrosion solution (contained substances and their components are: NH ₄ F: _{H 2} O ₂ :H ₂ O is 2:1:5) chemical corrosion for 5 seconds;

Buffer oxide layer etching solution KK-2 (contained substances and its components are: HF:NH4F is 1:10) for 2 seconds of chemical etching;

Wherein each chemical etching step is followed by 5 times of water washing.

After the above-mentioned treatment, the condition of the silicon layer on the back side of the No. 6 wafer is shown in FIG. 6 .

Wafer 7 underwent processing including:

360 (BG0401) abrasive grinding;

Stress relief corrosion solution KK-8 (contained substances and components are: HNO ₃ :CH ₃ COOH:HF 95:4:1) chemical corrosion for 2 seconds;

Decontamination and corrosion solution (contained substances and their components are: NH ₄ F: _{H 2} O ₂ :H ₂ O is 2:1:5) chemical corrosion for 5 seconds;

Buffer oxide layer etching solution KK-2 (contained substances and its components are: HF:NH4F is 1:10) chemical etching for 1 second;

Wherein each chemical etching step is followed by 5 times of water washing.

After the above-mentioned treatment, the condition of the silicon layer on the back side of the No. 7 wafer is shown in FIG. 7 .

Wafer 8 underwent processing including:

360 (BG1010) disc grinding;

Washing with water was performed 5 times.

After the above-mentioned treatment, the condition of the silicon layer on the back side of the No. 8 wafer is shown in FIG. 8 .

It can be seen from the above examples that the backside thinning process produces a large amount of damage, microcracks and stresses, which may cause a decrease in adhesion. A high grinding number can reduce back damage, but an overly smooth surface increases the difficulty of bonding metal and silicon. And cause an increase in contact resistance. The chemical etching solution (stress relief etching solution KK-8, decontamination etching solution and buffer oxide layer etching solution KK-2) can effectively remove nearly 2000A silicon damage layer, thereby reducing the mechanical stress.

Therefore, the method disclosed by the present invention can prevent the metal peeling off on the back of the chip, and can accurately judge whether there is metal peeling phenomenon; the silicon damage layer is effectively removed by the corrosion method to reduce the mechanical stress; the evaporation process adopts the method of segmented control process temperature The method reduces the stress mismatch of three different metals of Ti, Ni and Ag, so as to effectively solve the problem of metal peeling off the back of the chip without creating organic contamination.

Although the technical solution of the present invention has been described above in conjunction with preferred embodiments, those skilled in the art should understand that various modifications or changes to the above-mentioned embodiments are foreseeable, which should not be regarded as exceeding the The protection scope of the present invention, therefore, the protection scope of the present invention is not limited to the specific described embodiments above, but should be the broadest scope consistent with the innovative features disclosed herein.

Claims (9)

1. a method that prevents chip back metal peeling is characterized in that, comprising:

Adopt the abrasive disc of a predetermined mill number to carry out the chip back reduction process;

Use chemical corrosion liquid to remove the silicon affected layer of chip back;

Chip is washed, removed residual staining.

2. the method that prevents chip back metal peeling as claimed in claim 1 is characterized in that,

The silicon affected layer of described use chemical corrosion liquid removal chip back comprises the caustic solution of the collocation of using multiple corrosive liquid and multiple etching time.

3. the method that prevents chip back metal peeling as claimed in claim 2 is characterized in that, described number of chemical corrosive liquid comprises:

Stress is eliminated corrosive liquid KK-8, and contained material and component thereof are: HNO ₃: CH ₃COOH: HF is 95: 4: 1;

The decontamination corrosive liquid, contained material and component thereof are: NH ₄F: H ₂O ₂: H ₂O is 2: 1: 5;

Buffer oxide layer corrosive liquid KK-2, contained material and component thereof are: HF: NH ₄F is 1: 10.

4. the method that prevents chip back metal peeling as claimed in claim 3 is characterized in that, described multiple etching time comprises:

1 second, 2 seconds and 5 seconds.

5. the method that prevents chip back metal peeling as claimed in claim 3 is characterized in that, the collocation of multiple corrosive liquid of described use and multiple etching time comprises:

1 second stress is eliminated corrosive liquid KK-8 corrosion;

2 seconds stress is eliminated corrosive liquid KK-8 corrosion;

5 seconds decontamination corrosive liquid corrosion;

1 second buffer oxide layer corrosive liquid KK-2 corrosion;

2 seconds buffer oxide layer corrosive liquid KK-2 corrosion; Wherein

Use each corrosive liquid once to corrode.

6. the method that prevents chip back metal peeling as claimed in claim 5 is characterized in that, uses 5 washings of the laggard row of chemical corrosion corrosion each time.

7. the method that prevents chip back metal peeling as claimed in claim 6 is characterized in that,

In evaporation process, adopt the method for segmentation control technological temperature to reduce Ti, Ni, the stress mismatch of three kinds of different metals of Ag.

8. the method that prevents chip back metal peeling as claimed in claim 7 is characterized in that, the abrasive disc of described predetermined mill number is: the corase grind abrasive disc of the correct grinding abrasive disc or 360 (BG0401) of 2000 (BG1010).

9. as each described method that prevents chip back metal peeling in the claim 1 to 8, it is characterized in that, also comprise: measure the step of chip back metal bonding force, comprise,

Pad pasting, pad pasting on the metal level overleaf;

Chip is severed in scribing;

Chip pickup takes off chip from pad pasting, detects iron and is fascinated by whether the metal remained existence is arranged, if metal residual is arranged, illustrates there is back metal peeling that if there is not metal remained to exist, then explanation does not have back metal peeling.

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