JPS639731B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for forming a Ni-Cr thin film resistor, and aims to provide a highly accurate and stable Ni-Cr thin film resistor. Structure of conventional example and its problems Most commercially available Ni-Cr alloys have a purity of about 99.9% for use in vapor deposition. However, this purity is the purity of Ni and Cr in the base metal, and Ni−Cr
It is not pure as an alloy. Table 1 shows an example of the elemental analysis results of 80Ni-20Cr alloy, which is the most common material for vapor deposition. Even if you use a newly purchased Ni-Cr alloy to form a thin film resistor, it will still be a pure Ni-Cr alloy.
A thin film resistor could not be obtained, and a stable Ni--Cr thin film resistor could not be obtained because the vapor pressure differed depending on the element (see Table 2). Therefore, Ni−Cr
Features of thin film resistors (low TCR, stable electrical characteristics

【table】 Contains Co, Nb, Mo, V, Si, etc. in addition to the above

[Table] ru, etc.) were not fully demonstrated. OBJECTS OF THE INVENTION The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide a highly accurate and stable Ni-Cr thin film resistor. Structure of the Invention In order to achieve the above object, the method for forming a Ni-Cr thin film resistor of the present invention includes a method for forming a Ni-Cr thin film resistor on an insulating substrate.
After cleaning the surface of the Ni-Cr alloy, use an electron beam evaporator to deposit Ni while scanning the beam in vacuum.
- Cr alloy is uniformly melted, and if the volume of the Ni-Cr alloy is Nml, the amount of the Ni-Cr alloy consumed is at least 500 Å (1 to 2) N times or more, and the Ni-Cr alloy is deposited on an insulating substrate. It is deposited on top to form a Ni-Cr resistive film. DESCRIPTION OF EMBODIMENTS As an embodiment of the method for forming a Ni--Cr thin film resistor according to the present invention, a method for forming a thin film ladder resistor for a 14-bit D/A converter will be described below with reference to the drawings. Ni-Cr alloy (manufactured by Driver Harris,
After ultrasonically cleaning the heating wire (class 1 heating wire) with trichlorethylene, it was cleaned with Ni-Cr etching solution (trade name: TFC, obtained from Boxui Brown Co., Ltd.) for approximately 10 minutes.
It was soaked for a minute to remove surface impurities and oxides. Next, using an electron beam evaporator, the entire Ni-Cr alloy was melted uniformly in a vacuum of 10 ^-5 Torr or higher while scanning the electron beam so that it hit the entire Ni-Cr alloy (after starting melting) (This process was continued until the amount of Ni-Cr alloy consumed reached 1500 Å.) The Ni-Cr alloy subjected to the above treatment was evaporated to a thickness of 200 Å at a rate of 2 Å/sec onto a Si substrate heated to 300°C (with a thermal oxide film of about 800 Å formed on the surface). On top of that, Al was vapor-deposited for electrodes, and Al and Ni− on the Si substrate were deposited.
A Cr thin film was patterned by photolithography. Finally, after forming a protective film, Ni-Cr
Heat treatment was performed to stabilize the thin film resistor. The Ni--Cr thin film resistor thus obtained had sufficient characteristics as a ladder resistor for a 14-bit D/A converter. Next, the reason for setting the conditions for forming the Ni-Cr thin film resistor will be described. First of all, the reason for uniformly melting the Ni-Cr alloy while scanning the electron beam and then consuming 1500Å is to melt the Ni-Cr alloy uniformly and then start melting the Si.
When deposited on a substrate in 200 Å increments, this is the amount of consumption necessary for the deposited film to consist of only Ni and Cr (other elements are less than 0.5 wt%), and it is also sufficient to form a thin film for a 14-bit D/A converter. This is the amount that must be consumed to fully satisfy the characteristics as a ladder resistor. Figure 1 shows the consumption of Ni-Cr alloy and the composition ratio of the film deposited on the substrate. It shows the correlation with alignment error. As can be seen from Figure 1, when the consumption of Ni-Cr alloy is small, a large amount of Mn is deposited in addition to Ni and Cr, and the film is not formed as a pure Ni-Cr thin film resistor, and approximately When consuming more than 1500Å
It can be seen that a pure film of Ni and Cr is formed (Fe and Cu as impurities are not included in the figure because they were both less than 0.5 wt%). Also, from Figure 2, the overlay error, which is one of the characteristic evaluations of a D/A converter, is also affected by the consumption of Ni-Cr alloy.
It can be seen that a Ni-Cr thin film resistor satisfying 14-bit accuracy (0.003%) can be obtained when the thickness is 1500 Å or more. However, these data are for the case where the volume of the Ni-Cr alloy is 2.7 ml, and the consumption amount of the Ni-Cr alloy varies depending on the volume of the Ni-Cr alloy.
For example, if it is 5.0ml, it will be more than 3000Å, if it is 10ml, it will be more than 3000Å.
It was over 6500Å. Second, although the Si substrate is heated at 300°C in the example, it may be heated to 350°C or less. Figure 3 shows the heating temperature of the Si substrate and the temperature coefficient of the upper 7 bits of the Ni-Cr thin film ladder resistor for a 14-bit D/A converter. The variation between bit resistances is large, and although there are some differences in absolute values at heating temperatures below 350°C, the variation between bit resistances is extremely small.
As another characteristic evaluation method, 14-bit D/A
There is an overlay error in the converter, but this is hardly affected by the Si substrate heating temperature.
This is due to the variation in the measurement error range, and it satisfies 14-bit accuracy under all conditions. Thirdly, the film deposition speed on the Si substrate was set at 2 in the example.
Although this was done at a speed of 5 Å/second, any speed of 5 Å/second or less may be used. Figure 4 shows a Si substrate heated to room temperature, 150°C, and 350°C, and Ni-Cr coated at 2 Å/sec, 5 Å/sec, and 8 Å/sec.
The graph shows the correlation with the overlay error of the Ni--Cr thin film ladder resistor for a 14-bit D/A converter formed at a deposition rate of Å/sec. If the Si substrate heating temperature is 350°C or less, it can be seen from Figure 4 that the film deposition rate must be 5 Å/sec or less to satisfy the accuracy as a Ni-Cr thin film ladder resistor for a 14-bit D/A converter. . Finally, the ratio of Ni and Cr deposited on the insulating substrate is the Ni-Cr alloy (80Ni, 80Ni,
20Cr), the composition of the film deposited on the Si substrate is Ni40wt%,
The ratio will be around 60wt% Cr. However, as the number of evaporations increases, the amount of Cr in the Ni-Cr alloy decreases quickly, and the composition of the film on the Si substrate gradually changes.
The ratio of Ni increases. As the Ni content increases, the temperature coefficient of the resistor increases, and as is clear from Figure 5, when the Ni content exceeds 60wt% in the composition of the film deposited on the Si substrate, the temperature coefficient of the Ni-Cr thin film resistor increases rapidly. becomes larger. Conversely, Ni with a Cr content of 60wt% or more
As can be seen from FIG. 5, the -Cr thin film resistor exhibits a large negative temperature coefficient. Therefore, in order to obtain a Ni-Cr thin film resistor with a small temperature coefficient, Ni should be
60wt%, and Cr is preferably in the range of 60 to 40wt%. In addition, when forming a Ni-Cr thin film resistor by depositing any Ni-Cr alloy on an insulating substrate using the Ni-Cr alloy subjected to the consumption according to the present invention as a deposition target, the absolute value of the temperature coefficient If the value is ignored, a stable Ni-Cr thin film resistor can be obtained. For example, a Ni-Cr thin film resistor with a composition of 30wt% Ni and 70wt% Cr can be used to sufficiently satisfy the characteristics as a ladder resistor for a 14-bit D/A converter, and conversely, a resistor with a composition of 75wt% Ni and 70wt% Cr can be obtained.
Even a Ni-Cr thin film resistor with a composition of 25wt% Cr
A resistor that fully satisfies the characteristics of a ladder resistor for a 14-bit D/A converter can be obtained. Effects of the Invention As described above, according to the present invention, the deposition target
Ni-Cr alloy was deposited using an electron beam evaporator, and Nml of Ni-Cr was deposited while scanning the electron beam in vacuum.
Cr alloy in an amount (a
It is possible to form a highly accurate and stable Ni-Cr thin film resistor by controlling the deposition rate by using a material that has been consumed as much as 1 to 2) and controlling the deposition rate. Summer.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, and FIG.
A graph showing the consumption amount of Cr alloy and the composition ratio of the film deposited on the substrate. Figure 2 is a graph showing the correlation between the consumption amount of Ni-Cr alloy and the overlay error. Figure 3 is a graph showing the correlation between the consumption amount of Ni-Cr alloy and the overlay error. A graph showing the temperature coefficient of the deposited Ni-Cr thin film resistor. Fig. 4 is a graph showing the correlation between the Ni-Cr film deposition speed and overlay error. Fig. 5 shows the composition of the deposited film on the substrate and the resistor. It is a graph which shows the correlation of the temperature coefficient of.

Claims (1)

[Claims] 1. In the process of forming a Ni-Cr thin film resistor on an insulating substrate, after cleaning the surface of the Ni-Cr alloy to be deposited, a beam is applied in vacuum using an electron beam evaporator. Melt the Ni-Cr alloy uniformly while scanning, and if the volume of the Ni-Cr alloy is Nml, deposit the Ni-Cr alloy in an amount that is at least 500 Å (1 to 2) N times or more. A method for forming a Ni-Cr thin film resistor, which is deposited on an insulating substrate to form a Ni-Cr resistor film. 2. The Ni-Cr thin film resistor according to claim 1, wherein the composition of the Ni-Cr thin film resistor deposited on the insulating substrate is within the range of Ni (40 to 60 wt%) and Cr (60 to 40 wt%).
Method of forming Cr thin film resistor. 3. A method for forming a Ni-Cr thin film resistor according to claim 1, wherein the temperature of the substrate is maintained at 350° C. or lower when forming the Ni-Cr thin film resistor on an insulating substrate. 4. A method for forming a Ni-Cr thin film resistor according to claim 1, wherein the Ni-Cr deposition rate is 5 Å/sec or less.