CN113445005B - A kind of preparation method of low stress TiW film - Google Patents

Abstract

The invention discloses a preparation method of a low-stress TiW film, which is characterized in that a thin seed film layer grows on a substrate of a film to be deposited at a small deposition rate, a main film layer grows at a large deposition rate, and the two layers of films are optimally combined by controlling the growth thickness and rate to obtain the low-stress TiW film. The TiW film is deposited on the substrate step by step, the density of the seed film layer growing at a small deposition rate is high, and an interface with high reliability is obtained by mutual fusion with atoms of the substrate; the main thin film layer growing at a large deposition rate has enhanced film adhesion force on the basis of seed layer buffering, so that the TiW thin film has stable thickness and uniform distribution, and the stress on the substrate is weakened and dissipated, so that the deformation of the TiW thin film is small, and the TiW thin film with low stress and high quality is obtained. The TiW film can be prepared by a common deposition mode, and the obtained film has high stability, low film stress and better usability and popularization.

Description

A kind of preparation method of low stress TiW film

technical field

The invention relates to the field of electronic information semiconductors, in particular to a preparation method of a low-stress TiW thin film.

Background technique

TiW (Titanium Tungsten) alloy material is formed by doped tungsten particles in titanium metal. Due to its high strength, wear resistance, good toughness and light weight, TiW alloy is widely used in aerospace devices and components. Manufacturing, medical equipment, light industry and other fields. In addition to the above characteristics, with the rapid development of electronic information and semiconductor ultra-large-scale integrated circuit industries, TiW alloys also have low electron mobility, stable thermomechanical properties, corrosion resistance and chemical stability. Diffusion barrier layers are used in semiconductor chips, especially in high temperature and high current environments. Through the process of preparing high-purity thin films, they are widely used in semiconductor integrated circuits and device manufacturing industries.

Under the current thin film growth technology, most thin films have the problem of film stress more or less. The interaction between the film and the substrate it supports is usually influenced by the following two interactions: (1) the adhesion of the interface bonding strength; (2) the constraining film stress on the cross section. The film stress includes the following two types: (1) Intrinsic stress generated by the growth environment. Intrinsic stress includes interface and growth stress. For example, when the lattice structure of the substrate and the film is greatly different, the crystal structure of the film will be close to the substrate structure. And produce large distortion; (2) The thermal stress caused by the difference in thermal expansion coefficient between the film/substrate is generated when the temperature is lowered after growth. The invention technology of reducing stress is similar to that, the boron nitride with molecular crystal structure is inserted between the c-BN film and the substrate, which can reduce the lattice distortion and the composite structure of impurity doping; The method of alternately offsetting the stress; also includes using a double-layer film with opposite stretching tendency to reduce the internal stress and improve the internal stress of the semiconductor device; or applying metal stress on the backside of the substrate at the same time to compensate the stress generated by the front-side epitaxial layer.

The preparation of high-purity and high-quality TiW alloy films usually uses coating technology in a vacuum environment, mostly physical vapor deposition (PVD). For TiW thin film stress adjustment methods, there have been methods to change the deposition and cooling time by maintaining the deposition rate constant; there are also techniques to change the pressure and power of the TiW deposition process to obtain an ultra-wide stress variation range. However, the research on the control of stress by the specific growth rate of TiW is relatively rough. Relatively, when the film is grown at an excessively small deposition rate, the growth time will increase and the cost will increase; when the film is grown at an excessively large deposition rate, the substrate The wafer temperature will continue to rise, resulting in the deposition of TiW films with poor uniformity and low density. In addition, for semiconductor devices, an excessive deposition rate will cause excessive internal stress of the metallized film layer, and the internal stress of the TiW film will be too large. The structural layer of the device is deformed and warped until the adhesion of the interface bonding strength decreases, the substrate and the film layer will be broken, resulting in device failure, such as voltage instability and shortened life. There is also an inventive technique for preparing a chromium nitride film by depositing a transition layer on a substrate to release stress and then depositing a film. However, the internal stress of the film can not be completely eliminated. For the residual stress of the film prepared by PVD or CVD process, there are several GPa sizes, which can be tested and characterized by the optical lever method. For example, in the growth of TiW thin films, it is necessary to seek a new process growth technology to minimize the growth stress, so as to achieve the effect that can be applied to the device.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a method for preparing a low-stress TiW thin film, which firstly grows a thin TiW seed thin film layer on a substrate at a small deposition rate, and then grows a thicker TiW main thin film layer with a large deposition rate.

The object of the present invention is achieved in this way:

A method for preparing a low-stress TiW thin film, characterized in that: adopting physical vapor deposition technology, comprising a TiW thin film layer grown in two steps on a substrate, and the two-step growth of the TiW thin film layer respectively refers to, the first step is The growth of the TiW seed thin film layer, the second step is the growth of the main TiW thin film layer, the TiW seed thin film layer is grown between the main TiW thin film layer and the substrate, and the growth rate of the TiW thin film layer in the first step is the same as The growth rate of the TiW thin film layer in the second step is different, and the growth thickness of the TiW thin film layer in the first step is different from the growth thickness of the TiW thin film layer in the second step.

The first-step TiW thin film layer is grown at a small deposition rate, and the second-step TiW thin film layer is grown at a large deposition rate.

The small deposition growth rate ranges from 20 to 40 Å/min, and the large deposition growth rate ranges from 50 to 100 Å/min.

The thickness of the first-step TiW thin film layer does not exceed 20-30% of the thickness of the second-step TiW thin film layer.

The substrate on which the TiW thin film is grown includes, but is not limited to, third-generation semiconductor material, glass sheet, diamond, metal or metal matrix composite material.

In the present invention, the seed thin film layer grown at a small deposition rate has high density, and a highly reliable interface is obtained through mutual fusion with the atoms of the substrate; the main thin film layer grown at a large deposition rate is the thin film grown on the basis of the seed layer buffer. The adhesion is enhanced, the thickness of the TiW film is stable and the distribution is uniform, and the stress on the substrate is weakened and dissipated, so that the deformation amount is small and a low-stress and high-quality TiW film is obtained. Compared with the prior art, by using the two-step TiW thin film layer growth of the present invention, the beneficial effects are:

(1) A thin TiW seed film layer is grown on the substrate at a small deposition rate, maintaining a low temperature state of the substrate to reduce thermal stress, release the internal stress of lattice distortion in advance, and fuse with the atoms between the substrates to form high reliability interface to enhance the adhesion of the main TiW thin film layer and reduce the interface stress;

(2) On the TiW seed film layer, a thicker TiW main film layer is grown at a large deposition rate. Under the buffering effect of the TiW seed film layer, the surface defects and pores after stress release are filled to form the nucleation center of the new film phase. In order to increase the nucleation rate of the film; under the optimal power and air pressure, the dense film structure is quickly formed and the growth stress is reduced.

The TiW film of the present invention can be prepared by common deposition methods such as vacuum thermal evaporation, magnetron sputtering, ion plating, etc., and the obtained film has high stability, low film stress, and good usability and popularization.

Description of drawings

Figure 1 is a schematic diagram of the structure of the two-step growth on the substrate, including the TiW seed thin film layer and the TiW main thin film layer, wherein: 100-substrate, 101-TiW seed thin film layer, 102-TiW main thin film layer;

Figure 2 is a schematic diagram of the structure of the TiW film grown on the silicon substrate with the vapor deposited Ag layer, and the warpage stress height test, wherein: 200-silicon substrate, 201-Ag metal layer, 202-TiW seed film layer, 203-TiW main layer film layer;

Fig. 3 is the test principle diagram of the bending height of the substrate, wherein: 300-the warping height difference h of the Ag layer, 301-the horizontal scanning length L of the step meter, 303-the radius of curvature R;

Fig. 4 is a test result diagram between the warpage height difference h of the Ag layer and the horizontal scanning length L of the step meter;

Fig. 5 is a schematic diagram of PVD sputtering equipment, wherein: 500-air outlet, 501-heating table, 502-substrate, 503-chamber, 504-upper electrode, 505-air inlet.

Detailed ways

The present invention will be described in further detail below with reference to the accompanying drawings and specific examples, but the embodiments of the present invention include but are not limited to the scopes indicated in the following examples.

Referring to FIG. 1 , a schematic structural diagram of a low-stress TiW thin film includes a substrate, a TiW seed thin film layer, and a TiW main thin film layer in order from bottom to top. In order to achieve the above purpose, the present invention provides a method for preparing a two-step PVD sputtering low-stress TiW thin film. The main sputtering parameters include DC/RF power, deposition time, argon flow rate, and chamber vacuum pressure. Using the stable growth rate of PVD sputtering method, the deposition power and time are adjusted to precisely control the two-step TiW thin film.

Referring to FIG. 2 , a schematic structural diagram of a two-step PVD sputtering low-stress TiW thin film includes a silicon substrate, an Ag metal layer, a TiW seed thin film layer, and a main TiW thin film layer in order from bottom to top.

The preparation method of the above-mentioned low-stress TiW film of two-step PVD sputtering, comprises the following steps:

(1), loading step: load the substrate to be sputtered TiW layer and place it on the sputtering platform;

(2) Evacuation step: use a vacuum pump to evacuate air for high-vacuum chamber treatment;

(3) Ventilation step: Pour argon into the chamber and maintain a low-pressure atmosphere, while turning on the rotation of the sputtering target;

(4), pre-sputtering step: turn on the DC power, carry out the pretreatment of heating and target ablation, and carry out ignition;

(5) Deposition step: turn on the DC power and maintain the deposition preset time for TiW film deposition;

(6) Cooling step: stop the application of DC power, stop the introduction of argon gas, stop the rotation of the sputtering target, and maintain the cooling preset time;

(7) Pre-sputtering step: pass argon gas and maintain a low-pressure atmosphere, and turn on the rotation of the sputtering target;

(8) Repeat steps: Repeat steps (5), (6) and (7) until the thicknesses of the TiW seed thin film layer and the TiW main thin film layer are respectively prepared.

Further, according to the above stage, on the silicon substrate on which the Ag film has been evaporated, the TiW film is grown in two steps, firstly, the TiW seed film layer is grown at a small deposition rate, and then the main TiW film layer is grown at a large deposition rate.

Further, the deposition growth rate of the TiW seed thin film layer was 25-30 Å/min, and the deposition growth rate of the TiW main thin film layer was 75-80 Å/min.

Further, the thickness of the TiW seed thin film layer is 600 angstroms, and the thickness of the TiW main thin film layer is 2400 angstroms.

Further, the high vacuum chamber pressure of the evacuation step is 1×10 ⁻⁶ to 9×10 ⁻⁶ mTr.

Further, the vacuum pressure in the TiW thin film deposition step is 2 mTr to 15 mTr.

Referring to Figure 3, it is a schematic diagram of the principle of measuring the curvature of the substrate by using the "circular substrate curvature deformation method" in the substrate deformation method, using a step tester to test, the length of the measurement range is L, and the two ends of the measurement range are measured. Set the height as equal, and measure the height difference between the center depression and the two ends as h. Since h<<R, according to the equality theorem of the product of intersecting chords, we can get: R=L ² /8h.

4 is a graph of the test results between the warpage height difference h of the Ag layer and the horizontal scanning length L of the step meter, where h is positive for concave curvature, and h is negative for convex curvature; it can be seen from the results that the depression in the center of the substrate and The height difference between the two ends is relatively small, which reduces the internal stress of the TiW metal film to a certain extent.

The above embodiments are only used to illustrate the technical solutions of the present invention, but not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: , the recorded technical solutions are modified, or some technical features thereof are equivalently replaced; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions in the embodiments of the present invention.

Claims (4)

1. A preparation method of a low-stress TiW film is characterized by comprising the following steps: the method comprises the steps of adopting a physical vapor deposition technology, wherein the TiW thin film layer grows on a substrate in two steps, the TiW thin film layer grows in the first step, the main TiW thin film layer grows in the second step, the TiW seed thin film layer grows between the main TiW thin film layer and the substrate, the growth rate of the TiW thin film layer in the first step is different from that of the TiW thin film layer in the second step, and the growth thickness of the TiW thin film layer in the first step is different from that of the TiW thin film layer in the second step; the first step of TiW film layer grows at a small deposition rate, and the second step of TiW film layer grows at a large deposition rate.

2. The method for preparing the low-stress TiW film according to claim 1, wherein the method comprises the following steps: the small deposition growth rate range is 20-40A/min, and the large deposition growth rate range is 50-100A/min.

3. The method for preparing a low-stress TiW film according to claim 1, wherein: the thickness of the TiW film layer in the first step is not more than 20-30% of that of the TiW film layer in the second step.

4. The method for preparing a low-stress TiW film according to claim 1, wherein: the substrate for growing the TiW film comprises a third-generation semiconductor material, a glass sheet, diamond, metal or a metal-based composite material.

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