JPH033251A - Sample holder - Google Patents

Abstract

PURPOSE:To form a uniform electrified layer in the upper face of a sample and form a uniform film or perform uniform etching by separating an electrode layer into upper and lower layers with an insulating layer and applying DC voltage and high frequency to the upper and lower electrode layers respectively. CONSTITUTION:A sample mount 13 comprises upper and lower electrode layers 31 and 32 and an insulating layer 33 therebetween which are buried in an insulator 15 of ceramic or other materials and a high frequency application electrode rod 38 boring a cooling plate 11 is connected to the lower electrode layer 32. In adsorbing a sample 14, when a direct current is passed through a circuit the upper electrode layers 31a and 31b and the sample 14 are electrified to generate electrostatic power and the sample 14 is adsorbed to the sample mount 13. When high frequency is applied from an RF power source 38 to the lower electrode layer 32 and plasma is applied to form a film or perform etching, the upper face of the sample 14 is electrified negatively. Reactive gas ions are attracted to the electrified layer formed in the upper face of the sample 14 and a film is formed on the upper face of the sample 14 or the upper face of the sample 14 is etched.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a sample holding device, and more particularly, to a sample holding device that uses electrostatic adsorption to adsorb and hold a sample.
The present invention relates to a sample holding device used to hold a sample under high vacuum in the manufacturing process of semiconductor integrated circuits.

For example, electron cyclotron resonance (ElectronC
C V D lchemi, which forms a thin film of a desired substance on the surface of a sample using ECR plasma generated using yclotron Re5onancel.
In semiconductor integrated circuit manufacturing equipment such as cal vapor deposition equipment or dry etching equipment that forms fine circuit patterns or patterns on the surface of a specimen, the specimen is subjected to processing that is maintained in a high vacuum state. Electrostatic chuck-type sample holding devices that utilize electrostatic adsorption force are widely used to hold samples indoors.

A conventional sample holding device of this type generally employs a monopolar electrostatic chuck structure as shown in FIG.

The structure of this monopolar electrostatic chuck consists of a base (not shown)
A cooling plate 11 is placed on the cooling plate 11, and a flow path 12 for circulating a cooling liquid is formed inside the cooling plate 11. The flow path 12 is configured so that a cooling liquid can be introduced and led out from the outside, and a sample stage 13 is placed above the cooling plate 11 via a heat transfer body (not shown) such as silicone rubber. A sample 14 is placed on the top of this sample stage 13. The sample stage 13 is formed with an electrode layer 16 embedded inside an insulator 15 made of ceramic or the like, and an electrode rod 17 is connected to the electrode layer 16 by penetrating the cooling plate 11. There is. A direct current (DC) power source (not shown) and a radio frequency (RF) power source (not shown) are connected to the electrode rod 17.

An equivalent circuit diagram of the sample holding device with the above structure is shown in Figure 5.
In the figure, a capacitor C1 is connected between the sample 14 and the electrode layer 16.
The positive side of the DC power source 18 and the RF power source 19 are connected to the electrode layer 16 side, and the other ends of the DC power source 18 and the RF power source 19 are grounded. A coil 20 is interposed between the DC power source 18 and the electrode layer 16. Further, an auxiliary circuit 21 consisting of a plasma assist or a transfer arm is connected to the sample 14 side, and this auxiliary circuit 21
One end of is grounded.

Here, the adsorption force is proportional to the square of the applied voltage and inversely proportional to the square of the thickness of the insulating layer.

In the sample holding device configured as described above, a method for adsorbing and detaching the sample 14, which is an object to be adsorbed, will be explained. When using plasma assist as the auxiliary circuit 21, in order to attract and hold the sample 14, place the sample 14 on the top surface of the sample stage 13, turn on the DC power supply 18, and apply plasma to the top surface of the sample 14 for a short time. irradiate. 1
Since the i-pole layer 16 is positively charged by the positive DC voltage, the lower surface of the sample 14 tends to be negatively charged. At the same time, due to the plasma irradiation, the grounded auxiliary circuit 21 and the sample 14 are electrically connected via the capacitor CI, and an electric field is generated between the sample 14 and the electrode layer 16. Therefore, the sample 14 is attracted and held on the sample stage 13 by the electrostatic force between the positive and negative charges. After adsorbing the sample, the RF power source is turned on and processes such as film formation and etching are performed.

In processes such as film formation and etching, if only a DC voltage is applied, the charge on the surface of the sample 14 will be neutralized by plasma, but since a high frequency is applied, the charge on the sample 14 will be constantly changed in response to changes in this high frequency. Charging and discharging begin to occur between the sample 14 and the electrode layer 16, and the charge on the upper surface of the sample 14 changes alternately between positive and negative. Therefore, positive ions and electrons (e-) due to plasma irradiation are alternately attracted to the top surface of the sample 14, but since ions have a much larger mass than electrons, the speed of ions is lower than that of electrons. It will be very small. For this reason, as the frequency of the high frequency increases, the ions can no longer keep up with the rapid changes in the electric field, and only electrons gradually accumulate on the top surface of the sample 14, causing the top surface of the sample 14 to become negatively charged. Therefore, when performing a film forming process or an etching process, the reaction gas ions are attracted to the electric field due to the negative charge formed on the top surface of the sample 14, and the direction of incidence on the top surface of the sample 14 is guided vertically. Undesirable phenomena such as side etching are suppressed, and a good circuit pattern can be formed.

To detach the sample 14 from the sample stage 13, turn on the DC power supply 1.
8. When the RF power source 19 is turned off and plasma is irradiated to bring the sample 14 and the auxiliary circuit 21 into conduction, the charges accumulated in the sample 14 are grounded, and the adsorption force due to the electrostatic force disappears. Note that adsorption and retention of sample 14 are normally performed before film formation or etching treatment, but it is also possible to adsorb and retain sample 14 at the same time as these treatments by using plasma irradiation when performing these treatments. is also possible.

When using a transport arm as the auxiliary circuit 21, the electrode layer 1
When a DC voltage is applied to the electrode layer 6 and the grounded transport arm is brought into contact with the sample 14, the sample 14 and the electrode layer 16
An electric field is generated between them, and positive charges are accumulated on the electrode layer 16 side, while negative charges are accumulated on the sample 14 side.

The sample 14 is attracted and held on the sample stage 13 by the electrostatic force caused by the positive and negative charges. Thereafter, the RF power source 19 is normally turned on before etching processing or the like is started. To remove the sample 14 from the sample stage 13 after the etching process, etc., turn off the DC power supply 18 and the RF power supply 19.
When the transport arm is brought into contact with the sample 14 again, the electric charge accumulated on the sample 14 is discharged by the grounded transport arm, so that the adsorption force due to the electrostatic force disappears.

As explained above, with a monopolar electrostatic chuck, the sample 14
sample 1 by accumulating charge between the electrode layer 16 and
4, and when discharging this accumulated charge and detaching the sample 14, the auxiliary circuit 2
1 was essential.

Furthermore, when the sample 14 is adsorbed and detached by the auxiliary circuit 21, it is difficult for the charge to move smoothly.
There is a disadvantage that it takes time to obtain the electrostatic force necessary for attracting No. 4, and the number of pieces manufactured per unit time is reduced.

Furthermore, even when detached, there is a large amount of residual charge even if the charge in the sample 14 is grounded by the auxiliary circuit 21, and the sample 14 remains strongly attracted to the sample stage 13. There is a drawback that the sample 14 is easily damaged when attempting to lift it.

As described above, in a sample holding device having a monopolar electrostatic chuck structure, it is necessary to form an auxiliary circuit 21, it takes time to attract and hold the sample, and there is a risk that the sample may be damaged when detached due to residual charge. Due to certain problems, bipolar electrostatic chuck structures have been developed as an alternative to monopolar electrostatic chuck structures.

In this bipolar electrostatic chuck, as shown in FIG. 6, the electrode layer is formed separately into an electrode layer 22 to which a positive DC voltage is applied and an electrode layer 23 to which a negative DC voltage is applied. ,
Radio frequency (RF) is applied to both electrode layers 22 and 23, respectively. Therefore, with the bipolar electrostatic chuck structure, it is possible to attract and detach the sample 14 without an auxiliary circuit, and since DC voltage can be applied to each electrode layer 22 and 23 separately, it is easy to change the DC power supply. Various problems with the auxiliary circuit 21 can be solved, such as being able to apply an inversion voltage to the auxiliary circuit 21 and reducing the residual charge to zero.

is trying to.

The bipolar electrostatic chuck structure described above is not suitable for the monopolar electrostatic chuck structure using the auxiliary circuit 21, as it takes time to attract the sample and there is a risk that the sample may be damaged when detached due to residual charge. problems that can be solved. However, in the bipolar electrostatic chuck structure, when high frequency is applied to the electrode layers 22 and 23 when adsorbing the sample 14, even a slight difference in the introduction path of the high frequency causes a change in the impedance of the circuit. There was a drawback that it was difficult to apply uniform high frequency waves to the two electrode layers 22 and 23. As a result, the charge distribution of the charged layer formed on the top surface of the sample 14 due to the application of high frequency becomes non-uniform, and the distribution and directionality of the reactant gas ions incident on the top surface of the sample 14 are also disturbed. There is a problem in that the pattern formed by film processing or etching processing becomes non-uniform.

The present invention has been made in view of the above-mentioned problems, and is capable of uniformly applying a high frequency to a plurality of electrode layers at the same height level formed separately on a sample stage in a bipolar electrostatic chuck. Therefore, it is an object of the present invention to provide a sample holding device that can form good patterns in the manufacture of semiconductor integrated circuits.

In order to achieve the above-mentioned object, the present invention provides a sample holding device comprising a sample stage on which a sample is placed and an electrode layer embedded in the sample stage, in which the electrode layer is connected via an insulating layer. It is characterized by being composed of two layers, an upper and a lower layer, and the upper electrode layer is formed separately and is applied with a DC voltage, while the lower electrode layer is configured so that a high frequency is applied.

According to the above configuration, the high frequency is conducted to the lower electrode layer, passes through the insulating layer having substantially the same conditions between the upper and lower electrode layers, and is then applied to the plurality of upper electrode layers. In other words, the high frequency is not applied to multiple upper electrode layers separately;
Since the high frequency waves are simultaneously applied to a plurality of upper electrode layers via the lower electrode layer, the high frequency waves are equally conducted to each upper electrode layer.

Embodiments of the sample holding device according to the present invention will be described below with reference to the drawings. Note that parts having the same structure as those of the conventional example are given the same reference numerals.

As shown in FIG. 1, the structure of the electrostatic chuck in the sample holding device is that a cooling plate 11 is placed on a base (not shown), and a cooling liquid is circulated inside the cooling plate 11. A flow path 12 is formed for this purpose. This flow path 12 is configured so that a cooling liquid can be introduced into and led out from the outside. A sample stage 13 is placed above the cooling plate 11 via a heat transfer member (not shown) such as silicone rubber, and a sample 14 is placed on top of this sample stage 13. The sample stage 13 has two upper and lower electrode layers 31 and 32 inside an insulator 15 made of ceramic or the like, and an insulating layer 3.
An electrode rod 38 for high frequency application that penetrates through the cooling plate 11 is connected to the lower electrode layer 32. The upper electrode layer 31 is formed separately into two semicircular electrode layers 31a and 31b in plan view, and electrode rods 34 and 34 for applying a DC voltage penetrate through the cooling plate 11 and the lower electrode layer 32, respectively. (Fig. 2).

FIG. 3 shows an equivalent circuit diagram of the sample holding device. In the figure,
An RF power source 19 is connected to the lower electrode layer 32,
The lower electrode layer 32 forms capacitors C2 and C4 with the upper electrode layers 31a and 31b, and the upper electrode layer 31a
, 31b constitute a capacitor C, , C, with the sample 14. The capacitors C2, C, on the left side are each connected to the positive side of the DC power supply 35 via the coil 20, and the capacitors C4, Cs on the right side are each connected to the negative side of the DC power supply 36 via the coil 20. 35.
36 is designed to be able to switch between the left and right connected capacitors C, , C, and the capacitors C4 and C1 by switches 37 and 37. One ends of the RF power source 19 and the DC power sources 35 and 36 are grounded.

When the sample 14 is to be attracted, when a direct current is passed through this circuit, the upper electrode layers 31a, 31b and the sample 14 are charged, an electrostatic force is generated, and the sample 14 is attracted to the sample stage 13. When a high frequency is applied from the RFit source 38 to the lower electrode layer 32, the high frequency is applied to the capacitors C2, C4, C3,
It propagates to the sample 14 via Cs. Positive and negative charges are alternately generated on the upper surface of the sample 14 in response to changes in the applied high frequency, but when plasma irradiation is performed for film formation or etching, one reaction gas ion and electron (e- ), only those electrons that can respond to drastic changes in frequency are accumulated on the upper surface of the sample 14, and the upper surface of the sample 14 becomes negatively charged. Reactive gas ions are attracted to the charged layer formed on the upper surface of the sample 14, and a film is formed or etched on the upper surface of the sample 14.

When detaching the sample 14, when a reverse voltage is applied by switching the switch 37.37 of the DC power supply 35.36, the charges accumulated in the capacitors C2, C, , C, , Cs are discharged, and the adsorption force is reduced. Disappear.

As explained above, in this embodiment, the high frequency is not applied to the upper electrode layers separately, but is simultaneously applied to the upper electrode layers 31a and 31b via one lower electrode layer 32. can be uniformly conducted to each upper electrode layer 31a, 31b. Therefore, sample 14
Since the high frequency applied to the sample 14 becomes uniform, the charge distribution of the charged layer formed on the top surface of the sample 14 becomes uniform, and the distribution state and incident direction of the reactive gas ions colliding with the top surface of the sample 14 are uniformly guided over the entire surface. As a result, it becomes possible to make the circuit pattern formed by the film forming process or the etching process uniform.

In addition, although the above-described embodiment shows a case where the upper electrode layer is formed separately into two, the number of upper electrode layers is not limited to two, and may be three or more. do not have.

As is clear from the above description, the sample holding device according to the present invention includes a sample stage on which a sample is placed and an electrode layer embedded in the sample stage. , the electrode layer is composed of upper and lower layers with an insulating layer interposed therebetween,
The upper electrode layer is formed separately and is configured to be applied with a DC voltage, while the lower electrode layer is configured to be applied with a high frequency.

Therefore, by applying a DC voltage to multiple electrode layers,
While the drawbacks of the monopolar electrostatic chuck structure can be eliminated, the high frequency is not applied to the two upper electrode layers separately, but is applied simultaneously to both layers through a single lower electrode layer. , it is possible to equalize the high frequency waves applied to the sample from the plurality of upper electrode layers. As a result, the charged layer uniformly formed on the top surface of the sample by applying high frequency waves allows reactive gas ions to be incident uniformly over the entire surface of the sample, resulting in a uniform circuit pattern formed by film formation or etching. It becomes possible to

[Brief explanation of the drawing]

FIG. 1 is a schematic sectional view showing an embodiment of the sample holding device according to the present invention, FIG. 2 is a sectional view taken along line A-A in FIG. 1, and FIG. 3 is an equivalent circuit diagram of the same device. Fig. 4 is a schematic cross-sectional view showing a conventional sample holding device having a monopolar electrostatic chuck structure, Fig. 5 is an equivalent circuit diagram of the same device, and Fig. 6 is a sample holding device having a bipolar electrostatic chuck structure. FIG. 3 is an equivalent circuit diagram of the holding device. 13... Sample stage, 14... Sample, 19... RF power source, 31. 31a, 31b... Upper electrode layer, 32...
...Lower electrode layer, 33...Insulating layer, 35.36...
・DC power supply

Claims (1)

[Claims] In a sample holding device comprising a sample stage on which a sample is placed and an electrode layer embedded in the sample stage, the electrode layer is composed of two layers, upper and lower, with an insulating layer interposed therebetween, and the upper electrode layer is formed separately. A sample holding device characterized in that it is configured such that a DC voltage is applied to the lower electrode layer, while a high frequency wave is applied to the lower electrode layer.