CN102424355A - A method to enhance the adhesion between BCB and Au - Google Patents

Abstract

The invention relates to a method for enhancing the adhesion between a dielectric layer BCB and a metal layer Au in wafer-level radio frequency packaging. The method is characterized in that the adhesion between the BCB and the metal layer Au is enhanced only by selecting and optimizing process parameters without adding other adhesion materials. The method mainly comprises the following steps: firstly, performing surface pretreatment on a dielectric layer BCB, and then selecting and controlling the metal type of a sputtered seed layer and the thickness of the seed layer. After sputtering is finished, annealing treatment is carried out to increase the combination degree of the BCB and Au contact surfaces, and finally, annealing treatment is carried out again after electroplating to reduce stress generated after electroplating. Through the steps, the adhesion between BCB and Au is greatly improved, and the method is suitable for wafer-level radio frequency packaging. The process method provided by the invention has the advantages of simple process and low cost.

Description

A method to enhance the adhesion between BCB and Au

technical field

The invention relates to a method for enhancing the adhesion between BCB and Au, in particular to a method for enhancing the adhesion between BCB and Au in wafer-level radio frequency packaging, and belongs to the field of wafer-level radio frequency packaging.

Background technique

Wafer-level packaging can save costs and improve efficiency. In RF/microwave packaging, vertical interconnection can reduce the wiring path and reduce the influence of parasitic parameters. The packaging method often adopts a metal-dielectric-metal structure. As shown in Figure 1, the radio frequency chip MMIC 103 is embedded in the Si substrate 104, and the BCB dielectric layer 105 is coated on the surface, and then the metal layer 101 is electroplated. The thickness and number of metal layers or dielectric layers are determined, and metal vias 102 are used to interconnect the metal layers. The dielectric layer material BCB has a very low dielectric constant (2.65) and a small loss tangent (0.0008), which enables it to achieve higher operating frequency and lower transmission loss. In addition, it can be cured at low temperature (curing temperature range: 150°C-350°C) so that the device is not damaged, and it has good flatness, making the process simple; low moisture absorption rate and stable chemical mechanical thermal performance, increasing package reliability. The metal material Au has good ductility, good high-frequency characteristics, excellent electrical conductivity and simple manufacturing process, and is a good choice for the metal layer material in the package. Therefore, BCB and Au are ideal materials for interlayer interconnection.

However, there are not many studies on the adhesion between Au and BCB in the industry. Adopt conventional technology, its general steps (Fig. 2) are:

1. Sputtering a layer of seed layer metal Cr/Au 202 on the surface of BCB dielectric layer 105;

2. Spin-coat photoresist 204 on the seed layer, and perform photoetching on it to pattern the electroplating window;

3. Electroplating an Au metal layer 101 with a certain thickness;

4. Deglue the electroplated pattern and remove the metal Cr/Au 202 of the seed layer, and finally obtain the patterned metal layer 101.

However, according to this kind of process, it is easy to peel off between the metal and the dielectric layer in the subsequent process, which directly affects the yield and reliability of the manufacturing process. For this reason, the present invention intends to propose an improved process method to enhance the adhesion between BCB and Au.

Contents of the invention

Aiming at the disadvantage of poor adhesion between BCB and Au, the purpose of the present invention is to provide an improved process method for enhancing the adhesion between BCB and Au in wafer-level radio frequency packaging. The technical scheme of the present invention is to perform BCB surface pretreatment before sputtering the seed layer, optimize the thickness of the seed layer when sputtering the Cr/Au seed layer, perform annealing treatment after sputtering, and perform annealing after electroplating, Control the temperature and time of heating and cooling during annealing treatment.

The specific process steps are:

1. Before sputtering the seed layer on the BCB, perform surface pretreatment. In the microwave plasma ashing system Telpla 300, set the condition of O ₂ or N ₂ , the flow rate is 180-240ml/min, the power is 180-240W, and the treatment is 4-6min. After treatment, the surface activity of BCB can be improved, and the degree of combination with Cr can be enhanced.

2. Thickness of sputtering:

时，脱落概率会增高，一般以小于

为宜，即为

Au的厚度小于

一般为 The thickness of the Cr/Au seed layer should also be strictly controlled, and the thickness of Cr is greater than

When , the probability of shedding will increase, generally less than

as appropriate, that is

The thickness of Au is less than

Generally

3. The relationship between the temperature curve and time of the annealing treatment after sputtering:

After sputtering, in order to enhance the degree of bonding between the seed layer and BCB, an annealing treatment is performed. The relationship between temperature and time is that the temperature rises from room temperature to 180-210 °C for 20-40 minutes, and then cools down to room temperature for the same time. For 30min, the temperature-time curve is shown in Figure 3. The normal temperature generally refers to 18-25°C.

4. Do an annealing treatment after electroplating, the relationship between the annealing temperature curve and time during the annealing treatment:

Since there will be residual stress after the Au layer is electroplated, annealing is performed again to reduce the stress, which is not only beneficial to increase the adhesion, but also enhance the reliability of the package. The temperature curve is the same as the annealing after sputtering in step 3, as shown in Figure 3, rising from normal temperature to 180-210°C and then lowering to normal temperature, the heating and cooling processes are both 20-40min. Metal thickness is 2-4μm.

To sum up, the present invention is characterized in that the adhesion between the dielectric layer BCB and the metal layer Au is enhanced through reasonable selection and optimization of process parameters without adding other adhesive materials, and has the advantages of simple process and low cost.

Description of drawings

Figure 1: MMIC packaged in a metal-dielectric-metal structure.

Figure 2: Traditional process methods for depositing Au on BCB.

Figure 3: Temperature time curve during annealing.

Figure 4: Process flow for enhanced adhesion between BCB and Au.

Detailed ways

With reference to accompanying drawing 4, the substantive features and remarkable progress of the present invention will be further elaborated by describing the embodiments of the present invention, but the scope of the present invention is by no means limited to the following embodiments.

Example:

1. Coat the BCB layer on the silicon wafer and cure it.

2. Put the BCB to be sputtered with the seed layer in the microwave plasma ashing system Telpla 300, the gas is O2 or N2, the flow rate is 200ml/min, the power is 200W, and the treatment is 5 minutes.

3. Sputtering seed layer Cr/Au, the thickness is respectively

4. Anneal in a controllable constant temperature furnace, set the conditions as shown in Figure 3, rise from room temperature to 200°C and then drop to room temperature, the heating and cooling process are both 30min.

5. Coat the photoresist 5um, and photoetch the graphic window.

6. Electroplate Au for a certain period of time to make the thickness reach 3um.

7. After degumming, do annealing again, the setting conditions are the same as in 4.

Claims (4)

1. A method for increasing adhesion between BCB layers and Cu layers in wafer-level radio frequency packaging, characterized in that it comprises: 1. before sputtering seed layer, BCB is carried out surface pretreatment earlier; 2. sputtering Cr/ Au seed layer, to control the thickness of the Cr and Au layers of the seed layer; ③ annealing treatment after sputtering; ④ annealing treatment after the final electroplating; Among them, ① pretreat the surface of BCB in _O2 or _N2 atmosphere, pretreatment for 4-6min; ② The thickness of the sputtered seed layer Cr is less than

The thickness of Au is less than

③The annealing temperature after sputtering and electroplating is 180-210°C, and the time for heating from room temperature to 180-210°C and cooling from 180-210°C to room temperature is 20-40min. 2. by the described method of claim 1, it is characterized in that processing step is: ① Coat the BCB layer on the silicon wafer; ②Before sputtering the seed layer, carry out surface pretreatment on BCB, the surface pretreatment gas is O ₂ or N ₂ , the flow rate is 180-240ml/min, the power is 180-240W, and the treatment time is 4-6min; ③ Sputtering seed layer Cr/Au, where the thickness of Cr is

The thickness of Au is

④Annealing treatment in a controllable constant temperature furnace, rising from normal temperature to 180-210°C, and then lowering to normal temperature, the heating and cooling process are both 20-40min; ⑤ Coating photoresist, photoetching out graphic windows; ⑥ Electroplating Au, Au layer thickness is 2-4μm; ⑦ Carry out another annealing treatment, the annealing temperature and temperature rising and cooling time are the same as step ④. 3. The method according to claim 1 or 2, wherein the surface pretreatment of the BCB layer is carried out in a microwave plasma ashing system Telpla300 before sputtering the seed layer. 4. by the described method of claim 2, it is characterized in that: ① During the pretreatment before sputtering the seed layer, the _O2 or _N2 gas flow rate is 200ml/min, and the time is 5min; ②The thicknesses of sputtered seed layer Cr and Au are respectively

and

③ During post-sputtering annealing treatment and electroplating Au layer post-annealing, the temperature was raised from room temperature to 200°C and then lowered to room temperature. The heating and cooling processes were both 30 minutes.

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